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+The Project Gutenberg EBook of Turning and Boring, by Franklin D. Jones
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: Turning and Boring
+       A specialized treatise for machinists, students in the
+       industrial and engineering schools, and apprentices, on
+       turning and boring methods, etc.
+
+Author: Franklin D. Jones
+
+Release Date: October 4, 2010 [EBook #34030]
+
+Language: English
+
+Character set encoding: ISO-8859-1
+
+*** START OF THIS PROJECT GUTENBERG EBOOK TURNING AND BORING ***
+
+
+
+
+Produced by Juliet Sutherland, Harry Lamé and the Online
+Distributed Proofreading Team at https://www.pgdp.net
+
+
+
+
+
+
+
+
+
+    Transcriber's notes:
+    words in bold and italics have been transcribed as =word= and
+    _word_, respectively; superscripts are indicated by ^, subscripts
+    by _.
+    Greek letters have been transliterated as [alpha], [beta], etc.
+    Spelling and hyphenation have been standardised (see list at end
+    of text).
+
+
+
+
+                  TURNING AND
+                    BORING
+
+      A SPECIALIZED TREATISE FOR MACHINISTS,
+      STUDENTS IN INDUSTRIAL AND ENGINEERING
+          SCHOOLS, AND APPRENTICES, ON
+      TURNING AND BORING METHODS, INCLUDING
+          MODERN PRACTICE WITH ENGINE
+       LATHES, TURRET LATHES, VERTICAL AND
+          HORIZONTAL BORING MACHINES
+
+             BY FRANKLIN D. JONES
+
+        ASSOCIATE EDITOR OF MACHINERY
+       AUTHOR OF "PLANING AND MILLING"
+
+              _FIRST EDITION_
+              FIFTH PRINTING
+
+                 NEW YORK
+           THE INDUSTRIAL PRESS
+   LONDON: THE MACHINERY PUBLISHING CO., LTD.
+                   1919
+
+
+
+
+  COPYRIGHT, 1914
+  BY
+  THE INDUSTRIAL PRESS
+  NEW YORK
+
+
+
+
+PREFACE
+
+
+Specialization in machine-tool manufacture has been developed to such a
+degree that there is need also for treatises which specialize on
+different classes of tools and their application in modern practice.
+This book deals exclusively with the use of various types of turning and
+boring machines and their attachments, and is believed to be unusually
+complete. In addition to standard practice, it describes many special
+operations seldom or never presented in text-books. Very little space is
+given to mere descriptions of different types of machine tools, the
+principal purpose being to explain the use of the machine and the
+practical problems connected with its operation, rather than the
+constructional details. No attempt has been made to describe every
+machine or tool which might properly be included, but rather to deal
+with the more important and useful operations, especially those which
+illustrate general principles.
+
+Readers of mechanical literature are familiar with MACHINERY'S 25-cent
+Reference Books, of which one hundred and twenty-five different titles
+have been published during the past six years. Many subjects, however,
+cannot be adequately covered in all their phases in books of this size,
+and in response to a demand for more comprehensive and detailed
+treatments on the more important mechanical subjects, it has been deemed
+advisable to bring out a number of larger volumes, of which this is one.
+This work includes much of the material published in MACHINERY'S
+Reference Books Nos. 91, 92 and 95, together with a great amount of
+additional information on modern boring and turning methods.
+
+It is a pleasure to acknowledge our indebtedness to the manufacturers
+who generously supplied illustrations and data, including many
+interesting operations from actual practice. Much valuable information
+was also obtained from MACHINERY.
+
+  F. D. J.
+
+  NEW YORK, _May, 1914_.
+
+
+
+
+CONTENTS
+
+                                                                  PAGES
+
+
+  CHAPTER I
+
+  THE ENGINE LATHE--TURNING AND BORING OPERATIONS
+
+  General Description of an Engine Lathe--Example of Cylindrical
+  Turning--Facing the Ends Square with a Side-tool--Turning
+  Tool--Turning Work Cylindrical--Roughing and Finishing
+  Cuts--Filing and Finishing--Aligning Centers for Cylindrical
+  Turning--Application of Drivers or Dogs--Lathe Arbors or
+  Mandrels--Different Types of Lathe Arbors--Mandrel or Arbor
+  Press--Steadyrest for Supporting Flexible Parts--Application of
+  Steadyrest when Boring--The Follow-rest--Centering Parts to be
+  Turned--Centering Machine--Different Forms of Centers--Precaution
+  When Centering Tool Steel--Facing the Ends of Centered
+  Stock--Truing Lathe Centers--Universal, Independent and
+  Combination Chucks--Application of Chucks--Example of
+  Boring--Measuring Bored Holes--Setting Work in the
+  Chuck--Inaccuracy from Pressure of Chuck Jaws--Drilling and
+  Reaming--Holding Work on Faceplate--Application of Angle-plate to
+  Faceplate--Supporting Outer End of Chucked Work--Boring Large
+  Castings in the Lathe--Boring Holes to a Given Center
+  Distance--Turning Brass, Bronze and Copper--Machining Aluminum   1-53
+
+
+  CHAPTER II
+
+  LATHE TURNING TOOLS AND CUTTING SPEEDS
+
+  Turning Tools for General Work--Tool-holders with Inserted
+  Cutters--The Position of Turning Tools--Tool Grinding--Shape or
+  Contour of Cutting Edge--Direction of Top Slope for Turning
+  Tools--Clearance for the Cutting Edge--Angle of Tool-point and
+  Amount of Top Slope--Grinding a Lathe Tool--Cutting Speeds and
+  Feeds--Average Cutting Speeds for Turning--Factors which Limit
+  the Cutting Speed--Rules for Calculating Cutting Speeds--Feed of
+  Tool and Depth of Cut--Effect of Lubricant on Cutting
+  Speed--Lubricants Used for Turning--Lard Oil as a Cutting
+  Lubricant                                                       54-79
+
+
+  CHAPTER III
+
+  TAPER TURNING--SPECIAL OPERATIONS--FITTING
+
+  Setting Tailstock Center for Taper Turning--Example of Taper
+  Turning--Setting the Tailstock Center with a Caliper
+  Tool--Setting the Tailstock Center with a Square--The Taper
+  Attachment--Application of Taper Attachment--Height of Tool
+  when Turning Tapers--Taper Turning with the Compound
+  Rest--Accurate Measurement of Angles and Tapers--To Find
+  Center Distance for a Given Taper--To Find Center Distance
+  for a Given Angle--To Find Angle for Given Taper per Foot--To
+  Find Angle for Given Disk Dimensions--Use of the Center
+  Indicator--Locating Work by the Button Method--Eccentric
+  Turning--Turning a Crankshaft in a Lathe--Special Crankshaft
+  Lathe--Operation of Special Crankshaft Lathe--Spherical
+  Turning--Spherical Turning Attachments--Turning with Front
+  and Rear Tools--A Multiple-tool Lathe--Examples of Multiple
+  Turning--Knurling in the Lathe--Relieving
+  Attachment--Application of Relieving Attachment--Relieving
+  Hobs or Taps Having Spiral Flutes--Classes of Fits Used in
+  Machine Construction--Forced Fits--Allowance for Forced
+  Fits--Pressure for Forced Fits--Allowance for Given
+  Pressure-Shrinkage Fits                                        80-134
+
+
+  CHAPTER IV
+
+  THREAD CUTTING IN THE LATHE
+
+  Selecting the Change Gears for Thread Cutting--The Thread
+  Tool--Cutting the Thread--Indicator or Chasing Dial for
+  Catching Threads--Principle of the Thread
+  Indicator--Replacing Sharpened Thread Tool--Use of Compound
+  Rest for Thread Cutting--Threads Commonly Used--Multiple
+  Threads--Cutting a U. S. Standard Thread--Cutting a Left-hand
+  Thread--Cutting a Square Thread--Cutting Multiple
+  Threads--Setting Tool When Cutting Multiple Threads--Taper
+  Threading--Internal Threading--Stop for Thread Tools--The
+  Acme Standard Thread--The Whitworth Thread--Worm
+  Threads--Coarse Threading Attachment--Testing the Size of a
+  Thread--The Thread Micrometer--Three-wire System of Measuring
+  Threads--Rivett-Dock Threading Tool--Cutting Screws to
+  Compensate for Shrinkage--Calculating Change Gears for Thread
+  Cutting--Lathes with Compound Gearing--Fractional
+  Threads--Change Gears for Metric Pitches--Quick Change-gear
+  Type of Lathe                                                 135-177
+
+
+  CHAPTER V
+
+  TURRET LATHE PRACTICE
+
+  General Description of a Turret Lathe--Example of Turret
+  Lathe Work--Machining Flywheels in Turret Lathe--Finishing a
+  Flywheel at One Setting in Turret Lathe--Finishing a Webbed
+  Flywheel in Two Settings--Tools for Turret
+  Lathes--Box-tools--Examples of Box-tool Turning--Hollow
+  Mills--Releasing Die and Tap Holders--Self-opening Die
+  Heads--Collapsing Taps--Miscellaneous Turret Lathe
+  Tools--Turning Gasoline Engine Pistons in Turret
+  Lathe--Turning Piston Rings in Turret Lathe--Piston Turning
+  in Pratt and Whitney Turret Lathe--Attachment for Turning
+  Piston Rings--Turning Worm-gear Blanks in Turret
+  Lathe--Turning Bevel Gear Blanks--Shell Turning Operation in
+  Flat Turret Lathe--Chuck Work in Flat Turret
+  Lathe--Double-spindle Flat Turret Lathe--Automatic Chucking
+  and Turning Machine--Example of Work on Automatic Turning
+  Machine--Determining Speed and Feed Changes--Setting the
+  Turret Slide--Setting the Cross-slide Cam--Setting the Boring
+  Tool for Recessing--Adjustments for Automatic Feed and Speed
+  Changes--Turning Flywheel in Automatic Chucking and Turning
+  Machine--Automatic Multiple-spindle Chucking
+  Machine--Selecting Type of Turning Machine                    178-241
+
+
+  CHAPTER VI
+
+  VERTICAL BORING MILL PRACTICE
+
+  Boring and Turning in a Vertical Boring Mill--Holding and
+  Setting Work on Boring Mill Table--Turning in a Boring
+  Mill--Boring Operations--Turning Tools for the Vertical
+  Boring Mill--Turning a Flywheel on a Vertical Mill--Convex
+  Turning Attachment for Boring Mills--Turning Taper or Conical
+  Surfaces--Turret-lathe Type of Vertical Boring Mill--Examples
+  of Vertical Turret Lathe Work--Floating Reamer
+  Holders--Multiple Cylinder Boring Machine                     242-274
+
+
+  CHAPTER VII
+
+  HORIZONTAL BORING MACHINES
+
+  Horizontal Boring Machine with Vertical Table
+  Adjustment--Drilling and Boring--Cutters Used--Cutter-heads
+  for Boring Large Holes--Cylinder Boring--Boring a Duplex
+  Gasoline Engine Cylinder--Examples of Boring, Radial Facing
+  and Milling--Fixture for Cylinder Lining or
+  Bushing--Horizontal Boring Machine of Floor Type              275-297
+
+  INDEX                                                         299-307
+
+
+
+
+TURNING AND BORING
+
+
+
+
+CHAPTER I
+
+THE ENGINE LATHE--TURNING AND BORING OPERATIONS
+
+
+The standard "engine" lathe, which is the type commonly used by
+machinists for doing general work, is one of the most important tools in
+a machine shop, because it is adapted to a great variety of operations,
+such as turning all sorts of cylindrical and taper parts, boring holes,
+cutting threads, etc. The illustration Fig. 1 shows a lathe which, in
+many respects, represents a typical design, and while some of the parts
+are arranged differently on other makes, the general construction is
+practically the same as on the machine illustrated.
+
+The principal parts are the bed _B_, the headstock _H_, the tailstock
+_T_, and the carriage _C_. The headstock contains a spindle which is
+rotated by a belt that passes over the cone-pulley _P_, and this spindle
+rotates the work, which is usually held between pointed or conical
+centers _h_ and _h_{1}_ in the headstock and tailstock, or in a chuck
+screwed onto the spindle instead of the faceplate _F_. The carriage _C_
+can be moved lengthwise along the bed by turning handle _d_, and it can
+also be moved by power, the movement being transmitted from the
+headstock spindle either through gears _a_, _b_, _c_, and lead-screw
+_S_, or by a belt operating on pulleys _p_ and _p_{1}_, which drive the
+feed-rod _R_. The lead-screw _S_ is used when cutting threads, and the
+feed-rod _R_ for ordinary turning operations; in this way the wear on
+the lead-screw is reduced and its accuracy is preserved.
+
+[Illustration: Fig. 1. Bradford Belt-driven Lathe--View of Front or
+Operating Side]
+
+On the carriage, there is a cross-slide _D_ which can be moved at right
+angles to the lathe bed by handle _e_, and on _D_ there is an upper or
+compound slide _E_ which can be swiveled to different positions. The
+tool _t_, that does the turning, is clamped to the upper slide, as
+shown, and it can be moved with relation to the work by the movement of
+the carriage _C_ along the bed, or by moving slide _D_ crosswise. The
+lengthwise movement is used to feed the tool along the work when
+turning, boring or cutting a screw, and the crosswise movement for
+facing the ends of shafts, etc., or for radial turning. When the tool is
+to be fed at an angle, other than at right angles to the bed, slide _E_,
+which can be set to the required angle, is used. The lengthwise and
+crosswise feeding movements can be effected by power, the lengthwise
+feed being engaged by tightening knob _k_, and the cross-feed by
+tightening knob _l_. The direction of either of these movements can also
+be reversed by shifting lever _r_. Ordinarily the carriage and slide are
+adjusted by hand to bring the tool into the proper position for turning
+to the required diameter, and then the power feed (operating in the
+desired direction) is engaged. The tailstock _T_ can be clamped in
+different positions along the bed, to suit the length of the work, and
+its center _h_{1}_ can be moved in or out for a short distance, when
+adjusting it to the work, by turning handle _n_.
+
+[Illustration: Fig. 2. Plan View of Lathe Headstock showing Back-gears]
+
+[Illustration: Fig. 3. Feed Mechanism of Lathe Apron]
+
+As some metals are much harder than others, and as the diameters of
+parts to be turned also vary considerably, speed changes are necessary,
+because if the speed is excessive, the turning tool will become dull in
+too short a time. These speed changes (with a belt-driven lathe) are
+obtained by placing the driving belt on different steps of cone-pulley
+_P_, and also by the use of back-gears. The cone-pulley can be connected
+directly with the spindle or be disengaged from it by means of bolt _m_.
+When the pulley and spindle are connected, five speeds (with this
+particular lathe) are obtained by simply shifting the driving belt to
+different steps of the cone. When a slower speed is required than can be
+obtained with the belt on the largest step of the cone, the latter is
+disconnected from the spindle, and the back-gears _G_ and _G_{1}_ (shown
+in the plan view Fig. 2) are moved forward into mesh by turning handle
+_O_; the drive is then from cone-pulley _P_ and gear _L_ to gear _G_,
+and from gear _G_{1}_ to the large gear _J_ on the spindle. When driving
+through the back-gears, five more speed changes are obtained by shifting
+the position of the driving belt, as before. The fastest speed with the
+back-gears in mesh is somewhat slower than the slowest speed when
+driving direct or with the back-gears out of mesh; hence, with this
+particular lathe, a series of ten gradually increasing speeds is
+obtained. Changes of feed for the turning tool are also required, and
+these are obtained by shifting the belt operating on pulleys _p_ and
+_p_{1}_ to different-sized steps. On some lathes these feed changes are
+obtained through gears which can be shifted to give different ratios.
+Many lathes also have gears in the headstock for changing the speeds.
+
+[Illustration: Fig. 4. Rear View of Lathe Apron]
+
+Front and rear views of the carriage apron, which contains the feeding
+mechanism, are shown in Figs. 3 and 4, to indicate how the feeds are
+engaged and reversed. The feed-rod _R_ (Fig. 1) drives the small bevel
+gears _A_ and _A_{1}_ (Figs. 3 and 4), which are mounted on a slide _S_
+that can be moved by lever _r_ to bring either bevel gear into mesh with
+gear _B_. Gear _B_ is attached to pinion _b_ (see Fig. 3) meshing with
+gear _C_, which, when knob _k_ (Fig. 1) is tightened, is locked by a
+friction clutch to pinion _c_. The latter pinion drives gear _D_ which
+rotates shaft _E_. A pinion cut on the end of shaft _E_ engages rack _K_
+(Fig. 1) attached to the bed, so that the rotation of _E_ (which is
+controlled by knob _k_) moves the carriage along the bed. To reverse the
+direction of the movement, it is only necessary to throw gear _A_ into
+mesh and gear _A_{1}_ out, or _vice versa_, by operating lever _r_. When
+the carriage is traversed by hand, shaft _E_ and gear _D_ are rotated by
+pinion _d_{1}_ connected with handle _d_ (Fig. 1).
+
+The drive for the cross-feed is from gear _C_ to gear _F_ which can be
+engaged through a friction clutch (operated by knob _l_, Fig. 1) with
+gear _G_ meshing with a pinion _H_. The latter rotates the cross-feed
+screw, which passes through a nut attached to slide _D_ (Fig. 1), thus
+moving the latter at right angles to the ways of the bed. The cross-feed
+is also reversed by means of lever _r_. As previously explained,
+lead-screw _S_ is only used for feeding the carriage when cutting
+threads. The carriage is engaged with this screw by means of two
+half-nuts _N_ (Fig. 4) that are free to slide vertically and are closed
+around the screw by operating lever _u_. These half-nuts can only be
+closed when lever _r_ is in a central or neutral position, so that the
+screw feed and the regular turning feed cannot be engaged at the same
+time. As previously mentioned, lead-screw _S_, Fig. 1, is rotated from
+the lathe spindle, through gears _a_, _b_ and _c_, called change gears.
+An assortment of these gears, of various sizes, is provided with the
+lathe, for cutting screws of different pitch. The gears to use for any
+pitch within the range of the lathe are given on the plate _I_.
+
+=Example of Cylindrical Turning.=--Having now considered the principal
+features of what might be called a standard lathe, the method of using
+it in the production of machine parts will be explained. To begin with a
+simple example of work, suppose a steel shaft is to be turned to a
+diameter of 2-1/4 inches and a length of 14-1/2 inches, these being the
+finished dimensions. We will assume that the rough stock is cut off to a
+length of 14-5/8 inches and has a diameter of 2-5/8 inches. The first
+step in this operation is to form conically shaped center-holes in each
+end of the piece as indicated at _c_ in Fig. 5. As all work of this kind
+is held, while being turned, between the centers _h_ and _h_{1}_, holes
+corresponding in shape to these centers are necessary to keep the work
+in place. There are several methods of forming these center-holes, as
+explained later.
+
+After the work is centered, a dog _A_ is clamped to one end by
+tightening screw _s_; it is then placed between the centers of the
+lathe. The dog has a projecting end or "tail," as it is commonly called,
+which enters a slot in the faceplate _F_ and thereby drives or rotates
+the work, when power is applied to the lathe spindle onto which the
+faceplate is screwed. The tailstock center _h_1_, after being oiled,
+should be set up just tight enough to eliminate all play, without
+interfering with a free rotary movement of the work. This is done by
+turning handle _n_, and when the center is properly adjusted, the
+tailstock spindle containing the center is locked by tightening handle
+_p_. (Ordinary machine oil is commonly used for lubricating lathe
+centers, but a lubricant having more "body" should be used, especially
+when turning heavy parts. The following mixtures are recommended: 1. Dry
+or powdered red lead mixed with a good grade of mineral oil to the
+consistency of cream. 2. White lead mixed with sperm oil with enough
+graphite added to give the mixture a dark lead color.)
+
+[Illustration: Fig. 5. Plan View showing Work Mounted between Centers of
+Lathe]
+
+=Facing the Ends Square with a Side-tool.=--Everything is now ready for
+the turning operation. The ends of the piece should be faced square
+before turning the body to size, and the tool for this squaring
+operation is shown in Fig. 6; this is known as a side-tool. It has a
+cutting edge _e_ which shaves off the metal as indicated in the end view
+by the dotted lines. The side _f_ is ground to an angle so that when
+the tool is moved in the direction shown by the arrow, the cutting edge
+will come in contact with the part to be turned; in other words, side
+_f_ is ground so as to provide clearance for the cutting edge. In
+addition, the top surface against which the chip bears, is beveled to
+give the tool keenness so that it will cut easily. As the principles of
+tool grinding are treated separately in Chapter II we shall for the
+present consider the tool's use rather than its form.
+
+[Illustration: Fig. 6. Lathe Side-tool for Facing Ends of Shafts, etc.]
+
+For facing the end, the side tool is clamped in the toolpost by
+tightening the screw _u_, Fig. 5, and it should be set with the cutting
+edge slightly inclined from a right-angled position, the point being in
+advance so that it will first come into contact with the work. The
+cutting edge should also be about the same height as the center of the
+work. When the tool is set, the lathe (if belt-driven) is started by
+shifting an overhead belt and the tool is then moved in until the point
+is in the position shown at _A_, Fig. 7. The tool-point is then fed
+against the end by handle _d_, Fig. 5, until a light chip is being
+turned off, and then it is moved outward by handle _e_ (as indicated by
+the arrow at _B_, Fig. 7), the carriage remaining stationary. As the
+movement of the tool-point is guided by the cross-slide _D_, which is at
+right angles with the axis of the work, the end will be faced square.
+For short turning operations of this kind, the power feeds ordinarily
+are not used as they are intended for comparatively long cuts. If it
+were necessary to remove much metal from the end, a number of cuts would
+be taken across it; in this case, however, the rough stock is only 1/8
+inch too long so that this end need only be made true.
+
+[Illustration: Fig. 7. Facing End with Side-tool and Turning Work
+Cylindrical]
+
+After taking a cut as described, the surface, if left rough by the
+tool-point, should be made smooth by a second or finishing cut. If the
+tool is ground slightly round at the point and the cutting edge is set
+almost square, as at _C_, Fig. 7, a smooth finish can be obtained; the
+cut, however, should be light and the outward feed uniform. The work is
+next reversed in the centers and the driving dog is placed on the end
+just finished; the other end is then faced, enough metal being removed
+to make the piece 14-1/2 inches long, as required in this particular
+case. This completes the facing operation. If the end of the work does
+not need to be perfectly square, the facing operation can be performed
+by setting the tool in a right-angled position and then feeding it
+sidewise, thus removing a chip equal to the width of one side. Evidently
+this method is confined to comparatively small diameters and the
+squareness of the turned end will be determined by the position of the
+tool's cutting edge.
+
+=Turning Tool--Turning Work Cylindrical.=--The tool used to turn the
+body to the required diameter is shaped differently from the side-tool,
+the cutting edge _E_ of most tools used for plain cylindrical turning
+being curved as shown in Fig. 8. A tool of this shape can be used for a
+variety of cylindrical turning operations. As most of the work is done
+by that part of the edge marked by arrow _a_, the top of the tool is
+ground to slope back from this part to give it keenness. The end _F_, or
+the flank, is also ground to an angle to provide clearance for the
+cutting edge. If the tool did not have this clearance, the flank would
+rub against the work and prevent the cutting edge from entering the
+metal. This type of tool is placed about square with the work, for
+turning, and with the cutting end a little above the center.
+
+[Illustration: Fig. 8. Tool used for Cylindrical Turning]
+
+Before beginning to turn, a pair of outside calipers or a micrometer
+should be set to 2-1/4 inches, which, in this case, is the finished
+diameter of the work. Calipers are sometimes set by using a graduated
+scale as at _A_, Fig. 9, or they can be adjusted to fit a standard
+cylindrical gage of the required size as at _B_. Very often fixed
+caliper gages _C_ are used instead of the adjustable spring calipers.
+These fixed gages, sometimes called "snap" gages, are accurately made to
+different sizes, and they are particularly useful when a number of
+pieces have to be turned to exactly the same size.
+
+The turning tool is started at the right-hand end of the work and the
+tool should be adjusted with the left hand when beginning a cut, as
+shown in Fig. 10, in order to have the right hand free for calipering. A
+short space is first turned by hand feeding, as at _D_, Fig. 7, and when
+the calipers show that the diameter is slightly greater than the
+finished size (to allow for a light finishing cut, either in the lathe
+or grinding machine) the power feed for the carriage is engaged; the
+tool then moves along the work, reducing it as at _E_. Evidently, if the
+movement is along a line _b--b_, parallel with the axis _a--a_, the
+diameter _d_ will be the same at all points, and a true cylindrical
+piece will be turned. On the other hand, if the axis _a--a_ is inclined
+one way or the other, the work will be made tapering; in fact, the
+tailstock center _h_1_ can be adjusted laterally for turning tapers, but
+for straight turning, both centers must be in alignment with the
+carriage travel. Most lathes have lines on the stationary and movable
+parts of the tailstock base which show when the centers are set for
+straight turning. These lines, however, may not be absolutely correct,
+and it is good practice to test the alignment of the centers before
+beginning to turn. This can be done by taking trial cuts, at each end of
+the work (without disturbing the tool's crosswise position), and then
+comparing the diameters, or by testing the carriage travel with a true
+cylindrical piece held between the centers as explained later.
+
+[Illustration: Fig. 9. Setting Calipers by Scale--Setting by Gage--Fixed
+Gage]
+
+If the relative positions of the lathe centers are not known, the work
+should be calipered as the cut progresses to see if the diameter _d_ is
+the same at all points. In case the diameter gradually increases, the
+tailstock center should be shifted slightly to the rear before taking
+the next cut, but if the diameter gradually diminishes, the adjustment
+would, of course, be made in the opposite direction. The diameter is
+tested by attempting to pass the calipers over the work. When the
+measuring points just touch the work as they are gently passed across
+it, the diameter being turned is evidently the same as the size to which
+the calipers are set.
+
+[Illustration: Fig. 10. Views showing how the Cross-slide and Carriage
+are Manipulated by Hand when Starting a Cut--View to Left, Feeding Tool
+Laterally; View to Right, Feeding Tool in a Lengthwise Direction]
+
+As the driving dog is on one end, the cut cannot be taken over the
+entire length, and when the tool has arrived at say position _x_, Fig.
+5, it is returned to the starting point and the work is reversed in the
+centers, the dog being placed upon the other end. The unfinished part is
+then turned, and if the cross-slide is not moved, the tool will meet the
+first cut. It is not likely that the two cuts will be joined or blended
+together perfectly, however, and for this reason a cut should be
+continuous when this is possible.
+
+=Roughing and Finishing Cuts.=--Ordinarily in lathe work, as well as in
+other machine work, there are two classes of cuts, known as "roughing"
+and "finishing" cuts. Roughing cuts are for reducing the work as
+quickly as possible almost to the required size, whereas finishing cuts,
+as the name implies, are intended to leave the part smooth and of the
+proper size. When the rough stock is only a little larger than the
+finished diameter, a single cut is sufficient, but if there is
+considerable metal to turn away, one or more deep roughing cuts would
+have to be taken, and, finally, a light cut for finishing. In this
+particular case, one roughing and one finishing cut would doubtless be
+taken, as the diameter has to be reduced 3/8 inch. Ordinarily the
+roughing cut would be deep enough to leave the work about 1/32 or
+perhaps 1/16 inch above the finished size. When there is considerable
+metal to remove and a number of roughing cuts have to be taken, the
+depth of each cut and the feed of the tool are governed largely by the
+pulling power of the lathe and the strength of the work to withstand the
+strain of a heavy cut. The depth of roughing cuts often has to be
+reduced considerably because the part being turned is so flexible that a
+heavy cut would spring the work and cause the tool to gouge in. Of
+course, just as few cuts as possible should be taken in order to save
+time. The speed of the work should also be as fast as the conditions
+will allow for the same reason, but as there are many things which
+govern the speed, the feed of the tool, and the depth of the cut, these
+important points are referred to separately in Chapter II.
+
+=Filing and Finishing.=--In many cases the last or finishing cut does
+not leave as smooth a surface as is required and it is necessary to
+resort to other means. The method commonly employed for finishing in the
+lathe is by the use of a file and emery cloth. The work is rotated
+considerably faster for filing than for turning, and the entire surface
+is filed by a flat, single-cut file, held as shown in Fig. 11. The file
+is passed across the work and advanced sidewise for each forward stroke,
+until the entire surface is finished. The file should be kept in contact
+with the work continually, but on the return stroke the pressure should
+be relieved. The movement of the file during the forward or cutting
+stroke should be much slower than when filing in a vise. By moving the
+file slowly, the work can make a number of revolutions for each stroke,
+which tends to keep it round, as practically the same amount of metal is
+removed from the entire circumference. On the other hand, short rapid
+strokes tend to produce flat spots, or at least an irregular surface,
+especially if the work can only make part of a revolution for each
+cutting stroke. The pressure on the file during the forward stroke
+should also be kept as nearly uniform as possible.
+
+[Illustration: Fig. 11. Filing Work after Finishing Cut is taken]
+
+It is very difficult to file a part smooth and at the same time to keep
+it round and cylindrical, and the more filing that has to be done, the
+greater the chance of error. For this reason, the amount left for filing
+should be very small; in fact, the metal removed by filing should be
+just enough to take out the tool marks and give a smooth finish. Very
+often a satisfactory finish can be obtained with a turning tool, and
+filing is not necessary at all. The file generally used for lathe work
+is a "single-cut bastard" of "mill" section, having a length of from 12
+to 14 inches.
+
+Sometimes particles of metal collect between the teeth of a file and
+make deep scratches as the file is passed across the work. When this
+occurs, the teeth should be cleaned by using a wire brush or a file
+card, which is drawn across the file in the direction of the teeth. This
+forming of tiny particles between the teeth is known as "pinning" and it
+can sometimes be avoided by rubbing chalk on the file. Filing is not
+only done to obtain a smooth finish, but also to reduce the work to an
+exact diameter, as a very slight reduction can be made in this way.
+
+[Illustration: Fig. 12. Two Methods of Aligning Centers for Cylindrical
+Turning]
+
+If a polish is desired, this can be obtained by holding a piece of emery
+cloth tightly around the work as it revolves. The coarseness of emery
+cloth is indicated by letters and numbers corresponding to the grain
+number of loose emery. The letters and numbers for grits ranging from
+fine to coarse are as follows: _FF_, _F_, 120, 100, 90, 80, 70, 60, 54,
+46, 40. For large work roughly filed, use coarse cloth such as Nos. 46
+or 54, and then finer grades to obtain the required polish. If the work
+has been carefully filed, a good polish can be obtained with Nos. 60 and
+90 cloth, and a brilliant polish by finishing with No. 120 and
+flour-emery.
+
+Most cylindrical parts can be finished more quickly and accurately in
+the grinder than in the lathe, and many classes of work are, at the
+present time, simply rough-turned in the lathe and then ground to size
+in a cylindrical grinding machine.
+
+=Aligning Centers for Cylindrical Turning.=--When a rod or shaft must be
+turned cylindrical or to the same diameter throughout its entire length,
+it is good practice to test the alignment of the centers, before
+inserting the work. The position of the tailstock center for cylindrical
+turning may be indicated by the coincidence of graduation marks on the
+base, but if accuracy is necessary, the relative position of the two
+centers should be determined in a more positive way. A very simple and
+convenient method of testing the alignment is shown at _A_ in Fig. 12.
+The work is first turned for a short distance, near the dogged end, as
+shown, and the tool is left as set for this cut; then the tailstock
+center is withdrawn and the work is moved sufficiently to permit running
+the tool back to the tailstock end without changing its original
+setting. A short cut is then taken at this end and the diameters _d_ and
+_d_{1}_ are carefully compared. In case there is any variation, the
+tailstock center is adjusted laterally, other trial cuts are taken, and
+the test repeated.
+
+Another method is illustrated at _B_, which requires the use of a
+test-bar _t_. This bar should have accurately made centers and the ends
+finished to exactly the same diameter. The lathe centers are aligned by
+placing the bar between them and then testing the position of the ends.
+This can be done by comparing each end with a tool held in the toolpost
+and moved from one to the other by shifting the carriage, but a better
+method is to clamp a test indicator _i_ in the toolpost and bring it in
+contact with first one end of the bar and then the other. If the dial
+does not register the same at each end, it shows that the lathe centers
+are not in line. Even when centers are correctly set, lathes that have
+been in use a long time do not always turn cylindrical or straight,
+because if the ways that guide the carriage are worn unevenly, the tool
+as it moves along does not remain in the same plane and this causes a
+variation in the diameter of the part being turned.
+
+=Application of Drivers or Dogs.=--Work that is turned between centers
+is sometimes driven by a dog which is so short for the faceplate that
+the bent driving end bears against the bottom _a_ of the faceplate slot,
+as shown at _A_, Fig. 13. If the dog is nearly the right length, it may
+allow the headstock center to enter the center in the work part way,
+with the result that the turned surface is not true with the centers.
+When a driving dog of this type is used, care should be taken to see
+that it moves freely in the faceplate slot and does not bind against the
+bottom. By using a straight dog (_B_), which is driven by a pin _b_
+bolted to the faceplate, all danger from this source is eliminated. The
+straight dog, however, is used more particularly to do away with the
+leverage _l_ of a bent dog, as this leverage tends to spring a flexible
+part when a cut is being taken.
+
+[Illustration: Fig. 13. (A) Dog that is too Short for Faceplate. (B)
+Straight Driving Dog]
+
+Straight dogs are also made with two driving ends which engage pins on
+opposite sides of the faceplate. This type is preferable because it
+applies the power required for turning, evenly to the work, which still
+further reduces the tendency to spring it out of shape. The principal
+objection to the double-ended type lies in the difficulty of adjusting
+the driving pins so that each bears with equal pressure against the dog.
+The double-ended driver is often used for large work especially if deep
+roughing cuts are necessary.
+
+=Lathe Arbors or Mandrels.=--When it is necessary to turn the outside of
+a part having a hole through it, centers cannot, of course, be drilled
+in the ends and other means must be resorted to. We shall assume that
+the bushing _B_, Fig. 14, has a finished hole through the center, and
+it is desired to turn the outside cylindrical and concentric with the
+hole. This could be done by forcing a tightly-fitted arbor _M_, having
+accurately-centered ends, into the bushing and inserting the mandrel and
+work between the lathe centers _h_ and _h_{1}_ as shown. Evidently, if
+the arbor runs true on its centers, the hole in the bushing will also
+run true and the outside can be turned the same as though the arbor and
+bushing were a solid piece. From this it will be seen that an arbor
+simply forms a temporary support for parts that are bored and therefore
+cannot be centered.
+
+[Illustration: Fig. 14. Bushing mounted on Arbor for Turning]
+
+Another example of work that would be turned on an arbor is shown in
+Fig. 15. This is a small cast-iron wheel having a finished hole through
+the hub, and the outer surface and sides of the rim are to be turned
+true with this hole. In this case, the casting would also be held by
+pressing a mandrel through the hub; as shown. This method, however,
+would only apply to comparatively small wheels because it would be
+difficult, if not impossible, to prevent a large wheel from turning on
+the arbor when taking a cut, and even if it could be driven, large work
+could be done to better advantage on another type of machine. (The
+vertical boring mill is used extensively for turning large wheels, as
+explained in Chapter VI.) When turning the outside of the rim, a tool
+similar to that shown at _t_ should be used, but for facing or turning
+the sides, it might be better, if not necessary, to use tools having
+bent ends as shown by the dotted lines; in fact, turning tools of
+various kinds are made with the ends bent to the right or left, as this
+enables them to be used on surfaces that could not be reached very well
+with a straight tool. If a comparatively large pulley is mounted near
+the end of the arbor, it can be driven directly by pins attached to the
+faceplate and engaging the pulley arms. This method of driving is often
+employed when the diameter to be turned is large and the hole for the
+arbor is so small that there will not be sufficient friction for
+driving.
+
+[Illustration: Fig. 15. Turning Pulley Held on an Arbor]
+
+=Different Types of Lathe Arbors.=--Three different types of lathe
+arbors are shown in Fig. 16. The kind shown at _A_ is usually made of
+tool steel and the body is finished to a standard size. The ends are
+somewhat reduced and flat spots are milled, as shown, to give the
+clamping screw of the dog a good grip. The body of the arbor is usually
+tapered about 0.006 inch per foot. This taper makes it easier to insert
+the arbor in a close-fitting hole, and it also permits slight variations
+in the diameter of different holes. As to hardening, the practice at the
+present time among manufacturers is to harden arbors all over, but for
+extremely accurate work, an arbor having hardened ends and a soft body
+is generally considered superior, as there is less tendency of
+distortion from internal stresses. Hardened arbors are "seasoned" before
+finish-grinding to relieve these internal stresses.
+
+The solid type _A_, Fig. 16, is used very extensively, but in shops
+where a great variety of work is being done and there are many odd-sized
+holes, some form of expanding arbor _B_ can be used to advantage. This
+type, instead of being solid, consists of a tapering inner arbor _M_ on
+which is placed a split bushing that can be expanded, within certain
+limits, by driving in the tapering member. The advantage of this type is
+that a comparatively small stock of arbors is required, as
+different-sized bushings can be used. This type can also be fitted to
+holes of odd sizes, whereas a solid arbor must be provided for each
+different size hole, unless the variation is very slight. The latter
+are, however, more accurate than the expanding type.
+
+[Illustration: Fig. 16. Different Types of Lathe Arbors]
+
+Another form of expanding arbor is shown at _C_. This type has a
+straight body _N_ in which four tapering grooves are cut lengthwise, as
+shown, and there is a sleeve _S_, containing four slots that are located
+to correspond with the tapering grooves. Strips s are fitted into these
+slots, and as the part _N_ is driven in, the strips are moved outward as
+they ascend the tapering grooves. By having different sets of these
+strips of various heights, one arbor of this type can be made to cover
+quite a range of sizes. It is not suited, however, to thin work, as the
+pressure, being concentrated in four places, would spring a flexible
+part out of shape.
+
+The cone arbor or mandrel shown at _A_, in Fig. 17, is convenient for
+holding parts having comparatively large holes, as it can be adjusted
+for quite a range of diameters. The work is gripped between the two
+cones _c_ and _c_{1}_ which are forced together by nut _n_. The cones
+are prevented from turning upon the arbor by keys. This style of arbor
+should not be used for accurate work. The threaded arbor _B_ is used for
+facing the sides of nuts square with the tapped hole. When a nut is
+first put upon the arbor, the rough side comes against an equalizing
+washer _w_. This washer rests against a spherical seat so that it can
+shift to provide a uniform bearing for the rough side of the nut, even
+though it is not square with the tapped hole. This feature prevents the
+nut from being canted on the arbor and insures an accurately faced nut.
+The revolving conical center shown at _C_ is often used for holding a
+pipe or tube while turning the outside. The cone is adjusted to fit into
+the hole of the pipe, by means of the tailstock spindle, and the
+opposite end is usually held in a chuck.
+
+[Illustration: Fig. 17. (A) Cone Arbor. (B) Nut Arbor. (C) Pipe Center]
+
+Particular care should be taken to preserve the accuracy of the centers
+of lathe arbors by keeping them clean and well-oiled while in use.
+
+=Mandrel or Arbor Press.=--The best method of inserting an arbor of the
+solid type in a hole is by using a press, Fig. 18, designed for that
+purpose, but if such a press is not available and it is necessary to
+drive the mandrel in, a "soft" hammer, made of copper, lead or other
+soft material, should be used to protect the centered end of the arbor.
+In either case, the arbor should not be forced in too tightly, for if it
+fits properly, this will not be necessary in order to hold the work
+securely. On the other hand, the work might easily be broken by
+attempting to force the arbor in as far and as tightly as possible. In
+using the arbor press, the work is placed on the base _B_ with the hole
+in a vertical position, and the arbor (which should be oiled slightly)
+is forced down into it by ram _R_, operated by lever _L_. Slots are
+provided in the base, as shown, so that the end of the arbor can come
+through at the bottom of the hole. The lever of this particular press is
+counter-weighted so that it rises to a vertical position when released.
+The ram can then be adjusted quickly to any required height by the
+handwheel seen at the left.
+
+[Illustration: Fig. 18. Press for Forcing Arbors into Work]
+
+Some shops are equipped with power-driven mandrel or arbor presses.
+This type is particularly desirable for large work, owing to the greater
+pressure required for inserting mandrels that are comparatively large in
+diameter. One well-known type of power press is driven by a belt, and
+the downward pressure of the ram is controlled by a handwheel. The ram
+is raised or lowered by turning this handwheel in one direction or the
+other, and a gage shows how much pressure is being applied. This type of
+press can also be used for other purposes, such as forcing bushings or
+pins into or out of holes, bending or straightening parts, or for
+similar work.
+
+[Illustration: Fig. 19. Steadyrest and Follow-rest for Supporting
+Flexible Parts]
+
+=Steadyrest for Supporting Flexible Parts.=--Occasionally long slender
+shafts, rods, etc., which have to be turned, are so flexible that it is
+necessary to support them at some point between the lathe centers. An
+attachment for the lathe known as a steadyrest is often used for this
+purpose. A steadyrest is composed of a frame containing three jaws _J_
+(Fig. 19), that can be adjusted in or out radially by turning screws
+_S_. The frame is hinged at _h_, thus allowing the upper half to be
+swung back (as shown by the dotted lines) for inserting or removing the
+work. The bolt-clamp _c_ holds the hinged part in the closed position.
+The base of the frame has V-grooves in it that fit the ways of the lathe
+bed. When the steadyrest is in use, it is secured to the bed by clamp
+_C_, and the jaws _J_ are set in against the work, thus supporting or
+steadying it during the turning operation. The steadyrest must, of
+course, be located at a point where it will not interfere with the
+turning tool.
+
+[Illustration: Fig. 20. Application of Steadyrest to a Flexible Rod]
+
+Fig. 20 shows the application of the steadyrest to a long forged rod,
+having one small end, which makes it too flexible to be turned without
+support. As this forging is rough, a true surface _n_ a little wider
+than the jaws _J_ (Fig. 19) is first turned as a bearing for the jaws.
+This should be done very carefully to prevent the work from mounting the
+tool. A sharp pointed tool should be used and very light cuts taken. The
+steadyrest is next clamped to the lathe bed opposite the turned surface,
+and the jaws are adjusted in against this surface, thus forming a
+bearing. Care should be taken not to set up the jaws too tightly, as the
+work should turn freely but without play. The large part of the rod and
+central collar are then turned to size, this half being machined while
+the small part is in the rough and as stiff as possible. The rod is then
+reversed and the steadyrest is applied to the part just finished, as
+shown at _B_, thus supporting the work while the small end is being
+turned. That part against which the jaws bear should be kept well oiled,
+and if the surface is finished it should be protected by placing a strip
+of emery cloth beneath the jaws with the emery side out; a strip of
+belt leather is also used for this purpose, the object in each case
+being to prevent the jaws from scratching and marring the finished
+surface, as they tend to do, especially if at all rough.
+
+If the work were too flexible to permit turning a spot at _n_, this
+could be done by first "spotting" it at some point _o_, and placing the
+steadyrest at that point while turning another spot at _n_.
+
+Sometimes it is desirable to apply a steadyrest to a surface that does
+not run true and one which is not to be turned; in such a case a device
+called a "cat-head" is used. This is simply a sleeve _S_ (Fig. 21) which
+is placed over the untrue surface to serve as a bearing for the
+steadyrest. The sleeve is made to run true by adjusting the four
+set-screws at each end, and the jaws of the steadyrest are set against
+it, thus supporting the work.
+
+[Illustration: Fig. 21. Cat-head which is sometimes used as Bearing for
+Steadyrest]
+
+=Application of Steadyrest when Boring.=--Another example illustrating
+the use of the steadyrest is shown in Fig. 22. The rod _R_ is turned on
+the outside and a hole is to be bored in the end (as shown by dotted
+lines) true with the outer surface. If the centers used for turning the
+rod are still in the ends, as they would be ordinarily, this work could
+be done very accurately by the following method: The rod is first placed
+between the centers as for turning, with a driving dog _D_ attached, and
+the steadyrest jaws _J_ are set against it near the outer end, as shown.
+
+Before any machine work is done, means must be provided for holding the
+rod back against the headstock center _h_, because, for an operation of
+this kind, the outer end cannot be supported by the tailstock center;
+consequently the work tends to shift to the right. One method of
+accomplishing this is shown in the illustration. A hardwood piece _w_,
+having a hole somewhat larger than the work, is clamped against the dog,
+in a crosswise position, by the swinging bolts and thumb-screws shown.
+If the dog is not square with the work, the wood piece should be canted
+so that the bearing will not be all on one side. For large heavy parts a
+similar "bridle" or "hold-back"--as this is commonly called--is made by
+using steel instead of wood for the part _w_. Another very common method
+which requires no special equipment is illustrated in Fig. 23. An
+ordinary leather belt lacing _L_ is attached to the work and faceplate
+while the latter is screwed off a few turns as shown. Then the lacing is
+drawn up by hand and tied, and the faceplate is screwed onto the
+spindle, thus tightening the lacing and drawing the work against the
+headstock center. The method of applying the lacing is quite clearly
+indicated in the illustration. If a small driving faceplate is used, it
+may be necessary to drill holes for the belt lacing, as shown.
+
+[Illustration: Fig. 22. Shaft supported by Steadyrest for Drilling and
+Boring End]
+
+A hole is next drilled in the end of the rod by using a twist drill in
+the tailstock. If the hole is finished by boring, a depth mark should
+be made on the tool shank that will warn the workman of the cutting
+end's approach to the bottom. A chuck can also be used in connection
+with a steadyrest for doing work of this kind, as shown in Fig. 24, the
+end of the rod being held and driven by the chuck _C_. If the piece is
+centered, it can be held on these centers while setting the steadyrest
+and adjusting the chuck, but if the ends are without centers, a very
+good way is to make light centers in the ends with a punch; after these
+are properly located they are used for holding the work until the
+steadyrest and chuck jaws have been adjusted. In case it is necessary to
+have the end hole very accurate with the outside of the finished rod, a
+test indicator _I_ should be applied to the shaft as shown. This is an
+instrument which shows with great accuracy whether a rotating part runs
+true and it is also used for many other purposes in machine shops. The
+indicator is held in the lathe toolpost and the contact point beneath
+the dial is brought against the work. If the latter does not run true,
+the hand of the indicator vibrates and the graduations on the dial show
+how much the work is out in thousandths of an inch.
+
+[Illustration: Fig. 23. Hold-back used when Outer End of Work is held in
+Steadyrest]
+
+=The Follow-rest.=--When turning long slender parts, such as shafts,
+etc., a follow-rest is often used for supporting the work. The
+follow-rest differs from the steadyrest in that it is attached to and
+travels with the lathe carriage. The type illustrated to the right in
+Fig. 19 has two adjustable jaws which are located nearly opposite the
+turning tool, thus providing support where it is most needed. In using
+this rest, a cut is started at the end and the jaws are adjusted to this
+turned part. The tool is then fed across the shaft, which cannot spring
+away from the cut because of the supporting jaws. Some follow-rests
+have, instead of jaws, a bushing bored to fit the diameter being turned,
+different bushings being used for different diameters. The bushing forms
+a bearing for the work and holds it rigidly. Whether a bushing or jaws
+are used, the turning tool is slightly in advance of the supporting
+member.
+
+[Illustration: Fig. 24. Testing Work with Dial Indicator]
+
+=Centering Parts to be Turned.=--As previously mentioned, there are a
+number of different methods of forming center-holes in the ends of parts
+that have to be turned while held between lathe centers. A method of
+centering light work, and one that requires few special tools, is first
+to locate a central point on the end and then drill and ream the
+center-hole by using the lathe itself. Hermaphrodite dividers are useful
+for finding the center, as illustrated at _A_, Fig. 25, but if the work
+is fairly round, a center-square _B_ is preferable. A line is scribed
+across the end and then another line at right angles to the first by
+changing the position of the square; the intersection of these two lines
+will be the center, which should be marked by striking a pointed punch
+_C_ with a hammer. If a cup or bell center-punch _D_ is available, it
+will not be necessary to first make center lines, as the conical part
+shown locates the punch in a central position. This style of punch
+should only be used on work which is fairly round.
+
+[Illustration: Fig. 25. Centering End with Punch preparatory to
+Drilling]
+
+After small centers have been located in both ends, their position can
+be tested by placing the work between the lathe centers and rotating it
+rapidly by drawing the hand quickly across it. By holding a piece of
+chalk close to the work as it spins around, a mark will be made on the
+"high" side if the centers are not accurate; the centers are then
+shifted toward these marks. If the work is close to the finished
+diameter, the centers should, of course, be located quite accurately in
+order that the entire surface of the work will be turned true when it is
+reduced to the finished size.
+
+One method of forming these center-holes is indicated in Fig. 26. A
+chuck _C_ is screwed onto the spindle in place of the faceplate, and a
+combination center drill and reamer _R_ is gripped by the chuck jaws and
+set to run true. The center is then drilled and reamed at one end by
+pressing the work against the revolving drill with the tailstock
+spindle, which is fed out by turning handle _n_. The piece is then
+reversed for drilling the opposite end. The work may be kept from
+revolving while the centers are being drilled and reamed, by attaching a
+dog to it close to the tailstock end and then adjusting the cross-slide
+until the dog rests upon the slide. Many parts can be held by simply
+gripping them with one hand. From the foregoing it will be seen that the
+small centers made by punch _C_, Fig. 25, serve as a starting point for
+the drill and also as a support for the outer end of the work while the
+first hole is being drilled.
+
+[Illustration: Fig. 26. Drilling Centers in the Lathe]
+
+The form of center-hole produced by a combination drill and reamer is
+shown by the lower left-hand view in Fig. 27. A small straight hole a in
+the bottom prevents the point of the lathe center from coming in contact
+with the work and insures a good bearing on the conical surface _c_. The
+standard angle for lathe centers is sixty degrees, as the illustration
+shows, and the tapering part of all center-holes should be made to this
+angle.
+
+[Illustration: Fig. 27. Centers of Incorrect and Correct Form]
+
+[Illustration: Fig. 28. Special Machine for Centering Parts to be
+Turned]
+
+=Centering Machine.=--Many shops have a special machine for forming
+centers which enables the operation to be performed quickly. One type
+of centering machine is shown in Fig. 28. The work is gripped in a chuck
+_C_ that automatically locates it in a central position so that it is
+not necessary to lay out the end before drilling. There are two spindles
+_s_, one of which holds the drill and the other the countersink, and
+these are rotated by a belt passing over pulley _P_. Each of these
+spindles is advanced by lever _L_ and either of them can be moved to a
+position central with the work, as they are mounted in a swiveling
+frame. In operating this machine, a small straight hole is first made by
+a twist drill held in one of the spindles; the other spindle is then
+moved over to the center and the hole is reamed tapering. The
+arrangement is such that neither spindle can be advanced by the feeding
+lever except when in a central position. The amount that each spindle
+can be advanced is limited by a fixed collar inside the head, and there
+is also a swinging adjustable stop against which the end of the work
+should be placed before tightening the chuck. These two features make it
+possible to ream center holes of the same size or depth in any number of
+pieces.
+
+[Illustration: Fig. 29. The Imperfect Center Bearing is the Result of
+Centering before Straightening]
+
+=Different Forms of Centers.=--In some poorly equipped shops it is
+necessary to form centers by the use of a center-punch only, as there is
+no better tool. If the end of the punch has a sixty-degree taper, a fair
+center can be formed in this way, but it is not a method to be
+recommended, especially when accurate work is required. Sometimes
+centers are made with punches that are too blunt, producing a shallow
+center, such as the one shown in the upper left-hand view, Fig. 27. In
+this case all the bearing is on the point of the lathe center, which is
+the worst possible place for it. Another way is to simply drill a
+straight hole as in the upper view to the right; this is also bad
+practice in more than one respect. The lower view to the right shows a
+form of center which is often found in the ends of lathe arbors, the
+mouth of the center being rounded, at _r_, and the arbor end recessed as
+shown. The rounded corner prevents the point of the lathe center from
+catching when it is moved rapidly towards work which is not being held
+quite centrally (as shown by the illustration), and the end is recessed
+to protect the center against bruises. Stock that is bent should always
+be straightened before the centers are drilled and reamed. If the work
+is first centered and then straightened the bearing on the lathe center
+would be as shown in Fig. 29. The center will then wear unevenly with
+the result that the surfaces last turned will not be concentric with
+those which were finished first.
+
+[Illustration: Fig. 30. Tool Steel should be centered Concentric, in
+order to remove the Decarbonized Outer Surface]
+
+=Precaution When Centering Tool Steel.=--Ordinarily centers are so
+located that the stock runs approximately true before being turned, but
+when centering tool steel to be used in making tools, such as reamers,
+mills, etc., which need to be hardened, particular care should be taken
+to have the rough surface run fairly true. This is not merely to insure
+that the piece will "true-up," as there is a more important
+consideration, the disregard of which often affects the quality of the
+finished tool. As is well known, the degree of hardness of a piece of
+tool steel that has been heated and then suddenly cooled depends upon
+the amount of carbon that it contains, steel that is high in carbon
+becoming much harder than that which contains less carbon. Furthermore,
+the amount of carbon found at the surface, and to some little depth
+below the surface of a bar of steel, is less than the carbon content in
+the rest of the bar. This is illustrated diagrammatically in Fig. 30 by
+the shaded area in the view to the left. (This decarbonization is
+probably due to the action of the oxygen of the air on the bar during
+the process of manufacture.) If stock for a reamer is so centered that
+the tool removes the decarbonized surface only on one side, as
+illustrated to the right, evidently when the reamer is finished and
+hardened the teeth on the side _A_ will be harder than those on the
+opposite side, which would not have been the case if the rough bar had
+been centered true. To avoid any trouble of this kind, stock that is to
+be used for hardened tools should be enough larger than the finished
+diameter and so centered that this decarbonized surface will be entirely
+removed in turning.
+
+[Illustration: Fig. 31. Three Methods of Facing the Ends Square]
+
+=Facing the Ends of Centered Stock.=--As a piece of work is not properly
+centered until the ends are faced square, we will consider this
+operation in connection with centering. Some machinists prefer lathe
+centers that are cut away as shown at _A_, Fig. 31, so that the point of
+the side tool can be fed in far enough to face the end right up to the
+center hole. Others, instead of using a special center, simply loosen
+the regular one slightly and then, with the tool in a position as at
+_B_, face the projecting teat by feeding both tool and center inward as
+shown by the arrow. Whenever this method is employed, care should be
+taken to remove any chips from the center hole which may have entered. A
+method which makes it unnecessary to loosen the regular center, or to
+use a special one, is to provide clearance for the tool-point by
+grinding it to an angle of approximately forty-five degrees, as shown at
+_C_. If the tool is not set too high, it can then be fed right up to the
+lathe center and the end squared without difficulty. As for the special
+center _A_, the use of special tools and appliances should always be
+avoided unless they effect a saving in time or their use makes it
+possible to accomplish the same end with less work.
+
+=Truing Lathe Centers.=--The lathe centers should receive careful
+attention especially when accurate work must be turned. If the headstock
+center does not run true as it revolves with the work, a round surface
+may be turned, but if the position of the driving dog with reference to
+the faceplate is changed, the turned surface will not run true because
+the turned surface is not true with the work centers. Furthermore, if
+it is necessary to reverse the work for finishing the dogged or driving
+end, the last part turned will be eccentric to the first. Therefore, the
+lathe centers should be kept true in order to produce turned surfaces
+that are true or concentric with the centered ends, as it is often
+necessary to change the part being turned "end for end" for finishing,
+and any eccentricity between the different surfaces would, in many
+cases, spoil the work.
+
+[Illustration: Fig. 32. Grinder for Truing Lathe Centers]
+
+Some lathes are equipped with hardened centers in both the head-and
+tailstock and others have only one hardened center which is in the
+tailstock. The object in having a soft or unhardened headstock center is
+to permit its being trued by turning, but as a soft center is quite
+easily bruised and requires truing oftener than one that is hard, it is
+better to have both centers hardened. Special grinders are used for
+truing these hardened centers. One type that is very simple and easily
+applied to a lathe is shown in Fig. 32. This grinder is held in the
+lathe toolpost and is driven by a wheel _A_ that is held in contact with
+the cone-pulley. The emery wheel _B_ is moved to a position for grinding
+by adjusting the carriage and cross-slide, and it is traversed across
+the conical surface of the center by handle _C_. As the grinding
+proceeds, the wheel is fed inward slightly by manipulating the
+cross-slide.
+
+This grinder is set to the proper angle by placing the two centered ends
+_D_ and _D_{1}_ between the lathe centers, which should be aligned as
+for straight turning. The grinding spindle will then be 30 degrees from
+the axis of the lathe spindle. The grinder should be carefully clamped
+in the toolpost so that it will remain as located by the centered ends.
+After the tailstock center is withdrawn, the emery wheel is adjusted for
+grinding. As the wheel spindle is 30 degrees from the axis of the lathe
+spindle, the lathe center is not only ground true but to an included
+angle of 60 degrees, which is the standard angle for lathe centers.
+There are many other styles of center grinders on the market, some of
+which are driven by a small belt from the cone-pulley and others by
+electric motors which are connected with ordinary lighting circuits. The
+tailstock center is ground by inserting it in the spindle in place of
+the headstock center. Before a center is replaced in its spindle, the
+hole should be perfectly clean as even a small particle of dirt may
+affect the alignment. The center in the headstock is usually referred to
+as the "live center" because it turns around when the lathe is in use,
+and the center in the tailstock as the "dead center," because it remains
+stationary.
+
+=Universal, Independent and Combination Chucks.=--Many parts that are
+turned in the lathe are so shaped that they cannot be held between the
+lathe centers like shafts and other similar pieces and it is often
+necessary to hold them in a chuck _A_, Fig. 33, which is screwed onto
+the lathe spindle instead of the faceplate. The work is gripped by the
+jaws _J_ which can be moved in or out to accommodate various diameters.
+There are three classes of chucks ordinarily used on the lathe, known as
+the independent, universal and combination types. The independent chuck
+is so named because each jaw can be adjusted in or out independently of
+the others by turning the jaw screws S with a wrench. The jaws of the
+universal chuck all move together and keep the same distance from the
+center, and they can be adjusted by turning any one of the screws _S_,
+whereas with the independent type the chuck wrench must be applied to
+each jaw screw. The combination chuck, as the name implies, may be
+changed to operate either as an independent or universal type. The
+advantage of the universal chuck is that round and other parts of a
+uniform shape are located in a central position for turning without any
+adjustment. The independent type is, however, preferable in some
+respects as it is usually stronger and adapted for holding odd-shaped
+pieces because each jaw can be set to any required position.
+
+[Illustration: Fig. 33. (A) Lathe Chuck. (B) Faceplate Jaw]
+
+=Application of Chucks.=--As an example of chuck work, we shall assume
+that the sides of disk _D_, Fig. 34, are to be turned flat and parallel
+with each other and that an independent chuck is to be used. First the
+chuck is screwed onto the lathe spindle after removing the faceplate.
+The chuck jaws are then moved out or in, as the case may be, far enough
+to receive the disk and each jaw is set about the same distance from the
+center by the aid of concentric circles on the face of the chuck. The
+jaws are then tightened while the disk is held back against them to
+bring the rough inner surface in a vertical plane. If the work is quite
+heavy, it can be held against the chuck, before the jaws are tightened,
+by inserting a piece of wood between it and the tailstock center; the
+latter is then run out far enough to force the work back. The outside
+or periphery of the disk should run nearly true and it may be necessary
+to move the jaws in on one side and out on the other to bring the disk
+to a central position. To test its location, the lathe is run at a
+moderate speed and a piece of chalk is held near the outer surface. If
+the latter runs out, the "high" side will be marked by the chalk, and
+this mark can be used as a guide in adjusting the jaws. It should be
+remembered that the jaws are moved only one-half the amount that the
+work runs out.
+
+[Illustration: Fig. 34. (A) Radial Facing. (B) Boring Pulley Held in
+Chuck]
+
+A round-nosed tool _t_ of the shape shown can be used for radial facing
+or turning operations of the kind illustrated. This tool is similar to
+the form used when turning between centers, the principal difference
+being in the direction of the top slope. The radial facing tool should
+be ground to slope downward toward _a_ (see Fig. 35) whereas the regular
+turning tool slopes toward _b_, the inclination in each case being away
+from that part of the cutting edge which does the work. The cutting edge
+should be the same height as the lathe centers, and the cut is taken by
+feeding the tool from the outside in to the center. The cut is started
+by hand and then the power feed is engaged, except for small surfaces.
+The first cut should, if possible, be deep enough to get beneath the
+scale, especially if turning cast iron, as a tool which just grazes the
+hard outer surface will be dulled in a comparatively short time.
+
+If it were simply necessary to turn a true flat surface and the
+thickness of the disk were immaterial, two cuts would be sufficient,
+unless the surface were very uneven, the first or roughing cut being
+followed by a light finishing cut. For a finishing cut, the same tool
+could be used, but if there were a number of disks to be faced, a
+square-nosed tool _F_, Fig. 35, could probably be used to better
+advantage. This type has a broad flat cutting edge that is set parallel
+with the rough-turned surface and this broad edge enables a coarse feed
+to be taken, thus reducing the time required for the finishing cut. If a
+coarse feed were taken with the round tool, the turned surface would
+have spiral grooves in it, whereas with the broad cutting edge, a smooth
+surface is obtained even though the feed is coarse. The amount of feed
+per revolution of the work, however, should always be less than the
+width _w_ of the cutting edge. Very often broad tools cannot be used for
+finishing cuts, especially when turning steel, because their greater
+contact causes chattering and results in a rough surface. An old and
+worn lathe is more liable to chatter than one that is heavy and
+well-built, and as the diameter of the work also makes a difference, a
+broad tool cannot always be used for finishing, even though,
+theoretically, it would be preferable. After one side of the disk is
+finished, it is reversed in the chuck, the finished surface being placed
+against the jaws. The remaining rough side is then turned, care being
+taken when starting the first cut to caliper the width of the disk at
+several points to make sure that the two sides are parallel.
+
+[Illustration: Fig. 35. Tools Ground so that Top Slopes away from
+Working Part of Cutting Edge]
+
+=Example of Boring.=--Another example of chuck work is shown at _B_,
+Fig. 34. In this case a cast-iron pulley is to have a true hole _h_
+bored through the hub. (The finishing of internal cylindrical surfaces
+in a lathe is referred to as boring rather than turning.) The casting
+should be set true by the rim instead of by the rough-cored hole in the
+hub; this can be done by the use of chalk as previously explained. Even
+though a universal type of chuck were used, the jaws of which, as will
+be recalled, are self-centering, it might be necessary to turn the
+pulley relative to the chuck as a casting sometimes runs out because of
+rough spots or lumps which happen to come beneath one or more of the
+jaws.
+
+[Illustration: Fig. 36. Boring Tool]
+
+The shape of tool _t_ for boring is quite different from one used for
+outside turning, as shown by Fig. 36. The cutting end of a solid type of
+tool is forged approximately at right angles to the body or shank, and
+the top surface is ground to slope away from the working part _w_ of the
+cutting edge, as with practically all turning tools. The front part or
+flank, _f_ is also ground away to give the edge clearance. This type of
+tool is clamped in the toolpost with the body about parallel with the
+lathe spindle, and ordinarily the cutting edge would be about as high as
+the center of the hole, or a little below, if anything. When starting a
+cut, the tool is brought up to the work by moving the carriage and it is
+then adjusted radially to get the right depth of cut, by shifting the
+cross-slide. The power feed for the carriage is then used, the tool
+feeding back through the hole as indicated by the arrow, Fig. 34. In
+this case, as with all turning operations, the first cut should be deep
+enough to remove the hard outer scale at every part of the hole. Usually
+a rough-cored hole is so much smaller than the finished size that
+several cuts are necessary; in any case, the last or finishing cut
+should be very light to prevent the tool from springing away from the
+work, so that the hole will be as true as possible. Boring tools,
+particularly for small holes, are not as rigid as those used for outside
+turning, as the tool has to be small enough to enter the hole and for
+this reason comparatively light cuts have to be taken. When boring a
+small hole, the largest tool that will enter it without interference
+should be used to get the greatest rigidity possible.
+
+[Illustration: Fig. 37 (A) Setting Outside Calipers. (B) Transferring
+Measurements to Inside Calipers. (C) Micrometer Gage]
+
+=Measuring Bored Holes.=--The diameters of small holes that are being
+bored are usually measured with inside calipers or standard gages. If
+the pulley were being bored to fit over some shaft, the diameter of the
+shaft would first be measured by using outside calipers, as shown at
+_A_, Fig. 37, the measuring points of the calipers being adjusted until
+they just made contact with the shaft when passed over it. The inside
+calipers are then set as at _B_ to correspond with the size of the
+shaft, and the hole is bored just large enough to admit the inside
+calipers easily. Very accurate measurements can be made with calipers,
+but to become expert in their use requires experience. Some mechanics
+never become proficient in the art of calipering because their hands are
+"heavy" and they lack the sensitiveness and delicacy of touch that is
+necessary. For large holes, a gage _C_ is often used, the length _l_
+being adjusted to the diameter desired. Small holes are often bored to
+fit hardened steel plug gages (Fig. 38), the cylindrical measuring ends
+of which are made with great accuracy to standard sizes. This type of
+gage is particularly useful when a number of holes have to be bored to
+the same size, all holes being made just large enough to fit the gage
+without any perceptible play.
+
+[Illustration: Fig. 38. Standard Plug Gage]
+
+_Setting Work in the Chuck._--When setting a part in a chuck, care
+should be taken to so locate it that every surface to be turned will be
+true when machined to the finished size. As a simple illustration, let
+us assume that the hole through the cast-iron disk, Fig. 39, has been
+cored considerably out of center, as shown. If the work is set by the
+outside surface _S_, as it would be ordinarily, the hole is so much out
+of center that it will not be true when bored to the finished size, as
+indicated by the dotted lines. On the other hand, if the rough hole is
+set true, the outside cannot be finished all over, without making the
+diameter too small, when it is finally turned. In such a case, the
+casting should be shifted, as shown by the arrow, to divide the error
+between the two surfaces, both of which can then be turned as shown by
+the dotted lines in the view to the right. This principle of dividing
+the error when setting work can often be applied in connection with
+turning and boring. After a casting or other part has been set true by
+the most important surface, all other surfaces which require machining
+should be tested to make sure that they all can be finished to the
+proper size.
+
+=Inaccuracy from Pressure of Chuck Jaws.=--Work that is held in a chuck
+is sometimes sprung out of shape by the pressure of the chuck jaws so
+that when the part is bored or turned, the finished surfaces are untrue
+after the jaws are released and the work has resumed its normal shape.
+This applies more particularly to frail parts, such as rings, thin
+cylindrical parts, etc. Occasionally the distortion can be prevented by
+so locating the work with relation to the chuck jaws that the latter
+bear against a rigid part. When the work cannot be held tightly enough
+for the roughing cuts without springing it, the jaws should be released
+somewhat before taking the finishing cut, to permit the part to spring
+back to its natural shape.
+
+[Illustration: Fig. 39. Diagram Illustrating Importance of Setting Work
+with Reference to Surfaces to be Turned]
+
+[Illustration: Fig. 40. Drilling in the Lathe]
+
+=Drilling and Reaming.=--When a hole is to be bored from the solid, it
+is necessary to drill a hole before a boring tool can be used. One
+method of drilling in the lathe is to insert an ordinary twist drill in
+a holder or socket _S_, Fig. 40, which is inserted in the tailstock
+spindle in place of the center. The drill is then fed through the work
+by turning the handle _n_ and feeding the spindle outward as shown by
+the arrow. Before beginning to drill, it is well to turn a conical spot
+or center for the drill point so the latter will start true. This is
+often done by using a special tool having a point like a flat drill.
+This tool is clamped in the toolpost with the point at the same height
+as the lathe centers. It is then fed against the center of the work and
+a conical center is turned. If the drill were not given this true
+starting point, it probably would enter the work more or less off
+center. Drills can also be started without turning a center by bringing
+the square end or butt of a tool-shank held in the toolpost in contact
+with the drill near the cutting end. If the point starts off center,
+thus causing the drill to wobble, the stationary tool-shank will
+gradually force or bump it over to the center.
+
+[Illustration: Fig. 41. Flat Drill and Holder]
+
+Small holes are often finished in the lathe by drilling and reaming
+without the use of a boring tool. The form of drill that is used quite
+extensively for drilling cored holes in castings is shown in Fig. 41, at
+_A_. This drill is flat and the right end has a large center hole for
+receiving the center of the tailstock. To prevent the drill from
+turning, a holder _B_, having a slot _s_ in its end through which the
+drill passes, is clamped in the toolpost, as at _C_. This slot should be
+set central with the lathe centers, and the drill, when being started,
+should be held tightly in the slot by turning or twisting it with a
+wrench as indicated in the end view at _D_; this steadies the drill and
+causes it to start fairly true even though the cored hole runs out
+considerably.
+
+Another style of tool for enlarging cored holes is shown in Fig. 42, at
+_A_. This is a rose chucking reamer, having beveled cutting edges on the
+end and a cylindrical body, which fits closely in the reamed hole, thus
+supporting and guiding the cutting end. The reamer shown at _B_ is a
+fluted type with cutting edges that extend from _a_ to _b_; it is used
+for finishing holes and the drill or rose reamer preceding it should
+leave the hole very close to the required size. These reamers are held
+while in use in a socket inserted in the tailstock spindle, as when
+using a twist drill.
+
+[Illustration: Fig. 42. Rose and Fluted Reamers]
+
+=Holding Work on Faceplate.=--Some castings or forgings are so shaped
+that they cannot be held in a chuck very well, or perhaps not at all,
+and work of this kind is often clamped to a faceplate which is usually
+larger than the faceplate used for driving parts that are turned between
+the centers. An example of faceplate work is shown in Fig. 43. This is a
+rectangular-shaped casting having a round boss or projection, the end
+_e_ of which is to be turned parallel with the back face of the casting
+previously finished on a planer. A rough cored hole through the center
+of the boss also needs to be bored true.
+
+The best way to perform this operation in the lathe would be to clamp
+the finished surface of the casting directly against the faceplate by
+bolts and clamps _a_, _b_, _c_, and _d_, as shown; the work would then
+be turned just as though it were held in a chuck. By holding the casting
+in this way, face _e_ will be finished parallel with the back surface
+because the latter is clamped directly against the true-running surface
+of the faceplate. If a casting of this shape were small enough it could
+also be held in the jaws of an independent chuck, but if the surface e
+needs to be exactly parallel with the back face, it is better to clamp
+the work to the faceplate. Most lathes have two faceplates: One of small
+diameter used principally for driving work turned between centers, and a
+large one for holding heavy or irregularly shaped pieces; either of
+these can be screwed onto the spindle, and the large faceplate has a
+number of slots through which clamping bolts can be inserted.
+
+[Illustration: Fig. 43. Casting Clamped to Faceplate for Turning and
+Boring]
+
+The proper way to clamp a piece to the faceplate depends, of course,
+largely on its shape and the location of the surface to be machined, but
+in any case it is necessary to hold it securely to prevent any shifting
+after a cut is started. Sometimes castings can be held by inserting
+bolts through previously drilled holes, but when clamps are used in
+connection with the bolts, their outer ends are supported by hardwood or
+metal blocks which should be just high enough to make the clamp bear
+evenly on the work. When deep roughing cuts have to be taken,
+especially on large diameters, it is well to bolt a piece to the
+faceplate and against one side of the casting, as at _D_, to act as a
+driver and prevent the work from shifting; but a driver would not be
+needed in this particular case. Of course a faceplate driver is always
+placed to the rear, as determined by the direction of rotation, because
+the work tends to shift backward when a cut is being taken. If the
+surface which is clamped against the faceplate is finished as in this
+case, the work will be less likely to shift if a piece of paper is
+placed between it and the faceplate.
+
+[Illustration: Fig. 44. Cast Elbow held on Angle-plate attached to
+Faceplate]
+
+Work mounted on the faceplate is generally set true by some surface
+before turning. As the hole in this casting should be true with the
+round boss, the casting is shifted on the faceplate until the rough
+outer surface of the boss runs true; the clamps which were previously
+set up lightly are then tightened. The face e is first turned by using a
+round-nosed tool. This tool is then replaced by a boring tool and the
+hole is finished to the required diameter. If the hole being bored is
+larger than the central hole in the faceplate, the casting should be
+clamped against parallel pieces, and not directly against the faceplate,
+to provide clearance for the tool when it reaches the inner end of the
+hole and prevent it from cutting the faceplate. The parallel pieces
+should be of the same thickness and be located near the clamps to
+prevent springing the casting.
+
+=Application of Angle-plate to Faceplate.=--Another example of faceplate
+work is shown in Fig. 44. This is a cast-iron elbow _E_, the two flanges
+of which are to be faced true and square with each other. The shape of
+this casting is such that it would be very difficult to clamp it
+directly to the faceplate, but it is easily held on an angle-plate _P_,
+which is bolted to the faceplate. The two surfaces of this angle-plate
+are square with each other so that when one flange of the elbow is
+finished and bolted against the angle-plate, the other will be faced
+square. When setting up an angle-plate for work of this kind, the
+distance from its work-holding side to the center of the faceplate is
+made equal to the distance _d_ between the center of one flange and the
+face of the other, so that the flange to be faced will run about true
+when bolted in place. As the angle-plate and work are almost entirely on
+one side of the faceplate, a weight _W_ is attached to the opposite side
+for counterbalancing. Very often weights are also needed to
+counterbalance offset parts that are bolted directly to the faceplate.
+The necessity of counterbalancing depends somewhat upon the speed to be
+used for turning. If the surface to be machined is small in diameter so
+that the lathe can be run quite rapidly, any unbalanced part should
+always be counterbalanced.
+
+Sometimes it is rather difficult to hold heavy pieces against the
+vertical surface of the faceplate while applying the clamps, and
+occasionally the faceplate is removed and placed in a horizontal
+position on the bench; the work can then be located about right, and
+after it is clamped, the faceplate is placed on the lathe spindle by the
+assistance of a crane.
+
+Special faceplate jaws, such as the one shown to the right in Fig. 33,
+can often be used to advantage for holding work on large faceplates.
+Three or four of these jaws are bolted to the faceplate which is
+converted into a kind of independent chuck. These faceplate jaws are
+especially useful for holding irregularly shaped parts, as the different
+jaws can be located in any position.
+
+=Supporting Outer End of Chucked Work.=--Fig. 45 shows how the tailstock
+center is sometimes used for supporting the outer end of a long casting,
+the opposite end of which is held in a chuck. This particular casting
+is to be turned and bored to make a lining for the cylinder of a
+locomotive in order to reduce the diameter of the cylinder which has
+been considerably enlarged by re-boring a number of times. These
+bushings are rough-turned on the outside while the outer end is
+supported by the cross-shaped piece or "spider" which forms a
+center-bearing for the tailstock. This spider has set screws in the
+flanged ends of the arms, which are tightened against the inner surface
+of the casting and are adjusted one way or the other in order to locate
+it in a concentric position. After roughing the outside, the inside is
+bored to the finish size; then centered disks, which fit into the bore,
+are placed in the ends of the bushing and the latter is finish-turned.
+The object in rough turning the outside prior to boring is to avoid the
+distortion which might occur if this hard outer surface were removed
+last.
+
+[Illustration: Fig. 45. Rough Turning a Cylinder Lining--Note Method of
+Supporting Outer End]
+
+=Boring Large Castings in the Lathe.=--An ordinary engine lathe is
+sometimes used for boring engine or pump cylinders, linings, etc., which
+are too large to be held in the chuck or on a faceplate, and must be
+attached to the lathe carriage. As a rule, work of this class is done in
+a special boring machine (see "Horizontal Boring Machines"), but if
+such a machine is not available, it may be necessary to use a lathe.
+There are two general methods of boring.
+
+Fig. 46 shows how the lining illustrated in Fig. 45 is bored in a large
+engine lathe. The casting is held in special fixtures which are attached
+to the lathe carriage, and the boring-bar is rotated by the lathe
+spindle. The tool-head of this boring-bar carries two tools located 180
+degrees apart and it is fed along the bar by a star-feed mechanism shown
+attached to the bar and the tailstock spindle. Each time the bar
+revolves, the star wheel strikes a stationary pin and turns the
+feed-screw which, as the illustration shows, extends along a groove cut
+in one side of the bar. This feed-screw passes through a nut attached to
+the tool-head so that the latter is slowly fed through the bore. When
+using a bar of this type, the carriage, of course, remains stationary.
+
+[Illustration: Fig. 46. Boring a Cylinder Lining in an Ordinary Engine
+Lathe]
+
+Cylindrical parts attached to the carriage can also be bored by using a
+plain solid bar mounted between the centers. The bar must be provided
+with a cutter for small holes or a tool-head for larger diameters
+(preferably holding two or more tools) and the boring is done by
+feeding the carriage along the bed by using the regular power feed of
+the lathe. A symmetrically shaped casting like a bushing or lining is
+often held upon wooden blocks bolted across the carriage. These are
+first cut away to form a circular seat of the required radius, by using
+the boring-bar and a special tool having a thin curved edge. The casting
+is then clamped upon these blocks by the use of straps and bolts, and if
+the curved seats were cut to the correct radius, the work will be
+located concentric with the boring-bar. When using a boring-bar of this
+type, the bar must be long enough to allow the part being bored to feed
+from one side of the cutter-head to the other, the cutter-head being
+approximately in a central location.
+
+[Illustration: Fig. 47. Method of Setting Circle on Work Concentric with
+Lathe Spindle]
+
+=Boring Holes to a Given Center Distance.=--In connection with faceplate
+work, it is often necessary to bore two or more holes at a given
+distance apart. The best method of doing this may depend upon the
+accuracy required. For ordinary work sometimes two or more circles _A_
+and _B_ (Fig. 47) are drawn upon the part to be bored, in the position
+for the holes; the piece is then clamped to the faceplate and one of the
+circles is centered with the lathe spindle by testing it with a pointer
+C held in the toolpost; that is, when the pointer follows the circle as
+the work is turned, evidently the circle is concentric with the spindle.
+The hole is then drilled and bored. The other circle is then centered
+in the same way for boring the second hole. As will be seen, the
+accuracy of this method depends first, upon the accuracy with which the
+circles were laid out, and second; upon the care taken in setting them
+concentric. For a more accurate way of locating parts for boring, see
+"Use of Center Indicator" and "Locating Work by the Button Method."
+
+=Turning Brass, Bronze and Copper.=--When turning soft yellow brass, a
+tool should be used having very little or no slope or rake on the top
+surface against which the chip bears, and for plain cylindrical turning,
+the point of the tool is drawn out quite thin and rounded, by grinding,
+to a radius of about 1/8 or 3/16 inch. If a tool having very much top
+slope is used for brass, there is danger of its gouging into the metal,
+especially if the part being turned is at all flexible. The clearance
+angle of a brass tool is usually about 12 or 14 degrees, which is 3 or 4
+degrees greater than the clearance for steel turning tools. Most brass
+is easily turned, as compared with steel, and for that reason this
+increase in clearance is desirable, because it facilitates feeding the
+tool into the metal, especially when the carriage and cross-slide
+movements are being controlled by hand as when turning irregular shapes.
+
+The speed for turning soft brass is much higher than for steel, being
+ordinarily between 150 and 200 feet per minute. When turning phosphor,
+tobin or other tough bronze compositions, the tool should be ground with
+rake the same as for turning steel, and lard oil is sometimes used as a
+lubricant. The cutting speed for bronzes varies from 35 or 40 to 80 feet
+per minute, owing to the difference in the composition of bronze alloys.
+
+Turning tools for copper are ground with a little more top rake than is
+given steel turning tools, and the point should be slightly rounded. It
+is important to have a keen edge, and a grindstone is recommended for
+sharpening copper turning tools. Milk is generally considered the best
+lubricant to use when turning copper. The speed can be nearly as fast as
+for brass.
+
+=Machining Aluminum.=--Tools for turning aluminum should have acute
+cutting angles. After rough-grinding the tool, it is advisable to finish
+sharpening the cutting edge on a grindstone or with an oilstone for fine
+work, as a keen edge is very essential. High speeds and comparatively
+light cuts are recommended. The principal difficulty in the machining of
+aluminum and aluminum alloys is caused by the clogging of the chips,
+especially when using such tools as counterbores and milling cutters.
+This difficulty can be avoided largely by using the right kind of
+cutting lubricant. Soap-water and kerosene are commonly employed. The
+latter enables a fine finish to be obtained, provided the cutting tool
+is properly ground.
+
+The following information on this subject represents the experience of
+the Brown-Lipe Gear Co., where aluminum parts are machined in large
+quantities: For finishing bored holes, a bar equipped with cutters has
+been found more practicable than reamers. The cutters used for machining
+4-inch holes have a clearance of from 20 to 22 degrees and no rake or
+slope on the front faces against which the chips bear. The roughing
+cutters for this work have a rather sharp nose, being ground on the
+point to a radius of about 3/32 inch, but for securing a smooth surface,
+the finishing tools are rounded to a radius of about 3/4 inch. The
+cutting speed, as well as the feed, for machining aluminum is from 50 to
+60 per cent faster than the speeds and feeds for cast iron. The
+lubricant used by this company is composed of one part "aqualine" and 20
+parts water. This lubricant not only gives a smooth finish but preserves
+a keen cutting edge and enables tools to be used much longer without
+grinding. Formerly, a lubricant composed of one part of high-grade lard
+oil and one part of kerosene was used. This mixture costs approximately
+30 cents per gallon, whereas the aqualine and water mixture now being
+used costs less than 4 cents per gallon, and has proved more effective
+than the lubricant formerly employed.
+
+
+
+
+CHAPTER II
+
+LATHE TURNING TOOLS AND CUTTING SPEEDS
+
+
+Notwithstanding the fact that a great variety of work can be done in the
+lathe, the number of turning tools required is comparatively small. Fig.
+1 shows the forms of tools that are used principally, and typical
+examples of the application of these various tools are indicated in Fig.
+2. The reference letters used in these two illustrations correspond for
+tools of the same type, and both views should be referred to in
+connection with the following description.
+
+=Turning Tools for General Work.=--The tool shown at _A_ is the form
+generally used for rough turning, that is for taking deep cuts when
+considerable metal has to be removed. At _B_ a tool of the same type is
+shown, having a bent end which enables it to be used close up to a
+shoulder or surface _s_ that might come in contact with the tool-rest if
+the straight form were employed. Tool _C_, which has a straight cutting
+end, is used on certain classes of work for taking light finishing cuts,
+with a coarse feed. This type of tool has a flat or straight cutting
+edge at the end, and will leave a smooth finish even though the feed is
+coarse, provided the cutting edge is set parallel with the tool's travel
+so as to avoid ridges. Broad-nosed tools and wide feeds are better
+adapted for finishing cast iron than steel. When turning steel, if the
+work is at all flexible, a broad tool tends to gouge into it and for
+this reason round-nosed tools and finer feeds are generally necessary. A
+little experience in turning will teach more on this point than a whole
+chapter on the subject.
+
+[Illustration: Fig. 1. Set of Lathe Turning Tools for General Work]
+
+[Illustration: Fig. 2. Views illustrating Use of Various Types of Lathe
+Tools]
+
+The side-tools shown at _D_ and _E_ are for facing the ends of shafts,
+collars, etc. The first tool is known as a right side-tool because it
+operates on the right end or side of a shaft or collar, whereas the left
+side-tool _E_ is used on the opposite side, as shown in Fig. 2.
+Side-tools are also bent to the right or left because the cutting edge
+of a straight tool cannot always be located properly for facing certain
+surfaces. A bent right side-tool is shown at _F_. A form of tool that is
+frequently used is shown at _G_; this is known as a parting tool and is
+used for severing pieces and for cutting grooves, squaring corners, etc.
+The same type of tool having a bent end is shown at _H_ (Fig. 2)
+severing a piece held in the chuck. Work that is held between centers
+should not be entirely severed with a parting tool unless a steadyrest
+is placed between the tool and faceplate, as otherwise the tool may be
+broken by the springing of the work just before the piece is cut in two.
+It should be noted that the sides of this tool slope inward back of the
+cutting edge to provide clearance when cutting in a narrow groove.
+
+At _I_ a thread tool is shown for cutting a U. S. standard thread. This
+thread is the form most commonly used in this country at the present
+time. A tool for cutting a square thread is shown at _J_. This is shaped
+very much like a parting tool except that the cutting end is inclined
+slightly to correspond with the helix angle of the thread, as explained
+in Chapter IV, which contains descriptions of different thread forms and
+methods of cutting them. Internal thread tools are shown at _K_ and _L_
+for cutting U. S. standard and square threads in holes. It will be seen
+that these tools are somewhat like boring tools excepting the ends which
+are shaped to correspond with the thread which they are intended to cut.
+
+[Illustration: Fig. 3. Turning Tool with Inserted Cutter]
+
+A tool for turning brass is shown at _M_. Brass tools intended for
+general work are drawn out quite thin and they are given a narrow
+rounded point. The top of the brass tool is usually ground flat or
+without slope as otherwise it tends to gouge into the work, especially
+if the latter is at all flexible. The end of a brass tool is sometimes
+ground with a straight cutting edge for turning large rigid work, such
+as brass pump linings, etc., so that a coarse feed can be used without
+leaving a rough surface. The tools at _N_ and _O_ are for boring or
+finishing drilled or cored holes. Two sizes are shown, which are
+intended for small and large holes, respectively.
+
+The different tools referred to in the foregoing might be called the
+standard types because they are the ones generally used, and as Fig. 2
+indicates, they make it possible to turn an almost endless variety of
+forms. Occasionally some special form of tool is needed for doing odd
+jobs, having, perhaps, an end bent differently or a cutting edge shaped
+to some particular form. Tools of the latter type, which are known as
+"form tools," are sometimes used for finishing surfaces that are either
+convex, concave, or irregular in shape. The cutting edges of these tools
+are carefully filed or ground to the required shape, and the form given
+the tool is reproduced in the part turned. Ornamental or other irregular
+surfaces can be finished very neatly by the use of such tools. It is
+very difficult, of course, to turn convex or concave surfaces with a
+regular tool; in fact, it would not be possible to form a true spherical
+surface, for instance, without special equipment, because the tool could
+not be moved along a true curve by simply using the longitudinal and
+cross feeds. Form tools should be sharpened by grinding entirely on the
+top surface, as any grinding on the end or flank would alter the shape
+of the tool.
+
+[Illustration: Fig. 4. Heavy Inserted-cutter Turning Tool]
+
+=Tool-holders with Inserted Cutters.=--All of the tools shown in Fig. 1
+are forged from the bar, and when the cutting ends have been ground down
+considerably it is necessary to forge a new end. To eliminate the
+expense of this continual dressing of tools and also to effect a great
+reduction in the amount of tool steel required, tool-holders having
+small inserted cutters are used in many shops. A tool-holder of this
+type, for outside turning, is shown in Fig. 3. The cutter _C_ is held in
+a fixed position by the set-screw shown, and it is sharpened,
+principally, by grinding the end, except when it is desired to give the
+top of the cutter a different slope from that due to its angular
+position. Another inserted-cutter turning tool is shown in Fig. 4, which
+is a heavy type intended for roughing. The cutter in this case has teeth
+on the rear side engaging with corresponding teeth cut in the clamping
+block which is tightened by a set-screw on the side opposite that shown.
+With this arrangement, the cutter can be adjusted upward as the top is
+ground away.
+
+[Illustration: Fig. 5. Parting Tool with Inserted Blade]
+
+[Illustration: Fig. 6. Boring Tool with Inserted Cutter and Adjustable
+Bar]
+
+A parting tool of the inserted blade type is shown in Fig. 5. The blade
+_B_ is clamped by screw _S_ and also by the spring of the holder when
+the latter is clamped in the toolpost. The blade can, of course, be
+moved outward when necessary. Fig. 6 shows a boring tool consisting of a
+holder _H_, a bar _B_ that can be clamped in any position, and an
+inserted cutter _C_. With this type of boring tool, the bar can be
+extended beyond the holder just far enough to reach through the hole to
+be bored, which makes the tool very rigid. A thread tool of the holder
+type is shown in Fig. 7. The angular edge of the cutter _C_ is
+accurately ground by the manufacturers, so that the tool is sharpened
+by simply grinding it flat on the top. As the top is ground away, the
+cutter is raised by turning screw _S_, which can also be used for
+setting the tool to the proper height.
+
+=The Position of Turning Tools.=--The production of accurate lathe work
+depends partly on the condition of the lathe used and also on the care
+and judgment exercised by the man operating it. Even though a lathe is
+properly adjusted and in good condition otherwise, errors are often made
+which are due to other causes which should be carefully avoided. If the
+turning tool is clamped so that the cutting end extends too far from the
+supporting block, the downward spring of the tool, owing to the thrust
+of the cut, sometimes results in spoiled work, especially when an
+attempt is made to turn close to the finished size by taking a heavy
+roughing cut. Suppose the end of a cylindrical part is first reduced for
+a short distance by taking several trial cuts until the diameter _d_,
+Fig. 8, is slightly above the finished size and the power feed is then
+engaged. When the tool begins to take the full depth _e_ of the cut, the
+point, which ordinarily would be set a little above the center, tends to
+spring downward into the work, and if there were considerable springing
+action, the part would probably be turned below the finished size, the
+increased reduction beginning at the point where the full cut started.
+
+[Illustration: Fig. 7. Threading Tool]
+
+This springing action, as far as the tool is concerned, can be
+practically eliminated by locating the tool so that the distance _A_
+between the tool-block and cutting end, or the "overhang," is as short
+as possible. Even though the tool has little overhang it may tilt
+downward because the toolslide is loose on its ways, and for this reason
+the slide should have a snug adjustment that will permit an easy
+movement without unnecessary play. The toolslides of all lathes are
+provided with gibs which can be adjusted by screws to compensate for
+wear, or to secure a more rigid bearing.
+
+[Illustration: Fig. 8. To avoid springing, Overhang A of Tool should not
+be Excessive]
+
+When roughing cuts are to be taken, the tool should be located so that
+any change in its position which might be caused by the pressure of the
+cut will not spoil the work. This point is illustrated at _A_ in Fig. 9.
+Suppose the end of a rod has been reduced by taking a number of trial
+cuts, until it is 1/32 inch above the finished size. If the power feed
+is then engaged with the tool clamped in an oblique position, as shown,
+when the full cut is encountered at _c_, the tool, unless very tightly
+clamped, may be shifted backward by the lateral thrust of the cut, as
+indicated by the dotted lines. The point will then begin turning smaller
+than the finished size and the work will be spoiled. To prevent any
+change of position, it is good practice, especially when roughing, to
+clamp the tool square with the surface being turned, or in other words,
+at right angles to its direction of movement. Occasionally, however,
+there is a decided advantage in having the tool set at an angle. For
+example, if it is held about as shown at _B_, when turning the flange
+casting _C_, the surfaces _s_ and _s_{1}_ can be finished without
+changing the tool's position. Cylindrical and radial surfaces are often
+turned in this way in order to avoid shifting the tool, especially when
+machining parts in quantity.
+
+=Tool Grinding.=--In the grinding of lathe tools there are three things
+of importance to be considered: First, the cutting edge of the tool (as
+viewed from the top) needs to be given a certain shape; second, there
+must be a sufficient amount of clearance for the cutting edge; and
+third, tools, with certain exceptions, are ground with a backward slope
+or a side slope, or with a combination of these two slopes on that part
+against which the chip bears when the tool is in use.
+
+[Illustration: Fig. 9. (A) The Way in which Tool is sometimes displaced
+by Thrust of Cut, when set at an Angle. (B) Tool Set for Finishing both
+Cylindrical and Radial Surfaces]
+
+In Fig. 10 a few of the different types of tools which are used in
+connection with lathe work are shown. This illustration also indicates
+the meaning of the various terms used in tool grinding. As shown, the
+clearance of the tool is represented by the angle [alpha], the back
+slope is represented by the angle [beta], and the side slope by the
+angle [gamma]. The angle [delta] for a tool without side slope is known
+as the lip angle or the angle of keenness. When, however, the tool has
+both back and side slopes, this lip angle would more properly be the
+angle between the flank _f_ and the top of the tool, measured diagonally
+along a line _z--z_. It will be seen that the lines _A--B_ and _A--C_
+from which the angles of clearance and back slope are measured are
+parallel with the top and sides of the tool shank, respectively. For
+lathe tools, however, these lines are not necessarily located in this
+way when the tool is in use, as the height of the tool point with
+relation to the work center determines the position of these lines, so
+that the _effective_ angles of back slope, clearance and keenness are
+changed as the tool point is lowered or raised. The way the position of
+the tool affects these angles will be explained later.
+
+[Illustration: Fig. 10. Illustration showing the Meaning of Terms used
+in Tool Grinding as applied to Tools of Different Types]
+
+While tools must, of necessity, be varied considerably in shape to adapt
+them to various purposes, there are certain underlying principles
+governing their shape which apply generally; so in what follows we shall
+not attempt to explain in detail just what the form of each tool used on
+the lathe should be, as it is more important to understand how the
+cutting action of the tool and its efficiency is affected when it is
+improperly ground. When the principle is understood, the grinding of
+tools of various types and shapes is comparatively easy.
+
+[Illustration: Fig. 11. Plan View of Lathe Turning and Threading Tools]
+
+=Shape or Contour of Cutting Edge.=--In the first place we shall
+consider the shape or contour of the cutting edge of the tool as viewed
+from the top, and then take up the question of clearance and slope, the
+different elements being considered separately to avoid confusion. The
+contour of the cutting edge depends primarily upon the purpose for which
+the tool is intended. For example, the tool _A_, in Fig. 11, where a
+plan view of a number of different lathe tools is shown, has a very
+different shape from that of, say, tool _D_, as the first tool is used
+for rough turning, while tool _D_ is intended for cutting grooves or
+severing a turned part. Similarly, tool _E_ is V-shaped because it is
+used for cutting V-threads. Tools _A_, _B_ and _C_, however, are regular
+turning tools; that is, they are all intended for turning plain
+cylindrical surfaces, but the contour of the cutting edges varies
+considerably, as shown. In this case it is the characteristics of the
+work and the cut that are the factors which determine the shape. To
+illustrate, tool _A_ is of a shape suitable for rough-turning large and
+rigid work, while tool _B_ is adapted for smaller and more flexible
+parts. The first tool is well shaped for roughing because experiments
+have shown that a cutting edge of a large radius is capable of higher
+cutting speed than could be used with a tool like _B_, which has a
+smaller point. This increase in the cutting speed is due to the fact
+that the tool _A_ removes a thinner chip for a given feed than tool _B_;
+therefore, the speed may be increased without injuring the cutting edge
+to the same extent. If, however, tool _A_ were to be used for turning a
+long and flexible part, chattering might result; consequently, a tool
+_B_ having a point with a smaller radius would be preferable, if not
+absolutely necessary.
+
+The character of the work also affects the shape of tools. The tool
+shown at _C_ is used for taking light finishing cuts with a wide feed.
+Obviously, if the straight or flat part of the cutting edge is in line
+with the travel of the tool, the cut will be smooth and free from
+ridges, even though the feed is coarse, and by using a coarse feed the
+cut is taken in less time; but such a tool cannot be used on work that
+is not rigid, as chattering would result. Therefore, a smaller cutting
+point and a reduced feed would have to be employed. Tools with broad
+flat cutting edges and coarse feeds are often used for taking finishing
+cuts in cast iron, as this metal offers less resistance to cutting than
+steel, and is less conducive to chattering.
+
+The shape of a tool (as viewed from the top) which is intended for a
+more specific purpose than regular turning, can be largely determined by
+simply considering the tool under working conditions. This point may be
+illustrated by the parting tool _D_ which, as previously stated, is used
+for cutting grooves, squaring corners, etc. Evidently this tool should
+be widest at the cutting edge; that is, the sides _d_ should have a
+slight amount of clearance so that they will not bind as the tool is fed
+into a groove. As the tool at _E_ is for cutting a V-thread, the angle
+[alpha] between its cutting edges must equal the angle between the sides
+of a V-thread, or 60 degrees. The tool illustrated at _F_ is for cutting
+inside square threads. In this case the width _w_ should be made equal
+to one-half the pitch of the thread (or slightly greater to provide
+clearance for the screw), and the sides should be given a slight amount
+of side clearance, the same as with the parting tool _D_. So we see that
+the outline of the tool, as viewed from the top, must conform to and be
+governed by its use.
+
+=Direction of Top Slope for Turning Tools.=--Aside from the question of
+the shape of the cutting edge as viewed from the top, there remains to
+be determined the amount of clearance that the tool shall have, and also
+the slope (and its direction) of the top of the tool. By the top is
+meant that surface against which the chip bears while it is being
+severed. It may be stated, in a general way, that the direction in which
+the top of the tool should slope should be away from what is to be the
+_working part_ of the cutting edge. For example, the working edge of a
+roughing tool _A_ (Fig. 11), which is used for heavy cuts, would be,
+practically speaking, between points _a_ and _b_, or, in other words,
+most of the work would be done by this part of the cutting edge;
+therefore the top should slope back from this part of the edge.
+Obviously, a tool ground in this way will have both a back and a side
+slope.
+
+When most of the work is done on the point or nose of the tool, as, for
+example, with the lathe finishing tool _C_ which takes light cuts, the
+slope should be straight back from the point or cutting edge _a--b_. As
+the side tool shown in Fig. 10 does its cutting along the edge _a--b_,
+the top is given a slope back from this edge as shown in the end view.
+This point should be remembered, for when the top slopes in the right
+direction, less power is required for cutting. Tools for certain classes
+of work, such as thread tools, or those for turning brass or chilled
+iron, are ground flat on top, that is, without back or side slope.
+
+=Clearance for the Cutting Edge.=--In order that the cutting edge may
+work without interference, it must have clearance; that is, the flank
+_f_ (Fig. 10) must be ground to a certain angle [alpha] so that it will
+not rub against the work and prevent the cutting edge from entering the
+metal. This clearance should be just enough to permit the tool to cut
+freely. A clearance angle of eight or ten degrees is about right for
+lathe turning tools.
+
+The back slope of a tool is measured from a line _A--B_ which is
+parallel to the shank, and the clearance angle, from a line _A--C_ at
+right angles to line _A--B_. These lines do not, however, always occupy
+this position with relation to the tool shank when the tool is in use.
+As shown to the left in Fig. 12, the base line _A--B_ for a turning
+tool in use intersects with the point of the tool and center of the
+work, while the line _A--C_ remains at right angles to the first. It
+will be seen, then, that by raising the tool, as shown to the right, the
+_effective_ clearance angle [alpha] will be diminished, whereas lowering
+it, as shown by the dotted lines, will have the opposite effect.
+
+A turning tool for brass or other soft metal, particularly where
+considerable hand manipulation is required, could advantageously have a
+clearance of twelve or fourteen degrees, as it would then be easier to
+feed the tool into the metal; but, generally speaking, the clearance for
+turning tools should be just enough to permit them to cut freely.
+Excessive clearance weakens the cutting edge and may cause it to crumble
+under the pressure of the cut.
+
+[Illustration: Fig. 12. Illustrations showing how Effective Angles of
+Slope and Clearance change as Tool is raised or lowered]
+
+=Angle of Tool-point and Amount of Top Slope.=--The lip angle or the
+angle of keenness [delta] (Fig. 10) is another important consideration
+in connection with tool grinding, for it is upon this angle that the
+efficiency of the tool largely depends. By referring to the illustration
+it will be seen that this angle is governed by the clearance and the
+slope [beta], and as the clearance remains practically the same, it is
+the slope which is varied to meet different conditions. Now, the amount
+of slope a tool should have depends on the work for which it is
+intended. If, for example, a turning tool is to be used for roughing
+medium or soft steel, it should have a back slope of about eight degrees
+and a side slope ranging from fourteen to twenty degrees, while a tool
+for cutting very hard steel should have a back slope of about five
+degrees and a side slope of nine degrees.
+
+[Illustration: Fig. 13. (A) Blunt Tool for Turning Hard Steel. (B)
+Tool-point Ground to give Keenness]
+
+The reason for decreasing the slope and thus increasing the lip angle
+for harder metals is to give the necessary increased strength to the
+cutting edge to prevent it from crumbling under the pressure of the cut.
+The tool illustrated at _A_, Fig. 13, is much stronger than it would be
+if ground as shown at _B_, as the former is more blunt. If a tool ground
+as at _A_, however, were used for cutting very soft steel, there would
+be a greater chip pressure on the top and, consequently, a greater
+resistance to cutting, than if a keener tool had been employed;
+furthermore the cutting speed would have to be lower, which is of even
+greater importance than the chip pressure; therefore, the lip angle, as
+a general rule, should be as small as possible without weakening the
+tool so that it cannot do the required work. In order to secure a strong
+and well-supported cutting edge, tools used for turning very hard metal,
+such as chilled rolls, etc., are ground with practically no slope and
+with very little clearance. Brass tools, while given considerable
+clearance, as previously stated, are ground flat on top or without
+slope; this is not done, however, to give strength to the cutting edge,
+but rather to prevent the tool from gouging into the work, which it is
+likely to do if the part being turned is at all flexible and the tool
+has top slope.
+
+Experiments conducted by Mr. F. W. Taylor to determine the most
+efficient form for lathe roughing tools showed that the nearer the lip
+angle approached sixty-one degrees, the higher the cutting speed. This,
+however, does not apply to tools for turning cast iron, as the latter
+will work more efficiently with a lip angle of about sixty-eight
+degrees. This is doubtless because the chip pressure, when turning cast
+iron, comes closer to the cutting edge which should, therefore, be more
+blunt to withstand the abrasive action and heat. Of course, the
+foregoing remarks concerning lip angles apply more particularly to tools
+used for roughing.
+
+[Illustration: Fig. 14. Grinding the Top and Flank of a Turning Tool]
+
+=Grinding a Lathe Tool.=--The way a turning tool is held while the top
+surface is being ground is shown to the left in Fig. 14. By inclining
+the tool with the wheel face, it will be seen that both the back and
+side slopes may be ground at the same time. When grinding the flank of
+the tool it should be held on the tool-rest of the emery wheel or
+grindstone, as shown by the view to the right. In order to form a curved
+cutting edge, the tool is turned about the face of the stone while it is
+being ground. This rotary movement can be effected by supporting the
+inner end of the tool with one hand while the shank is moved to and fro
+with the other.
+
+Often a tool which has been ground properly in the first place is
+greatly misshapen after it has been sharpened a few times. This is
+usually the result of attempts on the part of the workman to re-sharpen
+it hurriedly; for example, it is easier to secure a sharp edge on the
+turning tool shown to the left in Fig. 12, by grinding the flank as
+indicated by the dotted line, than by grinding the entire flank. The
+clearance is, however, reduced and the lip angle changed.
+
+There is great danger when grinding a tool of burning it or drawing the
+temper from the fine cutting edge, and, aside from the actual shape of
+the cutting end, this is the most important point in connection with
+tool grinding. If a tool is pressed hard against an emery or other
+abrasive wheel, even though the latter has a copious supply of water,
+the temper will sometimes be drawn. When grinding a flat surface, to
+avoid burning, the tool should frequently be withdrawn from the stone so
+that the cooling water (a copious supply of which should be provided)
+can reach the surface being ground. A moderate pressure should also be
+applied, as it is better to spend an extra minute or two in grinding
+than to ruin the tool by burning, in an attempt to sharpen it quickly.
+Of course, what has been said about burning applies more particularly to
+carbon steel, but even self-hardening steels are not improved by being
+over-heated at the stone. In some shops, tools are ground to the
+theoretically correct shape in special machines instead of by hand. The
+sharpened tools are then kept in the tool-room and are given out as they
+are needed.
+
+=Cutting Speeds and Feeds.=--The term cutting speed as applied to
+turning operations is the speed in feet per minute of the surface being
+turned, or, practically speaking, it is equivalent to the length of a
+chip, in feet, which would be turned in one minute. The term cutting
+speed should not be confused with revolutions per minute, because the
+cutting speed depends not only upon the speed of the work but also upon
+its diameter. The feed of a tool is the amount it moves across the
+surface being turned for each revolution; that is, when turning a
+cylindrical piece, the feed is the amount that the tool moves sidewise
+for each revolution of the work. Evidently the time required for turning
+is governed largely by the cutting speed, the feed, and the depth of the
+cut; therefore, these elements should be carefully considered.
+
+Cutting Speeds and Feeds for Turning Tools[1]
+
+  +---------------------------------++---------------------------------+
+  |  Steel--Standard 7/8-inch Tool  ||Cast Iron--Standard 7/8-inch Tool|
+  +-----+-----+---------------------++-----+-----+---------------------+
+  |     |     |  Speed in Feet per  ||     |     |  Speed in Feet per  |
+  |Depth|Feed |  Minute for a Tool  ||Depth|Feed |  Minute for a Tool  |
+  | of  | in  |  which is to last   || of  | in  |  which is to last   |
+  | Cut | In- |  1-1/2 Hour before  || Cut | In- |  1-1/2 Hour before  |
+  | in  |ches |     Re-grinding     || in  |ches |     Re-grinding     |
+  | In- |     +------+------+-------++ In- |     +-------+------+------+
+  |ches |     | Soft |Medium| Hard  ||ches |     | Soft  |Medium| Hard |
+  |     |     |Steel |Steel |Steel  ||     |     | Cast  | Cast | Cast |
+  |     |     |      |      |       ||     |     | Iron  | Iron | Iron |
+  +-----+-----+------+------+-------++-----+-----+-------+------+------+
+  |     | 1/64| 476  | 238  | 108   ||     | 1/16| 122   | 61.2 | 35.7 |
+  |3/32 | 1/32| 325  | 162  |  73.8 ||3/32 | 1/8 |  86.4 | 43.2 | 25.2 |
+  |     | 1/16| 222  | 111  |  50.4 ||     | 3/16|  70.1 | 35.1 | 20.5 |
+  |     | 3/32| 177  |  88.4|  40.2 ++-----+-----+-------+------+------+
+  +-----+-----+------+------+-------++     | 1/32| 156   | 77.8 | 45.4 |
+  |     | 1/64| 420  | 210  |  95.5 || 1/8 | 1/16| 112   | 56.2 | 32.8 |
+  | 1/8 | 1/32| 286  | 143  |  65.0 ||     | 1/8 |  79.3 | 39.7 | 23.2 |
+  |     | 1/16| 195  |  97.6|  44.4 ||     | 3/16|  64.3 | 32.2 | 18.8 |
+  |     | 1/8 | 133  |  66.4|  30.2 ++-----+-----+-------+------+------+
+  +-----+-----+------+------+-------++     | 1/32| 137   | 68.6 | 40.1 |
+  |     | 1/64| 352  | 176  |  80.0 ||3/16 | 1/16|  99.4 | 49.7 | 29.0 |
+  |3/16 | 1/32| 240  | 120  |  54.5 ||     | 1/8 |  70.1 | 35.0 | 20.5 |
+  |     | 1/16| 164  |  82  |  37.3 ||     | 3/16|  56.8 | 28.4 | 16.6 |
+  |     | 1/8 | 112  |  56  |  25.5 ++-----+-----+-------+------+------+
+  +-----+-----+------+------+-------++     | 1/32| 126   | 62.9 | 36.7 |
+  |     | 1/64| 312  | 156  |  70.9 || 1/4 | 1/16|  90.8 | 45.4 | 26.5 |
+  | 1/4 | 1/32| 213  | 107  |  48.4 ||     | 1/8 |  64.1 | 32.0 | 18.7 |
+  |     | 1/16| 145  |  72.6|  33.0 ||     | 3/16|  52   | 26.0 | 15.2 |
+  |     | 3/32| 116  |  58.1|  26.4 ++-----+-----+-------+------+------+
+  +-----+-----+------+------+-------++     | 1/32| 111   | 55.4 | 32.3 |
+  |     | 1/64| 264  | 132  |  60.0 || 3/8 | 1/16|  80   | 40.0 | 23.4 |
+  | 3/8 | 1/32| 180  |  90.2|  41.0 ||     | 1/8 |  56.4 | 28.2 | 16.5 |
+  |     | 1/16| 122  |  61.1|  27.8 ++-----+-----+-------+------+------+
+  +-----+-----+------+------+-------++     | 1/32| 104   | 52.1 | 30.4 |
+  | 1/2 | 1/64| 237  | 118  |  53.8 || 1/2 | 1/16|  75.2 | 37.6 | 22.0 |
+  |     | 1/32| 162  |  80.8|  36.7 ||     | 1/8 |  43.1 | 21.6 | 12.6 |
+  +-----+-----+------+------+-------++-----+-----+-------+------+------+
+  |Steel--Standard 5/8-inch Tool    ||Cast Iron--Standard 5/8-inch Tool|
+  +-----+-----+------+------+-------++-----+-----+-------+------+------+
+  |Depth|Feed | Soft |Medium| Hard  ||Depth|Feed | Soft  |Medium| Hard |
+  | of  |     |Steel |Steel |Steel  || of  |     | Cast  | Cast | Cast |
+  | Cut |     |      |      |       || Cut |     | Iron  | Iron | Iron |
+  +-----+-----+------+------+-------++-----+-----+-------+------+------+
+  |     | 1/64| 548  | 274  | 125   ||     | 1/32| 160   | 80.0 | 46.6 |
+  |1/16 | 1/32| 358  | 179  |  81.6 ||3/32 | 1/16| 110   | 55.0 | 32.2 |
+  |     | 1/16| 235  | 117  |  53.3 ||     | 1/8 |  75.4 | 37.7 | 22.0 |
+  +-----+-----+------+------+-------++-----+-----+-------+------+------+
+  |     | 1/64| 467  | 234  | 106   ||     | 1/32| 148   | 74.0 | 43.3 |
+  |3/32 | 1/32| 306  | 153  |  69.5 || 1/8 | 1/16| 104   | 51.8 | 32.0 |
+  |     | 1/16| 200  | 100  |  45.5 ||     | 1/8 |  69.6 | 34.8 | 20.3 |
+  |     | 3/32| 156  |  78  |  35.5 ++-----+-----+-------+------+------+
+  +-----+-----+------+------+-------++     | 1/64| 183   | 91.6 | 68.0 |
+  |     | 1/64| 417  | 209  |  94.8 ||3/16 | 1/32| 135   | 67.5 | 39.4 |
+  | 1/8 | 1/32| 273  | 136  |  62.0 ||     | 1/16|  94   | 47.0 | 27.4 |
+  |     | 1/16| 179  |  89.3|  40.6 ||     | 1/8 |  64.3 | 32.2 | 18.8 |
+  |     | 3/32| 140  |  69.8|  31.7 ++-----+-----+-------+------+------+
+  +-----+-----+------+------+-------++     | 1/64| 171   | 85.7 | 50.1 |
+  |     | 1/64| 362  | 181  |  82.2 || 1/4 | 1/32| 126   | 63.2 | 36.9 |
+  |3/16 | 1/32| 236  | 118  |  53.8 ||     | 1/16|  87.8 | 43.9 | 25.6 |
+  |     | 1/16| 155  |  77.4|  35.2 ||     | 3/32|  70.4 | 35.2 | 20.6 |
+  +-----+-----+------+------+-------++-----+-----+-------+------+------+
+  | 1/4 | 1/64| 328  | 164  |  74.5 || 3/8 | 1/64| 156   | 77.8 | 45.4 |
+  |     | 1/32| 215  | 107  |  48.8 ||     | 1/32| 116   | 57.8 | 33.8 |
+  +-----+-----+------+------+-------++     | 1/16|  79.7 | 39.9 | 23.3 |
+  | 3/8 | 1/64| 286  | 143  |  65.0 ||     |     |       |      |      |
+  +-----+-----+------+------+-------++-----+-----+-------+------+------+
+
+[1] Cutting speeds for tools of a good grade of high-speed steel,
+properly ground and heat-treated.--From MACHINERY'S HANDBOOK.
+
+=Average Cutting Speeds for Turning.=--The cutting speed is governed
+principally by the hardness of the metal to be turned; the kind of steel
+of which the turning tool is made; the shape of the tool and its
+heat-treatment; the feed and depth of cut; whether or not a cooling
+lubricant is used on the tool; the power of the lathe and also its
+construction; hence it is impossible to give any definite rule for
+determining either the speed, feed, or depth of cut, because these must
+be varied to suit existing conditions. A general idea of the speeds used
+in ordinary machine shop practice may be obtained from the following
+figures:
+
+Ordinary machine steel is generally turned at a speed varying between 45
+and 65 feet per minute. For ordinary gray cast iron, the speed usually
+varies from 40 to 50 feet per minute; for annealed tool steel, from 25
+to 35 feet per minute; for soft yellow brass, from 150 to 200 feet per
+minute; for hard bronze, from 35 to 80 feet per minute, the speed
+depending upon the composition of the alloy. While these speeds
+correspond closely to general practice, they can be exceeded for many
+machining operations.
+
+The most economical speeds for a given feed and depth of cut, as
+determined by the experiments conducted by Mr. F. W. Taylor, are given
+in the table, "Cutting Speeds and Feeds for Turning Tools." The speeds
+given in this table represent results obtained with tools made of a good
+grade of high-speed steel properly heat-treated and correctly ground. It
+will be noted that the cutting speed is much slower for cast iron than
+for steel. Cast iron is cut with less pressure or resistance than soft
+steel, but the slower speed required for cast iron is probably due to
+the fact that the pressure of the chip is concentrated closer to the
+cutting edge, combined with the fact that cast iron wears the tool
+faster than steel. The speeds given are higher than those ordinarily
+used, and, in many cases, a slower rate would be necessary to prevent
+chattering or because of some other limiting condition.
+
+=Factors which limit the Cutting Speed.=--It is the durability of the
+turning tool or the length of time that it will turn effectively
+without grinding, that limits the cutting speed; and the hardness of the
+metal being turned combined with the quality of the tool are the two
+factors which largely govern the time that a tool can be used before
+grinding is necessary. The cutting speed for very soft steel or cast
+iron can be three or four times faster than the speed for hard steel or
+hard castings, but whether the material is hard or soft, the kind and
+quality of the tool used must also be considered, as the speed for a
+tool made of ordinary carbon steel will have to be much slower than for
+a tool made of modern "high-speed" steel.
+
+When the cutting speed is too high, even though high-speed steel is
+used, the point of the tool is softened to such an extent by the heat
+resulting from the pressure and friction of the chip, that the cutting
+edge is ruined in too short a time. On the other hand, when the speed is
+too slow, the heat generated is so slight as to have little effect and
+the tool point is dulled by being slowly worn or ground away by the
+action of the chip. While a tool operating at such a low speed can be
+used a comparatively long time without re-sharpening, this advantage is
+more than offset by the fact that too much time is required for removing
+a given amount of metal when the work is revolving so slowly.
+
+Generally speaking, the speed should be such that a fair amount of work
+can be done before the tool requires re-grinding. Evidently, it would
+not pay to grind a tool every few minutes in order to maintain a high
+cutting speed; neither would it be economical to use a very slow speed
+and waste considerable time in turning, just to save the few minutes
+required for grinding. For example, if a number of roughing cuts had to
+be taken over a heavy rod or shaft, time might be saved by running at
+such a speed that the tool would have to be sharpened (or be replaced by
+a tool previously sharpened) when it had traversed half-way across the
+work; that is, the time required for sharpening or changing the tool
+would be short as compared with the gain effected by the higher work
+speed. On the other hand, it might be more economical to run a little
+slower and take a continuous cut across the work with one tool.
+
+The experiments of Mr. Taylor led to the conclusion that, as a rule, it
+is not economical to use roughing tools at a speed so slow as to cause
+them to last more than 1-1/2 hour without being re-ground; hence the
+speeds given in the table previously referred to are based upon this
+length of time between grindings. Sometimes the work speed cannot be as
+high as the tool will permit, because of the chattering that often
+results when the lathe is old and not massive enough to absorb the
+vibrations, or when there is unnecessary play in the working parts. The
+shape of the tool used also affects the work speed, and as there are so
+many things to be considered, the proper cutting speed is best
+determined by experiment.
+
+=Rules for Calculating Cutting Speeds.=--The number of revolutions
+required to give any desired cutting speed can be found by multiplying
+the cutting speed, in feet per minute, by 12 and dividing the product by
+the circumference of the work in inches. Expressing this as a formula we
+have
+
+        _C_ × 12
+  _R_ = --------
+         [pi]_d_
+
+in which
+
+  _R_  = revolutions per minute;
+  _C_  = the cutting speed in feet per minute;
+  [pi] = 3.1416;
+  _d_  = the diameter in inches.
+
+For example if a cutting speed of 60 feet per minute is wanted and the
+diameter of the work is 5 inches, the required speed would be found as
+follows:
+
+         60 × 12
+  _R_ = ---------- = 46 revolutions per minute.
+        3.1416 × 5
+
+If the diameter is simply multiplied by 3 and the fractional part is
+omitted, the calculation can easily be made, and the result will be
+close enough for practical purposes. In case the cutting speed, for a
+given number of revolutions and diameter, is wanted, the following
+formula can be used:
+
+        _R_[pi]_d_
+  _C_ = ----------
+            12
+
+Machinists who operate lathes do not know, ordinarily, what cutting
+speeds, in feet per minute, are used for different classes of work, but
+are guided entirely by past experience.
+
+=Feed of Tool and Depth of Cut.=--The amount of feed and depth of cut
+also vary like the cutting speed, for different conditions. When turning
+soft machine steel the feed under ordinary conditions would vary between
+1/32 and 1/16 inch per revolution. For turning soft cast iron the feed
+might be increased to from 1/16 to 1/8 inch per revolution. These feeds
+apply to fairly deep roughing cuts. Coarser feeds might be used in many
+cases especially when turning large rigid parts in a powerful lathe. The
+depth of a roughing cut in machine steel might vary from 1/8 to 3/8
+inch, and in cast iron from 3/16 to 1/2 inch. These figures are intended
+simply to give the reader a general idea of feeds and cuts that are
+feasible under average conditions.
+
+Ordinarily coarser feeds and a greater depth of cut can be used for cast
+iron than for soft steel, because cast iron offers less resistance to
+turning, but in any case, with a given depth of cut, metal can be
+removed more quickly by using a coarse feed and the necessary slower
+speed, than by using a fine feed and the higher speed which is possible
+when the feed is reduced. When the turning operation is simply to remove
+metal, the feed should be coarse, and the cut as deep as practicable.
+Sometimes the cut must be comparatively light, either because the work
+is too fragile and springy to withstand the strain of a heavy cut, or
+the lathe has not sufficient pulling power. The difficulty with light
+slender work is that a heavy cut may cause the part being turned to bend
+under the strain, thus causing the tool to gouge in, which would
+probably result in spoiling the work. Steadyrests can often be used to
+prevent flexible parts from springing, as previously explained, but
+there are many kinds of light work to which the steadyrest cannot be
+applied to advantage.
+
+The amount of feed to use for a finishing cut might, properly, be either
+fine or coarse. Ordinarily, fine feeds are used for finishing steel,
+especially if the work is at all flexible, whereas finishing cuts in
+cast iron are often accompanied by a coarse feed. Fig. 15 illustrates
+the feeds that are often used when turning cast iron. The view to the
+left shows a deep roughing cut and the one to the right, a finishing
+cut. By using a broad flat cutting edge set parallel to the tool's
+travel, and a coarse feed for finishing, a smooth cut can be taken in a
+comparatively short time. Castings which are close to the finished size
+in the rough can often be finished to advantage by taking a single cut
+with a broad tool, provided the work is sufficiently rigid. It is not
+always practicable to use these broad tools and coarse feeds, as they
+sometimes cause chattering, and when used on steel, a broad tool tends
+to gouge or "dig in" unless the part being turned is rigid. Heavy steel
+parts, however, are sometimes finished in this way. The modern method of
+finishing many steel parts is to simply rough them out in a lathe to
+within, say, 1/32 inch of the required diameter and take the finishing
+cut in a cylindrical grinding machine.
+
+[Illustration: Fig. 15. Roughing Cut--Light Finishing Cut and Coarse
+Feed]
+
+=Effect of Lubricant on Cutting Speed.=--When turning iron or steel a
+higher cutting speed can be used, if a stream of soda water or other
+cooling lubricant falls upon the chip at the point where it is being
+removed by the tool. In fact, experiments have shown that the cutting
+speed, when using a large stream of cooling water and a high-speed steel
+tool, can be about 40 percent higher than when turning dry or without a
+cooling lubricant. For ordinary carbon steel tools, the gain was about
+25 per cent. The most satisfactory results were obtained from a stream
+falling at a rather slow velocity but in large volume. The gain in
+cutting speed, by the use of soda water or other suitable fluids, was
+found to be practically the same for all qualities of steel from the
+softest to the hardest.
+
+Cast iron is usually turned dry or without a cutting lubricant.
+Experiments, however, made to determine the effect of applying a heavy
+stream of cooling water to a tool turning cast iron, showed the
+following results: Cutting speed without water, 47 feet per minute;
+cutting speed with a heavy stream of water, nearly 54 feet per minute;
+increase in speed, 15 per cent. The dirt caused by mixing the fine
+cast-iron turnings with a cutting lubricant is an objectionable feature
+which, in the opinion of many, more than offsets the increase in cutting
+speed that might be obtained.
+
+Turret lathes and automatic turning machines are equipped with a pump
+and piping for supplying cooling lubricant to the tools in a continuous
+stream. Engine lathes used for general work, however, are rarely
+provided with such equipment and a lubricant, when used, is often
+supplied by a can mounted at the rear of the carriage, having a spout
+which extends above the tool. Owing to the inconvenience in using a
+lubricant on an engine lathe, steel, as well as cast iron, is often
+turned dry especially when the work is small and the cuts light and
+comparatively short.
+
+=Lubricants Used for Turning.=--A good grade of lard oil is an excellent
+lubricant for use when turning steel or wrought iron and it is
+extensively used on automatic screw machines, especially those which
+operate on comparatively small work. For some classes of work,
+especially when high-cutting speeds are used, lard oil is not as
+satisfactory as soda water or some of the commercial lubricants, because
+the oil is more sluggish and does not penetrate to the cutting point
+with sufficient rapidity. Many lubricants which are cheaper than oil are
+extensively used on "automatics" for general machining operations. These
+usually consist of a mixture of sal-soda (carbonate of soda) and water,
+to which is added some ingredient such as lard oil or soft soap to
+thicken or give body to the lubricant.
+
+A cheap lubricant for turning, milling, etc., and one that has been
+extensively used, is made in the following proportions: 1 pound of
+sal-soda, 1 quart of lard oil, 1 quart of soft soap, and enough water to
+make 10 or 12 gallons. This mixture is boiled for one-half hour,
+preferably by passing a steam coil through it. If the solution should
+have an objectionable odor, this can be eliminated by adding 2 pounds of
+unslaked lime. The soap and soda in this solution improve the
+lubricating quality and also prevent the surfaces from rusting. For
+turning and threading operations, plain milling, deep-hole drilling,
+etc., a mixture of equal parts of lard oil and paraffin oil will be
+found very satisfactory, the paraffin being added to lessen the expense.
+
+Brass or bronze is usually machined dry, although lard oil is sometimes
+used for automatic screw machine work. Babbitt metal is also worked dry,
+ordinarily, although kerosene or turpentine is sometimes used when
+boring or reaming. If babbitt is bored dry, balls of metal tend to form
+on the tool point and score the work. Milk is generally considered the
+best lubricant for machining copper. A mixture of lard oil and
+turpentine is also used for copper. For aluminum, the following
+lubricants can be used: Kerosene, a mixture of kerosene and gasoline,
+soap-water, or "aqualine" one part, water 20 parts.
+
+=Lard Oil as a Cutting Lubricant.=--After being used for a considerable
+time, lard oil seems to lose some of its good qualities as a cooling
+compound. There are several reasons for this: Some manufacturers use the
+same oil over and over again on different materials, such as brass,
+steel, etc. This is objectionable, for when lard oil has been used on
+brass it is practically impossible to get the fine dust separated from
+it in a centrifugal separator. When this impure oil is used on steel,
+especially where high-speed steels are employed, it does not give
+satisfactory results, owing to the fact that when the cutting tool
+becomes dull, the small brass particles "freeze" to the cutting tool and
+thus produce rough work. The best results are obtained from lard oil by
+keeping it thin, and by using it on the same materials--that is, not
+transferring the oil from a machine in which brass is being cut to one
+where it would be employed on steel. If the oil is always used on the
+same class of material, it will not lose any of its good qualities.
+
+Prime lard oil is nearly colorless, having a pale yellow or greenish
+tinge. The solidifying point and other characteristics of the oil depend
+upon the temperature at which it was expressed, winter-pressed lard oil
+containing less solid constituents of the lard than that expressed in
+warm weather. The specific gravity should not exceed 0.916; it is
+sometimes increased by adulterants, such as cotton-seed and maize oils.
+
+
+
+
+CHAPTER III
+
+TAPER TURNING--SPECIAL OPERATIONS--FITTING
+
+
+It is often necessary, in connection with lathe work, to turn parts
+tapering instead of straight or cylindrical. If the work is mounted
+between the centers, one method of turning a taper is to set the
+tailstock center out of alignment with the headstock center. When both
+of these centers are in line, the movement of the tool is parallel to
+the axis of the work and, consequently, a cylindrical surface is
+produced; but if the tailstock _h_{1}_ is set out of alignment, as shown
+in Fig. 1, the work will then be turned tapering as the tool is
+traversed from _a_ to _b_, because the axis _x--x_ is at an angle with
+the movement of the tool. Furthermore the amount of taper or the
+difference between the diameters at the ends for a given length, will
+depend on how much center _h_{1}_ is set over from the central position.
+
+[Illustration: Fig. 1. Taper Turning by the Offset-center Method]
+
+[Illustration: Fig. 2. Examples of Taper Work]
+
+The amount of taper is usually given on drawings in inches per foot, or
+the difference in the diameter at points twelve inches apart. For
+example, the taper of the piece shown at _A_, Fig. 2, is 1 inch per
+foot, as the length of the tapering surface is just twelve inches and
+the difference between the diameters at the ends is 1 inch. The conical
+roller shown at _B_ has a total length of 9 inches and a tapering
+surface 6 inches long, and in this case the taper per foot is also 1
+inch, there being a difference of 1/2 inch in a length of 6 inches or 1
+inch in twice that length. When the taper per foot is known, the amount
+that the tailstock center should be set over for turning that taper can
+easily be estimated, but it should be remembered that the setting
+obtained in this way is not absolutely correct, and is only intended to
+locate the center approximately. When a taper needs to be at all
+accurate, it is tested with a gage, or by other means, after taking a
+trial cut, as will be explained later, and the tailstock center is
+readjusted accordingly. There are also more accurate methods of setting
+the center, than by figuring the amount of offset, but as the latter is
+often convenient this will be referred to first.
+
+=Setting Tailstock Center for Taper Turning.=--Suppose the tailstock
+center is to be set for turning part _C_, Fig. 2, to a taper of
+approximately 1 inch per foot. In this case the center would simply be
+moved toward the front of the machine 1/2 inch, or one-half the required
+taper per foot, because the total length of the work happens to be just
+12 inches. This setting, however, would not be correct for all work
+requiring a taper of 1 inch per foot, as the adjustment depends not only
+on the _amount_ of the taper but on the _total length_ of the piece.
+
+[Illustration: Fig. 3. Detail View of Lathe Tailstock]
+
+For example, the taper roller _B_ has a taper of 1 inch per foot, but
+the center, in this case, would be offset less than one-half the taper
+per foot, because the total length is only 9 inches. For lengths longer
+or shorter than twelve inches, the taper per inch should be found first;
+this is then multiplied by the _total_ length of the work (not the
+length of the taper) which gives the taper for that length, and one-half
+this taper is the amount to set over the center. For example, the taper
+per inch of part _B_ equals 1 inch divided by 12 = 1/12 inch. The total
+length of 9 inches multiplied by 1/12 inch = 3/4 inch, and 1/2 of 3/4 =
+3/8, which is the distance that the tailstock center should be offset.
+In this example if the taper per foot were not known, and only the
+diameters of the large and small ends of the tapered part were given,
+the difference between these diameters should first be found (2-1/2-2 =
+1/2); this difference should then be divided by the length of the taper
+(1/2 ÷ 6 = 1/12 inch) to obtain the taper per inch. The taper per inch
+times the _total_ length represents what the taper would be if it
+extended throughout the entire length, and one-half of this equals the
+offset, which is 3/8 inch.
+
+=Example of Taper Turning.=--As a practical example of taper turning let
+us assume that the piece A, Fig. 4, which has been centered and
+rough-turned as shown, is to be made into a taper plug, as indicated at
+_B_, to fit a ring gage as at _C_. If the required taper is 1-1/2 inch
+per foot and the total length is 8 inches, the tailstock center would be
+offset 1/2 inch.
+
+[Illustration: Fig. 4. Taper Plug and Gage]
+
+To adjust the tailstock, the nuts _N_ (Fig. 3) are first loosened and
+then the upper part _A_ is shifted sidewise by turning screw _S_. Scales
+are provided on some tailstocks for measuring the amount of this
+adjustment; if there is no scale, draw a line across the movable and
+stationary parts _A_ and _B_, when the tailstock is set for straight
+turning. The movement of the upper line in relation to the lower will
+then show the offset, which can be measured with a scale.
+
+When the adjustment has been made, nuts _N_ are tightened and the part
+to be turned, with a dog attached, is placed between the centers the
+same as for straight turning. The taper end is then reduced by turning,
+but before it is near the finished size, the work is removed and the
+taper tested by inserting it in the gage. If it is much out, this can be
+felt, as the end that is too small can be shaken in the hole. Suppose
+the plug did not taper enough and only the small end came into contact
+with the gage, as shown somewhat exaggerated at _D_; in that case the
+center would be shifted a little more towards the front, whereas if the
+taper were too steep, the adjustment would, of course, be in the
+opposite direction. A light cut would then be taken, to be followed by
+another test. If the plug should fit the gage so well that there was no
+perceptible shake, it could be tested more closely as follows: Draw
+three or four chalk lines along the tapering surface, place the work in
+the gage and turn it a few times. The chalk marks will then show whether
+the taper of the plug corresponds to that of the gage; for example, if
+the taper is too great, the marks will be rubbed out on the large end,
+but if the taper is correct, the lines throughout their length will be
+partially erased.
+
+[Illustration: Fig. 5. Setting Work for Taper Turning by use of Caliper
+Gage]
+
+Another and more accurate method of testing tapers is to apply a thin
+coat of Prussian-blue to one-half of the tapering surface, in a
+lengthwise direction. The work is then inserted in the hole or gage and
+turned to mark the bearing. If the taper is correct, the bearing marks
+will be evenly distributed, whereas if the taper is incorrect, they will
+appear at one end. Tapering pieces that have to be driven tightly into a
+hole, such as a piston-rod, can be tested by the location of the bearing
+marks produced by actual contact.
+
+After the taper is found to be correct, the plug is reduced in size
+until it just enters the gage as at _C_. The final cut should leave it
+slightly above the required size, so that a smooth surface can be
+obtained by filing. It should be mentioned that on work of this kind,
+especially if great accuracy is required, the final finish is often
+obtained by grinding in a regular grinding machine, instead of by
+filing. When this method is employed, a lathe is used merely to
+rough-turn the part close to size.
+
+[Illustration: Fig. 6. Side View showing Relative Positions of Gage and
+Work]
+
+When the amount that the tailstock center should be offset is determined
+by calculating, as in the foregoing example, it is usually necessary to
+make slight changes afterward, and the work should be tested before it
+is too near the finished size so that in case one or more trial cuts are
+necessary, there will be material enough to permit this. When there are
+a number of tapered pieces to be turned to the same taper, the
+adjustment of the tailstock center will have to be changed unless the
+total length of each piece and the depth of the center holes are the
+same in each case.
+
+=Setting the Tailstock Center with a Caliper Tool.=--Another method of
+setting the tailstock center for taper turning is illustrated in Fig. 5.
+The end of an engine piston-rod is to be made tapering as at A and to
+dimensions _a_, _b_, _c_ and _d_. It is first turned with the centers in
+line as at _B_. The end _d_ is reduced to diameter _b_ up to the
+beginning of the taper and it is then turned to diameter _a_ as far as
+the taper part _c_ extends. The tailstock center is next set over by
+guess and a caliper tool is clamped in the toolpost. This tool, a side
+view of which is shown in Fig. 6, has a pointer _p_ that is free to
+swing about pivot _r_, which should be set to about the same height as
+the center of the work. The tailstock center is adjusted until this
+pointer just touches the work when in the positions shown by the full
+and dotted lines at _C_, Fig. 5; that is, until the pointer makes
+contact at the beginning and end of the taper part. The travel of the
+carriage will then be parallel to a line _x--x_, representing the taper;
+consequently, if a tool is started at the small end, as shown by the
+dotted lines at _D_, with the nose just grazing the work, it will also
+just graze it when fed to the extreme left as shown. Of course, if the
+taper were at all steep, more than one cut would be taken.
+
+[Illustration: Fig. 7. Obtaining Tailstock Center Adjustment by use of
+Square]
+
+If these various operations are carefully performed, a fairly accurate
+taper can be produced. The straight end _d_ is reduced to size after the
+tail-center is set back to the central position. Some mechanics turn
+notches or grooves at the beginning and end of the tapering part, having
+diameters equal to the largest and smallest part of the taper; the work
+is then set by these grooves with a caliper tool. The advantage of the
+first method is that most of the metal is removed while the centers are
+in alignment.
+
+[Illustration: Fig. 8. Second Step in Adjusting Tailstock Center by use
+of Square]
+
+=Setting the Tailstock Center with a Square.=--Still another method of
+adjusting the tailstock for taper turning, which is very simple and
+eliminates all figuring, is as follows: The part to be made tapering is
+first turned cylindrical or straight for 3 or 4 inches of its length,
+after the ends have been properly centered and faced square. The work is
+then removed and the tailstock is shifted along the bed until the
+distance _a--b_ between the extreme points of the centers is exactly 1
+foot. The center is next offset a distance _b--c_ equal to one-half the
+required taper per foot, after which a parallel strip _D_, having true
+sides, is clamped in the toolpost. Part _D_ is then set at right angles
+to a line passing from one center point to the other. This can be done
+conveniently by holding a 1-foot square (preferably with a sliding head)
+against one side of _D_ and adjusting the latter in the toolpost until
+edge _E_ of the square blade is exactly in line with both center points.
+After part _D_ is set, it should be clamped carefully to prevent
+changing the position. The angle between the side of _D_ and an
+imaginary line which is perpendicular to axis _a--b_ is now equal to
+one-half the angle of the required taper.
+
+The axis of the part to be turned should be set parallel with line _E_,
+which can be done by setting the cylindrical surface which was
+previously finished, at right angles to the side of _D_. In order to do
+this the work is first placed between centers, the tailstock being
+shifted along the bed if necessary; the tail-center is then adjusted
+laterally until the finished cylindrical surface is square with the side
+of _D_. A small try-square can be used for testing the position of the
+work, as indicated in Fig. 8. If the length of the work is less than 1
+foot, it will be necessary to move the center toward the rear of the
+machine, and if the length is greater than 1 foot, the adjustment is, of
+course, in the opposite direction.
+
+[Illustration: Fig. 9. A Lathe Taper Attachment]
+
+=The Taper Attachment.=--Turning tapers by setting over the tailstock
+center has some objectionable features. When the lathe centers are not
+in alignment, as when set for taper turning, they bear unevenly in the
+work centers because the axis of the work is at an angle with them; this
+causes the work centers to wear unevenly and results in inaccuracy.
+Furthermore, the adjustment of the tailstock center must be changed when
+turning duplicate tapers, unless the length of each piece and the depth
+of the center holes are the same. To overcome these objections, many
+modern lathes are equipped with a special device for turning tapers,
+known as a taper attachment, which permits the lathe centers to be kept
+in alignment, as for cylindrical turning, and enables more accurate work
+to be done.
+
+[Illustration: Fig. 10. Sectional View of Taper Attachment]
+
+Taper attachments, like lathes, vary some in their construction, but all
+operate on the same principle. An improved form of taper attachment is
+illustrated in Figs. 9 and 10. Fig. 9 shows a plan view of a lathe
+carriage with an attachment fitted to it, and Fig. 10 a sectional view.
+This attachment has an arm _A_ on which is mounted a slide _S_ that can
+be turned about a central pivot by adjusting screw _D_. The arm _A_ is
+supported by, and is free to slide on, a bracket _B_ (see also sectional
+view) that is fastened to the carriage, and on one end of the arm there
+is a clamp _C_ that is attached to the lathe bed when turning tapers. On
+the slide _S_ there is a shoe _F_ that is connected to bar _E_ which
+passes beneath the toolslide. The rear end of the cross-feed screw is
+connected to this bar, and the latter is clamped to the toolslide when
+the attachment is in use.
+
+When a taper is to be turned, the carriage is moved opposite the taper
+part and clamp _C_ is fastened to the bed; this holds arm _A_ and slide
+_S_ stationary so that the carriage, with bracket _B_ and shoe _F_, can
+be moved with relation to the slide. If this slide _S_ is set at an
+angle, as shown, the shoe as it moves along causes the toolslide and
+tool to move in or out, but if the slide is set parallel to the carriage
+travel, the toolslide remains stationary. Now if the tool, as it feeds
+lengthwise of the work, is also gradually moved crosswise, it will turn
+a taper, and as this crosswise movement is caused by the angularity of
+slide _S_, different tapers are obtained by setting the slide to
+different positions.
+
+By means of a graduated scale _G_ at the end of slide _S_, the taper
+that will be obtained for any angular position of the slide is shown. On
+some attachments there are two sets of graduations, one giving the taper
+in inches per foot and the other in degrees. While tapers are ordinarily
+given in inches per foot on drawings, sometimes the taper is given in
+degrees instead. The attachment is set for turning tapers by adjusting
+slide _S_ until pointer _p_ is opposite the division or fractional part
+of a division representing the taper. The whole divisions on the scale
+represent taper in inches per foot, and by means of the sub-divisions,
+the slide can be set for turning fractional parts of an inch per foot.
+When slide _S_ is properly set, it is clamped to arm _A_ by the nuts
+_N_. Bar _E_ is also clamped to the toolslide by bolt _H_, as previously
+stated. The attachment is disconnected for straight turning by simply
+loosening clamp _C_ and the bolt _H_.
+
+=Application of Taper Attachment.=--Practical examples of lathe work,
+which illustrate the use of the taper attachment, are shown in Figs, 11
+and 12. Fig. 11 shows how a taper hole is bored in an engine
+piston-head, preparatory to reaming. The casting must be held either in
+a chuck _C_ or on a faceplate if too large for the chuck. The side of
+the casting (after it has been "chucked") should run true, and also the
+circumference, unless the cored hole for the rod is considerably out of
+center, in which case the work should be shifted to divide the error.
+The side of the casting for a short space around the hole is faced true
+with a round nose turning tool, after which the rough-cored hole is
+bored with an ordinary boring tool _t_, and then it is finished with a
+reamer to exactly the right size and taper.
+
+This particular taper attachment is set to whatever taper is given on
+the drawing, by loosening nuts _N_ and turning slide _S_ until pointer
+_P_ is opposite that division on the scale which represents the taper.
+The attachment is then ready, after bolt _H_ and nuts _N_ are tightened,
+and clamp _C_ is fastened to the lathe bed. The hole is bored just as
+though it were straight, and as the carriage advances, the tool is
+gradually moved inward by the attachment. If the lathe did not have a
+taper attachment, the taper hole could be bored by using the compound
+rest.
+
+[Illustration: Fig. 11. Lathe with Taper Attachment arranged for Boring
+Taper Hole in Engine Piston]
+
+The hole should be bored slightly less than the finish size to allow for
+reaming. When a reamer is used in the lathe, the outer end is supported
+by the tailstock center and should have a deep center-hole. The lathe is
+run very slowly for reaming and the reamer is fed into the work by
+feeding out the tailstock spindle. The reamer can be kept from
+revolving, either by attaching a heavy dog to the end or, if the end is
+squared, by the use of a wrench long enough to rest against the lathe
+carriage. A common method is to clamp a dog to the reamer shank, and
+then place the tool-rest beneath it to prevent rotation. If the shank
+of a tool is clamped to the toolpost so that the dog rests against it,
+the reamer will be prevented from slipping off the center as it tends to
+do; with this arrangement, the carriage is gradually moved along as the
+tailstock spindle is fed outward. Some reamers are provided with
+stop-collars which come against the finished side of the casting when
+the hole has been reamed to size.
+
+After the reaming operation, the casting is removed from the chuck and a
+taper mandrel is driven into the hole for turning the outside of the
+piston. This mandrel should run true on its centers, as otherwise the
+outside surface of the piston will not be true with the bored hole. The
+driving dog, especially for large work of this kind, should be heavy and
+stiff, because light flexible clamps or dogs vibrate and frequently
+cause chattering. For such heavy work it is also preferable to drive at
+two points on opposite sides of the faceplate, but the driving pins
+should be carefully adjusted to secure a uniform bearing on both sides.
+
+The foregoing method of machining a piston is one that would ordinarily
+be followed when using a standard engine lathe, and it would, perhaps,
+be as economical as any if only one piston were being made; but where
+such work is done in large quantities, time could be saved by proceeding
+in a different way. For example, the boring and reaming operation could
+be performed much faster in a turret lathe, which is a type designed for
+just such work, but a turret lathe cannot be used for as great a variety
+of turning operations as a lathe of the regular type. There are also
+many other classes of work that can be turned more quickly in special
+types of machines, but as more or less time is required for arranging
+these special machines and often special tools have to be made, the
+ordinary lathe is frequently indispensable when only a few parts are
+needed; in addition, it is better adapted to some turning operations
+than any other machine.
+
+Fig. 12 illustrates how a taper attachment would be used for turning the
+taper fitting for the crosshead end of an engine piston-rod. Even though
+this taper corresponds to the taper of the hole in the piston, slide _S_
+would have to be reset to the corresponding division on the opposite
+side of the central zero mark, because the taper of the hole decreased
+in size during the boring operation, whereas the rod is smallest at the
+beginning of the cut, so that the tool must move outward rather than
+inward as it advances. The taper part is turned practically the same as
+a cylindrical part; that is, the power feed is used and, as the carriage
+moves along the bed, the tool is gradually moved outward by the taper
+attachment.
+
+[Illustration: Fig. 12. Taper Attachment Set for Turning Taper End of
+Piston-rod]
+
+If the rod is being fitted directly to the crosshead (as is usually the
+case), the approximate size of the small end of the taper could be
+determined by calipering, the calipers being set to the size of the hole
+at a distance from the shoulder or face side of the crosshead, equal to
+the length of the taper fitting on the rod. If the crosshead were bored
+originally to fit a standard plug gage, the taper on the rod could be
+turned with reference to this gage, but, whatever the method, the taper
+should be tested before turning too close to the finished size. The test
+is made by removing the rod from the lathe and driving it tightly into
+the crosshead. This shows how near the taper is to size, and when the
+rod is driven out, the bearing marks show whether the taper is exactly
+right or not. If the rod could be driven in until the shoulder is, say,
+1/8 inch from the crosshead face, it would then be near enough to finish
+to size by filing. When filing, the lathe is run much faster than for
+turning, and most of the filing should be done where the bearing marks
+are the heaviest, to distribute the bearing throughout the length of the
+taper. Care should be taken when driving the rod in or out, to protect
+the center-holes in the ends by using a "soft" hammer or holding a piece
+of soft metal against the driving end.
+
+[Illustration: Fig. 13. Tool Point should be in same Horizontal Plane as
+Axis of Work for Taper Turning]
+
+After the crosshead end is finished, the rod is reversed in the lathe
+for turning the piston end. The dog is clamped to the finished end,
+preferably over a piece of sheet copper to prevent the surface from
+being marred. When turning this end, either the piston reamer or the
+finished hole in the piston can be calipered. The size and angle of the
+taper are tested by driving the rod into the piston, and the end should
+be fitted so that by driving tightly, the shoulder will just come up
+against the finished face of the piston. When the taper is finished, the
+attachment is disengaged and a finishing cut is taken over the body of
+the rod, unless it is to be finished by grinding, which is the modern
+and most economical method.
+
+=Height of Tool when Turning Tapers.=--The cutting edge of the tool,
+when turning tapers, should be at the same height as the center or axis
+of the work, whether an attachment is used or not. The importance of
+this will be apparent by referring to Fig. 13. To turn the taper shown,
+the tool _T_ would be moved back a distance _x_ (assuming that an
+attachment is used) while traversing the length _l_. As an illustration,
+if the tool could be placed as high as point _a_, the setting of the
+attachment remaining as before, the tool would again move back a
+distance _x_, while traversing a distance _l_, but the large end would
+be under-sized (as shown by the dotted line) if the diameters of the
+small ends were the same in each case. Of course, if the tool point were
+only slightly above or below the center, the resulting error would also
+be small. The tool can easily be set central by comparing the height of
+the cutting edge at the point of the tool with one of the lathe centers
+before placing the work in the lathe.
+
+[Illustration: Fig. 14. Plan View showing Method of Turning a Taper with
+the Compound Rest]
+
+=Taper Turning with the Compound Rest.=--The amount of taper that can be
+turned by setting over the tailstock center and by the taper attachment
+is limited, as the centers can only be offset a certain distance, and
+the slide _S_ (Fig. 9) of the attachment cannot be swiveled beyond a
+certain position. For steep tapers, the compound rest _E_ is swiveled to
+the required angle and used as indicated in Fig. 14, which shows a plan
+view of a rest set for turning the valve _V_. This compound rest is an
+upper slide mounted on the lower or main cross-slide _D_, and it can be
+turned to any angular position so that the tool, which ordinarily is
+moved either lengthwise or crosswise of the bed, can be fed at an angle.
+The base of the compound rest is graduated in degrees and the position
+of these graduations shows to what angle the upper slide is set. Suppose
+the seat of valve _V_ is to be turned to an angle of 45 degrees with the
+axis or center, as shown on the drawing at _A_, Fig. 15. To set the
+compound rest, nuts _n_ on either side, which hold it rigidly to the
+lower slide, are first loosened and the slide is then turned until the
+45-degree graduation is exactly opposite the zero line; the slide is
+then tightened in this position. A cut is next taken across the valve by
+operating handle _w_ and feeding the tool in the direction of the arrow.
+
+[Illustration: Fig. 15. Example of Taper Work Turned by using Compound
+Rest]
+
+In this particular instance the compound rest is set to the same angle
+given on the drawing, but this is not always the case. If the draftsman
+had given the included angle of 90 degrees, as shown at _B_, which would
+be another way of expressing it, the setting of the compound rest would,
+of course, be the same as before, or to 45 degrees, but the number of
+degrees marked on the drawing does not correspond with the angle to
+which the rest must be set. As another illustration, suppose the valve
+were to be turned to an angle of 30 degrees with the axis as shown at
+_C_. In this case the compound rest would not be set to 30 degrees but
+to 60 degrees, because in order to turn the work to an angle of 30
+degrees, the rest must be 60 degrees from its zero position, as shown.
+From this it will be seen that the number of degrees marked on the
+drawing does not necessarily correspond to the angle to which the rest
+must be set, as the graduations on the rest show the number of degrees
+that it is moved from its zero position, which corresponds to the line
+_a--b_. The angle to which the compound rest should be set can be found,
+when the drawing is marked as at _A_ or _C_, by subtracting the angle
+given from 90 degrees. When the included angle is given, as at _B_,
+subtract one-half the included angle from 90 degrees to obtain the
+required setting. Of course, when using a compound rest, the lathe
+centers are set in line as for straight turning, as otherwise the angle
+will be incorrect.
+
+Rules for Figuring Tapers
+
++---------------------+---------------------+--------------------------+
+|      Given          |     To Find         |         Rule             |
++---------------------+---------------------+--------------------------+
+|The taper per foot.  |The taper per inch.  |Divide the taper per foot |
+|                     |                     |  by 12.                  |
+|                     |                     |                          |
+|The taper per inch.  |The taper per foot.  |Multiply the taper per    |
+|                     |                     |  inch by 12.             |
+|                     |                     |                          |
+|End diameters and    |The taper per foot.  |Subtract small diameter   |
+|  length of taper in |                     |  from large; divide by   |
+|  inches.            |                     |  length of taper, and    |
+|                     |                     |  multiply quotient by 12.|
+|                     |                     |                          |
+|Large diameter and   |Diameter at small    |Divide taper per foot by  |
+|  length of taper in |  end in inches.     |  12; multiply by length  |
+|  inches and taper   |                     |  of length of taper, and |
+|  per foot.          |                     |  subtract result from    |
+|                     |                     |  large diameter.         |
+|                     |                     |                          |
+|Small diameter and   |Diameter at large    |Divide taper per foot by  |
+|  length of taper in |  end in inches.     |  12; multiply by length  |
+|  inches, and taper  |                     |  of taper, and add result|
+|  per foot.          |                     |  to small diameter.      |
+|                     |                     |                          |
+|The taper per foot   |Distance between     | Subtract small diameter  |
+|  and two diameters  |  two given diameters|   from large; divide re- |
+|  in inches.         |  in inches.         |   mainder by taper per   |
+|                     |                     |   foot, and multiply     |
+|                     |                     |   quotient by 12.        |
+|                     |                     |                          |
+|The taper per foot.  |Amount of taper in   | Divide taper per foot by |
+|                     |  a certain length   |   12; multiply by given  |
+|                     |  given in inches.   |   length of tapered part.|
++---------------------+---------------------+--------------------------+
+
+=Accurate Measurement of Angles and Tapers.=--When great accuracy is
+required in the measurement of angles, or when originating tapers,
+disks are commonly used. The principle of the disk method of taper
+measurement is that if two disks of unequal diameters are placed either
+in contact or a certain distance apart, lines tangent to their
+peripheries will represent an angle or taper, the degree of which
+depends upon the diameters of the two disks and the distance between
+them. The gage shown in Fig. 16, which is a form commonly used for
+originating tapers or measuring angles accurately, is set by means of
+disks. This gage consists of two adjustable straight-edges _A_ and
+_A_{1}_, which are in contact with disks _B_ and _B_{1}_. The angle
+[alpha] or the taper between the straight-edges depends, of course, upon
+the diameters of the disks and the center distance _C_, and as these
+three dimensions can be measured accurately, it is possible to set the
+gage to a given angle within very close limits. Moreover, if a record of
+the three dimensions is kept, the exact setting of the gage can be
+reproduced quickly at any time. The following rules may be used for
+adjusting a gage of this type.
+
+[Illustration: Fig. 16. Disk Gage for Accurate Measurement of Angles and
+Tapers]
+
+=To Find Center Distance for a Given Taper.=--When the taper, in inches
+per foot, is given, to determine center distance _C_. _Rule:_ Divide the
+taper by 24 and find the angle corresponding to the quotient in a table
+of tangents; then find the sine corresponding to this angle and divide
+the difference between the disk diameters by twice the sine.
+
+_Example:_ Gage is to be set to 3/4 inch per foot, and disk diameters
+are 1.25 and 1.5 inch, respectively. Find the required center distance
+for the disks.
+
+  0.75
+  ---- = 0.03125.
+   24
+
+The angle whose tangent is 0.03125 equals 1 degree 47.4 minutes; sin 1°
+47.4' = 0.03123; 1.50 - 1.25 = 0.25 inch;
+
+  0.25
+  ----------- = 4.002 inches = center distance C.
+  2 × 0.03123
+
+=To Find Center Distance for a Given Angle.=--When straight-edges must
+be set to a given angle [alpha], to determine center distance _C_
+between disks of known diameter. _Rule:_ Find the sine of half the angle
+[alpha] in a table of sines; divide the difference between the disk
+diameters by double this sine.
+
+_Example:_ If an angle [alpha] of 20 degrees is required, and the disks
+are 1 and 3 inches in diameter, respectively, find the required center
+distance _C_.
+
+   20
+  ---- = 10 degrees; sin 10° = 0.17365;
+    2
+
+     3 - 1
+  ----------- = 5.759 inches = center distance _C_.
+  2 × 0.17365
+
+=To Find Angle for Given Taper per Foot.=--When the taper in inches per
+foot is known, and the corresponding angle [alpha] is required. _Rule:_
+Divide the taper in inches per foot by 24; find the angle corresponding
+to the quotient, in a table of tangents, and double this angle.
+
+_Example:_ What angle [alpha] is equivalent to a taper of 1-1/2 inch per
+foot?
+
+  1.5
+  --- = 0.0625.
+  24
+
+The angle whose tangent is 0.0625 equals 3 degrees 35 minutes, nearly;
+then, 3 deg. 35 min. × 2 = 7 deg. 10 min.
+
+=To Find Angle for Given Disk Dimensions.=--When the diameters of the
+large and small disks and the center distance are given, to determine
+the angle [alpha]. _Rule:_ Divide the difference between the disk
+diameters by twice the center distance; find the angle corresponding to
+the quotient, in a table of sines, and double the angle.
+
+_Example:_ If the disk diameters are 1 and 1.5 inch, respectively, and
+the center distance is 5 inches, find the included angle [alpha].
+
+  1.5 - 1
+  -------  = 0.05.
+   2 × 5
+
+The angle whose sine is 0.05 equals 2 degrees 52 minutes; then, 2 deg.
+52 min. × 2 = 5 deg. 44 min. = angle [alpha].
+
+[Illustration: Fig. 17. Setting Center Mark in Line with Axis of Lathe
+Spindle by use of Test Indicator]
+
+[Illustration: Fig. 18. Jig-plate with Buttons attached, ready for
+Boring]
+
+=Use of the Center Indicator.--=The center test indicator is used for
+setting a center-punch mark, the position of which corresponds with the
+center or axis of the hole to be bored, in alignment with the axis of
+the lathe spindle. To illustrate, if two holes are to be bored, say 5
+inches apart, small punch marks having that center-to-center distance
+would be laid out as accurately as possible. One of these marks would
+then be set central with the lathe spindle by using a center test
+indicator as shown in Fig. 17. This indicator has a pointer _A_ the end
+of which is conical and enters the punch mark. The pointer is held by
+shank _B_ which is fastened in the toolpost. The joint _C_ by means of
+which the pointer is held to the shank is universal; that is, it allows
+the pointer to move in any direction. Now when the part being tested is
+rotated by running the lathe, if the center-punch mark is not in line
+with the axes of the lathe spindle, obviously the outer end of pointer
+_A_ will vibrate, and as joint _C_ is quite close to the inner end, a
+very slight error in the location of the center-punch mark will cause a
+perceptible movement of the outer end, as indicated by the dotted lines.
+When the work has been adjusted until the pointer remains practically
+stationary, the punch mark is central, and the hole is bored. The other
+center-punch mark is then set in the same way for boring the second
+hole. The accuracy of this method depends, of course, upon the location
+of the center-punch marks. A still more accurate way of setting parts
+for boring holes to a given center-to-center distance is described in
+the following:
+
+=Locating Work by the Button Method.=--Among the different methods
+employed by machinists and toolmakers for accurately locating work such
+as jigs, etc., on the faceplate of a lathe, the one most commonly used
+is known as the button method. This scheme is so named because
+cylindrical bushings or buttons are attached to the work in positions
+corresponding to the holes to be bored, after which they are used in
+locating the work. These buttons, which are ordinarily about 1/2 inch in
+diameter, are ground and lapped to the same size and the ends squared.
+The diameter should, preferably, be such that the radius can be
+determined easily, and the hole through the center should be about 1/8
+inch larger than the retaining screw, so that the button can be shifted.
+
+As an illustration of the practical application of the button method, we
+shall consider, briefly, the way the holes would be accurately machined
+in the jig-plate in Fig. 18. First the centers of the seven holes should
+be laid off approximately correct by the usual methods, after which
+small holes should be drilled and tapped for the clamping screws _S_.
+After the buttons _B_ are clamped lightly in place, they are all set in
+correct relation with each other and with the jig-plate. The proper
+location of the buttons is very important as their positions largely
+determine the accuracy of the work. A definite method of procedure that
+would be applicable in all cases cannot, of course, be given, as the
+nature of the work as well as the tools available make it necessary to
+employ different methods.
+
+[Illustration: Fig. 19. Setting a Button True Preparatory to Boring, by
+use of Test Indicator]
+
+In this particular case, the three buttons _a_, _b_ and _c_ should be
+set first, beginning with the one in the center. As this central hole
+must be 2.30 and 2.65 inches from the finished sides _A_ and _A_{1}_,
+respectively, the work is first placed on an accurate surface-plate as
+shown; by resting it first on one of these sides and then on the other,
+and measuring with a vernier height gage, the central button can be
+accurately set. The buttons _a_ and _c_ are also set to the correct
+height from side _A_{1}_ by using the height gage, and in proper
+relation to the central button by using a micrometer or a vernier
+caliper and measuring the over-all dimension _x_. When measuring in this
+way, the diameter of one button would be deducted to obtain the correct
+center-to-center distance. After buttons _a_, _b_ and _c_ are set
+equidistant from side A_{1} and in proper relation to each other, the
+remaining buttons should be set radially from the central button _b_ and
+the right distance apart. By having two micrometers or gages, one set
+for the radial dimension _x_ and the other for the chordal distance _y_,
+the work may be done in a comparatively short time.
+
+[Illustration: Fig. 20. Testing Concentricity of Button with Dial Gage]
+
+After the buttons have been tightened, all measurements should be
+carefully checked; the work is then mounted on the faceplate of the
+lathe, and one of the buttons, say _b_, is set true by the use of a test
+indicator as shown in Fig. 19. When the end of this indicator (which is
+one of a number of types on the market) is brought into contact with the
+revolving button, the vibration of the pointer _I_ shows how much the
+button runs out of true. When the pointer remains practically
+stationary, thus showing that the button runs true, the latter should be
+removed. The hole is then drilled nearly to the required size, after
+which it is bored to the finish diameter. In a similar manner the other
+buttons are indicated and the holes bored, one at a time. It is evident
+that if each button is correctly located and set perfectly true in the
+lathe, the various holes will be located at the required
+center-to-center dimensions within very close limits.
+
+[Illustration: Fig. 21. Drilling a Bushing Hole]
+
+Fig. 20 shows how one of the buttons attached to a plate in which three
+holes are to be bored is set true or concentric. The particular
+indicator illustrated is of the dial type, any error in the location of
+the button being shown by a hand over a dial having graduations
+representing thousandths of an inch. Fig. 21 shows how the hole is
+drilled after the button is removed. It will be noted that the drill is
+held in a chuck, the taper shank of which fits into the tailstock
+spindle, this being the method of holding small drills. After drilling,
+the hole is bored as shown in Fig. 22. The boring tool should have a
+keen edge to avoid springing, and if the work when clamped in position,
+throws the faceplate out of balance, it is advisable to restore the
+balance, before boring, by the use of a counter-weight, because the
+lathe can be rotated quite rapidly when boring such a small hole.
+
+[Illustration: Fig. 22. Boring a Bushing Hole]
+
+When doing precision work of this kind, the degree of accuracy will
+depend upon the instruments used, the judgment and skill of the workman
+and the care exercised. A good general rule to follow when locating
+bushings or buttons is to use the method which is the most direct and
+which requires the least number of measurements. As an illustration of
+how errors may accumulate, let us assume that seven holes are to be
+bored in the jig-plate shown in Fig. 23, so that they are the same
+distance from each other and in a straight line. The buttons may be
+brought into alignment by the use of a straight-edge, and to simplify
+matters, it will be taken for granted that they have been ground and
+lapped to the same size. If the diameter of the buttons is first
+determined by measuring with a micrometer, and then this diameter is
+deducted from the center distance _x_, the difference will be the
+distance _y_ between adjacent buttons. Now if a temporary gage is made
+to length _y_, all the buttons can be set practically the same distance
+apart, the error between any two adjacent ones being very slight. If,
+however, the total length _z_ over the end buttons is measured by some
+accurate means, the chances are that this distance will not equal six
+times dimension _x_ plus the diameter of one button, as it should,
+because even a very slight error in the gage for distance _y_ would
+gradually accumulate as each button was set. If a micrometer were
+available that would span two of the buttons, the measurements could be
+taken direct and greater accuracy would doubtless be obtained. On work
+of this kind where there are a number of holes that need to have
+accurate over-all dimensions, the long measurements should first be
+taken when setting the buttons, providing, of course, there are proper
+facilities for so doing, and then the short ones. For example, the end
+buttons in this case should first be set, then the central one and
+finally those for the sub-divisions.
+
+[Illustration: Fig. 23. Example of Work illustrating Accumulation of
+Errors]
+
+=Eccentric Turning.=--When one cylindrical surface must be turned
+eccentric to another, as when turning the eccentric of a steam engine,
+an arbor having two sets of centers is commonly used, as shown in Fig.
+24. The distance _x_ between the centers must equal one-half the total
+"throw" or stroke of the eccentric. The hub of the eccentric is turned
+upon the centers _a--a_, and the tongued eccentric surface, upon the
+offset centers, as indicated by the illustration. Sometimes eccentrics
+are turned while held upon special fixtures attached to the faceplate.
+
+[Illustration: Fig. 24. Special Arbor for Turning Eccentrics]
+
+When making an eccentric arbor, the offset center in each end should be
+laid out upon radial lines which can be drawn across the arbor ends by
+means of a surface gage. Each center is then drilled and reamed to the
+same radius _x_ as near as possible. The uniformity of the distance _x_
+at each end is then tested by placing the mandrel upon the offset
+centers and rotating it, by hand, with a dial indicator in contact at
+first one end and then the other. The amount of offset can also be
+tested either by measuring from the point of a tool held in the
+toolpost, or by setting the tool to just graze the mandrel at extreme
+inner and outer positions, and noting the movement of the cross-slide by
+referring to the dial gage of the cross-feed screw.
+
+[Illustration: Fig. 25. Turning an Engine Crank-pin in an Ordinary
+Lathe]
+
+=Turning a Crankshaft in a Lathe.=--Another example of eccentric turning
+is shown in Fig. 25. The operation is that of turning the crank-pin of
+an engine crankshaft, in an ordinary lathe. The main shaft is first
+rough-turned while the forging revolves upon its centers _C_ and _C_{1}_
+and the ends are turned to fit closely the center-arms _A_ and _A_{1}_.
+After the sides _B_ and _B_{1}_ of the crank webs have been rough-faced,
+the center-arms are attached to the ends of the shaft as shown in the
+illustration. These arms have centers at _D_ and _D_{1}_ (located at the
+required crank radius) which should be aligned with the rough pin, when
+attaching the arms, and it is advisable to insert braces _E_ between the
+arms and crank to take the thrust of the lathe centers. With the forging
+supported in this way, the crank-pin and inner sides of the webs are
+turned and faced, the work revolving about the axis of the pin. The
+turning tools must extend beyond the tool-holder far enough to allow the
+crank to clear as it swings around. Owing to this overhang, the tool
+should be as heavy as possible to make it rigid and it is necessary to
+take comparatively light cuts and proceed rather cautiously. After
+finishing the crank-pin and inside of the crank, the center-arms are
+removed and the main body of the shaft and the sides _B_ and _B_{1}_ are
+finished. This method of turning crankshafts is often used in general
+repair shops, etc., especially where new shafts do not have to be turned
+very often. It is slow and inefficient, however, and where crankshafts
+are frequently turned, special machines or attachments are used.
+
+[Illustration: Fig. 26. LeBlond Lathe with Special Equipment for
+Crankshaft Turning]
+
+=Special Crankshaft Lathe.=--A lathe having special equipment for
+rough-turning gas engine crankshaft pins is shown in Fig. 26. This
+lathe is a heavy-duty type built by the R. K. LeBlond Machine Tool Co.
+It is equipped with special adjustable headstock and tailstock fixtures
+designed to take crankshafts having strokes up to about 6 inches. The
+tools are held in a three-tool turret type of toolpost and there are
+individual cross-stops for each tool. This lathe also has a roller
+steadyrest for supporting the crankshaft; automatic stops for the
+longitudinal feed, and a pump for supplying cutting lubricant. The
+headstock fixture is carried on a faceplate mounted on the spindle and
+so arranged as to be adjustable for cranks of different throw. When the
+proper adjustment for a given throw has been made, the slide is secured
+by four T-bolts. A graduated scale and adjusting screw permit of
+accurate adjustments.
+
+The revolving fixture is accurately indexed for locating different
+crank-pins in line with the lathe centers, by a hardened steel plunger
+in the slide which engages with hardened bushings in the fixture. The
+index is so divided that the fixture may be rotated 120 or 180 degrees,
+making it adjustable for 2-, 4- and 6-throw cranks. After indexing, the
+fixture is clamped by two T-bolts which engage a circular T-slot. The
+revolving fixture is equipped with removable split bushings which can be
+replaced to fit the line bearings of different sized crankshafts. The
+work is driven by a V-shaped dovetail piece having a hand-nut
+adjustment, which also centers the pin by the cheek or web. The crank is
+held in position by a hinged clamp on the fixture. The tailstock fixture
+is also adjustable and it is mounted on a spindle which revolves in a
+bushing in the tailstock barrel. The adjustment is obtained in the same
+manner as on the headstock fixture, and removable split bushings as well
+as a hinged clamp are also employed.
+
+The method of chucking a four-throw crank is as follows: The two
+fixtures are brought into alignment by two locking pins. One of these is
+located in the head and enters a bushing in the large faceplate and the
+other is in the tailstock and engages the tailstock fixture. The
+crankshaft is delivered to the machine with the line bearings
+rough-turned and it is clamped by the hinged clamp previously referred
+to and centered by the V-shaped driver. The locking pins for both
+fixtures are then withdrawn and the machine is ready to turn two of the
+pins. After these have been machined, the fixtures are again aligned by
+the locking pins, the two T-bolts of the headstock fixture and the
+hinged clamp at the tailstock are released, the indexing plunger is
+withdrawn and the headstock fixture and crank are turned 180 degrees or
+until the index plunger drops into place. The crank is then clamped at
+the tailstock end and the revolving fixture is secured by the two
+T-bolts previously referred to. After the locking pins are withdrawn,
+the lathe is ready to turn the two opposite pins.
+
+[Illustration: Fig. 27. Diagrams showing Arrangements of Tools on
+LeBlond Lathe]
+
+=Operation of Special Crankshaft Lathe.=--The total equipment of this
+machine (see Fig. 27) is carried on a three-tool turret tool-block. The
+method of turning a crankshaft is as follows: A round-nosed turning tool
+is first fed into a cross stop as illustrated in the plan view at _A_,
+which gives the proper diameter. The feed is then engaged and the tool
+feeds across the pin until the automatic stop lever engages the first
+stop, which throws out the feed automatically. The carriage is then
+moved against a positive stop by means of the handwheel. The roller
+back-rest is next adjusted against the work by the cross-feed handwheel
+operating through a telescopic screw, and the filleting tools are
+brought into position as at _B_. These are run in against a stop,
+removing the part left by the turning tool and giving the pin the proper
+width and fillets of the correct radius. If the crankshaft has straight
+webs which must be finished, two tools seen at _b_ are used for facing
+the webs to the correct width. During these last two operations, the
+crank is supported by the roller back-rest, thus eliminating any
+tendency of the work to spring.
+
+[Illustration: Fig. 28. (A) Spherical Turning with Compound Rest. (B)
+Concave Turning]
+
+After one pin is finished in the manner described, the back-rest is
+moved out of the way, the automatic stop lever raised, the carriage
+shifted to the next pin, and the operation repeated. The tools are held
+in position on the turret by studs, and they can be moved and other
+tools quickly substituted for pins of different widths. This machine is
+used for rough-turning the pins close to the required size, the
+finishing operation being done in a grinder. It should be mentioned, in
+passing, that many crankshafts, especially the lighter designs used in
+agricultural machinery, etc., are not turned at all but are ground from
+the rough.
+
+=Spherical Turning.=--Occasionally it may be necessary to turn a
+spherical surface in the lathe. Sketch _A_, Fig. 28, shows how a small
+ball-shaped end can be turned on a piece held in a chuck. The lathe
+carriage is adjusted so that the pin around which the compound rest
+swivels is directly under the center a. The bolts which hold the swivel
+are slightly loosened to allow the top slide to be turned, as indicated
+by the dotted lines; this causes the tool point to move in an arc about
+center _a_, and a spherical surface is turned. Light cuts must be taken
+as otherwise it would be difficult to turn the slide around by hand.
+
+[Illustration: Fig. 29. Spherical Turning Attachment for Engine Lathe]
+
+Sketch _B_ illustrates how a concave surface can be turned. The
+cross-slide is adjusted until swivel pin is in line with the lathe
+centers, and the carriage is moved along the bed until the horizontal
+distance between center _b_ of the swivel, and the face of the work,
+equals the desired radius of the concave surface. The turning is then
+done by swinging the compound rest as indicated by the dotted lines. The
+slide can be turned more evenly by using the tailstock center to force
+it around. A projecting bar is clamped across the end of the slide at
+_d_, to act as a lever, and a centered bar is placed between this lever
+and the tailstock center; then by screwing out the tailstock spindle,
+the slide is turned about pivot _b_. The alignment between the swivel
+pin and the lathe centers can be tested by taking a trial cut; if the
+swivel pin is too far forward, the tool will not touch the turned
+surface if moved past center _c_, and if the pin is too far back, the
+tool will cut in on the rear side.
+
+=Spherical Turning Attachments.=--When spherical turning must be done
+repeatedly, special attachments are sometimes used. Fig. 29 shows an
+attachment applied to a lathe for turning the spherical ends of
+ball-and-socket joints. The height or radius of the cutting tool and,
+consequently, the diameter of the turned ball, is regulated by adjusting
+screw _A_. The tool is swung around in an arc, by turning handle _B_
+which revolves a worm meshing with an enclosed worm-wheel. As will be
+seen, the work is held in a special chuck, owing to its irregular shape.
+
+[Illustration: Fig. 30. Attachment for Turning Spherical End of Gasoline
+Engine Piston]
+
+Another spherical turning attachment is shown in Fig. 30. This is used
+for machining the ends of gasoline engine pistons. The cross-slide has
+bolted to it a bar _A_ carrying a roller which is pressed against a
+forming plate _B_ by a heavy spring _C_. The forming plate _B_, which is
+attached to a cross-piece fastened to the ways of the lathe bed, is
+curved to correspond with the radius required on the piston end, and
+when the tool is fed laterally by moving the cross-slide, it follows the
+curve of plate _B_. The piston is held in a special hollow chuck which
+locates it in a central position and holds it rigidly.
+
+In connection with lathe work, special attachments and tools are often
+used, especially when considerable work of one class must be turned;
+however, if a certain part is required in large quantities, it is
+usually more economical to use some semi-automatic or automatic turning
+machine, especially designed for repetition work.
+
+=Turning with Front and Rear Tools.=--In ordinary engine lathe practice,
+one tool is used at a time, but some lathes are equipped with
+tool-holders at the front and rear of the carriage so that two tools can
+be used simultaneously. Fig. 31 shows a detail view of a lathe in which
+front and rear tools are being used. These tools are of the inserted
+cutter type and the one at the rear is inverted, as the rotary movement
+of the work is, of course, upward on the rear side. This particular
+lathe was designed for taking heavy roughing cuts and has considerable
+driving power.
+
+[Illustration: Fig. 31. Front and Rear Tools used for Roughing]
+
+The part shown in this illustration is a chrome-nickel steel bar which
+is being roughed out to form a milling machine spindle. It is necessary
+to reduce the diameter of the bar from 5-7/16 inches to 3-3/4 inches for
+a length of 27 inches, because of a collar on one end. This reduction is
+made in one passage of the two tools, with a feed of 1/32 inch per
+revolution and a speed of 60 revolutions per minute. The use of two
+tools for such heavy roughing cuts is desirable, especially when the
+parts are required in large quantities, because the thrust of the cut on
+one side, which tends to deflect the work, is counteracted by the thrust
+on the opposite side.
+
+[Illustration: Fig. 32. Lo-swing Lathe for Multiple Turning]
+
+Sometimes special tool-holders are made for the lathe, so that more than
+one tool can be used for turning different surfaces or diameters at the
+same time, the tools being set in the proper relation to each other. The
+advantage of this method has resulted in the design of a special lathe
+for multiple-tool turning.
+
+=A Multiple-tool Lathe.=--The lathe shown in Fig. 32 (which is built by
+the Fitchburg Machine Works and is known as the Lo-swing) is designed
+especially for turning shafts, pins and forgings not exceeding 3-1/2
+inches in diameter. It has two carriages _A_ and _B_ which, in
+conjunction with special tool-holders, make it possible to turn several
+different diameters simultaneously. At the front of this lathe there is
+an automatic stop-rod _C_ for disengaging the feed when the tools have
+turned a surface to the required length. This stop-rod carries
+adjustable stops _D_ which are set to correspond with shoulders, etc.,
+on the work. The rod itself is also adjustable axially, so that the
+tools, which are usually arranged in groups of two or more (depending
+upon the nature of the work), can be disengaged at a point nearer or
+farther from the headstock as may be required, owing to a variation in
+the depth of center holes. For example, if it were necessary to feed a
+group of tools farther toward the headstock after they had been
+automatically disengaged, the entire rod with its stops would be
+adjusted the required amount in that direction.
+
+[Illustration: Fig. 33. Lo-swing Lathe arranged for Turning a Steering
+Knuckle]
+
+The gage _G_, which is attached to a swinging arm, is used to set the
+stop bar with reference to a shoulder near the end of the work, when it
+is necessary to finish other parts to a given distance from such a
+shoulder or other surface. The use of this gage will be explained more
+fully later. Cooling lubricant for the tools is supplied through the
+tubes _E_. The lathe shown in the illustration is arranged for turning
+Krupp steel bars. A rough bar and also one that has been turned may be
+seen to the right. The plain cylindrical bar is turned to five different
+diameters, by groups of tools held on both carriages.
+
+[Illustration: Fig. 34. Plan View showing Method of driving Steering
+Knuckle and Arrangement of Tools]
+
+=Examples of Multiple Turning.=--Figs. 33 and 34 show how a Lo-swing
+lathe is used for turning the steering knuckle of an automobile. Four
+tools are used in this case, three cylindrical surfaces and one tapering
+surface being turned at the same time. For this job, the four tools are
+mounted on one carriage. The taper part is turned by the second tool
+from the headstock, which is caused to feed outward as the carriage
+advances by a taper attachment. This tool is held in a special holder
+and bears against a templet at the rear, which is tapered to correspond
+with the taper to be turned. This templet is attached to a bar which, in
+turn, is fastened to a stationary bracket seen to the extreme left in
+Fig. 33. This part is finished in two operations, the tool setting being
+identical for each operation, except for diameter adjustments. As the
+illustrations show, three of the four tools employed are used for
+straight turning on different diameters, while the fourth finishes the
+taper.
+
+These pieces, which are rough drop forgings, are first reduced to the
+approximate size. When it becomes necessary to grind the tools, they are
+reset and those parts which have been roughed out are turned to the
+finished size. The average time for the first operation, which includes
+starting, stopping, turning and replacing the piece, is one minute,
+while for the second operation with the finer feed, an average time of
+two minutes is required. The work is driven by sleeve _S_, which fits
+over the spindle and is held in position by the regular driver, as
+shown. This sleeve is notched to fit the knuckle, so that the latter can
+easily and quickly be replaced when finished.
+
+One of the interesting features of this job lies in the method of
+locating the shoulders on each knuckle, at the same distance from the
+hole _H_ which is drilled previously, and which receives the bolt on
+which the knuckle swivels when assembled in a car. As soon as the
+knuckle has been placed between the centers, a close-fitting plug _P_
+(Fig. 33) is inserted in this hole and the indicator arm with its
+attached gage or caliper _G_ is swung up to the position shown. The
+stop-rod on which the stops have been previously set for the correct
+distance between the shoulders is next adjusted axially until the gage
+_G_ just touches the plug _P_. The indicator is then swung out of the
+way, and the piece turned. If the next knuckle were centered, say,
+deeper than the previous one which would, of course, cause it to be
+located nearer the headstock, obviously all the shoulders would be
+located farther from the finished hole, provided the position of the
+stops remained the same as before. In such a case their position would,
+however, be changed by shifting the stop-rod until the gage _G_ again
+touched the plug thus locating all the stops with reference to the hole.
+As the adjustment of the stop-rod changes the position of the taper
+templet as well as the stops, it is evident that both the shoulders and
+the taper are finished the same distance from the hole in each case. The
+connection of the bracket (to which the templet arm is attached) with
+the stop-rod is clearly shown in Fig. 33. This bracket can either be
+locked to the ways or adjusted to slide when the stop-rod is moved.
+
+[Illustration: Fig. 35. First and Second Operations on Automobile
+Transmission Shaft--Lo-swing Lathe]
+
+The part illustrated in Fig. 35 is an automobile transmission shaft. In
+this particular case, cylindrical, tapering and spherical surfaces are
+turned. The upper view shows, diagrammatically, the arrangement of the
+tools and work for the first operation. After the shaft is "spotted" at
+_A_ for the steadyrest, the straight part _C_ and the collar _B_ are
+sized with tools _S_ and _R_ which are mounted on the left-hand
+carriage. A concave groove is then cut in collar _B_ by tool _R_, after
+which spherical end _D_ is formed by a special attachment mounted on the
+right-hand carriage. This attachment is the same, in principle, as the
+regular taper-turning attachment, the substitution of a circular templet
+_T_ for the straight kind used on taper work being the only practical
+difference.
+
+[Illustration: Fig. 36. Axle End turned in One Traverse of the Five
+Tools shown]
+
+After the surfaces mentioned have been finished on a number of pieces,
+the work is reversed and the tools changed as shown by the lower view.
+The first step in the second operation is to turn the body _E_ of the
+shaft with the tool _T_ on the left-hand carriage. The taper _F_ and the
+straight part _G_ are then finished, which completes the turning. It
+will be noted that in setting up the machine for this second operation,
+it is arranged for taper turning by simply replacing the circular
+templet with the straight one shown. When this taper attachment is not
+in use, the swiveling arm _M_, which is attached to a bracket, is swung
+out of the way.
+
+The method of driving this shaft is worthy of note. A dog having two
+driving arms each of which bears against a pin _N_ that passes through a
+hole in the spindle is used. As the ends of this pin, against which the
+dog bears, are beveled in opposite directions, the pin turns in its hole
+when the dog makes contact with it and automatically adjusts itself
+against the two driving members of the dog. The advantage of driving by
+a two-tailed dog, as most mechanics know, is in equalizing the tendency
+to spring slender parts while they are being turned.
+
+[Illustration: Fig. 37. Lathe Knurling Tool having Three Pairs of
+Knurls--Coarse, Medium and Fine]
+
+In Fig. 36 another turning operation on a lathe of this type is shown,
+the work in this case being a rear axle for a motor truck. The turning
+of this part is a good example of that class of work where the rapid
+removal of metal is the important feature. As the engraving shows, the
+stock, prior to turning, is 3-1/2 inches in diameter and it is reduced
+to a minimum diameter of 1-1/16 inch. This metal is turned off with one
+traverse of the carriage or by one passage of the five tools, and the
+weight of the chips removed from each end of the axle is approximately
+12 pounds. The time required for the actual turning is about 9 minutes,
+while the total time for the operation, which includes placing the heavy
+piece in the machine, turning, and removing the work from the lathe, is
+12 minutes. The axle revolves, while being turned, at 110 revolutions
+per minute and a feed equivalent to 1 inch of tool travel to 60
+revolutions of the work is used. It will be noticed that the taper
+attachment is also employed on this part, the taper being turned by the
+second tool from the left. As the axle is equipped with roller bearings,
+it was found desirable to finish the bearing part by a separate
+operation; therefore, in the operation shown the axle is simply roughed
+down rather close to the finished dimensions, leaving enough material
+for a light finishing cut.
+
+=Knurling in the Lathe.=--Knurling is done either to provide a rough
+surface which can be firmly gripped by the hand or for producing an
+ornamental effect. The handles of gages and other tools are often
+knurled, and the thumb-screws used on instruments, etc., usually have
+knurled edges. A knurled surface consists of a series of small ridges or
+diamond-shaped projections, and is produced in the lathe by the use of a
+tool similar to the one shown in Fig. 37, this being one of several
+different designs in common use. The knurling is done by two knurls _A_
+and _B_ having teeth or ridges which incline to the right on one knurl
+and to the left on the opposite knurl, as shown by the end view. When
+these two knurls are pressed against the work as the latter revolves,
+one knurl forms a series of left-hand ridges and the other knurl
+right-hand ridges, which cross and form the diamond-shaped knurling
+which is generally used.
+
+If the surface to be knurled is wider than the knurls, the power feed of
+the lathe should be engaged and the knurling tool be traversed back and
+forth until the diamond-shaped projections are well formed. To prevent
+forming a double set of projections, feed the knurl in with considerable
+pressure at the start, then partially relieve the pressure before
+engaging the power feed. Use oil when knurling.
+
+The knurls commonly used for lathe work have spiral teeth and ordinarily
+there are three classes, known as coarse, medium and fine. The medium
+pitch is generally used. The teeth of coarse knurls have a spiral angle
+of 36 degrees and the pitch of the knurled cut (measured parallel to the
+axis of the work) should be about 8 per inch. For medium knurls, the
+spiral angle is 29-1/2 degrees and the pitch, measured as before, is 12
+per inch. For fine knurls, the spiral angle is 25-3/4 degrees and the
+pitch 20 per inch. The knurls should be about 3/4 inch in diameter and
+3/8 inch wide. When made to these dimensions, coarse knurls have 34
+teeth; medium, 50 teeth; and fine knurls, 80 teeth.
+
+[Illustration: Fig. 38. Hendey Relieving Attachment applied to a Lathe]
+
+The particular tool illustrated in Fig. 37 has three pairs of knurls of
+coarse, medium and fine pitch. These are mounted in a revolving holder
+which not only serves to locate the required set of knurls in the
+working position, but enables each knurl to bear against the surface
+with equal pressure. Concave knurls are sometimes used for knurling
+rounded edges on screw heads, etc.
+
+=Relieving Attachment.=--Some lathes, particularly those used in
+toolrooms, are provided with relieving attachments which are used for
+"backing off" the teeth of milling cutters, taps, hobs, etc. If a
+milling cutter of special shape is to be made, the cutter blank is first
+turned to the required form with a special tool having a cutting edge
+that corresponds with the shape or profile of the cutter to be made. The
+blank is then fluted or gashed to form the teeth, after which the tops
+of the teeth are relieved or backed off to provide clearance for the
+cutting edges. The forming tool used for turning the blank is set to
+match the turned surface, and the teeth are backed off as the result of
+a reciprocating action imparted to the toolslide by the relieving
+attachment. The motion of the toolslide is so adjusted that the tool
+will meet the front of each tooth and the return movement begin promptly
+after the tool leaves the back end of the tooth.
+
+[Illustration: Fig. 39. Relieving a Formed Cutter]
+
+These attachments differ somewhat in their construction and arrangement
+but the principle of their operation is similar. Fig. 38 shows a Hendey
+relieving attachment applied to a lathe. A bracket carrying the gearing
+_A_ through which the attachment is driven is mounted upon the main gear
+box of the lathe, and the special slide _B_, which is used when
+relieving, is placed on the cross-slide after removing the regular
+compound rest. The gears at _A_ are changed to suit the number of flutes
+or gashes in the cutter, tap or whatever is to be relieved. If we assume
+that the work is a formed milling cutter having nine teeth, then with
+this particular attachment, a gear having 90 teeth would be placed on
+the "stud" and a 40-tooth gear on the cam-shaft, the two gears being
+connected by a 60-tooth intermediate gear. With this combination of
+gearing, the toolslide would move in and out nine times for each
+revolution of the work, so that the tool could back off the top of each
+tooth. (The gearing to use for various numbers of flutes is shown by an
+index plate on the attachment.) The amount of relief is varied to suit
+the work being done, by means of a toothed coupling which makes it
+possible to change the relative position between the eccentric which
+actuates the toolslide and the cam lever, thereby lengthening or
+shortening the reciprocating travel of the tool.
+
+[Illustration: Fig. 40. Relieving Side of Angular Milling Cutter]
+
+=Application of Relieving Attachment.=--Some typical examples of the
+kind of work for which the relieving attachment is used are shown in
+Figs. 39 to 42, inclusive. Fig. 39 shows how a formed milling cutter is
+relieved. The toolslide is set at right angles to the axis of the work,
+and the tool moves in as each tooth passes, and out while crossing the
+spaces or flutes between the teeth. As the result of this movement, the
+tops of the teeth are backed off eccentrically but the form or shape is
+the same from the front to the back of the tooth; hence, a cutter that
+has been relieved in this way can be ground repeatedly without changing
+the profile of the teeth, provided the faces are ground so as to lie in
+a radial plane.
+
+When relieving, the cutting speed should be much less than when turning
+in order to give the toolslide time to operate properly. A maximum of
+180 teeth per minute is recommended, and, if wide forming tools are
+used, it might be advisable to reduce the speed so low that only 8 teeth
+per minute would be relieved. It is also essential to use a tool having
+a keen edge, and the toolslide should work freely but be closely
+adjusted to the dovetail of the lower slide. Before beginning to back
+off the teeth, it is a good plan to color the work either by heating it
+or dipping into a strong solution of copper sulphate. This will enable
+one to see plainly the cutting action of the tool in order to stop
+relieving at the proper time.
+
+[Illustration: Fig. 41. Relieving a Right-hand Tap]
+
+Fig. 40 shows a method of relieving the teeth of an angular cutter. For
+an operation of this kind the toolslide is swiveled around at right
+angles to the side that is to be relieved. By the use of an additional
+universal joint and bearing to permit the toolslide to be swung to a
+90-degree angle, the teeth of counterbores, etc., can be relieved on the
+ends. When the attachment is used for relieving inside work, such as
+hollow mills and threading dies, the eccentric which controls the travel
+of the toolslide is set so that the relieving movement is away from the
+axis of the cutter instead of toward it. This change is made by the
+toothed coupling previously referred to, which connects the cam lever
+and oscillating shaft, the latter being turned beyond the zero mark in a
+clockwise direction as far as is necessary to obtain the desired amount
+of travel. For internal work it is also necessary to change the position
+of the opposing spring of the toolslide, so that it will press against
+the end of the slide and prevent the tool from jumping into the work.
+
+[Illustration: Fig. 42. Relieving a Hob having Spiral Flutes]
+
+Fig. 41 shows how a right-hand tap is relieved. The ordinary practice is
+to first set the tool the same as for cutting a thread. The motion of
+the toolslide is then adjusted so that the tool on the forward stroke
+will meet the front of each tooth, and start back as soon as the tool
+leaves the end of the land or top of the tooth. Taps having a left-hand
+thread can be relieved by two different methods. With the first method
+the cut starts at the cutting edge of each tooth, and ends at the
+"heel," the tool moving in toward the center of the work. With the
+second method, the cut begins at the heel and discontinues at the
+cutting edge, the tool being drawn away from the work during the cut.
+When using the first method the tap must be placed with the point toward
+the headstock, the shank end being supported by the tailstock center.
+This is done by providing an extension or blank end at the point of the
+tap long enough to hold the driving dog. With the second method, the tap
+is held between centers the same as one having a right-hand thread, but
+the travel of the toolslide is set the same as for inside relief.
+
+=Relieving Hobs or Taps Having Spiral Flutes.=--With this attachment,
+taps or hobs having "spiral" or helical flutes can also be relieved. (A
+spiral flute is preferable to one that is parallel to the axis, because
+with the former the tool has cutting edges which are square with the
+teeth; this is of especial importance when the lead of the hob or tap
+thread is considerable.) When relieving work having spiral flutes (as
+illustrated in Fig. 42), the lead of the spiral and the gears necessary
+to drive the attachment are first determined. After the attachment is
+geared for the number of flutes and to compensate for the spiral, the
+lead-screw is engaged and the backing-off operation is performed the
+same as though the flutes were straight. The carriage should not be
+disengaged from the lead-screw after starting the cut, the tool being
+returned by reversing the lathe.
+
+When gearing the attachment for relieving a tap or hob having spiral
+flutes, the gears are not selected for the actual number of flutes
+around the circumference but for a somewhat larger number which depends
+upon the lead of the hob thread and the lead of the spiral flutes. Let
+us assume that a hob has 6 spiral flutes and that the attachment is
+geared for that number. The result would be that as the tool advanced
+along the thread, it would not keep "in step" with the teeth because the
+faces of the teeth lie along a spiral (or helix which is the correct
+name for this curve); in other words, the tool would soon be moving in
+too late to begin cutting at the proper time, and to compensate for
+this, the attachment is geared so that the tool will make a greater
+number of strokes per revolution of the work than the actual number of
+flutes around the circumference.
+
+With this attachment, the two gears listed on the index plate for the
+actual number of flutes are selected, and then two compensating gears
+are added, thus forming a compound train of gearing. The ratio _R_ of
+these compensating gears is determined as follows:
+
+      _r_ + 1
+  R = -------
+        _r_
+
+in which
+
+  _r_ = _L_ ÷ _l_;
+  _L_ = lead of spiral;
+  _l_ = lead of hob thread.
+
+For example, if a hob has a pitch circumference of 3.25, a single thread
+of 0.75 inch lead, and 6 spiral flutes, what compensating gears would be
+required?
+
+The lead _L_ of the spiral flutes is first determined by dividing the
+square of the circumference _C_ of the hob at the pitch line by the lead
+_l_ of the hob thread. Thus lead _L_ = _C^2_/_l_, or, in this case, _L_
+= 3.25^2/0.75 = 14 inches, approximately. Then _r_ = 14 ÷ 0.75 = 18-2/3.
+Inserting these values in the formula for ratio R,
+
+        18-2/3 + 1   19-2/3   19-2/3 × 3   59
+  _R_ = ---------- = ------ = ---------- = --
+          18-2/3     18-2/3   18-2/3 × 3   56
+
+Hence, the compensating gears will have 56 and 59 teeth, respectively,
+the latter being the driver. As the gears for 6 flutes listed on the
+regular index plate are, stud-gear 60 teeth, cam-shaft gear 40 teeth,
+the entire train of gears would be as follows: Gear on stud, 60;
+_driven_ intermediate gear, 56; _driving_ intermediate gear, 59;
+cam-shaft gear, 40. It will be understood that the position of the
+driving gears or the driven gears can be transposed without affecting
+the ratio.
+
+=Classes of Fits Used in Machine Construction.=--In assembling machine
+parts it is necessary to have some members fit together tightly, whereas
+other parts such as shafts, etc., must be free to move or revolve with
+relation to each other. The accuracy required for a fitting varies for
+different classes of work. A shaft that revolves in its bearing must be
+slightly smaller than the bearing so that there will be room for a film
+of lubricant. A crank-pin that must be forced into the crank-disk is
+made a little larger in diameter than the hole, to secure a tight fit.
+When a very accurate fitting between two cylindrical parts that must be
+assembled without pressure is required, the diameter of the inner member
+is made as close to the diameter of the outer member as is possible. In
+ordinary machine construction, five classes of fits are used, _viz_;
+running fit, push fit, driving fit, forced fit and shrinkage fit. The
+running fit, as the name implies, is employed when parts must rotate;
+the push fit is not sufficiently free to rotate; the other classes
+referred to are used for assembling parts that must be held in fixed
+positions.
+
+=Forced Fits.=--This is the term used when a pin, shaft or other
+cylindrical part is forced into a hole of slightly smaller diameter, by
+the use of a hydraulic press or other means. As a rule, forced fits are
+restricted to parts of small and medium size, while shrinkage fits have
+no such limitations and are especially applicable when a maximum "grip"
+is desired, or when (as in the construction of ordnance) accurate
+results as to the intensity of stresses produced in the parts united are
+required. The proper allowance for a forced fit depends upon the mass of
+metal surrounding the hole, the size of the work, the kind and quality
+of the material of which the parts are composed and the smoothness and
+accuracy of the pin and bore. When a pin or other part is pressed into a
+hole a second time, the allowance for a given tonnage should be
+diminished somewhat because the surface of the bore is smoother and the
+metal more compact. The pressure required in assembling a forced fit
+will also vary for cast hubs of the same size, if they are not uniform
+in hardness. Then there is the personal factor which is much in evidence
+in work of this kind; hence, data and formulas for forced fit allowances
+must be general in their application.
+
+=Allowance for Forced Fits.=--The allowance per inch of diameter usually
+ranges from 0.001 inch to 0.0025 inch, 0.0015 being a fair average.
+Ordinarily, the allowance per inch decreases as the diameter increases;
+thus the total allowance for a diameter of 2 inches might be 0.004 inch,
+whereas for a diameter of 8 inches the total allowance might not be over
+0.009 or 0.010 inch. In some shops the allowance is made practically the
+same for all diameters, the increased surface area of the larger sizes
+giving sufficient increase in pressure. The parts to be assembled by
+forced fits are usually made cylindrical, although sometimes they are
+slightly tapered. The advantages of the taper form are that the
+possibility of abrasion of the fitted surfaces is reduced; that less
+pressure is required in assembling; and that the parts are more readily
+separated when renewal is required. On the other hand, the taper fit is
+less reliable, because if it loosens, the entire fit is free with but
+little axial movement. Some lubricant, such as white lead and lard oil
+mixed to the consistency of paint, should be applied to the pin and bore
+before assembling, to reduce the tendency of abrasion.
+
+Allowances for Different Classes of Fits
+
+(Newall Engineering Co.)
+
+  +-----+--------------------------------------------------------------+
+  |     |               Tolerances in Standard Holes[1]                |
+  |Class+------------+---------+---------+---------+---------+---------+
+  |     | Nominal    |  Up to  | 9/16"-1"| 1-1/16"-| 2-1/16"-| 3-1/16"-|
+  |     | Diameters  |   1/2"  |         |    2"   |    3"   |    4"   |
+  +-----+------------+---------+---------+---------+---------+---------+
+  |     | High Limit | +0.0002 | +0.0005 | +0.0007 | +0.0010 | +0.0010 |
+  |  A  | Low Limit  | -0.0002 | -0.0002 | -0.0002 | -0.0005 | -0.0005 |
+  |     | Tolerance  |  0.0004 |  0.0007 |  0.0009 |  0.0015 |  0.0015 |
+  +-----+------------+---------+---------+---------+---------+---------+
+  |     | High Limit | +0.0005 | +0.0007 | +0.0010 | +0.0012 | +0.0015 |
+  |  B  | Low Limit  | -0.0005 | -0.0005 | -0.0005 | -0.0007 | -0.0007 |
+  |     | Tolerance  |  0.0010 |  0.0012 |  0.0015 |  0.0019 |  0.0022 |
+  +-----+------------+---------+---------+---------+---------+---------+
+  |                       Allowances for Forced Fits                   |
+  +-----+------------+---------+---------+---------+---------+---------+
+  |     | High Limit | +0.0010 | +0.0020 | +0.0040 | +0.0060 | +0.0080 |
+  |  F  | Low Limit  | +0.0005 | +0.0015 | +0.0030 | +0.0045 | +0.0060 |
+  |     | Tolerance  |  0.0005 |  0.0005 |  0.0010 |  0.0015 |  0.0020 |
+  +-----+------------+---------+---------+---------+---------+---------+
+  |                      Allowances for Driving Fits                   |
+  +-----+------------+---------+---------+---------+---------+---------+
+  |     | High Limit | +0.0005 | +0.0010 | +0.0015 | +0.0025 | +0.0030 |
+  |  D  | Low Limit  | +0.0002 | +0.0007 | +0.0010 | +0.0015 | +0.0020 |
+  |     | Tolerance  |  0.0003 |  0.0003 |  0.0005 |  0.0010 |  0.0010 |
+  +-----+------------+---------+---------+---------+---------+---------+
+  |                       Allowances for Push Fits                     |
+  +-----+------------+---------+---------+---------+---------+---------+
+  |     | High Limit | -0.0002 | -0.0002 | -0.0002 | -0.0005 | -0.0005 |
+  |  P  | Low Limit  | -0.0007 | -0.0007 | -0.0007 | -0.0010 | -0.0010 |
+  |     | Tolerance  |  0.0005 |  0.0005 |  0.0005 |  0.0005 |  0.0005 |
+  +-----+------------+---------+---------+---------+---------+---------+
+  |                   Allowances for Running Fits[2]                   |
+  +-----+------------+---------+---------+---------+---------+---------+
+  |     | High Limit | -0.0010 | -0.0012 | -0.0017 | -0.0020 | -0.0025 |
+  |  X  | Low Limit  | -0.0020 | -0.0027 | -0.0035 | -0.0042 | -0.0050 |
+  |     | Tolerance  |  0.0010 |  0.0015 |  0.0018 |  0.0022 |  0.0025 |
+  |     | High Limit | -0.0007 | -0.0010 | -0.0012 | -0.0015 | -0.0020 |
+  |  Y  | Low Limit  | -0.0012 | -0.0020 | -0.0025 | -0.0030 | -0.0035 |
+  |     | Tolerance  |  0.0005 |  0.0010 |  0.0013 |  0.0015 |  0.0015 |
+  |     | High Limit | -0.0005 | -0.0007 | -0.0007 | -0.0010 | -0.0010 |
+  |  Z  | Low Limit  | -0.0007 | -0.0012 | -0.0015 | -0.0020 | -0.0022 |
+  |     | Tolerance  |  0.0002 |  0.0005 |  0.0008 |  0.0010 |  0.0012 |
+  +-----+------------+---------+---------+---------+---------+---------+
+
+[1] Tolerance is provided for holes, which ordinary standard reamers can
+produce, in two grades, Classes A and B, the selection of which is a
+question for the user's decision and dependent upon the quality of the
+work required; some prefer to use Class A as working limits and Class B
+as inspection limits.
+
+[2] Running fits, which are the most commonly required, are divided into
+three grades: Class X for engine and other work where easy fits are
+wanted; Class Y for high speeds and good average machine work; Class Z
+for fine tool work.
+
+=Pressure for Forced Fits.=--The pressure required for assembling
+cylindrical parts depends not only upon the allowance for the fit, but
+also upon the area of the fitted surfaces, the pressure increasing in
+proportion to the distance that the inner member is forced in. The
+approximate ultimate pressure in pounds can be determined by the use of
+the following formula in conjunction with the accompanying table of
+"Pressure Factors."
+
+=Pressure Factors=
+
+  +-----+-----++-----+-----++-----+-----++------+------++------+------+
+  |Diam-|Pres-||Diam-|Pres-||Diam-|Pres-||Diam- |Pres- ||Diam- |Pres- |
+  |eter,|sure ||eter,|sure ||eter,|sure ||eter, |sure  ||eter, |sure  |
+  |In-  |Fac- ||In-  |Fac- ||In-  |Fac- ||In-   |Fac-  ||In-   |Fac-  |
+  |ches | tor ||ches | tor ||ches | tor ||ches  |tor   ||ches  |tor   |
+  +-----+-----++-----+-----++-----+-----++------+------++------+------+
+  |1    | 500 ||3-1/2| 132 ||6    | 75  || 9    | 48.7 ||14    | 30.5 |
+  |1-1/4| 395 ||3-3/4| 123 ||6-1/4| 72  || 9-1/2| 46.0 ||14-1/2| 29.4 |
+  |1-1/2| 325 ||4    | 115 ||6-1/2| 69  ||10    | 43.5 ||15    | 28.3 |
+  |1-3/4| 276 ||4-1/4| 108 ||6-3/4| 66  ||10-1/2| 41.3 ||15-1/2| 27.4 |
+  |2    | 240 ||4-1/2| 101 ||7    | 64  ||11    | 39.3 ||16    | 26.5 |
+  |2-1/4| 212 ||4-3/4|  96 ||7-1/4| 61  ||11-1/2| 37.5 ||16-1/2| 25.6 |
+  |2-1/2| 189 ||5    |  91 ||7-1/2| 59  ||12    | 35.9 ||17    | 24.8 |
+  |2-3/4| 171 ||5-1/4|  86 ||7-3/4| 57  ||12-1/2| 34.4 ||17-1/2| 24.1 |
+  |3    | 156 ||5-1/2|  82 ||8    | 55  ||13    | 33.0 ||18    | 23.4 |
+  |3-1/4| 143 ||5-3/4|  78 ||8-1/2| 52  ||13-1/2| 31.7 ||....  | .... |
+  +-----+-----++-----+-----++-----+-----++------+------++------+------+
+
+Assuming that _A_ = area of fitted surface; _a_ = total allowance in
+inches; _P_ = ultimate pressure required, in tons; _F_ = pressure factor
+based upon assumption that the diameter of the hub is twice the
+diameter of the bore, that the shaft is of machine steel, and the hub of
+cast iron, then,
+
+        _A_ × _a_ × _F_
+  _P_ = ---------------
+               2
+
+_Example:_--What will be the approximate pressure required for forcing a
+4-inch machine steel shaft having an allowance of 0.0085 inch into a
+cast-iron hub 6 inches long?
+
+_A_ = 4 × 3.1416 × 6 = 75.39 square inches;
+
+_F_, for a diameter of 4 inches, = 115 (see table of "Pressure
+Factors"). Then,
+
+_P_ = (75.39 × 0.0085 × 115)/2 = 37 tons, approximately.
+
+=Allowance for Given Pressure.=--By transposing the preceding formula,
+the approximate allowance for a required ultimate tonnage can be
+determined. Thus, _a_ = 2_P_ ÷ _AF_. The average ultimate pressure in
+tons commonly used ranges from 7 to 10 times the diameter in inches.
+Assuming that the diameter of a machine steel shaft is 4 inches and an
+ultimate pressure of about 30 tons is desired for forcing it into a
+cast-iron hub having a length of 5-1/2 inches, what should be the
+allowance?
+
+_A_ = 4 × 3.1416 × 5-1/2 = 69 square inches,
+
+_F_, for a diameter of 4 inches, = 115. Then,
+
+          2 × 30
+  _a_ =  -------- = 0.0075 inch.
+         69 × 115
+
+=Shrinkage Fits.=--When heat is applied to a piece of metal, such as
+iron or steel, as is commonly known, a certain amount of expansion takes
+place which increases as the temperature is increased, and also varies
+somewhat with different kinds of metal, copper and brass expanding more
+for a given increase in temperature than iron and steel. When any part
+which has been expanded by the application of heat is cooled, it
+contracts and resumes its original size. This expansive property of
+metals has been taken advantage of by mechanics in assembling various
+machine details. A cylindrical part which is to be held in position by a
+shrinkage fit is first turned a few thousandths of an inch larger than
+the hole; the diameter of the latter is then increased by heating, and
+after the part is inserted, the heated outer member is cooled, causing
+it to grip the pin or shaft with tremendous pressure.
+
+General practice seems to favor a smaller allowance for shrinkage fits
+than for forced fits, although in many shops the allowances are
+practically the same in each case, and for some classes of work,
+shrinkage allowances exceed those for forced fits. In any case, the
+shrinkage allowance varies to a great extent with the form and
+construction of the part which has to be shrunk into place. The
+thickness or amount of metal around the hole is the most important
+factor. The way in which the metal is distributed also has an influence
+on the results. Shrinkage allowances for locomotive driving wheel tires
+adopted by the American Railway Master Mechanics Association are as
+follows:
+
+  Center diameter, inches      38    44    50    56    62    66
+  Allowance, inches          0.040 0.047 0.053 0.060 0.066 0.070
+
+Whether parts are to be assembled by forced or shrinkage fits depends
+upon conditions. For example, to press a driving wheel tire over its
+wheel center, without heating, would ordinarily be a rather awkward and
+difficult job. On the other hand, pins, etc., are easily and quickly
+forced into place with a hydraulic press and there is the additional
+advantage of knowing the exact pressure required in assembling, whereas
+there is more or less uncertainty connected with a shrinkage fit, unless
+the stresses are calculated. Tests to determine the difference in the
+quality of shrinkage and forced fits showed that the resistance of a
+shrinkage fit to slippage was, for an axial pull, 3.66 times greater
+than that of a forced fit, and in rotation or torsion, 3.2 times
+greater. In each comparative test, the dimensions and allowances were
+the same.
+
+The most important point to consider when calculating shrinkage fits is
+the stress in the hub at the bore, which depends chiefly upon the
+shrinkage allowance. If the allowance is excessive, the elastic limit of
+the material will be exceeded and permanent set will occur, or, in
+extreme cases, the ultimate strength of the metal will be exceeded and
+the hub will burst.
+
+
+
+
+CHAPTER IV
+
+THREAD CUTTING IN THE LATHE
+
+
+When threads are cut in the lathe a tool _t_ is used (see Fig. 2),
+having a point corresponding to the shape of the thread, and the
+carriage is moved along the bed a certain distance for each revolution
+of the work (the distance depending on the number of threads to the inch
+being cut) by the lead-screw _S_ which is rotated by gears _a_, _b_ and
+_c_, which receive their motion from the spindle. As the amount that the
+carriage travels per revolution of the work, and, consequently, the
+number of threads per inch that is cut, depends on the size of the gears
+_a_ and _c_ (called change gears) the latter have to be changed for
+cutting different threads. The proper change gears to use for cutting a
+given number of threads to the inch is ordinarily determined by
+referring to a table or "index plate" _I_ which shows what the size of
+gears _a_ and _c_ should be, or the number of teeth each should have,
+for cutting any given number of threads per inch.
+
+[Illustration: Fig. 1. Measuring Number of Threads per Inch--Setting
+Thread Tool]
+
+[Illustration: Fig. 2. Plan and Elevations of Engine Lathe]
+
+=Selecting the Change Gears for Thread Cutting.=--Suppose a V-thread is
+to be cut on the end of the bolt _B_, Fig. 2, having a diameter of 1-1/4
+inch and seven threads per inch of length, as shown at _A_ in Fig. 1,
+which is the standard number of threads per inch for that diameter.
+First the change gears to use are found on plate _I_ which is shown
+enlarged in Fig. 3. This plate has three columns: The first contains
+different numbers of threads to the inch, the second the size gear to
+place on the "spindle" or "stud" at _a_ (Fig. 2) for different threads,
+and the third the size of gear _c_ for the lead-screw. As the thread
+selected as an example has 7 threads per inch, gear _a_ should have 48
+teeth, this being the number given in the second column opposite figure
+7 in the first. By referring to the last column, we find that the
+lead-screw gear should have 84 teeth. These gears are selected from an
+assortment provided with the lathe and they are placed on the spindle
+and lead-screw, respectively.
+
+[Illustration: Fig. 3. Index Plate showing Gear Changes for Threading]
+
+Intermediate gear _b_ does not need to be changed as it is simply an
+"idler" for connecting gears _a_ and _c_. Gear _b_ is mounted on a
+swinging yoke _Y_ so that it can be adjusted to mesh properly with
+different gear combinations; after this adjustment is made, the lathe is
+geared for cutting 7 threads to the inch. (The change gears of many
+modern lathes are so arranged that different combinations are obtained
+by simply shifting a lever. A lathe having this quick-change gear
+mechanism is described in the latter part of this chapter.) The work _B_
+is placed between the centers just as it would be for turning, with the
+end to be threaded turned to a diameter of 1-1/4 inch, which is the
+outside diameter of the thread.
+
+=The Thread Tool.=--The form of tool used for cutting a V-thread is
+shown at _A_, Fig. 4. The end is ground V-shaped and to an angle of 60
+degrees, which corresponds to the angle of a standard V-thread. The
+front or flank, _f_ of the tool is ground back at an angle to provide
+clearance, but the top is left flat or without slope. As it is very
+important to grind the end to exactly 60 degrees, a gage _G_ is used,
+having 60-degree notches to which the tool-point is fitted. The tool is
+clamped in the toolpost as shown in the plan view, Fig. 2, square with
+the work, so that both sides of the thread will be cut to the same angle
+with the axis of the work. A very convenient way to set a thread tool
+square is illustrated at _B_, Fig. 1. The thread gage is placed against
+the part to be threaded, as shown, and the tool is adjusted until the
+angular sides of the point bear evenly in the 60-degree notch of the
+gage. The top of the tool point should be at the same height as the
+lathe centers, as otherwise the angle of the thread will not be correct.
+
+[Illustration: Fig. 4. Thread Tools and Gage for testing Angle of End]
+
+=Cutting the Thread.=--The lathe is now ready for cutting the thread.
+This is done by taking several cuts, as indicated at _A_, _B_, _C_ and
+_D_ in Fig. 5, the tool being fed in a little farther for each
+successive cut until the thread is finished. When these cuts are being
+taken, the carriage is moved along the bed, as previously explained, by
+the lead-screw _S_, Fig. 2. The carriage is engaged with the lead-screw
+by turning lever _u_ which causes the halves of a split nut to close
+around the screw. The way a lathe is handled when cutting a thread is as
+follows: After the lathe is started, the carriage is moved until the
+tool-point is slightly beyond the right end of the work, and the tool is
+fed in far enough to take the first cut which, ordinarily, would be
+about 1/16 inch deep. The carriage is then engaged with the lead-screw,
+by operating lever _u_, and the tool moves to the left (in this case 1/7
+inch for each revolution of the work) and cuts a winding groove as at
+_A_, Fig. 5. When the tool has traveled as far as the thread is wanted,
+it is withdrawn by a quick turn of cross-slide handle _e_, and the
+carriage is returned to the starting point for another cut. The tool is
+then fed in a little farther and a second cut is taken as at _B_, Fig.
+5, and this operation is repeated as at _C_ and _D_ until a "full"
+thread is cut or until the top of the thread is sharp. The thread is
+then tested for size but before referring to this part of the work, the
+way the carriage is returned to the starting point after each cut should
+be explained.
+
+[Illustration: Fig. 5. Thread is formed by taking a Number of Successive
+Cuts]
+
+When the tool is withdrawn at the end of the first cut, if the carriage
+is disengaged from the lead-screw and returned by hand, the tool may or
+may not follow the first cut when the carriage is again engaged with the
+lead-screw. If the number of threads to the inch being cut is a multiple
+of the number on the lead-screw _S_, then the carriage can be returned
+by hand and engaged with the lead-screw at random and the tool will
+follow the first cut. For example, if the lead-screw has six threads per
+inch, and 6, 12, 18 or any number of threads is being cut that is a
+multiple of six, the carriage can be engaged at any time and the tool
+will always follow the original cut. This is not the case, however, when
+the number of threads being cut is not a multiple of the number on the
+lead-screw.
+
+One method of bringing the carriage back to the starting point, when
+cutting threads which are not multiples, is to reverse the lathe (by
+shifting the overhead driving belts) in order to bring the tool back to
+the starting point without disengaging the carriage; in this way the
+tool is kept in the same relation to the work, and the carriage is not
+disengaged from the lead-screw until the thread is finished. This is a
+good method when cutting short threads having a length of say two or
+three inches; but when they are longer, and especially when the diameter
+is comparatively large (which means a slower speed), it is rather slow
+as considerable time is wasted while the tool is moving back to its
+starting point. This is due to the fact that the carriage is moved
+slowly by the lead-screw, but when disengaged, it can be traversed
+quickly by turning handle _d_, Fig. 2.
+
+A method of returning the carriage by hand when the number of threads
+being cut is not a multiple of the number on the lead-screw is as
+follows: The tool is moved a little beyond the right end of the work and
+the carriage or split nut is engaged with the lead-screw. The lathe is
+then turned forward by hand to take up any lost motion, and a line is
+made on the lathe bed showing the position of the carriage. The
+positions of the spindle and lead-screw are also marked by chalking a
+tooth on both the spindle and lead-screw gears, which happens to be
+opposite a corner or other point on the bed. After a cut is taken, the
+carriage is returned by hand to the original starting point as shown by
+the line on the bed, and is again engaged when the chalk marks show that
+the spindle and lead-screw are in their original position; the tool will
+then follow the first cut. If the body of the tailstock is moved against
+the bridge of the carriage before starting the first cut, the carriage
+can be located for each following cut by moving it back against the
+tailstock, and it will not be necessary to have a line on the bed.
+
+[Illustration: Fig. 6. Indicator used when Cutting Threads]
+
+=Indicator or Chasing Dial for Catching Threads.=--On some lathes there
+is an indicator for "catching threads," as this is called in shop
+language. This is a simple device attached to the carriage and consists
+of a graduated dial _D_ and a worm-wheel _W_ (see Figs. 2 and 6) which
+meshes with the lead-screw, so that the dial is revolved by the
+lead-screw when the carriage is stationary, and when the carriage is
+moved by the screw, the dial remains stationary. The indicator is used
+by engaging the carriage when one of the graduation lines is opposite
+the arrow mark; after a cut is taken the carriage is returned by hand
+and when one of the graduation lines again moves opposite the arrow, the
+half-nuts are thrown into mesh, as before, and this is repeated for each
+successive cut, thus causing the tool to always come right with the
+thread. If the number of threads per inch is even, engagement can be
+made when any line is opposite the arrow, but for odd numbers such as 3,
+7, 9, 11, etc., one of the four long or numbered lines must be used. Of
+course, if the thread being cut is a multiple of the number on the
+lead-screw, engagement can be made at any time, as previously
+mentioned.
+
+=Principle of the Thread Indicator.=--The principle upon which the
+thread indicator operates is as follows: The number of teeth in
+worm-wheel _W_ is some multiple of the number of threads per inch of the
+lead-screw, and the number of teeth in the worm-wheel, divided by the
+pitch of the screw, equals the number of graduations on the dial. For
+example, if the lead-screw has six threads per inch, the worm-wheel
+could have twenty-four teeth, in which case the dial would have four
+divisions, each representing an inch of carriage travel, and by
+sub-dividing the dial into eighths (as shown) each line would correspond
+to 1/2 inch of travel. The dial, therefore, would enable the carriage to
+be engaged with the lead-screw at points equal to a travel of one-half
+inch. To illustrate the advantage of this suppose ten threads per inch
+are being cut and (with the lathe stationary) the carriage is disengaged
+and moved 1/6 inch or one thread on the lead-screw; the tool point will
+also have moved 1/6 inch, but it will not be opposite the next thread
+groove in the work as the pitch is 1/10 inch. If the carriage is moved
+another thread on the lead-screw, or 2/6 inch, the tool will still be
+out of line with the thread on the work, but when it has moved three
+threads, or 1/2 inch, the tool will then coincide with the original cut
+because it has passed over exactly five threads. This would be true for
+any number of threads per inch that is divisible by 2. If the thread
+being cut had nine threads per inch or any other odd number, the tool
+would only coincide with the thread at points 1 inch apart. Therefore,
+the carriage can only be engaged when one of the four graduations
+representing an inch of travel is opposite the arrow, when cutting odd
+threads; whereas even numbers can be "caught" by using any one of the
+eight lines.
+
+This indicator can also be used for "catching" fractional threads. As an
+illustration, suppose 11-1/2 threads per inch are to be cut, and the
+carriage is engaged for the first cut when graduation line 1 is opposite
+the arrow; engagement would then be made for each successive cut, when
+either line 1 or 3 were opposite the arrow, or in other words at spaces
+equal to a carriage movement of 2 inches. As the use of the indicator
+when cutting fractional threads is liable to result in error, it is
+better to keep the half-nuts in engagement and return the carriage by
+reversing the lathe.
+
+=Replacing Sharpened Thread Tool.=--If it is necessary to sharpen the
+thread tool before the thread is finished, it should be reset square
+with the work by testing with the thread gage as at _B_, Fig. 1. The
+carriage is then engaged with the lead-screw and the lathe is turned
+forward to bring the tool opposite the partly finished thread and also
+to take up any backlash or lost motion in the gears or half-nut. If the
+tool-point is not in line with the thread groove previously cut, it can
+be shifted sidewise by feeding the compound rest _E_ in or out, provided
+the latter is set in an angular position as shown in the plan view, Fig.
+2.
+
+If the thread tool is ground flat on the top as at _A_, Fig. 4, it is
+not a good tool for removing metal rapidly as neither of its two cutting
+edges has any slope. In order to give each cutting edge a backward
+slope, it would be necessary to grind the top surface hollow or concave,
+which would be impracticable. When a course thread is to be cut, a tool
+shaped as at _B_ can be used to advantage for rough turning the thread
+groove, which is afterward finished to the correct depth and angle by
+tool _A_. This roughing tool is ground with a backward slope from the
+point and the latter is rounded to make it stronger.
+
+=Use of Compound Rest for Thread Cutting.=--Another form of thread tool
+is shown at _A_, Fig. 7, which is very good for cutting V-threads
+especially of coarse pitch. When this tool is used, the compound rest
+_E_ is set to an angle of 30 degrees, as shown, and it is fed in for the
+successive cuts by handle _w_ in the direction indicated by the arrow.
+It will be seen that the point a of the tool moves at an angle of 60
+degrees with the axis of the work, thus forming one side of the thread,
+and the cutting edge _a--b_, which can be set as shown at _B_, forms the
+opposite side and does all the cutting. As this edge is given a backward
+slope, as shown, it cuts easily and enables threading operations to be
+performed quickly. Threads cut in this way are often finished by taking
+a light cut with a regular thread tool. The cutting edge _a--b_ is
+ground to an angle of 60 degrees (or slightly less, if anything) with
+the side, as shown by sketch _A_.
+
+When cutting threads in steel or wrought iron, some sort of lubricant is
+usually applied to the tool to preserve the cutting end and give a
+smooth finish to the thread. Lard oil or a mixture of equal parts of
+lard oil and paraffin oil are often used for this purpose. If the thread
+is small, the lubricant may be applied from an ordinary oil can, but
+when cutting comparatively large threads, it is better to have a stream
+of oil constantly playing upon the tool-point. This constant flow may be
+obtained by mounting a can having a spout leading to the tool, on a
+bracket at the rear of the carriage.
+
+[Illustration: Fig. 7. Cutting Thread by using Compound Rest]
+
+[Illustration: Fig. 8. (A) V-thread. (B) U. S. Standard Thread. (C)
+Square Thread. (D) Left-hand Thread. (E) Double Square Thread. (F)
+Triple Square Thread]
+
+=Threads Commonly Used.=--Three forms of threads or screws which are in
+common use are shown in Fig. 8; these are the V-thread (_A_), the U. S.
+standard (_B_), and the square thread (_C_). The shapes of these threads
+are shown by the sectioned parts. The V-thread has straight sides which
+incline at an angle of 60 degrees with each other and at the same angle
+with the axis of the screw. The U. S. standard thread is similar to the
+V-thread except that the top of the thread and bottom of the groove is
+left flat, as shown, and the width of these flats is made equal to 1/8
+of the pitch. The square thread is square in section, the width _a_,
+depth _b_ and space _c_ being all equal. All of these threads are
+right-hand, which means that the grooves wind around to the right so
+that a nut will have to be turned toward the right to enter it on the
+thread. A left-hand thread winds in the other direction, as shown at
+_D_, and a nut is screwed on by turning it to the left.
+
+=Multiple Threads.=--Threads, in addition to being right-and
+left-handed, are single, as at _A_, _B_, _C_ and _D_, double, as at _E_,
+and triple, as at _F_, and for certain purposes quadruple threads or
+those of a higher multiple are employed. A double thread is different
+from a single thread in that it has two grooves, starting diametrically
+opposite, whereas a triple thread has three grooves cut as shown at _F_.
+The object of these multiple threads is to obtain an increase in lead
+without weakening the screw. For example, the threads shown at _C_ and
+_E_ have the same pitch _p_ but the lead _l_ of the double-threaded
+screw is twice that of the one with a single thread so that a nut would
+advance twice as far in one revolution, which is often a very desirable
+feature. To obtain the same lead with a single thread, the pitch would
+have to be double, thus giving a much coarser thread, which would weaken
+the screw, unless its diameter were increased. (The lead is the distance
+_l_ that one thread advances in a single turn, or the distance that a
+nut would advance in one turn, and it should not be confused with the
+pitch _p_, which is the distance between the centers of adjacent
+threads. Obviously the lead and pitch of a single thread are the same.)
+
+=Cutting a U. S. Standard Thread.=--The method of cutting a U. S.
+standard thread is the same as described for a V-thread, so far as
+handling the lathe is concerned. The thread tool must correspond, of
+course, to the shape of a U. S. standard thread. This tool is first
+ground to an angle of 60 degrees, as it would be for cutting a V-thread,
+and then the point is made flat as shown in Fig. 9. As will be recalled,
+the width of this flat should be equal to 1/8 of the pitch. By using a
+gage like the one shown at _G_, the tool can easily be ground for any
+pitch, as the notches around the periphery of the gage are marked for
+different pitches and the tool-point is fitted into the notch
+corresponding to the pitch wanted. If such a gage is not available, the
+width of the flat at the point can be tested by using, as a gage, a U.
+S. standard tap of the same pitch as the thread to be cut.
+
+When cutting the thread, the tool is set square with the blank, and a
+number of successive cuts are taken, the tool being fed in until the
+width w of the flat at the top of the thread is equal to the width at
+the bottom. The thread will then be the right size provided the outside
+diameter _D_ is correct and the tool is of the correct form. As it would
+be difficult to measure the width of this flat accurately, the thread
+can be tested by screwing a standard nut over it if a standard thread is
+being cut. If it is being fitted to a tapped hole, the tap itself is a
+very convenient gage to use, the method being to caliper the tap and
+then compare its size with the work.
+
+[Illustration: Fig. 9. U. S. Standard Thread, Thread Tool, and Gage]
+
+A good method of cutting a U. S. standard thread to a given size is as
+follows: First turn the outside of the blank accurately to diameter _D_,
+and then turn a small part of the end to diameter _r_ of the thread at
+the root. The finishing cut for the thread is then taken with the tool
+point set to just graze diameter _r_. If ordinary calipers were set to
+diameter _r_ and measurements taken in the thread groove, the size would
+be incorrect owing to the angularity of the groove, which makes it
+necessary to hold the calipers at an angle when measuring. To determine
+the root diameter divide 1.299 by the number of threads per inch and
+subtract the quotient from the outside diameter. Expressing this rule as
+a formula,
+
+               /1.299\
+  _r_ = _D_ - ( ----- )
+               \ _N_ /
+
+in which _D_ equals outside diameter; _N_, the number of threads per
+inch; and _r_, the root diameter. The number 1.299 is a constant that is
+always used.
+
+[Illustration: Fig. 10. End View of Lathe Headstock]
+
+=Cutting a Left-hand Thread.=--The only difference between cutting
+left-hand and right-hand threads in the lathe is in the movement of the
+tool with relation to the work. When cutting a right-hand thread, the
+tool moves from right to left, but this movement is reversed for
+left-hand threads because the thread winds around in the opposite
+direction. To make the carriage travel from left to right, the
+lead-screw is rotated backwards by means of reversing gears _a_ and _b_
+(Fig. 10) located in the headstock. Either of these gears can be
+engaged with the spindle gear by changing the position of lever _R_.
+When gear _a_ is in engagement, as shown, the drive from the spindle to
+gear _c_ is through gears _a_ and _b_, but when lever _R_ is raised thus
+shifting _b_ into mesh, the drive is direct and the direction of
+rotation is reversed. The thread is cut by starting the tool at _a_,
+Fig. 8, instead of at the end.
+
+[Illustration: Fig. 11. End of Square Thread Tool, and Graphic Method of
+Determining Helix Angle of Thread]
+
+=Cutting a Square Thread.=--The form of tool used for cutting a square
+thread is shown in Fig. 11. The width _w_ is made equal to one-half the
+pitch of the thread to be cut and the end _E_ is at an angle with the
+shank, which corresponds to the inclination _x--y_ of the threads. This
+angle _A_ depends upon the diameter of the screw and the lead of the
+thread; it can be determined graphically by drawing a line _a--b_ equal
+in length to the circumference of the screw to be cut, and a line
+_b--c_, at right angles, equal in length to the lead of the thread. The
+angle [alpha] between lines _a--b_ and _a--c_ will be the required angle
+_A_. (See end view of thread tool). It is not necessary to have this
+angle accurate, ordinarily, as it is simply to prevent the tool from
+binding against the sides of the thread. The end of a square thread tool
+is shown in section to the right, to illustrate its position with
+relation to the threads. The sides _e_ and _e_{1}_ are ground to slope
+inward, as shown, to provide additional clearance.
+
+When cutting multiple threads, which, owing to their increased lead,
+incline considerably with the axis of the screw, the angles for each
+side of the tool can be determined independently as follows: Draw line
+_a--b_ equal in length to the circumference of the thread, as before, to
+obtain the required angle _f_ of the rear or following side _e_{1}_; the
+angle _l_ of the opposite or leading side is found by making _a--b_
+equal to the circumference at the root of the thread. The tool
+illustrated is for cutting right-hand threads; if it were intended for a
+left-hand thread, the end, of course, would incline in the opposite
+direction. The square thread is cut so that the depth _d_ is equal to
+the width. When threading a nut for a square thread screw, it is the
+usual practice to use a tool having a width slightly greater than
+one-half the pitch, to provide clearance for the screw, and the width of
+a tool for threading square-thread taps to be used for tapping nuts is
+made slightly less than one-half the pitch.
+
+=Cutting Multiple Threads.=--When a multiple thread is to be cut, such
+as a double or triple thread, the lathe is geared with reference to the
+number of single threads to the inch. For example, the lead of the
+double thread, shown at _B_, Fig. 12, is one-half inch, or twice the
+pitch, and the number of single threads to the inch equals 1 ÷ 1/2 = 2.
+Therefore, the lathe is geared for cutting two threads per inch. The
+first cut is taken just as though a single thread were being cut,
+leaving the work as shown at _A_. When this cut is finished the work is
+turned one-half a revolution (for a double thread) without disturbing
+the position of the lead-screw or carriage, which brings the tool midway
+between the grooves of the single thread as indicated by dotted lines.
+The second groove is then cut, producing a double thread as shown at
+_B_. In the case of a triple thread, the work would be indexed one-third
+of a revolution after turning the first groove, and then another third
+revolution to locate the tool for cutting the last groove. Similarly,
+for a quadruple thread, it would be turned one-quarter revolution after
+cutting each successive groove or thread.
+
+There are different methods of indexing the work when cutting multiple
+threads, in order to locate the tool in the proper position for cutting
+another thread groove. Some machinists, when cutting a double thread,
+simply remove the work from the lathe and turn it one-half a revolution
+by placing the tail of the driving dog in the opposite slot of the
+faceplate. This is a very simple method, but if the slots are not
+directly opposite or 180 degrees apart, the last thread will not be
+central with the first. Another and better method is to disengage the
+idler gear from the gear on the stud, turn the spindle and work
+one-half, or one-third, of a revolution, as the case might be, and then
+connect the gears. For example, if the stud gear had 96 teeth, the tooth
+meshing with the idler gear would be marked with chalk, the gears
+disengaged, and the spindle turned until the chalked tooth had made the
+required part of a revolution, which could be determined by counting the
+teeth. When this method is used, the number of teeth in the stud gear
+must be evenly divisible by two if a double thread is being cut, or by
+three for a triple thread, etc. If the stud is not geared to the spindle
+so that each makes the same number of revolutions, the ratio of the
+gearing must be considered.
+
+[Illustration: Fig. 12. Views illustrating how a Double Square Thread is
+Cut]
+
+=Setting Tool When Cutting Multiple Threads.=--Another method, which can
+sometimes be used for setting the tool after cutting the first groove of
+a multiple thread, is to disengage the lock-nuts from the lead-screw
+(while the spindle is stationary) and move the carriage back whatever
+distance is required to locate the tool in the proper position for
+taking the second cut. Evidently this distance must not only locate the
+tool in the right place, but be such that the lock-nuts can be
+re-engaged with the lead-screw. Beginning with a simple illustration,
+suppose a double thread is being cut having a lead of 1 inch. After the
+first thread groove is cut, the tool can be set in a central position
+for taking the second cut, by simply moving the carriage back 1/2 inch
+(one-half the lead), or 1/2 inch plus the lead or any multiple of the
+lead. If the length of the threaded part were 5 inches, the tool would
+be moved back far enough to clear the end of the work, or say 1/2 + 5 =
+5-1/2 inches. In order to disengage the lock-nuts and re-engage them
+after moving the carriage 5-1/2 inches (or any distance equal, in this
+case, to one-half plus a whole number), the lead-screw must have an even
+number of threads per inch.
+
+Assume that a double thread is being cut having 1-1/4 single threads per
+inch. The lead then would equal 1 ÷ 1-1/4 = 0.8 inch, and if the
+carriage is moved back 0.8 ÷ 2 = 0.4 inch, the tool will be properly
+located for the second cut; but the lock-nuts could not be re-engaged
+unless the lead-screw had ten threads per inch, which is finer than the
+pitch found on the lead-screws of ordinary engine lathes. However, if
+the movement were 0.4 + 0.8 × 2 = 2 inches, the lock-nuts could be
+re-engaged regardless of the number of threads per inch on the
+lead-screw. The rule then, is as follows:
+
+_Divide the lead of the thread by 2 for a double thread, 3 for a triple
+thread, 4 for a quadruple thread, etc., thus obtaining the pitch; then
+add the pitch to any multiple of the lead, which will give a movement,
+in inches, that will enable the lock-nuts to be re-engaged with the
+lead-screw._
+
+Whenever the number obtained by this rule is a whole number, obviously,
+the movement can be obtained with a lead-screw of any pitch. If the
+number is fractional, the number of threads per inch on the lead-screw
+must be divisible by the denominator of the fraction.
+
+To illustrate the application of the foregoing rule, suppose a quadruple
+thread is to be cut having 1-1/2 single threads per inch (which would be
+the number the lathe would be geared to cut). Then the lead of the
+thread = 1 ÷ 1-1/2 = 0.6666 inch and the pitch = 0.6666 ÷ 4 = 0.1666
+inch; adding the pitch to twice the lead we have 0.1666 + 2 × 0.6666 =
+1.499 inch. Hence, if the carriage is moved 1-1/2 inch (which will
+require a lead-screw having an even number of threads per inch), the
+tool will be located accurately enough for practical purposes. When the
+tool is set in this way, if it does not clear the end of the part being
+threaded, the lathe can be turned backward to place the tool in the
+proper position.
+
+[Illustration: Fig. 13. Indexing Faceplate used for Multiple Thread
+Cutting]
+
+The foregoing rule, as applied to triple threads or those of a higher
+number, does not always give the only distance that the carriage can be
+moved. To illustrate, in the preceding example the carriage movement
+could be equal to 0.499, or what is practically one-half inch, instead
+of 1-1/2 inch, and the tool would be properly located. The rule,
+however, has the merit of simplicity and can be used in most cases.
+
+Special faceplates are sometimes used for multiple thread cutting, that
+enable work to be easily and accurately indexed. One of these is
+illustrated in Fig. 13; it consists of two parts _A_ and _B_, part _A_
+being free to rotate in relation to _B_ when bolts _C_ are loosened. The
+driving pin for the lathe dog is attached to plate _A_. When one groove
+of a multiple thread is finished, bolts _C_ are loosened and plate _A_
+is turned around an amount corresponding to the type of thread being
+cut. The periphery of plate _A_ is graduated in degrees, as shown, and
+for a double thread it would be turned one-half revolution or 180
+degrees, for a triple thread, 120 degrees, etc. This is a very good
+arrangement where multiple thread cutting is done frequently.
+
+[Illustration: Fig. 14. Correct and Incorrect Positions of Tool for
+Taper Thread Cutting]
+
+=Taper Threading.=--When a taper thread is to be cut, the tool should be
+set square with axis _a--a_ as at _A_, Fig. 14, and not by the tapering
+surface as at _B_. If there is a cylindrical part, the tool can be set
+as indicated by the dotted lines. All taper threads should be cut by the
+use of taper attachments. If the tailstock is set over to get the
+required taper, and an ordinary bent-tail dog is used for driving, the
+curve of the thread will not be true, or in other words the thread will
+not advance at a uniform rate; this is referred to by machinists as a
+"drunken thread." This error in the thread is due to the angularity
+between the driving dog and the faceplate, which causes the work to be
+rotated at a varying velocity. The pitch of a taper thread that is cut
+with the tailstock set over will also be slightly finer than the pitch
+for which the lathe is geared. The amount of these errors depends upon
+the angle of the taper and the distance that the center must be offset.
+
+=Internal Threading.=--Internal threading, or cutting threads in holes,
+is an operation performed on work held in the chuck or on a faceplate,
+as for boring. The tool used is similar to a boring tool except that the
+working end is shaped to conform to the thread to be cut. The method of
+procedure, when cutting an internal thread, is similar to that for
+outside work, as far as handling the lathe is concerned. The hole to be
+threaded is first bored to the root diameter _D_, Fig. 15, of the screw
+that is to fit into it. The tool-point (of a tool for a U. S. standard
+or V-thread) is then set square by holding a gage _G_ against the true
+side of the work and adjusting the point to fit the notch in the gage as
+shown. The view to the right shows the tool taking the first cut.
+
+[Illustration: Fig. 15. Method of setting and using Inside Thread Tool]
+
+Very often the size of a threaded hole can be tested by using as a gage
+the threaded part that is to fit into it. When making such a test, the
+tool is, of course, moved back out of the way. It is rather difficult to
+cut an accurate thread in a small hole, especially when the hole is
+quite deep, owing to the flexibility of the tool; for this reason
+threads are sometimes cut slightly under size with the tool, after which
+a tap with its shank end held straight by the tailstock center is run
+through the hole. In such a case, the tap should be calipered and the
+thread made just small enough with the tool to give the tap a light cut.
+Small square-threaded holes are often finished in this way, and if a
+number of pieces are to be threaded, the use of a tap makes the holes
+uniform in size.
+
+=Stop for Thread Tools.=--When cutting a thread, it is rather difficult
+to feed in the tool just the right amount for each successive cut,
+because the tool is moved in before it feeds up to the work. A stop is
+sometimes used for threading which overcomes this difficulty. This stop
+consists of a screw _S_, Fig. 16, which enters the tool slide and passes
+through a block _B_ clamped in front of the slide. The hole in the block
+through which the stop-screw passes is not threaded, but is large enough
+to permit the screw to move freely. When cutting a thread, the tool is
+set for the first cut and the screw is adjusted until the head is
+against the fixed block. After taking the first cut, the stop-screw is
+backed out, say one-half revolution, which allows the tool to be fed in
+far enough for a second cut. If this cut is about right for depth, the
+screw is again turned about one-half revolution for the next cut and
+this is continued for each successive cut until the thread is finished.
+By using a stop of this kind, there is no danger of feeding the tool in
+too far as is often done when the tool is set by guess. If this form of
+stop is used for internal threading, the screw, instead of passing
+through the fixed block, is placed in the slide so that the end or head
+will come against the stop _B_. This change is made because the tool is
+fed outward when cutting an internal thread.
+
+[Illustration: Fig. 16. Cross-slide equipped with Stop for Regulating
+Depth of Cut when Threading]
+
+=The Acme Standard Thread.=--The Acme thread is often used, at the
+present time, in place of a square thread. The angle between the sides
+of the Acme thread is 29 degrees (see Fig. 21) and the depth is made
+equal to one-half the pitch plus 0.010 inch to provide clearance and
+insure a bearing upon the sides. The thread tool is ordinarily ground to
+fit a gage having notches representing different pitches. An improved
+form of Acme thread gage is shown in Fig. 17. The tool point is first
+ground to the correct angle by fitting it to the 29-degree notch in the
+end of the gage, as at _A_. The end is then ground to the proper width
+for the pitch to be cut, by testing it, as at _B_. The numbers opposite
+the shallow notches for gaging the width represent the number of threads
+per inch. With this particular gage, the tool can be set square by
+placing edge _D_ against the turned surface to be threaded, and
+adjusting the tool until the end is in line with the gage, as at _C_. By
+placing the tool in this position, the angle between the side and the
+end can also be tested.
+
+[Illustration: Fig. 17. Gage for grinding and setting Acme Thread Tools]
+
+In case it should be necessary to measure the end width of an Acme
+thread tool, for a pitch not on the regular gage, this can be done by
+using a vernier gear-tooth caliper, as indicated in Fig. 18. If we
+assume that the caliper jaws bear on the sides of the tool at a distance
+_A_ from the top, equal to 1/4 inch, then the width of the tool point
+equals the caliper reading (as shown by the horizontal scale) minus
+0.1293 inch. For example, if the caliper reading was 0.315 inch, the
+width at the point would equal 0.315 - 0.1293 = 0.1857 inch, assuming that
+the sides were ground to the standard angle of 29 degrees. The constant
+to be subtracted from the caliper reading equals 2 _A_ tan 14° 30' or,
+in this case, 2 × 0.25 × 0.2586 = 0.1293.
+
+[Illustration: Fig. 18. Measuring Width of Acme Thread Tool with Vernier
+Gear-tooth Caliper]
+
+=The Whitworth Thread.=--The Whitworth (or British Standard Whitworth)
+thread, which is used principally in Great Britain, has an included
+angle of 55 degrees, and the threads are rounded at the top and at the
+root, as shown in Fig. 23. The shape of the tool used for cutting this
+thread is also shown in this illustration. The end is rounded to form
+the fillet at the root of the thread, and the round corners on the sides
+give the top of the thread the required curvature. Every pitch requires
+a different tool, and the cutting end is given the curved form by
+milling or hobbing. The hob used for this purpose is accurately threaded
+to correspond with the pitch for which the tool is required, and then it
+is fluted to form cutting edges, and is hardened. The hob is then used
+like a milling cutter for forming the end of the thread tool. The tool
+is sharpened by grinding on the top. The method of cutting a Whitworth
+thread is, of course, similar to that followed for a U. S. standard or
+V-thread, in that the tool is set square with the unthreaded blank and
+at the same height as the lathe centers, in order to secure a thread of
+the proper form. Care should be taken to turn the blank to the right
+diameter so that the top of the thread will be fully rounded when the
+screw is the required size.
+
+[Illustration: Fig. 19. United States Standard Thread]
+
+[Illustration: Fig. 20. Standard Sharp V-thread]
+
+[Illustration: Fig. 21. Acme Standard Thread]
+
+[Illustration: Fig. 22. Square Thread]
+
+[Illustration: Fig. 23. Whitworth Standard Thread]
+
+[Illustration: Fig. 24. Standard Worm Thread]
+
+=Worm Threads.=--The standard worm thread has an angle of 29 degrees
+between the sides, the same as an Acme thread, but the depth of a worm
+thread and the width of the flat at the top and bottom differ from the
+Acme standard, as will be seen by comparing Figs. 21 and 24. The whole
+depth of the thread equals the linear pitch multiplied by 0.6866, and
+the width of the thread tool at the end equals the linear pitch
+multiplied by 0.31. Gages notched for threads of different pitch are
+ordinarily used when grinding worm thread tools.
+
+When it is necessary to cut multiple-threaded worms of large lead in an
+ordinary lathe, difficulty is sometimes experienced because the
+lead-screw must be geared to run much faster than the spindle, thus
+imposing excessive strains on the gearing. This difficulty is sometimes
+overcome by mounting a belt pulley on the lead-screw, beside the change
+gear, and connecting it to the countershaft by a belt; the spindle is
+then driven through the change gearing from the lead-screw, instead of
+_vice versa_.
+
+=Coarse Threading Attachment.=--To avoid the difficulties connected with
+cutting threads of large lead, some lathes are equipped with a coarse
+screw-cutting attachment. The arrangement of this attachment, as made by
+the Bradford Machine Tool Co., is as follows: On the usual reversing
+shaft, and inside of the headstock, there is a sliding double gear, so
+arranged as to be engaged with either the usual gear on the spindle, or
+with a small pinion at the end of the cone. The gears are so
+proportioned that the ratio of the two engagements is as 10 to 1; that
+is, when engaged with the cone gear (the back-gears being thrown in) the
+mating gear will make ten revolutions to one of the spindle, so that
+when the lathe is ordinarily geared to cut one thread per inch, it will,
+when driven by the cone pinion, cut one thread in ten inches. This
+construction dispenses with the extra strain on the reverse gears due to
+moving the carriage at the rapid rate that would be necessary for such a
+large lead, when not using an attachment. These attachments are not only
+extensively used for the cutting of coarse screws but for cutting oil
+grooves on cylindrical parts.
+
+When cutting a thread of large lead or "steep pitch," the top of the
+thread tool should be ground so that it is at right angles to the
+thread; then the thread groove will be cut to the same width as the
+tool.
+
+=Testing the Size of a Thread.=--When the thread tool has been fed in
+far enough to form a complete thread, the screw is then tested for size.
+If we assume that a bolt is being threaded for a standard nut, it would
+be removed from the lathe and the test made by screwing a nut on the
+end. If the thread were too large, the nut might screw on very tightly
+or not at all; in either case, the work would again be placed in the
+lathe and a light cut taken over it to reduce the thread to the proper
+size. When replacing a threaded part between the centers, it should be
+put back in the original position, that is, with the "tail" of the
+driving dog in the same slot of the faceplate it previously occupied.
+
+[Illustration: Fig. 25. Testing Diameter of Thread with Calipers and
+Micrometer]
+
+As it is difficult to tell just when a thread is cut to the exact size,
+special thread calipers having wedge-shaped ends are sometimes used for
+measuring the diameter of a V-thread or a U. S. standard thread, at the
+bottom of the grooves or the root diameter, as shown at _A_ in Fig. 25.
+These calipers can be set from a tap corresponding to the size of the
+thread being cut, or from a previously threaded piece of the right
+size.
+
+=The Thread Micrometer.=--Another form of caliper for testing threads is
+shown at _B_. This is one of the micrometer type and is intended for
+very accurate work. The spindle of this micrometer has a conical end and
+the "anvil" is V-shaped, and these ends bear on the sides of the thread
+or the surfaces which form the bearing when the screw is inserted in a
+nut or threaded hole. The cone-shaped point is slightly rounded so that
+it will not bear in the bottom of the thread. There is also sufficient
+clearance at the bottom of the V-shaped anvil to prevent it from bearing
+on top of the thread. The diameter as indicated by this micrometer is
+the "pitch diameter" of the thread and is equal to the outside diameter
+minus the depth of one thread. This depth may be determined as follows:
+
+Depth of a V-thread = 0.866 ÷ No. of threads per inch;
+
+Depth of a U. S. standard thread = 0.6495 ÷ No. of threads per inch;
+
+Depth of Whitworth thread = 0.6403 ÷ No. of threads per inch.
+
+The movable point measures all pitches, but the fixed anvil is limited
+in its capacity, for if made large enough to measure a thread of, say,
+1/4-inch pitch, it would be too wide at the top to measure a thread of
+1/24-inch pitch, hence each caliper is limited in the range of threads
+that the anvil can measure. When measuring the "angle diameter" of a
+thread, the micrometer should be passed back and forth across the
+thread, in order to make sure that the largest dimension or the actual
+diameter is being measured. If the micrometer is placed over what seems
+to be the center of the screw and the reading is taken by simply
+adjusting in the anvil or point against the thread, without moving the
+micrometer back and forth across it, an incorrect reading may be
+obtained.
+
+If standard threaded reference gages are available, the size of the
+thread being cut can be tested by comparing it with the gage.
+Micrometers having small spherical measuring ends (see sketch _A_, Fig.
+26) are sometimes used for this purpose. The ball points are small
+enough to bear against the sides of the thread and the diameter, as
+compared with the reference gage, can be determined with great
+accuracy.
+
+[Illustration: Fig. 26. (A) Testing Size of Thread with Ball-point
+Micrometer. (B) Testing Size of V-thread by the Three-wire System. (C)
+Testing the Size of a U. S. Standard Thread]
+
+=Three-wire System of Measuring Threads.=--A method of measuring threads
+by using an ordinary micrometer and three wires of equal diameter is
+illustrated at _B_ and _C_, Fig. 26. Two wires are placed between the
+threads on one side and one on the opposite side of the screw. The
+dimension _M_ over the wires is then measured with an ordinary
+micrometer. When the thread is cut to a standard size, the dimension _M_
+for different threads is as follows:
+
+For a U. S. standard thread:
+
+_m_ = _d_ - 1.5155_p_ + 3_w_
+
+For a sharp V-thread:
+
+_m_ = _d_ - 1.732_p_ + 3_w_
+
+For a Whitworth standard thread:
+
+_m_ = _d_ - 1.6008_p_ + 3.1657_w_
+
+In these formulas, _d_ = standard outside diameter of screw; _m_ =
+measurement over wires; _w_ = diameter of wires; _p_ = pitch of thread =
+1 ÷ number of threads per inch.
+
+To illustrate the use of the formula for the U. S. standard thread, let
+us assume that a screw having 6 threads per inch (1/6-inch pitch) is to
+be cut to a diameter of 1-1/2 inch, and that wires 0.140 inch diameter
+are to be used in conjunction with a micrometer for measurement. Then
+the micrometer reading _m_ should be
+
+1-1/2 - 1.5155 × 1/6 + 3 × 0.140 = 1.6674 inch
+
+If the micrometer reading were 1.670 inch, it would indicate that the
+pitch diameter of the screw was too large, the error being equal to
+difference between 1.667 and the actual reading.
+
+[Illustration: Fig. 27. Rivett-Dock Circular Threading Tool in Working
+Position]
+
+=Rivett-Dock Threading Tool.=--A special form of thread tool, which
+overcomes a number of disadvantages common to an ordinary single-point
+thread tool, is shown in Fig. 27. This tool has a circular-shaped cutter
+_C_, having ten teeth around its circumference, which, beginning with
+tooth No. 1, gradually increase in height, cutter No. 2 being higher
+than No. 1, etc. This cutter is mounted on a slide _S_, that is fitted
+to the frame _F_, and can be moved in or out by lever _L_. The hub of
+this lever has an eccentric stud which moves slide _S_ and locks it when
+in the forward or cutting position. The action of the lever in moving
+the slide engages the cutter with pawl _P_, thus rotating the cutter one
+tooth at a time and presenting a different tooth to the work for each
+movement of the lever. When the slide is moved forward, the heel or
+underside of the tooth which is in the working position rests on a stop
+that takes the thrust of the cut.
+
+When the tool is in use, it is mounted on the tool-block of the lathe as
+shown in the illustration. The cutter is set for height by placing a
+tooth in the working position and setting the top level with the lathe
+center. The cutter is also set square with the work by using an ordinary
+square, and it is tilted slightly from the vertical to correspond with
+the angle of the thread to be cut, by adjusting frame _F_. At first a
+light cut is taken with lever _L_ moved forward and tooth No. 1 on the
+stop. After this cut is completed, the lever is reversed which rotates
+the cutter one tooth, and the return movement places tooth No. 2 in the
+working position. This operation is repeated until the tenth tooth
+finishes the thread. It is often necessary, when using a single-point
+thread tool, to re-sharpen it before taking the finishing cut, but with
+a circular tool this is not necessary, for by using the different teeth
+successively, the last tooth, which only takes finishing cuts, is kept
+in good condition.
+
+=Cutting Screws to Compensate for Shrinkage.=--Some tool steels are
+liable to shrink more or less when they are hardened; consequently if a
+very accurate hardened screw is required, it is sometimes cut so that
+the pitch is slightly greater than standard, to compensate for the
+shrinkage due to the hardening operation. As the amount of contraction
+incident to hardening is very little, it is not practicable to use
+change gears that will give the exact pitch required. A well-known
+method of obtaining this increase of pitch is by the use of a taper
+attachment.
+
+For example, suppose a tap having 8 threads per inch is to be threaded,
+and, owing to the contraction of the steel, the pitch must be 0.12502
+inch instead of 0.125 inch. The lathe is geared to cut 8 threads per
+inch or 0.125 inch pitch, and then the taper attachment is set to an
+angle _a_, Fig. 28, the cosine of which equals 0.125/0.12502; that is,
+the cosine of angle _a_ equals _the pitch required after hardening_,
+divided by the _pitch necessary to compensate for shrinkage_. The angle
+is then found by referring to a table of cosines. The tap blank is also
+set to the same angle a by adjusting the tailstock center, thus locating
+the axis of the work parallel with the slide of the taper attachment.
+When the carriage moves a distance _x_, the tool point will have moved a
+greater distance _y_ along the work, the difference between x and y
+depending upon angle _a_; hence the tool will cut a thread of slightly
+greater pitch than the lathe is geared to cut.
+
+To illustrate by using the preceding example, cosine of angle _a_ =
+0.125/0.12502 = 0.99984. By referring to a table of cosines, we find
+that 0.99984 is the cosine of 1 degree, approximately; hence, the taper
+attachment slide and the work should be set to this angle. (The angle
+_a_ in Fig. 28 has been exaggerated in order to more clearly illustrate
+the principle.)
+
+[Illustration: Fig. 28. Diagram Illustrating Method of Cutting a Thread
+to Compensate for the Error in Pitch due to Shrinkage in Hardening]
+
+As is well known, it is objectionable to cut a thread with the tailstock
+center offset, because the work is not rotated at a uniform velocity,
+owing to the fact that the driving dog is at an angle with the
+faceplate. For a small angle such as 1 degree, however, the error
+resulting from this cause would be very small.
+
+If a thread having a pitch slightly less than standard is needed to fit
+a threaded part which has contracted in hardening, the taper attachment
+can also be used provided the lathe is equipped with special gears to
+cut a little less than the required pitch. Suppose a screw having a
+pitch of 0.198 inch is required to fit the thread of a nut the pitch of
+which has been reduced from 0.200 inch to 0.198 inch. If gears having 83
+and 84 teeth are available, these can be inserted in a compound train,
+so as to reduce the 0.200 inch pitch that would be obtained with the
+regular gearing, to 83/84 of 0.200 or 0.19762 inch. This pitch, which is
+less than the 0.198 inch pitch required, is then increased by using the
+taper attachment as previously described. (This method was described by
+Mr. G. H. Gardner in MACHINERY, February, 1914.)
+
+=Calculating Change Gears for Thread Cutting.=--As previously mentioned,
+the change gears for cutting threads of various pitches are shown by a
+table or "index plate" attached to the lathe. The proper gears to be
+used can be calculated, but the use of the table saves time and tends to
+avoid mistakes. Every machinist, however, should know how to determine
+the size of gears used for cutting any number of threads to the inch.
+Before referring to any rules, let us first consider why a lathe cuts a
+certain number of threads to the inch and how this number is changed by
+the use of different gears.
+
+As the carriage _C_ and the tool are moved by the lead-screw _S_ (see
+Fig. 2), which is geared to the spindle, the number of threads to the
+inch that are cut depends, in every case, upon the number of turns the
+work makes while the lead-screw is moving the carriage one inch. If the
+lead-screw has six threads per inch, it will make six revolutions while
+the carriage and the thread tool travel one inch along the piece to be
+threaded. Now if the change gears _a_ and _c_ (see also sketch _A_, Fig.
+29) are so proportioned that the spindle makes the same number of
+revolutions as the lead-screw, in a given time, it is evident that the
+tool will cut six threads per inch. If the spindle revolved twice as
+fast as the lead-screw, it would make twelve turns while the tool moved
+one inch, and, consequently, twelve threads per inch would be cut; but
+to get this difference in speeds it is necessary to use a combination of
+gearing that will cause the lead-screw to revolve once while the lathe
+spindle and work make two revolutions.
+
+[Illustration: Fig. 29. (A) Lathe with Simple Gearing for Thread
+Cutting. (B) Compound Geared Lathe]
+
+Suppose that nine threads to the inch are to be cut and the lead-screw
+has six threads per inch. In this case the work must make nine
+revolutions while the lead-screw makes six and causes the carriage and
+thread tool to move one inch, or in other words, one revolution of the
+lead-screw corresponds to one and one-half revolution of the spindle;
+therefore, if the lead-screw gear _c_ has 36 teeth, the gear _a_ on the
+spindle stud should have 24 teeth. The spindle will then revolve one and
+one-half times faster than the lead-screw, provided the stud rotates at
+the same rate of speed as the main lathe spindle. The number of teeth in
+the change gears that is required for a certain pitch can be found by
+multiplying the number of threads per inch of the lead-screw, and the
+number of threads per inch to be cut, by the same trial multiplier. The
+formula which expresses the relation between threads per inch of
+lead-screw, threads per inch to be cut, and the number of teeth in the
+change gears, is as follows:
+
+  threads per inch of lead-screw   teeth in gear on spindle stud
+  ------------------------------ = -----------------------------
+    threads per inch to be cut      teeth in gear on lead-screw
+
+Applying this to the example given, we have 6/9 = 24/36. The values of
+36 and 24 are obtained by multiplying 6 and 9, respectively, by 4,
+which, of course, does not change the proportion. Any other number could
+be used as a multiplier, and if gears having 24 and 36 teeth were not
+available, this might be necessary. For example, if there were no gears
+of this size, some other multiplier as 5 or 6 might be used.
+
+Suppose the number of teeth in the change gears supplied with the lathe
+are 24, 28, 32, 36, etc., increasing by four teeth up to 100, and assume
+that the lead-screw has 6 threads per inch and that 10 threads per inch
+are to be cut. Then,
+
+   6    6 × 4   24
+  -- = ------ = --
+  10   10 × 4   40
+
+By multiplying both numerator and denominator by 4, we obtain two
+available gears having 24 and 40 teeth, respectively. The 24-tooth gear
+goes on the spindle stud and, the 40-tooth gear on the lead-screw. The
+number of teeth in the intermediate or "idler" gear _b_, which connects
+the stud and lead-screw gears, is not considered as it does not affect
+the ratios between gears _a_ and _c_, but is used simply to transmit
+motion from one gear to the other.
+
+We have assumed in the foregoing that the spindle stud (on which gear
+_a_ is mounted) and the main spindle of the lathe are geared in the
+ratio of one to one and make the same number of revolutions. In some
+lathes, however, these two members do not rotate at the same speed, so
+that if equal gears were placed on the lead-screw and spindle stud, the
+spindle would not make the same number of revolutions as the lead-screw.
+In that case if the actual number of threads per inch in the lead-screw
+were used when calculating the change gears, the result would be
+incorrect; hence, to avoid mistakes, the following general rule should
+be used as it gives the correct result, regardless of the ratios of the
+gears which connect the spindle and spindle stud:
+
+_Rule.--First find the number of threads per inch that is cut when gears
+of the same size are placed on the lead-screw and spindle, either by
+actual trial or by referring to the index plate. Then place this number
+as the numerator of a fraction and the number of threads per inch to be
+cut, as the denominator; multiply both numerator and denominator by some
+trial number, until numbers are obtained which correspond to numbers of
+teeth in gears that are available._ The product of the trial number and
+the numerator (or "lathe screw constant") represents the gear _a_ for
+the spindle stud, and the product of the trial number and the
+denominator, the gear for the lead-screw.
+
+=Lathes with Compound Gearing.=--When gearing is arranged as shown at
+_A_, Fig. 29, it is referred to as simple gearing, but sometimes it is
+necessary to introduce two gears between the stud and screw as at _B_,
+which is termed compound gearing. The method of figuring compound
+gearing is practically the same as that for simple gearing. To find the
+change gears used in compound gearing, place the "screw constant"
+obtained by the foregoing rule, as the numerator, and the number of
+threads per inch to be cut as the denominator of a fraction; resolve
+both numerator and denominator into two factors each, and multiply each
+"pair" of factors by the same number, until values are obtained
+representing numbers of teeth in available change gears. (One factor in
+the numerator and one in the denominator make a "pair" of factors.)
+
+Suppose the lathe cuts 6 threads per inch when gears of equal size are
+used, and that the number of teeth in the gears available are 30, 35, 40
+and so on, increasing by 5 up to 100. If 24 threads per inch are to be
+cut, the screw constant 6 is placed in the numerator and 24 in the
+denominator. The numerator and denominator are then divided into factors
+and each pair of factors is multiplied by the same number to find the
+gears, thus:
+
+   6   2 × 3   (2 × 20) × (3 × 10)   40 × 30
+  -- = ----- = ------------------- = -------
+  24   4 × 6   (4 × 20) × (6 × 10)   80 × 60
+
+The last four numbers indicate the gears which should be used. The upper
+two having 40 and 30 teeth are the _driving_ gears and the lower two
+having 80 and 60 teeth are the _driven_ gears. The driving gears are
+gear _a_ on the spindle stud and gear _c_ on the intermediate stud,
+meshing with the lead-screw gear, and the driven gears are gears _b_ and
+_d_. It makes no difference which of the driving gears is placed on the
+spindle stud, or which of the driven is placed on the lead-screw.
+
+=Fractional Threads.=--Sometimes the lead of a thread is given as a
+fraction of an inch instead of stating the number of threads per inch.
+For example, a thread may be required to be cut, having 3/8-inch lead.
+The expression "3/8-inch lead" should first be transformed to "number of
+threads per inch." The number of threads per inch (the thread being
+single) equals:
+
+   1        3   8
+  --- = 1 ÷ - = - = 2-2/3
+  3/8       8   3
+
+To find the change gears to cut 2-2/3 threads per inch in a lathe having
+a screw constant of 8 and change gears varying from 24 to 100 teeth,
+increasing by 4, proceed as follows:
+
+    8       2 × 4       (2 × 36) × (4 × 24)     72 × 96
+  ----- = --------- = ----------------------- = -------
+  2-2/3   1 × 2-2/3   (1 × 36) × (2-2/3 × 24)   36 × 64
+
+As another illustration, suppose we are to cut 1-3/4 thread per inch on
+a lathe having a screw constant of 8, and that the gears have 24, 28,
+32, 36, 40 teeth, etc., increasing by four up to one hundred. Following
+the rule:
+
+    8       2 × 4       (2 × 36) × (4 × 16)     72 × 64
+  ----- = --------- = ----------------------- = -------
+  1-3/4   1 × 1-3/4   (1 × 36) × (1-3/4 × 16)   36 × 28
+
+The gears having 72 and 64 teeth are the _driving_ gears, and those with
+36 and 28 teeth are the _driven_ gears.
+
+=Change Gears for Metric Pitches.=--When screws are cut in accordance
+with the metric system, it is the usual practice to give the lead of the
+thread in millimeters, instead of the number of threads per unit of
+measurement. To find the change gears for cutting metric threads, when
+using a lathe having an English lead-screw, first determine the number
+of threads per inch corresponding to the given lead in millimeters.
+Suppose a thread of 3 millimeters lead is to be cut in a lathe having an
+English lead-screw and a screw constant of 6. As there are 25.4
+millimeters per inch, the number of threads per inch will equal 25.4 ÷
+3. Place the screw constant as the numerator, and the number of threads
+per inch to be cut as the denominator:
+
+     6          25.4   6 × 3
+  ------- = 6 ÷ ---- = -----
+   25.4          3     25.4
+   ----
+    3
+
+The numerator and denominator of this fractional expression of the
+change-gear ratio are next multiplied by some trial number to determine
+the size of the gears. The first whole number by which 25.4 can be
+multiplied so as to get a whole number as the result is 5. Thus, 25.4 ×
+5 = 127; hence, one gear having 127 teeth is always used when cutting
+metric threads with an English lead-screw. The other gear required in
+this case has 90 teeth. Thus:
+
+  6 × 3 × 5   90
+  --------- = ---
+  25.4 × 5    127
+
+Therefore, the following rule can be used to find the change gears for
+cutting metric pitches with an English lead-screw:
+
+_Rule.--Place the lathe screw constant multiplied by the lead of the
+required thread in millimeters multiplied by 5, as the numerator of the
+fraction, and 127 as the denominator. The product of the numbers in the
+numerator equals the number of teeth for the spindle-stud gear, and 127
+is the number of teeth for the lead-screw gear._
+
+If the lathe has a metric pitch lead-screw, and a screw having a given
+number of threads per inch is to be cut, first find the "metric screw
+constant" of the lathe or the lead of thread in millimeters that would
+be cut with change gears of equal size on the lead-screw and spindle
+stud; then the method of determining the change gears is simply the
+reverse of the one already explained for cutting a metric thread with an
+English lead-screw.
+
+_Rule.--To find the change gears for cutting English threads with a
+metric lead-screw, place 127 in the numerator and the threads per inch
+to be cut, multiplied by the metric screw constant multiplied by 5, in
+the denominator; 127 is the number of teeth on the spindle-stud gear and
+the product of the numbers in the denominator equals the number of teeth
+in the lead-screw gear._
+
+=Quick Change-gear Type of Lathe.=--A type of lathe that is much used at
+the present time is shown in Fig. 30. This is known as the quick
+change-gear type, because it has a system of gearing which makes it
+unnecessary to remove the change gears and replace them with different
+sizes for cutting threads of various pitches. Changes of feed are also
+obtained by the same mechanism, but the feeding movement is transmitted
+to the carriage by the rod _R_, whereas the screw _S_{1}_ is used for
+screw cutting. As previously explained, the idea of using the screw
+exclusively for threading is to prevent it from being worn excessively,
+as it would be if continually used in place of rod _R_, for feeding the
+carriage when turning.
+
+[Illustration: Fig. 30. Lathe having Quick Change-gear Mechanism]
+
+[Illustration: Fig. 31. End and Side Views of Quick Change-gear
+Mechanism]
+
+The general construction of this quick change gear mechanism and the
+way the changes are made for cutting threads of different pitch, will be
+explained in connection with Figs. 30, 31 and 32, which are marked with
+the same reference letters for corresponding parts. Referring to Fig.
+30, the movement is transmitted from gear _s_ on the spindle stud
+through idler gear _I_, which can be moved sidewise to mesh with either
+of the three gears _a_, _b_ or _c_, Fig. 31. This cone of three gears
+engages gears _d_, _e_ and _f_, any one of which can be locked with
+shaft _T_ (Fig. 32) by changing the position of knob _K_. On shaft _T_
+there is a gear _S_ which can be moved along the shaft by hand lever _L_
+and, owing to the spline or key _t_, both the sliding gear and shaft
+rotate together. Shaft _T_, carrying gears _d_, _e_ and _f_ and the
+sliding gear _S_, is mounted in a yoke _Y_, which can be turned about
+shaft _N_, thus making it possible to lower sliding gear _S_ into mesh
+with any one of a cone of eight gears _C_, Fig. 31. The shaft on which
+the eight gears are mounted has at the end a small gear _m_ meshing with
+gear _n_ on the feed-rod, and the latter, in turn, drives the
+lead-screw, unless gear _o_ is shifted to the right out of engagement,
+which is its position except when cutting threads.
+
+[Illustration: Fig. 32. Sectional Views of Quick Change-gear Mechanism]
+
+With this mechanism, eight changes for different threads or feeds are
+obtained by simply placing gear _S_ into mesh with the various sized
+gears in cone _C_. As the speed of shaft _T_ depends on which of the
+three gears _d_, _e_ and _f_ are locked to it, the eight changes are
+tripled by changing the position of knob _K_, making twenty-four. Now by
+shifting idler gear _I_, three speed changes may be obtained for gears
+_a_, _b_ and _c_, which rotate together, so that the twenty-four changes
+are also tripled, giving a total of seventy-two variations without
+removing any gears, and if a different sized gear _s_ were placed on the
+spindle stud, an entirely different range could be obtained, but such a
+change would rarely be necessary. As shown in Fig. 30, there are eight
+hardened steel buttons _B_, or one for each gear of the cone _C_, placed
+at different heights in the casing. When lever _L_ is shifted sidewise
+to change the position of sliding gear _S_, it is lowered onto one of
+these buttons (which enters a pocket on the under side) and in this way
+gear _S_ is brought into proper mesh with any gear of the cone _C_. To
+shift lever _L_, the handle is pulled outward against the tension of
+spring _r_ (Fig. 32), which disengages latch _l_ and enables the lever
+to be lifted clear of the button; yoke _Y_ is then raised or lowered, as
+the case may be, and lever _L_ with the sliding gear is shifted
+laterally to the required position.
+
+[Illustration: Fig. 33. Index Plate showing Position of Control Levers
+for Cutting Threads of Different Pitch]
+
+The position of lever _L_ and knob _K_ for cutting threads of different
+pitches is shown by an index plate or table attached to the lathe and
+arranged as shown in Fig. 33. The upper section _a_ of this table shows
+the different numbers of threads to the inch that can be obtained when
+idler gear _I_ is in the position shown by the diagram _A_. Section _b_
+gives the changes when the idler gear is moved, as shown at _B_, and,
+similarly, section _c_ gives the changes for position _C_ of the idler.
+The horizontal row of figures from 1 to 8 below the word "stops"
+represents the eight positions for lever _L_, which has a plate _p_
+(Fig. 30) just beneath it with corresponding numbers, and the column to
+the left shows whether knob _K_ should be out, in a central position, or
+in.
+
+In order to find what the position of lever _L_ and knob _K_ should be
+for cutting any given number of threads to the inch, find what "stop"
+number is directly above the number of threads to be cut, which will
+indicate the location of lever _L_, and also what position should be
+occupied by knob _K_, as shown in the column to the left. For example,
+suppose the lathe is to be geared for cutting eight threads to the inch.
+By referring to section a we see that lever _L_ should be in position 4
+and knob _K_ in the center, provided the idler gear _I_ were in position
+_A_, as it would be ordinarily, because all standard numbers of threads
+per inch (U. S. standard) from 1/4 inch up to and including 4 inches in
+diameter can be cut with the idler gear in that position. As another
+illustration, suppose we want to cut twenty-eight threads per inch. This
+is listed in section _c_, which shows that lever _L_ must be placed in
+position 3 with knob _K_ pushed in and the idler gear shifted to the
+left as at _C_.
+
+The simplicity of this method as compared with the time-consuming
+operation of removing and changing gears is apparent. The diagram _D_ to
+the right shows an arrangement of gearing for cutting nineteen threads
+per inch. A 20-tooth gear is placed on the spindle stud (in place of the
+regular one having 16 teeth) and one with 95 teeth on the lead-screw,
+thus driving the latter direct as with ordinary change gears. Of course
+it will be understood that the arrangement of a quick change-gear
+mechanism varies somewhat on lathes of different make.
+
+
+
+
+CHAPTER V
+
+TURRET LATHE PRACTICE
+
+
+Turret lathes are adapted for turning duplicate parts in quantity. The
+characteristic feature of a turret lathe is the turret which is mounted
+upon a carriage and contains the tools which are successively brought
+into the working position by indexing or rotating the turret. In many
+instances, all the tools required can be held in the turret, although it
+is often necessary to use other tools, held on a cross-slide, for
+cutting off the finished part, facing a radial surface, knurling, or for
+some other operation. After a turret lathe is equipped with the tools
+needed for machining a certain part, it produces the finished work much
+more rapidly than would be possible by using an ordinary engine lathe,
+principally because each tool is carefully set for turning or boring to
+whatever size is required and the turret makes it possible to quickly
+place any tool in the working position. Turret lathes also have systems
+of stops or gages for controlling the travel of the turret carriage and
+cross-slide, in order to regulate the depth of a bored hole, the length
+of a cylindrical part or its diameter; hence, turning machines of this
+type are much more efficient than ordinary lathes for turning duplicate
+parts, unless the quantity is small, in which case, the advantage of the
+turret lathe might be much more than offset by the cost of the special
+tool equipment and the time required for "setting up" the machine. (See
+"Selecting Type of Turning Machine.")
+
+[Illustration: Fig. 1. Bardons & Oliver Turret Lathe of Motor-driven
+Geared-head Type]
+
+=General Description of a Turret Lathe.=--The turret lathe shown in Fig.
+1 has a hexagonal shaped turret _A_ with a hole in each side in which
+the tools are held. This turret is mounted on a slide _B_ which is
+carried by a saddle _C_ that can be moved along the bed to locate the
+turret slide with reference to the length of the tools in the turret and
+the room required for indexing. The turret slide can be moved
+longitudinally by turning the pilot wheel or turnstile _D_, or it can
+be fed by power. Ordinarily, the hand adjustment is used for quickly
+moving the carriage when the tools are not cutting, although sometimes
+the hand feed is preferable to a power feed when the tools are at work,
+especially if the cuts are short. After a turret tool has finished its
+cut, the turnstile is used to return the slide to the starting point,
+and at the end of this backward movement the turret is automatically
+indexed or turned one-sixth of a revolution, thus bringing the next tool
+into the working position. The turret is accurately located in each of
+its six positions by a lock bolt which engages notches formed in a large
+index ring at the turret base. A binder lever _E_ at the top of the
+turret stud is used to clamp the turret rigidly to the slide when the
+tools are cutting.
+
+The forward movement of the slide for each position of the turret is
+controlled by stops at _F_, which are set to suit the work being turned.
+When parts are being turned from bar stock, the latter passes through
+the hollow spindle of the headstock and extends just far enough beyond
+the end of the spindle to permit turning one of the parts. The bar is
+held while the turning tools are at work, by a chuck of the collet type
+at _G_. This chuck is opened or closed around the bar by turning
+handwheel _H_. After a finished part has been cut off by a tool held in
+cross-slide _J_, the chuck is released and further movement of wheel _H_
+causes ratchet feed dog _K_, and the bar which passes through it, to be
+drawn forward. This forward movement is continued until the end of the
+bar comes against a stop gage held in one of the turret holes, to insure
+feeding the bar out just the right amount for turning the next piece. On
+some turret lathes, the lever which operates the chuck also controls a
+power feed for the bar stock, the latter being pushed through the
+spindle against the stop.
+
+The machine illustrated has a power feed for the cross-slide as well as
+for the turret. The motion is obtained from the same shaft _L_ which
+actuates the turret slide, but the feed changes are independent. The
+cross-slide feed changes are varied by levers _M_ and those for the
+turret by levers _N_. For many turret lathe operations, such as turning
+castings, etc., a jawed chuck is screwed onto the spindle and the work
+is held the same as when a chuck is used on an engine lathe. Sometimes
+chucks are used having special jaws for holding castings of irregular
+shape, or special work-holding fixtures which are bolted to the
+faceplate. The small handle at _O_ is for moving the cross-slide along
+the bed when this is necessary in order to feed a tool sidewise.
+
+This particular machine is driven by a motor at the rear of the
+headstock, connection being made with the spindle through gearing. The
+necessary speed changes are obtained both by varying the speed of the
+motor and by shifting gears in the headstock. The motor is controlled by
+the turnstile _P_ and the gears are shifted by the vertical levers
+shown.
+
+While many of the features referred to are common to turret lathes in
+general, it will be understood that the details such as the control
+levers, arrangement of stops, etc., vary on turret lathes of different
+make.
+
+[Illustration: Figs. 2 and 3. Diagrams showing Turret Lathe Tool
+Equipment for Machining Automobile Hub Casting]
+
+=Example of Turret Lathe Work.=--The diagrams Figs. 2 and 3 show a
+turret lathe operation which is typical in many respects. The part to be
+turned is a hub casting for an automobile and it is machined in two
+series of operations. The first series is shown by the plan view, Fig.
+2. The casting _A_ is held in a three-jaw chuck _B_. Tool No. 1 on the
+cross-slide is equipped with two cutters and rough faces the flange and
+end, while the inner and outer surfaces of the cylindrical part are
+rough bored and turned by combination boring and turning tool No. 2.
+This tool has, in addition to a regular boring-bar, a bracket or
+tool-holder which projects above the work and carries cutters that
+operate on the top surface. Tools Nos. 3 and 4 next come into action,
+No. 3 finishing the surfaces roughed out by No. 2, and No. 4
+finish-facing the flange and end of the hub. The detailed side view of
+Tool No. 3 (which is practically the same as No. 2), shows the
+arrangement of the cutters _C_ and _D_, one of which turns the
+cylindrical surface and the other bevels the end of the hub. The hole in
+the hub is next finished by tool No. 5 which is a stepped reamer that
+machines the bore and counterbore to the required size within very
+close limits. The surfaces machined by the different tools referred to
+are indicated by the sectional view _E_ of the hub, which shows by the
+numbers what tools are used on each surface.
+
+For the second series of operations, the position of the hub is reversed
+and it is held in a spring or collet type of chuck as shown by the plan
+view Fig. 3. The finished cylindrical end of the hub is inserted in the
+split collet _F_ which is drawn back into the tapering collet ring by
+rod _G_ (operated by turnstile _H_, Fig. 1) thus closing the collet
+tightly around the casting. The first operation is that of facing the
+side of the flange and end of the hub with tool No. 6 on the
+cross-slide, which is shown in the working position. A broad cutter _H_
+is used for facing the flange and finishing the large fillet, and the
+end is faced by a smaller cutter _I_. When these tools are withdrawn,
+tool No. 7 is moved up for rough turning the outside of the cylindrical
+end (preparatory to cutting a thread) and rough boring the hole. These
+same surfaces are then finished by tool No. 8. The arrangement of tools
+Nos. 7 and 8 is shown by the detailed view. Tool _J_ turns the part to
+be threaded; tool _K_ turns the end beyond the threaded part; and tool
+_L_ bevels the corner or edge. The reaming tool No. 9 is next indexed to
+the working position for finishing the hole and beveling the outer edge
+slightly. At the same time, the form tool No. 10, held at the rear of
+the cross-slide, is fed up for beveling the flange to an angle of 60
+degrees. The final operation is that of threading the end, which is done
+with die No. 11. The boring-bars of tools Nos. 2, 3, 7 and 8 are all
+provided with pilots _N_ which enter close fitting bushings held in the
+spindle, to steady the bar while taking the cut. This is a common method
+of supporting turret lathe tools.
+
+The feed of the turret for both the first and second series of
+operations is 1/27 inch per revolution and the speeds 60 revolutions per
+minute for the roughing cuts and 90 revolutions per minute for the
+finishing cuts. The total time for machining one of these castings
+complete is about 7-1/2 minutes, which includes the time required for
+placing the work in the chuck.
+
+=Machining Flywheels in Turret Lathe.=--Figs. 4 to 6, inclusive,
+illustrate how a gasoline engine flywheel is finished all over in two
+cycles of operations. First the flywheel is turned complete on one side,
+the hole bored and reamed, and the outside of the rim finished; in the
+second cycle the other side of the flywheel is completed.
+
+[Illustration: Fig. 4. First Cycle of Operations in Finishing Gasoline
+Engine Flywheels on a Pond Turret Lathe]
+
+During the first operation, the work is held by the inside of the rim by
+means of a four-jaw chuck equipped with hard jaws. The side of the rim,
+the tapering circumference of the recess, the web, and the hub are first
+rough-turned, using tools held in the carriage toolpost. The hole is
+then rough-bored by bar _C_, which is supported in a bushing in the
+chuck, as shown in Fig. 4. The outside of the wheel rim is rough-turned
+at the same time by a cutter held in the extension turret tool-holder
+_T_ (Fig. 5), and the taper fit on the inside of the flywheel is turned
+by means of cutter _A_ (Fig. 4) held in a tool-holder attached to the
+turret.
+
+The outside of the wheel rim is next finish-turned with cutter _V_ (Fig.
+5) held in an extension turret tool-holder the same as the roughing
+tool _T_. At the same time, the bore is finished by a cutter in
+boring-bar _D_ (Fig. 4). The side of the rim and the hub of the wheel
+are also finished at this time by two facing cutters _H_ and _K_, held
+in tool-holders on the face of the turret. When the finishing cuts on
+the rim and hub are being taken, the work is supported by a bushing on
+the boring-bar which enters the bore of the wheel, the boring cutter and
+facing tools being set in such relation to each other that the final
+boring of the hole is completed before the facing cuts are taken.
+
+[Illustration: Fig. 5. Elevation of Turret and Tools for Finishing
+Flywheels--First Operation]
+
+The web of the wheel is next finish-faced with the facing cutter held in
+the holder _E_, and the taper surface on the inside of the rim is
+finished by the tool _L_, at the same time. While these last operations
+are performed, the work is supported by a bushing on a supporting arbor
+_J_, which enters the bore of the wheel. The bore is finally reamed to
+size by a reamer _F_ held in a "floating" reamer-holder. When the
+reaming operation is completed, a clearance groove _N_ is cut on the
+inside of the rim, using a tool _G_ held in the carriage toolpost. The
+first cycle of operations on the flywheel is now completed.
+
+The flywheel is then removed from the chuck, turned around, and held in
+"soft" jaws for the second cycle of operations, the jaws fitting the
+outside of the wheel rim. (Soft unhardened jaws are used to prevent
+marring the finished surface of the rim.) The operations on this side
+are very similar to those performed on the other side. First, the side
+of the rim, the inside of the rim, the web, and hub are rough-turned,
+using tools held in the carriage toolpost. The inside of the rim and the
+web are then finished by a cutter held in a tool-holder at _P_, Fig. 6,
+which is bolted to the face of the turret. The work is supported during
+this operation by a bushing held on a supporting arbor _U_, having a
+pilot which enters a bushing in the chuck. Finally, the rim and hub are
+finished, by the facing cutters _R_ and _S_, the work being supported by
+an arbor, as before.
+
+[Illustration: Fig. 6. Second Cycle of Operations on Flywheel]
+
+These operations illustrate the methods employed in automobile
+factories, and other shops where large numbers of engine flywheels,
+etc., must be machined.
+
+=Finishing a Flywheel at One Setting in Turret Lathe.=--The plan view
+_A_, Fig. 7, shows an arrangement of tools for finishing a flywheel
+complete at one setting. The hole for the shaft has to be bored and
+reamed and the hub faced on both sides. The sides and periphery of the
+rim also have to be finished and all four corners of the rim rounded.
+The tools for doing this work consist of boring-bars, a reamer, facing
+heads on the main turret, a turret toolpost on the slide rest
+(carrying, in this case, three tools) and a special supplementary wing
+rest attached to the front of the carriage at the extreme left.
+
+The casting is held by three special hardened jaws _b_ in a universal
+chuck. These jaws grip the work on the inner side of the rim, leaving
+room for a tool to finish the rear face without striking the chuck body
+or jaws. Three rests _c_ are provided between the chuck jaws. The work
+is pressed against these rests while being tightened in the chuck, and
+they serve to locate it so that the arms will run true so far as
+sidewise movement is concerned. These rests also locate the casting with
+relation to the stops for the turret and carriage movements. The chuck
+carries a bushing _r_ of suitable diameter to support the boring-bars in
+the main turret, as will be described.
+
+In the first operation, boring-bar _m_ is brought in line with the
+spindle and is entered in bushing _r_ in the chuck. Double-ended cutter
+_n_ is then fed through the hub of the pulley to true up the cored hole.
+While boring the hole, the scale on the front face of the rim and hub is
+removed by tool _j_. Tool _k_ is then brought into action to rough turn
+the periphery, after which tool _e_, in the wing rest, is fed down to
+clean up the back face of the rim. As soon as the scale is removed, the
+hole is bored nearly to size by cutter _n_{1}_ in bar _m_{1}_, and it is
+finally finished with reamer _q_ mounted on a floating arbor.
+
+The cutters _f_, _g_ and _h_, in the facing head, are next brought up to
+rough face the hub and rim, and round the corners of the rim on the
+front side. This operation is all done by broad shaving cuts. The facing
+head in which the tools are held is provided with a pilot bar _t_ which
+fits the finished hole in the flywheel hub, and steadies the head during
+the operation. The cutters _f_, _g_ and _h_ are mounted in holders which
+may be so adjusted as to bring them to the proper setting for the
+desired dimensions. This completes the roughing operations.
+
+[Illustration: Fig. 7. Turret Lathe Tool Equipment for Machining
+Flywheels]
+
+The periphery of the rim is now finished by cutter _l_ in the turret
+toolpost which is indexed to the proper position for this operation. The
+rear face of the rim is finished by the same tool _e_ with which the
+roughing was done. Tool _e_ is then removed and replaced with _d_
+which rounds the inner corner of the rim. Tool _d_ is also replaced with
+a third tool for rounding the outer corner of the rear side. For
+finishing the front faces of the rim and hub and rounding the corners of
+the rim, a second facing head, identical with the first one, is
+employed. This is shown in position in the illustration. Cutters
+_f_{1}_, _g_{1}_ and _h_{1}_ correspond with the cutters _f_, _g_ and
+_h_, previously referred to, and perform the same operations.
+
+The remaining operation of finishing the back of the hub is effected by
+cutter _p_. This cutter is removed from the bar, which is then inserted
+through the bore; the cutter is then replaced in its slot and the rear
+end of the hub is faced by feeding the carriage away from the headstock.
+This completes the operations, the flywheel being finished at one
+setting.
+
+=Finishing a Webbed Flywheel in Two Settings.=--The plan views _B_ and
+_C_, Fig. 7, show the arrangement of tools for finishing a webbed
+flywheel which has to be machined all over. This, of course, requires
+two operations. In the first of these (see sketch _B_) the rough casting
+is chucked on the inside of the rim with regular inside hard chuck jaws
+_b_. The cored hole is first rough bored with cutter _n_ attached to the
+end of boring-bar _m_, and guided by the drill support _d_ pivoted to
+the carriage. Next, the boring-bar _m_{1}_ is brought into position, the
+drill support being swung back out of the way. This bar is steadied by
+its bearing in bushing _r_ in the chuck. Two cutters, _n_{1}_ and
+_n_{2}_, are used to roughly shape the hole to the desired taper, the
+small end being finished to within 0.002 inch of the required diameter.
+While boring with the bar _m_{1}_, the scale is broken on the web and
+hub of the casting by the tool _k_ in the turret toolpost. The latter is
+then shifted to bring the tool _j_ into position for removing the scale
+on the periphery of the wheel. Next, the hole is reamed with taper
+reamer _q_, the pilot of which is supported by bushing _r_.
+
+The first of the facing heads is now brought into action. This facing
+head carries a guide _t_ which is steadied in a taper bushing _c_,
+driven into the taper hole of the hub for that purpose. The top cutter
+_f_ turns the periphery, cutter _g_ turns the hub and faces the web,
+and cutter _h_ faces the rim. A fourth cutter _e_ on the under side of
+the head faces the hub. This casting is now machined approximately to
+size.
+
+For finishing, similar cutters, _e_{1}_, _f_{1}_, _g_{1}_ and _h_{1}_,
+in the other facing head are used, the latter being supported by the
+taper bushing _c_ in the same way. A very light cut is taken for
+finishing. Tool _l_ in the carriage turret is used to round the outer
+and inner corners of the rim, which completes the work on this face of
+the casting.
+
+In the second cycle of operations, shown at _C_, the casting is chucked
+on the outside with the soft jaws _b_, which are bored to the exact
+diameter of the finished rim. The work is further supported and centered
+by sliding bushing _c_, which is tapered to fit the finished hole in the
+hub, and has an accurate bearing in bushing _r_ in the chuck. This
+bushing is provided with a threaded collar for forcing it into the work
+and withdrawing it. The scale on the web and the inside and face of the
+rim is first broken with the tool _k_ in the turret toolpost. These
+surfaces are then roughed off with cutters _f_, _g_ and _h_, in the
+facing head. This latter is steadied by a pilot _t_ which enters the
+hole in the sliding bushing _c_ on which the work is supported. A light
+cut is next taken with cutters _f_{1}_, _g_{1}_ and _h_{1}_, in the
+finishing facing head, which completes the operation.
+
+=Tools for Turret Lathes.=--The operation of a turret lathe after the
+tools have been properly arranged is not particularly difficult, but
+designing and making the tools, determining what order of operations
+will give the most efficient and accurate results, and setting the tools
+on the machine, requires both skill and experience. For some classes of
+work, especially if of a rather complicated nature, many of the tools
+must be specially designed, although there are certain standard types
+used on turret lathes which are adapted to general turning operations.
+Some of the principal types are referred to in the following.
+
+=Box-tools.=--Tools of this type are used for turning bar stock. There
+are many different designs, some of which are shown in Figs. 8, 9 and
+10. Box-tools are held in the turret and they have back-rests opposite
+the turning tools, for supporting the part being turned. The box-tool
+shown at _A_, Fig. 8, is for roughing. The cutter _a_ is a piece of
+high-speed steel beveled on the cutting end to produce a keen edge. It
+takes a shearing tangent cut on top of the bar and the latter is kept
+from springing away by means of the adjustable, hardened tool-steel
+back-rest _b_. This tool is considered superior to a hollow mill
+whenever a fair amount of stock must be removed. If considerable
+smoothness and accuracy are necessary, the finishing box-tool shown at
+_B_ should follow the roughing box tool, but in most cases, especially
+if the part is to be threaded by a die, a finishing cut is unnecessary.
+
+[Illustration: Fig. 8. Different Types of Box-tools for Turret Lathe]
+
+The finishing box-tool _B_ is also used to follow a hollow mill if
+special accuracy or smoothness is desired. This tool is only intended
+for light finishing cuts, the allowances varying from 0.005 inch to
+0.015 inch in diameter. The cutters are made of square tool steel of
+commercial size, and are ground and set to take a scraping end cut. This
+particular tool has two tool-holders which permit finishing two
+diameters at once. If a larger number of sizes must be turned, extra
+tool-holders can be applied.
+
+The single-cutter box-tool shown at _C_ is bolted directly to the face
+of the turret instead of being held by a shank in the turret hole, and
+it is adapted for heavy cuts such as are necessary when turning
+comparatively large bar stock. The tool-holder _a_ swivels on a stud,
+thus allowing the cutter to be withdrawn from the work while being
+returned, which prevents marring the turned surface. The high-speed
+steel cutter is ground to take a side cut on the end of the bar. The
+latter is supported by hardened and ground tool-steel rolls _b_ which
+revolve on hardened and ground studs. These rolls are mounted on
+swinging arms which have a screw adjustment for different diameters.
+They can also be adjusted parallel to the bar, thus enabling them to be
+set either in advance of or back of the cutter. The opening in the base
+allows the stock to pass into the turret when it is not larger than the
+turret hole.
+
+The box-tool shown at _D_ is similar to the one just described, except
+that it has two or more cutters and roller back-rests, thus enabling
+different diameters to be turned simultaneously. The cutters are ground
+to take a side cut. Ordinarily this gives a satisfactory finish, but if
+special accuracy and smoothness are desired, two tools should be used,
+one for roughing and one for finishing, the latter being ground to take
+a light scraping end cut.
+
+The taper-turning box-tool shown at _E_ is designed for accurately
+turning tapers on brass or cast-iron parts, when there is a small amount
+of stock to be removed. The taper is obtained by cross motion imparted
+to the cutter slide as the turret advances. The taper-turning box-tool
+shown at _F_, instead of having a single-point cutter, is provided with
+a wide cutter _a_. This tool is designed to turn tapering parts of
+small or medium diameter, requiring the use of a support which cannot be
+provided with a straight forming tool and holder mounted on the cut-off
+slide. The cutter is backed up by the screws shown, which also provide
+adjustment for different tapers within a limited range. The bar is
+supported by the three back-rests shown, which also have screw
+adjustment.
+
+=Examples of Box-tool Turning.=--Box-tools are not only used for
+cylindrical and taper turning on the end of a bar, but for many other
+operations. Figs. 9 and 10 show a number of box-tools of different
+designs, with examples of the work for which each is intended. While
+these tools are designed for some specific part, they can, of course,
+with slight modifications be adapted to other work.
+
+[Illustration: Fig. 9. Box-tools and Work for which they are Intended]
+
+A box-tool of the pilot type that is used for finishing, after the
+surplus stock has been removed by roughing tools, is shown at _A_, Fig.
+9. The work, which is the cone for a ball bearing, is shown at _a_ by
+the dotted lines and also by the detail view to the right. The pilot _b_
+enters the work before either of the cutters begins to operate on its
+respective surface. The inverted cutter _c_, which sizes the flange of
+the cone, is held in position by a clamp _d_, which is forced down by a
+collar-head screw. The cutter is further secured against a beveled
+shoulder at _g_ by the set-screws _f_, and it is adjusted forward by the
+screw _e_. By loosening the screws _f_ and the collar-head screw, the
+cutter may be removed for sharpening. The cutter _h_ is adjusted to cut
+to the proper diameter, by the screws _l_, after which the clamp _k_ is
+made level by the screw _j_. The collar-screw _m_ is then used to secure
+the tool in place. The cutter is made from drill rod and it is slightly
+cupped out on the cutting end to give keenness to the cutting edge. The
+adjusting screw _o_, which passes through plate _p_, prevents the cutter
+from backing away from the work. This adjusting screw plate has its
+screw holes slotted to avoid removing the screws when it becomes
+necessary to remove the plate and cutter for sharpening. Pilot _b_ is
+held firmly to the tool body by set-screw _r_. The hole _s_ through the
+shank makes it easy to remove the pilot, in case this is necessary.
+
+A pilot box-tool for finishing another type of ball bearing cone is
+shown at _B_. The shape of the work itself is indicated by the dotted
+lines _a_ and by the detail view. This tool is somewhat similar in its
+construction to the one just described. The cutters _b_ and _c_ are
+inverted and are used to face the flange at _d_ and to turn it to the
+proper diameter. These cutters are held by the clamp _f_ and screws _g_
+and are adjusted forward by the screw _h_. The cutter _j_, which
+operates on top of the stock, rests on a bolster, of the proper angle
+and is adjusted up or down by the screws _k_. The clamp _l_, which binds
+against this tool, is beveled to correspond with the angle of the tool.
+This clamp is secured by the collar-screw shown and it is leveled by
+set-screws _s_. The adjusting screw _p_ prevents the cutter from
+slipping back. The holes in the adjusting-screw plate are also slotted
+in this case so that it will not be necessary to remove any screws when
+the cutter has to be taken out of the holder.
+
+A box-tool for finishing a treadle-rod cone for a sewing machine is
+shown at _C_. This tool is also of the pilot type. The cutters in it
+operate on opposite sides of the cone _a_. The inverted cutter _b_ sizes
+the cylindrical part of the cone, while the front cutter _d_ is set at
+the proper angle to finish the tapered part. The rear cutter _b_ is held
+in place by the clamp _g_ and a collar screw. It is adjusted forward by
+the screw _h_ in the plate _i_ which is held by screws as shown. The
+pilot is retained by a set-screw, and it is easily removed by inserting
+a small rod in the hole _l_ which passes through the shank. The cutter
+_d_ is held by clamp _m_ and is adjusted by screw _n_ which passes
+through a tapped hole in plate _o_. The screw holes in both the
+adjusting plates _i_ and _o_ are slotted to facilitate their removal.
+
+The box-tool illustrated at _A_, Fig. 10, is used for finishing the
+bushing of a double-taper cone bearing _a_. The cutters are so arranged
+that they all cut on the center; that is, the cutting edges lie in a
+horizontal plane. The inverted cutter _b_ at the rear forms the short
+angular surface, and the cutter _c_ in front forms the long tapering
+part of the bearing. The large diameter is turned, to size by cutter
+_d_. The pilot _e_ has a bearing in the bore nearly equal to the length
+of the work and it is provided with oil grooves, as shown. The taper
+shank of this pilot is tapped for the screw _i_ which extends the whole
+length of the shank and is used to draw the pilot back to its seat. It
+is not necessary to remove adjusting-screw plate _k_ to take out the
+cutter _b_, as the latter can be drawn out from the front after the
+collar-screw _m_ is loosened. The cutter _c_ is removed by taking off
+the adjusting-screw plate _s_ after loosening the collar-screw _n_. The
+cutter _d_ is held in a dove-tailed slot by two headless set-screws _q_.
+It is also backed up by an adjusting screw in the plate _s_. These
+adjusting screws should all have fine threads, say from 32 to 40 per
+inch, and be nicely fitted so they will not loosen after being adjusted.
+
+The box-tools shown at _B_ and _C_, Fig. 10, are for turning the sides
+of a loose pulley for a sewing machine. This pulley (shown by the dotted
+lines) is finished in two operations. The box-tool for finishing the
+side of the pulley on which the hub projects beyond the rim, is shown at
+_B_. The inverted cutter _a_, which faces the end of the hub, is held by
+a clamp _c_ (clearly shown in the end view) from the under side and it
+has no adjustment. The collar-screw _d_ is tapped into this clamp, which
+is prevented from getting out of place by the dowel-pin _f_. The pilot
+_g_ is made small in the shank, so that tool _a_ can be so placed as to
+insure the removal of all burrs around the bore of the hub. The pilot is
+held by a set-screw and it is provided with oil grooves. The cutter _j_
+sizes the outside of the hub, and the cutter _k_ faces the side of the
+pulley rim. These cutters are both held by the clamp _l_ and the
+collar-screw _m_. No side plates are used on this tool, and the cutters
+are all easily removed.
+
+[Illustration: Fig. 10. Examples of Box-tool Designs]
+
+Sketch _C_ shows the box-tool used for the second operation. As the hub
+is flush with the rim on the side for which this tool is intended, it
+needs only one cutter to face both. This is done by the wide cutter _a_
+which is held in a dove-tailed slot in the front of the tool and is
+fastened by the clamp _b_ and collar-screw _c_. The bushing _d_, in
+which the end of the work arbor is supported, is held by the
+collar-screw _e_, and to obtain the necessary compression, the body of
+the tool is slotted as far back as _f_. This bushing is provided with
+oil grooves and one side is cut away to clear the cutter _a_. The
+pilot end of the arbor on which the work is mounted is 1/16 inch smaller
+than the bore of the pulley, which allows the cutter to be set in far
+enough to prevent any burr which might form at the edge of the bore. A
+disk _i_ is inserted back of bushing _d_, so that the latter may be
+easily removed by passing a rod through the hollow shank. The special
+chuck used for this second operation on the loose pulley is screwed onto
+the spindle, and the work is mounted on a projecting arbor and driven by
+the pins engaging holes in the pulley web. The arbor is made a driving
+fit for the work, and the end or pilot is a running fit in the bushing
+of the box-tool. A counterbore in the arbor hub provides clearance for
+the hub of the pulley which projects beyond the rim on one side.
+
+[Illustration: Fig. 11. (A) Hollow Mill and Holder. (B) Spring
+Screw-threading Die and Releasing Die-holder]
+
+=Hollow Mills.=--A hollow mill such as is shown at _A_ in Fig. 11 is
+sometimes used in place of a box-tool (especially when turning brass)
+for short roughing cuts preceding a threading operation. The turning is
+done by the cutting edges _e_, and the turned part enters the mill and
+is steadied by it. If this type of tool is used for long, straight cuts,
+especially on square stock and when making screws with large heads from
+the bar, it should always be followed by a finishing box-tool to insure
+accurate work. A hollow mill can be sharpened readily by grinding the
+ends without materially changing the cutting size. A slight adjustment
+can be obtained by means of the clamp collar shown to the left, although
+this is not generally used. When making these mills, they should be
+reamed out tapering from the rear to give clearance to the cutting
+edges. For turning steel, the cutting edge should be about 1/10 of the
+diameter ahead of the center, whereas for brass, it should be on the
+center-line.
+
+[Illustration: Fig. 12. Geometric Adjustable Hollow Milling Tool]
+
+Hollow mills are also made adjustable. The design shown in Fig. 12 is
+especially adapted for brass finishing. It can also be used for taking
+light cuts on cast iron or steel but its use in place of roughing or
+finishing box-tools for general use is not recommended. With the
+exception of the cutters and screws, the complete tool consists of three
+parts, _viz._, the holder, cam, and ring. The cam serves to adjust the
+cutters for different diameters. The adjustment is made by the two
+screws shown, the amount being indicated by a micrometer scale. When
+adjusting the cutters for a given diameter, the use of a hardened steel
+plug of the required size is advisable, the cutters being adjusted
+against the plug.
+
+=Releasing Die and Tap Holders.=--Threads are cut in the turret lathe by
+means of dies for external threading, and taps for internal threading,
+the die or tap being held in a holder attached to the turret. A simple
+form of releasing die holder is shown at _B_, Fig. 11. This holder was
+designed for the spring-screw type of threading die shown to the left.
+The die is clamped in the holder _a_ by the set-screw shown, and the
+shank _b_ of the holder is inserted in the turret hole. Holder _a_ has
+an extension _c_ which passes through the hollow shank. When the die is
+pressed against the end of the work, holder _a_ and its extension moves
+back until lug _d_ on the holder engages lug _e_ on the shank. The die
+and holder are then prevented from rotating with the work and the die
+begins to cut a thread. It continues to screw itself onto the work with
+the turret following, until the thread has been cut to the required
+length; the turret is then stopped and as the die and holder _a_ are
+drawn forward, lugs _d_ and _e_ disengage so that the die simply rotates
+with the work without continuing to advance. The lathe spindle is then
+reversed and as the turret is moved back by hand, pin _f_ comes around
+and enters notch _g_, thus holding the die stationary; the die then
+backs off from the threaded end. Some tap holders are also constructed
+the same as this die holder, so far as the releasing mechanism is
+concerned. There are also many other designs in use, some of which
+operate on this same principle.
+
+[Illustration: Fig. 13. Geometric Self-opening and Adjustable
+Screw-cutting Die Head]
+
+=Self-opening Die Heads.=--The type of die holder shown at _B_ in Fig.
+11 is objectionable because of the time required for backing the die off
+the threaded end; hence, self-opening dies are extensively used in
+turret lathe work. As the name implies, this type of die, instead of
+being solid, has several chasers which are opened automatically when the
+thread has been cut to the required length. The turret can then be
+returned without reversing the lathe spindle. The dies are opened by
+simply stopping the travel of the turret slide, the stop-rod for the
+feed of the turret being adjusted to give the proper amount of travel.
+
+[Illustration: Fig. 14. Geometric Collapsing Tap]
+
+A well-known die head of the self-opening type is shown in Fig. 13. The
+dies open automatically as soon as the travel of the head is retarded,
+or they can be opened at any point by simply holding back on the
+turnstile or lever by which the turret slide is moved. The die is closed
+again by means of the small handle seen projecting at right-angles from
+the side of the head. The closing may be done by hand or automatically
+by screwing a pin into a threaded hole opposite the handle and attaching
+a small piece of flat steel to the back edge of the turret slide. The
+latter will then engage the pin as the turret revolves, thus closing the
+die head. This die head has a roughing and finishing attachment which is
+operated by handle _A_. When this handle is moved forward, the dies are
+adjusted outward 0.01 inch for the roughing cut, whereas returning the
+handle closes and locks the dies for the finishing cut. The die head has
+a micrometer scale which is used when making slight adjustments to
+compensate for the wear of the chasers or to make either a tight-or a
+loose-fitting thread.
+
+=Collapsing Taps.=--The collapsing tap shown in Fig. 14 is one of many
+different designs that are manufactured. They are often used in turret
+lathe practice in place of solid taps. When using this particular style
+of collapsing tap, the adjustable gage _A_ is set for the length of
+thread required. When the tap has been fed to this depth, the gage comes
+into contact with the end of the work, which causes the chasers to
+collapse automatically. The tool is then withdrawn, after which the
+chasers are again expanded and locked in position by the handle seen at
+the side of the holder. In all threading operations, whether using taps
+or dies, a suitable lubricant should be used, as a better thread is
+obtained and there is less wear on the tools. Lard oil is a good
+lubricant, although cheaper compounds give satisfactory results on many
+classes of work.
+
+=Miscellaneous Turret Lathe Tools.=--The chamfering tool shown at _A_,
+Fig. 15, is used for pointing the end of a bar before running on a
+roughing box-tool. This not only finishes the end of the bar but
+provides an even surface for the box-tool to start on. The cutter is
+beveled on the end to form a cutting edge and it is held at an angle.
+The back-rest consists of a bell-mouthed, hardened tool-steel bushing
+which supports the bar while the cut is being taken.
+
+The stop gages _B_ and _C_ are used in the turret to govern the length
+of stock that is fed through the spindle. When a finished piece has been
+cut off, the rough bar is fed through the spindle and up against the
+stop gage, thus locating it for another operation. This gage may be a
+plain cylindrical piece of hardened steel, as at _B_, or it may have an
+adjusting screw as at _C_; for special work, different forms or shapes
+are also required. The stop gages on some machines, instead of being
+held in the turret, are attached to a swinging arm or bracket that is
+fastened to the turret slide and is swung up in line with the spindle
+when the stock is fed forward.
+
+The center drilling tool _D_ is designed to hold a standard combination
+center drill and reamer. This type of tool is often used when turning
+parts that must be finished afterwards by grinding, to form a center for
+the grinding machine. The adjustable turning tool _E_ is used for
+turning the outside of gear blanks, pulley hubs or the rims of small
+pulleys. The pilot _a_ enters the finished bore to steady the tool, and
+cutter _b_ is adjusted to turn to the required diameter.
+
+[Illustration: Fig. 15. Various Types of Tools for the Turret Lathe]
+
+The cutting-off tool-holder _F_ (which is held on the cross-slide of the
+turret lathe) is usually more convenient than a regular toolpost, as the
+blade can be set closer to the chuck. The blade is held in an inclined
+position, as shown, to provide rake for the cutting edge; the inclined
+blade can also be adjusted vertically, a limited amount, by moving it in
+or out. The multiple cutting-off tool _G_ holds two or more blades and
+is used for cutting off several washers, collars, etc., simultaneously.
+By changing the distance pieces between the cutters, the latter are
+spaced for work of different widths. The flat drill holder _H_ is used
+for drilling short holes, and also to form a true "spot" or starting
+point for other drills.
+
+Knurling tools are shown at _I_ and _J_. The former is intended for
+knurling short lengths and is sometimes clamped on top of the cut-off
+tool on the cross-slide, the end being swung back after knurling (as
+shown by the dotted lines) to prevent interference with the work when
+the cutting-off tool is in operation. The knurling tool _J_ has a shank
+and is held in the turret. The two knurls are on opposite sides of the
+work so that the pressure of knurling is equalized. By adjusting the
+arms which hold the knurls, the tool can be set for different diameters.
+
+Three styles of drill holders are shown at _K_, _L_ and _M_. Holder _K_
+is provided with a split collet (seen to the left) which is tightened on
+the drill shank by a set-screw in the holder. This holder requires a
+separate collet for each size drill. The taper shank drill holder _L_
+has a standard taper hole into which the shank of the drill is inserted.
+The adjustable type of holder _M_ is extensively used, especially on
+small and medium sized machines when several sizes of drills are
+necessary. This holder is simply a drill chuck fitted with a special
+shank. For large drills the plain style of holder _K_ is recommended,
+and if only a few sizes of drills are required, it is more satisfactory
+and economical than the adjustable type.
+
+The various types of small turret lathe tools referred to in the
+foregoing for turning, threading, tapping, knurling, etc., are a few of
+the many different designs of tools used in turret lathe practice.
+Naturally, the tool equipment for each particular job must be changed
+somewhat to suit the conditions governing each case. The tools referred
+to, however, represent in a general way, the principal types used in
+ordinary practice. Some of the more special tools are shown in
+connection with examples of turret lathe work, which are referred to in
+the following.
+
+=Turning Gasoline Engine Pistons in Turret Lathe.=--The making of
+pistons for gas engines, especially in automobile factories, is done on
+such a large scale that rapid methods of machining them are necessary.
+The plan view _A_, Fig. 16, shows the turret lathe tools used in one
+shop for doing this work. As is often advisable with work done in large
+quantities, the rough castings are made with extra projections so
+arranged as to assist in holding them. These projections are, of course,
+removed when the piece is completed. In this case the piston casting _a_
+has a ring about 1-1/4 inch long and a little less in diameter than the
+piston, at the chucking end. The piston is held in suitable chuck jaws
+_b_ which are tightened against the inside of this ring. The set-screws
+in these special jaws are then tightened, thus clamping the casting
+between the points of the screws and the jaws. This method of holding
+permits the whole exterior of the piston to be turned, since it projects
+beyond the chuck jaws. This is the object in providing the piston with
+the projecting ring by which it is held.
+
+[Illustration: Fig. 16. (A) Method of Boring and Turning Pistons in
+Gisholt Lathe. (B) Special Chuck and Tools for Turning, Boring and
+Cutting Off Eccentric Piston Rings]
+
+The first operation consists in rough-boring the front end of the
+piston. The double-ended cutter _n_ is held in boring-bar _m_, which is,
+in turn, supported by a drill-holder, clamped to one of the faces of
+the turret. This bar is steadied by a bushing in the drill support _c_
+which is attached to the carriage, and may be swung into or out of the
+operating position, as required. After this cut is completed, the turret
+is revolved half way around and the casting is finish-bored in a similar
+manner, with double-ended cutter _n_{1}_ held in bar _m_{1}_, the drill
+support being used as in the previous case. The support is then turned
+back out of the way to allow the turning tools in the turret toolpost to
+be used.
+
+The outside of the piston is next rough-turned with tool _k_ in the
+turret toolpost, which is revolved to bring this cutter into action. The
+toolpost is then turned to the position shown, and the outside is
+finish-turned by tool _j_, which takes a broad shaving cut. The turret
+tool-holder is again revolved to bring form tool _l_ into position. This
+tool cuts the grooves for the piston rings. Suitable positive stops are,
+of course, provided for both the longitudinal and cross movements of the
+turret toolpost.
+
+In the second operation, the piston _a_ is reversed and held in soft
+jaws, which are used in place of the hardened jaws _b_ shown in the
+illustration. These jaws are bored to the outside diameter of the
+piston, so that when closed, they hold the work true or concentric with
+the lathe spindle. In this operation the chucking ring by which the
+piston was previously held is cut off, and the end of the piston is
+faced true. If the crank-pin hole is to be finished, a third operation
+is necessary, a self-centering chuck-plate and boring and reaming tools
+being used. (These are not shown in the illustration.)
+
+=Turning Piston Rings in Turret Lathe.=--One method of turning piston
+rings is shown at _B_ in Fig. 16. The piston rings are cut from a
+cast-iron cylindrical piece which has three lugs _b_ cast on one end and
+so arranged that they may be held in a three-jawed chuck. This
+cylindrical casting is about 10 inches long, and when the rings are to
+have their inside and outside surfaces concentric, the casting is held
+by the lugs in the regular jaws furnished with the chuck. (The
+arrangement used for turning and boring eccentric rings, which is that
+shown in the illustration, will be described later.)
+
+The casting _a_, from which the rings are made, is first rough-bored
+with double-ended cutter _n_ in boring-bar _m_, after which it is
+finish-bored with cutter _n_{1}_ in bar _m_{1}_. While taking these
+cuts, the bars _m_ and _m_{1}_ are supported by their extension ends
+which enter bushing _r_ located in the central hole of the chuck. This
+furnishes a rigid support so that a heavy cut can be taken.
+
+The outside of the casting is next rough-turned with tool _k_, held in
+the turret toolpost. This toolpost is then revolved to bring tool _j_
+into position, by which the outside is turned true to size, a broad
+shaving chip being taken. The toolpost is again swung around, to bring
+the cutting-off tool-holder _l_ into position. This holder contains four
+blades set the proper distance apart to give rings of the desired width.
+Each blade, from right to left, is set a little back of the preceding
+one, so that the rings are cut off one after the other, the outer rings
+being supported until they are completely severed. After the first four
+rings are cut off, the carriage is moved ahead to a second stop, and
+four more rings are severed, this operation being continued until the
+casting has been entirely cut up into rings.
+
+When the bore of the ring is to be eccentric with the outside, the
+holding arrangement shown in the illustration is used. The casting a is
+bolted to a sliding chuck-plate _c_, and the outside is rough-turned
+with tool _k_ in the toolpost. Finishing tool _j_ is then brought into
+action, and the outside diameter is turned accurately to size. Then the
+sliding chuck-plate _c_, carrying the work, is moved over a distance
+equal to the eccentricity desired, and the work is bored with cutters
+_n_ and _n_{1}_ as in the previous case. The turret toolpost is next
+revolved and the tools _l_ are used for cutting off the rings. The
+reason for finishing the outside first is to secure smooth rings in
+cutting off, as this operation should be done when the work is running
+concentric with the bore, rather than with the exterior surface.
+
+It will be evident that this method gives a far greater output of rings
+than is possible by finishing them in the more primitive way on engine
+lathes. The faces of the rings may be finished in a second operation if
+desired, or they may be ground, depending on the method used in the
+shop where the work is being done, and the accuracy required.
+
+[Illustration: Fig. 17. Turning Gasoline Engine Pistons in Pratt &
+Whitney Turret Lathe]
+
+=Piston Turning in Pratt and Whitney Turret Lathe.=--A turret lathe
+equipped with tools for turning, facing and grooving automobile gasoline
+engine pistons is shown in Fig. 17. The piston is held on an expanding
+pin chuck which is so constructed that all of the pins are forced
+outward with equal pressure and automatically conform to any
+irregularities on the inside of the piston. Tool _A_ rough-turns the
+outside, and just as this tool completes its cut, a center hole is
+drilled and reamed in the end of the piston by combination drill and
+reamer _B_. The turret is then indexed one-half a revolution and a
+finishing cut is taken by tool _C_. After the cylindrical body of the
+piston has been turned, tools held in a special holder _E_ attached to
+the cut-off slide are used to face the ends of the piston and cut the
+packing-ring grooves. While the grooves are being cut, the outer end of
+the piston is supported by center _D_. The center hole in the end also
+serves to support the piston while being ground to the required diameter
+in a cylindrical grinding machine. The edge at the open end of the
+piston may also be faced square and the inner corner beveled by a hook
+tool mounted on the rear cross-slide, although this is usually done in a
+separate operation. (This provides a true surface by which to hold this
+end when grinding.)
+
+[Illustration: Fig. 18. Pratt & Whitney Turret Lathe equipped with
+Special Attachment for Turning Eccentric Piston Rings]
+
+This illustration (Fig. 17) shows very clearly the stops which
+automatically disengage the turret feed. A bracket _F_ is bolted to the
+front of the bed and contains six stop-rods _G_ (one for each position
+or side of the turret). When one of these stop-rods strikes lever _H_,
+the feed is disengaged, the stop being adjusted to throw out the feed
+when the tool has completed its cut. Lever _H_ is automatically aligned
+with the stop-rods for different sides of the turret by a cam _J_ on the
+turret base. A roller _K_ bears against this cam and, through the
+connecting shaft and lever shown, causes lever _H_ to move opposite the
+stop-rod for whatever turret face is in the working position. Lever _L_
+is used for engaging the feed and lever _R_ for disengaging it by hand.
+
+The indexing of the turret at the end of the backward movement of the
+slide is controlled by stop _M_ against which rod _N_ strikes, thus
+disengaging the lock bolt so that the turret can turn. This stop _M_ is
+adjusted along the bed to a position depending upon the length of the
+turret tools and the distance the turret must move back to allow the
+tools to clear as they swing around.
+
+[Illustration: Fig. 19. Tool Equipment for Machining Worm Gear
+Blanks--Davis Turret Lathe]
+
+=Attachment for Turning Piston Rings.=--Fig. 18 shows a special
+attachment applied to a Pratt & Whitney turret lathe for turning
+eccentric, gas-engine piston rings. The boring of the ring casting,
+turning the outside and cutting off the rings, is done simultaneously.
+The interior of the casting is turned concentric with the lathe spindle
+by a heavy boring-bar, the end of which is rigidly supported by a
+bushing in the spindle. The slide which carries the outside turning tool
+is mounted on a heavy casting which straddles the turret. The outside of
+the ring casting is turned eccentric to the bore as a result of an
+in-and-out movement imparted to the tool by a cam on shaft _A_ which is
+rotated from the lathe spindle through the gearing shown. For each
+revolution of the work, the tool recedes from the center and advances
+toward it an amount sufficient to give the required eccentricity. When
+the turning and boring tools have fed forward about 2 inches, then the
+cutting-off tools which are held in holder _B_ come into action. The end
+of each cutting-off tool, from right to left, is set a little farther
+away from the work than the preceding tool, so that the end rings are
+always severed first as the tools are fed in by the cross-slide. A
+number of the completed rings may be seen in the pan of the machine.
+
+[Illustration: Fig. 20. Turning Bevel Gear Blanks in Davis Turret
+Lathe--First Operation]
+
+=Turning Worm-gear Blanks in Turret Lathe.=--This is a second operation,
+the hub of worm-gear blank _G_ (Fig. 19) having previously been bored,
+reamed, and faced on the rear side. The casting is mounted upon a
+close-fitting arbor attached to a plate bolted to the faceplate of the
+lathe, and is driven by two pins which engage holes on the rear side.
+The rim is first rough-turned by a tool _A_ which operates on top, and
+the side is rough-faced by a toothed or serrated cutter _B_. A similar
+tool-holder having a tool _C_ and a smooth cutter _D_ is then used to
+turn the rim to the required diameter and finish the side. The end of
+the hub is faced by cutters mounted in the end of bars _E_ and _F_, one
+being the roughing cutter and the other the finishing cutter. The work
+arbor projects beyond the hub, as will be seen, and forms a pilot that
+steadies these cutter bars. The curved rim of the gear is turned to the
+required radius (preparatory to gashing and bobbing the worm-wheel
+teeth) by a formed tool _H_ held on the cross-slide.
+
+[Illustration: Fig. 21. Second Operation on Bevel Gear Blanks]
+
+=Turning Bevel Gear Blanks.=--Fig. 20 shows a plan view of the tools
+used for the first turning operation on bevel gear blanks (these gears
+are used for driving drill press spindles). The cored hole is beveled
+true at the end by flat drill _A_ to form a true starting surface for
+the three-fluted drill _B_ which follows. The hole is bored close to the
+required size by a tool (not shown) held in the end of bar _C_, and it
+is finished by reamer _D_. The cylindrical end of the gear blank or hub
+is rough-and finish-turned by tools held in holders _E_ and _F_,
+respectively. (These holders were made to set at an angle of 45 degrees,
+instead of being directly over the work, as usual, so that the cutters
+would be in view when setting up the machine.) It will be noted that the
+chuck is equipped with special jaws which fit the beveled part of the
+casting.
+
+[Illustration: Fig. 22. Sectional View of Tapering Mold Shell which is
+turned in Hartness Flat Turret Lathe, as illustrated in Figs. 23 to 27,
+Inclusive]
+
+The second and final operation on this blank is shown in Fig. 21. The
+work _A_ is held by a special driver plate attached to the faceplate of
+the machine. This driver plate has two pins which engage holes drilled
+in the gear blank and prevent it from rotating. The blank is also held
+by a bolt _B_ which forces a bushing against the cylindrical end. First,
+the broad beveled side which is to be the toothed part of the gear, is
+rough-turned by toothed cutters _C_, and a recess is formed in the end
+of the blank, by a turning tool in this same tool-holder. A similar
+tool-holder _E_, having finishing cutters, is then used to finish the
+bevel face and recess. The other tools seen in the turret are not used
+for this second operation. The rear bevel is roughed and finished by
+tools and held on the cross-slide.
+
+=Shell Turning Operation in Flat Turret Lathe.=--The "flat turret lathe"
+is so named because the turret is a flat circular plate mounted on a low
+carriage to secure direct and rigid support from the lathe bed. The
+tools, instead of being held by shanks inserted in holes in the turret,
+are designed so that they can be clamped firmly onto the low circular
+turret plate.
+
+An interesting example of flat turret lathe work is shown in Fig. 22.
+This is a steel shell which must be accurately finished to a slight
+taper, both inside and out, threaded and plain recesses are required at
+the ends, and, in addition, one or two minor operations are necessary.
+This work is done in the Hartness flat turret lathe, built by the Jones
+& Lamson Machine Co. The shells are turned from cold-drawn seamless
+steel tubing, having a carbon content of 0.20 per cent, and they are
+finished at the rate of one in nine minutes. The tubing comes to the
+machine in 12-foot lengths, and the tube being operated upon is, of
+course, fed forward through the hollow spindle as each successive shell
+is severed.
+
+[Illustration: Fig. 23. First Operation on Shell Illustrated in Fig.
+22--Rough-turning and Boring]
+
+In finishing this shell, five different operations are required. During
+the first operation the shell is rough-bored and turned by one passage
+of a box-tool, Fig. 23, and the recess _A_, Fig. 22, at the outer end,
+is finished to size by a second cutter located in the boring-bar close
+to the turret. The turret is then indexed to the second station which
+brings the threading attachment _G_ into position, as shown in Fig. 24.
+After the thread is finished, the recess _B_, Fig. 22, is turned by a
+flat cutter _K_, Fig. 25. The inner and outer surfaces are then finished
+to size by a box-tool mounted on the fourth station of the turret and
+shown in position in Fig. 26. The final operation, Fig. 27, is performed
+by three tools held on an auxiliary turret cross-slide, and consists in
+rounding the corners at _b_ and _c_, Fig. 22, and severing the finished
+shell.
+
+[Illustration: Fig. 24. Second Operation--Cutting Internal Thread]
+
+One of the interesting features connected with the machining of this
+shell is the finishing of the inner and outer tapering surfaces. The
+taper on the outside is 3/32 inch Per foot, while the bore has a taper
+of only 1/64 inch per foot, and these surfaces are finished
+simultaneously. The box-tool employed is of a standard type, with the
+exception of an inserted boring-bar, and the taper on the outside is
+obtained by the regular attachment which consists of a templet _D_ (Fig.
+23) of the required taper, that causes the turning tool to recede at a
+uniform rate as it feeds along. To secure the internal taper, the
+headstock of the machine is swiveled slightly on its transverse ways by
+the use of tapering gibs. By this simple method, the double taper is
+finished to the required accuracy without special tools or equipment.
+
+As those familiar with this machine know, the longitudinal movements of
+the turret as well as the transverse movements of the headstock are
+controlled by positive stops. The headstock of this machine has ten
+stops which are mounted in a revolving holder and are brought into
+position, as required, by manipulating a lever at the front. The stops
+for length, or those controlling the turret travel, are divided into two
+general groups, known as "A" and "B". Each of these groups has six stops
+so that there are two stops for each of the six positions or stations of
+the turret, and, in addition, five extra stops are available for any one
+tool, by the engagement of a pin at the rear of the turret. The change
+from the "A" to the "B" stops is made by adjusting lever _L_, Fig. 26,
+which also has a neutral position.
+
+[Illustration: Fig. 25. Third Operation--Turning Recess at Rear End;
+Tool is shown withdrawn]
+
+After the box-tool for the roughing cut, shown at work in Fig. 23, has
+reached the end of its travel, further movement is arrested by a stop of
+the "A" group. The outside turning tool is then withdrawn by operating
+lever _E_ and the turret is run back and indexed to the second station,
+thus bringing the threading attachment into position. The surface speed
+of 130 feet per minute which is used for turning is reduced to about 30
+feet per minute for threading by manipulating levers _H_, Fig. 24. After
+the turret is located by another stop of the "A" group, the threading
+attachment is made operative by depressing a small plunger _I_, which
+connects a vertical driving shaft from the spindle with the splined
+transmission shaft _J_. A reciprocating movement is then imparted to the
+thread chaser _t_ which advances on the cutting stroke and then
+automatically retreats to clear the thread on the return. This movement
+is repeated until the thread is cut to the proper depth, as determined
+by one of the stops for the headstock. While the thread is being cut,
+the carriage is locked to the bed by the lever _N_, Fig. 26. It was
+found necessary to perform the threading operation before taking the
+outside finishing cut, owing to a slight distortion of the shell wall,
+caused by the threading operation.
+
+[Illustration: Fig. 26. Fourth Operation--Finishing the Bore and
+Outside]
+
+After the thread is finished, the turret is turned to the third station
+as shown in Fig. 25, and tool _K_ for the inner recess _B_, Fig. 22, is
+brought into position and fed to the proper depth, as determined by
+another cross-stop. The turret is also locked in position for this
+operation. The finishing cuts for the bore and the outside are next
+taken by a box-tool which is shown near the end of its cut in Fig. 26.
+This box-tool is similar to the one used for roughing, but it is
+equipped with differently shaped cutters to obtain the required finish.
+The outside turning tool has a straight cutting edge set tangent to the
+cylindrical surface and at an angle, while the boring tool has a cutting
+edge of large radius. An end view of this box-tool is shown in Fig. 27.
+A reduced feed is employed for the finishing cut, and the speed is
+increased to 130 feet per minute, which is the same as that used for
+roughing.
+
+[Illustration: Fig. 27. Fifth Operation--Rounding Ends, Scoring Large
+End, and Cutting Off]
+
+During the next and final operation, the turret, after being indexed to
+the position shown in Fig. 27, is first located by a stop of the "A"
+group so that the cutting-off tool _R_ in front can be used for rounding
+the corner _b_, Fig. 22. The stop lever _L_ is then shifted and the
+turret is moved to a second stop of the "B" group. The corner _c_ is
+then rounded and the shell is scored at _d_ by two inverted tools _S_
+and _T_ at the rear, after which the finished work is severed by the
+cut-off tool at the front. The cross-movement of these three tools is
+controlled by positive stops on the cross-slide, and the latter is moved
+to and fro by hand lever _O_. After the shell is cut off, the stop _M_,
+mounted on the turret, Fig. 26, is swung into position, and the tube is
+automatically fed forward to the swinging stop by the roll feed, as soon
+as the chuck is released by operating lever _Q_. This completes the
+cycle of operations. A copious supply of lubricant is, of course,
+furnished to the tools during these operations, and the two boring-tool
+shanks are hollow so that lubricant can be forced through them and be
+made to play directly upon the cutters.
+
+=Chuck Work in Flat Turret Lathe.=--Two examples of chuck work on the
+Acme combination flat turret lathe are shown in Figs. 28 and 29. Fig. 28
+shows the tool equipment for turning a cylindrical part _A_ which is
+held in a three-jaw universal chuck. The front flange is first
+rough-turned by a bent turning tool _B_. The diameter is regulated by
+one of the cross-stops at _D_ which has been previously set and controls
+the movement of the turret cross-slide. The longitudinal feed is
+disengaged when the flange has been turned, by an independent stop. This
+machine has twelve longitudinal stops, there being one for each turret
+face and six auxiliary stops, in addition to the stops for the
+cross-slide.
+
+[Illustration: Fig. 28. Tool Equipment for Turning Scroll Gear Blank on
+Acme Flat Turret Lathe]
+
+After roughing the flange, the turret carriage is locked or clamped
+rigidly to the bed to prevent any lengthwise movement, and the back face
+of the front flange is rough-turned by tool _B_ in to the diameter of
+the hub which is indicated by a micrometer dial on the cross-feed screw.
+The carriage is then unlocked and auxiliary stop No. 7 is engaged (by
+turning a knob at the front of the slide) and the cylindrical hub is
+turned back to the rear flange, the feed being disengaged by the
+auxiliary stop just as the tool reaches the flange. The cross-slide is
+now moved outward, longitudinal auxiliary stop No. 8 is engaged, the
+turret slide is moved against the stop, the carriage is locked and the
+front sides of both the front and rear flanges are rough-faced by tools
+_B_ and _C_. The turret is next indexed and the hole rough-bored by
+cutter _E_. After again indexing the turret, the hub and flanges are
+finish-turned and faced by tools _F_ and _G_, as described for the
+rough-turning operation. The final operation is that of finishing the
+bore by cutter _H_.
+
+[Illustration: Fig. 29. Acme Flat Turret Lathe Arranged for Turning
+Roller Feed Body]
+
+The operation shown in Fig. 29 is that of turning the body of a roller
+feed mechanism for a turret lathe. The casting is held in a three-jaw
+universal chuck and it is first rough-bored by tool _A_. The turret is
+then indexed and the side of the body and end of the hub are rough-faced
+by tools at _B_. The turret is again indexed for rough-turning the
+outside of the hub and body, by tools _C_ and _D_. Similar tools _E_
+and _F_ are then used to finish these same surfaces, after which the end
+of the hub and side of the body are finished by tools _G_ and _H_
+similar to those located at _B_. The final operation is that of
+finishing the bore by tool _J_ and cutting a groove in the outside of
+the hub by the bent tool _K_.
+
+[Illustration: Fig. 30. Turret and Head of Jones & Lamson Double-spindle
+Flat Turret Lathe]
+
+=Double-spindle Flat Turret Lathe.=--The extent to which modern turning
+machines have been developed, especially for turning duplicate parts in
+quantity, is illustrated by the design of turret lathe the turret and
+head of which is shown in Fig. 30. This machine has two spindles and a
+large flat turret which holds a double set of tools, so that two
+duplicate castings or forgings can be turned at the same time. It was
+designed primarily for chuck work and can be used as a single-spindle
+machine if desirable. When two spindles are employed for machining two
+duplicate parts simultaneously, considerably more time is required for
+setting up the machine than is necessary for the regular single-spindle
+type, but it is claimed that the increased rate of production obtained
+with the two-spindle design more than offsets this initial handicap.
+The manufacturers consider the single-spindle machine the best type for
+ordinary machine building operations, regardless of whether the work is
+turned from the bar or is of the chucking variety. On the other hand,
+the double-spindle type is preferred when work is to be produced in such
+quantities that the time for setting up the machine becomes a secondary
+consideration.
+
+[Illustration: Fig. 31. Diagram showing Tool Equipment and Successive
+Steps in Machining Sprocket Blanks on Double-spindle Flat Turret Lathe]
+
+When the double-spindle machine is used as a single-spindle type, a
+chuck 17 inches in diameter is used, and when both spindles are in
+operation, two 9-inch chucks are employed. The general outline of the
+turret is square, and the tools are rigidly held, with a minimum amount
+of overhang, by means of tool-blocks and binding screws connected with
+the clamping plates. Two duplicate sets of tools are clamped to each
+side of the turret and these operate simultaneously on the two pieces
+held in the chucks or on faceplates. Primarily the turret is used in
+but four positions, but when a 17-inch chuck or faceplate is employed,
+corner blocks may be held by the clamping plates in which tools are
+supported, giving, if necessary, four additional operations by indexing
+the turret to eight positions.
+
+A typical job to demonstrate the application of the double-spindle flat
+turret lathe is illustrated in Fig. 31. The parts to be turned are
+sprocket wheels which are held in the two 9-inch chucks. At the first
+position of the turret (which is the one illustrated), the inside is
+rough-bored by tools _A_. At the second position of the turret, tools
+_B_ rough-face the inner sides of the flanges; tools _C_ face the outer
+sides of the flanges, while tools _D_ turn the faces of the flanges. At
+the third position of the turret, tools _E_ finish-turn the inside of
+the flanges; tools _F_ finish-turn the outside of the flanges, while
+tools _G_ finish the faces of the flanges. At the fourth position of the
+turret, tools _H_ finish-bore the sprockets; tools _I_ complete the
+turning on the outside of the flanges, while tools _J_ accurately size
+the interior of the flanges.
+
+With the double-spindle flat turret lathe, each operation is a double
+operation, and the speeds are varied according to the nature of the cut;
+thus, if at one position of the turret, the tools are required to rough
+out the work, this may be done rapidly, for it has no bearing on the
+other operations that are subsequently performed. Furthermore, if the
+following operation has to be performed with great care, this may be
+done without reducing the speed of the less exacting operations.
+
+[Illustration: Fig. 32. Potter & Johnston Automatic Chucking and Turning
+Machine]
+
+=Automatic Chucking and Turning Machine.=--The chucking and turning
+machine shown in Fig. 32 is automatic in its operation, the feeding of
+the tools, indexing of the turret, etc., being done automatically after
+the machine is properly arranged, and the work is placed in the chuck.
+This machine is adapted to turning and boring a great variety of
+castings, forgings or parts from bar stock, and it is often used in
+preference to the hand-operated turret lathe, especially when a great
+many duplicate parts are required. It is provided with mechanism for
+operating the cross-slide, feeding the turret slide forward, returning
+it rapidly, rotating the turret to a new position, and feeding it
+forward quickly for taking a new cut. The cross-slide and turret-slide
+movements are effected by cams mounted on the large drum _E_ seen
+beneath the turret, while the various speed and feed changes are
+effected by dogs and pins carried on disk _D_ which is keyed to the same
+shaft that the cam drum is mounted upon. This shaft with the cam drum
+and governing disk _D_, makes one revolution for each piece of work
+completed. The cams for operating the turret slide are mounted upon the
+periphery of drum _E_. The roll which engages the angular faces of these
+cams and imparts movement to the turret is carried by an intermediate
+slide which has rack teeth engaging a pinion on the square shaft _C_. By
+turning this shaft with a crank, the position of the turret-slide, with
+relation to the cam, may be adjusted for long or short work and long or
+short tools, as may be required.
+
+[Illustration: Fig. 33. Rear View of Machine showing the Cross-slide
+Mechanism, Driving Gearing, etc.]
+
+The cams which operate the cross-slide are mounted on the right-hand end
+of drum _E_ and actuate the yoke _A_ (see Fig. 33) which extends
+diagonally upward. The rear end of this yoke has rack teeth meshing with
+the teeth of a segmental pinion, which is fastened to rock-shaft _B_.
+At the headstock end, this rock-shaft carries another segmental pinion
+meshing with rack teeth formed on the cross-slide. The movement imparted
+to the yoke by the cams is thus transmitted through the pinions and
+rock-shaft to the cross-slide.
+
+[Illustration: Fig. 34. The Automatic Controlling Mechanism for Feeds
+and Speeds]
+
+The cam drum _E_ is driven by a pinion meshing with a gear attached to
+its front side. This pinion is driven through a train of gearing from
+pulley _L_ (see Fig. 34) which is belted to the spindle. The feeds are
+thus always dependent on the spindle speed. By means of epicyclic
+gearing and suitable clutches, the motion thus derived from the spindle
+may be made rapid for returning the turret to be indexed and then
+advancing it to the cutting position again, or very slow for the forward
+feed when the tools are at work. These changes from slow to fast or
+_vice versa_ are controlled by disk _D_. This disk carries pins which
+strike a star wheel located back of the disk at the top, and as this
+star wheel is turned, the speeds are changed by operation of the gearing
+and clutches referred to. The first pin _M_ that strikes the star wheel
+advances it one-sixth of a rotation, changing the feed from fast to
+slow; the next pin that strikes it advances it another sixth of a
+rotation, changing the feed from slow to fast and so on. By adjusting
+the pins for each piece of work, the feed changes are made to take place
+at the proper time. Handwheel _E_ is geared with the cam-shaft on which
+the star wheel is mounted, so that the feeds may be changed by hand if
+desired.
+
+In addition to these feed-changing pins, disk _D_ has a dog which
+operates a lever by which the feed movement is stopped when the work has
+been completed. Four rates of feed are provided by quick change gearing
+of the sliding gear type, operated by handle _K_. With this handle set
+in the central position, the feed is disengaged. On the periphery of
+disk _D_ are also clamped dogs or cams _N_, which operate a horizontal
+swinging lever _P_ connected by a link with vertical lever _J_, which
+controls the two spindle speeds with which the machine is provided.
+Either one of these speeds can be automatically engaged at any time, by
+adjusting the cams _N_ on disk _D_.
+
+Lever _H_ connects or disconnects the driving pulley from the shaft on
+which it is mounted, thus starting or stopping the machine. The square
+shaft _G_ serves to operate the drums by hand and is turned with a
+crank. The rotation of the turret, which takes place at the rear of its
+travel, is, of course, effected automatically. A dog, which may be seen
+in Fig. 32 at the side of the bed, is set to trip the turret revolving
+mechanism at the proper point in the travel, to avoid interference
+between the tools and the work. The turret is provided with an automatic
+clamping device. The mechanism first withdraws the locking pin, unclamps
+the turret, revolves it, then throws in the locking pin and clamps the
+turret again.
+
+=Example of Work on Automatic Turning Machine.=--The piece selected for
+illustrating the "setting up" and operation of the automatic chucking
+and turning machine is shown in Fig. 35. This is a second operation, and
+a very simple one which will clearly illustrate the principles involved.
+In the first operation, the hole was drilled, bored and reamed, the
+small end of the bushing faced, and the outside diameter finished, as
+indicated by the sketch to the left. (The enlarged diameter at the end
+was used for holding the work in the chuck.) In the second operation
+(illustrated to the right), the enlarged chucking end is cut off and, in
+order to prevent wasting this piece, it is made into a collar for
+another part of the machine for which the bushing is intended; hence,
+the outside diameter is turned and the outside end faced, before cutting
+off the collar. In addition, the bushing is recessed in the second
+operation, and the outer end faced. In order to have the surfaces
+finished in the second operation, concentric with those machined in the
+first operation, the chuck is equipped with a set of soft "false jaws"
+which have been carefully bored to exactly the diameter of the work to
+be held.
+
+[Illustration: Fig. 35. Simple Example of Work done in Automatic
+Chucking and Turning Machine]
+
+The first thing to determine when setting up a machine of this type is
+the order of operations. In this particular case, the order is as
+follows: At the first position of the turret, the outside collar is
+rough-turned and the outer end rough-faced. At the second position, the
+collar is turned to the required diameter and the outer face is
+finished. The third face of the turret is not equipped with tools, this
+part of the cycle being taken up in cutting off the collar with a
+cut-off tool on the rear cross-slide. The fourth operation is that of
+recessing the bushing, and the fifth operation, facing the end to remove
+the rough surface left by the cutting-off tool.
+
+The tools _A_ and _B_, Fig. 36, used for turning the outside of the
+flange, are held in brackets _C_ bolted to the face of the turret.
+These brackets are each provided with three holes for carrying turning
+tool-holders. This arrangement provides for turning a number of
+diameters at different positions, simultaneously, but for this
+particular operation, a single cutting tool for each tool-holder is all
+that is necessary. A special device is used for recessing and will be
+described later.
+
+[Illustration: Fig. 36. Front View of Machine set up for the Finishing
+Operation on the Recessed Bushing and Collar shown in the Foreground and
+in Fig. 35]
+
+=Determining Speed and Feed Changes.=--As previously mentioned, the
+particular machine illustrated in Fig. 32 can be arranged for two
+automatic changes of speed to suit different diameters on the work. The
+change gears that will give the required spindle speeds should first be
+selected. These change gears for different speeds are listed on a speed
+and feed plate attached to the headstock of the machine (see Fig. 37).
+It is possible to use one speed from the list given for the fast train
+of gears, and one from the list for the slow train, so long as the same
+gears are not used in each case. The diameter of the collar on the work
+shown in Fig. 35 is 2-1/2 inches, and the diameter of the body is 2
+inches. Assuming that the surface speed for this job should be about 40
+feet per minute, a little calculation shows that the 66 revolutions per
+minute, given by the fast train of gears, is equivalent to a surface
+speed of 43 feet per minute on a diameter of 2-1/2 inches. Moreover, the
+78 revolutions per minute obtained from the slow train of gearing, gives
+about 41 feet per minute on a diameter of 2 inches. The spindle gearing
+indicated for these speeds is, therefore, placed in position on the
+proper studs at the back of the machine.
+
+[Illustration: Fig. 37. Plate on the Headstock of Machine Illustrated in
+Fig. 32 giving the Speeds and Feeds]
+
+Next we have to determine on which faces of the turret to place the
+different tools. Each turret face is numbered to agree with the
+corresponding feed cam on the drum. The speed and feed plate (Fig. 37)
+gives the various feeds obtainable per revolution of the spindle. As
+will be seen, the different cams give different feeds. Cam No. 1 has a
+coarse feed suitable for roughing; cam No. 2 a finer feed adapted to
+finishing, and so on. Since the first operation consists in
+rough-turning, cam No. 1 is used. Cam No. 2, which gives a finer feed,
+is used for the finish-turning operation. Cam No. 4, which is ordinarily
+used for reaming, could, in this case, be used for recessing, as this
+recess is for clearance only and may be bored with a coarse feed.
+
+The final operation, which is that of facing, can be done with any cam
+and cam No. 5 may be used. It will be understood that for facing
+operations, the feeds given do not apply. As the roll passes over the
+point of the feed cam at the extreme end of the movement, the feed of
+the turret slide is gradually slowed down to zero; since the facing
+takes place in the last eighth or sixteenth inch of this movement, it is
+done at a feed which is gradually reduced to zero. This is, of course,
+as it should be, and it is not necessary to pay any attention to the
+tabulated feeds in facing operations.
+
+=Setting the Turret Slide.=--The next adjustment is that of setting the
+turret slide. In making this adjustment the turret is set in such
+relation to the work that the tools will have but a small amount of
+overhang, the cam-shaft being revolved by hand until the cam-roll is at
+the extreme top of the forward feeding cam, so that the turret slide is
+at the extreme of its forward movement. When this adjustment has been
+made by the means provided, set the turret index tripping dog so as to
+revolve the turret at the proper point. After a turning tool-holder and
+tool is attached to the face of the turret, cam No. 1 is placed in its
+operating position and is revolved by hand until the roll is on the
+point of the cam and the turret at the forward extreme of its motion. At
+this point the tool-holder is set so that the cutter will be far enough
+forward to complete its turning operation. The feed cam is then turned
+backward, thus returning the turret slide, and the cutter is set to turn
+the flange to the proper diameter for the roughing cut. The turret slide
+is fed forward and back while the cutter is adjusted, and when it is
+properly set, the flange is turned, the cam-drum being fed by hand. This
+is the first trial cut on the piece.
+
+A facing tool, shown in the working position in Fig. 36, is placed at
+this station of the turret, being held in the turret hole. This tool has
+a pilot bar and a holder which contains a facing blade. Feeding by hand,
+as before, the tool is adjusted lengthwise so as to rough-face the work
+to the dimension desired. In a similar way the finish-turning and
+facing tools for the second position of the turret are set, the
+cam-shaft being revolved by hand to bring this second face and second
+cam into the working position. (The finish-facing tool is not shown in
+place in Fig. 36.)
+
+[Illustration: Fig. 38. Diagram of Cross-slide Cams and Feeding
+Mechanism]
+
+=Setting the Cross-slide Cam.=--As previously mentioned, the third
+turret face has no tool, the cutting off of the collar being done during
+this part of the cycle of operations. It has been taken for granted that
+in setting the turret slide, room has been left between it and the chuck
+for the cross-slide. The cross-slide is clamped in a longitudinal
+position on the bed, convenient for the cutting-off operation, which is
+done with a tool _D_ (Fig. 36) in the rear toolpost, thus leaving the
+front unobstructed for the operator. When both forming and cutting off
+are to be done, the forming tool is generally held at the front and the
+cutting-off tool at the back because heavier and more accurate forming
+can be done with the work revolving downward toward a tool in the front
+toolpost, than with the tool at the rear where it is subjected to a
+lifting action.
+
+The arrangement of the cross-slide cams is shown in Fig. 38, which is an
+end view of the large drum _E_, Fig. 32. The rear feed cam is the one to
+be used, and since this cutting-off operation is a short one, it may be
+done during the return of the turret for position No. 3. The cam drum
+is, therefore, rotated by hand until the turret face No. 3 has begun to
+return. The cross-slide cams are then loosened and the rear feed cam is
+swung around to just touch the roller _R_ which operates arm _A_, the
+cross-slide having been adjusted out to nearly the limit of its forward
+travel, leaving approximately enough movement for cutting off the
+collar. The rear feed cam is then clamped in this position.
+
+A cutting-off tool is next placed in the rear toolpost at the proper
+height. The rear toolpost slide is then adjusted to bring the point of
+the cutting-off tool up to the work, and the cam drum is revolved by
+hand until the piece is cut off. The cross-slide tool is, of course, set
+in the proper position to make a collar of the required thickness.
+Feeding by hand is discontinued when the roll is on the point of the
+cam; the cutting-off tool slide is then permanently set on the
+cross-slide so that the point of the cutting-off tool enters the bore
+just far enough to completely sever the collar from the bushing. The
+motion of the cam drum is continued, by hand, until the roll is over the
+point of the feed cam. The cross-slide is then pushed back, by hand,
+until the cam and roll are again in contact, when the return cam is
+brought up and clamped in position, so that there is just room for the
+roll between the feed cam and the return cam. The rear return cam (as
+the hand feed of the cam drum is continued) brings the cross-slide back
+to its central position. Since there is no front tool used for this
+series of operations (although a tool is shown in the front toolpost,
+Fig. 36), the first feed and return cams are allowed to remain wherever
+they happen to be. These cam adjustments can all be made from the front
+of the machine.
+
+=Setting the Boring Tool for Recessing.=--The feeding of the turret
+slide is now continued to make sure that the cutting-off tool is
+returned to its normal position before the facing tool in the next face
+of the turret begins to work. The facing of the bushing, so far as the
+setting of the tool is concerned, is merely a repetition of the facing
+operation at the first position of the turret. The recessing tool is
+next set. This tool, which is shown diagrammatically in Fig. 39, is very
+simple as compared with the somewhat complex operation it has to
+perform. This recess is for clearance only, and accurate dimensions and
+fine finish are not necessary. The recessing tool consists simply of a
+slender boring-bar held in the turret and carrying a cutter suitably
+located about midway the bar. The forward end of the bar is small enough
+to enter a bell-mouthed bushing held in the chuck. The boring-bar is
+bent to one side far enough so that the cutter clears the hole as the
+bar enters, but is forced into the work as the rounded hole of the
+bushing engages the end of the bar and deflects it into the working
+position. The upper diagram shows the position of the bar as it enters
+the hole, and the lower one the position after it has entered the
+bushing and is engaged in turning the recess. This bar is set in the
+turret so that at the extreme forward travel of the turret slide, the
+recess will be bored to the required length. The cutter must also be
+adjusted to bore to the desired diameter. This completes the setting of
+the cutting tools.
+
+[Illustration: Fig. 39. Flexible Boring Tool used for Recessing a
+Bushing in Automatic Chucking and Turning Machine]
+
+=Adjustments for Automatic Feed and Speed Changes.=--The machine must
+now be set to perform automatically the desired changes of spindle speed
+and the fast and slow cam movements for the tools. After placing a new
+piece of work in the machine (the first one having been completed in the
+setting-up operation), the cam-shaft is revolved by hand until the
+turning tool in turret face No. 1 is just about to begin its cut. The
+control wheel _D_, Fig. 34, is rotated in its normal direction until the
+next graduation marked "slow" is in line with an index mark on the base
+of the machine. Then the nearest pin _M_ is moved up until it bears
+against a tooth of the star wheel (previously referred to) and is
+clamped in this position. The pin should now be in the proper location,
+but to test its position, rotate the cam shaft backward by hand and
+throw in the automatic feed; then watch the cut to see if the drum slows
+down just before the tool begins to work. If it does not, the pin should
+be adjusted a little, one way or the other, as may be required. (In
+going over a piece of work for the first time, it is best to have the
+feed set to the smallest rate, feed change handle _K_ being in position
+No. 1.)
+
+After the cut has been completed and the turret feed cam-roll is on the
+high part of the cam, the power feed should again be stopped and the
+handwheel revolved until the next graduation marked "fast" is opposite
+the index mark. The next stop pin is then moved up until it just touches
+the star wheel, where it is clamped in position. The feed being again
+thrown in, the turret will be returned rapidly, indexed, and moved
+forward for the second operation. After stopping the automatic movement,
+the pins are set for this face, and so on for all the operations,
+including that in which the cross-slide is used for cutting off the
+finished collar.
+
+As the first, second, and third operations are on comparatively large
+diameters, they should be done at the slow speed, handle _J_, Fig. 34,
+being set to give that speed. While the turret slide is being returned
+between operations 3 and 4, one of the spindle speed-changing dogs _N_
+should be clamped to the rim of disk _D_ so as to change the spindle
+speed to the fast movement. This speed is continued until the last
+operation is completed, when a second dog is clamped in place to again
+throw in the slow movement. The feed knock-off dog should also be
+clamped in place on the disk to stop the machine at the completion of
+the fifth operation, when the turret is in its rear position. This
+completes the setting up of the machine. If the feed is finer than is
+necessary, the feed change handle _K_ may now be moved to a position
+which will give the maximum feed that can be used.
+
+It has taken considerable time to describe the setting up of the machine
+for this simple operation, but in the hands of a competent man it can be
+done quite rapidly. While a simple operation has been referred to in the
+foregoing, it will be understood that a great variety of work can be
+done on a machine of this type. It is not unusual to see as many as ten
+cutting tools operating simultaneously on a piece of work, the tools
+being carried by the turret, cross-slide and back facing attachment. The
+latter is operated from a separate cam applied to the cam-shaft and
+acting through levers on a back facing bar which passes through a hole
+in the spindle. In this back facing bar may be mounted drills, cutters,
+facing tools, etc. for machining the rear face of a casting held in the
+chuck jaws. Where extreme accuracy is required, a double back facing
+attachment may be used, arranged with cutters for taking both roughing
+and finishing cuts. The use of this attachment often saves a second
+operation. This automatic chucking and turning machine is also adapted
+for bar work, especially in diameters varying from 3 to 6 inches.
+
+=Turning Flywheel in Automatic Chucking and Turning Machine.=--A typical
+operation on the Potter & Johnston automatic chucking and turning
+machine is illustrated in Fig. 40, which shows the machine arranged for
+turning the cast-iron flywheel for the engine of a motor truck. The rim
+is turned and faced on both sides and the hub is bored, reamed and faced
+on both sides. The flywheel casting is held in a chuck by three special
+jaws which grip the inside of the rim. The order of the operations is as
+follows:
+
+The rear end of the hub is faced by the back facing bar; the cored hole
+is started by a four-lipped drill in the turret and the front end of the
+hub is rough-faced. (These tools are on the rear side of the turret
+when the latter is in the position shown in the illustration.) After the
+turret indexes, the hole is rough-bored by tool _A_ and while this is
+being done, the outside of the rim is rough-turned by tool _B_ held in a
+special bracket attached to the turret. Both sides of the rim are also
+rough-faced by tools _C_ and _D_ held at the front of the cross-slide,
+this operation taking place at the same time that the rim is turned and
+the hole is being bored.
+
+[Illustration: Fig. 40. Machining Flywheels in Potter & Johnston
+Automatic Chucking and Turning Machine]
+
+The turret again automatically recedes and indexes, thus locating bar
+_E_ and turning tool _G_ in the working position. The hole is then
+finish-bored by tool _E_ and the hub is finish-faced by blade _F_; at
+the same time the rim is finish-turned by tool _G_ and the sides are
+finish-faced to the proper width by two tools held at the rear of the
+cross-slide. The turret automatically recedes and indexes a third time,
+thus locating the flat-cutter reamer-bar _H_ in the working position and
+then the hole is reamed to the required diameter. This completes the
+cycle of operations. The total time for machining this flywheel is forty
+minutes.
+
+=Automatic Multiple-spindle Chucking Machine.=--An example of the
+specialized machines now used for producing duplicate parts, is shown in
+Fig. 41. This is a "New Britain" automatic multiple-spindle chucking
+machine of the single-head type and it is especially adapted for boring,
+reaming and facing operations on castings or forgings which can readily
+be held in chuck jaws. This particular machine has five spindles, which
+carry and revolve the tools. The work being machined is held stationary
+in the multiple chuck turret _A_ which holds each part in line with one
+of the spindles and automatically indexes, so that the work passes from
+one spindle to another until it is finished. The turret then indexes the
+finished piece to a sixth or "loading position" which is not opposite a
+spindle, where the part is removed and replaced with a rough casting.
+Each pair of chuck jaws is operated independently of the others by the
+use of a chuck wrench. These jaws are made to suit the shape of the
+work.
+
+[Illustration: Fig. 41. New Britain Multiple-spindle Automatic Chucking
+Machine of Single-head Type]
+
+When a single-head machine is in operation, the turret advances and
+feeds the work against the revolving tools so that a number of pieces
+are operated upon at the same time. The turret is fed by a cam drum _B_.
+Cam strips are bolted to the outside of this drum and act directly
+against a roller attached to the yoke _C_ which can be clamped in
+different positions on the spindle _D_, the position depending upon the
+length of the work. On the opposite end of the turret spindle is the
+indexing mechanism _E_. An automatically spring-operated latch _F_
+engages notches in the rim of the dividing wheel, thus accurately
+locating the turret. The turret is locked by a steadyrest _G_, which,
+for each working position, automatically slides into engagement with one
+of the notches in the turret. This relieves the indexing mechanism of
+all strain.
+
+[Illustration: Fig. 42. Detail View of New Britain Double-head
+Eight-spindle Machine, Boring, Reaming and Facing Castings]
+
+This type of machine is also built with two spindle heads, the
+double-head design being used for work requiring operations on both
+ends. When the double-head machine is in operation, the revolving
+spindles and tools advance on both sides of the chuck turret, the latter
+remaining stationary except when indexing. The feed drums on the
+double-head machine are located directly beneath each group of spindles.
+
+Fig. 42 shows an example of work on a machine of the double-head design.
+This is an eight-spindle machine, there being two groups of four
+spindles on each side of the turret. The castings _E_ are for the wheel
+hubs of automobiles. The order of the operations on one of the castings,
+as it indexes around, is as follows: The hole in the hub is first
+rough-reamed by taper reamer _A_ and the opposite end of the hub is
+rough-faced and counterbored by a tool in spindle _A_{1}_. When the
+turret indexes, this same casting is reamed close to the finished size
+by reamer _B_ and the left end of the hub is rough-faced by cutter _F_,
+while a tool in the opposite spindle _B_{1}_ finishes the counterboring
+and facing operation. At the third position, reamer _C_ finishes the
+hole accurately to size, and when the work is indexed to the fourth
+position, the hub on the left side is finish-faced by a tool in spindle
+_D_. (The third and fourth spindles of the right-hand group are not used
+for this particular operation.) When the turret again indexes, the
+finished casting is removed and replaced with a rough one. While the
+successive operations on a single casting have just been described, it
+will be understood that all of the tools operate simultaneously and that
+a finished casting arrives at the unloading and loading position each
+time the turret indexes. Three hundred of these malleable castings are
+machined in nine hours.
+
+=Selecting Type of Turning Machine.=--The variety of machine tools now
+in use is very extensive, and as different types can often be employed
+for the same kind of work, the selection of the best and most efficient
+machine is often a rather difficult problem. To illustrate, there are
+many different types and designs of turning machines, such as the
+ordinary engine lathe, the hand-operated turret lathe, the
+semi-automatic turning machine, and the fully automatic type, which,
+after it is "set up" and started, is entirely independent. Hence, when a
+certain part must be turned, the question is, what kind of machine
+should be used, assuming that it would be possible to employ several
+different machines? The answer to this question usually depends
+principally upon the number of parts that must be turned.
+
+For example, a certain casting or forging might be turned in a lathe,
+which could be finished in some form of automatic or semi-automatic
+turning machine much more quickly. It does not necessarily follow,
+however, that the automatic is the best machine to use, because the
+lathe is designed for general work and the part referred to could
+doubtless be turned with the regular lathe equipment, whereas the
+automatic machine would require special tools and it would also need to
+be carefully adjusted. Therefore, if only a few parts were needed, the
+lathe might be the best tool to use, but if a large number were
+required, the automatic or semi-automatic machine would doubtless be
+preferable, because the saving in time effected by the latter type would
+more than offset the extra expense for tool equipment and setting the
+machine. It is also necessary, in connection with some work, to consider
+the degree of accuracy required, as well as the rate of production, and
+it is because of these varying conditions that work of the same general
+class is often done in machines of different types, in order to secure
+the most efficient results.
+
+
+
+
+CHAPTER VI
+
+VERTICAL BORING MILL PRACTICE
+
+
+All the different types of turning machines now in use originated from
+the lathe. Many of these tools, however, do not resemble the lathe
+because, in the process of evolution, there have been many changes made
+in order to develop turning machines for handling certain classes of
+work to the best advantage. The machine illustrated in Fig. 1 belongs to
+the lathe family and is known as a vertical boring and turning mill.
+This type, as the name implies, is used for boring and turning
+operations, and it is very efficient for work within its range. The part
+to be machined is held to the table _B_ either by clamps or in chuck
+jaws attached to the table. When the machine is in operation, the table
+revolves and the turning or boring tools (which are held in tool-blocks
+_T_) remain stationary, except for the feeding movement. Very often more
+than one tool is used at a time, as will be shown later by examples of
+vertical boring mill work. The tool-blocks _T_ are inserted in tool-bars
+_T_{1}_ carried by saddles _S_ which are mounted on cross-rail _C_. Each
+tool-head (consisting of a saddle and tool-bar) can be moved
+horizontally along cross-rail _C_, and the tool-bars _T_{1}_ have a
+vertical movement. These movements can be effected either by hand or
+power.
+
+When a surface is being turned parallel to the work table, the entire
+tool-head moves horizontally along the cross-rail, but when a
+cylindrical surface is being turned, the tool-bar moves vertically. The
+tool-heads are moved horizontally by the screws _H_ and _H_{1}_, and the
+vertical feed for the tool-bars is obtained from the splined shafts _V_
+and _V_{1}_, there being a separate screw and shaft for each head so
+that the feeding movements are independent. These feed shafts are
+rotated for the power feed by vertical shafts _A_ and _A_{1}_ on each
+side of the machine.
+
+These vertical shafts connect with the feed shafts through bevel and
+spur gears located at the ends of the cross-rail. On most boring mills,
+connection is made with one of the splined shafts _V_ or screw _H_, by a
+movable gear, which is placed on whichever shaft will give the desired
+direction of feed. The particular machine illustrated is so arranged
+that either the right or left screw or feed shaft can be engaged by
+simply shifting levers _D_{1}_ or _D_.
+
+[Illustration: Fig. 1. Gisholt Vertical Boring and Turning Mill]
+
+The amount of feed per revolution of the table is varied for each
+tool-head by feed-changing mechanisms _F_ on each side of the machine.
+These feed boxes contain gears of different sizes, and by changing the
+combinations of these gears, the amount of feed is varied. Five feed
+changes are obtained on this machine by shifting lever _E_, and this
+number is doubled by shifting lever _G_. By having two feed boxes, the
+feeding movement of each head can be varied independently. The direction
+of either the horizontal or vertical feed can be reversed by lever _R_,
+which is also used for engaging or disengaging the feeds. This machine
+is equipped with the dials _I_ and _I_{1}_ which can be set to
+automatically disengage the feed at any predetermined point. There are
+also micrometer dials graduated to thousandths of an inch and used for
+adjusting the tools without the use of measuring instruments.
+
+The work table _B_ is driven indirectly from a belt pulley at the rear,
+which transmits the power through gearing. The speed of the table can be
+varied for turning large or small parts, by levers _J_ and _K_ and the
+table can be started, stopped or rotated part of a revolution by lever
+_L_ which connects with a friction clutch. There are corresponding feed
+and speed levers on the opposite side, so that the machine can be
+controlled from either position.
+
+The heads can be adjusted along the cross-rail for setting the tools by
+hand-cranks _N_, and the tool slides can be moved vertically by turning
+shafts _V_ with the same cranks. With this machine, however, these
+adjustments do not have to be made by hand, ordinarily, as there are
+rapid power movements controlled by levers _M_. These levers
+automatically disengage the feeds and enable the tool-heads to be
+rapidly shifted to the required position, the direction of the movement
+depending upon the position of the feed reverse lever _R_ and lever _D_.
+This rapid traverse, which is a feature applied to modern boring mills
+of medium and large size, saves time and the labor connected with hand
+adjustments. The cross-rail _C_ has a vertical adjustment on the faces
+of the right and left housings which support it, in order to locate the
+tool-heads at the right height for the work. This adjustment is effected
+by power and is controlled by levers at the sides of the housings.
+Normally, the cross-rail is bolted to the housings, and these bolts must
+be loosened before making the adjustment, and must always be tightened
+afterwards.
+
+The function of these different levers has been explained to show, in a
+general way, how a vertical boring machine is operated. It should be
+understood, however, that the arrangement differs considerably on
+machines of other makes. The construction also varies considerably on
+machines of the same make but of different size.
+
+[Illustration: Fig. 2. Small Boring and Turning Mill with Single
+Turret-head]
+
+All modern vertical boring mills of medium and large sizes are equipped
+with two tool-heads, as shown in Fig. 1, because a great deal of work
+done on a machine of this type can have two surfaces machined
+simultaneously. On the other hand, small mills of the type illustrated
+in Fig. 2 have a single head. The toolslide of this machine, instead of
+having a single tool-block, carries a five-sided turret _T_ in which
+different tools can be mounted. These tools are shifted to the working
+position as they are needed, by loosening binder lever _L_ and turning
+or "indexing" the turret. The turret is located and locked in any of its
+five positions by lever _I_, which controls a plunger that engages
+notches at the rear. Frequently, all the tools for machining a part can
+be held in the turret, so that little time is required for changing from
+one tool to the next. Some large machines having two tool-heads are also
+equipped with a turret on one head.
+
+=Boring and Turning in a Vertical Boring Mill.=--The vertical boring
+mill is, in many respects, like a lathe placed in a vertical position,
+the table of the mill corresponding to the faceplate or chuck of the
+lathe and the tool-head to the lathe carriage. Much of the work done by
+a vertical mill could also be machined in a lathe, but the former is
+much more efficient for work within its range. To begin with, it is more
+convenient to clamp work to a horizontal table than to the vertical
+surface of a lathe faceplate, or, as someone has aptly said, "It is
+easier to lay a piece down than to hang it up." This is especially true
+of the heavy parts for which the boring mill is principally used. Very
+deep roughing cuts can also be taken with a vertical mill. This type of
+machine mill is designed for turning and boring work which, generally
+speaking, is quite large in diameter in proportion to the width or
+height. The work varies greatly, especially in regard to its diameter,
+so that boring mills are built in a large range of sizes. The small and
+medium sizes will swing work varying from about 30 inches to 6 or 7 feet
+in diameter, whereas large machines, such as are used for turning very
+large flywheels, sheaves, etc., have a swing of 16 or 20 feet, and
+larger sizes are used in some shops. The size of a vertical mill, like
+any other machine tool, should be somewhat in proportion to the size of
+the work for which it is intended, as a very large machine is unwieldy,
+and, therefore, inefficient for machining comparatively small parts.
+
+=Holding and Setting Work on Boring Mill Table.=--There are three
+general methods of holding work to the table of a boring mill; namely,
+by the use of chucks, by ordinary bolts and clamps, or in special
+fixtures. Chucks which are built into the table (as illustrated in Fig.
+2) and have both universal and independent adjustments for the jaws can
+be used to advantage for holding castings that are either round or
+irregular in shape. The universal adjustment is used for cylindrical
+parts, such as disks, flywheels, gear blanks, etc., and the independent
+adjustment, for castings of irregular shape. Chucks which have either an
+independent or universal movement for the jaws are known as a
+"combination" type and usually have three jaws. There is also a four-jaw
+type which has the independent adjustment only. This style is preferable
+for work that is not cylindrical and which must be held very securely.
+Chuck jaws that do not form a part of the machine table, but are bolted
+to it in the required position, are also employed extensively,
+especially on comparatively large machines.
+
+Most of the work done in a vertical mill is held in a chuck.
+Occasionally, however, it is preferable to clamp a part directly to the
+table. This may be desirable because of the shape and size of the work,
+or because it is necessary to hold a previously machined surface
+directly against the table in order to secure greater accuracy.
+Sometimes a casting is held in the chuck for turning one side, and then
+the finished side is clamped against the table for turning the opposite
+side. Parts which are to be machined in large quantities are often held
+in special fixtures. This method is employed when it enables the work to
+be set up more quickly than would be possible if regular clamps or chuck
+jaws were used.
+
+Work that is to be turned or bored should first be set so that the part
+to be machined is about central with the table. For example, the rim of
+a flywheel should be set to run true so that it can be finished by
+removing about the same amount of metal around the entire rim; in other
+words, the rim should be set concentric with the table, as shown in Fig.
+3, and the sides of the rim should also be parallel to the table.
+
+[Illustration: Fig. 3. Plan View showing Flywheel Casting Chucked for
+Turning]
+
+A simple tool that is very useful for testing the position of any
+cylindrical casting consists of a wooden shank into which is inserted a
+piece of wire, having one end bent. This tool is clamped in the toolpost
+and as the work revolves the wire is adjusted close to the cylindrical
+surface being tested. The movement of the work with relation to the
+stationary wire point will, of course, show whether or not the part runs
+true. The advantage of using a piece of wire for testing, instead of a
+rigid tool, is that the wire, owing to its flexibility, will simply be
+bent backward if it is moved too close to a surface which is
+considerably out of true. The upper surface of a casting can be tested
+for parallelism with the table by using this same wire gage, or by
+comparing the surface, as the table is revolved slowly, with a tool held
+in the toolpost. An ordinary surface gage is also used for this purpose.
+The proper surface to set true, in any case, depends upon the
+requirements. A plain cylindrical disk would be set so that the outside
+ran true and the top surface was parallel with the table. When setting a
+flywheel, if the inside of the rim is to remain rough, the casting
+should be set by this surface rather than by the outside, so that the
+rim, when finished, will be uniform in thickness.
+
+As far as possible, chucks should be used for holding cylindrical parts,
+owing to their convenience. The jaws should be set against an interior
+cylindrical surface whenever this is feasible. To illustrate, the
+flywheel in Fig. 3 is gripped by the inside of the rim which permits the
+outside to be turned at this setting of the work. It is also advisable
+to set a flywheel casting in the chuck so that a spoke rests against one
+of the jaws as at _d_, if this is possible. This jaw will then act as a
+driver and prevent the casting from slipping or turning in the chuck
+jaws, owing to the tangential pressure of the turning tool. When a cut
+is being taken, the table and work rotate as shown by arrow _a_, and the
+thrust of the cut (taken by tool _t_) tends to move the wheel backward
+against the direction of rotation, as shown by arrow _b_. If one of the
+chuck jaws bears against one of the spokes, this movement is prevented.
+It is not always feasible to use a chuck jaw as a driver and then a
+special driver having the form of a small angle-plate or block is
+sometimes bolted directly to the table. Another method of driving is to
+set a brace between a spoke or projection on the work and a chuck jaw or
+strip attached to the table. Drivers are not only used when turning
+flywheels, but in connection with any large casting, especially when
+heavy cuts have to be taken. Of course, some castings are so shaped that
+drivers cannot be employed.
+
+=Turning in a Boring Mill.=--The vertical type of boring mill is used
+more for turning cylindrical surfaces than for actual boring, although a
+large part of the work requires both turning and boring. We shall first
+consider, in a general way, how surfaces are turned and then refer to
+some boring operations. The diagram _A_, Fig. 4, illustrates how a
+horizontal surface would be turned. The tool _t_ is clamped in
+tool-block _t_{1}_, in a vertical position, and it is fed horizontally
+as the table and work rotate. The tool is first adjusted by hand for the
+proper depth of cut and the automatic horizontal feed is then engaged.
+When a cylindrical surface is to be turned, the tool (provided a
+straight tool is used) is clamped in a horizontal position and is fed
+downward as indicated at _B_. The amount that the tool should feed per
+revolution of the work, depends upon the kind of material being turned,
+the diameter of the turned part and the depth of the cut.
+
+[Illustration: Fig. 4. (A) Turning a Flat Surface. (B) Turning a
+Cylindrical Surface]
+
+Most of the parts machined in a vertical boring mill are made of cast
+iron and, ordinarily, at least one roughing and one finishing cut is
+taken. The number of roughing cuts required in any case depends, of
+course, upon the amount of metal to be removed. An ordinary roughing cut
+in soft cast iron might vary in depth from 1/8 or 3/16 inch to 3/8 or
+1/2 inch and the tool would probably have a feed per revolution of from
+1/16 to 1/8 inch, although deeper cuts and coarser feeds are sometimes
+taken. These figures are merely given to show, in a general way, what
+cuts and feeds are practicable. The tool used for roughing usually has a
+rounded end which leaves a ridged or rough surface. To obtain a smooth
+finish, broad flat tools are used. The flat cutting edge is set parallel
+to the tool's travel and a coarse feed is used in order to reduce the
+time required for taking the cut. The finishing feeds for cast iron vary
+from 1/4 to 3/4 inch on ordinary work. The different tools used on the
+vertical mill will be referred to more in detail later.
+
+All medium and large sized vertical boring mills are equipped with two
+tool-heads and two tools are frequently used at the same time,
+especially on large work. Fig. 9 illustrates the use of two tools
+simultaneously. The casting shown is a flywheel, and the tool on the
+right side turns the upper side of the rim, while the tool on the left
+side turns the outside or cylindrical surface. As a boring mill table
+rotates in a counter-clockwise direction, the left-hand tool is reversed
+to bring the cutting edge at the rear. By turning two surfaces at once,
+the total time for machining the casting is, of course, greatly reduced.
+The turning of flywheels is a common vertical boring mill operation, and
+this work will be referred to in detail later on.
+
+[Illustration: Fig. 5. Tools for Boring and Reaming Holes]
+
+=Boring Operations.=--There are several methods of machining holes when
+using a vertical boring mill. Ordinarily, small holes are cored in
+castings and it is simply necessary to finish the rough surface to the
+required diameter. Some of the tools used for boring and finishing
+comparatively small holes are shown in Fig. 5. Sketch _A_ shows a boring
+tool consisting of a cutter _c_ inserted in a shank, which, in turn, is
+held in the tool slide, or in a turret attached to the tool slide. With
+a tool of this type, a hole is bored by taking one or more cuts down
+through it. The tool shown at _B_ is a four-lipped drill which is used
+for drilling cored holes preparatory to finishing by a cutter or reamer.
+This drill would probably finish a hole to within about 1/32 inch of the
+finish diameter, thus leaving a small amount of metal for the reamer to
+remove. The tool illustrated at _C_ has a double-ended flat cutter _c_,
+which cuts on both sides. These cutters are often made in sets for
+boring duplicate parts. Ordinarily, there are two cutters in a set, one
+being used for roughing and the other for finishing. The cutter passes
+through a rectangular slot in the bar and this particular style is
+centrally located by shoulders _s_, and is held by a taper pin _p_. Some
+cutter bars have an extension end, or "pilot" as it is called, which
+passes through a close-fitting bushing in the table to steady the bar.
+Sketch _D_ shows a finishing reamer. This tool takes a very light cut
+and is intended to finish holes that have been previously bored close to
+the required size. Sometimes a flat cutter _C_ is used for roughing and
+a reamer for finishing. The reamer is especially desirable for
+interchangeable work, when all holes must have a smooth finish and be of
+the same diameter. When a reamer is held rigidly to a turret or
+toolslide, it is liable to produce a hole that is either tapering or
+larger than the reamer diameter. To prevent this, the reamer should be
+held in a "floating" holder which, by means of a slight adjustment,
+allows the reamer to align itself with the hole. There are several
+methods of securing this "floating" movement. (See "Floating Reamer
+Holders.")
+
+[Illustration: Fig. 6. Boring with Regular Turning Tools]
+
+Large holes or interior cylindrical surfaces are bored by tools held in
+the regular tool-head. The tool is sometimes clamped in a horizontal
+position as shown at _A_, Fig. 6, or a bent type is used as at _B_. Cast
+iron is usually finished by a broad flat tool as at _C_, the same as
+when turning exterior surfaces. Obviously a hole that is bored in this
+way must be large enough to admit the tool-block.
+
+[Illustration: Fig. 7. Set of Boring Mill Tools]
+
+=Turning Tools for the Vertical Boring Mill.=--A set of turning tools
+for the vertical boring mill is shown in Fig. 7. These tools can be used
+for a wide variety of ordinary turning operations. When a great many
+duplicate parts are to be machined, special tool equipment can often be
+used to advantage, but as the form of this equipment depends upon the
+character of the work, only standard tools have been shown in this
+illustration. The tool shown at _A_ is a right-hand, roughing tool, and
+a left-hand tool of the same type is shown at _B_. Tool _C_ is an offset
+or bent, left-hand round nose for roughing, and _D_ is a right-hand
+offset roughing tool. A straight round nose is shown at _E_. Tool _F_
+has a flat, broad cutting edge and is used for finishing. Left-and
+right-hand finishing tools of the offset type are shown at _G_ and _H_,
+respectively. Tool _I_ has a square end and is used for cutting grooves.
+Right-and left-hand parting tools are shown at _J_ and _K_, and tool _L_
+is a form frequently used for rounding corners.
+
+[Illustration: Fig. 8. Diagrams Illustrating Use of Different Forms of
+Tools]
+
+The diagrams in Fig. 8 show, in a general way, how each of the tools
+illustrated in Fig. 7 are used, and corresponding tools are marked by
+the same reference letters in both of these illustrations. The right-and
+left-hand roughing tools _A_ and _B_ are especially adapted for taking
+deep roughing cuts. One feeds away from the center of the table, or to
+the right (when held in the right-hand tool-block) and the other tool is
+ground to feed in the opposite direction. Ordinarily, when turning plain
+flat surfaces, the cut is started at the outside and the tool feeds
+toward the center, as at _B_, although it is sometimes more convenient
+to feed in the opposite direction, as at _A_, especially when there is a
+rim or other projecting part at the outside edge. The tool shown at _A_
+could also be used for turning cylindrical surfaces, by clamping it in a
+horizontal position across the bottom of the tool-block. The feeding
+movement would then be downward or at right-angles to the work table.
+
+The offset round-nose tools _C_ and _D_ are for turning exterior or
+interior cylinder surfaces. The shank of this tool is clamped in the
+tool-block in a vertical position and as the bent end extends below the
+tool-block, it can be fed down close to a shoulder. The straight type
+shown at _E_ is commonly used for turning steel or iron, and when the
+point is drawn out narrower, it is also used for brass, although the
+front is then ground without slope. Tool _F_ is for light finishing cuts
+and broad feeds. The amount of feed per revolution of the work should
+always be less than the width of the cutting edge as otherwise ridges
+will be left on the turned surface. The offset tools _G_ and _H_ are for
+finishing exterior and interior cylindrical surfaces. These tools also
+have both vertical and horizontal cutting edges and are sometimes used
+for first finishing a cylindrical and then a horizontal surface, or
+_vice versa_. Tool _I_ is adapted to such work as cutting packing-ring
+grooves in engine pistons, forming square or rectangular grooves, and
+similar work. The parting tools _J_ and _K_ can also be used for forming
+narrow grooves or for cutting off rings, etc. The sketch _K_ (Fig. 8)
+indicates how a tool of this kind might be used for squaring a corner
+under a shoulder. Tool _L_ is frequently used on boring mills for
+rounding the corners of flywheel rims, in order to give them a more
+finished appearance. It has two cutting edges so that either side can be
+used as when rounding the inner and outer corners of a rim.
+
+The turning tools of a vertical boring mill are similar, in many
+respects, to those used in a lathe, although the shanks of the former
+are shorter and more stocky than those of lathe tools. The cutting edges
+of some of the tools also differ somewhat in form, but the principles
+which govern the grinding of lathe and boring mill tools are identical,
+and those who are not familiar with tool grinding are referred to
+Chapter II, in which this subject is treated.
+
+=Turning a Flywheel on a Vertical Mill.=--The turning of a flywheel is a
+good example of the kind of work for which a vertical boring mill is
+adapted. A flywheel should preferably be machined on a double-head mill
+so that one side and the periphery of the rim can be turned at the same
+time. A common method of holding a flywheel is shown in Fig. 9. The rim
+is gripped by four chuck jaws _D_ which, if practicable, should be on
+the inside where they will not interfere with the movement of the tool.
+Two of the jaws, in this case, are set against the spokes on opposite
+sides of the wheel, to act as drivers and prevent any backward shifting
+of work when a heavy cut is being taken. The illustration shows the tool
+to the right rough turning the side of the rim, while the left-hand tool
+turns the periphery. Finishing cuts are also taken over the rim, at this
+setting, and the hub is turned on the outside, faced on top, and the
+hole bored.
+
+[Illustration: Fig. 9. Turning the Rim of a Flywheel]
+
+The three tools _A_, _B_ and _C_, for finishing the hole, are mounted in
+the turret. Bar _A_, which carries a cutter at its end, first rough
+bores the hole. The sizing cutter _B_ is then used to straighten it
+before inserting the finishing reamer _C_. Fig. 10 shows the turret
+moved over to a central position and the sizing cutter _B_ set for
+boring. The head is centrally located (on this particular machine) by a
+positive center-stop. The turret is indexed for bringing the different
+tools into the working position, by loosening the clamping lever _L_ and
+pulling down lever _I_ which disengages the turret lock-pin. When all
+the flywheels in a lot have been machined as described, the opposite
+side is finished.
+
+[Illustration: Fig. 10. Tool B set for Boring the Hub]
+
+[Illustration: Fig. 11. Diagrams showing Method of Turning and Boring a
+Flywheel on a Double-head Mill having one Turret Head]
+
+In order to show more clearly the method of handling work of this class,
+the machining of a flywheel will be explained more in detail in
+connection with Fig. 11, which illustrates practically the same
+equipment as is shown in Figs. 9 and 10. The successive order in which
+the various operations are performed is as follows: Tool _a_ (see sketch
+_A_) rough turns the side of the rim, while tool _b_, which is set with
+its cutting edge toward the rear, rough turns the outside. The direction
+of the feeding movement for each tool is indicated by the arrows. When
+tool _a_ has crossed the rim, it is moved over for facing the hub, as
+shown by the dotted lines. The side and periphery of the rim are next
+finished by the broad-nose finishing tools _c_ and _d_ (see sketch _B_).
+The feed should be increased for finishing, so that each tool will have
+a movement of say 1/4 or 3/8 inch per revolution of the work, and the
+cuts should, at least, be deep enough to remove the marks made by the
+roughing tools. Tool _c_ is also used for finishing the hub as indicated
+by the dotted lines. After these cuts are taken, the outside of the hub
+and inner surface of the rim are usually turned down as far as the
+spokes, by using offset tools similar to the ones shown at _C_ and _D_
+in Fig. 7. The corners of the rim and hub are also rounded to give the
+work a more finished appearance, by using a tool _L_.
+
+The next operation is that of finishing the hole through the hub. The
+hard scale is first removed by a roughing cutter _r_ (sketch _C_), which
+is followed by a "sizing" cutter _s_. The hole is then finished smooth
+and to the right diameter by reamer _f_. The bars carrying cutters _r_
+and _s_ have extensions or "pilots" which enter a close-fitting bushing
+in the table, in order to steady the bar and hold it in alignment.
+
+When the hole is finished, the wheel is turned over, so that the lower
+side of the rim and hub can be faced. The method of holding the casting
+for the final operation is shown at _D_. The chuck jaws are removed, and
+the finished side of the rim is clamped against parallels _p_ resting on
+the table. The wheel is centrally located for turning this side by a
+plug _e_ which is inserted in a hole in the table and fits the bore of
+the hub. The wheel is held by clamps which bear against the spokes.
+Roughing and finishing cuts are next taken over the top surface of the
+rim and hub and the corners are rounded, which completes the machining
+operations. If the rim needs to be a certain width, about the same
+amount of metal should be removed from each side, unless sandy spots or
+"blow-holes" in the casting make it necessary to take more from one side
+than from the other. That side of the rim which was up in the mold when
+the casting was made should be turned first, because the porous, spongy
+spots usually form on the "cope" or top side of a casting.
+
+=Convex Turning Attachment for Boring Mills.=--Fig. 12 shows a vertical
+boring mill arranged for turning pulleys having convex rims; that is,
+the rim, instead of being cylindrical, is rounded somewhat so that it
+slopes from the center toward either side. (The reason for turning a
+pulley rim convex is to prevent the belt from running off at one side,
+as it sometimes tends to do when a cylindrical pulley is used.) The
+convex surface is produced by a special attachment which causes the
+turning tool to gradually move outward as it feeds down, until the
+center of the rim is reached, after which the movement is inward.
+
+[Illustration: Fig. 12. Gisholt Mill equipped with Convex Turning
+Attachment]
+
+The particular attachment shown in Fig. 12 consists of a special
+box-shaped tool-head _F_ containing a sliding holder _G_, in which the
+tool is clamped by set-screws passing through elongated slots in the
+front of the tool-head. In addition, there is a radius link _L_ which
+swivels on a stud at the rear of the tool-head and is attached to
+vertical link _H_. Link _L_ is so connected to the sliding tool-block
+that any downward movement of the tool-bar _I_ causes the tool to move
+outward until the link is in a horizontal position, after which the
+movement is reversed. When the attachment is first set up, the turning
+tool is placed at the center of the rim and then link _L_ is clamped to
+the vertical link while in a horizontal position. The cut is started at
+the top edge of the rim, and the tool is fed downward by power, the
+same as when turning a cylindrical surface. The amount of curvature or
+convexity of a rim can be varied by inserting the clamp bolt _J_ in
+different holes in link _L_.
+
+[Illustration: Fig. 13. Turning a Taper or Conical Surface]
+
+The tools for machining the hub and sides of the rim are held in a
+turret mounted on the left-hand head, as shown. The special tool-holder
+_A_ contains two bent tools for turning the upper and lower edges of the
+pulley rim at the same time as the tool-head is fed horizontally.
+Roughing and finishing tools _B_ are for facing the hub, and the tools
+_C_, _D_, and _E_ rough bore, finish bore, and ream the hole for the
+shaft.
+
+=Turning Taper or Conical Surfaces.=--Conical or taper surfaces are
+turned in a vertical boring mill by swiveling the tool-bar to the proper
+angle as shown in Fig. 13. When the taper is given in degrees, the
+tool-bar can be set by graduations on the edge of the circular base _B_,
+which show the angle _a_ to which the bar is swiveled from a vertical
+position. The base turns on a central stud and is secured to the saddle
+_S_ by the bolts shown, which should be tightened after the tool-bar is
+set. The vertical power feed can be used for taper turning the same as
+for cylindrical work.
+
+[Illustration: Fig. 14. Turning a Conical Surface by using the Combined
+Vertical and Horizontal Feeds]
+
+Occasionally it is necessary to machine a conical surface which has such
+a large included angle that the tool-bar cannot be swiveled far enough
+around to permit turning by the method illustrated in Fig. 13. Another
+method, which is sometimes resorted to for work of this class, is to use
+the combined vertical and horizontal feeds. Suppose we want to turn the
+conical casting _W_ (Fig. 14), to an angle of 30 degrees, as shown, and
+that the tool-head of the boring mill moves horizontally 1/4 inch per
+turn of the feed-screw and has a vertical movement of 3/16 inch per turn
+of the upper feed-shaft. If the two feeds are used simultaneously, the
+tool will move a distance _h_ of say 8 inches, while it moves downward a
+distance _v_ of 6 inches, thus turning the surface to an angle _y_. This
+angle is greater (as measured from a horizontal plane) than the angle
+required, but, if the tool-bar is swiveled to an angle _x_, the tool, as
+it moves downward, will also be advanced horizontally, in addition to
+the regular horizontal movement. The result is that the angle _y_ is
+diminished and if the tool-bar is set over the right amount, the
+conical surface can be turned to an angle _a_ of 30 degrees. The
+problem, then, is to determine what the angle _x_ should be for turning
+to a given angle _a_.
+
+[Illustration: Fig. 15. Diagram showing Method of Obtaining Angular
+Position of Tool-head when Turning Conical Surfaces by using Vertical
+and Horizontal Feeding Movements]
+
+The way angle _x_ is calculated will be explained in connection with the
+enlarged diagram, Fig. 15, which shows one-half of the casting. The sine
+of the known angle _a_ is first found in a table of natural sines. Then
+the sine of angle _b_, between the taper surface and center-line of the
+tool-head, is determined as follows: sin_b_ = (sin_a_ × _h_) ÷ _v_, in
+which _h_ represents the rate of horizontal feed and _v_ the rate of
+vertical feed. The angle corresponding to sine _b_ is next found in a
+table of sines. We now have angles _b_ and _a_, and by subtracting the
+sum of these angles from 90 degrees, the desired angle _x_ is obtained.
+To illustrate: The sine of 30 degrees is 0.5; then sin _b_ = (0.5 × 1/4)
+÷ 3/16 = 0.6666; hence angle _b_ = 41 degrees 49 minutes, and _x_ =
+90°-(30° + 41° 49') = 18 degrees 11 minutes. Hence to turn the casting
+to angle _a_ in a boring mill having the horizontal and vertical feeds
+given, the tool-head would be set over from the vertical 18 degrees and
+11 minutes which is equivalent to about 18-1/6 degrees.
+
+If the required angle _a_ were greater than angle _y_ obtained from the
+combined feeds with the tool-bar in a vertical position, it would then
+be necessary to swing the lower end of the bar to the left rather than
+to the right of a vertical plane. When the required angle _a_ exceeds
+angle _y_, the sum of angles _a_ and _b_ is greater than 90 degrees so
+that angle _x_ for the tool-head = (_a_ + _b_) - 90 degrees.
+
+=Turret-lathe Type of Vertical Boring Mill.=--The machine illustrated in
+Fig. 16 was designed to combine the advantages of the horizontal turret
+lathe and the vertical boring mill. It is known as a "vertical turret
+lathe," but resembles, in many respects, a vertical boring mill. This
+machine has a turret on the cross-rail the same as many vertical boring
+mills, and, in addition, a side-head _S_. The side-head has a vertical
+feeding movement, and the tool-bar _T_ can be fed horizontally. The
+tool-bar is also equipped with a four-sided turret for holding turning
+tools. This arrangement of the tool-heads makes it possible to use two
+tools simultaneously upon comparatively small work. When both heads are
+mounted on the cross-rail, as with a double-head boring mill, it is
+often impossible to machine certain parts to advantage, because one head
+interferes with the other.
+
+The drive to the table (for the particular machine illustrated) is from
+a belt pulley at the rear, and fifteen speed changes are available. Five
+changes are obtained by turning the pilot-wheel _A_ and this series of
+five speeds is compounded three times by turning lever _B_. Each spoke
+of pilot-wheel _A_ indicates a speed which is engaged only when the
+spoke is in a vertical position, and the three positions for _B_ are
+indicated, by slots in the disk shown. The number of table revolutions
+per minute for different positions of pilot-wheel _A_ and lever _B_ are
+shown by figures seen through whichever slot is at _C_. There are five
+rows of figures corresponding to the five spokes of the pilot-wheel and
+three figures in a row, and the speed is shown by arrows on the sides of
+the slots. The segment disk containing these figures also serves as an
+interlocking device which prevents moving more than one speed
+controlling lever at a time, in order to avoid damaging the driving
+mechanism.
+
+[Illustration: Fig. 16. Bullard Vertical Turret Lathe]
+
+The feeding movement for each head is independent. Lever _D_ controls
+the engagement or disengagement of the vertical or cross feeds for the
+head on the cross-rail. The feed for the side-head is controlled by
+lever _E_. When this lever is pushed inward, the entire head feeds
+vertically, but when it is pulled out, the tool-bar feeds horizontally.
+These two feeds can be disengaged by placing the lever in a neutral
+position. The direction of the feeding movement for either head can be
+reversed by lever _R_. The amount of feed is varied by feed-wheel _F_
+and clutch-rod _G_. When lever _E_ is in the neutral position, the
+side-head or tool-bar can be adjusted by the hand-cranks _H_ and _I_,
+respectively. The cross-rail head and its turret slide have rapid power
+traverse movements for making quick adjustments. This rapid traverse is
+controlled by the key-handles _J_.
+
+The feed-screws for the vertical head have micrometer dials _K_ for
+making accurate adjustments. There are also large dials at _L_ which
+indicate vertical movements of the side head and horizontal movements of
+the tool slide. All of these dials have small adjustable clips _c_ which
+are numbered to correspond to numbers on the faces of the respective
+turrets. These clips or "observation stops" are used in the production
+of duplicate parts. For example, suppose a tool in face No. 1 for the
+main turret is set for a given diameter and height of shoulder on a part
+which is to be duplicated. To obtain the same setting of the tools for
+the next piece, clips No. 1, on both the vertical feed rod and screw
+dials, are placed opposite the graduations which are intersected by
+stationary pointers secured to the cross-rail. The clips are set in this
+way after the first part has been machined to the required size and
+before disturbing the final position of the tools. For turning a
+duplicate part, the tools are simply brought to the same position by
+turning the feed screws until the clips and stationary pointers again
+coincide. For setting tools on other faces of either turret, this
+operation is repeated, except that clips are used bearing numbers
+corresponding to the turret face in use.
+
+The main turret of this machine has five holes in which are inserted the
+necessary boring and turning tools, drills or reamers, as may be
+required. By having all the tools mounted in the turret, they can be
+quickly and accurately set in the working position. When the turret is
+indexed from one face to the next, binder lever _N_ is first loosened.
+The turret then moves forward, away from its seat, thus disengaging the
+indexing and registering pins which accurately locate it in any one of
+the five positions. The turret is revolved by turning crank _M_, one
+turn of this handle moving the turret 1/5 revolution or from one hole to
+the next. The side-head turret is turned by loosening lever _O_. The
+turret slide can be locked rigidly in any position by lever _P_ and its
+saddle is clamped to the cross-rail by lever _Q_. The binder levers for
+the saddle and toolslide of the side-head are located at _U_ and _V_,
+respectively. A slide that does not require feeding movements is locked
+in order to obtain greater rigidity. To illustrate, if the main tool
+slide were to feed vertically and not horizontally, it might be
+advisable to lock the saddle to the cross-rail, while taking the
+vertical cut.
+
+[Illustration: Fig. 17. Turning a Gear Blank on a Vertical Turret Lathe]
+
+The vertical slide can be set at an angle for taper turning, and the
+turret is accurately located over the center of the table for boring or
+reaming, by a positive center stop. The machine is provided with a brake
+for stopping the work table quickly, which is operated by lifting the
+shaft of pilot-wheel _A_. The side-and cross-rails are a unit and are
+adjusted together to accommodate work of different heights. This
+adjustment is effected by power on the particular machine illustrated,
+and it is controlled by a lever near the left end of the cross-rail.
+Before making this adjustment, all binder bolts which normally hold the
+rails rigidly to the machine column must be released, and care should be
+taken to tighten them after the adjustment is made.
+
+[Illustration: Fig. 18. Turning Gasoline Engine Flywheel on Vertical
+Turret Lathe--First Position]
+
+=Examples of Vertical Turret Lathe Work.=--In order to illustrate how a
+vertical turret lathe is used, one or two examples of work will be
+referred to in detail. These examples also indicate, in a general way,
+the class of work for which this type of machine is adapted. Fig. 17
+shows how a cast-iron gear blank is machined. The work is gripped on the
+inside of the rim by three chuck jaws, and all of the tools required for
+the various operations are mounted in the main and side turrets. The
+illustration shows the first operation which is that of rough turning
+the hub, the top side of the blank and its periphery. The tools _A_ for
+facing the hub and upper surface are both held in one tool-block on the
+main turret, and tool _A_{1}_ for roughing the periphery is in the side
+turret. With this arrangement, the three surfaces can be turned
+simultaneously.
+
+[Illustration: Fig. 19. Turning Gasoline Engine Flywheel--Second
+Position]
+
+[Illustration: Fig. 20. Diagrams showing How Successive Operations are
+Performed by Different Tools in the Turret]
+
+The main turret is next indexed one-sixth of a revolution which brings
+the broad finishing tools _B_ into position, and the side turret is also
+turned to locate finishing tool _B_{1}_ at the front. (The indexing of
+the main turret on this particular machine is effected by loosening
+binder lever n and raising the turret lock-pin by means of lever _p_.)
+The hub, side and periphery of the blank are then finished. When tools
+_B_ are clamped in the tool-blocks, they are, of course, set for
+turning the hub to the required height. The third operation is performed
+by the tools at _C_, one of which "breaks" or chamfers the corner of the
+cored hole in the hub, to provide a starting surface for drill _D_, and
+the other turns the outside of the hub, after the chamfering tool is
+removed. The four-lipped shell-drill _D_ is next used to drill the cored
+hole and then this hole is bored close to the finished size and
+concentric with the circumference of the blank by boring tool _E_, which
+is followed by the finishing reamer _F_. When the drill, boring tool and
+reamer are being used, the turret is set over the center or axis of the
+table, by means of a positive center stop on the left-side of the turret
+saddle. If it is necessary to move the turret beyond the central
+position, this stop can be swung out of the way.
+
+Figs. 18 and 19 illustrate the turning of an automobile flywheel, which
+is another typical example of work for a machine of this type. The
+flywheel is finished in two settings. Its position for the first series
+of operations is shown in Fig. 18, and the successive order of the four
+operations for the first setting is shown by the diagrams, Fig. 20. The
+first operation requires four tools which act simultaneously. The three
+held in tool-block _A_ of the turret, face the hub, the web and the rim
+of the flywheel, while tool _a_ in the side-head rough turns the outside
+diameter. The outside diameter is also finished by broad-nosed tool _b_
+which is given a coarse feed. In the second operation, the under face of
+the rim is finished by tool _c_, the outer corners are rounded by tool
+_d_ and the inner surface of the rim is rough turned by a bent tool _B_,
+which is moved into position by indexing the main turret. In the third
+operation, the side-head is moved out of the way and the inside of the
+rim is finished by another bent tool _B_{1}_. The final operation at
+this setting is the boring of the central hole, which is done with a bar
+_C_ having interchangeable cutters which make it possible to finish the
+hole at one setting of the turret.
+
+The remaining operations are performed on the opposite side of the work
+which is held in "soft" jaws _J_ accurately bored to fit the finished
+outside diameter as indicated in Fig. 19. The tool in the main turret
+turns the inside of the rim, and the side-head is equipped with two
+tools for facing the web and hub simultaneously. As the tool in the main
+turret operates on the left side of the rim, it is set with the cutting
+edge toward the rear. In order to move the turret to this position,
+which is beyond the center of the table, the center stop previously
+referred to is swung out of the way.
+
+=Floating Reamer Holders.=--If a reamer is held rigidly in the turret of
+a boring mill or turret lathe, it is liable to produce a hole which
+tapers slightly or is too large. When a hole is bored with a
+single-point boring tool, it is concentric with the axis of rotation,
+and if a reamer that is aligned exactly with the bored hole is fed into
+the work, the finished hole should be cylindrical and the correct size.
+It is very difficult, however, to locate a reamer exactly in line with a
+bored hole, because of slight variations in the indexing of the turret,
+or errors resulting from wear of the guiding ways or other important
+parts of the machine.
+
+To prevent inaccuracies due to this cause, reamers are often held in
+what is known as a "floating" holder. This type of holder is so arranged
+that the reamer, instead of being held rigidly, is allowed a slight free
+or floating movement so that it can follow a hole which has been bored
+true, without restraint. In this way the hole is reamed straight and to
+practically the same size as the reamer.
+
+[Illustration: Fig. 21. Two Types of Floating Reamer Holders]
+
+There are many different designs of floating holders but the general
+principle upon which they are based is illustrated by the two types
+shown in Fig. 21. The reamer and holder shown to the left has a
+ball-shank _A_ which bears against a backing-up screw _B_ inserted in
+the end of holder _C_ through which the driving pin passes. The lower
+end of the reamer shank is also spherical-shaped at _D_, and screw-pin
+_E_ secures the shell reamer to this end. It will be noted that the hole
+in the shank for pin _E_ is "bell-mouthed" on each side of the center
+and that there is clearance at _F_ between the shank and reamer shell;
+hence the reamer has a free floating action in any direction. This
+holder has given very satisfactory results.
+
+[Illustration: Fig. 22. Multiple-spindle Cylinder Boring Machine]
+
+The holder shown to the right is attached to the face of the turret by
+four fillister-head screws. Sleeve _C_ is held in plate _A_ by means of
+two steel pins _B_ which are tight in plate _A_ and made to fit freely
+in bayonet grooves _D_. Reamer holder _E_ floats on sleeve _C_, the
+floating motion being obtained through the four steel pins _G_ extending
+into driving ring _F_. Two of the pins are tight in the holder _E_ and
+two in sleeve _C_. The faces of sleeve _C_, driving ring _F_, and reamer
+holder _E_ are held tightly against each other by means of spring _H_
+which insures the reamer being held perfectly true. Spring _H_ is
+adjusted by means of nut _I_ which is turned with a spanner wrench
+furnished with each holder. The reamer is so held that its axis is
+always maintained parallel to the center of the hole, and, at the same
+time, it has a slight self-adjusting tendency radially, so that the hole
+and reamer will automatically keep in perfect alignment with each
+other.
+
+=Multiple Cylinder Boring Machine.=--In automobile and other factories
+where a great many gasoline engine cylinders are required,
+multiple-spindle boring machines of the vertical type are commonly used.
+The machine shown in Fig. 22 is a special design for boring four
+cylinders which are cast _en bloc_ or in one solid casting. The work is
+held in a box jig which has a top plate equipped with guide bearings for
+holding the spindles rigidly while boring. The lower end of each spindle
+has attached to it a cutter-head and the boring is done by feeding the
+table and casting vertically. This feeding movement is effected by power
+and it is disengaged automatically when the cutters have bored to the
+required depth. The particular machine illustrated is used for rough
+boring only, the cylinders being finished by reaming in another similar
+machine. The cylinders are bored to a diameter of 3-5/8 inches, and
+about 3/8 inch of metal is removed by the roughing cut. The spindles
+have fixed center-to-center distances as the machine is intended for
+constant use on cylinders of one size, so that adjustment is not
+necessary. Of course, a special machine of this kind is only used in
+shops where large numbers of cylinders of one design are required
+continually. Some cylinder boring machines of the vertical type have
+spindles which can be adjusted for different center-to-center distances
+if this should be necessary in order to accommodate a cylinder of
+another size.
+
+
+
+
+CHAPTER VII
+
+HORIZONTAL BORING MACHINES
+
+
+A boring machine of the horizontal type is shown in Fig. 1. The
+construction and operation of this machine is very different from that
+of a vertical boring mill and it is also used for an entirely different
+class of work. The horizontal machine is employed principally for
+boring, drilling or milling, whereas the vertical design is especially
+adapted to turning and boring. The horizontal type is also used for
+turning or facing flanges or similar surfaces when such an operation can
+be performed to advantage in connection with other machine work on the
+same part.
+
+The type of machine illustrated in Fig. 1 has a heavy base or bed to
+which is bolted the column _C_ having vertical ways on which the
+spindle-head _H_ is mounted. This head contains a sleeve or quill in
+which the spindle _S_ slides longitudinally. The spindle carries cutters
+for boring, whereas milling cutters or the auxiliary facing arm are
+bolted to the end _A_ of the spindle sleeve. The work itself is attached
+either directly or indirectly to the table or platen _P_. When the
+machine is in operation, the cutter or tool revolves with the spindle
+sleeve or spindle and either the cutter or the part being machined is
+given a feeding movement, depending on the character of the work. The
+spindle can be moved in or out by hand for adjustment, or by power for
+feeding the cutter, as when boring or drilling.
+
+[Illustration: Fig. 1. Lucas Horizontal Boring, Drilling and Milling
+Machine]
+
+The entire spindle-head _H_ can also be moved vertically on the face of
+the column _C_, by hand, for setting the spindle to the proper height,
+or by power for feeding a milling cutter in a vertical direction. When
+the vertical position of the spindle-head is changed, the outboard
+bearing block _B_ also moves up or down a corresponding amount, the two
+parts being connected by shafts and gearing. Block _B_ steadies the
+outer end of the boring-bar and the back-rest in which this block is
+mounted can be shifted along the bed to suit the length of the work, by
+turning the squared end of shaft _D_ with a crank. The platen _P_ has a
+cross-feed, and the saddle _E_ on which it is mounted can be traversed
+lengthwise on the bed; both of these movements can also be effected by
+hand or power. There is a series of power feeding movements for the
+cutters and, in addition, rapid power movements _in a reverse direction
+from the feed_ for returning a cutter quickly to its starting position,
+when this is desirable.
+
+This machine is driven by a belt connecting pulley _G_ with an overhead
+shaft. When the machine is in operation, this pulley is engaged with the
+main driving shaft by a friction clutch _F_ controlled by lever _L_.
+This main shaft drives through gearing a vertical shaft _I_, which by
+means of other gears in the spindle-head imparts a rotary movement to
+the spindle. As a machine of this type is used for boring holes of
+various diameters and for a variety of other work, it is necessary to
+have a number of speed changes for the spindle. Nine speeds are obtained
+by changing the position of the sliding gears controlled by levers _R_
+and this number is doubled by back-gears in the spindle-head and
+controlled by lever _J_.
+
+The amount of feed for the spindle, spindle-head, platen or saddle is
+varied by two levers _K_ and _K_{1}_ which control the position of
+sliding gears through which the feeding movements are transmitted. The
+direction of the feed can be reversed by shifting lever _O_. With this
+particular machine, nine feed changes are available for each position of
+the spindle back-gears, making a total of eighteen changes. The feeding
+movement is transmitted to the spindle-head, spindle, platen or saddle,
+as required, by the three distributing levers _T_, _U_ and _V_, which
+control clutches connecting with the transmission shafts or feed screws.
+When lever _T_ is turned to the left, the longitudinal power feed for
+the spindle is engaged, whereas turning it to the right throws in the
+vertical feed for the spindle-head. Lever _U_ engages the cross-feed for
+platen _P_ and lever _V_, the longitudinal feed for saddle _E_. These
+levers have a simple but ingenious interlocking device which makes it
+impossible to engage more than one feed at a time. For example, if lever
+_T_ is set for feeding the spindle, levers _U_ and _V_ are locked
+against movement.
+
+The feeds are started and stopped by lever _M_ which also engages the
+rapid power traverse when thrown in the opposite direction. This rapid
+traverse operates for whatever feed is engaged by the distributing
+levers and, as before stated, in a reverse direction. For example, if
+the reverse lever _O_ is set for feeding the spindle to the right, the
+rapid traverse would be to the left, and _vice versa_. The cross-feed
+for the platen can be automatically tripped at any point by setting an
+adjustable stop in the proper position and the feed can also be tripped
+by a hand lever at the side of the platen.
+
+All the different feeding movements can be effected by hand as well as
+by power. By means of handwheel _N_, the spindle can be moved in or out
+slowly, for feeding a cutter by hand. When the friction clamp _Q_ is
+loosened, the turnstile _W_ can be used for traversing the spindle, in
+case a hand adjustment is desirable. The spindle-head can be adjusted
+vertically by turning squared shaft _X_ with a crank, and the saddle can
+be shifted along the bed by turning shaft _Y_. The hand adjustment of
+the platen is effected by shaft _Z_. The spindle-head, platen and saddle
+can also be adjusted from the end of the machine, when this is more
+convenient. Shafts _X_, _Y_ and _Z_ are equipped with micrometer dials
+which are graduated to show movements of one-thousandth inch. These
+dials are used for accurately adjusting the spindle or work and for
+boring holes or milling surfaces that must be an exact distance apart.
+
+=Horizontal Boring Machine with Vertical Table Adjustment.=--Another
+horizontal boring machine is partly shown in Fig. 2. This machine is of
+the same type as that illustrated in Fig. 1, but its construction is
+quite different, as will be seen. The spindle cannot be adjusted
+vertically as with the first design described, but it is mounted and
+driven very much like the spindle of a lathe, and adjustment for height
+is obtained by raising or lowering the work table. The design is just
+the reverse, in this respect, of the machine shown in Fig. 1, which has
+a vertical adjustment for the spindle, and a work table that remains in
+the same horizontal plane. The raising or lowering of the table is
+effected by shaft _E_, which rotates large nuts engaging the screws _S_.
+Shaft _E_ is turned either by hand or power.
+
+[Illustration: Fig. 2. Horizontal Boring and Drilling Machine with
+Vertical Table Adjustment]
+
+The main spindle is driven by a cone pulley _P_, either directly, or
+indirectly through the back-gears shown. This arrangement gives six
+spindle speeds, and double this number is obtained by using a two-speed
+countershaft overhead. The motion for feeding the spindle longitudinally
+is transmitted through a cone of gears, which gives the required
+changes, to a pinion meshing with a rack which traverses the spindle.
+The large handwheel _H_ and a corresponding wheel on the opposite side
+are used for adjusting the spindle rapidly by hand. The yoke or outboard
+bearing _B_ for the boring-bars can be clamped in any position along the
+bed for supporting the bar as close to the work as possible.
+
+Horizontal boring machines are built in many other designs, but they all
+have the same general arrangement as the machines illustrated and
+operate on the same principle, with the exception of special types
+intended for handling certain classes of work exclusively. The
+horizontal boring, drilling and milling machine is very efficient for
+certain classes of work because it enables all the machining operations
+on some parts to be completed at one setting. To illustrate, a casting
+which requires drilling, boring and milling at different places, can
+often be finished without disturbing its position on the platen after it
+is clamped in place. Frequently a comparatively small surface needs to
+be milled after a part has been bored. If this milling operation can be
+performed while the work is set up for boring, accurate results will be
+obtained (provided the machine is in good condition) and the time saved
+that would otherwise be required for re-setting the part on another
+machine. Some examples of work on which different operations are
+performed at the same setting will be referred to later. The horizontal
+boring machine also makes it possible to machine duplicate parts without
+the use of jigs, which is important, especially on large work, owing to
+the cost of jigs.
+
+=Drilling and Boring--Cutters Used.=--Holes are drilled in a horizontal
+machine by simply inserting a drill of required size either directly in
+the spindle _S_ (see Fig. 1), or in a reducing socket, and then feeding
+the spindle outward either by hand or power. When a hole is to be bored,
+a boring-bar _B_{1}_ is inserted in the spindle and the cutter is
+attached to this bar. The latter is then fed through the hole as the
+cutter revolves. The distinction made by machinists between drilling and
+boring is as follows: A hole is said to be drilled when it is formed by
+sinking a drill into solid metal, whereas boring means the enlargement
+of a drilled or cored hole either by the use of a single boring tool, a
+double-ended cutter which operates on both sides of the hole, or a
+cutter-head having several tools.
+
+There are various methods of attaching cutters to boring-bars and the
+cutters used vary for different classes of work. A simple style of
+cutter which is used widely for boring small holes is shown at _A_ in
+Fig. 3. The cutter _c_ is made from flat stock and the cutting is done
+by the front edges _e_ and _e_{1}_, which are beveled in opposite
+directions. The cutter is held in the bar by a taper wedge _w_ and it
+is centered by shoulders at _s_, so that the diameter of the hole will
+equal the length across the cutter. The outer corners at the front
+should be slightly rounded, as a sharp corner would be dulled quickly.
+These cutters are made in different sizes and also in sets for roughing
+and finishing. The roughing cutter bores holes to within about 1/32 inch
+of the finish size and it is then replaced by the finishing cutter. A
+cutter having rounded ends, as shown by the detail sketch _a_, is
+sometimes used for light finishing cuts. These rounded ends form the
+cutting edges and give a smooth finish.
+
+[Illustration: Fig. 3. Boring-cutters of Different Types]
+
+Another method of holding a flat cutter is shown at _B_. The conical end
+of a screw bears against a conical seat in, the cutter, thus binding the
+latter in its slot. The conical seat also centers the cutter. A very
+simple and inexpensive form of cutter is shown at _C_. This is made from
+a piece of round steel, and it is held in the bar by a taper pin which
+bears against a circular recess in the side of the cutter. This form
+has the advantage of only requiring a hole through the boring-bar,
+whereas it is necessary to cut a rectangular slot for the flat cutter.
+
+[Illustration: Fig. 4. Boring with a Flat Double-ended Cutter]
+
+Fig. 4 shows how a hole is bored by cutters of the type referred to. The
+bar rotates as indicated by the arrow _a_ and at the same time feeds
+longitudinally as shown by arrow _b_. The speed of rotation depends upon
+the diameter of the hole and the kind of material being bored, and the
+feed per revolution must also be varied to suit conditions. No definite
+rule can be given for speed or feed. On some classes of work a long
+boring-bar is used, which passes through the hole to be bored and is
+steadied at its outer end by the back-rest _B_, Figs, 1 and 2. On other
+work, a short bar is inserted in the spindle having a cutter at the
+outer end. An inexpensive method of holding a cutter at the end of a bar
+is shown at _D_, Fig. 3. The cutter passes through a slot and is clamped
+by a bolt as shown. When it is necessary to bore holes that are "blind"
+or closed at the bottom, a long boring-bar which passes through the work
+cannot, of course, be used.
+
+Sometimes it is necessary to have a cutter mounted at the extreme end of
+a bar in order to bore close to a shoulder or the bottom of a hole. One
+method of holding a cutter so that it projects beyond the end of a bar
+is indicated at _E_. A screw similar to the one shown at _B_ is used,
+and the conical end bears in a conical hole in the cutter. This hole
+should be slightly offset so that the cutter will be forced back
+against its seat. The tool shown at _F_ has adjustable cutters. The
+inner end of each cutter is tapering and bears against a conical-headed
+screw _b_ which gives the required outward adjustment. The cutters are
+held against the central bolt by fillister-head screws _f_ and they are
+clamped by the screws _c_. Boring tools are made in many different
+designs and the number and form of the cutters is varied somewhat for
+different kinds of work.
+
+[Illustration: Fig. 5. Cutter-heads for Boring Large Holes]
+
+=Cutter-heads for Boring Large Holes.=--When large holes are to be
+bored, the cutters are usually held in a cast-iron head which is mounted
+on the boring-bar. One type of cutter-head is shown in Fig. 5. This
+particular head is double-ended and carries two cutters _c_. The
+cutter-head is bored to fit the bar closely and it is prevented from
+turning by a key against which a set-screw is tightened. By referring to
+the end view, it will be seen that each cutter is offset with relation
+to the center of the bar, in order to locate the front of the tool on a
+radial line. The number of cutters used in a cutter-head varies. By
+having several cutters, the work of removing a given amount of metal in
+boring is distributed, and holes can be bored more quickly with a
+multiple cutter-head, although more power is required to drive the
+boring-bar. The boring-bar is also steadied by a multiple cutter-head,
+because the tendency of any one cutter to deflect the bar is
+counteracted by the cutters on the opposite side.
+
+A disk-shaped head having four cutters is illustrated in Fig. 6. The
+cutters are inserted in slots or grooves in the face of the disk and
+they are held by slotted clamping posts. The shape of these posts is
+shown by the sectional view. The tool passes through an elongated slot
+and it is tightly clamped against the disk by tightening nut _n_. This
+head is also driven by a key which engages a keyway in the boring-bar.
+
+[Illustration: Fig. 6. Cutter-head with Four Boring Tools]
+
+Two other designs of cutter-heads are shown in Fig. 7. The one
+illustrated at _A_ has three equally spaced cutters which are held in an
+inclined position. The cutters are clamped by screws _c_ and they can be
+adjusted within certain limits by screws _s_. The cutters are placed at
+an angle so that they will extend beyond the front of the head, thus
+permitting the latter to be moved up close to a shoulder. The
+cutter-heads shown in Figs. 5 and 6 can also be moved up close to a
+shoulder if bent cutters are used as shown in the right-hand view, Fig.
+5. The idea in bending the cutters is to bring the cutting edges in
+advance of the clamping posts so that they will reach a shoulder before
+the binding posts strike it. The arrangement of cutter-head _B_ (Fig. 7)
+is clearly shown by the illustration.
+
+Cutter-heads are often provided with two sets of cutters, one set being
+used for roughing and the other for finishing. It is a good plan to make
+these cutters so that the ends _e_ (Fig. 6) will rest against the bar or
+bottom of the slot, when the cutting edge is set to the required radius.
+The cutters can then be easily set for boring duplicate work. One method
+of making cutters in sets is to clamp the annealed stock in the
+cutter-head and then turn the ends to the required radius by placing the
+head in the lathe. After both sets of cutters have been turned in this
+way, they are ground to shape and then hardened.
+
+[Illustration: Fig. 7. Cutter-heads equipped with Adjustable Tools]
+
+Boring cutters intended for roughing and finishing cuts are shown in the
+detail view Fig. 8 at _A_ and _B_, respectively. The side of the
+roughing cutter _A_ is ground to a slight angle _c_ to provide clearance
+for the cutting edge, and the front has a backward slope _s_ to give the
+tool keenness. This tool is a good form to use for roughing cuts in cast
+iron. The finishing tool at _B_ has a broad flat edge _e_ and it is
+intended for coarse feeds and light cuts in cast iron. If a round
+cutting edge is used for finishing, a comparatively fine feed is
+required in order to obtain a smooth surface. The corners of tool _B_
+are rounded and they should be ground to slope inward as shown in the
+plan view. The top or ends _d_ of both of these tools are "backed off"
+slightly to provide clearance. This clearance should be just enough to
+prevent the surface back of the cutting edge from dragging over the
+work. Excessive end clearance not only weakens the cutting edge, but
+tends to cause chattering. As a finishing tool cuts on the upper end
+instead of on the side, the front should slope backward as shown in the
+side view, rather than sidewise as with a roughing cutter. The angle of
+the slope should be somewhat greater for steel than cast iron, unless
+the steel is quite hard, thus requiring a strong blunt tool.
+
+[Illustration: Fig. 8. Boring Tools for Roughing and Finishing Cuts]
+
+=Cylinder Boring.=--Fig. 9 illustrates the use of a cutter-head for
+cylinder boring. After the cylinder casting is set on the platen of the
+machine, the boring-bar with the cutter-head mounted on it is inserted
+in the spindle. The bar _B_ has a taper shank and a driving tang similar
+to a drill shank, which fits a taper hole in the end of the spindle. The
+cutter-head _C_ is fastened to the bar so that it will be in the
+position shown when the spindle is shifted to the right, as the feeding
+movement (with this particular machine) is to be in the opposite
+direction. The casting _A_ should be set central with the bar by
+adjusting the work-table vertically and laterally, if necessary, and the
+outer support _F_ should be moved close to the work, to make the bar as
+rigid as possible.
+
+The cylinder is now ready to be bored. Ordinarily, one or two roughing
+cuts and one finishing cut would be sufficient, unless the rough bore
+were considerably below the finish diameter. As previously explained,
+the speed and feed must be governed by the kind of material being bored
+and the diameter of the cut. The power and rigidity of the boring
+machine and the quality of the steel used for making the cutters also
+affect the cutting speed and feed. As the finishing cut is very light, a
+tool having a flat cutting edge set parallel to the bar is ordinarily
+used when boring cast iron. The coarse feed enables the cut to be taken
+in a comparatively short time and the broad-nosed tool gives a smooth
+finish if properly ground.
+
+[Illustration: Fig. 9. Cylinder mounted on Horizontal Machine for
+Boring]
+
+The coarse finishing feed is not always practicable, especially if the
+boring machine is in poor condition, owing to the chattering of the
+tool, which results in a rough surface. The last or finishing cut should
+invariably be a continuous one, for if the machine is stopped before the
+cut is completed, there will be a ridge in the bore at the point where
+the tool temporarily left off cutting. This ridge is caused by the
+cooling and resulting contraction and shortening of the tool during the
+time that it is stationary. For this reason independent drives are
+desirable for boring machines.
+
+Facing arms are attached to the bar on either side of the cylinder for
+facing the flanges after the boring operation. The turning tool of a
+facing arm is fastened to a slide which is fed outward a short distance
+each revolution, by a star-wheel that is caused to turn as it strikes
+against a stationary pin. By facing the flanges in this way, they are
+finished square with the bore.
+
+When setting a cylinder which is to be bored it should, when the design
+will permit, be set true by the outside of the flange, or what is even
+better, by the outside of the cylinder itself, rather than by the rough
+bore, in order that the walls of the finished cylinder will have a
+uniform thickness. The position of very large cylinders, while they are
+being bored, is an important consideration. Such cylinders should be
+bored in the position which they will subsequently occupy when
+assembled. For example, the cylinder for a large horizontal engine
+should be bored while in a horizontal position, as the bore is liable to
+spring to a slight oval shape when the cylinder is placed horizontal
+after being bored while standing in a vertical position. If, however,
+the cylinder is bored while in the position in which it will be placed
+in the assembled engine, this trouble is practically eliminated.
+
+There is a difference of opinion among machinists as to the proper shape
+of the cutting point of a boring tool for finishing cuts, some
+contending that a wide cutting edge is to be preferred, while others
+advocate the use of a comparatively narrow edge with a reduced feed. It
+is claimed, that the narrow tool produces a more perfect bore, as it is
+not so easily affected by hard spots in the iron, and it is also pointed
+out that the minute ridges left by the narrow tool are an advantage
+rather than a disadvantage, as they form pockets for oil and aid in
+lubricating the cylinder. It is the modern practice, however, to use a
+broad tool and a coarse feed for the light finishing cut, provided the
+tool does not chatter.
+
+The type of machine tool used for boring cylinders, and also the method
+of procedure is determined largely by the size of the work and the
+quantity which is to be machined. The turret lathe, as well as
+horizontal and vertical boring mills, is used for this work, and in
+automobile factories or other shops where a great many cylinders are
+bored, special machines and fixtures are often employed.
+
+[Illustration: Fig. 10. Boring a Duplex Cylinder on a Horizontal
+Machine]
+
+=Boring a Duplex Gasoline Engine Cylinder.=--The method of holding work
+on a horizontal boring machine depends on its shape. A cylinder or other
+casting having a flat base can be clamped directly to the platen, but
+pieces of irregular shape are usually held in special fixtures. Fig. 10
+shows how the cylinder casting of a gasoline engine is set up for the
+boring operation. The casting _W_ is placed in a fixture _F_ which is
+clamped to the machine table. One end of the casting rests on the
+adjustable screws _S_ and it is clamped by set-screws located in the top
+and sides of the fixture. There are two cylinders cast integral and
+these are bored by a short stiff bar mounted in the end of the spindle
+and having cutters at the outer end. A long bar of the type which passes
+through the work and is supported by the outboard bearing _B_, could not
+be used for this work, because the top of each cylinder is closed.
+
+When one cylinder is finished the other is set in line with the spindle
+by adjusting the work-table laterally. This adjustment is effected by
+screw _C_, and the required center-to-center distance between the two
+cylinders can be gaged by the micrometer dial _M_ on the cross-feed
+screw, although positive stops are often used in preference. After the
+first cylinder is bored, the dial is set to the zero position by
+loosening the small knurled screw shown, and turning the dial around.
+The feed screw is then rotated until the dial shows that the required
+lateral adjustment is made, which locates the casting for boring the
+second cylinder. The end of the casting is also faced true by a milling
+cutter. Ordinarily, milling cutters are bolted directly to the spindle
+sleeve _A_ on this particular machine, which gives a rigid support for
+the cutter and a powerful drive.
+
+[Illustration: Fig. 11. Cylinder turned around for Machining Valve
+Seats]
+
+The next operation is that of boring and milling the opposite end of the
+cylinder. This end is turned toward the spindle (as shown in Fig. 11)
+without unclamping the work or fixture, by simply turning the circular
+table _T_ half way around. This table is an attachment which is clamped
+to the main table for holding work that must be turned to different
+positions for machining the various parts. Its position is easily
+changed, and as the work remains fixed with relation to the table, the
+alignment between different holes or surfaces is assured, if the table
+is turned the right amount. In this case, the casting needs to be
+rotated one-half a revolution or 180 degrees, and this is done by means
+of angular graduations on the base of the table. The illustration shows
+the casting set for boring the inlet and exhaust valve chambers. The
+different cutters required for boring are mounted on one bar as shown,
+and the casting is adjusted crosswise to bring each valve chamber in
+position, by using the micrometer dial. The single-ended cutter _c_
+forms a shallow circular recess or seat in the raised pad which
+surrounds the opening. The cover joint directly back of the cylinders is
+finished by milling.
+
+[Illustration: Fig. 12. Boring Differential Gear Casing]
+
+=Examples of Boring, Radial Facing and Milling.=--Another example of
+boring, in which the circular table is used, is shown in Fig. 12. The
+work _W_ is a casing for the differential gears of an automobile. It is
+mounted in a fixture _F_ which is bolted to the table. The casting has
+round ends, which are clamped in V-blocks, thus aligning the work. This
+fixture has a guide-bushing _G_ which is centered with the bar and
+cutter in order to properly locate the casting. There is a bearing at
+each end of the casing, and two larger ones in the center. These are
+bored by flat cutters similar to the style illustrated at _A_ in Fig. 3.
+The cutter for the inner bearings is shown at _c_.
+
+[Illustration: Fig. 13. Facing and Turning Flange of Differential Gear
+Casing]
+
+After the bearings are bored, the circular table is turned 90 degrees
+and the work is moved closer to the spindle (as shown in Fig. 13) for
+facing flange _F_ at right angles to the bearings. Circular flanges of
+this kind are faced in a horizontal boring machine by a special
+facing-arm or head _H_. For this particular job this head is clamped
+directly to the spindle sleeve, but it can also be clamped to the
+spindle if necessary. The turning tool is held in a slotted toolpost,
+and it is fed radially for turning the side or face of the flange, by
+the well-known star feed at _S_. When this feed is in operation the bent
+finger _E_ is turned downward so that it strikes one of the star wheel
+arms for each revolution; this turns the wheel slightly, and the
+movement is transmitted to the tool-block by a feed-screw. The
+illustration shows the tool set for turning the outside or periphery of
+the flange. This is done by setting the tool to the proper radius and
+then feeding the work horizontally by shifting the work-table along the
+bed. By referring to Fig. 12 it will be seen that the facing head does
+not need to be removed for boring, as it is attached to the spindle
+driving quill and does not interfere with the longitudinal adjustment of
+the spindle. This facing head is also used frequently for truing the
+flanges of cylinders which are to be bored, and for similar work.
+
+[Illustration: Fig. 14. Example of Work requiring Boring and Milling]
+
+Fig. 14 shows another example of work which requires boring and milling.
+This casting is mounted on a fixture which is bolted to the main table.
+In this case the circular table is not necessary, because the work can
+be finished without swiveling it around. After the boring is completed
+the edge _E_ is trued by the large-face milling cutter _M_ bolted to the
+spindle sleeve. The irregular outline of the edge is followed by moving
+the table crosswise and the spindle vertically, as required.
+
+=Fixture for Cylinder Lining or Bushing.=--A method of holding a
+cylinder lining or bushing while it is being bored is shown in Fig. 15.
+The lining _L_ is mounted in two cast-iron ring-shaped fixtures _F_.
+These fixtures are circular in shape and have flat bases which are
+bolted to the table of the machine. On the inside of each fixture, there
+are four equally spaced wedges _W_ which fit into grooves as shown in
+the end view. These wedges are drawn in against the work by bolts, and
+they prevent the lining from rotating when a cut is being taken. This
+form of fixture is especially adapted for holding thin bronze linings,
+such as are used in pump cylinders, because only a light pressure
+against the wedges is required, and thin work can be held without
+distorting it. If a very thin lining is being bored, it is well to
+loosen the wedges slightly before taking the finishing cut, so that the
+work can spring back to its normal shape.
+
+[Illustration: Fig. 15. Cylinder Lining mounted in Fixture for Boring]
+
+[Illustration: Fig. 16. Detrick & Harvey Horizontal Boring Machine of
+the Floor Type Boring Engine Bed Casting]
+
+=Horizontal Boring Machine of Floor Type.=--The type of horizontal
+boring, drilling and milling machine, shown in Fig. 16, is intended for
+boring heavy parts such as the cylinders of large engines or pumps, the
+bearings of heavy machine beds and similar work. This machine can also
+be used for drilling and milling, although it is intended primarily for
+boring, and the other operations are usually secondary. This design is
+ordinarily referred to as the "floor type," because the work-table is
+low for accommodating large heavy castings. The spindle _S_ which drives
+the boring-bar, and the spindle feeding mechanism, are carried by a
+saddle. This saddle is free to move vertically on the face of column
+_C_ which is mounted on transverse ways extending across the right-hand
+end of the main bed. This construction permits the spindle to move
+vertically or laterally (by traversing the column) either for adjusting
+it to the required position or for milling operations. The spindle also
+has a longitudinal movement for boring. There is an outer bearing _B_
+for supporting the boring-bar, which also has lateral and vertical
+adjustments, so that it can be aligned with the bar.
+
+The work done on a machine of this type is either clamped directly to
+the large bed-plate _A_ (which has a number of T-slots for receiving the
+heads of the clamping bolts) or, in some cases, a special fixture may be
+used or an auxiliary table. Boring machines of this same general
+construction are built in many different sizes. The main spindle of the
+machine illustrated is driven by a motor located at the rear of the
+vertical column _C_, the motion being transmitted to the spindle through
+shafts and gearing. The casting _D_, shown in this particular
+illustration, is for a steam engine of the horizontal type, and the
+operation is that of boring the cylindrical guides or bearings for the
+crosshead. These bearings have a diameter of 15-3/4 inches and are
+37-3/4 inches long. In boring them, two roughing cuts and one finishing
+cut are taken. The end of the casting, which in the assembled engine
+bears against the cylinder, is then faced by means of a regular facing
+arm.
+
+After removing the boring-bar the table _E_ of the special fixture on
+which the casting is mounted is turned one quarter of a revolution. A
+large milling cutter 24 inches in diameter is next mounted on the
+spindle of the machine, and one side of the main bearing, as well as the
+pads for the valve-rod guide-bar brackets, are milled. The table is then
+revolved and the opposite side of the main bearing is milled in the same
+way, the table being accurately located in the different positions by an
+index plunger _F_ which engages holes on the under side. The spindle is
+now moved upward to allow the table to be turned so as to locate the
+bearing end of the frame next to the headstock of the machine. The
+milling cutter is then used to machine the inside and top surfaces of
+the main bearing. By turning the fixture and not changing the position
+of the casting after it is bolted into place, the various surfaces are
+machined in the correct relation to one another without difficulty. This
+is a good example of the work done on horizontal boring machines of the
+floor type.
+
+
+
+
+INDEX
+
+
+                                                                 PAGE
+
+  Acme flat turret lathe, examples of chuck work                  219
+  Acme standard thread and tool for cutting                       159
+  Acme standard thread gage                                       157
+  Acme thread tool, measuring width with vernier caliper     157, 158
+  Accumulation of errors                                     105, 106
+  Aligning lathe centers for cylindrical turning                   16
+  Allowances, average, for forced fits                            130
+    for different classes of fits                                 131
+    for driving fits                                              131
+    for forced fits of given pressure                             133
+    for push fits                                                 131
+    for running fits                                              131
+    for shrinkage fits                                            133
+  Aluminum, lubricant for machining                                53
+    shape of tools for turning                                     53
+    speed and feed for machining                                   53
+  Angle-plate applied to lathe faceplate                           48
+  Angles, gage for accurate measurement of                         97
+  Apron of lathe                                                 4, 5
+  Arbor or mandrel press                                           22
+  Arbors or mandrels for lathe work, types of                      19
+    use of                                                         17
+  Attachment, application of Hendey relieving                     125
+    convex turning for vertical boring mill                       259
+    for coarse threading in lathe                                 160
+    for spherical turning                                         113
+    for taper turning in lathe                                     88
+    Hendey relieving                                              123
+  Automatic chucking and turning machine, Potter & Johnston       223
+    Potter & Johnston, method of "setting-up"                     227
+    Potter & Johnston, turning flywheel in                        236
+
+  Back-gears of lathe                                            3, 4
+  Bardons & Oliver turret lathe, general description              178
+  Bored holes, measuring diameter of                               41
+  Boring and reaming tools for vertical mill                      251
+  Boring and turning mill, vertical, general description          242
+    vertical, holding and setting work                            247
+    vertical, turning in                                          249
+  Boring and turning mill, vertical, turning tools for            253
+  Boring-bar cutters and methods of holding                       280
+  Boring cutters for roughing and finishing cuts                  285
+  Boring cylinders on horizontal machine                          286
+  Boring holes to given center distance in lathe                   51
+  Boring in lathe, example of                                      39
+  Boring large castings in lathe                                   49
+  Boring large holes, cutter-heads used for                       283
+  Boring machine, horizontal                                      275
+    horizontal, examples of work on                           289-297
+    horizontal, floor type                                        294
+    vertical, multiple-spindle type                               274
+  Boring tool, lathe                                               40
+  Box-tools, different designs and examples of work               193
+    for general turret lathe work                                 190
+  Bradford belt-driven lathe, general description                   1
+  Bradford quick change-gear type of lathe                        173
+  Brass, speed for turning                                         52
+    tool for turning in lathe                                      52
+  "Bridle" or "hold-back" for lathe                            26, 27
+  Bullard vertical turret lathe                                   264
+    examples of work                                              268
+  Button method of locating work                                  101
+
+  Caliper tool for taper turning                                   85
+  Calipers, methods of setting                                 10, 11
+  "Cat-head," application in lathe work                            25
+  Center holes, incorrect and correct forms                        32
+  Center indicator, use of                                        100
+  Centered stock, methods of facing ends                           34
+  Centers, lathe, aligning for cylindrical turning                 16
+    lathe, grinder for truing                                      34
+  Centering machine                                                30
+  Centering parts to be turned                                     28
+  Centering, precaution for tool steel                             33
+  Change gears, calculating for thread cutting                    167
+    compound, for thread cutting                                  170
+    for cutting fractional threads                                171
+    for cutting metric pitches                                    171
+    for thread cutting                                            135
+  Chasing dial for "catching threads" when screw cutting          141
+  Chuck, inaccuracy from pressure of jaws                          42
+    lathe, application of                                          37
+    setting work in                                                42
+    universal, independent and combination                         36
+  Chucking and turning machine, Potter & Johnston automatic       223
+    Potter & Johnston automatic, method of "setting-up"           227
+    Potter & Johnston automatic, turning flywheel in              236
+  Chucking machine, New Britain, multiple-spindle type            238
+  Clearance angle for turning tools                                66
+  Clearance of turning tools, meaning of                       62, 63
+  Coarse threading attachment for lathe                           160
+  Collapsing tap, Geometric                                       202
+  Combination chuck for lathe                                      36
+  Compound rest, applied to screw or thread cutting               143
+    applied to taper turning                                       95
+  Convex turning attachment for vertical boring mills             259
+  Copper, tool for turning in lathe                                52
+  Crankshaft lathe, description of R. K. LeBlond special          108
+    operation of R. K. LeBlond                                    110
+  Crankshaft turning in engine lathe                              107
+  Cross-slide stop for threading                                  155
+  Cuts, average depth for turning                                  75
+    roughing and finishing in lathe                        12, 75, 76
+  Cutter-heads, for boring, equipped with adjustable tools   284, 285
+    for horizontal boring machine                                 283
+  Cutters, boring, roughing and finishing types                   285
+    for boring-bars                                               280
+  Cutting lubricants for turning tools                             77
+  Cutting speeds, average for turning                              72
+    based on Taylor's experiments                                  71
+    effect of lubricant on                                         76
+    factors which limit speeds for turning                         72
+    rules for calculating                                          74
+  Cylinder boring machine, multiple-spindle type                  274
+  Cylinder boring on horizontal machine                           286
+  Cylinder lining, fixture for holding when boring                293
+  Cylindrical turning, simple example of                            6
+
+  Davis turret lathe, turning bevel gear blanks                   212
+    turning worm-gear blanks                                      211
+  Depth of cut for turning, average                                75
+  Detrick & Harvey horizontal boring machine, floor type          294
+  Dial for "catching threads" when screw cutting                  141
+  Dial gage, testing concentricity of button with            103, 104
+  Die and tap holders, releasing                                  199
+  Die-heads, self-opening type                                    200
+  Disk gage, for angles and tapers                                 97
+    rules for setting                                          98, 99
+  Dogs or drivers, lathe, application of                           16
+  Drill, flat, for lathe                                           44
+  Drilling and reaming in lathe                                    43
+  Drivers or dogs, lathe, application of                           16
+  Driving fits, allowances for                                    131
+
+  Eccentric turning in lathe                                      106
+  Engine lathe, general description                                 1
+  Errors, accumulation of                                    105, 106
+
+  Faceplate, indexing for multiple-thread cutting                 153
+    lathe, application of angle-plate to                           48
+    lathe, holding work on                                         45
+  Facing ends of centered stock, different methods                 34
+  Feed and depth of cut for turning, average                       75
+  Feeds and speeds for turning based on Taylor's experiments       71
+  Filing and polishing in lathe                                    13
+  Finishing and roughing cuts in lathe                         75, 76
+  Fits, allowances for different classes                          131
+    different classes used in machine construction                129
+    driving, allowances for                                       131
+    forced, allowances for given pressure                         133
+    forced, average allowance for                                 130
+    forced, pressure for                                          132
+    push, allowances for                                          131
+    running, allowances for                                       131
+    shrinkage, allowances for                                     133
+  Fixture for holding thin lining when boring                     293
+  Flat drill and holder for lathe                                  44
+  Flat turret lathe, Acme, examples of chuck work                 219
+    Hartness, example of turning                                  213
+    Jones & Lamson double-spindle type                            221
+  Floating reamer holders                                         271
+  Flywheel, finishing in one setting in turret lathe              186
+    finishing in two settings in turret lathe                     189
+    machining in turret lathe                                     184
+    turning in Potter & Johnston automatic                        236
+    turning in vertical boring mill                               255
+  Follow-rest for lathe                                            27
+  Forced fits, allowances for given pressure                      133
+    average allowance for                                         130
+    pressure generally used in assembling                         132
+  Fractional threads, change gears for cutting                    171
+
+  Gage, disk, for angles and tapers                                97
+    disk, rules for setting                                    98, 99
+    for testing V-thread tool                                     138
+    standard plug, for holes                                       42
+    thread, Acme standard                                         157
+  Geometric collapsing tap                                        202
+  Geometric self-opening die-head                                 200
+  Gisholt convex attachment for vertical mill                     259
+  Gisholt vertical boring mill, general description               242
+  Grinder for truing lathe centers                                 34
+  Grinding lathe tools                                             62
+
+  Hartness flat turret lathe, example of turning                  213
+  Hendey relieving attachment                                     123
+    application of, for relieving taps, cutters and hobs          125
+  "Hold-back" or "bridle" for lathe                            26, 27
+  Hollow mills for turret lathe                                   198
+  Horizontal boring machine                                       275
+    Detrick & Harvey floor type                                   294
+    examples of work                                          289-297
+
+  Independent chuck for lathe                                      36
+  Index plate, change gear, for lathe                             137
+  Indicator, center, use on lathe                                 100
+    for "catching threads" when screw cutting                     141
+    test, truing buttons with                                102, 103
+    thread, for lathe apron, principle of                         142
+  Inserted cutter turning tools for lathe                          58
+  Internal threading                                              154
+
+  Jones & Lamson double-spindle flat turret lathe                 221
+
+  Knurling in lathe and tool used                                 122
+
+  Lard oil as a cutting lubricant                                  78
+  Lathe, boring holes to given center distance in                  51
+    boring large castings in                                       49
+    boring small hole with                                   104, 105
+    cutting threads in                                            135
+    drilling small hole with                                      104
+    general description of Bradford                                 1
+    LeBlond crankshaft, operation of                              110
+    Lo-swing, general description                                 115
+    method of handling when cutting threads                       138
+    quick change-gear type                                        173
+    R. K. LeBlond special crankshaft                              108
+    turret type, general description                              178
+  Lathe centers, grinder for truing                                34
+  Lathe chucks, application of                                     37
+    universal, independent and combination                         36
+  Lathe faceplate, holding work on                                 45
+  Lathe follow-rest                                                27
+  Lathe steadyrest                                                 23
+    application of, when boring                                    25
+  Lathe taper attachment                                           88
+    practical application of                                       90
+  Lathe tool grinding                                              62
+  Lathe tools, angle of clearance                                  66
+    angle of keenness                                              67
+    application of various types                                   56
+    slope of cutting edge                                      66, 67
+  Lathe turning tools, inserted-cutter type                        58
+    set of tools for general work                                  54
+  Lead of thread, definition of                                   146
+  LeBlond, R. K., lathe for crankshaft turning                    108
+  Left-hand thread, method of cutting                             148
+  Lining, fixture for holding when boring                         293
+  Lo-swing lathe, general description                             115
+    example of multiple-turning                                   117
+  Lubricant, effect on cutting speed                               76
+    for cooling turning tools                                      77
+    for machining aluminum                                         53
+    lard oil as a cutting                                          78
+  Lucas horizontal boring machine                                 275
+
+  Mandrel or arbor press                                           22
+  Mandrels or arbors for lathe work, types of                      19
+    for lathe work, use of                                         17
+  Metric pitches, change gears for cutting                        171
+  Micrometer for measuring threads                                162
+  Mills, hollow, for turret lathe                                 198
+  Multiple-spindle chucking machine, New Britain                  238
+  Multiple-thread cutting, indexing faceplate for                 153
+  Multiple threads                                                146
+    method of cutting                                             150
+    setting tool when cutting                                     152
+  Multiple-turning in Lo-swing lathe                              117
+
+  New Britain multiple-spindle chucking machine                   238
+  Newall Engineering Co's fit allowances                          131
+
+  Pistons, gasoline engine, turning in turret lathe               204
+  Piston rings, attachment for turning in turret lathe            210
+    turning in turret lathe                                       206
+  Piston turning in Pratt & Whitney turret lathe                  208
+  Pitch, metric, change gears for cutting                         171
+  Pitch of thread, definition of                                  146
+  Plug gage, standard                                              42
+  Polishing and filing in lathe                                    13
+  Potter & Johnston automatic chucking and turning machine        223
+    method of "setting-up"                                        227
+    turning flywheel in                                           236
+  Pratt & Whitney turret lathe, arranged for piston turning       208
+    equipped with piston ring turning attachment                  210
+  Press for arbors or mandrels                                     22
+  Pressure generally used in assembling forced fits               132
+  Push fits, allowances for                                       131
+
+  Quick change-gear type of lathe                                 173
+
+  Reamer holders, floating type                                   271
+  Reaming and drilling in lathe                                    43
+  Releasing die and tap holders                                   199
+  Relieving attachment, Hendey                                    123
+  Relieving attachment, Hendey, application of                    125
+  Relieving hobs or taps having spiral flutes                     128
+  Rivett-Dock threading tool                                      164
+  Roughing and finishing cuts in lathe                         75, 76
+  Running fits, allowances for                                    131
+
+  Screw cutting, calculating change gears for                     167
+    compound gearing for                                          170
+    in engine lathe                                               135
+    method of handling lathe                                      138
+    selecting change gears for                                    135
+    with compound rest                                            143
+  Screws, cutting to compensate for shrinkage                     165
+    metric, change gears for cutting                              171
+    testing size of                                               161
+  Selecting type of turning machine                               240
+  Shrinkage, cutting screws to compensate for                     165
+  Shrinkage fits, allowances for                                  133
+  Side-tool, facing with                                            7
+  Speeds for turning, average                                      72
+    based on Taylor's experiments                                  71
+    effect of lubricant                                            76
+    factors which limit                                            72
+    rules for calculating                                          74
+  Spherical turning                                               111
+    attachments for                                               113
+  "Spider" for supporting bushing while turning                48, 49
+  Spiral flutes, method of relieving hobs or taps with            128
+  Square thread and method of cutting                        149, 159
+  Steadyrest, application of when boring                           25
+    for engine lathe                                               23
+  Stop for lathe cross-slide when threading                       155
+
+  Tap and die holders, releasing type                             199
+  Taper attachment for lathe                                       88
+    practical application of                                       90
+  Taper boring with taper attachment                               90
+  Taper threading, position of tool for                           154
+  Taper turning, adjustment of tailstock center for                82
+    by offset-center method                                        80
+    examples of                                                    83
+    height of tool for                                             94
+    in vertical boring mill                                       261
+    in vertical mill with horizontal and vertical feeds           262
+    setting tailstock center with caliper tool                     85
+    setting tailstock center with square                           87
+    with compound rest                                             95
+    with taper attachment                                      92, 93
+  Tapers, gage for accurate measurement of                         97
+  Tapers, rules for figuring                                       97
+  Test indicator, truing buttons with                        102, 103
+  Test or center indicator for use on lathe                       100
+  Thread cutting, calculating change gears for                    167
+    compound gearing for                                          170
+    cross-slide stop used for                                     155
+    indexing faceplate for multiple threads                       153
+    in engine lathe                                               135
+    internal                                                      154
+    method of handling lathe                                      138
+    selecting change gears for                                    135
+    taper, position of tool for                                   154
+    with compound rest                                            143
+  Thread gage, Acme standard                                      157
+  Thread indicator for lathe apron                           141, 142
+  Thread micrometer                                               162
+  Thread tool, Acme, measuring width with vernier caliper    157, 158
+    for cutting V-thread                                          138
+  Thread tools for standard threads                               159
+  Threads, Acme standard, and tool for cutting                    159
+    change gears for fractional                                   171
+    cutting to compensate for shrinkage                           165
+    different forms of                                            144
+    left-hand, method of cutting                                  148
+    metric, change gears for cutting                              171
+    multiple                                                      146
+    multiple, method of cutting                                   150
+    multiple, setting tool when cutting                           152
+    sharp V, and tool for cutting                                 159
+    square, and method of cutting                            149, 159
+    testing size of                                               161
+    three-wire system for measuring                               163
+    U. S. standard, and tool for cutting                     146, 159
+    Whitworth standard, and tool for cutting                 158, 159
+    worm, and tool for cutting                               159, 160
+  Threading attachment, lathe, for coarse threads                 160
+  Threading tool, Rivett-Dock                                     164
+  Tool grinding                                                    62
+  Tools for lathe, set for general turning                         54
+  Tools for turning, angle of clearance                            66
+    angle of keenness                                              67
+    inserted-cutter type                                           58
+    slope of cutting edge                                      66, 67
+  Tools for turret lathe                                          190
+  Tools, lathe, application of various types                       56
+  Turning, cylindrical, simple example of                           6
+    eccentric                                                     106
+    multiple, in Lo-swing lathe                                   117
+    with front and rear tools                                     114
+  Turning speeds, average for lathe                                72
+    based on Taylor's experiments                                  71
+    factors which limit                                            72
+    rules for calculating                                          74
+  Turning tools, angle of clearance                                66
+    angle of keenness                                              67
+    for aluminum                                                   53
+    for brass                                                      52
+    for copper                                                     52
+    for lathe, position of                                         60
+    for lathe, set of, for general work                            54
+    inserted-cutter type for lathe                                 58
+    slope of cutting edge                                      66, 67
+  Turret lathe, Bardons & Oliver, general description             178
+    examples of chuck work in Acme flat                           219
+    Hartness flat, example of turning                             213
+    Jones & Lamson double-spindle type                            221
+    machining flywheels in                                        184
+    Pratt & Whitney arranged for piston turning                   208
+    piston ring turning attachment for                            210
+    tools for general work                                        190
+    turning bevel gear blanks in Davis                            212
+    turning gasoline engine pistons in                            204
+    turning piston rings in                                       206
+    turning worm-gear blanks in Davis                             211
+    typical example of turret lathe work                          181
+  Turret lathe tools, miscellaneous types                         202
+  Turret lathe type of vertical boring mill                       264
+  Type of turning machine, factors which govern selection         240
+
+  U. S. standard thread                                           159
+    method of cutting                                             146
+  Universal chuck for lathe                                        36
+
+  V-thread and tool for cutting                                   159
+  Vertical boring mill, Bullard turret lathe type                 264
+    convex turning attachment                                     259
+    general description                                           242
+    holding and setting work                                      247
+    taper turning in                                              261
+    taper turning with horizontal and vertical feeds              262
+    tools for boring and reaming                                  251
+    turning flywheel in                                           255
+    turning tools for                                             253
+  Vertical turret lathe, Bullard, examples of work                268
+
+  Whitworth standard thread and tool for cutting             158, 159
+  Wire system for measuring threads                               163
+  Worm thread and tool for cutting                           159, 160
+
+
+
+
+  Transcriber's notes on changes made to text:
+    Left as in original:
+      use of degree, deg. and °; use of minute, min. and '.
+
+    Standardised to the most commonly used in the book:
+      backgear to back-gear; camshaft to cam-shaft; crankpin to
+      crank-pin; face-plate to faceplate; out-board to outboard;
+      over-hang to overhang; setscrew to set-screw; steady-rest
+      to steadyrest; subdivision(s) to sub-division(s); tail-stock
+      to tailstock; thumbscrew to thumb-screw; tool-post to toolpost;
+      tool-slide to toolslide; hand-wheel to handwheel; U.S. to U. S.
+
+    Page 64 had a blotched (illegible) word, this has been replaced by
+    (large and rigid) work.
+
+    Table of Contents: largely re-compiled to create one-to-one links
+    with named paragraphs and sections in text.
+
+
+
+
+
+End of the Project Gutenberg EBook of Turning and Boring, by Franklin D. Jones
+
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+<pre>
+
+The Project Gutenberg EBook of Turning and Boring, by Franklin D. Jones
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: Turning and Boring
+       A specialized treatise for machinists, students in the
+              industrial and engineering schools, and apprentices, on
+              turning and boring methods, etc.
+
+Author: Franklin D. Jones
+
+Release Date: October 4, 2010 [EBook #34030]
+
+Language: English
+
+Character set encoding: ISO-8859-1
+
+*** START OF THIS PROJECT GUTENBERG EBOOK TURNING AND BORING ***
+
+
+
+
+Produced by Juliet Sutherland, Harry Lamé and the Online
+Distributed Proofreading Team at https://www.pgdp.net
+
+
+
+
+
+
+</pre>
+
+
+<p class="center fsize275 gesp"><b>TURNING AND<br />BORING</b></p>
+
+<div class="ind40">
+<p class="center">A SPECIALIZED TREATISE FOR MACHINISTS,
+STUDENTS IN INDUSTRIAL AND ENGINEERING
+SCHOOLS, AND APPRENTICES, ON
+TURNING AND BORING METHODS, INCLUDING
+MODERN PRACTICE WITH ENGINE
+LATHES, TURRET LATHES, VERTICAL AND
+HORIZONTAL BORING MACHINES</p>
+</div>
+
+<p>&nbsp;</p>
+
+<p class="center smcap"><b>By<span class="gesp"> FRANKLIN D. JONES</span></b></p>
+
+<p class="smcap center fsize80">Associate Editor of MACHINERY<br />
+Author of &#8220;Planing and Milling&#8221;</p>
+<p>&nbsp;</p>
+
+<hr class="c10" />
+
+<p class="center fsize80"><i><span class="gesp">FIRST EDITION</span></i><br />
+FIFTH PRINTING</p>
+
+<hr class="c10" />
+
+<p>&nbsp;</p>
+
+<p class="center"><span class="fsize80">NEW YORK</span><br />
+<span class="gesp">THE INDUSTRIAL PRESS</span><br />
+<span class="smcap fsize80">London: THE MACHINERY PUBLISHING CO., Ltd.<br />
+1919</span></p>
+
+<hr class="c25" />
+
+<p class="center"><span class="smcap fsize80">Copyright, 1914</span><br />
+<span class="fsize80">BY</span><br />
+<span class="gesp">THE INDUSTRIAL PRESS</span><br />
+NEW YORK</p>
+
+<hr class="c25" />
+<span class="pagenum"><a name="Pg_v" id="Pg_v">[v]</a></span>
+<h2>PREFACE</h2>
+<hr class="c05" />
+
+<p>Specialization in machine-tool manufacture has been developed
+to such a degree that there is need also for treatises which
+specialize on different classes of tools and their application in
+modern practice. This book deals exclusively with the use of
+various types of turning and boring machines and their attachments,
+and is believed to be unusually complete. In addition
+to standard practice, it describes many special operations
+seldom or never presented in text-books. Very little space is
+given to mere descriptions of different types of machine tools, the
+principal purpose being to explain the use of the machine and the
+practical problems connected with its operation, rather than
+the constructional details. No attempt has been made to
+describe every machine or tool which might properly be included,
+but rather to deal with the more important and useful
+operations, especially those which illustrate general principles.</p>
+
+<p>Readers of mechanical literature are familiar with <span class="smcap">Machinery's</span>
+25-cent Reference Books, of which one hundred and
+twenty-five different titles have been published during the past
+six years. Many subjects, however, cannot be adequately
+covered in all their phases in books of this size, and in response
+to a demand for more comprehensive and detailed treatments
+on the more important mechanical subjects, it has been deemed
+advisable to bring out a number of larger volumes, of which this
+is one. This work includes much of the material published in
+<span class="smcap">Machinery's</span> Reference Books Nos. 91, 92 and 95, together
+with a great amount of additional information on modern boring
+and turning methods.</p>
+
+<p>It is a pleasure to acknowledge our indebtedness to the manufacturers
+who generously supplied illustrations and data, including
+many interesting operations from actual practice.
+Much valuable information was also obtained from <span class="smcap">Machinery</span>.</p>
+
+<p class="textright">F. D. J.</p>
+
+<p><span class="smcap">New York</span>, <i>May, 1914</i>.</p>
+<p>&nbsp;</p>
+
+<hr class="c25" />
+<p class="pagenum"><a name="Pg_vii" id="Pg_vii">[vii]</a></p>
+<h2>CONTENTS</h2>
+<hr class="c05" />
+
+<table border="0" cellpadding="1" cellspacing="1" summary="ToC" class="tab70">
+
+<tr><td>&nbsp;</td><td align="right"><span class="smcap">Pages</span></td></tr>
+
+<tr><td align="center" colspan="2" style="padding-bottom: 0.7em;"><span class="smcap"><a href="#Chapnum_1">Chapter I</a></span></td></tr>
+<tr><td align="center" colspan="2" style="padding-bottom: 0.7em;"><a href="#Chapnum_1">THE ENGINE LATHE&mdash;TURNING AND BORING OPERATIONS</a></td></tr>
+<tr><td class="toc">
+<a href="#Secnum_1_1">General Description of an Engine Lathe</a>&mdash;<a href="#Secnum_1_2">Example of Cylindrical
+Turning</a>&mdash;<a href="#Secnum_1_3">Facing the Ends Square with a Side-tool</a>&mdash;<a href="#Secnum_1_4">Turning
+Tool&mdash;Turning Work Cylindrical</a>&mdash;<a href="#Secnum_1_5">Roughing and Finishing Cuts</a>&mdash;<a href="#Secnum_1_6">Filing
+and Finishing</a>&mdash;<a href="#Secnum_1_7">Aligning Centers for Cylindrical Turning</a>&mdash;<a href="#Secnum_1_8">Application
+of Drivers or Dogs</a>&mdash;<a href="#Secnum_1_9">Lathe Arbors or Mandrels</a>&mdash;<a href="#Secnum_1_10">Different Types of
+Lathe Arbors</a>&mdash;<a href="#Secnum_1_11">Mandrel or Arbor Press</a>&mdash;<a href="#Secnum_1_12">Steadyrest for Supporting
+Flexible Parts</a>&mdash;<a href="#Secnum_1_13">Application of Steadyrest when Boring</a>&mdash;<a href="#Secnum_1_14">The
+Follow-rest</a>&mdash;<a href="#Secnum_1_15">Centering Parts to be Turned</a>&mdash;<a href="#Secnum_1_16">Centering
+Machine</a>&mdash;<a href="#Secnum_1_17">Different Forms of Centers</a>&mdash;<a href="#Secnum_1_18">Precaution When Centering Tool
+Steel</a>&mdash;<a href="#Secnum_1_19">Facing the Ends of Centered Stock</a>&mdash;<a href="#Secnum_1_20">Truing Lathe
+Centers</a>&mdash;<a href="#Secnum_1_21">Universal, Independent and Combination Chucks</a>&mdash;<a href="#Secnum_1_22">Application
+of Chucks</a>&mdash;<a href="#Secnum_1_23">Example of Boring</a>&mdash;<a href="#Secnum_1_24">Measuring Bored
+Holes</a>&mdash;<a href="#Secnum_1_25">Setting Work in the Chuck</a>&mdash;<a href="#Secnum_1_26">Inaccuracy from Pressure of Chuck
+Jaws</a>&mdash;<a href="#Secnum_1_27">Drilling and Reaming</a>&mdash;<a href="#Secnum_1_28">Holding Work on
+Faceplate</a>&mdash;<a href="#Secnum_1_29">Application of Angle-plate to Faceplate</a>&mdash;<a href="#Secnum_1_30">Supporting Outer
+End of Chucked Work</a>&mdash;<a href="#Secnum_1_31">Boring Large Castings in the Lathe</a>&mdash;<a href="#Secnum_1_32">Boring Holes
+to a Given Center Distance</a>&mdash;<a href="#Secnum_1_33">Turning Brass, Bronze and Copper</a>&mdash;<a href="#Secnum_1_34">Machining
+Aluminum</a></td><td style="width: 10%" align="right" valign="bottom">&nbsp;<a href="#Pg_1">1-53</a>&nbsp;</td></tr>
+<tr><td colspan="2">&nbsp;</td></tr>
+
+<tr><td align="center" colspan="2" style="padding-bottom: 0.7em;"><span class="smcap"><a href="#Chapnum_2">Chapter II</a></span></td></tr>
+<tr><td align="center" colspan="2" style="padding-bottom: 0.7em;"><a href="#Chapnum_2">LATHE TURNING TOOLS AND CUTTING SPEEDS</a></td></tr>
+<tr><td class="toc">
+<a href="#Secnum_2_1">Turning Tools for General Work</a>&mdash;<a href="#Secnum_2_2">Tool-holders with Inserted
+Cutters</a>&mdash;<a href="#Secnum_2_3">The Position of Turning Tools</a>&mdash;<a href="#Secnum_2_4">Tool
+Grinding</a>&mdash;<a href="#Secnum_2_5">Shape or Contour of Cutting Edge</a>&mdash;<a href="#Secnum_2_6">Direction of Top Slope for
+Turning Tools</a>&mdash;<a href="#Secnum_2_7">Clearance for the Cutting Edge</a>&mdash;<a href="#Secnum_2_8">Angle of Tool-point and
+Amount of Top Slope</a>&mdash;<a href="#Secnum_2_9">Grinding a Lathe Tool</a>&mdash;<a href="#Secnum_2_10">Cutting Speeds and
+Feeds</a>&mdash;<a href="#Secnum_2_11">Average Cutting Speeds for Turning</a>&mdash;<a href="#Secnum_2_12">Factors which Limit the
+Cutting Speed</a>&mdash;<a href="#Secnum_2_13">Rules for Calculating Cutting Speeds</a>&mdash;<a href="#Secnum_2_14">Feed of Tool and
+Depth of Cut</a>&mdash;<a href="#Secnum_2_15">Effect of Lubricant on Cutting Speed</a>&mdash;<a href="#Secnum_2_16">Lubricants Used for
+Turning</a>&mdash;<a href="#Secnum_2_17">Lard Oil as a Cutting Lubricant</a>
+</td><td align="right" valign="bottom">&nbsp;<a href="#Pg_54">54-79</a>&nbsp;
+</td></tr><tr><td colspan="2">&nbsp;</td></tr>
+
+<tr><td align="center" colspan="2" style="padding-bottom: 0.7em;"><span class="smcap"><a href="#Chapnum_3">Chapter III</a></span></td></tr>
+<tr><td align="center" colspan="2" style="padding-bottom: 0.7em;"><a href="#Chapnum_3">TAPER TURNING&mdash;SPECIAL OPERATIONS&mdash;FITTING</a></td></tr>
+<tr><td class="toc">
+<a href="#Secnum_3_1">Setting Tailstock Center for Taper Turning</a>&mdash;<a href="#Secnum_3_2">Example of Taper
+Turning</a>&mdash;<a href="#Secnum_3_3">Setting the Tailstock Center with a Caliper Tool</a>&mdash;<a href="#Secnum_3_4">Setting the
+Tailstock Center with a Square</a>&mdash;<a href="#Secnum_3_5">The Taper Attachment</a>&mdash;<a href="#Secnum_3_6">Application of
+Taper Attachment</a>&mdash;<a href="#Secnum_3_7">Height of Tool when Turning Tapers</a>&mdash;<a href="#Secnum_3_8">Taper Turning with
+the Compound Rest</a>&mdash;<a href="#Secnum_3_9">Accurate Measurement of Angles and Tapers</a>&mdash;<a href="#Secnum_3_10">To Find
+Center Distance for a Given Taper</a>&mdash;<a href="#Secnum_3_11">To Find Center Distance for a Given
+Angle</a>&mdash;<a href="#Secnum_3_12">To Find Angle for Given Taper per Foot</a>&mdash;<a href="#Secnum_3_13">To Find Angle for Given
+Disk Dimensions</a>&mdash;<a href="#Secnum_3_14">Use of the Center Indicator</a>&mdash;<a href="#Secnum_3_15">Locating Work by the Button
+Method</a>&mdash;<a href="#Secnum_3_16">Eccentric Turning</a>&mdash;<a href="#Secnum_3_17">Turning a Crankshaft in a
+Lathe</a>&mdash;<a href="#Secnum_3_18">Special Crankshaft Lathe</a>&mdash;<a href="#Secnum_3_19">Operation of Special Crankshaft
+Lathe</a>&mdash;<a href="#Secnum_3_20">Spherical Turning</a>&mdash;<a href="#Secnum_3_21">Spherical Turning Attachments</a>&mdash;<a
+href="#Secnum_3_22">Turning with Front and Rear Tools</a>&mdash;<a href="#Secnum_3_23">A Multiple-tool Lathe</a>&mdash;<a
+href="#Secnum_3_24">Examples of Multiple Turning</a>&mdash;<a href="#Secnum_3_25">Knurling in the Lathe</a>&mdash;<a
+href="#Secnum_3_26">Relieving Attachment</a>&mdash;<a href="#Secnum_3_27">Application of Relieving Attachment</a>&mdash;<a
+href="#Secnum_3_28">Relieving Hobs or Taps Having Spiral Flutes</a>&mdash;<a href="#Secnum_3_29">Classes of Fits Used in Machine
+Construction</a>&mdash;<a href="#Secnum_3_30">Forced Fits</a>&mdash;<a href="#Secnum_3_31">Allowance for Forced Fits</a>&mdash;<a
+href="#Secnum_3_32">Pressure for Forced Fits</a>&mdash;<a href="#Secnum_3_33">Allowance for Given Pressure</a>&mdash;<a
+href="#Secnum_3_34">Shrinkage Fits</a>
+</td><td align="right" valign="bottom">&nbsp;<a href="#Pg_80">80-134</a>&nbsp;</td></tr>
+<tr><td colspan="2">&nbsp;</td></tr>
+
+<tr><td colspan="2"></td></tr><tr><td align="center" colspan="2" style="padding-bottom: 0.7em;"><span class="smcap"><a href="#Chapnum_4">Chapter IV</a></span>
+<span class="pagenum"><a name="Pg_viii" id="Pg_viii">[viii]</a></span></td></tr>
+<tr><td align="center" colspan="2" style="padding-bottom: 0.7em;"><a href="#Chapnum_4">THREAD CUTTING IN THE LATHE</a></td></tr>
+<tr><td class="toc">
+<a href="#Secnum_4_1">Selecting the Change Gears for Thread Cutting</a>&mdash;<a href="#Secnum_4_2">The Thread Tool</a>&mdash;<a
+href="#Secnum_4_3">Cutting the Thread</a>&mdash;<a href="#Secnum_4_4">Indicator or Chasing Dial for Catching Threads</a>&mdash;<a
+href="#Secnum_4_5">Principle of the Thread Indicator</a>&mdash;<a href="#Secnum_4_6">Replacing Sharpened Thread Tool</a>&mdash;<a
+href="#Secnum_4_7">Use of Compound Rest for Thread Cutting</a>&mdash;<a href="#Secnum_4_8">Threads Commonly Used</a>&mdash;<a
+href="#Secnum_4_9">Multiple Threads</a>&mdash;<a href="#Secnum_4_10">Cutting a U. S. Standard Thread</a>&mdash;<a
+href="#Secnum_4_11">Cutting a Left-hand Thread</a>&mdash;<a href="#Secnum_4_12">Cutting a Square Thread</a>&mdash;<a
+href="#Secnum_4_13">Cutting Multiple Threads</a>&mdash;<a href="#Secnum_4_14">Setting Tool When Cutting Multiple Threads</a>&mdash;<a
+href="#Secnum_4_15">Taper Threading</a>&mdash;<a href="#Secnum_4_16">Internal Threading</a>&mdash;<a href="#Secnum_4_17">Stop for Thread
+Tools</a>&mdash;<a href="#Secnum_4_18">The Acme Standard Thread</a>&mdash;<a href="#Secnum_4_19">The Whitworth Thread</a>&mdash;<a
+href="#Secnum_4_20">Worm Threads</a>&mdash;<a href="#Secnum_4_21">Coarse Threading Attachment</a>&mdash;<a href="#Secnum_4_22">Testing
+the Size of a Thread</a>&mdash;<a href="#Secnum_4_23">The Thread Micrometer</a>&mdash;<a href="#Secnum_4_24">Three-wire System of
+Measuring Threads</a>&mdash;<a href="#Secnum_4_25">Rivett-Dock Threading Tool</a>&mdash;<a href="#Secnum_4_26">Cutting Screws to
+Compensate for Shrinkage</a>&mdash;<a href="#Secnum_4_27">Calculating Change Gears for Thread Cutting</a>&mdash;<a
+href="#Secnum_4_28">Lathes with Compound Gearing</a>&mdash;<a href="#Secnum_4_29">Fractional Threads</a>&mdash;<a
+href="#Secnum_4_30">Change Gears for Metric Pitches</a>&mdash;<a href="#Secnum_4_31">Quick Change-gear Type of Lathe</a>
+</td><td align="right" valign="bottom">&nbsp;<a href="#Pg_135">135-177</a>&nbsp;</td></tr>
+<tr><td colspan="2">&nbsp;</td></tr>
+
+<tr><td align="center" colspan="2" style="padding-bottom: 0.7em;"><span class="smcap"><a href="#Chapnum_5">Chapter V</a></span></td></tr>
+<tr><td align="center" colspan="2" style="padding-bottom: 0.7em;"><a href="#Chapnum_5">TURRET LATHE PRACTICE</a></td></tr>
+<tr><td class="toc">
+<a href="#Secnum_5_1">General Description of a Turret Lathe</a>&mdash;<a href="#Secnum_5_2">Example of Turret Lathe Work</a>&mdash;<a
+href="#Secnum_5_3">Machining Flywheels in Turret Lathe</a>&mdash;<a href="#Secnum_5_4">Finishing a Flywheel at One Setting in Turret
+Lathe</a>&mdash;<a href="#Secnum_5_5">Finishing a Webbed Flywheel in Two Settings</a>&mdash;<a href="#Secnum_5_6">Tools for Turret
+Lathes</a>&mdash;<a href="#Secnum_5_7">Box-tools</a>&mdash;<a href="#Secnum_5_8">Examples of Box-tool Turning</a>&mdash;<a
+href="#Secnum_5_9">Hollow Mills</a>&mdash;<a href="#Secnum_5_10">Releasing Die and Tap Holders</a>&mdash;<a
+href="#Secnum_5_11">Self-opening Die Heads</a>&mdash;<a href="#Secnum_5_12">Collapsing Taps</a>&mdash;<a href="#Secnum_5_13">Miscellaneous
+Turret Lathe Tools</a>&mdash;<a href="#Secnum_5_14">Turning Gasoline Engine Pistons in Turret Lathe</a>&mdash;<a
+href="#Secnum_5_15">Turning Piston Rings in Turret Lathe</a>&mdash;<a href="#Secnum_5_16">Piston Turning in Pratt and Whitney Turret
+Lathe</a>&mdash;<a href="#Secnum_5_17">Attachment for Turning Piston Rings</a>&mdash;<a href="#Secnum_5_18">Turning Worm-gear Blanks in
+Turret Lathe</a>&mdash;<a href="#Secnum_5_19">Turning Bevel Gear Blanks</a>&mdash;<a href="#Secnum_5_20">Shell Turning Operation in Flat
+Turret Lathe</a>&mdash;<a href="#Secnum_5_21">Chuck Work in Flat Turret Lathe</a>&mdash;<a href="#Secnum_5_22">Double-spindle Flat Turret
+Lathe</a>&mdash;<a href="#Secnum_5_23">Automatic Chucking and Turning Machine</a>&mdash;<a href="#Secnum_5_24">Example of Work on
+Automatic Turning Machine</a>&mdash;<a href="#Secnum_5_25">Determining Speed and Feed Changes</a>&mdash;<a href="#Secnum_5_26">Setting the
+Turret Slide</a>&mdash;<a href="#Secnum_5_27">Setting the Cross-slide Cam</a>&mdash;<a href="#Secnum_5_28">Setting the Boring Tool for
+Recessing</a>&mdash;<a href="#Secnum_5_29">Adjustments for Automatic Feed and Speed Changes</a>&mdash;<a href="#Secnum_5_30">Turning
+Flywheel in Automatic Chucking and Turning Machine</a>&mdash;<a href="#Secnum_5_31">Automatic Multiple-spindle Chucking
+Machine</a>&mdash;<a href="#Secnum_5_32">Selecting Type of Turning Machine</a></td>
+<td align="right" valign="bottom">&nbsp;<a href="#Pg_178">178-241</a>&nbsp;</td></tr>
+<tr><td colspan="2">&nbsp;</td></tr>
+
+<tr><td align="center" colspan="2" style="padding-bottom: 0.7em;"><span class="smcap"><a href="#Chapnum_6">Chapter VI</a></span>
+<span class="pagenum"><a name="Pg_ix" id="Pg_ix">[ix]</a></span></td></tr>
+<tr><td align="center" colspan="2" style="padding-bottom: 0.7em;"><a href="#Chapnum_6">VERTICAL BORING MILL PRACTICE</a></td></tr>
+<tr><td class="toc">
+<a href="#Secnum_6_1">Boring and Turning in a Vertical Boring Mill</a>&mdash;<a href="#Secnum_6_2">Holding and Setting Work on Boring Mill
+Table</a>&mdash;<a href="#Secnum_6_3">Turning in a Boring Mill</a>&mdash;<a href="#Secnum_6_4">Boring Operations</a>&mdash;<a
+href="#Secnum_6_5">Turning Tools for the Vertical Boring Mill</a>&mdash;<a href="#Secnum_6_6">Turning a Flywheel on a Vertical
+Mill</a>&mdash;<a href="#Secnum_6_7">Convex Turning Attachment for Boring Mills</a>&mdash;<a href="#Secnum_6_8">Turning Taper or Conical
+Surfaces</a>&mdash;<a href="#Secnum_6_9">Turret-lathe Type of Vertical Boring Mill</a>&mdash;<a href="#Secnum_6_10">Examples of Vertical
+Turret Lathe Work</a>&mdash;<a href="#Secnum_6_11">Floating Reamer Holders</a>&mdash;<a href="#Secnum_6_12">Multiple Cylinder Boring
+Machine</a>
+</td><td align="right" valign="bottom">&nbsp;<a href="#Pg_242">242-274</a>&nbsp;
+</td></tr>
+<tr><td colspan="2">&nbsp;</td></tr>
+
+<tr><td align="center" colspan="2" style="padding-bottom: 0.7em;"><span class="smcap"><a href="#Chapnum_7">Chapter VII</a></span></td></tr>
+<tr><td align="center" colspan="2" style="padding-bottom: 0.7em;"><a href="#Chapnum_7">HORIZONTAL BORING MACHINES</a></td></tr>
+<tr><td class="toc">
+<a href="#Secnum_7_1">Horizontal Boring Machine with Vertical Table Adjustment</a>&mdash;<a href="#Secnum_7_2">Drilling and
+Boring&mdash;Cutters Used</a>&mdash;<a href="#Secnum_7_3">Cutter-heads for Boring Large Holes</a>&mdash;<a href="#Secnum_7_4">Cylinder
+Boring</a>&mdash;<a href="#Secnum_7_5">Boring a Duplex Gasoline Engine Cylinder</a>&mdash;<a href="#Secnum_7_6">Examples of Boring, Radial
+Facing and Milling</a>&mdash;<a href="#Secnum_7_7">Fixture for Cylinder Lining or Bushing</a>&mdash;<a href="#Secnum_7_8">Horizontal
+Boring Machine of Floor Type</a>
+</td><td align="right" valign="bottom">&nbsp;<a href="#Pg_275">275-297</a>&nbsp;</td></tr>
+<tr><td colspan="2">&nbsp;</td></tr>
+
+<tr><td align="justify"><a href="#Pg_299">Index</a></td><td align="right" valign="bottom"><a href="#Pg_299">299</a>&nbsp;</td></tr>
+</table>
+<p>&nbsp;</p>
+
+<hr class="c25" />
+<p class="pagenum"><a name="Pg_1" id="Pg_1">[1]</a></p>
+<h1>TURNING AND BORING</h1>
+<hr class="c25" />
+
+<a name="Chapnum_1" id="Chapnum_1"></a><h2>CHAPTER I</h2>
+<h3>THE ENGINE LATHE&mdash;TURNING AND BORING OPERATIONS</h3>
+<hr class="c05" />
+
+<a name="Secnum_1_1" id="Secnum_1_1"></a><p>The standard &#8220;engine&#8221; lathe, which is the type commonly
+used by machinists for doing general work, is one of the most
+important tools in a machine shop, because it is adapted to a
+great variety of operations, such as turning all sorts of cylindrical
+and taper parts, boring holes, cutting threads, etc. The
+illustration <a href="#Fig_1_1">Fig. 1</a> shows a lathe which, in many respects, represents
+a typical design, and while some of the parts are arranged
+differently on other makes, the general construction is practically
+the same as on the machine illustrated.</p>
+
+<a name="Fig_1_1" id="Fig_1_1"></a>
+<div class="figcenter"><img src="images/010sm.jpg" alt="Bradford Belt-driven Lathe&mdash;View of Front or Operating Side" />
+<p class="caption750">Fig. 1. Bradford Belt-driven Lathe&mdash;View of Front or Operating Side</p></div>
+
+<p>The principal parts are the bed <i>B</i>, the headstock <i>H</i>, the tailstock
+<i>T</i>, and the carriage <i>C</i>. The headstock contains a spindle
+which is rotated by a belt that passes over the cone-pulley <i>P</i>,
+and this spindle rotates the work, which is usually held between
+pointed or conical centers <i>h</i> and <i>h<sub>1</sub></i> in the headstock and
+tailstock, or in a chuck screwed onto the spindle instead of the
+faceplate <i>F</i>. The carriage <i>C</i> can be moved lengthwise along
+the bed by turning handle <i>d</i>, and it can also be moved by power,
+the movement being transmitted from the headstock spindle
+either through gears <i>a</i>, <i>b</i>, <i>c</i>, and lead-screw <i>S</i>, or by a belt operating
+on pulleys <i>p</i> and <i>p<sub>1</sub></i>, which drive the feed-rod <i>R</i>. The
+lead-screw <i>S</i> is used when cutting threads, and the feed-rod <i>R</i>
+for ordinary turning operations; in this way the wear on the
+lead-screw is reduced and its accuracy is preserved.</p>
+
+<span class="pagenum"><a name="Pg_2" id="Pg_2">[2]</a></span>
+
+<p>On the carriage, there is a cross-slide <i>D</i> which can be moved
+at right angles to the lathe bed by handle <i>e</i>, and on <i>D</i> there is
+an upper or compound slide <i>E</i> which can be swiveled to different
+positions. The tool <i>t</i>, that does the turning, is clamped to the
+<span class="pagenum"><a name="Pg_3" id="Pg_3">[3]</a></span>
+upper slide, as shown, and it can be moved with relation to the
+work by the movement of the carriage <i>C</i> along the bed, or by
+moving slide <i>D</i> crosswise. The lengthwise movement is used to
+feed the tool along the work when turning, boring or cutting a
+screw, and the crosswise movement for facing the ends of shafts,
+etc., or for radial turning. When the tool is to be fed at an
+angle, other than at right angles to the bed, slide <i>E</i>, which can
+be set to the required angle, is used. The lengthwise and crosswise
+feeding movements can be effected by power, the lengthwise
+feed being engaged by tightening knob <i>k</i>, and the cross-feed by
+tightening knob <i>l</i>. The direction of either of these movements
+can also be reversed by shifting lever <i>r</i>. Ordinarily the carriage
+and slide are adjusted by hand to bring the tool into the
+proper position for turning to the required diameter, and then
+the power feed (operating in the desired direction) is engaged.
+The tailstock <i>T</i> can be clamped in different positions along the
+bed, to suit the length of the work, and its center <i>h<sub>1</sub></i> can be
+moved in or out for a short distance, when adjusting it to the
+work, by turning handle <i>n</i>.</p>
+
+<a name="Fig_1_2" id="Fig_1_2"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/011sm.png" alt="Plan View of Lathe Headstock showing Back-gears" /></div>
+<p class="caption750">Fig. 2. Plan View of Lathe Headstock showing Back-gears</p>
+</div>
+
+<p>As some metals are much harder than others, and as the<span class="pagenum"><a name="Pg_4" id="Pg_4">[4]</a></span>
+diameters of parts to be turned also vary considerably, speed
+changes are necessary, because if the speed is excessive, the
+turning tool will become dull in too short a time. These speed
+changes (with a belt-driven lathe) are obtained by placing the
+driving belt on different steps of cone-pulley <i>P</i>, and also by the
+use of back-gears. The cone-pulley can be connected directly
+with the spindle or be disengaged from it by means of bolt <i>m</i>.
+When the pulley and spindle are connected, five speeds (with
+this particular lathe) are obtained by simply shifting the driving
+belt to different steps of the cone. When a slower speed is
+required than can be obtained with the belt on the largest step
+of the cone, the latter is disconnected from the spindle, and the
+back-gears <i>G</i> and <i>G<sub>1</sub></i> (shown in the plan view <a href="#Fig_1_2">Fig. 2</a>) are moved
+forward into mesh by turning handle <i>O</i>; the drive is then from
+cone-pulley <i>P</i> and gear <i>L</i> to gear <i>G</i>, and from gear <i>G<sub>1</sub></i> to the
+large gear <i>J</i> on the spindle. When driving through the back-gears,
+five more speed changes are obtained by shifting the
+position of the driving belt, as before. The fastest speed with
+the back-gears in mesh is somewhat slower than the slowest
+speed when driving direct or with the back-gears out of mesh;
+hence, with this particular lathe, a series of ten gradually increasing
+speeds is obtained. Changes of feed for the turning<span class="pagenum"><a name="Pg_5" id="Pg_5">[5]</a></span>
+tool are also required, and these are obtained by shifting the
+belt operating on pulleys <i>p</i> and <i>p<sub>1</sub></i> to different-sized steps. On
+some lathes these feed changes are obtained through gears
+which can be shifted to give different ratios. Many lathes also
+have gears in the headstock for changing the speeds.</p>
+
+<a name="Fig_1_3" id="Fig_1_3"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/012sm.png" alt="Feed Mechanism of Lathe Apron" /></div>
+<p class="caption750">Fig. 3. Feed Mechanism of Lathe Apron</p>
+</div>
+
+<p>Front and rear views of the carriage apron, which contains
+the feeding mechanism, are shown in <a href="#Fig_1_3">Figs. 3</a> and <a href="#Fig_1_4">4</a>, to indicate
+how the feeds are engaged and reversed. The feed-rod <i>R</i>
+(<a href="#Fig_1_1">Fig. 1</a>) drives the small bevel gears <i>A</i> and <i>A<sub>1</sub></i> (<a href="#Fig_1_3">Figs. 3</a>
+and <a href="#Fig_1_4">4</a>), which are mounted on a slide <i>S</i> that can be moved by lever <i>r</i>
+to bring either bevel gear into mesh with gear <i>B</i>. Gear <i>B</i> is
+attached to pinion <i>b</i> (see <a href="#Fig_1_3">Fig. 3</a>) meshing with gear <i>C</i>, which,
+when knob <i>k</i> (<a href="#Fig_1_1">Fig. 1</a>) is tightened, is locked by a friction clutch
+to pinion <i>c</i>. The latter pinion drives gear <i>D</i> which rotates
+shaft <i>E</i>. A pinion cut on the end of shaft <i>E</i> engages rack <i>K</i>
+(<a href="#Fig_1_1">Fig. 1</a>) attached to the bed, so that the rotation of <i>E</i> (which is
+controlled by knob <i>k</i>) moves the carriage along the bed. To
+reverse the direction of the movement, it is only necessary to
+throw gear <i>A</i> into mesh and gear <i>A<sub>1</sub></i> out, or <i>vice versa</i>, by operating
+lever <i>r</i>. When the carriage is traversed by hand, shaft
+<i>E</i> and gear <i>D</i> are rotated by pinion <i>d<sub>1</sub></i> connected with handle <i>d</i>
+(<a href="#Fig_1_1">Fig. 1</a>).</p>
+
+<a name="Fig_1_4" id="Fig_1_4"></a>
+<div class="figcenter"><img src="images/013sm.jpg" alt="Rear View of Lathe Apron" />
+<p class="caption750">Fig. 4. Rear View of Lathe Apron</p>
+</div>
+
+<p>The drive for the cross-feed is from gear <i>C</i> to gear <i>F</i> which
+<span class="pagenum"><a name="Pg_6" id="Pg_6">[6]</a></span>
+can be engaged through a friction clutch (operated by knob <i>l</i>,
+<a href="#Fig_1_1">Fig. 1</a>) with gear <i>G</i> meshing with a pinion <i>H</i>. The latter rotates
+the cross-feed screw, which passes through a nut attached to
+slide <i>D</i> (<a href="#Fig_1_1">Fig. 1</a>), thus moving the latter at right angles to the
+ways of the bed. The cross-feed is also reversed by means of
+lever <i>r</i>. As previously explained, lead-screw <i>S</i> is only used for
+feeding the carriage when cutting threads. The carriage is engaged
+with this screw by means of two half-nuts <i>N</i> (<a href="#Fig_1_4">Fig. 4</a>)
+that are free to slide vertically and are closed around the screw
+by operating lever <i>u</i>. These half-nuts can only be closed when
+lever <i>r</i> is in a central or neutral position, so that the screw feed
+and the regular turning feed cannot be engaged at the same
+time. As previously mentioned, lead-screw <i>S</i>, <a href="#Fig_1_1">Fig. 1</a>, is rotated
+from the lathe spindle, through gears <i>a</i>, <i>b</i> and <i>c</i>, called change
+gears. An assortment of these gears, of various sizes, is provided
+with the lathe, for cutting screws of different pitch. The
+gears to use for any pitch within the range of the lathe are
+given on the plate <i>I</i>.</p>
+
+<a name="Fig_1_5" id="Fig_1_5"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/015sm.png" alt="Mounted Work" /></div>
+<p class="caption750">Fig. 5. Plan View showing Work Mounted between Centers of Lathe</p>
+</div>
+
+<a name="Secnum_1_2" id="Secnum_1_2"></a><p><b>Example of Cylindrical Turning.</b>&mdash;Having now considered
+the principal features of what might be called a standard lathe,
+the method of using it in the production of machine parts will
+be explained. To begin with a simple example of work, suppose
+a steel shaft is to be turned to a diameter of 2<sup class="enum">1</sup>/<sub class="denom">4</sub> inches and a
+length of 14<sup class="enum">1</sup>/<sub class="denom">2</sub> inches, these being the finished dimensions. We
+will assume that the rough stock is cut off to a length of 14<sup class="enum">5</sup>/<sub class="denom">8</sub>
+inches and has a diameter of 2<sup class="enum">5</sup>/<sub class="denom">8</sub> inches. The first step in this
+operation is to form conically shaped center-holes in each end
+of the piece as indicated at <i>c</i> in <a href="#Fig_1_5">Fig. 5</a>. As all work of this
+kind is held, while being turned, between the centers <i>h</i> and <i>h<sub>1</sub></i>,
+holes corresponding in shape to these centers are necessary to
+keep the work in place. There are several methods of forming
+these center-holes, as explained later.</p>
+
+<p>After the work is centered, a dog <i>A</i> is clamped to one end by
+tightening screw <i>s</i>; it is then placed between the centers of the
+lathe. The dog has a projecting end or &#8220;tail,&#8221; as it is commonly
+called, which enters a slot in the faceplate <i>F</i> and thereby drives
+<span class="pagenum"><a name="Pg_7" id="Pg_7">[7]</a></span>
+or rotates the work, when power is applied to the lathe spindle
+onto which the faceplate is screwed. The tailstock center <i>h<sub>1</sub></i>,
+after being oiled, should be set up just tight enough to eliminate
+all play, without interfering with a free rotary movement of the
+work. This is done by turning handle <i>n</i>, and when the center
+is properly adjusted, the tailstock spindle containing the center
+is locked by tightening handle <i>p</i>. (Ordinary machine oil is
+commonly used for lubricating lathe centers, but a lubricant
+having more &#8220;body&#8221; should be used, especially when turning
+heavy parts. The following mixtures are recommended: 1. Dry
+or powdered red lead mixed with a good grade of mineral oil to
+the consistency of cream. 2. White lead mixed with sperm oil
+with enough graphite added to give the mixture a dark lead
+color.)</p>
+
+<a name="Fig_1_6" id="Fig_1_6"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/016sm.png" alt="Lathe Side-tool for Facing Ends of Shafts, etc." /></div>
+<p class="caption750">Fig. 6. Lathe Side-tool for Facing Ends of Shafts, etc.</p>
+</div>
+
+<a name="Secnum_1_3" id="Secnum_1_3"></a><p><b>Facing the Ends Square with a Side-tool.</b>&mdash;Everything is
+now ready for the turning operation. The ends of the piece
+should be faced square before turning the body to size, and the
+tool for this squaring operation is shown in <a href="#Fig_1_6">Fig. 6</a>; this is known
+as a side-tool. It has a cutting edge <i>e</i> which shaves off the
+metal as indicated in the end view by the dotted lines. The
+side <i>f</i> is ground to an angle so that when the tool is moved in
+the direction shown by the arrow, the cutting edge will come in
+contact with the part to be turned; in other words, side <i>f</i> is<span class="pagenum"><a name="Pg_8" id="Pg_8">[8]</a></span>
+ground so as to provide clearance for the cutting edge. In addition,
+the top surface against which the chip bears, is beveled
+to give the tool keenness so that it will cut easily. As the principles
+of tool grinding are treated separately in <a href="#Chapnum_2">Chapter II</a> we
+shall for the present consider the tool's use rather than its form.</p>
+
+<a name="Fig_1_7" id="Fig_1_7"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/017sm.png" alt="Facing End with Side-tool and Turning Work Cylindrical" /></div>
+<p class="caption750">Fig. 7. Facing End with Side-tool and Turning Work Cylindrical</p>
+</div>
+
+<p>For facing the end, the side tool is clamped in the toolpost by
+tightening the screw <i>u</i>, <a href="#Fig_1_5">Fig. 5</a>, and it should be set with the
+cutting edge slightly inclined from a right-angled position, the
+point being in advance so that it will first come into contact
+with the work. The cutting edge should also be about the same
+height as the center of the work. When the tool is set, the
+lathe (if belt-driven) is started by shifting an overhead belt and
+the tool is then moved in until the point is in the position shown
+at <i>A</i>, <a href="#Fig_1_7">Fig. 7</a>. The tool-point is then fed against the end by
+handle <i>d</i>, <a href="#Fig_1_5">Fig. 5</a>, until a light chip is being turned off, and then
+it is moved outward by handle <i>e</i> (as indicated by the arrow at
+<i>B</i>, <a href="#Fig_1_7">Fig. 7</a>), the carriage remaining stationary. As the movement
+of the tool-point is guided by the cross-slide <i>D</i>, which is at
+right angles with the axis of the work, the end will be faced
+square. For short turning operations of this kind, the power
+feeds ordinarily are not used as they are intended for comparatively
+long cuts. If it were necessary to remove much
+metal from the end, a number of cuts would be taken across it;
+in this case, however, the rough stock is only <sup class="enum">1</sup>/<sub class="denom">8</sub> inch too long so
+that this end need only be made true.</p>
+
+<p>After taking a cut as described, the surface, if left rough by<span class="pagenum"><a name="Pg_9" id="Pg_9">[9]</a></span>
+the tool-point, should be made smooth by a second or finishing
+cut. If the tool is ground slightly round at the point and the
+cutting edge is set almost square, as at <i>C</i>, <a href="#Fig_1_7">Fig. 7</a>, a smooth finish
+can be obtained; the cut, however, should be light and the outward
+feed uniform. The work is next reversed in the centers
+and the driving dog is placed on the end just finished; the other
+end is then faced, enough metal being removed to make the
+piece 14<sup class="enum">1</sup>/<sub class="denom">2</sub> inches long, as required in this particular case. This
+completes the facing operation. If the end of the work does
+not need to be perfectly square, the facing operation can be performed
+by setting the tool in a right-angled position and then
+feeding it sidewise, thus removing a chip equal to the width of
+one side. Evidently this method is confined to comparatively
+small diameters and the squareness of the turned end will be
+determined by the position of the tool's cutting edge.</p>
+
+<a name="Fig_1_8" id="Fig_1_8"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/018sm.png" alt="Tool used for Cylindrical Turning" /></div>
+<p class="caption750">Fig. 8. Tool used for Cylindrical Turning</p>
+</div>
+
+<a name="Secnum_1_4" id="Secnum_1_4"></a><p><b>Turning Tool&mdash;Turning Work Cylindrical.</b>&mdash;The tool used to
+turn the body to the required diameter is shaped differently
+from the side-tool, the cutting edge <i>E</i> of most tools used for
+plain cylindrical turning being curved as shown in <a href="#Fig_1_8">Fig. 8</a>. A
+<span class="pagenum"><a name="Pg_10" id="Pg_10">[10]</a></span>
+tool of this shape can be used for a variety of cylindrical turning
+operations. As most of the work is done by that part of
+the edge marked by arrow <i>a</i>, the top of the tool is ground to
+slope back from this part to give it keenness. The end <i>F</i>, or
+the flank, is also ground to an angle to provide clearance for the
+cutting edge. If the tool did not have this clearance, the flank
+would rub against the work and prevent the cutting edge from
+entering the metal. This type of tool is placed about square
+with the work, for turning, and with the cutting end a little
+above the center.</p>
+
+<a name="Fig_1_9" id="Fig_1_9"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/019sm.png" alt="Setting Calipers by Scale&mdash;Setting by Gage&mdash;Fixed Gage" /></div>
+<p class="caption750">Fig. 9. Setting Calipers by Scale&mdash;Setting by Gage&mdash;Fixed Gage</p>
+</div>
+
+<p>Before beginning to turn, a pair of outside calipers or a micrometer
+should be set to 2<sup class="enum">1</sup>/<sub class="denom">4</sub> inches, which, in this case, is the
+finished diameter of the work. Calipers are sometimes set by
+using a graduated scale as at <i>A</i>, <a href="#Fig_1_9">Fig. 9</a>, or they can be adjusted
+to fit a standard cylindrical gage of the required size as at <i>B</i>.
+Very often fixed caliper gages <i>C</i> are used instead of the adjustable
+spring calipers. These fixed gages, sometimes called &#8220;snap&#8221;
+gages, are accurately made to different sizes, and they are particularly
+useful when a number of pieces have to be turned to
+exactly the same size.</p>
+
+<a name="Fig_1_10" id="Fig_1_10"></a>
+<div class="figcenter"><img src="images/020sm.jpg" alt="Views showing how the Cross-slide and Carriage are Manipulated by Hand when Starting a Cut" />
+<p class="caption750">Fig. 10. Views showing how the Cross-slide and Carriage are Manipulated<br />by
+Hand when Starting a Cut&mdash;<br />View to Left, Feeding Tool Laterally;<br />View to
+Right, Feeding Tool in a Lengthwise Direction</p>
+</div>
+
+<p>The turning tool is started at the right-hand end of the work
+and the tool should be adjusted with the left hand when beginning
+a cut, as shown in <a href="#Fig_1_10">Fig. 10</a>, in order to have the right hand
+free for calipering. A short space is first turned by hand feeding,
+as at <i>D</i>, <a href="#Fig_1_7">Fig. 7</a>, and when the calipers show that the diameter is
+slightly greater than the finished size (to allow for a light finishing
+<span class="pagenum"><a name="Pg_11" id="Pg_11">[11]</a></span>
+cut, either in the lathe or grinding machine) the power feed
+for the carriage is engaged; the tool then moves along the work,
+reducing it as at <i>E</i>. Evidently, if the movement is along a
+line <i>b&mdash;b</i>, parallel with the axis <i>a&mdash;a</i>, the diameter <i>d</i> will be the
+same at all points, and a true cylindrical piece will be turned.
+On the other hand, if the axis <i>a&mdash;a</i> is inclined one way or the
+other, the work will be made tapering; in fact, the tailstock
+center <i>h<sub>1</sub></i> can be adjusted laterally for turning tapers, but for
+straight turning, both centers must be in alignment with the
+carriage travel. Most lathes have lines on the stationary and
+movable parts of the tailstock base which show when the centers
+are set for straight turning. These lines, however, may not be
+absolutely correct, and it is good practice to test the alignment
+of the centers before beginning to turn. This can be done by
+taking trial cuts, at each end of the work (without disturbing
+the tool's crosswise position), and then comparing the diameters,
+or by testing the carriage travel with a true cylindrical piece
+held between the centers as explained later.</p>
+
+<p>If the relative positions of the lathe centers are not known,
+the work should be calipered as the cut progresses to see if
+the diameter <i>d</i> is the same at all points. In case the diameter
+gradually increases, the tailstock center should be shifted
+slightly to the rear before taking the next cut, but if the diameter<span class="pagenum"><a name="Pg_12" id="Pg_12">[12]</a></span>
+gradually diminishes, the adjustment would, of course, be made
+in the opposite direction. The diameter is tested by attempting
+to pass the calipers over the work. When the measuring points
+just touch the work as they are gently passed across it, the
+diameter being turned is evidently the same as the size to which
+the calipers are set.</p>
+
+<p>As the driving dog is on one end, the cut cannot be taken
+over the entire length, and when the tool has arrived at say
+position <i>x</i>, <a href="#Fig_1_5">Fig. 5</a>, it is returned to the starting point and the
+work is reversed in the centers, the dog being placed upon the
+other end. The unfinished part is then turned, and if the cross-slide
+is not moved, the tool will meet the first cut. It is not
+likely that the two cuts will be joined or blended together perfectly,
+however, and for this reason a cut should be continuous
+when this is possible.</p>
+
+<a name="Secnum_1_5" id="Secnum_1_5"></a><p><b>Roughing and Finishing Cuts.</b>&mdash;Ordinarily in lathe work, as
+well as in other machine work, there are two classes of cuts,
+known as &#8220;roughing&#8221; and &#8220;finishing&#8221; cuts.
+Roughing cuts are<span class="pagenum"><a name="Pg_13" id="Pg_13">[13]</a></span>
+for reducing the work as quickly as possible almost to the required
+size, whereas finishing cuts, as the name implies, are intended
+to leave the part smooth and of the proper size. When
+the rough stock is only a little larger than the finished diameter,
+a single cut is sufficient, but if there is considerable metal to
+turn away, one or more deep roughing cuts would have to be
+taken, and, finally, a light cut for finishing. In this particular
+case, one roughing and one finishing cut would doubtless be
+taken, as the diameter has to be reduced <sup class="enum">3</sup>/<sub class="denom">8</sub> inch. Ordinarily the
+roughing cut would be deep enough to leave the work about <sup class="enum">1</sup>/<sub class="denom">32</sub>
+or perhaps <sup class="enum">1</sup>/<sub class="denom">16</sub> inch above the finished size. When there is considerable
+metal to remove and a number of roughing cuts have
+to be taken, the depth of each cut and the feed of the tool are
+governed largely by the pulling power of the lathe and the
+strength of the work to withstand the strain of a heavy cut.
+The depth of roughing cuts often has to be reduced considerably
+because the part being turned is so flexible that a heavy cut
+would spring the work and cause the tool to gouge in. Of
+course, just as few cuts as possible should be taken in order to
+save time. The speed of the work should also be as fast as the
+conditions will allow for the same reason, but as there are many
+things which govern the speed, the feed of the tool, and the
+depth of the cut, these important points are referred to separately
+in <a href="#Chapnum_2">Chapter II</a>.</p>
+
+<a name="Fig_1_11" id="Fig_1_11"></a>
+<div class="figcenter"><img src="images/022sm.jpg" alt="Filing Work" />
+<p class="caption750">Fig. 11. Filing Work after Finishing Cut is taken</p>
+</div>
+
+<a name="Secnum_1_6" id="Secnum_1_6"></a><p><b>Filing and Finishing.</b>&mdash;In many cases the last or finishing
+cut does not leave as smooth a surface as is required and it is
+necessary to resort to other means. The method commonly
+employed for finishing in the lathe is by the use of a file and
+emery cloth. The work is rotated considerably faster for filing
+than for turning, and the entire surface is filed by a flat, single-cut
+file, held as shown in <a href="#Fig_1_11">Fig. 11</a>. The file is passed across the
+work and advanced sidewise for each forward stroke, until the
+entire surface is finished. The file should be kept in contact
+with the work continually, but on the return stroke the pressure
+should be relieved. The movement of the file during the forward
+or cutting stroke should be much slower than when filing
+in a vise. By moving the file slowly, the work can make a<span class="pagenum"><a name="Pg_14" id="Pg_14">[14]</a></span>
+number of revolutions for each stroke, which tends to keep it
+round, as practically the same amount of metal is removed from
+the entire circumference. On the other hand, short rapid strokes
+tend to produce flat spots, or at least an irregular surface, especially
+if the work can only make part of a revolution for
+each cutting stroke. The pressure on the file during the forward
+stroke should also be kept as nearly uniform as possible.</p>
+
+<p>It is very difficult to file a part smooth and at the same time
+to keep it round and cylindrical, and the more filing that has to
+be done, the greater the chance of error. For this reason, the
+amount left for filing should be very small; in fact, the metal
+removed by filing should be just enough to take out the tool
+marks and give a smooth finish. Very often a satisfactory
+finish can be obtained with a turning tool, and filing is not
+necessary at all. The file generally used for lathe work is a
+&#8220;single-cut bastard&#8221; of &#8220;mill&#8221; section, having a length of from
+12 to 14 inches.</p>
+
+<p>Sometimes particles of metal collect between the teeth of a
+file and make deep scratches as the file is passed across the
+work. When this occurs, the teeth should be cleaned by using<span class="pagenum"><a name="Pg_15" id="Pg_15">[15]</a></span>
+a wire brush or a file card, which is drawn across the file in the
+direction of the teeth. This forming of tiny particles between
+the teeth is known as &#8220;pinning&#8221; and it can sometimes be avoided
+by rubbing chalk on the file. Filing is not only done to obtain
+a smooth finish, but also to reduce the work to an exact diameter,
+as a very slight reduction can be made in this way.</p>
+
+<p>If a polish is desired, this can be obtained by holding a piece
+of emery cloth tightly around the work as it revolves. The
+coarseness of emery cloth is indicated by letters and numbers
+corresponding to the grain number of loose emery. The letters
+and numbers for grits ranging from fine to coarse are as follows:
+<i>FF</i>, <i>F</i>, 120, 100, 90, 80, 70, 60, 54, 46, 40. For large work
+roughly filed, use coarse cloth such as Nos. 46 or 54, and then
+finer grades to obtain the required polish. If the work has been
+carefully filed, a good polish can be obtained with Nos. 60 and
+90 cloth, and a brilliant polish by finishing with No. 120 and
+flour-emery.</p>
+
+<p>Most cylindrical parts can be finished more quickly and
+accurately in the grinder than in the lathe, and many classes of
+work are, at the present time, simply rough-turned in the lathe
+and then ground to size in a cylindrical grinding machine.</p>
+
+<a name="Fig_1_12" id="Fig_1_12"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/023sm.png" alt="Two Methods of Aligning Centers for Cylindrical Turning" /></div>
+<p class="caption750">Fig. 12. Two Methods of Aligning Centers for Cylindrical Turning</p>
+</div>
+
+<a name="Secnum_1_7" id="Secnum_1_7"></a><p><span class="pagenum"><a name="Pg_16" id="Pg_16">[16]</a></span>
+<b>Aligning Centers for Cylindrical Turning.</b>&mdash;Whena rod or
+shaft must be turned cylindrical or to the same diameter throughout
+its entire length, it is good practice to test the alignment
+of the centers, before inserting the work. The position of the
+tailstock center for cylindrical turning may be indicated by the
+coincidence of graduation marks on the base, but if accuracy is
+necessary, the relative position of the two centers should be determined
+in a more positive way. A very simple and convenient
+method of testing the alignment is shown at <i>A</i> in <a href="#Fig_1_12">Fig. 12</a>. The
+work is first turned for a short distance, near the dogged end, as
+shown, and the tool is left as set for this cut; then the tailstock
+center is withdrawn and the work is moved sufficiently to
+permit running the tool back to the tailstock end without changing
+its original setting. A short cut is then taken at this end
+and the diameters <i>d</i> and <i>d<sub>1</sub></i> are carefully compared. In case
+there is any variation, the tailstock center is adjusted laterally,
+other trial cuts are taken, and the test repeated.</p>
+
+<p>Another method is illustrated at <i>B</i>, which requires the use of
+a test-bar <i>t</i>. This bar should have accurately made centers and
+the ends finished to exactly the same diameter. The lathe
+centers are aligned by placing the bar between them and then
+testing the position of the ends. This can be done by comparing
+each end with a tool held in the toolpost and moved from
+one to the other by shifting the carriage, but a better method
+is to clamp a test indicator <i>i</i> in the toolpost and bring it in contact
+with first one end of the bar and then the other. If the dial
+does not register the same at each end, it shows that the lathe
+centers are not in line. Even when centers are correctly set,
+lathes that have been in use a long time do not always turn
+cylindrical or straight, because if the ways that guide the carriage
+are worn unevenly, the tool as it moves along does not
+remain in the same plane and this causes a variation in the
+diameter of the part being turned.</p>
+
+<a name="Fig_1_13" id="Fig_1_13"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/025sm.png" alt="Dog that is too Short for Faceplate and Straight Driving Dog" /></div>
+<p class="caption750">Fig. 13. (A) Dog that is too Short for Faceplate.<br />(B) Straight Driving Dog</p>
+</div>
+
+<a name="Secnum_1_8" id="Secnum_1_8"></a><p><b>Application of Drivers or Dogs.</b>&mdash;Work that is turned between
+centers is sometimes driven by a dog which is so short
+for the faceplate that the bent driving end bears against the
+bottom <i>a</i> of the faceplate slot, as shown at <i>A</i>, <a href="#Fig_1_13">Fig. 13</a>. If the
+<span class="pagenum"><a name="Pg_17" id="Pg_17">[17]</a></span>
+dog is nearly the right length, it may allow the headstock center
+to enter the center in the work part way, with the result that
+the turned surface is not true with the centers. When a driving
+dog of this type is used, care should be taken to see that it moves
+freely in the faceplate slot and does not bind against the bottom.
+By using a straight dog (<i>B</i>), which is driven by a pin <i>b</i> bolted
+to the faceplate, all danger from this source is eliminated. The
+straight dog, however, is used more particularly to do away
+with the leverage <i>l</i> of a bent dog, as this leverage tends to spring
+a flexible part when a cut is being taken.</p>
+
+<p>Straight dogs are also made with two driving ends which
+engage pins on opposite sides of the faceplate. This type is
+preferable because it applies the power required for turning,
+evenly to the work, which still further reduces the tendency to
+spring it out of shape. The principal objection to the double-ended
+type lies in the difficulty of adjusting the driving pins
+so that each bears with equal pressure against the dog. The
+double-ended driver is often used for large work especially if
+deep roughing cuts are necessary.</p>
+
+<a name="Fig_1_14" id="Fig_1_14"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/026sm.png" alt="Bushing mounted on Arbor for Turning" /></div>
+<p class="caption750">Fig. 14. Bushing mounted on Arbor for Turning</p>
+</div>
+
+<a name="Secnum_1_9" id="Secnum_1_9"></a><p><b>Lathe Arbors or Mandrels.</b>&mdash;When it is necessary to turn
+the outside of a part having a hole through it, centers cannot,
+of course, be drilled in the ends and other means must be resorted
+to. We shall assume that the bushing <i>B</i>, <a href="#Fig_1_14">Fig. 14</a>, has a
+<span class="pagenum"><a name="Pg_18" id="Pg_18">[18]</a></span>
+finished hole through the center, and it is desired to turn the
+outside cylindrical and concentric with the hole. This could be
+done by forcing a tightly-fitted arbor <i>M</i>, having accurately-centered
+ends, into the bushing and inserting the mandrel and
+work between the lathe centers <i>h</i> and <i>h<sub>1</sub></i> as shown. Evidently,
+if the arbor runs true on its centers, the hole in the bushing will
+also run true and the outside can be turned the same as though
+the arbor and bushing were a solid piece. From this it will be
+seen that an arbor simply forms a temporary support for parts
+that are bored and therefore cannot be centered.</p>
+
+<a name="Fig_1_15" id="Fig_1_15"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/027sm.png" alt="Turning Pulley Held on an Arbor" /></div>
+<p class="caption750">Fig. 15. Turning Pulley Held on an Arbor</p>
+</div>
+
+<p>Another example of work that would be turned on an arbor
+is shown in <a href="#Fig_1_15">Fig. 15</a>. This is a small cast-iron wheel having a
+finished hole through the hub, and the outer surface and sides
+of the rim are to be turned true with this hole. In this case, the
+casting would also be held by pressing a mandrel through the
+hub; as shown. This method, however, would only apply to
+comparatively small wheels because it would be difficult, if not
+impossible, to prevent a large wheel from turning on the arbor
+when taking a cut, and even if it could be driven, large work
+could be done to better advantage on another type of machine.
+(The vertical boring mill is used extensively for turning large
+wheels, as explained in <a href="#Chapnum_6">Chapter VI</a>.) When turning the outside
+of the rim, a tool similar to that shown at <i>t</i> should be used, but
+for facing or turning the sides, it might be better, if not necessary,
+to use tools having bent ends as shown by the dotted lines; in<span class="pagenum"><a name="Pg_19" id="Pg_19">[19]</a></span>
+fact, turning tools of various kinds are made with the ends bent
+to the right or left, as this enables them to be used on surfaces
+that could not be reached very well with a straight tool. If a
+comparatively large pulley is mounted near the end of the
+arbor, it can be driven directly by pins attached to the faceplate
+and engaging the pulley arms. This method of driving is
+often employed when the diameter to be turned is large and the
+hole for the arbor is so small that there will not be sufficient
+friction for driving.</p>
+
+<a name="Fig_1_16" id="Fig_1_16"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/028sm.png" alt="Different Types of Lathe Arbors" /></div>
+<p class="caption750">Fig. 16. Different Types of Lathe Arbors</p>
+</div>
+
+<a name="Secnum_1_10" id="Secnum_1_10"></a><p><b>Different Types of Lathe Arbors.</b>&mdash;Three different types of
+lathe arbors are shown in <a href="#Fig_1_16">Fig. 16</a>. The kind shown at <i>A</i> is
+usually made of tool steel and the body is finished to a standard
+size. The ends are somewhat reduced and flat spots are milled,
+as shown, to give the clamping screw of the dog a good grip.
+The body of the arbor is usually tapered about 0.006 inch per
+foot. This taper makes it easier to insert the arbor in a close-fitting
+hole, and it also permits slight variations in the diameter
+of different holes. As to hardening, the practice at the present
+time among manufacturers is to harden arbors all over, but for
+extremely accurate work, an arbor having hardened ends and a
+soft body is generally considered superior, as there is less tendency
+of distortion from internal stresses. Hardened arbors are &#8220;seasoned&#8221;
+before finish-grinding to relieve these internal stresses.</p>
+
+<p>The solid type <i>A</i>, <a href="#Fig_1_16">Fig. 16</a>, is used very extensively, but in
+<span class="pagenum"><a name="Pg_20" id="Pg_20">[20]</a></span>
+shops where a great variety of work is being done and there are
+many odd-sized holes, some form of expanding arbor <i>B</i> can be
+used to advantage. This type, instead of being solid, consists
+of a tapering inner arbor <i>M</i> on which is placed a split bushing
+that can be expanded, within certain limits, by driving in the
+tapering member. The advantage of this type is that a comparatively
+small stock of arbors is required, as different-sized
+bushings can be used. This type can also be fitted to holes of
+odd sizes, whereas a solid arbor must be provided for each
+different size hole, unless the variation is very slight. The latter
+are, however, more accurate than the expanding type.</p>
+
+<p>Another form of expanding arbor is shown at <i>C</i>. This type
+has a straight body <i>N</i> in which four tapering grooves are cut
+lengthwise, as shown, and there is a sleeve <i>S</i>, containing four
+slots that are located to correspond with the tapering grooves.
+Strips s are fitted into these slots, and as the part <i>N</i> is driven in,
+the strips are moved outward as they ascend the tapering grooves.
+By having different sets of these strips of various heights, one
+arbor of this type can be made to cover quite a range of sizes.
+It is not suited, however, to thin work, as the pressure, being
+concentrated in four places, would spring a flexible part out of
+shape.</p>
+
+<a name="Fig_1_17" id="Fig_1_17"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/029sm.png" alt="Cone Arbor, Nut Arbor, Pipe Center" /></div>
+<p class="caption750">Fig. 17. (A) Cone Arbor.<br />(B) Nut Arbor.<br />(C) Pipe Center</p>
+</div>
+
+<p>The cone arbor or mandrel shown at <i>A</i>, in <a href="#Fig_1_17">Fig. 17</a>, is convenient
+<span class="pagenum"><a name="Pg_21" id="Pg_21">[21]</a></span>
+for holding parts having comparatively large holes, as
+it can be adjusted for quite a range of diameters. The work is
+gripped between the two cones <i>c</i> and <i>c<sub>1</sub></i> which are forced together
+by nut <i>n</i>. The cones are prevented from turning upon the
+arbor by keys. This style of arbor should not be used for
+accurate work. The threaded arbor <i>B</i> is used for facing the sides
+of nuts square with the tapped hole. When a nut is first put
+upon the arbor, the rough side comes against an equalizing
+washer <i>w</i>. This washer rests against a spherical seat so that it
+can shift to provide a uniform bearing for the rough side of the
+nut, even though it is not square with the tapped hole. This
+feature prevents the nut from being canted on the arbor and
+insures an accurately faced nut. The revolving conical center
+shown at <i>C</i> is often used for holding a pipe or tube while turning
+the outside. The cone is adjusted to fit into the hole of
+the pipe, by means of the tailstock spindle, and the opposite
+end is usually held in a chuck.</p>
+
+<p>Particular care should be taken to preserve the accuracy of<span class="pagenum"><a name="Pg_22" id="Pg_22">[22]</a></span>
+the centers of lathe arbors by keeping them clean and well-oiled
+while in use.</p>
+
+<div class="figcenter"><a name="Fig_1_18" id="Fig_1_18"></a>
+<img src="images/030sm.jpg" alt="Press for Forcing Arbors into Work" />
+<p class="caption750">Fig. 18. Press for Forcing Arbors into Work</p>
+</div>
+
+<a name="Secnum_1_11" id="Secnum_1_11"></a><p><b>Mandrel or Arbor Press.</b>&mdash;The best method of inserting an
+arbor of the solid type in a hole is by using a press, <a href="#Fig_1_18">Fig. 18</a>,
+designed for that purpose, but if such a press is not available
+and it is necessary to drive the mandrel in, a &#8220;soft&#8221; hammer,
+made of copper, lead or other soft material, should be used to protect
+the centered end of the arbor. In either case, the arbor should
+not be forced in too tightly, for if it fits properly, this will not
+be necessary in order to hold the work securely. On the other
+hand, the work might easily be broken by attempting to force
+the arbor in as far and as tightly as possible. In using the
+arbor press, the work is placed on the base <i>B</i> with the hole in a
+vertical position, and the arbor (which
+should be oiled slightly) is forced down into it by ram <i>R</i>,
+operated by lever <i>L</i>. Slots are provided in the base, as shown,
+so that the end of the arbor can come through at the bottom
+of the hole. The lever of this particular press is counter-weighted
+so that it rises to a vertical position when released.
+The ram can then be adjusted quickly to any required height
+by the handwheel seen at the left.</p>
+
+<p>Some shops are equipped with power-driven mandrel or<span class="pagenum"><a name="Pg_23" id="Pg_23">[23]</a></span>
+arbor presses. This type is particularly desirable for large
+work, owing to the greater pressure required for inserting mandrels
+that are comparatively large in diameter. One well-known
+type of power press is driven by a belt, and the downward
+pressure of the ram is controlled by a handwheel. The ram is
+raised or lowered by turning this handwheel in one direction or
+the other, and a gage shows how much pressure is being applied.
+This type of press can also be used for other purposes, such as
+forcing bushings or pins into or out of holes, bending or straightening
+parts, or for similar work.</p>
+
+<div class="figcenter">
+<a name="Fig_1_19" id="Fig_1_19"></a><div class="illobox450">
+<img src="images/031sm.png" alt="Steadyrest and Follow-rest for Supporting Flexible Parts" /></div>
+<p class="caption750">Fig. 19. Steadyrest and Follow-rest for Supporting Flexible Parts</p>
+</div>
+
+<a name="Secnum_1_12" id="Secnum_1_12"></a><p><b>Steadyrest for Supporting Flexible Parts.</b>&mdash;Occasionally
+long slender shafts, rods, etc., which have to be turned, are so
+flexible that it is necessary to support them at some point between
+the lathe centers. An attachment for the lathe known
+as a steadyrest is often used for this purpose. A steadyrest is
+composed of a frame containing three jaws <i>J</i> (<a href="#Fig_1_19">Fig. 19</a>), that can
+be adjusted in or out radially by turning screws <i>S</i>. The frame
+is hinged at <i>h</i>, thus allowing the upper half to be swung back
+(as shown by the dotted lines) for inserting or removing the
+work. The bolt-clamp <i>c</i> holds the hinged part in the closed
+position. The base of the frame has V-grooves in it that fit
+the ways of the lathe bed. When the steadyrest is in use, it is
+<span class="pagenum"><a name="Pg_24" id="Pg_24">[24]</a></span>
+secured to the bed by clamp <i>C</i>, and the jaws <i>J</i> are set in against
+the work, thus supporting or steadying it during the turning
+operation. The steadyrest must, of course, be located at a
+point where it will not interfere with the turning tool.</p>
+
+<div class="figcenter"><a name="Fig_1_20" id="Fig_1_20"></a>
+<div class="illobox450"><img src="images/032sm.png" alt="Application of Steadyrest to a Flexible Rod" /></div>
+<p class="caption750">Fig. 20. Application of Steadyrest to a Flexible Rod</p>
+</div>
+
+<p><a href="#Fig_1_20">Fig. 20</a> shows the application of the steadyrest to a long
+forged rod, having one small end, which makes it too flexible to
+be turned without support. As this forging is rough, a true
+surface <i>n</i> a little wider than the jaws <i>J</i> (<a href="#Fig_1_19">Fig. 19</a>) is first turned
+as a bearing for the jaws. This should be done very carefully
+to prevent the work from mounting the tool. A sharp pointed
+tool should be used and very light cuts taken. The steadyrest
+is next clamped to the lathe bed opposite the turned surface,
+and the jaws are adjusted in against this surface, thus forming
+a bearing. Care should be taken not to set up the jaws too
+tightly, as the work should turn freely but without play. The
+large part of the rod and central collar are then turned to size,
+this half being machined while the small part is in the rough and
+as stiff as possible. The rod is then reversed and the steadyrest
+is applied to the part just finished, as shown at <i>B</i>, thus supporting
+the work while the small end is being turned. That
+part against which the jaws bear should be kept well oiled, and
+if the surface is finished it should be protected by placing a
+strip of emery cloth beneath the jaws with the emery side out;<span class="pagenum"><a name="Pg_25" id="Pg_25">[25]</a></span>
+a strip of belt leather is also used for this purpose, the object
+in each case being to prevent the jaws from scratching and
+marring the finished surface, as they tend to do, especially if at
+all rough.</p>
+
+<p>If the work were too flexible to permit turning a spot at <i>n</i>,
+this could be done by first &#8220;spotting&#8221; it at some point <i>o</i>, and
+placing the steadyrest at that point while turning another spot
+at <i>n</i>.</p>
+
+<div class="figcenter"><a name="Fig_1_21" id="Fig_1_21"></a>
+<div class="illobox450"><img src="images/033sm.png" alt="Cat-head which is sometimes used as Bearing for Steadyrest" /></div>
+<p class="caption750">Fig. 21. Cat-head which is sometimes used as Bearing for Steadyrest</p>
+</div>
+
+<p>Sometimes it is desirable to apply a steadyrest to a surface
+that does not run true and one which is not to be turned; in
+such a case a device called a &#8220;cat-head&#8221; is used. This is simply
+a sleeve <i>S</i> (<a href="#Fig_1_21">Fig. 21</a>) which is placed over the untrue surface to
+serve as a bearing for the steadyrest. The sleeve is made to
+run true by adjusting the four set-screws at each end, and the
+jaws of the steadyrest are set against it, thus supporting the
+work.</p>
+
+<a name="Fig_1_22" id="Fig_1_22"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/034sm.png"
+alt="Shaft supported by Steadyrest for Drilling and Boring End" /></div>
+<p class="caption750">Fig. 22. Shaft supported by Steadyrest for Drilling and Boring End</p>
+</div>
+
+<a name="Secnum_1_13" id="Secnum_1_13"></a><p><b>Application of Steadyrest when Boring.</b>&mdash;Another example
+illustrating the use of the steadyrest is shown in <a href="#Fig_1_22">Fig. 22</a>. The
+rod <i>R</i> is turned on the outside and a hole is to be bored in the
+end (as shown by dotted lines) true with the outer surface. If
+the centers used for turning the rod are still in the ends, as they
+would be ordinarily, this work could be done very accurately by
+the following method: The rod is first placed between the centers
+as for turning, with a driving dog <i>D</i> attached, and the steadyrest
+jaws <i>J</i> are set against it near the outer end, as shown.</p>
+
+<div class="figcenter"><div class="illobox450"><a name="Fig_1_23" id="Fig_1_23"></a><img src="images/035sm.png"
+alt="Hold-back used when Outer End of Work is held in Steadyrest" /></div>
+<p class="caption750">Fig. 23. Hold-back used when Outer End of Work is held in Steadyrest</p>
+</div>
+
+<p>Before any machine work is done, means must be provided
+for holding the rod back against the headstock center <i>h</i>, because,
+for an operation of this kind, the outer end cannot be supported<span class="pagenum"><a name="Pg_26" id="Pg_26">[26]</a></span>
+by the tailstock center; consequently the work tends to shift
+to the right. One method of accomplishing this is shown in the
+illustration. A hardwood piece <i>w</i>, having a hole somewhat
+larger than the work, is clamped against the dog, in a crosswise
+position, by the swinging bolts and thumb-screws shown. If the
+dog is not square with the work, the wood piece should be canted
+so that the bearing will not be all on one side. For large heavy
+parts a similar &#8220;bridle&#8221; or &#8220;hold-back&#8221;&mdash;as this is commonly
+called&mdash;is made by using steel instead of wood for the
+part <i>w</i>. Another very common method which requires no
+special equipment is illustrated in <a href="#Fig_1_23">Fig. 23</a>. An ordinary leather
+belt lacing <i>L</i> is attached to the work and faceplate while the
+latter is screwed off a few turns as shown. Then the lacing is
+drawn up by hand and tied, and the faceplate is screwed onto
+the spindle, thus tightening the lacing and drawing the work
+against the headstock center. The method of applying the
+lacing is quite clearly indicated in the illustration. If a small
+driving faceplate is used, it may be necessary to drill holes for
+the belt lacing, as shown.</p>
+
+<a name="Fig_1_24" id="Fig_1_24"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/036sm.png" alt="Testing Work with Dial Indicator" /></div>
+<p class="caption750">Fig. 24. Testing Work with Dial Indicator</p>
+</div>
+
+<p>A hole is next drilled in the end of the rod by using a twist
+drill in the tailstock. If the hole is finished by boring, a depth<span class="pagenum"><a name="Pg_27" id="Pg_27">[27]</a></span>
+mark should be made on the tool shank that will warn the workman
+of the cutting end's approach to the bottom. A chuck can
+also be used in connection with a steadyrest for doing work of
+this kind, as shown in <a href="#Fig_1_24">Fig. 24</a>, the end of the rod being held and
+driven by the chuck <i>C</i>. If the piece is centered, it can be held
+on these centers while setting the steadyrest and adjusting the
+chuck, but if the ends are without centers, a very good way is to
+make light centers in the ends with a punch; after these are
+properly located they are used for holding the work until the
+steadyrest and chuck jaws have been adjusted. In case it is
+necessary to have the end hole very accurate with the outside
+of the finished rod, a test indicator <i>I</i> should be applied to the
+shaft as shown. This is an instrument which shows with great
+accuracy whether a rotating part runs true and it is also used
+for many other purposes in machine shops. The indicator is
+held in the lathe toolpost and the contact point beneath the
+dial is brought against the work. If the latter does not run
+true, the hand of the indicator vibrates and the graduations on
+the dial show how much the work is out in thousandths of an
+inch.</p>
+
+<a name="Secnum_1_14" id="Secnum_1_14"></a><p><b>The Follow-rest.</b>&mdash;When turning long slender parts, such as
+shafts, etc., a follow-rest is often used for supporting the work.
+The follow-rest differs from the steadyrest in that it is attached<span class="pagenum"><a name="Pg_28" id="Pg_28">[28]</a></span>
+to and travels with the lathe carriage. The type illustrated to
+the right in <a href="#Fig_1_19">Fig. 19</a> has two adjustable jaws which are located
+nearly opposite the turning tool, thus providing support where
+it is most needed. In using this rest, a cut is started at the
+end and the jaws are adjusted to this turned part. The tool is
+then fed across the shaft, which cannot spring away from the
+cut because of the supporting jaws. Some follow-rests have,
+instead of jaws, a bushing bored to fit the diameter being turned,
+different bushings being used for different diameters. The
+bushing forms a bearing for the work and holds it rigidly.
+Whether a bushing or jaws are used, the turning tool is slightly
+in advance of the supporting member.</p>
+
+<a name="Fig_1_25" id="Fig_1_25"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/037sm.png" alt="Centering End with Punch preparatory to Drilling" /></div>
+<p class="caption750">Fig. 25. Centering End with Punch preparatory to Drilling</p>
+</div>
+
+<a name="Secnum_1_15" id="Secnum_1_15"></a><p><b>Centering Parts to be Turned.</b>&mdash;As previously mentioned,
+there are a number of different methods of forming center-holes
+in the ends of parts that have to be turned while held
+between lathe centers. A method of centering light work, and
+one that requires few special tools, is first to locate a central
+point on the end and then drill and ream the center-hole by
+using the lathe itself. Hermaphrodite dividers are useful for
+finding the center, as illustrated at <i>A</i>, <a href="#Fig_1_25">Fig. 25</a>, but if the work is
+fairly round, a center-square <i>B</i> is preferable. A line is scribed
+across the end and then another line at right angles to the first
+by changing the position of the square; the intersection of these
+two lines will be the center, which should be marked by striking<span class="pagenum"><a name="Pg_29" id="Pg_29">[29]</a></span>
+a pointed punch <i>C</i> with a hammer. If a cup or bell center-punch
+<i>D</i> is available, it will not be necessary to first make
+center lines, as the conical part shown locates the punch in a
+central position. This style of punch should only be used on
+work which is fairly round.</p>
+
+<p>After small centers have been located in both ends, their
+position can be tested by placing the work between the lathe
+centers and rotating it rapidly by drawing the hand quickly
+across it. By holding a piece of chalk close to the work as it
+spins around, a mark will be made on the &#8220;high&#8221; side if the
+centers are not accurate; the centers are then shifted toward
+these marks. If the work is close to the finished diameter, the
+centers should, of course, be located quite accurately in order
+that the entire surface of the work will be turned true when it
+is reduced to the finished size.</p>
+
+<a name="Fig_1_26" id="Fig_1_26"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/038asm.png" alt="Drilling Centers in the Lathe" /></div>
+<p class="caption750">Fig. 26. Drilling Centers in the Lathe</p>
+</div>
+
+<p>One method of forming these center-holes is indicated in <a href="#Fig_1_26">Fig.
+26</a>. A chuck <i>C</i> is screwed onto the spindle in place of the faceplate,
+and a combination center drill and reamer <i>R</i> is gripped
+by the chuck jaws and set to run true. The center is then
+drilled and reamed at one end by pressing the work against the
+revolving drill with the tailstock spindle, which is fed out by
+turning handle <i>n</i>. The piece is then reversed for drilling the
+opposite end. The work may be kept from revolving while the
+centers are being drilled and reamed, by attaching a dog to it
+close to the tailstock end and then adjusting the cross-slide<span class="pagenum"><a name="Pg_30" id="Pg_30">[30]</a></span>
+until the dog rests upon the slide. Many parts can be held by
+simply gripping them with one hand. From the foregoing it
+will be seen that the small centers made by punch <i>C</i>, <a href="#Fig_1_25">Fig. 25</a>,
+serve as a starting point for the drill and also as a support for
+the outer end of the work while the first hole is being drilled.</p>
+
+<a name="Fig_1_27" id="Fig_1_27"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/038bsm.png" alt="Centers of Incorrect and Correct Form" /></div>
+<p class="caption750">Fig. 27. Centers of Incorrect and Correct Form</p>
+</div>
+
+<p>The form of center-hole produced by a combination drill and
+reamer is shown by the lower left-hand view in <a href="#Fig_1_27">Fig. 27</a>. A
+small straight hole a in the bottom prevents the point of the
+lathe center from coming in contact with the work and insures
+a good bearing on the conical surface <i>c</i>. The standard angle
+for lathe centers is sixty degrees, as the illustration shows, and
+the tapering part of all center-holes should be made to this
+angle.</p>
+
+<a name="Fig_1_28" id="Fig_1_28"></a>
+<div class="figcenter"><img src="images/039sm.jpg" alt="Special Machine for Centering Parts to be Turned" />
+<p class="caption750">Fig. 28. Special Machine for Centering Parts to be Turned</p>
+</div>
+
+<a name="Secnum_1_16" id="Secnum_1_16"></a><p><b>Centering Machine.</b>&mdash;Many shops have a special machine
+for forming centers which enables the operation to be performed<span class="pagenum"><a name="Pg_31" id="Pg_31">[31]</a></span>
+quickly. One type of centering machine is shown in <a href="#Fig_1_28">Fig. 28</a>.
+The work is gripped in a chuck <i>C</i> that automatically locates it
+in a central position so that it is not necessary to lay out the
+end before drilling. There are two spindles <i>s</i>, one of which
+holds the drill and the other the countersink, and these are
+rotated by a belt passing over pulley <i>P</i>. Each of these spindles
+is advanced by lever <i>L</i> and either of them can be moved to a
+position central with the work, as they are mounted in a swiveling
+frame. In operating this machine, a small straight hole is
+first made by a twist drill held in one of the spindles; the other
+spindle is then moved over to the center and the hole is reamed
+tapering. The arrangement is such that neither spindle can be
+advanced by the feeding lever except when in a central position.<span class="pagenum"><a name="Pg_32" id="Pg_32">[32]</a></span>
+The amount that each spindle can be advanced is limited by a
+fixed collar inside the head, and there is also a swinging adjustable
+stop against which the end of the work should be placed
+before tightening the chuck. These two features make it possible
+to ream center holes of the same size or depth in any
+number of pieces.</p>
+
+<a name="Fig_1_29" id="Fig_1_29"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/040sm.png" alt="The Imperfect Center Bearing is the Result of Centering before Straightening" /></div>
+<p class="caption750">Fig. 29. The Imperfect Center Bearing is the Result of Centering
+before Straightening</p>
+</div>
+
+<a name="Secnum_1_17" id="Secnum_1_17"></a><p><b>Different Forms of Centers.</b>&mdash;In some poorly equipped shops
+it is necessary to form centers by the use of a center-punch
+only, as there is no better tool. If the end of the punch has a
+sixty-degree taper, a fair center can be formed in this way, but
+it is not a method to be recommended, especially when accurate
+work is required. Sometimes centers are made with punches
+that are too blunt, producing a shallow center, such as the one
+shown in the upper left-hand view, <a href="#Fig_1_27">Fig. 27</a>. In this case all the
+bearing is on the point of the lathe center, which is the worst
+possible place for it. Another way is to simply drill a straight
+hole as in the upper view to the right; this is also bad practice
+in more than one respect. The lower view to the right shows
+a form of center which is often found in the ends of lathe arbors,
+the mouth of the center being rounded, at <i>r</i>, and the arbor end
+recessed as shown. The rounded corner prevents the point of
+the lathe center from catching when it is moved rapidly towards
+work which is not being held quite centrally (as shown by the
+illustration), and the end is recessed to protect the center against
+bruises. Stock that is bent should always be straightened before
+the centers are drilled and reamed. If the work is first
+centered and then straightened the bearing on the lathe center
+would be as shown in <a href="#Fig_1_29">Fig. 29</a>. The center will then wear unevenly
+<span class="pagenum"><a name="Pg_33" id="Pg_33">[33]</a></span>
+with the result that the surfaces last turned will not be
+concentric with those which were finished first.</p>
+
+<a name="Fig_1_30" id="Fig_1_30"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/041sm.png" alt="Tool Steel should be centered Concentric, in order to remove the Decarbonized Outer Surface" /></div>
+<p class="caption750">Fig. 30. Tool Steel should be centered Concentric, in order to remove
+the Decarbonized Outer Surface</p>
+</div>
+
+<a name="Secnum_1_18" id="Secnum_1_18"></a><p><b>Precaution When Centering Tool Steel.</b>&mdash;Ordinarily centers
+are so located that the stock runs approximately true before
+being turned, but when centering tool steel to be used in making
+tools, such as reamers, mills, etc., which need to be hardened,
+particular care should be taken to have the rough surface run
+fairly true. This is not merely to insure that the piece will
+&#8220;true-up,&#8221; as there is a more important consideration, the disregard
+of which often affects the quality of the finished tool.
+As is well known, the degree of hardness of a piece of tool steel
+that has been heated and then suddenly cooled depends upon
+the amount of carbon that it contains, steel that is high in carbon
+becoming much harder than that which contains less carbon.
+Furthermore, the amount of carbon found at the surface, and
+to some little depth below the surface of a bar of steel, is less
+than the carbon content in the rest of the bar. This is illustrated
+diagrammatically in <a href="#Fig_1_30">Fig. 30</a> by the shaded area in the
+view to the left. (This decarbonization is probably due to the
+action of the oxygen of the air on the bar during the process of
+manufacture.) If stock for a reamer is so centered that the
+tool removes the decarbonized surface only on one side, as
+illustrated to the right, evidently when the reamer is finished
+and hardened the teeth on the side <i>A</i> will be harder than those
+on the opposite side, which would not have been the case if the
+rough bar had been centered true. To avoid any trouble of
+this kind, stock that is to be used for hardened tools should be<span class="pagenum"><a name="Pg_34" id="Pg_34">[34]</a></span>
+enough larger than the finished diameter and so centered that
+this decarbonized surface will be entirely removed in turning.</p>
+
+<a name="Fig_1_31" id="Fig_1_31"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/042sm.png" alt="Three Methods Facing the Ends Square" /></div>
+<p class="caption750">Fig. 31. Three Methods of Facing the Ends Square</p>
+</div>
+
+<a name="Secnum_1_19" id="Secnum_1_19"></a><p><b>Facing the Ends of Centered Stock.</b>&mdash;As a piece of work is
+not properly centered until the ends are faced square, we will
+consider this operation in connection with centering. Some
+machinists prefer lathe centers that are cut away as shown at
+<i>A</i>, <a href="#Fig_1_31">Fig. 31</a>, so that the point of the side tool can be fed in far
+enough to face the end right up to the center hole. Others, instead
+of using a special center, simply loosen the regular one
+slightly and then, with the tool in a position as at <i>B</i>, face the
+projecting teat by feeding both tool and center inward as shown
+by the arrow. Whenever this method is employed, care should
+be taken to remove any chips from the center hole which may
+have entered. A method which makes it unnecessary to loosen
+the regular center, or to use a special one, is to provide clearance
+for the tool-point by grinding it to an angle of approximately
+forty-five degrees, as shown at <i>C</i>. If the tool is not set
+too high, it can then be fed right up to the lathe center and the
+end squared without difficulty. As for the special center <i>A</i>,
+the use of special tools and appliances should always be avoided
+unless they effect a saving in time or their use makes it possible
+to accomplish the same end with less work.</p>
+
+<a name="Secnum_1_20" id="Secnum_1_20"></a><p><b>Truing Lathe Centers.</b>&mdash;The lathe centers should receive
+careful attention especially when accurate work must be turned.
+If the headstock center does not run true as it revolves with
+the work, a round surface may be turned, but if the position of
+the driving dog with reference to the faceplate is changed, the
+turned surface will not run true because the turned surface is<span class="pagenum"><a name="Pg_35" id="Pg_35">[35]</a></span>
+not true with the work centers. Furthermore, if it is necessary
+to reverse the work for finishing the dogged or driving end, the last
+part turned will be eccentric to the first. Therefore, the lathe
+centers should be kept true in order to produce turned surfaces
+that are true or concentric with the centered ends, as it is often
+necessary to change the part being turned &#8220;end for end&#8221; for
+finishing, and any eccentricity between the different surfaces
+would, in many cases, spoil the work.</p>
+
+<a name="Fig_1_32" id="Fig_1_32"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/043sm.png" alt="Grinder for Truing Lathe Centers" /></div>
+<p class="caption750">Fig. 32. Grinder for Truing Lathe Centers</p>
+</div>
+
+<p>Some lathes are equipped with hardened centers in both the
+head-and tailstock and others have only one hardened center
+which is in the tailstock. The object in having a soft or unhardened
+headstock center is to permit its being trued by turning,
+but as a soft center is quite easily bruised and requires
+truing oftener than one that is hard, it is better to have both
+centers hardened. Special grinders are used for truing these
+hardened centers. One type that is very simple and easily applied
+to a lathe is shown in <a href="#Fig_1_32">Fig. 32</a>. This grinder is held in the
+lathe toolpost and is driven by a wheel <i>A</i> that is held in contact
+with the cone-pulley. The emery wheel <i>B</i> is moved to a position
+for grinding by adjusting the carriage and cross-slide, and it is<span class="pagenum"><a name="Pg_36" id="Pg_36">[36]</a></span>
+traversed across the conical surface of the center by handle <i>C</i>.
+As the grinding proceeds, the wheel is fed inward slightly by
+manipulating the cross-slide.</p>
+
+<p>This grinder is set to the proper angle by placing the two
+centered ends <i>D</i> and <i>D<sub>1</sub></i> between the lathe centers, which should
+be aligned as for straight turning. The grinding spindle will
+then be 30 degrees from the axis of the lathe spindle. The
+grinder should be carefully clamped in the toolpost so that it
+will remain as located by the centered ends. After the tailstock
+center is withdrawn, the emery wheel is adjusted for grinding.
+As the wheel spindle is 30 degrees from the axis of the lathe
+spindle, the lathe center is not only ground true but to an
+included angle of 60 degrees, which is the standard angle for
+lathe centers. There are many other styles of center grinders
+on the market, some of which are driven by a small belt from
+the cone-pulley and others by electric motors which are connected
+with ordinary lighting circuits. The tailstock center is
+ground by inserting it in the spindle in place of the headstock
+center. Before a center is replaced in its spindle, the hole
+should be perfectly clean as even a small particle of dirt may
+affect the alignment. The center in the headstock is usually
+referred to as the &#8220;live center&#8221; because it turns around when
+the lathe is in use, and the center in the tailstock as the &#8220;dead
+center,&#8221; because it remains stationary.</p>
+
+<a name="Fig_1_33" id="Fig_1_33"></a>
+<div class="figcenter"><img src="images/045sm.jpg" alt="Lathe Chuck, Faceplate Jaw" />
+<p class="caption750">Fig. 33. (A) Lathe Chuck.<br />(B) Faceplate Jaw</p>
+</div>
+
+<a name="Secnum_1_21" id="Secnum_1_21"></a><p><b>Universal, Independent and Combination Chucks.</b>&mdash;Many
+parts that are turned in the lathe are so shaped that they cannot
+be held between the lathe centers like shafts and other
+similar pieces and it is often necessary to hold them in a chuck
+<i>A</i>, <a href="#Fig_1_33">Fig. 33</a>, which is screwed onto the lathe spindle instead of
+the faceplate. The work is gripped by the jaws <i>J</i> which can be
+moved in or out to accommodate various diameters. There are
+three classes of chucks ordinarily used on the lathe, known as
+the independent, universal and combination types. The independent
+chuck is so named because each jaw can be adjusted in
+or out independently of the others by turning the jaw screws S
+with a wrench. The jaws of the universal chuck all move together
+and keep the same distance from the center, and they<span class="pagenum"><a name="Pg_37" id="Pg_37">[37]</a></span>
+can be adjusted by turning any one of the screws <i>S</i>, whereas
+with the independent type the chuck wrench must be applied
+to each jaw screw. The combination chuck, as the name implies,
+may be changed to operate either as an independent or
+universal type. The advantage of the universal chuck is that
+round and other parts of a uniform shape are located in a central
+position for turning without any adjustment. The independent
+type is, however, preferable in some respects as it is usually
+stronger and adapted for holding odd-shaped pieces because
+each jaw can be set to any required position.</p>
+
+<a name="Fig_1_34" id="Fig_1_34"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/046sm.png" alt="Radial Facing, Boring Pulley Held in Chuck" /></div>
+<p class="caption750">Fig. 34. (A) Radial Facing.<br />(B) Boring Pulley Held in Chuck</p>
+</div>
+
+<a name="Secnum_1_22" id="Secnum_1_22"></a><p><b>Application of Chucks.</b>&mdash;As an example of chuck work, we
+shall assume that the sides of disk <i>D</i>, <a href="#Fig_1_34">Fig. 34</a>, are to be turned
+flat and parallel with each other and that an independent chuck
+is to be used. First the chuck is screwed onto the lathe spindle
+after removing the faceplate. The chuck jaws are then moved
+out or in, as the case may be, far enough to receive the disk
+and each jaw is set about the same distance from the center
+by the aid of concentric circles on the face of the chuck. The
+jaws are then tightened while the disk is held back against
+them to bring the rough inner surface in a vertical plane. If
+the work is quite heavy, it can be held against the chuck, before
+the jaws are tightened, by inserting a piece of wood between
+it and the tailstock center; the latter is then run out far<span class="pagenum"><a name="Pg_38" id="Pg_38">[38]</a></span>
+enough to force the work back. The outside or periphery of
+the disk should run nearly true and it may be necessary to
+move the jaws in on one side and out on the other to bring the
+disk to a central position. To test its location, the lathe is
+run at a moderate speed and a piece of chalk is held near the
+outer surface. If the latter runs out, the &#8220;high&#8221; side will be
+marked by the chalk, and this mark can be used as a guide in
+adjusting the jaws. It should be remembered that the jaws are
+moved only one-half the amount that the work runs out.</p>
+
+<a name="Fig_1_35" id="Fig_1_35"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/047sm.png" alt="Tools Ground so that Top Slopes away from Working Part of Cutting Edge" /></div>
+<p class="caption750">Fig. 35. Tools Ground so that Top Slopes away from Working Part of
+Cutting Edge</p>
+</div>
+
+<p>A round-nosed tool <i>t</i> of the shape shown can be used for
+radial facing or turning operations of the kind illustrated.
+This tool is similar to the form used when turning between
+centers, the principal difference being in the direction of the
+top slope. The radial facing tool should be ground to slope
+downward toward <i>a</i> (see <a href="#Fig_1_35">Fig. 35</a>) whereas the regular turning
+tool slopes toward <i>b</i>, the inclination in each case being away
+from that part of the cutting edge which does the work. The
+cutting edge should be the same height as the lathe centers, and
+the cut is taken by feeding the tool from the outside in to the
+center. The cut is started by hand and then the power feed is
+engaged, except for small surfaces. The first cut should, if
+possible, be deep enough to get beneath the scale, especially if
+turning cast iron, as a tool which just grazes the hard outer
+surface will be dulled in a comparatively short time.</p>
+
+<p>If it were simply necessary to turn a true flat surface and the<span class="pagenum"><a name="Pg_39" id="Pg_39">[39]</a></span>
+thickness of the disk were immaterial, two cuts would be sufficient,
+unless the surface were very uneven, the first or roughing
+cut being followed by a light finishing cut. For a finishing cut,
+the same tool could be used, but if there were a number of disks
+to be faced, a square-nosed tool <i>F</i>, <a href="#Fig_1_35">Fig. 35</a>, could probably be
+used to better advantage. This type has a broad flat cutting
+edge that is set parallel with the rough-turned surface and this
+broad edge enables a coarse feed to be taken, thus reducing the
+time required for the finishing cut. If a coarse feed were taken
+with the round tool, the turned surface would have spiral grooves
+in it, whereas with the broad cutting edge, a smooth surface is
+obtained even though the feed is coarse. The amount of feed
+per revolution of the work, however, should always be less than
+the width <i>w</i> of the cutting edge. Very often broad tools cannot
+be used for finishing cuts, especially when turning steel,
+because their greater contact causes chattering and results in a
+rough surface. An old and worn lathe is more liable to chatter
+than one that is heavy and well-built, and as the diameter of
+the work also makes a difference, a broad tool cannot always
+be used for finishing, even though, theoretically, it would be
+preferable. After one side of the disk is finished, it is reversed
+in the chuck, the finished surface being placed against the jaws.
+The remaining rough side is then turned, care being taken when
+starting the first cut to caliper the width of the disk at several
+points to make sure that the two sides are parallel.</p>
+
+<a name="Secnum_1_23" id="Secnum_1_23"></a><p><b>Example of Boring.</b>&mdash;Another example of chuck work is
+shown at <i>B</i>, <a href="#Fig_1_34">Fig. 34</a>. In this case a cast-iron pulley is to have a<span class="pagenum"><a name="Pg_40"
+id="Pg_40">[40]</a></span>
+true hole <i>h</i> bored through the hub. (The finishing of internal
+cylindrical surfaces in a lathe is referred to as boring rather than
+turning.) The casting should be set true by the rim instead of
+by the rough-cored hole in the hub; this can be done by the use
+of chalk as previously explained. Even though a universal type
+of chuck were used, the jaws of which, as will be recalled, are
+self-centering, it might be necessary to turn the pulley relative
+to the chuck as a casting sometimes runs out because of rough
+spots or lumps which happen to come beneath one or more of
+the jaws.</p>
+
+<div class="figcenter">
+<a name="Fig_1_36" id="Fig_1_36"></a>
+<div class="illobox450"><img src="images/048sm.png" alt="Boring Tool" /></div>
+<p class="caption750">Fig. 36. Boring Tool</p>
+</div>
+
+<p>The shape of tool <i>t</i> for boring is quite different from one used
+for outside turning, as shown by <a href="#Fig_1_36">Fig. 36</a>. The cutting end of a
+solid type of tool is forged approximately at right angles to the
+body or shank, and the top surface is ground to slope away from
+the working part <i>w</i> of the cutting edge, as with practically all
+turning tools. The front part or flank, <i>f</i> is also ground away to
+give the edge clearance. This type of tool is clamped in the
+toolpost with the body about parallel with the lathe spindle,
+and ordinarily the cutting edge would be about as high as the
+center of the hole, or a little below, if anything. When starting
+a cut, the tool is brought up to the work by moving the carriage
+and it is then adjusted radially to get the right depth of cut, by
+shifting the cross-slide. The power feed for the carriage is then
+used, the tool feeding back through the hole as indicated by
+the arrow, <a href="#Fig_1_34">Fig. 34</a>. In this case, as with all turning operations,
+the first cut should be deep enough to remove the hard outer
+scale at every part of the hole. Usually a rough-cored hole is
+so much smaller than the finished size that several cuts are
+necessary; in any case, the last or finishing cut should be very<span class="pagenum"><a name="Pg_41" id="Pg_41">[41]</a></span>
+light to prevent the tool from springing away from the work,
+so that the hole will be as true as possible. Boring tools, particularly
+for small holes, are not as rigid as those used for outside
+turning, as the tool has to be small enough to enter the hole
+and for this reason comparatively light cuts have to be taken.
+When boring a small hole, the largest tool that will enter it
+without interference should be used to get the greatest rigidity
+possible.</p>
+
+<a name="Fig_1_37" id="Fig_1_37"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/049sm.png" alt="Setting Outside Calipers, Transferring Measurements to Inside Calipers, Micrometer Gage" /></div>
+<p class="caption750">Fig. 37 (A) Setting Outside Calipers.<br />(B) Transferring Measurements to
+Inside Calipers.<br />(C) Micrometer Gage</p>
+</div>
+
+<a name="Fig_1_38" id="Fig_1_38"></a>
+<div class="figcenter"><img src="images/050sm.jpg" alt="Plug Gage" />
+<p class="caption750">Fig. 38. Standard Plug Gage</p>
+</div>
+
+<a name="Secnum_1_24" id="Secnum_1_24"></a><p><b>Measuring Bored Holes.</b>&mdash;The diameters of small holes
+that are being bored are usually measured with inside calipers
+or standard gages. If the pulley were being bored to fit over
+some shaft, the diameter of the shaft would first be measured by
+using outside calipers, as shown at <i>A</i>, <a href="#Fig_1_37">Fig. 37</a>, the measuring
+points of the calipers being adjusted until they just made contact
+with the shaft when passed over it. The inside calipers
+are then set as at <i>B</i> to correspond with the size of the shaft, and
+the hole is bored just large enough to admit the inside calipers
+easily. Very accurate measurements can be made with calipers,
+but to become expert in their use requires experience. Some
+mechanics never become proficient in the art of calipering because
+their hands are &#8220;heavy&#8221; and they lack the sensitiveness
+and delicacy of touch that is necessary. For large holes, a
+gage <i>C</i> is often used, the length <i>l</i> being adjusted to the diameter<span class="pagenum"><a name="Pg_42"
+id="Pg_42">[42]</a></span>
+desired. Small holes are often bored to fit hardened steel plug
+gages (<a href="#Fig_1_38">Fig. 38</a>), the cylindrical measuring ends of which are
+made with great accuracy to standard sizes. This type of gage
+is particularly useful when a number of holes have to be bored
+to the same size, all holes being made just large enough to fit
+the gage without any perceptible play.</p>
+
+<a name="Fig_1_39" id="Fig_1_39"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/051asm.png" alt="Diagram Illustrating Importance of Setting Work with Reference to Surfaces to be Turned" /></div>
+<p class="caption750">Fig. 39. Diagram Illustrating Importance of Setting Work with Reference
+to Surfaces to be Turned</p>
+</div>
+
+<a name="Secnum_1_25" id="Secnum_1_25"></a><p><b>Setting Work in the Chuck.</b>&mdash;When setting a part in a chuck,
+care should be taken to so locate it that every surface to be
+turned will be true when machined to the finished size. As a
+simple illustration, let us assume that the hole through the cast-iron
+disk, <a href="#Fig_1_39">Fig. 39</a>, has been cored considerably out of center, as
+shown. If the work is set by the outside surface <i>S</i>, as it would
+be ordinarily, the hole is so much out of center that it will not
+be true when bored to the finished size, as indicated by the
+dotted lines. On the other hand, if the rough hole is set true,
+the outside cannot be finished all over, without making the
+diameter too small, when it is finally turned. In such a case,
+the casting should be shifted, as shown by the arrow, to divide
+the error between the two surfaces, both of which can then be
+turned as shown by the dotted lines in the view to the right.
+This principle of dividing the error when setting work can often
+be applied in connection with turning and boring. After a casting
+or other part has been set true by the most important surface,
+all other surfaces which require machining should be tested to
+make sure that they all can be finished to the proper size.</p>
+
+<a name="Secnum_1_26" id="Secnum_1_26"></a><p><b>Inaccuracy from Pressure of Chuck Jaws.</b>&mdash;Work that is
+held in a chuck is sometimes sprung out of shape by the pressure<span class="pagenum"><a name="Pg_43" id="Pg_43">[43]</a></span>
+of the chuck jaws so that when the part is bored or turned,
+the finished surfaces are untrue after the jaws are released and
+the work has resumed its normal shape. This applies more particularly
+to frail parts, such as rings, thin cylindrical parts, etc.
+Occasionally the distortion can be prevented by so locating the
+work with relation to the chuck jaws that the latter bear against
+a rigid part. When the work cannot be held tightly enough for
+the roughing cuts without springing it, the jaws should be released
+somewhat before taking the finishing cut, to permit the
+part to spring back to its natural shape.</p>
+
+<a name="Fig_1_40" id="Fig_1_40"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/051bsm.png" alt="Drilling in the Lathe" /></div>
+<p class="caption750">Fig. 40. Drilling in the Lathe</p>
+</div>
+
+<a name="Secnum_1_27" id="Secnum_1_27"></a><p><b>Drilling and Reaming.</b>&mdash;When a hole is to be bored from the
+solid, it is necessary to drill a hole before a boring tool can be
+used. One method of drilling in the lathe is to insert an ordinary
+twist drill in a holder or socket <i>S</i>, <a href="#Fig_1_40">Fig. 40</a>, which is inserted
+<span class="pagenum"><a name="Pg_44" id="Pg_44">[44]</a></span>
+in the tailstock spindle in place of the center. The drill is then
+fed through the work by turning the handle <i>n</i> and feeding the
+spindle outward as shown by the arrow. Before beginning to
+drill, it is well to turn a conical spot or center for the drill point
+so the latter will start true. This is often done by using a special
+tool having a point like a flat drill. This tool is clamped in
+the toolpost with the point at the same height as the lathe
+centers. It is then fed against the center of the work and a
+conical center is turned. If the drill were not given this true
+starting point, it probably would enter the work more or less
+off center. Drills can also be started without turning a center
+by bringing the square end or butt of a tool-shank held in
+the toolpost in contact with the drill near the cutting end. If
+the point starts off center, thus causing the drill to wobble, the
+stationary tool-shank will gradually force or bump it over to
+the center.</p>
+
+<a name="Fig_1_41" id="Fig_1_41"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/052sm.png" alt="Flat Drill and Holder" /></div>
+<p class="caption750">Fig. 41. Flat Drill and Holder</p>
+</div>
+
+<p>Small holes are often finished in the lathe by drilling and
+reaming without the use of a boring tool. The form of drill
+that is used quite extensively for drilling cored holes in castings
+is shown in <a href="#Fig_1_41">Fig. 41</a>, at <i>A</i>. This drill is flat and the right end has
+a large center hole for receiving the center of the tailstock. To<span class="pagenum"><a name="Pg_45" id="Pg_45">[45]</a></span>
+prevent the drill from turning, a holder <i>B</i>, having a slot <i>s</i> in its
+end through which the drill passes, is clamped in the toolpost,
+as at <i>C</i>. This slot should be set central with the lathe centers,
+and the drill, when being started, should be held tightly in the
+slot by turning or twisting it with a wrench as indicated in the
+end view at <i>D</i>; this steadies the drill and causes it to start
+fairly true even though the cored hole runs out considerably.</p>
+
+<a name="Fig_1_42" id="Fig_1_42"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/053sm.png" alt="Rose and Fluted Reamers" /></div>
+<p class="caption750">Fig. 42. Rose and Fluted Reamers</p>
+</div>
+
+<p>Another style of tool for enlarging cored holes is shown in
+<a href="#Fig_1_42">Fig. 42</a>, at <i>A</i>. This is a rose chucking reamer, having beveled
+cutting edges on the end and a cylindrical body, which fits
+closely in the reamed hole, thus supporting and guiding the
+cutting end. The reamer shown at <i>B</i> is a fluted type with
+cutting edges that extend from <i>a</i> to <i>b</i>; it is used for finishing
+holes and the drill or rose reamer preceding it should leave the
+hole very close to the required size. These reamers are held
+while in use in a socket inserted in the tailstock spindle, as when
+using a twist drill.</p>
+
+<a name="Fig_1_43" id="Fig_1_43"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/054sm.png" alt="Casting Clamped to Faceplate for Turning and Boring" /></div>
+<p class="caption750">Fig. 43. Casting Clamped to Faceplate for Turning and Boring</p>
+</div>
+
+<a name="Secnum_1_28" id="Secnum_1_28"></a><p><b>Holding Work on Faceplate.</b>&mdash;Some castings or forgings are
+so shaped that they cannot be held in a chuck very well, or perhaps
+not at all, and work of this kind is often clamped to a faceplate
+which is usually larger than the faceplate used for driving
+parts that are turned between the centers. An example of faceplate
+work is shown in <a href="#Fig_1_43">Fig. 43</a>. This is a rectangular-shaped
+casting having a round boss or projection, the end <i>e</i> of which is
+to be turned parallel with the back face of the casting previously
+finished on a planer. A rough cored hole through the
+center of the boss also needs to be bored true.</p>
+
+<p>The best way to perform this operation in the lathe would be<span class="pagenum"><a name="Pg_46" id="Pg_46">[46]</a></span>
+to clamp the finished surface of the casting directly against the
+faceplate by bolts and clamps <i>a</i>, <i>b</i>, <i>c</i>, and <i>d</i>, as shown; the
+work would then be turned just as though it were held in a
+chuck. By holding the casting in this way, face <i>e</i> will be finished
+parallel with the back surface because the latter is clamped
+directly against the true-running surface of the faceplate. If a
+casting of this shape were small enough it could also be held in
+the jaws of an independent chuck, but if the surface e needs to
+be exactly parallel with the back face, it is better to clamp the
+work to the faceplate. Most lathes have two faceplates: One
+of small diameter used principally for driving work turned between
+centers, and a large one for holding heavy or irregularly
+shaped pieces; either of these can be screwed onto the spindle,
+and the large faceplate has a number of slots through which
+clamping bolts can be inserted.</p>
+
+<p>The proper way to clamp a piece to the faceplate depends, of
+course, largely on its shape and the location of the surface to be
+machined, but in any case it is necessary to hold it securely to
+prevent any shifting after a cut is started. Sometimes castings
+can be held by inserting bolts through previously drilled holes,
+but when clamps are used in connection with the bolts, their
+outer ends are supported by hardwood or metal blocks which
+should be just high enough to make the clamp bear evenly on<span class="pagenum"><a name="Pg_47" id="Pg_47">[47]</a></span>
+the work. When deep roughing cuts have to be taken, especially
+on large diameters, it is well to bolt a piece to the faceplate
+and against one side of the casting, as at <i>D</i>, to act as a
+driver and prevent the work from shifting; but a driver would
+not be needed in this particular case. Of course a faceplate
+driver is always placed to the rear, as determined by the direction
+of rotation, because the work tends to shift backward when a
+cut is being taken. If the surface which is clamped against the
+faceplate is finished as in this case, the work will be less likely to
+shift if a piece of paper is placed between it and the faceplate.</p>
+
+<p>Work mounted on the faceplate is generally set true by some
+surface before turning. As the hole in this casting should be
+true with the round boss, the casting is shifted on the faceplate
+until the rough outer surface of the boss runs true; the clamps
+which were previously set up lightly are then tightened. The
+face e is first turned by using a round-nosed tool. This tool is
+then replaced by a boring tool and the hole is finished to the
+required diameter. If the hole being bored is larger than the
+central hole in the faceplate, the casting should be clamped
+against parallel pieces, and not directly against the faceplate,
+to provide clearance for the tool when it reaches the inner end
+of the hole and prevent it from cutting the faceplate. The
+parallel pieces should be of the same thickness and be located
+near the clamps to prevent springing the casting.</p>
+
+<a name="Fig_1_44" id="Fig_1_44"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/055sm.png" alt="Cast Elbow held on Angle-plate attached to Faceplate" /></div>
+<p class="caption750">Fig. 44. Cast Elbow held on Angle-plate attached to Faceplate</p>
+</div>
+
+<p><span class="pagenum"><a name="Pg_48" id="Pg_48">[48]</a></span>
+<a name="Secnum_1_29" id="Secnum_1_29"></a><b>Application of Angle-plate to Faceplate.</b>&mdash;Another example
+of faceplate work is shown in <a href="#Fig_1_44">Fig. 44</a>. This is a cast-iron elbow
+<i>E</i>, the two flanges of which are to be faced true and square
+with each other. The shape of this casting is such that it would
+be very difficult to clamp it directly to the faceplate, but it is
+easily held on an angle-plate <i>P</i>, which is bolted to the faceplate.
+The two surfaces of this angle-plate are square with
+each other so that when one flange of the elbow is finished and
+bolted against the angle-plate, the other will be faced square.
+When setting up an angle-plate for work of this kind, the distance
+from its work-holding side to the center of the faceplate is
+made equal to the distance <i>d</i> between the center of one flange
+and the face of the other, so that the flange to be faced will run
+about true when bolted in place. As the angle-plate and work
+are almost entirely on one side of the faceplate, a weight <i>W</i> is
+attached to the opposite side for counterbalancing. Very often
+weights are also needed to counterbalance offset parts that
+are bolted directly to the faceplate. The necessity of counterbalancing
+depends somewhat upon the speed to be used for
+turning. If the surface to be machined is small in diameter so
+that the lathe can be run quite rapidly, any unbalanced part
+should always be counterbalanced.</p>
+
+<p>Sometimes it is rather difficult to hold heavy pieces against
+the vertical surface of the faceplate while applying the clamps,
+and occasionally the faceplate is removed and placed in a horizontal
+position on the bench; the work can then be located
+about right, and after it is clamped, the faceplate is placed on
+the lathe spindle by the assistance of a crane.</p>
+
+<p>Special faceplate jaws, such as the one shown to the right in
+<a href="#Fig_1_33">Fig. 33</a>, can often be used to advantage for holding work on
+large faceplates. Three or four of these jaws are bolted to the
+faceplate which is converted into a kind of independent chuck.
+These faceplate jaws are especially useful for holding irregularly
+shaped parts, as the different jaws can be located in any position.</p>
+
+<a name="Fig_1_45" id="Fig_1_45"></a>
+<div class="figcenter"><img src="images/057sm.jpg" alt="Rough Turning a Cylinder Lining" />
+<p class="caption750">Fig. 45. Rough Turning a Cylinder Lining&mdash;Note Method of Supporting
+Outer End</p>
+</div>
+
+<a name="Secnum_1_30" id="Secnum_1_30"></a><p><b>Supporting Outer End of Chucked Work.</b>&mdash;<a href="#Fig_1_45">Fig. 45</a> shows
+how the tailstock center is sometimes used for supporting the
+outer end of a long casting, the opposite end of which is held in<span class="pagenum"><a name="Pg_49" id="Pg_49">[49]</a></span>
+a chuck. This particular casting is to be turned and bored to
+make a lining for the cylinder of a locomotive in order to reduce
+the diameter of the cylinder which has been considerably enlarged
+by re-boring a number of times. These bushings are
+rough-turned on the outside while the outer end is supported by
+the cross-shaped piece or &#8220;spider&#8221; which forms a center-bearing
+for the tailstock. This spider has set screws in the flanged
+ends of the arms, which are tightened against the inner surface
+of the casting and are adjusted one way or the other in order
+to locate it in a concentric position. After roughing the outside,
+the inside is bored to the finish size; then centered disks, which
+fit into the bore, are placed in the ends of the bushing and the
+latter is finish-turned. The object in rough turning the outside
+prior to boring is to avoid the distortion which might occur if
+this hard outer surface were removed last.</p>
+
+<a name="Secnum_1_31" id="Secnum_1_31"></a><p><b>Boring Large Castings in
+the Lathe.</b>&mdash;An ordinary engine
+lathe is sometimes used for boring engine or pump cylinders,
+linings, etc., which are too large to be held in the chuck or on a
+faceplate, and must be attached to the lathe carriage. As a
+rule, work of this class is done in a special boring machine (see<span class="pagenum"><a name="Pg_50" id="Pg_50">[50]</a></span>
+<a href="#Chapnum_7">&#8220;Horizontal Boring Machines&#8221;</a>), but if such a machine is not
+available, it may be necessary to use a lathe. There are two
+general methods of boring.</p>
+
+<a name="Fig_1_46" id="Fig_1_46"></a>
+<div class="figcenter"><img src="images/058sm.jpg" alt="Boring a Cylinder Lining in an Ordinary Engine Lathe" />
+<p class="caption750">Fig. 46. Boring a Cylinder Lining in an Ordinary Engine Lathe</p>
+</div>
+
+<p><a href="#Fig_1_46">Fig. 46</a> shows how the lining illustrated in <a href="#Fig_1_45">Fig. 45</a> is bored
+in a large engine lathe. The casting is held in special fixtures
+which are attached to the lathe carriage, and the boring-bar is
+rotated by the lathe spindle. The tool-head of this boring-bar
+carries two tools located 180 degrees apart and it is fed along
+the bar by a star-feed mechanism shown attached to the bar
+and the tailstock spindle. Each time the bar revolves, the star
+wheel strikes a stationary pin and turns the feed-screw which,
+as the illustration shows, extends along a groove cut in one
+side of the bar. This feed-screw passes through a nut attached
+to the tool-head so that the latter is slowly fed through the
+bore. When using a bar of this type, the carriage, of course,
+remains stationary.</p>
+
+<p>Cylindrical parts attached to the carriage can also be bored
+by using a plain solid bar mounted between the centers. The
+bar must be provided with a cutter for small holes or a tool-head
+for larger diameters (preferably holding two or more tools)<span class="pagenum"><a name="Pg_51" id="Pg_51">[51]</a></span>
+and the boring is done by feeding the carriage along the bed by
+using the regular power feed of the lathe. A symmetrically
+shaped casting like a bushing or lining is often held upon wooden
+blocks bolted across the carriage. These are first cut away to
+form a circular seat of the required radius, by using the boring-bar
+and a special tool having a thin curved edge. The casting
+is then clamped upon these blocks by the use of straps and
+bolts, and if the curved seats were cut to the correct radius,
+the work will be located concentric with the boring-bar. When
+using a boring-bar of this type, the bar must be long enough to
+allow the part being bored to feed from one side of the cutter-head
+to the other, the cutter-head being approximately in a
+central location.</p>
+
+<a name="Fig_1_47" id="Fig_1_47"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/059sm.png" alt="Method of Setting Circle on Work Concentric with Lathe Spindle" /></div>
+<p class="caption750">Fig. 47. Method of Setting Circle on Work Concentric with Lathe Spindle</p>
+</div>
+
+<a name="Secnum_1_32" id="Secnum_1_32"></a><p><b>Boring Holes to a Given Center Distance.</b>&mdash;In connection
+with faceplate work, it is often necessary to bore two or more
+holes at a given distance apart. The best method of doing this
+may depend upon the accuracy required. For ordinary work
+sometimes two or more circles <i>A</i> and <i>B</i> (<a href="#Fig_1_47">Fig. 47</a>) are drawn
+upon the part to be bored, in the position for the holes; the
+piece is then clamped to the faceplate and one of the circles is
+centered with the lathe spindle by testing it with a pointer C
+held in the toolpost; that is, when the pointer follows the circle
+as the work is turned, evidently the circle is concentric with
+the spindle. The hole is then drilled and bored. The other<span class="pagenum"><a name="Pg_52" id="Pg_52">[52]</a></span>
+circle is then centered in the same way for boring the second
+hole. As will be seen, the accuracy of this method depends
+first, upon the accuracy with which the circles were laid out,
+and second; upon the care taken in setting them concentric.
+For a more accurate way of locating parts for boring, see &#8220;<a href="#Secnum_3_14">Use
+of Center Indicator</a>&#8221; and &#8220;<a href="#Secnum_3_15">Locating Work by the Button
+Method</a>.&#8221;</p>
+
+<a name="Secnum_1_33" id="Secnum_1_33"></a><p><b>Turning Brass, Bronze and
+Copper.</b>&mdash;When turning soft
+yellow brass, a tool should be used having very little or no
+slope or rake on the top surface against which the chip bears,
+and for plain cylindrical turning, the point of the tool is drawn
+out quite thin and rounded, by grinding, to a radius of about
+<sup class="enum">1</sup>/<sub class="denom">8</sub> or <sup class="enum">3</sup>/<sub class="denom">16</sub>
+inch. If a tool having very much top slope is used for
+brass, there is danger of its gouging into the metal, especially if
+the part being turned is at all flexible. The clearance angle of
+a brass tool is usually about 12 or 14 degrees, which is 3 or 4
+degrees greater than the clearance for steel turning tools. Most
+brass is easily turned, as compared with steel, and for that
+reason this increase in clearance is desirable, because it facilitates
+feeding the tool into the metal, especially when the carriage
+and cross-slide movements are being controlled by hand
+as when turning irregular shapes.</p>
+
+<p>The speed for turning soft brass is much higher than for
+steel, being ordinarily between 150 and 200 feet per minute.
+When turning phosphor, tobin or other tough bronze compositions,
+the tool should be ground with rake the same as for
+turning steel, and lard oil is sometimes used as a lubricant.
+The cutting speed for bronzes varies from 35 or 40 to 80 feet
+per minute, owing to the difference in the composition of bronze
+alloys.</p>
+
+<p>Turning tools for copper are ground with a little more top
+rake than is given steel turning tools, and the point should be
+slightly rounded. It is important to have a keen edge, and
+a grindstone is recommended for sharpening copper turning
+tools. Milk is generally considered the best lubricant to use
+when turning copper. The speed can be nearly as fast as for
+brass.</p>
+
+<p><span class="pagenum"><a name="Pg_53" id="Pg_53">[53]</a></span>
+<a name="Secnum_1_34" id="Secnum_1_34"></a><b>Machining Aluminum.</b>&mdash;Tools for turning aluminum should
+have acute cutting angles. After rough-grinding the tool, it is
+advisable to finish sharpening the cutting edge on a grindstone
+or with an oilstone for fine work, as a keen edge is very essential.
+High speeds and comparatively light cuts are recommended.
+The principal difficulty in the machining of aluminum and aluminum
+alloys is caused by the clogging of the chips, especially
+when using such tools as counterbores and milling cutters.
+This difficulty can be avoided largely by using the right kind
+of cutting lubricant. Soap-water and kerosene are commonly
+employed. The latter enables a fine finish to be obtained, provided
+the cutting tool is properly ground.</p>
+
+<p>The following information on this subject represents the experience
+of the Brown-Lipe Gear Co., where aluminum parts
+are machined in large quantities: For finishing bored holes, a
+bar equipped with cutters has been found more practicable than
+reamers. The cutters used for machining 4-inch holes have a
+clearance of from 20 to 22 degrees and no rake or slope on the
+front faces against which the chips bear. The roughing cutters
+for this work have a rather sharp nose, being ground on the
+point to a radius of about <sup class="enum">3</sup>/<sub class="denom">32</sub> inch, but for securing a smooth
+surface, the finishing tools are rounded to a radius of about
+<sup class="enum">3</sup>/<sub class="denom">4</sub> inch. The cutting speed, as well as the feed, for machining
+aluminum is from 50 to 60 per cent faster than the speeds and
+feeds for cast iron. The lubricant used by this company is
+composed of one part &#8220;aqualine&#8221; and 20 parts water. This
+lubricant not only gives a smooth finish but preserves a keen
+cutting edge and enables tools to be used much longer without
+grinding. Formerly, a lubricant composed of one part of high-grade
+lard oil and one part of kerosene was used. This mixture
+costs approximately 30 cents per gallon, whereas the aqualine
+and water mixture now being used costs less than 4 cents per
+gallon, and has proved more effective than the lubricant formerly
+employed.</p>
+
+<hr class="c25" />
+<span class="pagenum"><a name="Pg_54" id="Pg_54">[54]</a></span>
+<a name="Chapnum_2" id="Chapnum_2"></a><h2>CHAPTER II</h2>
+<h3>LATHE TURNING TOOLS AND CUTTING SPEEDS</h3>
+<hr class="c05" />
+
+<p>Notwithstanding the fact that a great variety of work can
+be done in the lathe, the number of turning tools required is
+comparatively small. <a href="#Fig_2_1">Fig. 1</a> shows the forms of tools that are
+used principally, and typical examples of the application of
+these various tools are indicated in <a href="#Fig_2_2">Fig. 2</a>. The reference letters
+used in these two illustrations correspond for tools of the same
+type, and both views should be referred to in connection with
+the following description.</p>
+
+<a name="Fig_2_1" id="Fig_2_1"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/063sm.png" alt="Set of Lathe Turning Tools for General Work" /></div>
+<p class="caption750">Fig. 1. Set of Lathe Turning Tools for General Work</p>
+</div>
+
+<a name="Fig_2_2" id="Fig_2_2"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/064sm.png" alt="Views illustrating Use of Various Types of Lathe Tools" /></div>
+<p class="caption750">Fig. 2. Views illustrating Use of Various Types of Lathe Tools</p>
+</div>
+
+<a name="Secnum_2_1" id="Secnum_2_1"></a><p><b>Turning Tools for General Work.</b>&mdash;The tool shown at <i>A</i> is
+the form generally used for rough turning, that is for taking
+deep cuts when considerable metal has to be removed. At <i>B</i> a
+tool of the same type is shown, having a bent end which enables
+it to be used close up to a shoulder or surface <i>s</i> that might come
+in contact with the tool-rest if the straight form were employed.
+Tool <i>C</i>, which has a straight cutting end, is used on certain
+classes of work for taking light finishing cuts, with a coarse
+feed. This type of tool has a flat or straight cutting edge at
+the end, and will leave a smooth finish even though the feed is
+coarse, provided the cutting edge is set parallel with the tool's
+travel so as to avoid ridges. Broad-nosed tools and wide feeds
+are better adapted for finishing cast iron than steel. When
+turning steel, if the work is at all flexible, a broad tool tends to
+gouge into it and for this reason round-nosed tools and finer
+feeds are generally necessary. A little experience in turning
+will teach more on this point than a whole chapter on the subject.</p>
+
+<p>The side-tools shown at <i>D</i> and <i>E</i> are for facing the ends of
+shafts, collars, etc. The first tool is known as a right side-tool
+because it operates on the right end or side of a shaft or collar,
+whereas the left side-tool <i>E</i> is used on the opposite side, as shown
+in <a href="#Fig_2_2">Fig. 2</a>. Side-tools are also bent to the right or left because
+<span class="pagenum"><a name="Pg_55" id="Pg_55">[55]</a></span>
+the cutting edge of a straight tool cannot always be located
+properly for facing certain surfaces. A bent right side-tool is
+shown at <i>F</i>. A form of tool that is frequently used is shown at
+<i>G</i>; this is known as a parting tool and is used for severing pieces
+and for cutting grooves, squaring corners, etc. The same type
+of tool having a bent end is shown at <i>H</i> (<a href="#Fig_2_2">Fig. 2</a>) severing a piece
+held in the chuck. Work that is held between centers should
+not be entirely severed with a parting tool unless a steadyrest is<span class="pagenum"><a name="Pg_56" id="Pg_56">[56]</a></span>
+placed between the tool and faceplate, as otherwise the tool may
+be broken by the springing of the work just before the piece is
+cut in two. It should be noted that the sides of this tool slope<span class="pagenum"><a name="Pg_57" id="Pg_57">[57]</a></span>
+inward back of the cutting edge to provide clearance when
+cutting in a narrow groove.</p>
+
+<p>At <i>I</i> a thread tool is shown for cutting a U. S. standard thread.
+This thread is the form most commonly used in this country at
+the present time. A tool for cutting a square thread is shown
+at <i>J</i>. This is shaped very much like a parting tool except that
+the cutting end is inclined slightly to correspond with the helix
+angle of the thread, as explained in <a href="#Chapnum_4">Chapter IV</a>, which contains
+descriptions of different thread forms and methods of cutting
+them. Internal thread tools are shown at <i>K</i> and <i>L</i> for cutting
+U. S. standard and square threads in holes. It will be seen
+that these tools are somewhat like boring tools excepting the
+ends which are shaped to correspond with the thread which
+they are intended to cut.</p>
+
+<p>A tool for turning brass is shown at <i>M</i>. Brass tools intended
+for general work are drawn out quite thin and they are given a
+narrow rounded point. The top of the brass tool is usually
+ground flat or without slope as otherwise it tends to gouge into
+the work, especially if the latter is at all flexible. The end of a
+brass tool is sometimes ground with a straight cutting edge for
+turning large rigid work, such as brass pump linings, etc., so
+that a coarse feed can be used without leaving a rough surface.
+The tools at <i>N</i> and <i>O</i> are for boring or finishing drilled or cored
+holes. Two sizes are shown, which are intended for small and
+large holes, respectively.</p>
+
+<p>The different tools referred to in the foregoing might be called
+the standard types because they are the ones generally used,
+and as <a href="#Fig_2_2">Fig. 2</a> indicates, they make it possible to turn an almost
+<span class="pagenum"><a name="Pg_58" id="Pg_58">[58]</a></span>
+endless variety of forms. Occasionally some special form of
+tool is needed for doing odd jobs, having, perhaps, an end bent
+differently or a cutting edge shaped to some particular form.
+Tools of the latter type, which are known as &#8220;form tools,&#8221; are
+sometimes used for finishing surfaces that are either convex,
+concave, or irregular in shape. The cutting edges of these
+tools are carefully filed or ground to the required shape, and
+the form given the tool is reproduced in the part turned. Ornamental
+or other irregular surfaces can be finished very neatly
+by the use of such tools. It is very difficult, of course, to turn
+convex or concave surfaces with a regular tool; in fact, it would
+not be possible to form a true spherical surface, for instance,
+without special equipment, because the tool could not be moved
+along a true curve by simply using the longitudinal and cross
+feeds. Form tools should be sharpened by grinding entirely on
+the top surface, as any grinding on the end or flank would alter
+the shape of the tool.</p>
+
+<a name="Fig_2_3" id="Fig_2_3"></a>
+<div class="figcenter"><img src="images/065sm.jpg" alt="Turning Tool with Inserted Cutter" />
+<p class="caption750">Fig. 3. Turning Tool with Inserted Cutter</p>
+</div>
+
+<a name="Fig_2_4" id="Fig_2_4"></a>
+<div class="figcenter"><img src="images/066sm.jpg" alt="Heavy Inserted-cutter Turning Tool" />
+<p class="caption750">Fig. 4. Heavy Inserted-cutter Turning Tool</p>
+</div>
+
+<a name="Secnum_2_2" id="Secnum_2_2"></a><p><b>Tool-holders with Inserted Cutters.</b>&mdash;All of the tools shown
+in Fig. 1 are forged from the bar, and when the cutting ends
+have been ground down considerably it is necessary to forge a
+new end. To eliminate the expense of this continual dressing of
+tools and also to effect a great reduction in the amount of tool
+steel required, tool-holders having small inserted cutters are
+used in many shops. A tool-holder of this type, for outside
+turning, is shown in <a href="#Fig_2_3">Fig. 3</a>. The cutter <i>C</i> is held in a fixed
+position by the set-screw shown, and it is sharpened, principally,
+by grinding the end, except when it is desired to give the top of<span class="pagenum"><a name="Pg_59" id="Pg_59">[59]</a></span>
+the cutter a different slope from that due to its angular position.
+Another inserted-cutter turning tool is shown in <a href="#Fig_2_4">Fig. 4</a>, which
+is a heavy type intended for roughing. The cutter in this case
+has teeth on the rear side engaging with corresponding teeth
+cut in the clamping block which is tightened by a set-screw on
+the side opposite that shown. With this arrangement, the cutter
+can be adjusted upward as the top is ground away.</p>
+
+<a name="Fig_2_5" id="Fig_2_5"></a>
+<div class="figcenter"><img src="images/067asm.jpg" alt="Parting Tool with Inserted Blade" />
+<p class="caption750">Fig. 5. Parting Tool with Inserted Blade</p>
+</div>
+
+<a name="Fig_2_6" id="Fig_2_6"></a>
+<div class="figcenter"><img src="images/067bsm.jpg" alt="Boring Tool with Inserted Cutter and Adjustable Bar" />
+<p class="caption750">Fig. 6. Boring Tool with Inserted Cutter and Adjustable Bar</p>
+</div>
+
+<a name="Fig_2_7" id="Fig_2_7"></a>
+<div class="figcenter"><img src="images/068sm.jpg" alt="Threading Tool" />
+<p class="caption750">Fig. 7. Threading Tool</p>
+</div>
+
+<p>A parting tool of the inserted blade type is shown in <a href="#Fig_2_5">Fig. 5</a>.
+The blade <i>B</i> is clamped by screw <i>S</i> and also by the spring of
+the holder when the latter is clamped in the toolpost. The
+blade can, of course, be moved outward when necessary. <a href="#Fig_2_6">Fig. 6</a>
+shows a boring tool consisting of a holder <i>H</i>, a bar <i>B</i> that can
+be clamped in any position, and an inserted cutter <i>C</i>. With this
+type of boring tool, the bar can be extended beyond the holder
+just far enough to reach through the hole to be bored, which
+makes the tool very rigid. A thread tool of the holder type is
+shown in <a href="#Fig_2_7">Fig. 7</a>. The angular edge of the cutter <i>C</i> is accurately
+<span class="pagenum"><a name="Pg_60" id="Pg_60">[60]</a></span>
+ground by the manufacturers, so that the tool is sharpened by
+simply grinding it flat on the top. As the top is ground away,
+the cutter is raised by turning screw <i>S</i>, which can also be used
+for setting the tool to the proper height.</p>
+
+<a name="Fig_2_8" id="Fig_2_8"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/069sm.png" alt="To Avoid springing, Overhang A of Tool should not be Excessive" /></div>
+<p class="caption750">Fig. 8. To avoid springing, Overhang A of Tool should not be Excessive</p>
+</div>
+
+<a name="Secnum_2_3" id="Secnum_2_3"></a><p><b>The Position of Turning Tools.</b>&mdash;The production of accurate
+lathe work depends partly on the condition of the lathe used
+and also on the care and judgment exercised by the man operating
+it. Even though a lathe is properly adjusted and in good
+condition otherwise, errors are often made which are due to
+other causes which should be carefully avoided. If the turning
+tool is clamped so that the cutting end extends too far from the
+supporting block, the downward spring of the tool, owing to
+the thrust of the cut, sometimes results in spoiled work, especially
+when an attempt is made to turn close to the finished
+size by taking a heavy roughing cut. Suppose the end of a
+cylindrical part is first reduced for a short distance by taking
+several trial cuts until the diameter <i>d</i>, <a href="#Fig_2_8">Fig. 8</a>, is slightly above
+the finished size and the power feed is then engaged. When
+the tool begins to take the full depth <i>e</i> of the cut, the point,
+which ordinarily would be set a little above the center, tends to
+spring downward into the work, and if there were considerable
+springing action, the part would probably be turned below the
+finished size, the increased reduction beginning at the point
+where the full cut started.</p>
+
+<p>This springing action, as far as the tool is concerned, can be
+practically eliminated by locating the tool so that the distance<span class="pagenum"><a name="Pg_61" id="Pg_61">[61]</a></span>
+<i>A</i> between the tool-block and cutting end, or the &#8220;overhang,&#8221;
+is as short as possible. Even though the tool has little overhang
+it may tilt downward because the toolslide is loose on its ways,
+and for this reason the slide should have a snug adjustment
+that will permit an easy movement without unnecessary play.
+The toolslides of all lathes are provided with gibs which can
+be adjusted by screws to compensate for wear, or to secure a
+more rigid bearing.</p>
+
+<a name="Fig_2_9" id="Fig_2_9"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/070sm.png" alt="Tool Displacement" /></div>
+<p class="caption750">Fig. 9. (A) The Way in which Tool is sometimes displaced by Thrust of Cut,
+when set at an Angle.<br />(B) Tool Set for Finishing both Cylindrical and
+Radial Surfaces</p>
+</div>
+
+<p>When roughing cuts are to be taken, the tool should be located
+so that any change in its position which might be caused by the
+pressure of the cut will not spoil the work. This point is illustrated
+at <i>A</i> in <a href="#Fig_2_9">Fig. 9</a>. Suppose the end of a rod has been reduced
+by taking a number of trial cuts, until it is <sup class="enum">1</sup>/<sub class="denom">32</sub> inch above the
+finished size. If the power feed is then engaged with the tool
+clamped in an oblique position, as shown, when the full cut is
+encountered at <i>c</i>, the tool, unless very tightly clamped, may be
+shifted backward by the lateral thrust of the cut, as indicated
+by the dotted lines. The point will then begin turning smaller
+than the finished size and the work will be spoiled. To prevent
+any change of position, it is good practice, especially when
+roughing, to clamp the tool square with the surface being turned,
+or in other words, at right angles to its direction of movement.
+Occasionally, however, there is a decided advantage in having<span class="pagenum"><a name="Pg_62" id="Pg_62">[62]</a></span>
+the tool set at an angle. For example, if it is held about as
+shown at <i>B</i>, when turning the flange casting <i>C</i>, the surfaces <i>s</i>
+and <i>s<sub>1</sub></i> can be finished without changing the tool's position.
+Cylindrical and radial surfaces are often turned in this way
+in order to avoid shifting the tool, especially when machining
+parts in quantity.</p>
+
+<a name="Secnum_2_4" id="Secnum_2_4"></a><p><b>Tool Grinding.</b>&mdash;In the grinding of lathe tools there are
+three things of importance to be considered: First, the cutting
+edge of the tool (as viewed from the top) needs to be given a
+certain shape; second, there must be a sufficient amount of
+clearance for the cutting edge; and third, tools, with certain
+exceptions, are ground with a backward slope or a side slope,
+or with a combination of these two slopes on that part against
+which the chip bears when the tool is in use.</p>
+
+<a name="Fig_2_10" id="Fig_2_10"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/071sm.png" alt="Illustration showing the Meaning of Terms used in Tool Grinding as applied to Tools of Different Types" /></div>
+<p class="caption750">Fig. 10. Illustration showing the Meaning of Terms used<br />in Tool
+Grinding as applied to Tools of Different Types</p>
+</div>
+
+<p>In <a href="#Fig_2_10">Fig. 10</a> a few of the different types of tools which are used
+in connection with lathe work are shown. This illustration also
+indicates the meaning of the various terms used in tool grinding.
+As shown, the clearance of the tool is represented by the
+angle <i>&alpha;</i>, the back slope is represented by the angle <i>&beta;</i>, and the
+side slope by the angle <i>&gamma;</i>. The angle <i>&delta;</i> for a tool without side
+slope is known as the lip angle or the angle of keenness. When,<span class="pagenum"><a name="Pg_63" id="Pg_63">[63]</a></span>
+however, the tool has both back and side slopes, this lip angle
+would more properly be the angle between the flank <i>f</i> and the
+top of the tool, measured diagonally along a line <i>z&mdash;z</i>. It will
+be seen that the lines <i>A&mdash;B</i> and <i>A&mdash;C</i> from which the angles
+of clearance and back slope are measured are parallel with the
+top and sides of the tool shank, respectively. For lathe tools,
+however, these lines are not necessarily located in this way
+when the tool is in use, as the height of the tool point with
+relation to the work center determines the position of these
+lines, so that the <i>effective</i> angles of back slope, clearance and
+keenness are changed as the tool point is lowered or raised.
+The way the position of the tool affects these angles will be
+explained later.</p>
+
+<p>While tools must, of necessity, be varied considerably in shape
+to adapt them to various purposes, there are certain underlying
+principles governing their shape which apply generally;
+so in what follows we shall not attempt to explain in detail just
+what the form of each tool used on the lathe should be, as it is
+more important to understand how the cutting action of the
+tool and its efficiency is affected when it is improperly ground.<span class="pagenum"><a name="Pg_64" id="Pg_64">[64]</a></span>
+When the principle is understood, the grinding of tools of various
+types and shapes is comparatively easy.</p>
+
+<a name="Fig_2_11" id="Fig_2_11"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/072sm.png" alt="Plan View of Lathe Turning and Threading Tools" /></div>
+<p class="caption750">Fig. 11. Plan View of Lathe Turning and Threading Tools</p>
+</div>
+
+<a name="Secnum_2_5" id="Secnum_2_5"></a><p><b>Shape or Contour of Cutting Edge.</b>&mdash;In the first place we
+shall consider the shape or contour of the cutting edge of the
+tool as viewed from the top, and then take up the question of
+clearance and slope, the different elements being considered
+separately to avoid confusion. The contour of the cutting edge
+depends primarily upon the purpose for which the tool is intended.
+For example, the tool <i>A</i>, in <a href="#Fig_2_11">Fig. 11</a>, where a plan view
+of a number of different lathe tools is shown, has a very different
+shape from that of, say, tool <i>D</i>, as the first tool is used for rough
+turning, while tool <i>D</i> is intended for cutting grooves or severing
+a turned part. Similarly, tool <i>E</i> is V-shaped because it is used
+for cutting V-threads. Tools <i>A</i>, <i>B</i> and <i>C</i>, however, are regular
+turning tools; that is, they are all intended for turning plain
+cylindrical surfaces, but the contour of the cutting edges varies
+considerably, as shown. In this case it is the characteristics of
+the work and the cut that are the factors which determine the
+shape. To illustrate, tool <i>A</i> is of a shape suitable for rough-turning
+large and rigid work, while tool <i>B</i> is adapted for smaller
+and more flexible parts. The first tool is well shaped for roughing
+because experiments have shown that a cutting edge of a
+large radius is capable of higher cutting speed than could be
+used with a tool like <i>B</i>, which has a smaller point. This increase<span class="pagenum">
+<a name="Pg_65" id="Pg_65">[65]</a></span>
+in the cutting speed is due to the fact that the tool <i>A</i>
+removes a thinner chip for a given feed than tool <i>B</i>; therefore,
+the speed may be increased without injuring the cutting edge
+to the same extent. If, however, tool <i>A</i> were to be used for
+turning a long and flexible part, chattering might result; consequently,
+a tool <i>B</i> having a point with a smaller radius would
+be preferable, if not absolutely necessary.</p>
+
+<p>The character of the work also affects the shape of tools.
+The tool shown at <i>C</i> is used for taking light finishing cuts with
+a wide feed. Obviously, if the straight or flat part of the cutting
+edge is in line with the travel of the tool, the cut will be smooth
+and free from ridges, even though the feed is coarse, and by
+using a coarse feed the cut is taken in less time; but such a
+tool cannot be used on work that is not rigid, as chattering
+would result. Therefore, a smaller cutting point and a reduced
+feed would have to be employed. Tools with broad flat cutting
+edges and coarse feeds are often used for taking finishing cuts
+in cast iron, as this metal offers less resistance to cutting than
+steel, and is less conducive to chattering.</p>
+
+<p>The shape of a tool (as viewed from the top) which is intended
+for a more specific purpose than regular turning, can be largely
+determined by simply considering the tool under working conditions.
+This point may be illustrated by the parting tool <i>D</i>
+which, as previously stated, is used for cutting grooves, squaring
+corners, etc. Evidently this tool should be widest at the
+cutting edge; that is, the sides <i>d</i> should have a slight amount
+of clearance so that they will not bind as the tool is fed into a
+groove. As the tool at <i>E</i> is for cutting a V-thread, the angle <i>&alpha;</i>
+between its cutting edges must equal the angle between the
+sides of a V-thread, or 60 degrees. The tool illustrated at <i>F</i> is
+for cutting inside square threads. In this case the width <i>w</i>
+should be made equal to one-half the pitch of the thread (or
+slightly greater to provide clearance for the screw), and the
+sides should be given a slight amount of side clearance, the
+same as with the parting tool <i>D</i>. So we see that the outline of
+the tool, as viewed from the top, must conform to and be governed
+by its use.</p>
+
+<a name="Secnum_2_6" id="Secnum_2_6"></a><p><span class="pagenum"><a name="Pg_66" id="Pg_66">[66]</a></span>
+<b>Direction of Top Slope for Turning Tools.</b>&mdash;Aside from the
+question of the shape of the cutting edge as viewed from the
+top, there remains to be determined the amount of clearance
+that the tool shall have, and also the slope (and its direction) of
+the top of the tool. By the top is meant that surface against
+which the chip bears while it is being severed. It may be stated,
+in a general way, that the direction in which the top of the tool
+should slope should be away from what is to be the <i>working
+part</i> of the cutting edge. For example, the working edge of a
+roughing tool <i>A</i> (<a href="#Fig_2_11">Fig. 11</a>), which is used for heavy cuts, would
+be, practically speaking, between points <i>a</i> and <i>b</i>, or, in other
+words, most of the work would be done by this part of the cutting
+edge; therefore the top should slope back from this part
+of the edge. Obviously, a tool ground in this way will have
+both a back and a side slope.</p>
+
+<p>When most of the work is done on the point or nose of the
+tool, as, for example, with the lathe finishing tool <i>C</i> which takes
+light cuts, the slope should be straight back from the point or
+cutting edge <i>a&mdash;b</i>. As the side tool shown in <a href="#Fig_2_10">Fig. 10</a> does its
+cutting along the edge <i>a&mdash;b</i>, the top is given a slope back from
+this edge as shown in the end view. This point should be
+remembered, for when the top slopes in the right direction, less
+power is required for cutting. Tools for certain classes of work,
+such as thread tools, or those for turning brass or chilled iron,
+are ground flat on top, that is, without back or side slope.</p>
+
+<a name="Secnum_2_7" id="Secnum_2_7"></a><p><b>Clearance for the Cutting Edge.</b>&mdash;In order that the cutting
+edge may work without interference, it must have clearance;
+that is, the flank <i>f</i> (Fig. 10) must be ground to a certain angle <i>&alpha;</i>
+so that it will not rub against the work and prevent the cutting
+edge from entering the metal. This clearance should be just
+enough to permit the tool to cut freely. A clearance angle of
+eight or ten degrees is about right for lathe turning tools.</p>
+
+<a name="Fig_2_12" id="Fig_2_12"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/075sm.png" alt="Illustrations showing how Effective Angles of Slope and Clearance change as Tool is raised or lowered" /></div>
+<p class="caption750">Fig. 12. Illustrations showing how Effective Angles of Slope<br />and
+Clearance change as Tool is raised or lowered</p>
+</div>
+
+<p>The back slope of a tool is measured from a line <i>A&mdash;B</i> which is
+parallel to the shank, and the clearance angle, from a line <i>A&mdash;C</i>
+at right angles to line <i>A&mdash;B</i>. These lines do not, however, always
+occupy this position with relation to the tool shank when
+the tool is in use. As shown to the left in <a href="#Fig_2_12">Fig. 12</a>, the base line
+<span class="pagenum"><a name="Pg_67" id="Pg_67">[67]</a></span>
+<i>A&mdash;B</i> for a turning tool in use intersects with the point of the
+tool and center of the work, while the line <i>A&mdash;C</i> remains at right
+angles to the first. It will be seen, then, that by raising the
+tool, as shown to the right, the <i>effective</i> clearance angle <i>&alpha;</i> will
+be diminished, whereas lowering it, as shown by the dotted
+lines, will have the opposite effect.</p>
+
+<p>A turning tool for brass or other soft metal, particularly
+where considerable hand manipulation is required, could advantageously
+have a clearance of twelve or fourteen degrees,
+as it would then be easier to feed the tool into the metal; but,
+generally speaking, the clearance for turning tools should be
+just enough to permit them to cut freely. Excessive clearance
+weakens the cutting edge and may cause it to crumble under
+the pressure of the cut.</p>
+
+<a name="Secnum_2_8" id="Secnum_2_8"></a><p><b>Angle of Tool-point and Amount of Top Slope.</b>&mdash;The lip
+angle or the angle of keenness <i>&delta;</i> (<a href="#Fig_2_10">Fig. 10</a>) is another important
+consideration in connection with tool grinding, for it is upon
+this angle that the efficiency of the tool largely depends. By
+referring to the illustration it will be seen that this angle is
+governed by the clearance and the slope <i>&beta;</i>, and as the clearance
+remains practically the same, it is the slope which is varied to
+meet different conditions. Now, the amount of slope a tool
+should have depends on the work for which it is intended. If,
+for example, a turning tool is to be used for roughing medium
+or soft steel, it should have a back slope of about eight degrees
+and a side slope ranging from fourteen to twenty degrees, while
+<span class="pagenum"><a name="Pg_68" id="Pg_68">[68]</a></span>
+a tool for cutting very hard steel should have a back slope of
+about five degrees and a side slope of nine degrees.</p>
+
+<a name="Fig_2_13" id="Fig_2_13"></a>
+<div class="figcenter"><img src="images/076sm.jpg" alt="Blunt Tool for Turning Hard Steel, Tool-point Ground to give Keenness" />
+<p class="caption750">Fig. 13. (A) Blunt Tool for Turning Hard Steel.<br />(B) Tool-point
+Ground to give Keenness</p>
+</div>
+
+<p>The reason for decreasing the slope and thus increasing the
+lip angle for harder metals is to give the necessary increased
+strength to the cutting edge to prevent it from crumbling under
+the pressure of the cut. The tool illustrated at <i>A</i>, <a href="#Fig_2_13">Fig. 13</a>, is
+much stronger than it would be if ground as shown at <i>B</i>, as
+the former is more blunt. If a tool ground as at <i>A</i>, however,
+were used for cutting very soft steel, there would be a greater
+chip pressure on the top and, consequently, a greater resistance
+to cutting, than if a keener tool had been employed; furthermore
+the cutting speed would have to be lower, which is of
+even greater importance than the chip pressure; therefore, the
+lip angle, as a general rule, should be as small as possible without
+weakening the tool so that it cannot do the required work.
+In order to secure a strong and well-supported cutting edge,
+tools used for turning very hard metal, such as chilled rolls,
+etc., are ground with practically no slope and with very little
+clearance. Brass tools, while given considerable clearance, as
+previously stated, are ground flat on top or without slope; this
+is not done, however, to give strength to the cutting edge, but
+rather to prevent the tool from gouging into the work, which it
+is likely to do if the part being turned is at all flexible and the
+tool has top slope.</p>
+
+<p>Experiments conducted by Mr. F. W. Taylor to determine
+the most efficient form for lathe roughing tools showed that the<span class="pagenum"><a name="Pg_69" id="Pg_69">[69]</a></span>
+nearer the lip angle approached sixty-one degrees, the higher
+the cutting speed. This, however, does not apply to tools for
+turning cast iron, as the latter will work more efficiently with a
+lip angle of about sixty-eight degrees. This is doubtless because
+the chip pressure, when turning cast iron, comes closer
+to the cutting edge which should, therefore, be more blunt to
+withstand the abrasive action and heat. Of course, the foregoing
+remarks concerning lip angles apply more particularly to
+tools used for roughing.</p>
+
+<a name="Fig_2_14" id="Fig_2_14"></a>
+<div class="figcenter"><img src="images/077sm.jpg" alt="Grinding the Top and Flank of a Turning Tool" />
+<p class="caption750">Fig. 14. Grinding the Top and Flank of a Turning Tool</p>
+</div>
+
+<a name="Secnum_2_9" id="Secnum_2_9"></a><p><b>Grinding a Lathe Tool.</b>&mdash;The way a turning tool is held
+while the top surface is being ground is shown to the left in
+<a href="#Fig_2_14">Fig. 14</a>. By inclining the tool with the wheel face, it will be
+seen that both the back and side slopes may be ground at the
+same time. When grinding the flank of the tool it should be
+held on the tool-rest of the emery wheel or grindstone, as shown
+by the view to the right. In order to form a curved cutting
+edge, the tool is turned about the face of the stone while it is
+being ground. This rotary movement can be effected by supporting
+the inner end of the tool with one hand while the shank
+is moved to and fro with the other.</p>
+
+<p>Often a tool which has been ground properly in the first place
+is greatly misshapen after it has been sharpened a few times.
+This is usually the result of attempts on the part of the workman
+to re-sharpen it hurriedly; for example, it is easier to secure<span class="pagenum"><a name="Pg_70" id="Pg_70">[70]</a></span>
+a sharp edge on the turning tool shown to the left in <a href="#Fig_2_12">Fig. 12</a>, by
+grinding the flank as indicated by the dotted line, than by
+grinding the entire flank. The clearance is, however, reduced
+and the lip angle changed.</p>
+
+<p>There is great danger when grinding a tool of burning it or
+drawing the temper from the fine cutting edge, and, aside from
+the actual shape of the cutting end, this is the most important
+point in connection with tool grinding. If a tool is pressed
+hard against an emery or other abrasive wheel, even though the
+latter has a copious supply of water, the temper will sometimes
+be drawn. When grinding a flat surface, to avoid burning, the
+tool should frequently be withdrawn from the stone so that the
+cooling water (a copious supply of which should be provided)
+can reach the surface being ground. A moderate pressure
+should also be applied, as it is better to spend an extra minute
+or two in grinding than to ruin the tool by burning, in an attempt
+to sharpen it quickly. Of course, what has been said
+about burning applies more particularly to carbon steel, but
+even self-hardening steels are not improved by being over-heated
+at the stone. In some shops, tools are ground to the
+theoretically correct shape in special machines instead of by
+hand. The sharpened tools are then kept in the tool-room and
+are given out as they are needed.</p>
+
+<a name="Secnum_2_10" id="Secnum_2_10"></a><p><b>Cutting Speeds and Feeds.</b>&mdash;The term cutting speed as applied
+to turning operations is the speed in feet per minute of
+the surface being turned, or, practically speaking, it is equivalent
+to the length of a chip, in feet, which would be turned in
+one minute. The term cutting speed should not be confused
+with revolutions per minute, because the cutting speed depends
+not only upon the speed of the work but also upon its diameter.
+The feed of a tool is the amount it moves across the surface
+being turned for each revolution; that is, when turning a cylindrical
+piece, the feed is the amount that the tool moves sidewise
+for each revolution of the work. Evidently the time required
+for turning is governed largely by the cutting speed, the feed,
+and the depth of the cut; therefore, these elements should be
+carefully considered.</p>
+
+<p class="pagenum"><a name="Pg_71" id="Pg_71">[71]</a></p>
+<h4>Cutting Speeds and Feeds for Turning Tools<a name="Fnanchor_1" id="Fnanchor_1"></a><a href="#Fn_1" class="fnanchor">[1]</a></h4>
+
+<table align="center" class="center" width="80%" cellpadding="0" cellspacing="0" summary="Cutting Speeds">
+
+<tr><td class="bt bl" colspan="8">Steel&mdash;Standard <sup class="enum">7</sup>/<sub class="denom">8</sub>-inch Tool</td>
+<td class="bt bl br" colspan="8">Cast Iron&mdash;Standard <sup class="enum">7</sup>/<sub class="denom">8</sub>-inch Tool
+</td></tr>
+
+<tr><td class="bt bl" rowspan="2">Depth of Cut in Inches</td>
+<td class="bt bl" rowspan="2">Feed in Inches</td>
+<td class="bt bl" colspan="6">Speed in Feet per Minute for a Tool which is to last 1<sup class="enum">1</sup>/<sub class="denom">2</sub>
+Hour before Re-grinding</td>
+<td class="bt bl" rowspan="2">Depth of Cut in Inches</td>
+<td class="bt bl" rowspan="2">Feed in Inches</td>
+<td class="bt bl br" colspan="6">Speed in Feet per Minute for a Tool which is to last 1<sup class="enum">1</sup>/<sub class="denom">2</sub>
+Hour before Re-grinding</td></tr>
+
+<tr><td class="bt bl" colspan="2">Soft<br />Steel</td>
+<td class="bt bl" colspan="2">Medium<br />Steel</td>
+<td class="bt bl" colspan="2">Hard<br />Steel</td>
+<td class="bt bl" colspan="2">Soft<br />Cast Iron</td>
+<td class="bt bl" colspan="2">Medium<br />Cast Iron</td>
+<td class="bt bl br" colspan="2">Hard<br />Cast Iron</td></tr>
+
+<tr>
+<td class="bt bl" rowspan="4" style="width: 10%"><sup class="enum">3</sup>/<sub class="denom">32</sub></td>
+<td class="bt bl" style="width: 10%"><sup class="enum">1</sup>/<sub class="denom">64</sub></td>
+<td class="bt bl" align="right" style="width: 6%">476</td>
+<td class="bt" align="left" style="width: 4%">&nbsp;</td>
+<td class="bt bl" align="right" style="width: 6%">238</td>
+<td class="bt" align="left" style="width: 4%">&nbsp;</td>
+<td class="bt bl" align="right" style="width: 6%">108</td>
+<td class="bt" align="left" style="width: 4%">&nbsp;</td>
+<td class="bt bl" rowspan="3" style="width: 10%"><sup class="enum">3</sup>/<sub class="denom">32</sub></td>
+<td class="bt bl" style="width: 10%"><sup class="enum">1</sup>/<sub class="denom">16</sub></td>
+<td class="bt bl" align="right" style="width: 6%">122</td>
+<td class="bt" align="left" style="width: 4%">&nbsp;</td>
+<td class="bt bl" align="right" style="width: 6%">61</td>
+<td class="bt" align="left" style="width: 4%">.2</td>
+<td class="bt bl" align="right" style="width: 6%">35</td>
+<td class="bt br" align="left" style="width: 4%">.7</td>
+</tr>
+
+<tr>
+<td class="bt bl" ><sup class="enum">1</sup>/<sub class="denom">32</sub></td>
+<td class="bt bl" align="right">325</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">162</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">73</td>
+<td class="bt" align="left">.8</td>
+<td class="bt bl" ><sup class="enum">1</sup>/<sub class="denom">8</sub></td>
+<td class="bt bl" align="right">86</td>
+<td class="bt" align="left">.4</td>
+<td class="bt bl" align="right">43</td>
+<td class="bt" align="left">.2</td>
+<td class="bt bl" align="right">25</td>
+<td class="bt br" align="left">.2</td>
+</tr>
+
+<tr>
+<td class="bt bl" ><sup class="enum">1</sup>/<sub class="denom">16</sub></td>
+<td class="bt bl" align="right">222</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">111</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">50</td>
+<td class="bt" align="left">.4</td>
+<td class="bt bl" ><sup class="enum">3</sup>/<sub class="denom">16</sub></td>
+<td class="bt bl" align="right">70</td>
+<td class="bt" align="left">.1</td>
+<td class="bt bl" align="right">35</td>
+<td class="bt" align="left">.1</td>
+<td class="bt bl" align="right">20</td>
+<td class="bt br" align="left">.5</td>
+</tr>
+
+<tr>
+<td class="bt bl" ><sup class="enum">3</sup>/<sub class="denom">32</sub></td>
+<td class="bt bl" align="right">177</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">88</td>
+<td class="bt" align="left">.4</td>
+<td class="bt bl" align="right">40</td>
+<td class="bt" align="left">.2</td>
+<td class="bt bl" rowspan="4"><sup class="enum">1</sup>/<sub class="denom">8</sub></td>
+<td class="bt bl" ><sup class="enum">1</sup>/<sub class="denom">32</sub></td>
+<td class="bt bl" align="right">156</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">77</td>
+<td class="bt" align="left">.8</td>
+<td class="bt bl" align="right">45</td>
+<td class="bt br" align="left">.4</td>
+</tr>
+
+<tr>
+<td class="bt bl" rowspan="4"><sup class="enum">1</sup>/<sub class="denom">8</sub></td>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">64</sub></td>
+<td class="bt bl" align="right">420</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">210</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">95</td>
+<td class="bt" align="left">.5</td>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">16</sub></td>
+<td class="bt bl" align="right">112</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">56</td>
+<td class="bt" align="left">.2</td>
+<td class="bt bl" align="right">32</td>
+<td class="bt br" align="left">.8</td>
+</tr>
+
+<tr>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">32</sub></td>
+<td class="bt bl" align="right">286</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">143</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">65</td>
+<td class="bt" align="left">.0</td>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">8</sub></td>
+<td class="bt bl" align="right">79</td>
+<td class="bt" align="left">.3</td>
+<td class="bt bl" align="right">39</td>
+<td class="bt" align="left">.7</td>
+<td class="bt bl" align="right">23</td>
+<td class="bt br" align="left">.2</td>
+</tr>
+
+<tr>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">16</sub></td>
+<td class="bt bl" align="right">195</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">97</td>
+<td class="bt" align="left">.6</td>
+<td class="bt bl" align="right">44</td>
+<td class="bt" align="left">.4</td>
+<td class="bt bl"><sup class="enum">3</sup>/<sub class="denom">16</sub></td>
+<td class="bt bl" align="right">64</td>
+<td class="bt" align="left">.3</td>
+<td class="bt bl" align="right">32</td>
+<td class="bt" align="left">.2</td>
+<td class="bt bl" align="right">18</td>
+<td class="bt br" align="left">.8</td>
+</tr>
+
+<tr>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">8</sub></td>
+<td class="bt bl" align="right">133</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">66</td>
+<td class="bt" align="left">.4</td>
+<td class="bt bl" align="right">30</td>
+<td class="bt" align="left">.2</td>
+<td rowspan="4" class="bl bt"><sup class="enum">3</sup>/<sub class="denom">16</sub></td>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">32</sub></td>
+<td class="bt bl" align="right">137</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">68</td>
+<td class="bt" align="left">.6</td>
+<td class="bt bl" align="right">40</td>
+<td class="bt br" align="left">.1</td>
+</tr>
+
+<tr>
+<td rowspan="4" class="bl bt"><sup class="enum">3</sup>/<sub class="denom">16</sub></td>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">64</sub></td>
+<td class="bt bl" align="right">352</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">176</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">80</td>
+<td class="bt" align="left">.0</td>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">16</sub></td>
+<td class="bt bl" align="right">99</td>
+<td class="bt" align="left">.4</td>
+<td class="bt bl" align="right">49</td>
+<td class="bt" align="left">.7</td>
+<td class="bt bl" align="right">29</td>
+<td class="bt br" align="left">.0</td>
+</tr>
+
+<tr>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">32</sub></td>
+<td class="bt bl" align="right">240</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">120</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">54</td>
+<td class="bt" align="left">.5</td>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">8</sub></td>
+<td class="bt bl" align="right">70</td>
+<td class="bt" align="left">.1</td>
+<td class="bt bl" align="right">35</td>
+<td class="bt" align="left">.0</td>
+<td class="bt bl" align="right">20</td>
+<td class="bt br" align="left">.5</td>
+</tr>
+
+<tr>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">16</sub></td>
+<td class="bt bl" align="right">164</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">82</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">37</td>
+<td class="bt" align="left">.3</td>
+<td class="bt bl"><sup class="enum">3</sup>/<sub class="denom">16</sub></td>
+<td class="bt bl" align="right">56</td>
+<td class="bt" align="left">.8</td>
+<td class="bt bl" align="right">28</td>
+<td class="bt" align="left">.4</td>
+<td class="bt bl" align="right">16</td>
+<td class="bt br" align="left">.6</td>
+</tr>
+
+<tr>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">8</sub></td>
+<td class="bt bl" align="right">112</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">56</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">25</td>
+<td class="bt" align="left">.5</td>
+<td rowspan="4" class="bt bl"><sup class="enum">1</sup>/<sub class="denom">4</sub></td>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">32</sub></td>
+<td class="bt bl" align="right">126</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">62</td>
+<td class="bt" align="left">.9</td>
+<td class="bt bl" align="right">36</td>
+<td class="bt br" align="left">.7</td>
+</tr>
+
+<tr>
+<td class="bt bl" rowspan="4"><sup class="enum">1</sup>/<sub class="denom">4</sub></td>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">64</sub></td>
+<td class="bt bl" align="right">312</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">156</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">70</td>
+<td class="bt" align="left">.9</td>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">16</sub></td>
+<td class="bt bl" align="right">90</td>
+<td class="bt" align="left">.8</td>
+<td class="bt bl" align="right">45</td>
+<td class="bt" align="left">.4</td>
+<td class="bt bl" align="right">26</td>
+<td class="bt br" align="left">.5</td>
+</tr>
+
+<tr>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">32</sub></td>
+<td class="bt bl" align="right">213</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">107</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">48</td>
+<td class="bt" align="left">.4</td>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">8</sub></td>
+<td class="bt bl" align="right">64</td>
+<td class="bt" align="left">.1</td>
+<td class="bt bl" align="right">32</td>
+<td class="bt" align="left">.0</td>
+<td class="bt bl" align="right">18</td>
+<td class="bt br" align="left">.7</td>
+</tr>
+
+<tr>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">16</sub></td>
+<td class="bt bl" align="right">145</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">72</td>
+<td class="bt" align="left">.6</td>
+<td class="bt bl" align="right">33</td>
+<td class="bt" align="left">.0</td>
+<td class="bt bl"><sup class="enum">3</sup>/<sub class="denom">16</sub></td>
+<td class="bt bl" align="right">52</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">26</td>
+<td class="bt" align="left">.0</td>
+<td class="bt bl" align="right">15</td>
+<td class="bt br" align="left">.2</td>
+</tr>
+
+<tr>
+<td class="bt bl"><sup class="enum">3</sup>/<sub class="denom">32</sub></td>
+<td class="bt bl" align="right">116</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">58</td>
+<td class="bt" align="left">.1</td>
+<td class="bt bl" align="right">26</td>
+<td class="bt" align="left">.4</td>
+<td class="bt bl" rowspan="3"><sup class="enum">3</sup>/<sub class="denom">8</sub></td>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">32</sub></td>
+<td class="bt bl" align="right">111</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">55</td>
+<td class="bt" align="left">.4</td>
+<td class="bt bl" align="right">32</td>
+<td class="bt br" align="left">.3</td>
+</tr>
+
+<tr>
+<td class="bt bl" rowspan="3"><sup class="enum">3</sup>/<sub class="denom">8</sub></td>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">64</sub></td>
+<td class="bt bl" align="right">264</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">132</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">60</td>
+<td class="bt" align="left">.0</td>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">16</sub></td>
+<td class="bt bl" align="right">80</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">40</td>
+<td class="bt" align="left">.0</td>
+<td class="bt bl" align="right">23</td>
+<td class="bt br" align="left">.4</td>
+</tr>
+
+<tr>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">32</sub></td>
+<td class="bt bl" align="right">180</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">90</td>
+<td class="bt" align="left">.2</td>
+<td class="bt bl" align="right">41</td>
+<td class="bt" align="left">.0</td>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">8</sub></td>
+<td class="bt bl" align="right">56</td>
+<td class="bt" align="left">.4</td>
+<td class="bt bl" align="right">28</td>
+<td class="bt" align="left">.2</td>
+<td class="bt bl" align="right">16</td>
+<td class="bt br" align="left">.5</td>
+</tr>
+
+<tr>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">16</sub></td>
+<td class="bt bl" align="right">122</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">61</td>
+<td class="bt" align="left">.1</td>
+<td class="bt bl" align="right">27</td>
+<td class="bt" align="left">.8</td>
+<td class="bt bl" rowspan="3"><sup class="enum">1</sup>/<sub class="denom">2</sub></td>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">32</sub></td>
+<td class="bt bl" align="right">104</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">52</td>
+<td class="bt" align="left">.1</td>
+<td class="bt bl" align="right">30</td>
+<td class="bt br" align="left">.4</td>
+</tr>
+
+<tr>
+<td class="bt bl" rowspan="2"><sup class="enum">1</sup>/<sub class="denom">2</sub></td>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">64</sub></td>
+<td class="bt bl" align="right">237</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">118</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">53</td>
+<td class="bt" align="left">.8</td>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">16</sub></td>
+<td class="bt bl" align="right">75</td>
+<td class="bt" align="left">.2</td>
+<td class="bt bl" align="right">37</td>
+<td class="bt" align="left">.6</td>
+<td class="bt bl" align="right">22</td>
+<td class="bt br" align="left">.0</td>
+</tr>
+
+<tr>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">32</sub></td>
+<td class="bt bl" align="right">162</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">80</td>
+<td class="bt" align="left">.8</td>
+<td class="bt bl" align="right">36</td>
+<td class="bt" align="left">.7</td>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">8</sub></td>
+<td class="bt bl" align="right">43</td>
+<td class="bt" align="left">.1</td>
+<td class="bt bl" align="right">21</td>
+<td class="bt" align="left">.6</td>
+<td class="bt bl" align="right">12</td>
+<td class="bt br" align="left">.6</td>
+</tr>
+
+<tr>
+<td class="bl bt" colspan="8">Steel&mdash;Standard <sup class="enum">5</sup>/<sub class="denom">8</sub>-inch Tool</td>
+<td class="bt br bl" colspan="8">Cast Iron&mdash;Standard <sup class="enum">5</sup>/<sub class="denom">8</sub>-inch Tool</td>
+</tr>
+
+<tr>
+<td class="bl bt">Depth of Cut</td>
+<td class="bl bt">Feed</td>
+<td colspan="2" class="bl bt">Soft<br />Steel</td>
+<td colspan="2" class="bl bt">Medium<br />Steel</td>
+<td colspan="2" class="bl bt">Hard<br />Steel</td>
+<td class="bl bt">Depth of Cut</td>
+<td class="bl bt">Feed</td>
+<td colspan="2" class="bl bt">Soft<br />Cast Iron</td>
+<td colspan="2" class="bl bt">Medium<br />Cast Iron</td>
+<td colspan="2" class="bl bt br">Hard<br />Cast Iron</td>
+</tr>
+
+<tr>
+<td class="bt bl" rowspan="3"><sup class="enum">1</sup>/<sub class="denom">16</sub></td>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">64</sub></td>
+<td class="bt bl" align="right">548</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">274</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">125</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" rowspan="3"><sup class="enum">3</sup>/<sub class="denom">32</sub></td>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">32</sub></td>
+<td class="bt bl" align="right">160</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">80</td>
+<td class="bt" align="left">.0</td>
+<td class="bt bl" align="right">46</td>
+<td class="bt br" align="left">.6</td>
+</tr>
+
+<tr>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">32</sub></td>
+<td class="bt bl" align="right">358</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">179</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">81</td>
+<td class="bt" align="left">.6</td>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">16</sub></td>
+<td class="bt bl" align="right">110</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">55</td>
+<td class="bt" align="left">.0</td>
+<td class="bt bl" align="right">32</td>
+<td class="bt br" align="left">.2</td>
+</tr>
+
+<tr>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">16</sub></td>
+<td class="bt bl" align="right">235</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">117</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">53</td>
+<td class="bt" align="left">.3</td>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">8</sub></td>
+<td class="bt bl" align="right">75</td>
+<td class="bt" align="left">.4</td>
+<td class="bt bl" align="right">37</td>
+<td class="bt" align="left">.7</td>
+<td class="bt bl" align="right">22</td>
+<td class="bt br" align="left">.0</td>
+</tr>
+
+<tr>
+<td class="bt bl" rowspan="4"><sup class="enum">3</sup>/<sub class="denom">32</sub></td>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">64</sub></td>
+<td class="bt bl" align="right">467</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">234</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">106</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" rowspan="3"><sup class="enum">1</sup>/<sub class="denom">8</sub></td>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">32</sub></td>
+<td class="bt bl" align="right">148</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">74</td>
+<td class="bt" align="left">.0</td>
+<td class="bt bl" align="right">43</td>
+<td class="bt br" align="left">.3</td>
+</tr>
+
+<tr>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">32</sub></td>
+<td class="bt bl" align="right">306</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">153</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">69</td>
+<td class="bt" align="left">.5</td>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">16</sub></td>
+<td class="bt bl" align="right">104</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">51</td>
+<td class="bt" align="left">.8</td>
+<td class="bt bl" align="right">32</td>
+<td class="bt br" align="left">.0</td>
+</tr>
+
+<tr>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">16</sub></td>
+<td class="bt bl" align="right">200</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">100</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">45</td>
+<td class="bt" align="left">.5</td>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">8</sub></td>
+<td class="bt bl" align="right">69</td>
+<td class="bt" align="left">.6</td>
+<td class="bt bl" align="right">34</td>
+<td class="bt" align="left">.8</td>
+<td class="bt bl" align="right">20</td>
+<td class="bt br" align="left">.3</td>
+</tr>
+
+<tr>
+<td class="bt bl"><sup class="enum">3</sup>/<sub class="denom">32</sub></td>
+<td class="bt bl" align="right">156</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">78</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">35</td>
+<td class="bt" align="left">.5</td>
+<td class="bt bl" rowspan="4"><sup class="enum">3</sup>/<sub class="denom">16</sub></td>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">64</sub></td>
+<td class="bt bl" align="right">183</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">91</td>
+<td class="bt" align="left">.6</td>
+<td class="bt bl" align="right">68</td>
+<td class="bt br" align="left">.0</td>
+</tr>
+
+<tr>
+<td class="bt bl" rowspan="4"><sup class="enum">1</sup>/<sub class="denom">8</sub></td>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">64</sub></td>
+<td class="bt bl" align="right">417</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">209</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">94</td>
+<td class="bt" align="left">.8</td>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">32</sub></td>
+<td class="bt bl" align="right">135</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">67</td>
+<td class="bt" align="left">.5</td>
+<td class="bt bl" align="right">39</td>
+<td class="bt br" align="left">.4</td>
+</tr>
+
+<tr>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">32</sub></td>
+<td class="bt bl" align="right">273</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">136</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">62</td>
+<td class="bt" align="left">.0</td>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">16</sub></td>
+<td class="bt bl" align="right">94</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">47</td>
+<td class="bt" align="left">.0</td>
+<td class="bt bl" align="right">27</td>
+<td class="bt br" align="left">.4</td>
+</tr>
+
+<tr>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">16</sub></td>
+<td class="bt bl" align="right">179</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">89</td>
+<td class="bt" align="left">.3</td>
+<td class="bt bl" align="right">40</td>
+<td class="bt" align="left">.6</td>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">8</sub></td>
+<td class="bt bl" align="right">64</td>
+<td class="bt" align="left">.3</td>
+<td class="bt bl" align="right">32</td>
+<td class="bt" align="left">.2</td>
+<td class="bt bl" align="right">18</td>
+<td class="bt br" align="left">.8</td>
+</tr>
+
+<tr>
+<td class="bt bl"><sup class="enum">3</sup>/<sub class="denom">32</sub></td>
+<td class="bt bl" align="right">140</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">69</td>
+<td class="bt" align="left">.8</td>
+<td class="bt bl" align="right">31</td>
+<td class="bt" align="left">.7</td>
+<td class="bt bl" rowspan="4"><sup class="enum">1</sup>/<sub class="denom">4</sub></td>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">64</sub></td>
+<td class="bt bl" align="right">171</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">85</td>
+<td class="bt" align="left">.7</td>
+<td class="bt bl" align="right">50</td>
+<td class="bt br" align="left">.1</td>
+</tr>
+
+<tr>
+<td class="bt bl" rowspan="3"><sup class="enum">3</sup>/<sub class="denom">16</sub></td>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">64</sub></td>
+<td class="bt bl" align="right">362</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">181</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">82</td>
+<td class="bt" align="left">.2</td>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">32</sub></td>
+<td class="bt bl" align="right">126</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">63</td>
+<td class="bt" align="left">.2</td>
+<td class="bt bl" align="right">36</td>
+<td class="bt br" align="left">.9</td>
+</tr>
+
+<tr>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">32</sub></td>
+<td class="bt bl" align="right">236</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">118</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">53</td>
+<td class="bt" align="left">.8</td>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">16</sub></td>
+<td class="bt bl" align="right">87</td>
+<td class="bt" align="left">.8</td>
+<td class="bt bl" align="right">43</td>
+<td class="bt" align="left">.9</td>
+<td class="bt bl" align="right">25</td>
+<td class="bt br" align="left">.6</td>
+</tr>
+
+<tr>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">16</sub></td>
+<td class="bt bl" align="right">155</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">77</td>
+<td class="bt" align="left">.4</td>
+<td class="bt bl" align="right">35</td>
+<td class="bt" align="left">.2</td>
+<td class="bt bl"><sup class="enum">3</sup>/<sub class="denom">32</sub></td>
+<td class="bt bl" align="right">70</td>
+<td class="bt" align="left">.4</td>
+<td class="bt bl" align="right">35</td>
+<td class="bt" align="left">.2</td>
+<td class="bt bl" align="right">20</td>
+<td class="bt br" align="left">.6</td>
+</tr>
+
+<tr>
+<td class="bt bl" rowspan="2"><sup class="enum">1</sup>/<sub class="denom">4</sub></td>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">64</sub></td>
+<td class="bt bl" align="right">328</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">164</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">74</td>
+<td class="bt" align="left">.5</td>
+<td class="bt bl bb" rowspan="3"><sup class="enum">3</sup>/<sub class="denom">8</sub></td>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">64</sub></td>
+<td class="bt bl" align="right">156</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">77</td>
+<td class="bt" align="left">.8</td>
+<td class="bt bl" align="right">45</td>
+<td class="bt br" align="left">.4</td>
+</tr>
+
+<tr>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">32</sub></td>
+<td class="bt bl" align="right">215</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">107</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">48</td>
+<td class="bt" align="left">.8</td>
+<td class="bt bl"><sup class="enum">1</sup>/<sub class="denom">32</sub></td>
+<td class="bt bl" align="right">116</td>
+<td class="bt" align="left">&nbsp;</td>
+<td class="bt bl" align="right">57</td>
+<td class="bt" align="left">.8</td>
+<td class="bt bl" align="right">33</td>
+<td class="bt br" align="left">.8</td>
+</tr>
+
+<tr>
+<td class="bb bt bl"><sup class="enum">3</sup>/<sub class="denom">8</sub></td>
+<td class="bb bt bl"><sup class="enum">1</sup>/<sub class="denom">64</sub></td>
+<td class="bb bt bl" align="right">286</td>
+<td class="bb bt" align="left">&nbsp;</td>
+<td class="bb bt bl" align="right">143</td>
+<td class="bb bt" align="left">&nbsp;</td>
+<td class="bb bt bl" align="right">65</td>
+<td class="bb bt" align="left">.0</td>
+<td class="bb bt bl"><sup class="enum">1</sup>/<sub class="denom">16</sub></td>
+<td class="bb bt bl" align="right">79</td>
+<td class="bb bt" align="left">.7</td>
+<td class="bb bt bl" align="right">39</td>
+<td class="bb bt" align="left">.9</td>
+<td class="bb bt bl" align="right">23</td>
+<td class="bb bt br" align="left">.3</td>
+</tr>
+
+</table>
+<p>&nbsp;</p>
+
+<hr class="l10" />
+<div class="footnote"><a name="Fn_1" id="Fn_1"></a><span class="label"><a href="#Fnanchor_1">[1]</a></span>Cutting speeds for tools of
+a good grade of high-speed steel, properly ground and heat-treated.&mdash;From <span class="smcap">Machinery's Handbook</span>.</div>
+<hr class="l10" />
+
+<p><span class="pagenum"><a name="Pg_72" id="Pg_72">[72]</a></span>
+<a name="Secnum_2_11" id="Secnum_2_11"></a><b>Average Cutting Speeds for Turning.</b>&mdash;The cutting speed is
+governed principally by the hardness of the metal to be turned;
+the kind of steel of which the turning tool is made; the shape
+of the tool and its heat-treatment; the feed and depth of cut;
+whether or not a cooling lubricant is used on the tool; the
+power of the lathe and also its construction; hence it is impossible
+to give any definite rule for determining either the
+speed, feed, or depth of cut, because these must be varied to
+suit existing conditions. A general idea of the speeds used in
+ordinary machine shop practice may be obtained from the following
+figures:</p>
+
+<p>Ordinary machine steel is generally turned at a speed varying
+between 45 and 65 feet per minute. For ordinary gray cast
+iron, the speed usually varies from 40 to 50 feet per minute;
+for annealed tool steel, from 25 to 35 feet per minute; for soft
+yellow brass, from 150 to 200 feet per minute; for hard bronze,
+from 35 to 80 feet per minute, the speed depending upon the
+composition of the alloy. While these speeds correspond
+closely to general practice, they can be exceeded for many
+machining operations.</p>
+
+<p>The most economical speeds for a given feed and depth of
+cut, as determined by the experiments conducted by Mr. F. W.
+Taylor, are given in the table, &#8220;<a href="#Fnanchor_1">Cutting Speeds and Feeds for
+Turning Tools</a>.&#8221; The speeds given in this table represent results
+obtained with tools made of a good grade of high-speed
+steel properly heat-treated and correctly ground. It will be
+noted that the cutting speed is much slower for cast iron than
+for steel. Cast iron is cut with less pressure or resistance than
+soft steel, but the slower speed required for cast iron is probably
+due to the fact that the pressure of the chip is concentrated
+closer to the cutting edge, combined with the fact that cast
+iron wears the tool faster than steel. The speeds given are
+higher than those ordinarily used, and, in many cases, a slower
+rate would be necessary to prevent chattering or because of
+some other limiting condition.</p>
+
+<a name="Secnum_2_12" id="Secnum_2_12"></a><p><b>Factors which limit the Cutting Speed.</b>&mdash;It is the durability
+of the turning tool or the length of time that it will turn effectively<span class="pagenum"><a name="Pg_73" id="Pg_73">[73]</a></span>
+without grinding, that limits the cutting speed; and the
+hardness of the metal being turned combined with the quality
+of the tool are the two factors which largely govern the time
+that a tool can be used before grinding is necessary. The cutting
+speed for very soft steel or cast iron can be three or four
+times faster than the speed for hard steel or hard castings, but
+whether the material is hard or soft, the kind and quality of
+the tool used must also be considered, as the speed for a tool
+made of ordinary carbon steel will have to be much slower than
+for a tool made of modern &#8220;high-speed&#8221; steel.</p>
+
+<p>When the cutting speed is too high, even though high-speed
+steel is used, the point of the tool is softened to such an extent
+by the heat resulting from the pressure and friction of the chip,
+that the cutting edge is ruined in too short a time. On the
+other hand, when the speed is too slow, the heat generated is
+so slight as to have little effect and the tool point is dulled by
+being slowly worn or ground away by the action of the chip.
+While a tool operating at such a low speed can be used a comparatively
+long time without re-sharpening, this advantage is
+more than offset by the fact that too much time is required for
+removing a given amount of metal when the work is revolving
+so slowly.</p>
+
+<p>Generally speaking, the speed should be such that a fair
+amount of work can be done before the tool requires re-grinding.
+Evidently, it would not pay to grind a tool every few
+minutes in order to maintain a high cutting speed; neither
+would it be economical to use a very slow speed and waste considerable
+time in turning, just to save the few minutes required
+for grinding. For example, if a number of roughing cuts had
+to be taken over a heavy rod or shaft, time might be saved by
+running at such a speed that the tool would have to be sharpened
+(or be replaced by a tool previously sharpened) when it had
+traversed half-way across the work; that is, the time required
+for sharpening or changing the tool would be short as compared
+with the gain effected by the higher work speed. On the
+other hand, it might be more economical to run a little slower
+and take a continuous cut across the work with one tool.</p>
+
+<p><span class="pagenum"><a name="Pg_74" id="Pg_74">[74]</a></span>The experiments of Mr. Taylor led to the conclusion that, as
+a rule, it is not economical to use roughing tools at a speed so
+slow as to cause them to last more than 1<sup class="enum">1</sup>/<sub class="denom">2</sub> hour without being
+re-ground; hence the speeds given in the <a href="#Fnanchor_1">table</a> previously referred
+to are based upon this length of time between grindings.
+Sometimes the work speed cannot be as high as the tool will
+permit, because of the chattering that often results when the
+lathe is old and not massive enough to absorb the vibrations, or
+when there is unnecessary play in the working parts. The shape
+of the tool used also affects the work speed, and as there are so
+many things to be considered, the proper cutting speed is best
+determined by experiment.</p>
+
+<a name="Secnum_2_13" id="Secnum_2_13"></a><p><b>Rules for Calculating Cutting Speeds.</b>&mdash;The number of revolutions
+required to give any desired cutting speed can be found
+by multiplying the cutting speed, in feet per minute, by 12 and
+dividing the product by the circumference of the work in inches.
+Expressing this as a formula we have</p>
+
+<div class="formula center">
+<table border="0" cellpadding="0" cellspacing="0" summary="Formula 74_1">
+<tr><td>&nbsp;</td><td>&nbsp;</td><td><i>C</i>&nbsp;&times;&nbsp;12</td></tr>
+<tr><td><i>&nbsp;R&nbsp;</i></td><td>&nbsp;=&nbsp;</td><td>&nbsp;&mdash;&mdash;&mdash;&nbsp;</td></tr>
+<tr><td>&nbsp;</td><td>&nbsp;</td><td><i>&pi;d</i></td></tr>
+</table>
+</div>
+
+<p>in which</p>
+
+<div class="formsymb">
+<table border="0" cellpadding="0" cellspacing="0" summary="Formula 74_1 symbols">
+<tr><td><i>&nbsp;R&nbsp;</i></td><td>&nbsp;=&nbsp;</td><td>&nbsp;revolutions per minute;</td></tr>
+<tr><td><i>&nbsp;C&nbsp;</i></td><td>&nbsp;=&nbsp;</td><td>&nbsp;the cutting speed in feet per minute;</td></tr>
+<tr><td><i>&nbsp;&pi;&nbsp;</i></td><td>&nbsp;=&nbsp;</td><td>&nbsp;3.1416;</td></tr>
+<tr><td><i>&nbsp;d&nbsp;</i></td><td>&nbsp;=&nbsp;</td><td>&nbsp;the diameter in inches.</td></tr>
+</table></div>
+
+<p>For example if a cutting speed of 60 feet per minute is wanted
+and the diameter of the work is 5 inches, the required speed
+would be found as follows:</p>
+
+<div class="formula center">
+<table border="0" cellpadding="0" cellspacing="0" summary="Formula 74_2">
+<tr><td>&nbsp;</td><td>&nbsp;</td><td>60&nbsp;&times;&nbsp;12</td><td>&nbsp;</td><td>&nbsp;</td></tr>
+<tr><td><i>&nbsp;R&nbsp;</i></td><td>&nbsp;=&nbsp;</td><td>&nbsp;&mdash;&mdash;&mdash;&mdash;&mdash;&nbsp;</td>
+<td>&nbsp;=&nbsp;</td><td>&nbsp;46 revolutions per minute.</td></tr>
+<tr><td>&nbsp;</td><td>&nbsp;</td><td>3.1416&nbsp;&times;&nbsp;5</td><td>&nbsp;</td><td>&nbsp;</td></tr>
+</table></div>
+
+<p>If the diameter is simply multiplied by 3 and the fractional
+part is omitted, the calculation can easily be made, and the result
+will be close enough for practical purposes. In case the cutting
+speed, for a given number of revolutions and diameter, is wanted,
+the following formula can be used:</p>
+
+<div class="formula center">
+<table border="0" cellpadding="0" cellspacing="0" summary="Formula 74_3">
+<tr><td>&nbsp;</td><td>&nbsp;</td><td>&nbsp;<i>R&pi;d</i>&nbsp;</td></tr>
+<tr><td>&nbsp;<i>C</i>&nbsp;</td><td>&nbsp;=&nbsp;</td><td>&nbsp;&mdash;&mdash;&nbsp;</td></tr>
+<tr><td>&nbsp;</td><td>&nbsp;</td><td>12</td></tr>
+</table></div>
+
+<p><span class="pagenum"><a name="Pg_75" id="Pg_75">[75]</a></span>Machinists who operate lathes do not know, ordinarily, what
+cutting speeds, in feet per minute, are used for different classes
+of work, but are guided entirely by past experience.</p>
+
+<a name="Secnum_2_14" id="Secnum_2_14"></a><p><b>Feed of Tool and Depth of Cut.</b>&mdash;The amount of feed and
+depth of cut also vary like the cutting speed, for different conditions.
+When turning soft machine steel the feed under
+ordinary conditions would vary between <sup class="enum">1</sup>/<sub
+class="denom">32</sub> and <sup class="enum">1</sup>/<sub class="denom">16</sub> inch per
+revolution. For turning soft cast iron the feed might be increased
+to from <sup class="enum">1</sup>/<sub class="denom">16</sub> to <sup class="enum">1</sup>/<sub
+class="denom">8</sub> inch per revolution. These feeds
+apply to fairly deep roughing cuts. Coarser feeds might be
+used in many cases especially when turning large rigid parts in
+a powerful lathe. The depth of a roughing cut in machine
+steel might vary from <sup class="enum">1</sup>/<sub class="denom">8</sub> to <sup class="enum">3</sup>/<sub
+class="denom">8</sub> inch, and in cast iron from <sup class="enum">3</sup>/<sub class="denom">16</sub> to
+<sup class="enum">1</sup>/<sub class="denom">2</sub> inch. These figures are intended simply to give the reader a
+general idea of feeds and cuts that are feasible under average
+conditions.</p>
+
+<p>Ordinarily coarser feeds and a greater depth of cut can be
+used for cast iron than for soft steel, because cast iron offers
+less resistance to turning, but in any case, with a given depth of
+cut, metal can be removed more quickly by using a coarse feed
+and the necessary slower speed, than by using a fine feed and
+the higher speed which is possible when the feed is reduced.
+When the turning operation is simply to remove metal, the feed
+should be coarse, and the cut as deep as practicable. Sometimes
+the cut must be comparatively light, either because the
+work is too fragile and springy to withstand the strain of a
+heavy cut, or the lathe has not sufficient pulling power. The
+difficulty with light slender work is that a heavy cut may cause
+the part being turned to bend under the strain, thus causing the
+tool to gouge in, which would probably result in spoiling the
+work. Steadyrests can often be used to prevent flexible parts
+from springing, as previously explained, but there are many
+kinds of light work to which the steadyrest cannot be applied
+to advantage.</p>
+
+<a name="Fig_2_15" id="Fig_2_15"></a>
+<div class="figcenter"><img src="images/084sm.jpg" alt="Roughing Cut&mdash;Light Finishing Cut and Coarse Feed" />
+<p class="caption750">Fig. 15. Roughing Cut&mdash;Light Finishing Cut and Coarse Feed</p>
+</div>
+
+<p>The amount of feed to use for a finishing cut might, properly, be
+either fine or coarse. Ordinarily, fine feeds are used for finishing
+steel, especially if the work is at all flexible, whereas finishing<span class="pagenum"><a name="Pg_76" id="Pg_76">[76]</a></span>
+cuts in cast iron are often accompanied by a coarse feed.
+<a href="#Fig_2_15">Fig. 15</a> illustrates the feeds that are often used when turning
+cast iron. The view to the left shows a deep roughing cut and
+the one to the right, a finishing cut. By using a broad flat
+cutting edge set parallel to the tool's travel, and a coarse feed
+for finishing, a smooth cut can be taken in a comparatively
+short time. Castings which are close to the finished size in
+the rough can often be finished to advantage by taking a single
+cut with a broad tool, provided the work is sufficiently rigid.
+It is not always practicable to use these broad tools and coarse
+feeds, as they sometimes cause chattering, and when used on
+steel, a broad tool tends to gouge or &#8220;dig in&#8221; unless the part
+being turned is rigid. Heavy steel parts, however, are sometimes
+finished in this way. The modern method of finishing
+many steel parts is to simply rough them out in a lathe to
+within, say, <sup class="enum">1</sup>/<sub class="denom">32</sub> inch of the required diameter and take the finishing
+cut in a cylindrical grinding machine.</p>
+
+<a name="Secnum_2_15" id="Secnum_2_15"></a><p><b>Effect of Lubricant on Cutting Speed.</b>&mdash;When turning iron
+or steel a higher cutting speed can be used, if a stream of soda
+water or other cooling lubricant falls upon the chip at the point
+where it is being removed by the tool. In fact, experiments
+have shown that the cutting speed, when using a large stream of
+cooling water and a high-speed steel tool, can be about 40 percent
+higher than when turning dry or without a cooling lubricant.<span class="pagenum"><a name="Pg_77" id="Pg_77">[77]</a></span>
+For ordinary carbon steel tools, the gain was about
+25 per cent. The most satisfactory results were obtained from
+a stream falling at a rather slow velocity but in large volume.
+The gain in cutting speed, by the use of soda water or other
+suitable fluids, was found to be practically the same for all
+qualities of steel from the softest to the hardest.</p>
+
+<p>Cast iron is usually turned dry or without a cutting lubricant.
+Experiments, however, made to determine the effect of applying
+a heavy stream of cooling water to a tool turning cast iron,
+showed the following results: Cutting speed without water, 47
+feet per minute; cutting speed with a heavy stream of water,
+nearly 54 feet per minute; increase in speed, 15 per cent. The
+dirt caused by mixing the fine cast-iron turnings with a cutting
+lubricant is an objectionable feature which, in the opinion of
+many, more than offsets the increase in cutting speed that
+might be obtained.</p>
+
+<p>Turret lathes and automatic turning machines are equipped
+with a pump and piping for supplying cooling lubricant to the
+tools in a continuous stream. Engine lathes used for general
+work, however, are rarely provided with such equipment and
+a lubricant, when used, is often supplied by a can mounted at
+the rear of the carriage, having a spout which extends above the
+tool. Owing to the inconvenience in using a lubricant on an
+engine lathe, steel, as well as cast iron, is often turned dry
+especially when the work is small and the cuts light and comparatively
+short.</p>
+
+<a name="Secnum_2_16" id="Secnum_2_16"></a><p><b>Lubricants Used for Turning.</b>&mdash;A good grade of lard oil is
+an excellent lubricant for use when turning steel or wrought
+iron and it is extensively used on automatic screw machines,
+especially those which operate on comparatively small work.
+For some classes of work, especially when high-cutting speeds
+are used, lard oil is not as satisfactory as soda water or some of
+the commercial lubricants, because the oil is more sluggish and
+does not penetrate to the cutting point with sufficient rapidity.
+Many lubricants which are cheaper than oil are extensively
+used on &#8220;automatics&#8221; for general machining operations. These
+usually consist of a mixture of sal-soda (carbonate of soda) and<span class="pagenum"><a name="Pg_78" id="Pg_78">[78]</a></span>
+water, to which is added some ingredient such as lard oil or soft
+soap to thicken or give body to the lubricant.</p>
+
+<p>A cheap lubricant for turning, milling, etc., and one that has
+been extensively used, is made in the following proportions:
+1 pound of sal-soda, 1 quart of lard oil, 1 quart of soft soap,
+and enough water to make 10 or 12 gallons. This mixture is
+boiled for one-half hour, preferably by passing a steam coil
+through it. If the solution should have an objectionable odor,
+this can be eliminated by adding 2 pounds of unslaked lime. The
+soap and soda in this solution improve the lubricating quality
+and also prevent the surfaces from rusting. For turning and
+threading operations, plain milling, deep-hole drilling, etc., a
+mixture of equal parts of lard oil and paraffin oil will be found
+very satisfactory, the paraffin being added to lessen the expense.</p>
+
+<p>Brass or bronze is usually machined dry, although lard oil is
+sometimes used for automatic screw machine work. Babbitt
+metal is also worked dry, ordinarily, although kerosene or
+turpentine is sometimes used when boring or reaming. If
+babbitt is bored dry, balls of metal tend to form on the tool
+point and score the work. Milk is generally considered the best
+lubricant for machining copper. A mixture of lard oil and
+turpentine is also used for copper. For aluminum, the following
+lubricants can be used: Kerosene, a mixture of kerosene
+and gasoline, soap-water, or &#8220;aqualine&#8221; one part, water 20
+parts.</p>
+
+<a name="Secnum_2_17" id="Secnum_2_17"></a><p><b>Lard Oil as a Cutting Lubricant.</b>&mdash;After being used for a considerable
+time, lard oil seems to lose some of its good qualities
+as a cooling compound. There are several reasons for this:
+Some manufacturers use the same oil over and over again on
+different materials, such as brass, steel, etc. This is objectionable,
+for when lard oil has been used on brass it is practically
+impossible to get the fine dust separated from it in a centrifugal
+separator. When this impure oil is used on steel, especially
+where high-speed steels are employed, it does not give satisfactory
+results, owing to the fact that when the cutting tool
+becomes dull, the small brass particles &#8220;freeze&#8221; to the cutting
+tool and thus produce rough work. The best results are obtained<span class="pagenum"><a name="Pg_79" id="Pg_79">[79]</a></span>
+from lard oil by keeping it thin, and by using it on the
+same materials&mdash;that is, not transferring the oil from a machine
+in which brass is being cut to one where it would be employed
+on steel. If the oil is always used on the same class of material,
+it will not lose any of its good qualities.</p>
+
+<p>Prime lard oil is nearly colorless, having a pale yellow or
+greenish tinge. The solidifying point and other characteristics
+of the oil depend upon the temperature at which it was expressed,
+winter-pressed lard oil containing less solid constituents of the
+lard than that expressed in warm weather. The specific gravity
+should not exceed 0.916; it is sometimes increased by adulterants,
+such as cotton-seed and maize oils.</p>
+
+<hr class="c25" />
+<span class="pagenum"><a name="Pg_80" id="Pg_80">[80]</a></span>
+<h2><a name="Chapnum_3" id="Chapnum_3">CHAPTER III</a></h2>
+<h3>TAPER TURNING&mdash;SPECIAL OPERATIONS&mdash;FITTING</h3>
+<hr class="c05" />
+
+<p>It is often necessary, in connection with lathe work, to turn
+parts tapering instead of straight or cylindrical. If the work is
+mounted between the centers, one method of turning a taper is
+to set the tailstock center out of alignment with the headstock
+center. When both of these centers are in line, the movement
+of the tool is parallel to the axis of the work and, consequently, a
+cylindrical surface is produced; but if the tailstock <i>h<sub>1</sub></i> is set out
+of alignment, as shown in <a href="#Fig_3_1">Fig. 1</a>, the work will then be turned
+tapering as the tool is traversed from <i>a</i> to <i>b</i>, because the axis
+<i>x&mdash;x</i> is at an angle with the movement of the tool. Furthermore
+<span class="pagenum"><a name="Pg_81" id="Pg_81">[81]</a></span>
+the amount of taper or the difference between the diameters
+at the ends for a given length, will depend on how much
+center <i>h<sub>1</sub></i> is set over from the central position.</p>
+
+<a name="Fig_3_1" id="Fig_3_1"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/088sm.png" alt="Taper Turning by the Offset-center Method" /></div>
+<p class="caption750">Fig. 1. Taper Turning by the Offset-center Method</p>
+</div>
+
+<p>The amount of taper is usually given on drawings in inches
+per foot, or the difference in the diameter at points twelve
+inches apart. For example, the taper of the piece shown at <i>A</i>,
+<a href="#Fig_3_2">Fig. 2</a>, is 1 inch per foot, as the length of the tapering surface
+is just twelve inches and the difference between the diameters
+at the ends is 1 inch. The conical roller shown at <i>B</i> has a total
+length of 9 inches and a tapering surface 6 inches long, and in
+this case the taper per foot is also 1 inch, there being a difference
+of <sup class="enum">1</sup>/<sub class="denom">2</sub> inch in a length of 6 inches or 1 inch in twice that
+length. When the taper per foot is known, the amount that
+the tailstock center should be set over for turning that taper
+can easily be estimated, but it should be remembered that the
+setting obtained in this way is not absolutely correct, and is
+only intended to locate the center approximately. When a
+taper needs to be at all accurate, it is tested with a gage, or by
+other means, after taking a trial cut, as will be explained later,
+and the tailstock center is readjusted accordingly. There are
+also more accurate methods of setting the center, than by figuring
+<span class="pagenum"><a name="Pg_82" id="Pg_82">[82]</a></span>
+the amount of offset, but as the latter is often convenient
+this will be referred to first.</p>
+
+<a name="Fig_3_2" id="Fig_3_2"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/089sm.png" alt="Examples of Taper Work" /></div>
+<p class="caption750">Fig. 2. Examples of Taper Work</p>
+</div>
+
+<a name="Secnum_3_1" id="Secnum_3_1"></a><p><b>Setting Tailstock Center for Taper Turning.</b>&mdash;Suppose the
+tailstock center is to be set for turning part <i>C</i>, <a href="#Fig_3_2">Fig. 2</a>, to a taper
+of approximately 1 inch per foot. In this case the center would
+simply be moved toward the front of the machine <sup class="enum">1</sup>/<sub class="denom">2</sub> inch, or
+one-half the required taper per foot, because the total length
+of the work happens to be just 12 inches. This setting, however,
+would not be correct for all work requiring a taper of 1
+inch per foot, as the adjustment depends not only on the <i>amount</i>
+of the taper but on the <i>total length</i> of the piece.</p>
+
+<a name="Fig_3_3" id="Fig_3_3"></a>
+<div class="figcenter"><img src="images/090sm.jpg" alt="Detail View of Lathe Tailstock" />
+<p class="caption750">Fig. 3. Detail View of Lathe Tailstock</p>
+</div>
+
+<p>For example, the taper
+roller <i>B</i> has a taper of
+1 inch per foot, but the
+center, in this case, would
+be offset less than one-half
+the taper per foot,
+because the total length
+is only 9 inches. For
+lengths longer or shorter
+than twelve inches, the
+taper per inch should be
+found first; this is then
+multiplied by the <i>total</i> length of the work (not the length of the
+taper) which gives the taper for that length, and one-half this
+taper is the amount to set over the center. For example, the
+taper per inch of part <i>B</i> equals 1 inch divided by 12 = <sup class="enum">1</sup>/<sub class="denom">12</sub> inch.
+The total length of 9 inches multiplied by <sup class="enum">1</sup>/<sub class="denom">12</sub> inch =
+<sup class="enum">3</sup>/<sub class="denom">4</sub> inch, and
+<sup class="enum">1</sup>/<sub class="denom">2</sub> of <sup class="enum">3</sup>/<sub class="denom">4</sub> =
+<sup class="enum">3</sup>/<sub class="denom">8</sub>, which is the distance that the tailstock center should
+be offset. In this example if the taper per foot were not known,
+and only the diameters of the large and small ends of the tapered
+part were given, the difference between these diameters should
+first be found (2<sup class="enum">1</sup>/<sub class="denom">2</sub> - 2 = <sup class="enum">1</sup>/<sub class="denom">2</sub>);
+this difference should then be divided
+by the length of the taper (<sup class="enum">1</sup>/<sub class="denom">2</sub>&nbsp;&divide;&nbsp;6 = <sup class="enum">1</sup>/<sub
+class="denom">12</sub> inch) to obtain the taper
+per inch. The taper per inch times the <i>total</i> length represents
+what the taper would be if it extended throughout the entire
+length, and one-half of this equals the offset, which is <sup class="enum">3</sup>/<sub class="denom">8</sub> inch.</p>
+
+<a name="Fig_3_4" id="Fig_3_4"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/091sm.png" alt="Taper Plug and Gage" /></div>
+<p class="caption750">Fig. 4. Taper Plug and Gage</p>
+</div>
+
+<a name="Secnum_3_2" id="Secnum_3_2"></a><p><span class="pagenum"><a name="Pg_83" id="Pg_83">[83]</a></span>
+<b>Example of Taper Turning.</b>&mdash;As a practical example of taper
+turning let us assume that the piece A, <a href="#Fig_3_4">Fig. 4</a>, which has been
+centered and rough-turned as shown, is to be made into a taper
+plug, as indicated at <i>B</i>, to fit a ring gage as at <i>C</i>. If the required
+taper is 1<sup class="enum">1</sup>/<sub class="denom">2</sub> inch per foot and the total length is 8 inches,
+the tailstock center would be offset <sup class="enum">1</sup>/<sub class="denom">2</sub> inch.</p>
+
+<p>To adjust the tailstock, the nuts <i>N</i> (<a href="#Fig_3_3">Fig. 3</a>) are first loosened
+and then the upper part <i>A</i> is shifted sidewise by turning screw <i>S</i>.
+Scales are provided on some tailstocks for measuring the amount
+of this adjustment; if there is no scale, draw a line across the
+movable and stationary parts <i>A</i> and <i>B</i>, when the tailstock is
+set for straight turning. The movement of the upper line in
+relation to the lower will then show the offset, which can be
+measured with a scale.</p>
+
+<p>When the adjustment has been made, nuts <i>N</i> are tightened
+and the part to be turned, with a dog attached, is placed between
+the centers the same as for straight turning. The taper
+end is then reduced by turning, but before it is near the finished
+size, the work is removed and the taper tested by inserting it
+in the gage. If it is much out, this can be felt, as the end that
+is too small can be shaken in the hole. Suppose the plug did
+not taper enough and only the small end came into contact with
+the gage, as shown somewhat exaggerated at <i>D</i>; in that case<span class="pagenum"><a name="Pg_84" id="Pg_84">[84]</a></span>
+the center would be shifted a little more towards the front,
+whereas if the taper were too steep, the adjustment would, of
+course, be in the opposite direction. A light cut would then be
+taken, to be followed by another test. If the plug should fit
+the gage so well that there was no perceptible shake, it could be
+tested more closely as follows: Draw three or four chalk lines
+along the tapering surface, place the work in the gage and turn
+it a few times. The chalk marks will then show whether the
+taper of the plug corresponds to that of the gage; for example,
+if the taper is too great, the marks will be rubbed out on the
+large end, but if the taper is correct, the lines throughout their
+length will be partially erased.</p>
+
+<p>Another and more accurate method of testing tapers is to
+apply a thin coat of Prussian-blue to one-half of the tapering
+surface, in a lengthwise direction. The work is then inserted in
+the hole or gage and turned to mark the bearing. If the taper
+is correct, the bearing marks will be evenly distributed, whereas
+if the taper is incorrect, they will appear at one end. Tapering
+pieces that have to be driven tightly into a hole, such as a piston-rod,
+can be tested by the location of the bearing marks produced
+by actual contact.</p>
+
+<p>After the taper is found to be correct, the plug is reduced in
+size until it just enters the gage as at <i>C</i>. The final cut should
+leave it slightly above the required size, so that a smooth surface<span class="pagenum"><a name="Pg_85" id="Pg_85">[85]</a></span>
+can be obtained by filing. It should be mentioned that on
+work of this kind, especially if great accuracy is required, the
+final finish is often obtained by grinding in a regular grinding
+machine, instead of by filing. When this method is employed,
+a lathe is used merely to rough-turn the part close to size.</p>
+
+<a name="Fig_3_5" id="Fig_3_5"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/092sm.png" alt="Setting Work for Taper Turning by use of Caliper Gage" /></div>
+<p class="caption750">Fig. 5. Setting Work for Taper Turning by use of Caliper Gage</p>
+</div>
+
+<p>When the amount that the tailstock center should be offset
+is determined by calculating, as in the foregoing example, it is
+usually necessary to make slight changes afterward, and the
+work should be tested before it is too near the finished size so
+that in case one or more trial cuts are necessary, there will be
+material enough to permit this. When there are a number of
+tapered pieces to be turned to the same taper, the adjustment
+of the tailstock center will have to be changed unless the total
+length of each piece and the depth of the center holes are the
+same in each case.</p>
+
+<a name="Fig_3_6" id="Fig_3_6"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/093sm.png" alt="Side View showing Relative Positions of Gage and Work" /></div>
+<p class="caption750">Fig. 6. Side View showing Relative Positions of Gage and Work</p>
+</div>
+
+<a name="Secnum_3_3" id="Secnum_3_3"></a><p><b>Setting the Tailstock Center with a Caliper Tool.</b>&mdash;Another
+method of setting the tailstock center for taper turning is illustrated
+in <a href="#Fig_3_5">Fig. 5</a>. The end of an engine piston-rod is to be made
+tapering as at A and to dimensions <i>a</i>, <i>b</i>, <i>c</i> and <i>d</i>. It is first
+turned with the centers in line as at <i>B</i>. The end <i>d</i> is reduced to
+diameter <i>b</i> up to the beginning of the taper and it is then turned
+to diameter <i>a</i> as far as the taper part <i>c</i> extends. The tailstock
+center is next set over by guess and a caliper tool is clamped in
+the toolpost. This tool, a side view of which is shown in <a href="#Fig_3_6">Fig. 6</a>,
+<span class="pagenum"><a name="Pg_86" id="Pg_86">[86]</a></span>
+has a pointer <i>p</i> that is free to swing about pivot <i>r</i>, which should
+be set to about the same height as the center of the work. The
+tailstock center is adjusted until this pointer just touches the
+work when in the positions shown by the full and dotted lines
+at <i>C</i>, <a href="#Fig_3_5">Fig. 5</a>; that is, until the pointer makes contact at the beginning
+and end of the taper part. The travel of the carriage
+will then be parallel to a line <i>x&mdash;x</i>, representing the taper; consequently,
+if a tool is started at the small end, as shown by the
+dotted lines at <i>D</i>, with the nose just grazing the work, it will
+also just graze it when fed to the extreme left as shown. Of
+course, if the taper were at all steep, more than one cut would
+be taken.</p>
+
+<a name="Fig_3_7" id="Fig_3_7"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/094sm.png" alt="Obtaining Tailstock Center Adjustment by use of Square" /></div>
+<p class="caption750">Fig. 7. Obtaining Tailstock Center Adjustment by use of Square</p>
+</div>
+
+<p>If these various operations are carefully performed, a fairly
+accurate taper can be produced. The straight end <i>d</i> is reduced
+to size after the tail-center is set back to the central
+position. Some mechanics turn notches or grooves at the beginning
+and end of the tapering part, having diameters equal to
+the largest and smallest part of the taper; the work is then set
+by these grooves with a caliper tool. The advantage of the<span class="pagenum"><a name="Pg_87" id="Pg_87">[87]</a></span>
+first method is that most of the metal is removed while the
+centers are in alignment.</p>
+
+<a name="Secnum_3_4" id="Secnum_3_4"></a><p><b>Setting the Tailstock Center with a Square.</b>&mdash;Still another
+method of adjusting the tailstock for taper turning, which is
+very simple and eliminates all figuring, is as follows: The part
+to be made tapering is first turned cylindrical or straight for
+3 or 4 inches of its length, after the ends have been properly
+centered and faced square. The work is then removed and the
+tailstock is shifted along the bed until the distance <i>a&mdash;b</i> between
+the extreme points of the centers is exactly 1 foot. The center
+is next offset a distance <i>b&mdash;c</i> equal to one-half the required
+taper per foot, after which a parallel strip <i>D</i>, having true sides,
+is clamped in the toolpost. Part <i>D</i> is then set at right angles
+to a line passing from one center point to the other. This can
+be done conveniently by holding a 1-foot square (preferably with
+a sliding head) against one side of <i>D</i> and adjusting the latter in
+the toolpost until edge <i>E</i> of the square blade is exactly in line
+with both center points. After part <i>D</i> is set, it should be
+clamped carefully to prevent changing the position. The angle
+between the side of <i>D</i> and an imaginary line which is perpendicular
+to axis <i>a&mdash;b</i> is now equal to one-half the angle of the
+required taper.</p>
+
+<a name="Fig_3_8" id="Fig_3_8"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/095sm.png" alt="Second Step in Adjusting Tailstock Center by use of Square" /></div>
+<p class="caption750">Fig. 8. Second Step in Adjusting Tailstock Center by use of Square</p>
+</div>
+
+<p><span class="pagenum"><a name="Pg_88" id="Pg_88">[88]</a></span>The axis of the part to be turned should be set parallel with
+line <i>E</i>, which can be done by setting the cylindrical surface
+which was previously finished, at right angles to the side of <i>D</i>.
+In order to do this the work is first placed between centers, the
+tailstock being shifted along the bed if necessary; the tail-center
+is then adjusted laterally until the finished cylindrical
+surface is square with the side of <i>D</i>. A small try-square can be
+used for testing
+the position of the
+work, as indicated
+in <a href="#Fig_3_8">Fig. 8</a>. If the
+length of the work
+is less than 1 foot,
+it will be necessary
+to move the
+center toward the
+rear of the machine,
+and if the
+length is greater
+than 1 foot, the
+adjustment is, of
+course, in the opposite
+direction.</p>
+
+<a name="Secnum_3_5" id="Secnum_3_5"></a><p><b>The Taper Attachment.</b>&mdash;Turning
+tapers by
+setting over the
+tailstock center has some objectionable features. When the
+lathe centers are not in alignment, as when set for taper turning,
+they bear unevenly in the work centers because the axis
+of the work is at an angle with them; this causes the work
+centers to wear unevenly and results in inaccuracy. Furthermore,
+the adjustment of the tailstock center must be changed
+when turning duplicate tapers, unless the length of each piece
+and the depth of the center holes are the same. To overcome
+these objections, many modern lathes are equipped with a
+special device for turning tapers, known as a taper attachment,<span class="pagenum"><a name="Pg_89" id="Pg_89">[89]</a></span>
+which permits the lathe centers to be kept in alignment, as
+for cylindrical turning, and enables more accurate work to be
+done.</p>
+
+<a name="Fig_3_9" id="Fig_3_9"></a>
+<div class="figcenter"><img src="images/096sm.jpg" alt="A Lathe Taper Attachment" />
+<p class="caption750">Fig. 9. A Lathe Taper Attachment</p>
+</div>
+
+<p>Taper attachments, like lathes, vary some in their construction,
+but all operate on the same principle. An improved form
+of taper attachment is illustrated in <a href="#Fig_3_9">Figs. 9</a> and <a href="#Fig_3_10">10</a>. <a href="#Fig_3_9">Fig. 9</a>
+shows a plan view of a lathe carriage with an attachment
+fitted to it, and <a href="#Fig_3_10">Fig. 10</a> a sectional view. This attachment has
+an arm <i>A</i> on which is mounted a slide <i>S</i> that can be turned
+about a central pivot by adjusting screw <i>D</i>. The arm <i>A</i> is
+supported by, and is free to slide on, a bracket <i>B</i> (see also sectional
+view) that is fastened to the carriage, and on one end of
+the arm there is a clamp <i>C</i> that is attached to the lathe bed
+when turning tapers. On the slide <i>S</i> there is a shoe <i>F</i> that is
+connected to bar <i>E</i> which passes beneath the toolslide. The
+rear end of the cross-feed screw is connected to this bar, and
+the latter is clamped to the toolslide when the attachment is
+in use.</p>
+
+<a name="Fig_3_10" id="Fig_3_10"></a>
+<div class="figcenter"><img src="images/097sm.jpg" alt="Sectional View of Taper Attachment" />
+<p class="caption750">Fig. 10. Sectional View of Taper Attachment</p>
+</div>
+
+<p>When a taper is to be turned, the carriage is moved opposite
+the taper part and clamp <i>C</i> is fastened to the bed; this holds
+arm <i>A</i> and slide <i>S</i> stationary so that the carriage, with bracket
+<i>B</i> and shoe <i>F</i>, can be moved with relation to the slide. If this
+slide <i>S</i> is set at an angle, as shown, the shoe as it moves along
+causes the toolslide and tool to move in or out, but if the slide
+is set parallel to the carriage travel, the toolslide remains
+stationary. Now if the tool, as it feeds lengthwise of the work,
+is also gradually moved crosswise, it will turn a taper, and as<span class="pagenum"><a name="Pg_90" id="Pg_90">[90]</a></span>
+this crosswise movement is caused by the angularity of slide <i>S</i>,
+different tapers are obtained by setting the slide to different
+positions.</p>
+
+<p>By means of a graduated scale <i>G</i> at the end of slide <i>S</i>, the
+taper that will be obtained for any angular position of the slide
+is shown. On some attachments there are two sets of graduations,
+one giving the taper in inches per foot and the other in
+degrees. While tapers are ordinarily given in inches per foot
+on drawings, sometimes the taper is given in degrees instead.
+The attachment is set for turning tapers by adjusting slide <i>S</i>
+until pointer <i>p</i> is opposite the division or fractional part of a
+division representing the taper. The whole divisions on the
+scale represent taper in inches per foot, and by means of the
+sub-divisions, the slide can be set for turning fractional parts of
+an inch per foot. When slide <i>S</i> is properly set, it is clamped to
+arm <i>A</i> by the nuts <i>N</i>. Bar <i>E</i> is also clamped to the toolslide by
+bolt <i>H</i>, as previously stated. The attachment is disconnected
+for straight turning by simply loosening clamp <i>C</i> and the bolt <i>H</i>.</p>
+
+<a name="Fig_3_11" id="Fig_3_11"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/099sm.png" alt="Lathe with Taper Attachment arranged for Boring Taper Hole in Engine Piston" /></div>
+<p class="caption750">Fig. 11. Lathe with Taper Attachment arranged for Boring Taper Hole in Engine Piston</p>
+</div>
+
+<a name="Secnum_3_6" id="Secnum_3_6"></a><p><b>Application of Taper Attachment.</b>&mdash;Practical examples of
+lathe work, which illustrate the use of the taper attachment,
+are shown in <a href="#Fig_3_11">Figs. 11</a> and <a href="#Fig_3_12">12</a>. <a href="#Fig_3_11">Fig. 11</a> shows how a taper hole
+is bored in an engine piston-head, preparatory to reaming.
+The casting must be held either in a chuck <i>C</i> or on a faceplate
+if too large for the chuck. The side of the casting (after it has
+been &#8220;chucked&#8221;) should run true, and also the circumference,
+unless the cored hole for the rod is considerably out of center,
+in which case the work should be shifted to divide the error.
+The side of the casting for a short space around the hole is faced
+true with a round nose turning tool, after which the rough-cored
+hole is bored with an ordinary boring tool <i>t</i>, and then it is
+finished with a reamer to exactly the right size and taper.</p>
+
+<a name="Fig_3_12" id="Fig_3_12"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/101sm.png" alt="Taper Attachment Set for Turning Taper End of Piston-rod" /></div>
+<p class="caption750">Fig. 12. Taper Attachment Set for Turning Taper End of Piston-rod</p>
+</div>
+
+<p>This particular taper attachment is set to whatever taper is
+given on the drawing, by loosening nuts <i>N</i> and turning slide <i>S</i>
+until pointer <i>P</i> is opposite that division on the scale which represents
+the taper. The attachment is then ready, after bolt <i>H</i>
+and nuts <i>N</i> are tightened, and clamp <i>C</i> is fastened to the lathe
+bed. The hole is bored just as though it were straight, and<span class="pagenum"><a name="Pg_91" id="Pg_91">[91]</a></span>
+as the carriage advances, the tool is gradually moved inward by
+the attachment. If the lathe did not have a taper attachment,
+the taper hole could be bored by using the compound rest.</p>
+
+<p>The hole should be bored slightly less than the finish size to
+allow for reaming. When a reamer is used in the lathe, the
+outer end is supported by the tailstock center and should have
+a deep center-hole. The lathe is run very slowly for reaming
+and the reamer is fed into the work by feeding out the tailstock
+spindle. The reamer can be kept from revolving, either by attaching
+a heavy dog to the end or, if the end is squared, by the
+use of a wrench long enough to rest against the lathe carriage.
+A common method is to clamp a dog to the reamer shank, and
+then place the tool-rest beneath it to prevent rotation. If the<span class="pagenum"><a name="Pg_92" id="Pg_92">[92]</a></span>
+shank of a tool is clamped to the toolpost so that the dog rests
+against it, the reamer will be prevented from slipping off the
+center as it tends to do; with this arrangement, the carriage is
+gradually moved along as the tailstock spindle is fed outward.
+Some reamers are provided with stop-collars which come against
+the finished side of the casting when the hole has been reamed
+to size.</p>
+
+<p>After the reaming operation, the casting is removed from the
+chuck and a taper mandrel is driven into the hole for turning
+the outside of the piston. This mandrel should run true on its
+centers, as otherwise the outside surface of the piston will not
+be true with the bored hole. The driving dog, especially for
+large work of this kind, should be heavy and stiff, because light
+flexible clamps or dogs vibrate and frequently cause chattering.
+For such heavy work it is also preferable to drive at two points
+on opposite sides of the faceplate, but the driving pins should
+be carefully adjusted to secure a uniform bearing on both sides.</p>
+
+<p>The foregoing method of machining a piston is one that
+would ordinarily be followed when using a standard engine
+lathe, and it would, perhaps, be as economical as any if only one
+piston were being made; but where such work is done in large
+quantities, time could be saved by proceeding in a different
+way. For example, the boring and reaming operation could be
+performed much faster in a turret lathe, which is a type designed
+for just such work, but a turret lathe cannot be used for
+as great a variety of turning operations as a lathe of the regular
+type. There are also many other classes of work that can be
+turned more quickly in special types of machines, but as more
+or less time is required for arranging these special machines and
+often special tools have to be made, the ordinary lathe is frequently
+indispensable when only a few parts are needed; in
+addition, it is better adapted to some turning operations than
+any other machine.</p>
+
+<p><a href="#Fig_3_12">Fig. 12</a> illustrates how a taper attachment would be used for
+turning the taper fitting for the crosshead end of an engine
+piston-rod. Even though this taper corresponds to the taper of
+the hole in the piston, slide <i>S</i> would have to be reset to the corresponding
+<span class="pagenum"><a name="Pg_93" id="Pg_93">[93]</a></span>
+division on the opposite side of the central zero
+mark, because the taper of the hole decreased in size during the
+boring operation, whereas the rod is smallest at the beginning
+of the cut, so that the tool must move outward rather than inward
+as it advances. The taper part is turned practically the
+same as a cylindrical part; that is, the power feed is used and,
+as the carriage moves along the bed, the tool is gradually moved
+outward by the taper attachment.</p>
+
+<p>If the rod is being fitted directly to the crosshead (as is usually
+the case), the approximate size of the small end of the taper
+could be determined by calipering, the calipers being set to the
+size of the hole at a distance from the shoulder or face side of
+the crosshead, equal to the length of the taper fitting on the
+rod. If the crosshead were bored originally to fit a standard
+plug gage, the taper on the rod could be turned with reference
+to this gage, but, whatever the method, the taper should be
+tested before turning too close to the finished size. The test is
+made by removing the rod from the lathe and driving it tightly<span class="pagenum"><a name="Pg_94" id="Pg_94">[94]</a></span>
+into the crosshead. This shows how near the taper is to size,
+and when the rod is driven out, the bearing marks show whether
+the taper is exactly right or not. If the rod could be driven in
+until the shoulder is, say, <sup class="enum">1</sup>/<sub class="denom">8</sub> inch from the crosshead face, it
+would then be near enough to finish to size by filing. When
+filing, the lathe is run much faster than for turning, and most
+of the filing should be done where the bearing marks are the
+heaviest, to distribute the bearing throughout the length of the
+taper. Care should be taken when driving the rod in or out,
+to protect the center-holes in the ends by using a &#8220;soft&#8221; hammer
+or holding a piece of soft metal against the driving end.</p>
+
+<p>After the crosshead end is finished, the rod is reversed in the
+lathe for turning the piston end. The dog is clamped to the
+finished end, preferably over a piece of sheet copper to prevent
+the surface from being marred. When turning this end, either
+the piston reamer or the finished hole in the piston can be calipered.
+The size and angle of the taper are tested by driving the
+rod into the piston, and the end should be fitted so that by
+driving tightly, the shoulder will just come up against the
+finished face of the piston. When the taper is finished, the attachment
+is disengaged and a finishing cut is taken over the
+body of the rod, unless it is to be finished by grinding, which is
+the modern and most economical method.</p>
+
+<a name="Fig_3_13" id="Fig_3_13"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/102sm.png" alt="Tool Point should be in same Horizontal Plane as Axis of Work for Taper Turning" /></div>
+<p class="caption750">Fig. 13. Tool Point should be in same Horizontal Plane as Axis
+of Work for Taper Turning</p>
+</div>
+
+<a name="Secnum_3_7" id="Secnum_3_7"></a><p><b>Height of Tool when Turning Tapers.</b>&mdash;The cutting edge of
+the tool, when turning tapers, should be at the same height as
+the center or axis of the work, whether an attachment is used or<span class="pagenum"><a name="Pg_95" id="Pg_95">[95]</a></span>
+not. The importance of this will be apparent by referring to
+<a href="#Fig_3_13">Fig. 13</a>. To turn the taper shown, the tool <i>T</i> would be moved
+back a distance <i>x</i> (assuming that an attachment is used) while
+traversing the length <i>l</i>. As an illustration, if the tool could
+be placed as high as point <i>a</i>, the setting of the attachment remaining
+as before, the tool would again move back a distance <i>x</i>,
+while traversing a distance <i>l</i>, but the large end would be under-sized
+(as shown by the dotted line) if the diameters of the small
+ends were the same in each case. Of course, if the tool point
+were only slightly above or below the center, the resulting error
+would also be small. The tool can easily be set central by comparing
+the height of the cutting edge at the point of the tool with
+one of the lathe centers before placing the work in the lathe.</p>
+
+<a name="Fig_3_14" id="Fig_3_14"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/103sm.png" alt="Plan View showing Method of Turning a Taper with the Compound Rest" /></div>
+<p class="caption750">Fig. 14. Plan View showing Method of Turning a Taper with the Compound Rest</p>
+</div>
+
+<a name="Secnum_3_8" id="Secnum_3_8"></a><p><b>Taper Turning with the Compound Rest.</b>&mdash;The amount of
+taper that can be turned by setting over the tailstock center
+and by the taper attachment is limited, as the centers can
+only be offset a certain distance, and the slide <i>S</i> (<a href="#Fig_3_9">Fig. 9</a>) of the
+attachment cannot be swiveled beyond a certain position. For
+steep tapers, the compound rest <i>E</i> is swiveled to the required<span class="pagenum"><a name="Pg_96" id="Pg_96">[96]</a></span>
+angle and used as indicated in <a href="#Fig_3_14">Fig. 14</a>, which shows a plan view
+of a rest set for turning the valve <i>V</i>. This compound rest is an
+upper slide mounted on the lower or main cross-slide <i>D</i>, and it
+can be turned to any angular position so that the tool, which
+ordinarily is moved either lengthwise or crosswise of the bed,
+can be fed at an angle. The base of the compound rest is
+graduated in degrees and the position of these graduations
+shows to what angle the upper slide is set. Suppose the seat of
+valve <i>V</i> is to be turned to an angle of 45 degrees with the axis
+or center, as shown on the drawing at <i>A</i>, <a href="#Fig_3_15">Fig. 15</a>. To set the
+compound rest, nuts <i>n</i> on either side, which hold it rigidly to
+the lower slide, are first loosened and the slide is then turned
+until the 45-degree graduation is exactly opposite the zero line;
+the slide is then tightened in this position. A cut is next taken
+across the valve by operating handle <i>w</i> and feeding the tool in
+the direction of the arrow.</p>
+
+<a name="Fig_3_15" id="Fig_3_15"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/104sm.png" alt="Example of Taper Work Turned by using Compound Rest" /></div>
+<p class="caption750">Fig. 15. Example of Taper Work Turned by using Compound Rest</p>
+</div>
+
+<p>In this particular instance the compound rest is set to the
+same angle given on the drawing, but this is not always the
+case. If the draftsman had given the included angle of 90
+degrees, as shown at <i>B</i>, which would be another way of expressing
+it, the setting of the compound rest would, of course,
+be the same as before, or to 45 degrees, but the number of degrees
+marked on the drawing does not correspond with the angle
+to which the rest must be set. As another illustration, suppose
+the valve were to be turned to an angle of 30 degrees with the<span class="pagenum"><a name="Pg_97" id="Pg_97">[97]</a></span>
+axis as shown at <i>C</i>. In this case the compound rest would not
+be set to 30 degrees but to 60 degrees, because in order to turn
+the work to an angle of 30 degrees, the rest must be 60 degrees
+from its zero position, as shown. From this it will be seen
+that the number of degrees marked on the drawing does not
+necessarily correspond to the angle to which the rest must be
+set, as the graduations on the rest show the number of degrees
+that it is moved from its zero position, which corresponds to
+the line <i>a&mdash;b</i>. The angle to which the compound rest should be
+set can be found, when the drawing is marked as at <i>A</i> or <i>C</i>,
+by subtracting the angle given from 90 degrees. When the included
+angle is given, as at <i>B</i>, subtract one-half the included
+angle from 90 degrees to obtain the required setting. Of course,
+when using a compound rest, the lathe centers are set in line as
+for straight turning, as otherwise the angle will be incorrect.</p>
+
+<h4>Rules for Figuring Tapers</h4>
+
+<table class="left" align="center" width="60%" border="0" cellpadding="5" cellspacing="0" summary="Figuring Tapers">
+
+<tr>
+<td style="width: 33%" class="center bt br bb bl">Given</td>
+<td style="width: 33%" class="center bt bb br">To Find</td>
+<td style="width: 33%" class="center bt bb br">Rule</td>
+</tr>
+
+<tr valign="top">
+<td class="bl br">The taper per foot.</td>
+<td class="br">The taper per inch.</td>
+<td class="br">Divide the taper per foot by 12.</td>
+</tr>
+
+<tr valign="top">
+<td class="bl br">The taper per inch.</td>
+<td class="br">The taper per foot.</td>
+<td class="br">Multiply the taper per inch by 12.</td>
+</tr>
+
+<tr valign="top">
+<td class="bl br">End diameters and length of taper in inches.</td>
+<td class="br">The taper per foot.</td>
+<td class="br">Subtract small diameter from large; divide by length of taper, and multiply quotient by 12.</td>
+</tr>
+
+<tr valign="top">
+<td class="bl br">Large diameter and length of taper in inches and taper per foot.</td>
+<td class="br">Diameter at small end in inches.</td>
+<td class="br">Divide taper per foot by 12; multiply by length of taper, and subtract result from large diameter.</td>
+</tr>
+
+<tr valign="top">
+<td class="bl br">Small diameter and length of taper in inches, and taper per foot.</td>
+<td class="br">Diameter at large end in inches.</td>
+<td class="br">Divide taper per foot by 12; multiply by length of taper, and add result to small diameter.</td>
+</tr>
+
+<tr valign="top">
+<td class="bl br">The taper per foot and two diameters in inches.</td>
+<td class="br">Distance between two given diameters in inches.</td>
+<td class="br">Subtract small diameter from large; divide remainder by taper per foot, and multiply quotient by 12.</td>
+</tr>
+
+<tr valign="top">
+<td class="bl br bb">The taper per foot.</td>
+<td class="br bb">Amount of taper in a certain length given in inches.</td>
+<td class="br bb">Divide taper per foot by 12; multiply by given length of tapered part.</td>
+</tr>
+
+</table>
+<p>&nbsp;</p>
+
+<a name="Fig_3_16" id="Fig_3_16"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/106sm.png" alt="Disk Gage for Accurate Measurement of Angles and Tapers" /></div>
+<p class="caption750">Fig. 16. Disk Gage for Accurate Measurement of Angles and Tapers</p>
+</div>
+
+<a name="Secnum_3_9" id="Secnum_3_9"></a><p><b>Accurate Measurement of Angles and Tapers.</b>&mdash;When great
+accuracy is required in the measurement of angles, or when<span class="pagenum"><a name="Pg_98" id="Pg_98">[98]</a></span>
+originating tapers, disks are commonly used. The principle of
+the disk method of taper measurement is that if two disks of
+unequal diameters are placed either in contact or a certain distance
+apart, lines tangent to their peripheries will represent an
+angle or taper, the degree of which depends upon the diameters
+of the two disks and the distance between them. The gage
+shown in <a href="#Fig_3_16">Fig. 16</a>, which is a form commonly used for originating
+tapers or measuring angles accurately, is set by means of disks.
+This gage consists of two adjustable straight-edges <i>A</i> and <i>A<sub>1</sub></i>,
+which are in contact with disks <i>B</i> and <i>B<sub>1</sub></i>. The angle <i>&alpha;</i> or the
+taper between the straight-edges depends, of course, upon the
+diameters of the disks and the center distance <i>C</i>, and as these
+three dimensions can be measured accurately, it is possible to
+set the gage to a given angle within very close limits. Moreover,
+if a record of the three dimensions is kept, the exact setting
+of the gage can be reproduced quickly at any time. The following
+rules may be used for adjusting a gage of this type.</p>
+
+<a name="Secnum_3_10" id="Secnum_3_10"></a><p><b>To Find Center Distance for a Given Taper.</b>&mdash;When the
+taper, in inches per foot, is given, to determine center distance
+<i>C</i>. <i>Rule:</i> Divide the taper by 24 and find the angle corresponding
+to the quotient in a table of tangents; then find the
+sine corresponding to this angle and divide the difference between
+the disk diameters by twice the sine.</p>
+
+<p><span class="pagenum"><a name="Pg_99" id="Pg_99">[99]</a></span>
+<i>Example:</i> Gage is to be set to <sup class="enum">3</sup>/<sub class="denom">4</sub> inch per foot, and disk diameters
+are 1.25 and 1.5 inch, respectively. Find the required
+center distance for the disks.</p>
+
+<table class="formula" summary="Formula 99_1">
+<tr><td>&nbsp;0.75&nbsp;</td><td>&nbsp;</td><td>&nbsp;</td></tr>
+<tr><td>&nbsp;&mdash;&mdash;&nbsp;</td><td>&nbsp;=&nbsp;</td><td>&nbsp;0.03125.</td></tr>
+<tr><td>&nbsp;24&nbsp;</td><td>&nbsp;</td><td>&nbsp;</td></tr>
+</table>
+
+<p>The angle whose tangent is 0.03125 equals 1 degree 47.4 minutes;</p>
+
+<table class="formula" summary="Formula 99_22">
+<tr><td>&nbsp;sin 1&deg; 47.4' = 0.03123;  1.50 - 1.25 = 0.25 inch;</td></tr>
+</table>
+
+<p class="fsize60">&nbsp;</p>
+
+<table class="formula" summary="Formula 99_3">
+<tr><td>&nbsp;0.25&nbsp;</td><td>&nbsp;</td><td>&nbsp;</td></tr>
+<tr><td>&nbsp;&mdash;&mdash;&mdash;&mdash;&mdash;&nbsp;</td><td>&nbsp;=&nbsp;</td><td>&nbsp;4.002 inches = center distance <i>C</i>.
+</td></tr>
+<tr><td>&nbsp;2&nbsp;&times;&nbsp;0.03123&nbsp;</td><td>&nbsp;</td><td>&nbsp;</td></tr>
+</table>
+
+<a name="Secnum_3_11" id="Secnum_3_11"></a><p><b>To Find Center Distance for a Given Angle.</b>&mdash;When straight-edges
+must be set to a given angle <i>&alpha;</i>, to determine center distance
+<i>C</i> between disks of known diameter. <i>Rule:</i> Find the sine
+of half the angle <i>&alpha;</i> in a table of sines; divide the difference
+between the disk diameters by double this sine.</p>
+
+<p><i>Example:</i> If an angle <i>&alpha;</i> of 20 degrees is required, and the
+disks are 1 and 3 inches in diameter, respectively, find the required
+center distance <i>C</i>.</p>
+
+<table class="formula" summary="Formula 99_4">
+<tr><td>&nbsp;20&nbsp;</td><td>&nbsp;</td><td>&nbsp;</td></tr>
+<tr><td>&nbsp;&mdash;&mdash;&nbsp;</td><td>&nbsp;=&nbsp;</td><td>&nbsp;10 degrees; sin 10&deg; = 0.17365;</td></tr>
+<tr><td>&nbsp;2&nbsp;</td><td>&nbsp;</td><td>&nbsp;</td></tr>
+</table>
+
+<p class="fsize60">&nbsp;</p>
+
+<table class="formula" summary="Formula 99_5">
+<tr><td>&nbsp;3 - 1&nbsp;</td><td>&nbsp;</td><td>&nbsp;</td></tr>
+<tr><td>&nbsp;&mdash;&mdash;&mdash;&mdash;&mdash;&nbsp;</td><td>&nbsp;=&nbsp;</td><td>5.759 inches = center distance <i>C</i>.</td></tr>
+<tr><td>&nbsp;2&nbsp;&times;&nbsp;0.17365&nbsp;</td><td>&nbsp;</td><td>&nbsp;</td></tr>
+</table>
+
+<a name="Secnum_3_12" id="Secnum_3_12"></a><p><b>To Find Angle for Given Taper per Foot.</b>&mdash;When the taper
+in inches per foot is known, and the corresponding angle <i>&alpha;</i> is
+required. <i>Rule:</i> Divide the taper in inches per foot by 24;
+find the angle corresponding to the quotient, in a table of tangents,
+and double this angle.</p>
+
+<p><i>Example:</i> What angle <i>&alpha;</i> is equivalent to a taper of 1<sup class="enum">1</sup>/<sub class="denom">2</sub> inch
+per foot?</p>
+
+<table class="formula" summary="Formula 99_6">
+<tr><td>&nbsp;1.5&nbsp;</td><td>&nbsp;</td><td>&nbsp;</td></tr>
+<tr><td>&nbsp;&mdash;&mdash;&nbsp;</td><td>&nbsp;=&nbsp;</td><td>&nbsp;0.0625.&nbsp;</td></tr>
+<tr><td>&nbsp;24&nbsp;</td><td>&nbsp;</td><td>&nbsp;</td></tr>
+</table>
+
+<p>The angle whose tangent is 0.0625 equals 3 degrees 35 minutes,
+nearly; then, 3 deg. 35 min.&nbsp;&times;&nbsp;2 = 7 deg. 10 min.</p>
+
+<a name="Secnum_3_13" id="Secnum_3_13"></a><p><b>To Find Angle for Given Disk Dimensions.</b>&mdash;When the
+diameters of the large and small disks and the center distance
+are given, to determine the angle <i>&alpha;</i>. <i>Rule:</i> Divide the difference
+<span class="pagenum"><a name="Pg_100" id="Pg_100">[100]</a></span>
+between the disk diameters by twice the center distance;
+find the angle corresponding to the quotient, in a table of sines,
+and double the angle.</p>
+
+<p><i>Example:</i> If the disk diameters are 1 and 1.5 inch, respectively,
+and the center distance is 5 inches, find the included
+angle <i>&alpha;</i>.</p>
+
+<table class="formula" summary="Formula 100_1">
+<tr><td>&nbsp;1.5 - 1&nbsp;</td><td>&nbsp;</td><td>&nbsp;</td></tr>
+<tr><td>&nbsp;&mdash;&mdash;&mdash;&nbsp;</td><td>&nbsp;=&nbsp;</td><td>&nbsp;0.05.</td></tr>
+<tr><td>&nbsp;2&nbsp;&times;&nbsp;5&nbsp;</td><td>&nbsp;</td><td>&nbsp;</td></tr>
+</table>
+
+<p>The angle whose sine is 0.05 equals 2 degrees 52 minutes; then,
+2 deg. 52 min.&nbsp;&times;&nbsp;2 = 5 deg. 44 min. = angle <i>&alpha;</i>.</p>
+
+<a name="Fig_3_17" id="Fig_3_17"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/108sm.png" alt="Setting Center Mark in Line with Axis of Lathe Spindle by use of Test Indicator" /></div>
+<p class="caption750">Fig. 17. Setting Center Mark in Line with Axis of Lathe Spindle
+by use of Test Indicator</p>
+</div>
+
+<a name="Secnum_3_14" id="Secnum_3_14"></a><p><b>Use of the Center Indicator.&mdash;</b>The center test indicator is
+used for setting a center-punch mark, the position of which
+corresponds with the center or axis of the hole to be bored, in
+alignment with the axis of the lathe spindle. To illustrate, if
+two holes are to be bored, say 5 inches apart, small punch
+marks having that center-to-center distance would be laid out
+as accurately as possible. One of these marks would then be
+set central with the lathe spindle by using a center test indicator
+as shown in <a href="#Fig_3_17">Fig. 17</a>. This indicator has a pointer <i>A</i> the
+end of which is conical and enters the punch mark. The pointer
+is held by shank <i>B</i> which is fastened in the toolpost. The
+joint <i>C</i> by means of which the pointer is held to the shank is
+universal; that is, it allows the pointer to move in any direction.
+Now when the part being tested is rotated by running the<span class="pagenum"><a name="Pg_101" id="Pg_101">[101]</a></span>
+lathe, if the center-punch mark is not in line with the axes of
+the lathe spindle, obviously the outer end of pointer <i>A</i> will
+vibrate, and as joint <i>C</i> is quite close to the inner end, a very
+slight error in the location of the center-punch mark will cause
+a perceptible movement of the outer end, as indicated by the
+dotted lines. When the work has been adjusted until the
+pointer remains practically stationary, the punch mark is central,
+and the hole is bored. The other center-punch mark is
+then set in the same way for boring the second hole. The
+accuracy of this method depends, of course, upon the location
+of the center-punch marks. A still more accurate way of
+setting parts for boring holes to a given center-to-center distance
+is described in the following:</p>
+
+<a name="Secnum_3_15" id="Secnum_3_15"></a><p><b>Locating Work by the Button Method.</b>&mdash;Among the different
+methods employed by machinists and toolmakers for accurately
+locating work such as jigs, etc., on the faceplate of a lathe, the
+one most commonly used is known as the button method.
+This scheme is so named because cylindrical bushings or buttons
+are attached to the work in positions corresponding to the
+holes to be bored, after which they are used in locating the
+work. These buttons, which are ordinarily about <sup class="enum">1</sup>/<sub class="denom">2</sub> inch in
+diameter, are ground and lapped to the same size and the ends
+squared. The diameter should, preferably, be such that the<span class="pagenum"><a name="Pg_102" id="Pg_102">[102]</a></span>
+radius can be determined easily, and the hole through the center
+should be about <sup class="enum">1</sup>/<sub class="denom">8</sub> inch larger than the retaining screw, so that
+the button can be shifted.</p>
+
+<a name="Fig_3_18" id="Fig_3_18"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/109sm.png" alt="Jig Plate with Buttons attached, ready for Boring" /></div>
+<p class="caption750">Fig. 18. Jig-plate with Buttons attached, ready for Boring</p>
+</div>
+
+<p>As an illustration of the practical application of the button
+method, we shall consider, briefly, the way the holes would be
+accurately machined in the jig-plate in <a href="#Fig_3_18">Fig. 18</a>. First the centers
+of the seven holes should be laid off approximately correct
+by the usual methods, after which small holes should be drilled
+and tapped for the clamping screws <i>S</i>. After the buttons <i>B</i>
+are clamped lightly in place, they are all set in correct relation
+with each other and with the jig-plate. The proper location of
+the buttons is very important as their positions largely determine
+the accuracy of the work. A definite method of procedure
+that would be applicable in all cases cannot, of course,
+be given, as the nature of the work as well as the tools available
+make it necessary to employ different methods.</p>
+
+<p>In this particular case, the three buttons <i>a</i>, <i>b</i> and <i>c</i> should be
+set first, beginning with the one in the center. As this central
+hole must be 2.30 and 2.65 inches from the finished sides <i>A</i> and
+<i>A<sub>1</sub></i>, respectively, the work is first placed on an accurate surface-plate
+as shown; by resting it first on one of these sides and then
+on the other, and measuring with a vernier height gage, the
+central button can be accurately set. The buttons <i>a</i> and <i>c</i> are
+also set to the correct height from side <i>A<sub>1</sub></i> by using the height
+<span class="pagenum"><a name="Pg_103" id="Pg_103">[103]</a></span>
+gage, and in proper relation to the central button by using a
+micrometer or a vernier caliper and measuring the over-all
+dimension <i>x</i>. When measuring in this way, the diameter of one
+button would be deducted to obtain the correct center-to-center
+distance. After buttons <i>a</i>, <i>b</i> and <i>c</i> are set equidistant from
+side A<sub>1</sub> and in proper relation to each other, the remaining
+buttons should be set radially from the central button <i>b</i> and the
+right distance apart. By having two micrometers or gages,
+one set for the radial dimension <i>x</i> and the other for the chordal
+distance <i>y</i>, the work may be done in a comparatively short
+time.</p>
+
+<a name="Fig_3_19" id="Fig_3_19"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/110sm.png" alt="Setting a Button True Preparatory to Boring, by use of Test Indicator" /></div>
+<p class="caption750">Fig. 19. Setting a Button True Preparatory to Boring, by use of
+Test Indicator</p>
+</div>
+
+<p>After the buttons have been tightened, all measurements
+should be carefully checked; the work is then mounted on the
+faceplate of the lathe, and one of the buttons, say <i>b</i>, is set true
+by the use of a test indicator as shown in <a href="#Fig_3_19">Fig. 19</a>. When the
+end of this indicator (which is one of a number of types on
+the market) is brought into contact with the revolving button,
+the vibration of the pointer <i>I</i> shows how much the button runs
+out of true. When the pointer remains practically stationary,
+thus showing that the button runs true, the latter should be
+removed. The hole is then drilled nearly to the required size,
+after which it is bored to the finish diameter. In a similar<span class="pagenum"><a name="Pg_104" id="Pg_104">[104]</a></span>
+manner the other buttons are indicated and the holes bored,
+one at a time. It is evident that if each button is correctly
+located and set perfectly true in the lathe, the various holes
+will be located at the required center-to-center dimensions
+within very close limits.</p>
+
+<a name="Fig_3_20" id="Fig_3_20"></a>
+<div class="figcenter"><img src="images/111sm.jpg" alt="Testing Concentricity of Button with Dial Gage" />
+<p class="caption750">Fig. 20. Testing Concentricity of Button with Dial Gage</p>
+</div>
+
+<a name="Fig_3_21" id="Fig_3_21"></a>
+<div class="figcenter"><img src="images/112sm.jpg" alt="Drilling a Bushing Hole" />
+<p class="caption750">Fig. 21. Drilling a Bushing Hole</p>
+</div>
+
+<p><a href="#Fig_3_20">Fig. 20</a> shows how one of the buttons attached to a plate
+in which three holes are to be bored is set true or concentric.
+The particular indicator illustrated is of the dial type, any
+error in the location of the button being shown by a hand over
+a dial having graduations representing thousandths of an inch.
+<a href="#Fig_3_21">Fig. 21</a> shows how the hole is drilled after the button is removed.
+It will be noted that the drill is held in a chuck, the
+taper shank of which fits into the tailstock spindle, this being
+the method of holding small drills. After drilling, the hole is
+bored as shown in <a href="#Fig_3_22">Fig. 22</a>. The boring tool should have a
+keen edge to avoid springing, and if the work when clamped in
+position, throws the faceplate out of balance, it is advisable to
+restore the balance, before boring, by the use of a counter-weight,
+because the lathe can be rotated quite rapidly when
+boring such a small hole.</p>
+
+<a name="Fig_3_22" id="Fig_3_22"></a>
+<div class="figcenter"><img src="images/113sm.jpg" alt="Boring a Bushing Hole" />
+<p class="caption750">Fig. 22. Boring a Bushing Hole</p>
+</div>
+
+<a name="Fig_3_23" id="Fig_3_23"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/114asm.png" alt="Example of Work illustrating Accumulation of Errors" /></div>
+<p class="caption750">Fig. 23. Example of Work illustrating Accumulation of Errors</p>
+</div>
+
+<p>When doing precision work of this kind, the degree of accuracy
+will depend upon the instruments used, the judgment<span class="pagenum"><a name="Pg_105" id="Pg_105">[105]</a></span>
+and skill of the workman and the care exercised. A good
+general rule to follow when locating bushings or buttons is to
+use the method which is the most direct and which requires
+the least number of measurements. As an illustration of how
+errors may accumulate, let us assume that seven holes are to
+be bored in the jig-plate shown in <a href="#Fig_3_23">Fig. 23</a>, so that they are the
+same distance from each other and in a straight line. The
+buttons may be brought into alignment by the use of a straight-edge,
+and to simplify matters, it will be taken for granted that
+they have been ground and lapped to the same size. If the
+diameter of the buttons is first determined by measuring with a
+micrometer, and then this diameter is deducted from the center
+distance <i>x</i>, the difference will be the distance <i>y</i> between adjacent
+buttons. Now if a temporary gage is made to length <i>y</i>,
+all the buttons can be set practically the same distance apart,
+the error between any two adjacent ones being very slight.
+If, however, the total length <i>z</i> over the end buttons is measured
+by some accurate means, the chances are that this distance will
+not equal six times dimension <i>x</i> plus the diameter of one button,
+as it should, because even a very slight error in the gage for
+distance <i>y</i> would gradually accumulate as each button was
+set. If a micrometer were available that would span two of<span class="pagenum"><a name="Pg_106" id="Pg_106">[106]</a></span>
+the buttons, the measurements could be taken direct and greater
+accuracy would doubtless be obtained. On work of this kind
+where there are a number of holes that need to have accurate
+over-all dimensions, the long measurements should first be
+taken when setting the buttons, providing, of course, there are
+proper facilities for so doing, and then the short ones. For example,
+the end buttons in this case should first be set, then the
+central one and finally those for the sub-divisions.</p>
+
+<a name="Fig_3_24" id="Fig_3_24"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/114bsm.png" alt="Special Arbor for Turning Eccentrics" /></div>
+<p class="caption750">Fig. 24. Special Arbor for Turning Eccentrics</p>
+</div>
+
+<a name="Secnum_3_16" id="Secnum_3_16"></a><p><b>Eccentric Turning.</b>&mdash;When one cylindrical surface must be
+turned eccentric to another, as when turning the eccentric of
+a steam engine, an arbor having two sets of centers is commonly
+used, as shown in <a href="#Fig_3_24">Fig. 24</a>. The distance <i>x</i> between the
+centers must equal one-half the total &#8220;throw&#8221; or stroke of the
+eccentric. The hub of the eccentric is turned upon the centers
+<i>a&mdash;a</i>, and the tongued eccentric surface, upon the offset centers,
+as indicated by the illustration. Sometimes eccentrics are
+turned while held upon special fixtures attached to the faceplate.</p>
+
+<p>When making an eccentric arbor, the offset center in each
+end should be laid out upon radial lines which can be drawn<span class="pagenum"><a name="Pg_107" id="Pg_107">[107]</a></span>
+across the arbor ends by means of a surface gage. Each center
+is then drilled and reamed to the same radius <i>x</i> as near as
+possible. The uniformity of the distance <i>x</i> at each end is then
+tested by placing the mandrel upon the offset centers and rotating
+it, by hand, with a dial indicator in contact at first one end
+and then the other. The amount of offset can also be tested
+either by measuring from the point of a tool held in the toolpost,
+or by setting the tool to just graze the mandrel at extreme
+inner and outer positions, and noting the movement of
+the cross-slide by referring to the dial gage of the cross-feed
+screw.</p>
+
+<a name="Fig_3_25" id="Fig_3_25"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/115sm.png" alt="Turning Engine Crank-pin in an Ordinary Lathe" /></div>
+<p class="caption750">Fig. 25. Turning an Engine Crank-pin in an Ordinary Lathe</p>
+</div>
+
+<a name="Secnum_3_17" id="Secnum_3_17"></a><p><b>Turning a Crankshaft in a Lathe.</b>&mdash;Another example of
+eccentric turning is shown in <a href="#Fig_3_25">Fig. 25</a>. The operation is that of
+turning the crank-pin of an engine crankshaft, in an ordinary
+lathe. The main shaft is first rough-turned while the forging
+revolves upon its centers <i>C</i> and <i>C<sub>1</sub></i> and the ends are turned to
+fit closely the center-arms <i>A</i> and <i>A<sub>1</sub></i>. After the sides <i>B</i> and
+<i>B<sub>1</sub></i> of the crank webs have been rough-faced, the center-arms
+are attached to the ends of the shaft as shown in the illustration.
+These arms have centers at <i>D</i> and <i>D<sub>1</sub></i> (located at the required
+crank radius) which should be aligned with the rough pin, when<span class="pagenum"><a name="Pg_108" id="Pg_108">[108]</a></span>
+attaching the arms, and it is advisable to insert braces <i>E</i> between
+the arms and crank to take the thrust of the lathe centers.
+With the forging supported in this way, the crank-pin and inner
+sides of the webs are turned and faced, the work revolving
+about the axis of the pin. The turning tools must extend beyond
+the tool-holder far enough to allow the crank to clear as it
+swings around. Owing to this overhang, the tool should be as
+heavy as possible to make it rigid and it is necessary to take
+comparatively light cuts and proceed rather cautiously. After
+finishing the crank-pin and inside of the crank, the center-arms
+are removed and the main body of the shaft and the sides <i>B</i>
+and <i>B<sub>1</sub></i> are finished. This method of turning crankshafts is
+often used in general repair shops, etc., especially where new
+shafts do not have to be turned very often. It is slow and inefficient,
+however, and where crankshafts are frequently turned,
+special machines or attachments are used.</p>
+
+<a name="Fig_3_26" id="Fig_3_26"></a>
+<div class="figcenter"><img src="images/116sm.jpg" alt="LeBlond Lathe with Special Equipment for Crankshaft Turning" />
+<p class="caption750">Fig. 26. LeBlond Lathe with Special Equipment for Crankshaft Turning</p>
+</div>
+
+<a name="Secnum_3_18" id="Secnum_3_18"></a><p><b>Special Crankshaft Lathe.</b>&mdash;A lathe having special equipment
+for rough-turning gas engine crankshaft pins is shown in<span class="pagenum"><a name="Pg_109" id="Pg_109">[109]</a></span>
+<a href="#Fig_3_26">Fig. 26</a>. This lathe is a heavy-duty type built by the R. K.
+LeBlond Machine Tool Co. It is equipped with special adjustable
+headstock and tailstock fixtures designed to take crankshafts
+having strokes up to about 6 inches. The tools are held
+in a three-tool turret type of toolpost and there are individual
+cross-stops for each tool. This lathe also has a roller steadyrest
+for supporting the crankshaft; automatic stops for the
+longitudinal feed, and a pump for supplying cutting lubricant.
+The headstock fixture is carried on a faceplate mounted on the
+spindle and so arranged as to be adjustable for cranks of different
+throw. When the proper adjustment for a given throw has
+been made, the slide is secured by four T-bolts. A graduated
+scale and adjusting screw permit of accurate adjustments.</p>
+
+<p>The revolving fixture is accurately indexed for locating different
+crank-pins in line with the lathe centers, by a hardened steel
+plunger in the slide which engages with hardened bushings in
+the fixture. The index is so divided that the fixture may be
+rotated 120 or 180 degrees, making it adjustable for 2-, 4- and
+6-throw cranks. After indexing, the fixture is clamped by two
+T-bolts which engage a circular T-slot. The revolving fixture
+is equipped with removable split bushings which can be replaced
+to fit the line bearings of different sized crankshafts.
+The work is driven by a V-shaped dovetail piece having a
+hand-nut adjustment, which also centers the pin by the cheek
+or web. The crank is held in position by a hinged clamp on
+the fixture. The tailstock fixture is also adjustable and it is
+mounted on a spindle which revolves in a bushing in the tailstock
+barrel. The adjustment is obtained in the same manner
+as on the headstock fixture, and removable split bushings as
+well as a hinged clamp are also employed.</p>
+
+<p>The method of chucking a four-throw crank is as follows:
+The two fixtures are brought into alignment by two locking
+pins. One of these is located in the head and enters a bushing
+in the large faceplate and the other is in the tailstock and engages
+the tailstock fixture. The crankshaft is delivered to the
+machine with the line bearings rough-turned and it is clamped
+by the hinged clamp previously referred to and centered by the<span class="pagenum"><a name="Pg_110" id="Pg_110">[110]</a></span>
+V-shaped driver. The locking pins for both fixtures are then
+withdrawn and the machine is ready to turn two of the pins.
+After these have been machined, the fixtures are again aligned
+by the locking pins, the two T-bolts of the headstock fixture
+and the hinged clamp at the tailstock are released, the indexing
+plunger is withdrawn and the headstock fixture and crank are
+turned 180 degrees or until the index plunger drops into place.
+The crank is then clamped at the tailstock end and the revolving
+fixture is secured by the two T-bolts previously referred to.
+After the locking pins are withdrawn, the lathe is ready to
+turn the two opposite pins.</p>
+
+<a name="Fig_3_27" id="Fig_3_27"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/118sm.png" alt="Diagrams showing Arrangements of Tools on LeBlond Lathe" /></div>
+<p class="caption750">Fig. 27. Diagrams showing Arrangements of Tools on LeBlond Lathe</p>
+</div>
+
+<a name="Secnum_3_19" id="Secnum_3_19"></a><p><b>Operation of Special Crankshaft Lathe.</b>&mdash;The total equipment
+of this machine (see <a href="#Fig_3_27">Fig. 27</a>) is carried on a three-tool
+turret tool-block. The method of turning a crankshaft is as
+follows: A round-nosed turning tool is first fed into a cross stop
+as illustrated in the plan view at <i>A</i>, which gives the proper
+diameter. The feed is then engaged and the tool feeds across
+the pin until the automatic stop lever engages the first stop,
+which throws out the feed automatically. The carriage is then
+moved against a positive stop by means of the handwheel.
+The roller back-rest is next adjusted against the work by the
+cross-feed handwheel operating through a telescopic screw, and<span class="pagenum"><a name="Pg_111" id="Pg_111">[111]</a></span>
+the filleting tools are brought into position as at <i>B</i>. These are
+run in against a stop, removing the part left by the turning tool
+and giving the pin the proper width and fillets of the correct
+radius. If the crankshaft has straight webs which must be
+finished, two tools seen at <i>b</i> are used for facing the webs to
+the correct width. During these last two operations, the crank
+is supported by the roller back-rest, thus eliminating any tendency
+of the work to spring.</p>
+
+<p>After one pin is finished in the manner described, the back-rest
+is moved out of the way, the automatic stop lever raised,
+the carriage shifted to the next pin, and the operation repeated.
+The tools are held in position on the turret by studs,
+and they can be moved and other tools quickly substituted for
+pins of different widths. This machine is used for rough-turning
+the pins close to the required size, the finishing operation
+being done in a grinder. It should be mentioned, in
+passing, that many crankshafts, especially the lighter designs
+used in agricultural machinery, etc., are not turned at all but
+are ground from the rough.</p>
+
+<a name="Fig_3_28" id="Fig_3_28"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/119sm.png" alt="Spherical Turning with Compound Rest, Concave Turning" /></div>
+<p class="caption750">Fig. 28. (A) Spherical Turning with Compound Rest.<br />(B) Concave Turning</p>
+</div>
+
+<a name="Secnum_3_20" id="Secnum_3_20"></a><p><b>Spherical Turning.</b>&mdash;Occasionally it may be necessary to
+turn a spherical surface in the lathe. Sketch <i>A</i>, <a href="#Fig_3_28">Fig. 28</a>, shows
+<span class="pagenum"><a name="Pg_112" id="Pg_112">[112]</a></span>
+how a small ball-shaped end can be turned on a piece held in a
+chuck. The lathe carriage is adjusted so that the pin around
+which the compound rest swivels is directly under the center a.
+The bolts which hold the swivel are slightly loosened to allow
+the top slide to be turned, as indicated by the dotted lines;
+this causes the tool point to move in an arc about center <i>a</i>, and
+a spherical surface is turned. Light cuts must be taken as
+otherwise it would be difficult to turn the slide around by
+hand.</p>
+
+<p>Sketch <i>B</i> illustrates how a concave surface can be turned.
+The cross-slide is adjusted until swivel pin is in line with the
+lathe centers, and the carriage is moved along the bed until
+the horizontal distance between center <i>b</i> of the swivel, and the
+face of the work, equals the desired radius of the concave surface.
+The turning is then done by swinging the compound
+rest as indicated by the dotted lines. The slide can be turned
+more evenly by using the tailstock center to force it around.
+A projecting bar is clamped across the end of the slide at <i>d</i>, to
+act as a lever, and a centered bar is placed between this lever
+and the tailstock center; then by screwing out the tailstock
+spindle, the slide is turned about pivot <i>b</i>. The alignment between
+the swivel pin and the lathe centers can be tested by
+taking a trial cut; if the swivel pin is too far forward, the tool
+will not touch the turned surface if moved past center <i>c</i>, and if
+the pin is too far back, the tool will cut in on the rear side.</p>
+
+<a name="Fig_3_29" id="Fig_3_29"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/120sm.png" alt="Spherical Turning Attachment for Engine Lathe" /></div>
+<p class="caption750">Fig. 29. Spherical Turning Attachment for Engine Lathe</p>
+</div>
+
+<a name="Secnum_3_21" id="Secnum_3_21"></a><p><span class="pagenum"><a name="Pg_113" id="Pg_113">[113]</a></span>
+<b>Spherical Turning Attachments.</b>&mdash;When spherical turning
+must be done repeatedly, special attachments are sometimes
+used. <a href="#Fig_3_29">Fig. 29</a> shows an attachment applied to a lathe for turning
+the spherical ends of ball-and-socket joints. The height or
+radius of the cutting tool and, consequently, the diameter of
+the turned ball, is regulated by adjusting screw <i>A</i>. The tool is
+swung around in an arc, by turning handle <i>B</i> which revolves a
+worm meshing with an enclosed worm-wheel. As will be seen,
+the work is held in a special chuck, owing to its irregular
+shape.</p>
+
+<a name="Fig_3_30" id="Fig_3_30"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/121sm.png" alt="Attachment for Turning Spherical End of Gasoline Engine Piston" /></div>
+<p class="caption750">Fig. 30. Attachment for Turning Spherical End of Gasoline
+Engine Piston</p>
+</div>
+
+<p>Another spherical turning attachment is shown in <a href="#Fig_3_30">Fig. 30</a>.
+This is used for machining the ends of gasoline engine pistons.
+The cross-slide has bolted to it a bar <i>A</i> carrying a roller which
+is pressed against a forming plate <i>B</i> by a heavy spring <i>C</i>. The
+forming plate <i>B</i>, which is attached to a cross-piece fastened to
+the ways of the lathe bed, is curved to correspond with the
+radius required on the piston end, and when the tool is fed
+laterally by moving the cross-slide, it follows the curve of plate<span class="pagenum"><a name="Pg_114" id="Pg_114">[114]</a></span>
+<i>B</i>. The piston is held in a special hollow chuck which locates
+it in a central position and holds it rigidly.</p>
+
+<p>In connection with lathe work, special attachments and tools
+are often used, especially when considerable work of one class
+must be turned; however, if a certain part is required in large
+quantities, it is usually more economical to use some semi-automatic
+or automatic turning machine, especially designed
+for repetition work.</p>
+
+<a name="Fig_3_31" id="Fig_3_31"></a>
+<div class="figcenter"><img src="images/122sm.jpg" alt="Front and Rear Tools used for Roughing" />
+<p class="caption750">Fig. 31. Front and Rear Tools used for Roughing</p>
+</div>
+
+<a name="Secnum_3_22" id="Secnum_3_22"></a><p><b>Turning with Front and Rear Tools.</b>&mdash;In ordinary engine
+lathe practice, one tool is used at a time, but some lathes are
+equipped with tool-holders at the front and rear of the carriage
+so that two tools can be used simultaneously. <a href="#Fig_3_31">Fig. 31</a> shows a
+detail view of a lathe in which front and rear tools are being
+used. These tools are of the inserted cutter type and the one
+at the rear is inverted, as the rotary movement of the work is,
+of course, upward on the rear side. This particular lathe was
+designed for taking heavy roughing cuts and has considerable
+driving power.</p>
+
+<p>The part shown in this illustration is a chrome-nickel steel
+bar which is being roughed out to form a milling machine<span class="pagenum"><a name="Pg_115" id="Pg_115">[115]</a></span>
+spindle. It is necessary to reduce the diameter of the bar from
+5<sup class="enum">7</sup>/<sub class="denom">16</sub> inches to 3<sup class="enum">3</sup>/<sub
+class="denom">4</sub> inches for a length of 27 inches, because of a
+collar on one end. This reduction is made in one passage of the
+two tools, with a feed of <sup class="enum">1</sup>/<sub class="denom">32</sub> inch per revolution and a speed of
+60 revolutions per minute. The use of two tools for such heavy
+roughing cuts is desirable, especially when the parts are required
+in large quantities, because the thrust of the cut on one
+side, which tends to deflect the work, is counteracted by the
+thrust on the opposite side.</p>
+
+<p>Sometimes special tool-holders are made for the lathe, so
+that more than one tool can be used for turning different surfaces
+or diameters at the same time, the tools being set in the
+proper relation to each other. The advantage of this method
+has resulted in the design of a special lathe for multiple-tool
+turning.</p>
+
+<a name="Fig_3_32" id="Fig_3_32"></a>
+<div class="figcenter"><img src="images/123sm.jpg" alt="Lo-swing Lathe for Multiple Turning" />
+<p class="caption750">Fig. 32. Lo-swing Lathe for Multiple Turning</p>
+</div>
+
+<a name="Secnum_3_23" id="Secnum_3_23"></a><p><b>A Multiple-tool Lathe.</b>&mdash;The lathe shown in <a href="#Fig_3_32">Fig. 32</a> (which
+is built by the Fitchburg Machine Works and is known as the
+Lo-swing) is designed especially for turning shafts, pins and
+forgings not exceeding 3<sup class="enum">1</sup>/<sub class="denom">2</sub> inches in diameter. It has two carriages
+<span class="pagenum"><a name="Pg_116" id="Pg_116">[116]</a></span>
+<i>A</i> and <i>B</i> which, in conjunction with special tool-holders,
+make it possible to turn several different diameters simultaneously.
+At the front of this lathe there is an automatic stop-rod
+<i>C</i> for disengaging the feed when the tools have turned a
+surface to the required length. This stop-rod carries adjustable
+stops <i>D</i> which are set to correspond with shoulders, etc.,
+on the work. The rod itself is also adjustable axially, so that
+the tools, which are usually arranged in groups of two or more
+(depending upon the nature of the work), can be disengaged at
+a point nearer or farther from the headstock as may be required,
+owing to a variation in the depth of center holes. For example,
+if it were necessary to feed a group of tools farther toward the
+headstock after they had been automatically disengaged, the
+entire rod with its stops would be adjusted the required amount
+in that direction.</p>
+
+<p>The gage <i>G</i>, which is attached to a swinging arm, is used to
+set the stop bar with reference to a shoulder near the end of
+the work, when it is necessary to finish other parts to a given
+distance from such a shoulder or other surface. The use of<span class="pagenum"><a name="Pg_117" id="Pg_117">[117]</a></span>
+this gage will be explained more fully later. Cooling lubricant
+for the tools is supplied through the tubes <i>E</i>. The lathe shown
+in the illustration is arranged for turning Krupp steel bars.
+A rough bar and also one that has been turned may be seen to
+the right. The plain cylindrical bar is turned to five different
+diameters, by groups of tools held on both carriages.</p>
+
+<a name="Fig_3_33" id="Fig_3_33"></a>
+<div class="figcenter"><img src="images/124sm.jpg" alt="Plan View showing Method of driving Steering Knuckle and Arrangement of Tools" />
+<p class="caption750">Fig. 33. Plan View showing Method of driving Steering Knuckle and Arrangement of Tools</p>
+</div>
+
+<a name="Secnum_3_24" id="Secnum_3_24"></a><p><b>Examples of Multiple Turning.</b>&mdash;<a href="#Fig_3_33">Figs. 33</a>
+and <a href="#Fig_3_34">34</a> show how a Lo-swing lathe is used for turning the steering knuckle of an
+automobile. Four tools are used in this case, three cylindrical
+surfaces and one tapering surface being turned at the same
+time. For this job, the four tools are mounted on one carriage.
+The taper part is turned by the second tool from the
+headstock, which is caused to feed outward as the carriage<span class="pagenum"><a name="Pg_118" id="Pg_118">[118]</a></span>
+advances by a taper attachment. This tool is held in a special
+holder and bears against a templet at the rear, which is tapered
+to correspond with the taper to be turned. This templet is
+attached to a bar which, in turn, is fastened to a stationary
+bracket seen to the extreme left in <a href="#Fig_3_33">Fig. 33</a>. This part is finished
+in two operations, the tool setting being identical for each
+operation, except for diameter adjustments. As the illustrations
+show, three of the four tools employed are used for straight
+turning on different diameters, while the fourth finishes the
+taper.</p>
+
+<a name="Fig_3_34" id="Fig_3_34"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/125sm.png" alt="Plan View showing Method of driving Steering Knuckle and Arrangement of Tools" /></div>
+<p class="caption750">Fig. 34. Plan View showing Method of driving Steering Knuckle and
+Arrangement of Tools</p>
+</div>
+
+<p>These pieces, which are rough drop forgings, are first reduced
+to the approximate size. When it becomes necessary to
+grind the tools, they are reset and those parts which have been
+roughed out are turned to the finished size. The average time
+for the first operation, which includes starting, stopping, turning
+and replacing the piece, is one minute, while for the second
+operation with the finer feed, an average time of two minutes
+is required. The work is driven by sleeve <i>S</i>, which fits over the
+spindle and is held in position by the regular driver, as shown.
+This sleeve is notched to fit the knuckle, so that the latter can
+easily and quickly be replaced when finished.</p>
+
+<p>One of the interesting features of this job lies in the method
+of locating the shoulders on each knuckle, at the same distance
+from the hole <i>H</i> which is drilled previously, and which receives
+the bolt on which the knuckle swivels when assembled
+in a car. As soon as the knuckle has been placed between the
+centers, a close-fitting plug <i>P</i> (<a href="#Fig_3_33">Fig. 33</a>) is inserted in this hole
+and the indicator arm with its attached gage or caliper <i>G</i> is
+swung up to the position shown. The stop-rod on which the
+stops have been previously set for the correct distance between
+the shoulders is next adjusted axially until the gage <i>G</i>
+just touches the plug <i>P</i>. The indicator is then swung out of
+the way, and the piece turned. If the next knuckle were
+centered, say, deeper than the previous one which would, of
+course, cause it to be located nearer the headstock, obviously
+all the shoulders would be located farther from the finished
+hole, provided the position of the stops remained the same as<span class="pagenum"><a name="Pg_119" id="Pg_119">[119]</a></span>
+before. In such a case their position would, however, be changed
+by shifting the stop-rod until the gage <i>G</i> again touched the plug
+thus locating all the stops with reference to the hole. As the
+adjustment of the stop-rod changes the position of the taper
+templet as well as the stops, it is evident that both the shoulders
+and the taper are finished the same distance from the hole in
+each case. The connection of the bracket (to which the templet
+arm is attached) with the stop-rod is clearly shown in <a href="#Fig_3_33">Fig. 33</a>.
+This bracket can either be locked to the ways or adjusted to
+slide when the stop-rod is moved.</p>
+
+<a name="Fig_3_35" id="Fig_3_35"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/127sm.png" alt="First and Second Operations on Automobile Transmission Shaft&mdash;Lo-swing Lathe" /></div>
+<p class="caption750">Fig. 35. First and Second Operations on Automobile Transmission
+Shaft&mdash;Lo-swing Lathe</p>
+</div>
+
+<p>The part illustrated in <a href="#Fig_3_35">Fig. 35</a> is an automobile transmission
+shaft. In this particular case, cylindrical, tapering and spherical
+surfaces are turned. The upper view shows, diagrammatically,
+the arrangement of the tools and work for the first operation.
+After the shaft is &#8220;spotted&#8221; at <i>A</i> for the steadyrest, the<span class="pagenum"><a name="Pg_120" id="Pg_120">[120]</a></span>
+straight part <i>C</i> and the collar <i>B</i> are sized with tools <i>S</i> and <i>R</i>
+which are mounted on the left-hand carriage. A concave groove
+is then cut in collar <i>B</i> by tool <i>R</i>, after which spherical end <i>D</i> is
+formed by a special attachment mounted on the right-hand carriage.
+This attachment is the same, in principle, as the regular
+taper-turning attachment, the substitution of a circular templet
+<i>T</i> for the straight kind used on taper work being the only practical
+difference.</p>
+
+<p>After the surfaces mentioned have been finished on a number
+of pieces, the work is reversed and the tools changed as shown
+by the lower view. The first step in the second operation is to
+turn the body <i>E</i> of the shaft with the tool <i>T</i> on the left-hand
+carriage. The taper <i>F</i> and the straight part <i>G</i> are then finished,
+which completes the turning. It will be noted that in setting
+up the machine for this second operation, it is arranged for
+taper turning by simply replacing the circular templet with the
+straight one shown. When this taper attachment is not in use,
+the swiveling arm <i>M</i>, which is attached to a bracket, is swung
+out of the way.</p>
+
+<p><span class="pagenum"><a name="Pg_121" id="Pg_121">[121]</a></span>The method of driving this shaft is worthy of note. A dog
+having two driving arms each of which bears against a pin <i>N</i>
+that passes through a hole in the spindle is used. As the ends
+of this pin, against which the dog bears, are beveled in opposite
+directions, the pin turns in its hole when the dog makes contact
+with it and automatically adjusts itself against the two driving
+members of the dog. The advantage of driving by a two-tailed
+dog, as most mechanics know, is in equalizing the tendency
+to spring slender parts while they are being turned.</p>
+
+<a name="Fig_3_36" id="Fig_3_36"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/128sm.png" alt="Axle End turned in One Traverse of the Five Tools shown" /></div>
+<p class="caption750">Fig. 36. Axle End turned in One Traverse of the Five Tools shown</p>
+</div>
+
+<p>In <a href="#Fig_3_36">Fig. 36</a> another turning operation on a lathe of this type
+is shown, the work in this case being a rear axle for a motor
+truck. The turning of this part is a good example of that class
+of work where the rapid removal of metal is the important
+feature. As the engraving shows, the stock, prior to turning,
+is 3<sup class="enum">1</sup>/<sub class="denom">2</sub> inches in diameter and it is reduced to a minimum diameter
+of 1<sup class="enum">1</sup>/<sub class="denom">16</sub> inch. This metal is turned off with one traverse of
+the carriage or by one passage of the five tools, and the weight
+of the chips removed from each end of the axle is approximately
+12 pounds. The time required for the actual turning is about
+9 minutes, while the total time for the operation, which includes
+placing the heavy piece in the machine, turning, and<span class="pagenum"><a name="Pg_122" id="Pg_122">[122]</a></span>
+removing the work from the lathe, is 12 minutes. The axle revolves,
+while being turned, at 110 revolutions per minute and a
+feed equivalent to 1 inch of tool travel to 60 revolutions of the
+work is used. It will be noticed that the taper attachment is also
+employed on this part, the taper being turned by the second
+tool from the left. As the axle is equipped with roller bearings,
+it was found desirable to finish the bearing part by a separate
+operation; therefore, in the operation shown the axle is simply
+roughed down rather close to the finished dimensions, leaving
+enough material for a light finishing cut.</p>
+
+<a name="Fig_3_37" id="Fig_3_37"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/129sm.png" alt="Lathe Knurling Tool having Three Pairs of Knurls&mdash;Coarse, Medium and Fine" /></div>
+<p class="caption750">Fig. 37. Lathe Knurling Tool having Three Pairs of Knurls&mdash;Coarse,
+Medium and Fine</p>
+</div>
+
+<a name="Secnum_3_25" id="Secnum_3_25"></a><p><b>Knurling in the Lathe.</b>&mdash;Knurling is done either to provide
+a rough surface which can be firmly gripped by the hand or for
+producing an ornamental effect. The handles of gages and
+other tools are often knurled, and the thumb-screws used on
+instruments, etc., usually have knurled edges. A knurled surface
+consists of a series of small ridges or diamond-shaped projections,
+and is produced in the lathe by the use of a tool similar
+to the one shown in <a href="#Fig_3_37">Fig. 37</a>, this being one of several different
+designs in common use. The knurling is done by two knurls
+<i>A</i> and <i>B</i> having teeth or ridges which incline to the right on one
+knurl and to the left on the opposite knurl, as shown by the
+end view. When these two knurls are pressed against the work
+as the latter revolves, one knurl forms a series of left-hand
+ridges and the other knurl right-hand ridges, which cross and
+form the diamond-shaped knurling which is generally used.</p>
+
+<p>If the surface to be knurled is wider than the knurls, the
+power feed of the lathe should be engaged and the knurling tool
+be traversed back and forth until the diamond-shaped projections
+are well formed. To prevent forming a double set of
+projections, feed the knurl in with considerable pressure at the
+start, then partially relieve the pressure before engaging the
+power feed. Use oil when knurling.</p>
+
+<p>The knurls commonly used for lathe work have spiral teeth
+and ordinarily there are three classes, known as coarse, medium
+and fine. The medium pitch is generally used. The teeth of
+coarse knurls have a spiral angle of 36 degrees and the pitch
+of the knurled cut (measured parallel to the axis of the work)<span class="pagenum"><a name="Pg_123" id="Pg_123">[123]</a></span>
+should be about 8 per inch. For medium knurls, the spiral
+angle is 29<sup class="enum">1</sup>/<sub class="denom">2</sub> degrees and the pitch, measured as before, is 12
+per inch. For fine knurls, the spiral angle is 25<sup class="enum">3</sup>/<sub class="denom">4</sub> degrees and
+the pitch 20 per inch. The knurls should be about <sup class="enum">3</sup>/<sub class="denom">4</sub> inch in
+diameter and <sup class="enum">3</sup>/<sub class="denom">8</sub> inch wide. When made to these dimensions,
+coarse knurls have 34 teeth; medium, 50 teeth; and fine knurls,
+80 teeth.</p>
+
+<p>The particular tool illustrated in <a href="#Fig_3_37">Fig. 37</a> has three pairs of
+knurls of coarse, medium and fine pitch. These are mounted
+in a revolving holder which not only serves to locate the required
+set of knurls in the working position, but enables each
+knurl to bear against the surface with equal pressure. Concave
+knurls are sometimes used for knurling rounded edges on screw
+heads, etc.</p>
+
+<a name="Secnum_3_26" id="Secnum_3_26"></a><p><b>Relieving Attachment.</b>&mdash;Some lathes, particularly those used
+in toolrooms, are provided with relieving attachments which
+are used for &#8220;backing off&#8221; the teeth of milling cutters, taps,
+hobs, etc. If a milling cutter of special shape is to be made, the
+cutter blank is first turned to the required form with a special
+tool having a cutting edge that corresponds with the shape or
+profile of the cutter to be made. The blank is then fluted or
+gashed to form the teeth, after which the tops of the teeth are<span class="pagenum"><a name="Pg_124" id="Pg_124">[124]</a></span>
+relieved or backed off to provide clearance for the cutting edges.
+The forming tool used for turning the blank is set to match the
+turned surface, and the teeth are backed off as the result of a
+reciprocating action imparted to the toolslide by the relieving
+attachment. The motion of the toolslide is so adjusted that
+the tool will meet the front of each tooth and the return movement
+begin promptly after the tool leaves the back end of the
+tooth.</p>
+
+<a name="Fig_3_38" id="Fig_3_38"></a>
+<div class="figcenter"><img src="images/131sm.jpg" alt="Hendey Relieving Attachment applied to a Lathe" />
+<p class="caption750">Fig. 38. Hendey Relieving Attachment applied to a Lathe</p>
+</div>
+
+<p>These attachments differ somewhat in their construction and
+arrangement but the principle of their operation is similar.
+<a href="#Fig_3_38">Fig. 38</a> shows a Hendey relieving attachment applied to a lathe.
+A bracket carrying the gearing <i>A</i> through which the attachment
+is driven is mounted upon the main gear box of the lathe, and
+the special slide <i>B</i>, which is used when relieving, is placed on
+the cross-slide after removing the regular compound rest. The
+gears at <i>A</i> are changed to suit the number of flutes or gashes in
+the cutter, tap or whatever is to be relieved. If we assume that
+the work is a formed milling cutter having nine teeth, then with
+this particular attachment, a gear having 90 teeth would be
+placed on the &#8220;stud&#8221; and a 40-tooth gear on the cam-shaft, the
+two gears being connected by a 60-tooth intermediate gear.<span class="pagenum"><a name="Pg_125" id="Pg_125">[125]</a></span>
+With this combination of gearing, the toolslide would move in
+and out nine times for each revolution of the work, so that the
+tool could back off the top of each tooth. (The gearing to use
+for various numbers of flutes is shown by an index plate on the
+attachment.) The amount of relief is varied to suit the work
+being done, by means of a toothed coupling which makes it
+possible to change the relative position between the eccentric
+which actuates the toolslide and the cam lever, thereby lengthening
+or shortening the reciprocating travel of the tool.</p>
+
+<a name="Fig_3_39" id="Fig_3_39"></a>
+<div class="figcenter"><img src="images/132sm.jpg" alt="Relieving a Formed Cutter" />
+<p class="caption750">Fig. 39. Relieving a Formed Cutter</p>
+</div>
+
+<a name="Secnum_3_27" id="Secnum_3_27"></a><p><b>Application of Relieving Attachment.</b>&mdash;Some typical examples
+of the kind of work for which the relieving attachment
+is used are shown in <a href="#Fig_3_39">Figs. 39</a> to <a href="#Fig_3_42">42</a>, inclusive. <a href="#Fig_3_39">Fig. 39</a> shows
+how a formed milling cutter is relieved. The toolslide is set at
+right angles to the axis of the work, and the tool moves in as
+each tooth passes, and out while crossing the spaces or flutes
+between the teeth. As the result of this movement, the tops of
+the teeth are backed off eccentrically but the form or shape is
+the same from the front to the back of the tooth; hence, a
+cutter that has been relieved in this way can be ground repeatedly
+without changing the profile of the teeth, provided the
+faces are ground so as to lie in a radial plane.</p>
+
+<p><span class="pagenum"><a name="Pg_126" id="Pg_126">[126]</a></span>When relieving, the cutting speed should be much less than
+when turning in order to give the toolslide time to operate
+properly. A maximum of 180 teeth per minute is recommended,
+and, if wide forming tools are used, it might be advisable
+to reduce the speed so low that only 8 teeth per minute
+would be relieved. It is also essential to use a tool having a keen
+edge, and the toolslide should work freely but be closely adjusted
+to the dovetail of the lower slide. Before beginning to
+back off the teeth, it is a good plan to color the work either by
+heating it or dipping into a strong solution of copper sulphate.
+This will enable one to see plainly the cutting action of the
+tool in order to stop relieving at the proper time.</p>
+
+<a name="Fig_3_40" id="Fig_3_40"></a>
+<div class="figcenter"><img src="images/133sm.jpg" alt="Relieving Side of Angular Milling Cutter" />
+<p class="caption750">Fig. 40. Relieving Side of Angular Milling Cutter</p>
+</div>
+
+<p><a href="#Fig_3_40">Fig. 40</a> shows a method of relieving the teeth of an angular
+cutter. For an operation of this kind the toolslide is swiveled
+around at right angles to the side that is to be relieved. By
+the use of an additional universal joint and bearing to permit
+the toolslide to be swung to a 90-degree angle, the teeth of
+counterbores, etc., can be relieved on the ends. When the attachment
+is used for relieving inside work, such as hollow mills
+and threading dies, the eccentric which controls the travel of
+the toolslide is set so that the relieving movement is away from<span class="pagenum"><a name="Pg_127" id="Pg_127">[127]</a></span>
+the axis of the cutter instead of toward it. This change is
+made by the toothed coupling previously referred to, which
+connects the cam lever and oscillating shaft, the latter being
+turned beyond the zero mark in a clockwise direction as far as
+is necessary to obtain the desired amount of travel. For internal
+work it is also necessary to change the position of the
+opposing spring of the toolslide, so that it will press against
+the end of the slide and prevent the tool from jumping into
+the work.</p>
+
+<a name="Fig_3_41" id="Fig_3_41"></a>
+<div class="figcenter"><img src="images/134sm.jpg" alt="Relieving a Right-hand Tap" />
+<p class="caption750">Fig. 41. Relieving a Right-hand Tap</p>
+</div>
+
+<p><a href="#Fig_3_41">Fig. 41</a> shows how a right-hand tap is relieved. The ordinary
+practice is to first set the tool the same as for cutting a thread.
+The motion of the toolslide is then adjusted so that the tool on
+the forward stroke will meet the front of each tooth, and start
+back as soon as the tool leaves the end of the land or top of the
+tooth. Taps having a left-hand thread can be relieved by two
+different methods. With the first method the cut starts at the
+cutting edge of each tooth, and ends at the &#8220;heel,&#8221; the tool
+moving in toward the center of the work. With the second
+method, the cut begins at the heel and discontinues at the cutting
+edge, the tool being drawn away from the work during the<span class="pagenum"><a name="Pg_128" id="Pg_128">[128]</a></span>
+cut. When using the first method the tap must be placed with
+the point toward the headstock, the shank end being supported
+by the tailstock center. This is done by providing an
+extension or blank end at the point of the tap long enough to
+hold the driving dog. With the second method, the tap is held
+between centers the same as one having a right-hand thread,
+but the travel of the toolslide is set the same as for inside relief.</p>
+
+<a name="Fig_3_42" id="Fig_3_42"></a>
+<div class="figcenter"><img src="images/135sm.jpg" alt="Relieving a Hob having Spiral Flutes" />
+<p class="caption750">Fig. 42. Relieving a Hob having Spiral Flutes</p>
+</div>
+
+<a name="Secnum_3_28" id="Secnum_3_28"></a><p><b>Relieving Hobs or Taps Having Spiral Flutes.</b>&mdash;With
+this attachment, taps or hobs having &#8220;spiral&#8221; or helical flutes
+can also be relieved. (A spiral flute is preferable to one that is
+parallel to the axis, because with the former the tool has cutting
+edges which are square with the teeth; this is of especial importance
+when the lead of the hob or tap thread is considerable.)
+When relieving work having spiral flutes (as illustrated in <a href="#Fig_3_42">Fig.
+42</a>), the lead of the spiral and the gears necessary to drive the
+attachment are first determined. After the attachment is
+geared for the number of flutes and to compensate for the spiral,
+the lead-screw is engaged and the backing-off operation is
+performed the same as though the flutes were straight. The
+carriage should not be disengaged from the lead-screw after
+starting the cut, the tool being returned by reversing the lathe.</p>
+
+<p>When gearing the attachment for relieving a tap or hob
+having spiral flutes, the gears are not selected for the actual
+number of flutes around the circumference but for a somewhat
+larger number which depends upon the lead of the hob thread
+and the lead of the spiral flutes. Let us assume that a hob
+has 6 spiral flutes and that the attachment is geared for that
+number. The result would be that as the tool advanced along
+the thread, it would not keep &#8220;in step&#8221; with the teeth because
+the faces of the teeth lie along a spiral (or helix which is the
+correct name for this curve); in other words, the tool would
+soon be moving in too late to begin cutting at the proper time,
+and to compensate for this, the attachment is geared so that the
+tool will make a greater number of strokes per revolution of the
+work than the actual number of flutes around the circumference.</p>
+
+<p>With this attachment, the two gears listed on the index plate
+for the actual number of flutes are selected, and then two compensating
+<span class="pagenum"><a name="Pg_129" id="Pg_129">[129]</a></span>
+gears are added, thus forming a compound train of
+gearing. The ratio <i>R</i> of these compensating gears is determined
+as follows:</p>
+
+<table class="formula" summary="Formula 129_1">
+<tr><td>&nbsp;</td><td>&nbsp;</td><td>&nbsp;<i>r</i> + 1&nbsp;</td></tr>
+<tr><td>&nbsp;<i>R</i>&nbsp;</td><td>&nbsp;=&nbsp;</td><td>&nbsp;&mdash;&mdash;&mdash;&nbsp;</td></tr>
+<tr><td>&nbsp;</td><td>&nbsp;</td><td>&nbsp;<i>r</i>&nbsp;</td></tr>
+</table>
+
+in which
+
+<table class="formsymb" summary="Formula 129_2">
+<tr><td>&nbsp;<i>r</i>&nbsp;</td><td>&nbsp;=&nbsp;</td><td>&nbsp;<i>L</i>&nbsp;&divide;&nbsp;<i>l</i>;&nbsp;</td></tr>
+<tr><td>&nbsp;<i>L</i>&nbsp;</td><td>&nbsp;=&nbsp;</td><td>&nbsp;lead of spiral;</td></tr>
+<tr><td>&nbsp;<i>l</i>&nbsp;</td><td>&nbsp;=&nbsp;</td><td>&nbsp;lead of hob thread.&nbsp;</td></tr>
+</table>
+
+<p>For example, if a hob has a pitch circumference of 3.25, a
+single thread of 0.75 inch lead, and 6 spiral flutes, what compensating
+gears would be required?</p>
+
+<p>The lead <i>L</i> of the spiral flutes is first determined by dividing
+the square of the circumference <i>C</i> of the hob at the pitch line by
+the lead <i>l</i> of the hob thread. Thus lead <i>L = C<sup>2</sup>&nbsp;&divide;&nbsp;l</i>, or, in this case,
+<i>L</i> = 3.25<sup>2</sup>&nbsp;&divide;&nbsp;0.75 = 14 inches, approximately. Then <i>r</i> = 14&nbsp;&divide;&nbsp;0.75 =
+18<sup class="enum">2</sup>/<sub class="denom">3</sub>. Inserting these values in the formula for ratio R,</p>
+
+<table class="formula2" summary="Formula 129_3">
+<tr>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+<td>18<sup class="enum">2</sup>/<sub class="denom">3</sub> + 1&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;19<sup class="enum">2</sup>/<sub class="denom">3</sub>&nbsp;</td>
+<td>&nbsp;</td>
+<td>19<sup class="enum">2</sup>/<sub class="denom">3</sub>&nbsp;&times;&nbsp;3&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;59&nbsp;</td>
+</tr>
+
+<tr>
+<td>&nbsp;<i>R</i>&nbsp;</td>
+<td>&nbsp;=&nbsp;</td>
+<td>&nbsp;&mdash;&mdash;&mdash;&mdash;&nbsp;</td>
+<td>&nbsp;=&nbsp;</td>
+<td>&nbsp;&mdash;&mdash;&mdash;&nbsp;</td>
+<td>&nbsp;=&nbsp;</td>
+<td>&nbsp;&mdash;&mdash;&mdash;&mdash;&nbsp;</td>
+<td>&nbsp;=&nbsp;</td>
+<td>&nbsp;&mdash;&mdash;&nbsp;</td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+<td>18<sup class="enum">2</sup>/<sub class="denom">3</sub></td>
+<td>&nbsp;</td>
+<td>18<sup class="enum">2</sup>/<sub class="denom">3</sub></td>
+<td>&nbsp;</td>
+<td>18<sup class="enum">2</sup>/<sub class="denom">3</sub>&nbsp;&times;&nbsp;3</td>
+<td>&nbsp;</td>
+<td>&nbsp;56&nbsp;</td>
+</tr>
+</table>
+
+<p>Hence, the compensating gears will have 56 and 59 teeth, respectively,
+the latter being the driver. As the gears for 6 flutes
+listed on the regular index plate are, stud-gear 60 teeth, cam-shaft
+gear 40 teeth, the entire train of gears would be as follows:
+Gear on stud, 60; <i>driven</i> intermediate gear, 56; <i>driving</i> intermediate
+gear, 59; cam-shaft gear, 40. It will be understood that
+the position of the driving gears or the driven gears can be
+transposed without affecting the ratio.</p>
+
+<a name="Secnum_3_29" id="Secnum_3_29"></a><p><b>Classes of Fits Used in Machine Construction.</b>&mdash;In assembling
+machine parts it is necessary to have some members fit
+together tightly, whereas other parts such as shafts, etc., must be
+free to move or revolve with relation to each other. The accuracy
+required for a fitting varies for different classes of work.
+A shaft that revolves in its bearing must be slightly smaller
+than the bearing so that there will be room for a film of lubricant.
+A crank-pin that must be forced into the crank-disk is<span class="pagenum"><a name="Pg_130" id="Pg_130">[130]</a></span>
+made a little larger in diameter than the hole, to secure a tight
+fit. When a very accurate fitting between two cylindrical parts
+that must be assembled without pressure is required, the
+diameter of the inner member is made as close to the diameter
+of the outer member as is possible. In ordinary machine construction,
+five classes of fits are used, <i>viz</i>; running fit, push
+fit, driving fit, forced fit and shrinkage fit. The running fit,
+as the name implies, is employed when parts must rotate; the
+push fit is not sufficiently free to rotate; the other classes referred
+to are used for assembling parts that must be held in
+fixed positions.</p>
+
+<a name="Secnum_3_30" id="Secnum_3_30"></a><p><b>Forced Fits.</b>&mdash;This is the term used when a pin, shaft or
+other cylindrical part is forced into a hole of slightly smaller
+diameter, by the use of a hydraulic press or other means. As a
+rule, forced fits are restricted to parts of small and medium
+size, while shrinkage fits have no such limitations and are especially
+applicable when a maximum &#8220;grip&#8221; is desired, or when
+(as in the construction of ordnance) accurate results as to the
+intensity of stresses produced in the parts united are required.
+The proper allowance for a forced fit depends upon the mass of
+metal surrounding the hole, the size of the work, the kind and
+quality of the material of which the parts are composed and the
+smoothness and accuracy of the pin and bore. When a pin or
+other part is pressed into a hole a second time, the allowance
+for a given tonnage should be diminished somewhat because the
+surface of the bore is smoother and the metal more compact.
+The pressure required in assembling a forced fit will also vary
+for cast hubs of the same size, if they are not uniform in hardness.
+Then there is the personal factor which is much in evidence
+in work of this kind; hence, data and formulas for forced
+fit allowances must be general in their application.</p>
+
+<span class="pagenum"><a name="Pg_131" id="Pg_131">[131]</a></span>
+
+<h4>Allowances for Different Classes of Fits</h4>
+
+<p class="fsize80 center">(Newall Engineering Co.)</p>
+
+<table align="center" class="center" width="55%" cellpadding="0" cellspacing="0" summary="Allowances for Fits">
+
+<tr>
+<td class="bt bl" rowspan="2">Class</td>
+<td class="bt bl br" colspan="11">Tolerances in Standard Holes<a name="Fnanchor_2"></a><a href="#Fn_2" class="fnanchor">[1]</a></td>
+</tr>
+
+<tr>
+<td class="bt bl">Nominal Diameters</td>
+<td class="bt bl" colspan="2">Up to <sup class="enum">1</sup>/<sub class="denom">2</sub>"</td>
+<td class="bt bl" colspan="2">&nbsp;<sup class="enum">9</sup>/<sub class="denom">16</sub>"&nbsp;-&nbsp;1"&nbsp;</td>
+<td class="bt bl" colspan="2">&nbsp;1<sup class="enum">1</sup>/<sub class="denom">16</sub>"&nbsp;-&nbsp;2"&nbsp;</td>
+<td class="bt bl" colspan="2">&nbsp;2<sup class="enum">1</sup>/<sub class="denom">16</sub>"&nbsp;-&nbsp;3"&nbsp;</td>
+<td class="bt bl br" colspan="2">&nbsp;3<sup class="enum">1</sup>/<sub class="denom">16</sub>"&nbsp;-&nbsp;4"&nbsp;</td>
+</tr>
+
+<tr>
+<td class="bt bl" style="width: 15%" rowspan="3">A</td>
+<td class="bt bl" style="width: 20%">High Limit</td>
+<td class="bt bl" align="right" style="width: 3%">+</td>
+<td class="bt" align="left" style="width: 10%">0.0002</td>
+<td class="bt bl" align="right" style="width: 3%">+</td>
+<td class="bt" align="left" style="width: 10%">0.0005</td>
+<td class="bt bl" align="right" style="width: 3%">+</td>
+<td class="bt" align="left" style="width: 10%">0.0007</td>
+<td class="bt bl" align="right" style="width: 3%">+</td>
+<td class="bt" align="left" style="width: 10%">0.0010</td>
+<td class="bt bl" align="right" style="width: 3%">+</td>
+<td class="bt br" align="left" style="width: 10%">0.0010</td>
+</tr>
+
+<tr>
+<td class="bl">Low Limit</td>
+<td class="bl" align="right">-</td>
+<td align="left">0.0002</td>
+<td class="bl" align="right">-</td>
+<td align="left">0.0002</td>
+<td class="bl" align="right">-</td>
+<td align="left">0.0002</td>
+<td class="bl" align="right">-</td>
+<td align="left">0.0005</td>
+<td class="bl" align="right">-</td>
+<td class="br" align="left">0.0005</td>
+</tr>
+
+<tr>
+<td class="bl">Tolerance</td>
+<td class="bl" align="right">&nbsp;</td>
+<td align="left">0.0004</td>
+<td class="bl" align="right">&nbsp;</td>
+<td align="left">0.0007</td>
+<td class="bl" align="right">&nbsp;</td>
+<td align="left">0.0009</td>
+<td class="bl" align="right">&nbsp;</td>
+<td align="left">0.0015</td>
+<td class="bl" align="right">&nbsp;</td>
+<td class="br" align="left">0.0015</td>
+</tr>
+
+<tr>
+<td class="bt bl" rowspan="3">B</td>
+<td class="bt bl" >High Limit</td>
+<td class="bt bl" align="right">+</td>
+<td class="bt" align="left">0.0005</td>
+<td class="bt bl" align="right">+</td>
+<td class="bt" align="left">0.0007</td>
+<td class="bt bl" align="right">+</td>
+<td class="bt" align="left">0.0010</td>
+<td class="bt bl" align="right">+</td>
+<td class="bt" align="left">0.0012</td>
+<td class="bt bl" align="right">+</td>
+<td class="bt br" align="left">0.0015</td>
+</tr>
+
+<tr>
+<td class="bl">Low Limit</td>
+<td class="bl" align="right">-</td>
+<td align="left">0.0005</td>
+<td class="bl" align="right">-</td>
+<td align="left">0.0005</td>
+<td class="bl" align="right">-</td>
+<td align="left">0.0005</td>
+<td class="bl" align="right">-</td>
+<td align="left">0.0007</td>
+<td class="bl" align="right">-</td>
+<td class="br" align="left">0.0007</td>
+</tr>
+
+<tr>
+<td class="bl">Tolerance</td>
+<td class="bl" align="right">&nbsp;</td>
+<td align="left">0.0010</td>
+<td class="bl" align="right">&nbsp;</td>
+<td align="left">0.0012</td>
+<td class="bl" align="right">&nbsp;</td>
+<td align="left">0.0015</td>
+<td class="bl" align="right">&nbsp;</td>
+<td align="left">0.0019</td>
+<td class="bl" align="right">&nbsp;</td>
+<td class="br" align="left">0.0022</td>
+</tr>
+
+<tr>
+<td class="bt br bl" colspan="12">Allowances for Forced Fits</td>
+</tr>
+
+<tr>
+<td class="bt bl" rowspan="3">F</td>
+<td class="bt bl">High Limit</td>
+<td class="bt bl" align="right">+</td>
+<td class="bt" align="left">0.0010</td>
+<td class="bt bl" align="right">+</td>
+<td class="bt" align="left">0.0020</td>
+<td class="bt bl" align="right">+</td>
+<td class="bt" align="left">0.0040</td>
+<td class="bt bl" align="right">+</td>
+<td class="bt" align="left">0.0060</td>
+<td class="bt bl" align="right">+</td>
+<td class="bt br" align="left">0.0080</td>
+</tr>
+
+<tr>
+<td class="bl">Low Limit</td>
+<td class="bl" align="right">+</td>
+<td align="left">0.0005</td>
+<td class="bl" align="right">+</td>
+<td align="left">0.0015</td>
+<td class="bl" align="right">+</td>
+<td align="left">0.0030</td>
+<td class="bl" align="right">+</td>
+<td align="left">0.0045</td>
+<td class="bl" align="right">+</td>
+<td class="br" align="left">0.0060</td>
+</tr>
+
+<tr>
+<td class="bl">Tolerance</td>
+<td class="bl" align="right">&nbsp;</td>
+<td align="left">0.0005</td>
+<td class="bl" align="right">&nbsp;</td>
+<td align="left">0.0005</td>
+<td class="bl" align="right">&nbsp;</td>
+<td align="left">0.0010</td>
+<td class="bl" align="right">&nbsp;</td>
+<td align="left">0.0015</td>
+<td class="bl" align="right">&nbsp;</td>
+<td class="br" align="left">0.0020</td>
+</tr>
+
+<tr>
+<td class="bt br bl" colspan="12">Allowances for Driving Fits</td>
+</tr>
+
+<tr>
+<td class="bt bl" rowspan="3">D</td>
+<td class="bt bl">High Limit</td>
+<td class="bt bl" align="right">+</td>
+<td class="bt" align="left">0.0005</td>
+<td class="bt bl" align="right">+</td>
+<td class="bt" align="left">0.0010</td>
+<td class="bt bl" align="right">+</td>
+<td class="bt" align="left">0.0015</td>
+<td class="bt bl" align="right">+</td>
+<td class="bt" align="left">0.0025</td>
+<td class="bt bl" align="right">+</td>
+<td class="bt br" align="left">0.0030</td>
+</tr>
+
+<tr>
+<td class="bl">Low Limit</td>
+<td class="bl" align="right">+</td>
+<td align="left">0.0002</td>
+<td class="bl" align="right">+</td>
+<td align="left">0.0007</td>
+<td class="bl" align="right">+</td>
+<td align="left">0.0010</td>
+<td class="bl" align="right">+</td>
+<td align="left">0.0015</td>
+<td class="bl" align="right">+</td>
+<td class="br" align="left">0.0020</td>
+</tr>
+
+<tr>
+<td class="bl">Tolerance</td>
+<td class="bl" align="right">&nbsp;</td>
+<td align="left">0.0003</td>
+<td class="bl" align="right">&nbsp;</td>
+<td align="left">0.0003</td>
+<td class="bl" align="right">&nbsp;</td>
+<td align="left">0.0005</td>
+<td class="bl" align="right">&nbsp;</td>
+<td align="left">0.0010</td>
+<td>&nbsp;</td>
+<td class="br" align="left">0.0010</td>
+</tr>
+
+<tr>
+<td class="bt br bl" colspan="12">Allowances for Push Fits</td>
+</tr>
+
+<tr>
+<td class="bt bl" rowspan="3">P</td>
+<td class="bt bl">High Limit</td>
+<td class="bt bl" align="right">-</td>
+<td class="bt" align="left">0.0002</td>
+<td class="bt bl" align="right">-</td>
+<td class="bt" align="left">0.0002</td>
+<td class="bt bl" align="right">-</td>
+<td class="bt" align="left">0.0002</td>
+<td class="bt bl" align="right">-</td>
+<td class="bt" align="left">0.0005</td>
+<td class="bt bl" align="right">-</td>
+<td class="bt br" align="left">0.0005</td>
+</tr>
+
+<tr>
+<td class="bl">Low Limit</td>
+<td class="bl" align="right">-</td>
+<td align="left">0.0007</td>
+<td class="bl" align="right">-</td>
+<td align="left">0.0007</td>
+<td class="bl" align="right">-</td>
+<td align="left">0.0007</td>
+<td class="bl" align="right">-</td>
+<td align="left">0.0010</td>
+<td class="bl" align="right">-</td>
+<td class="br" align="left">0.0010</td>
+</tr>
+
+<tr>
+<td class="bl">Tolerance</td>
+<td class="bl" align="right">&nbsp;</td>
+<td align="left">0.0005</td>
+<td class="bl" align="right">&nbsp;</td>
+<td align="left">0.0005</td>
+<td class="bl" align="right">&nbsp;</td>
+<td align="left">0.0005</td>
+<td class="bl" align="right">&nbsp;</td>
+<td align="left">0.0005</td>
+<td class="bl" align="right">&nbsp;</td>
+<td class="br" align="left">0.0005</td>
+</tr>
+
+<tr>
+<td class="bt br bl" colspan="12">Allowances for Running Fits<a name="Fnanchor_3"></a><a href="#Fn_3" class="fnanchor">[2]</a></td>
+</tr>
+
+<tr>
+<td class="bt bl" rowspan="3">X</td>
+<td class="bt bl">High Limit</td>
+<td class="bt bl" align="right">-</td>
+<td class="bt" align="left">0.0010</td>
+<td class="bt bl" align="right">-</td>
+<td class="bt" align="left">0.0012</td>
+<td class="bt bl" align="right">-</td>
+<td class="bt" align="left">0.0017</td>
+<td class="bt bl" align="right">-</td>
+<td class="bt" align="left">0.0020</td>
+<td class="bt bl" align="right">-</td>
+<td class="bt br" align="left">0.0025</td>
+</tr>
+
+<tr>
+<td class="bl">Low Limit</td>
+<td class="bl" align="right">-</td>
+<td align="left">0.0020</td>
+<td class="bl" align="right">-</td>
+<td align="left">0.0027</td>
+<td class="bl" align="right">-</td>
+<td align="left">0.0035</td>
+<td class="bl" align="right">-</td>
+<td align="left">0.0042</td>
+<td class="bl" align="right">-</td>
+<td class="br" align="left">0.0050</td>
+</tr>
+
+<tr>
+<td class="bl">Tolerance</td>
+<td class="bl" align="right">&nbsp;</td>
+<td align="left">0.0010</td>
+<td class="bl" align="right">&nbsp;</td>
+<td align="left">0.0015</td>
+<td class="bl" align="right">&nbsp;</td>
+<td align="left">0.0018</td>
+<td class="bl" align="right">&nbsp;</td>
+<td align="left">0.0022</td>
+<td class="bl" align="right">&nbsp;</td>
+<td class="br" align="left">0.0025</td>
+</tr>
+
+<tr>
+<td class="bt bl" rowspan="3">Y</td>
+<td class="bt bl">High Limit</td>
+<td class="bt bl" align="right">-</td>
+<td class="bt" align="left">0.0007</td>
+<td class="bt bl" align="right">-</td>
+<td class="bt" align="left">0.0010</td>
+<td class="bt bl" align="right">-</td>
+<td class="bt" align="left">0.0012</td>
+<td class="bt bl" align="right">-</td>
+<td class="bt" align="left">0.0015</td>
+<td class="bt bl" align="right">-</td>
+<td class="bt br" align="left">0.0020</td>
+</tr>
+
+<tr>
+<td class="bl">Low Limit</td>
+<td class="bl" align="right">-</td>
+<td align="left">0.0012</td>
+<td class="bl" align="right">-</td>
+<td align="left">0.0020</td>
+<td class="bl" align="right">-</td>
+<td align="left">0.0025</td>
+<td class="bl" align="right">-</td>
+<td align="left">0.0030</td>
+<td class="bl" align="right">-</td>
+<td class="br" align="left">0.0035</td>
+</tr>
+
+<tr>
+<td class="bl">Tolerance</td>
+<td class="bl" align="right">&nbsp;</td>
+<td align="left">0.0005</td>
+<td class="bl" align="right">&nbsp;</td>
+<td align="left">0.0010</td>
+<td class="bl" align="right">&nbsp;</td>
+<td align="left">0.0013</td>
+<td class="bl" align="right">&nbsp;</td>
+<td align="left">0.0015</td>
+<td class="bl" align="right">&nbsp;</td>
+<td class="br" align="left">0.0015</td>
+</tr>
+
+<tr>
+<td class="bt bl bb" rowspan="3">Z</td>
+<td class="bt bl">High Limit</td>
+<td class="bt bl" align="right">-</td>
+<td class="bt" align="left">0.0005</td>
+<td class="bt bl" align="right">-</td>
+<td class="bt" align="left">0.0007</td>
+<td class="bt bl" align="right">-</td>
+<td class="bt" align="left">0.0007</td>
+<td class="bt bl" align="right">-</td>
+<td class="bt" align="left">0.0010</td>
+<td class="bt bl" align="right">-</td>
+<td class="bt br" align="left">0.0010</td>
+</tr>
+
+<tr>
+<td class="bl">Low Limit</td>
+<td class="bl" align="right">-</td>
+<td align="left">0.0007</td>
+<td class="bl" align="right">-</td>
+<td align="left">0.0012</td>
+<td class="bl" align="right">-</td>
+<td align="left">0.0015</td>
+<td class="bl" align="right">-</td>
+<td align="left">0.0020</td>
+<td class="bl" align="right">-</td>
+<td class="br" align="left">0.0022</td>
+</tr>
+
+<tr>
+<td class="bl bb">Tolerance</td>
+<td class="bl bb" align="right">&nbsp;</td>
+<td class="bb" align="left">0.0002</td>
+<td class="bl bb" align="right">&nbsp;</td>
+<td class="bb" align="left">0.0005</td>
+<td class="bl bb" align="right">&nbsp;</td>
+<td class="bb" align="left">0.0008</td>
+<td class="bl bb" align="right">&nbsp;</td>
+<td class="bb" align="left">0.0010</td>
+<td class="bl bb" align="right">&nbsp;</td>
+<td class="br bb" align="left">0.0012</td>
+</tr>
+
+</table>
+<p>&nbsp;</p>
+
+<hr class="l10" />
+<p class="footnote"><a name="Fn_2" id="Fn_2"></a><span class="label"><a href="#Fnanchor_2">[1]</a>
+</span>Tolerance is provided for holes, which ordinary standard reamers can produce, in two grades,
+Classes A and B, the selection of which is a question for the user's decision and dependent upon
+the quality of the work required; some prefer to use Class A as working limits and Class B as
+inspection limits.</p>
+
+<p class="footnote"><a name="Fn_3" id="Fn_3"></a><span class="label"><a href="#Fnanchor_3">[2]</a>
+</span>Running fits, which are the most commonly required, are divided into three grades:
+Class X for engine and other work where easy fits are wanted; Class Y for high speeds and good
+average machine work; Class Z for fine tool work.</p>
+<hr class="l10" />
+
+<a name="Secnum_3_31" id="Secnum_3_31"></a><p><b>Allowance for Forced Fits.</b>&mdash;The allowance per inch of
+diameter usually ranges from 0.001 inch to 0.0025 inch, 0.0015
+being a fair average. Ordinarily, the allowance per inch decreases
+as the diameter increases; thus the total allowance for
+a diameter of 2 inches might be 0.004 inch, whereas for a diameter
+of 8 inches the total allowance might not be over 0.009 or<span class="pagenum"><a name="Pg_132" id="Pg_132">[132]</a></span>
+0.010 inch. In some shops the allowance is made practically
+the same for all diameters, the increased surface area of the
+larger sizes giving sufficient increase in pressure. The parts to
+be assembled by forced fits are usually made cylindrical, although
+sometimes they are slightly tapered. The advantages
+of the taper form are that the possibility of abrasion of the
+fitted surfaces is reduced; that less pressure is required in
+assembling; and that the parts are more readily separated
+when renewal is required. On the other hand, the taper fit is
+less reliable, because if it loosens, the entire fit is free with but
+little axial movement. Some lubricant, such as white lead and
+lard oil mixed to the consistency of paint, should be applied to
+the pin and bore before assembling, to reduce the tendency of
+abrasion.</p>
+
+<a name="Secnum_3_32" id="Secnum_3_32"></a><p><b>Pressure for Forced Fits.</b>&mdash;The pressure required for assembling
+cylindrical parts depends not only upon the allowance for
+the fit, but also upon the area of the fitted surfaces, the pressure
+increasing in proportion to the distance that the inner member
+is forced in. The approximate ultimate pressure in pounds can
+be determined by the use of the following formula in conjunction
+with the accompanying table of &#8220;<a href="#Pg_132">Pressure Factors</a>.&#8221;</p>
+
+<h4>Pressure Factors</h4>
+
+<table align="center" class="center" width="60%" frame="border" rules="all" cellpadding="4" cellspacing="4" summary="Pressure Factors">
+
+<tr>
+<td>Diameter, Inches</td>
+<td class="br2">Pressure Factor</td>
+<td>Diameter, Inches</td>
+<td class="br2">Pressure Factor</td>
+<td>Diameter, Inches</td>
+<td class="br2">Pressure Factor</td>
+<td>Diameter, Inches</td>
+<td class="br2">Pressure Factor</td>
+<td>Diameter, Inches</td>
+<td>Pressure Factor</td>
+</tr>
+
+<tr>
+<td>1</td>
+<td class="br2">500</td>
+<td>3<sup class="enum">1</sup>/<sub class="denom">2</sub></td>
+<td class="br2">132</td>
+<td>6</td>
+<td class="br2">75</td>
+<td>9</td>
+<td class="br2">48.7</td>
+<td>14</td>
+<td>30.5</td>
+</tr>
+
+<tr>
+<td>1<sup class="enum">1</sup>/<sub class="denom">4</sub></td>
+<td class="br2">395</td>
+<td>3<sup class="enum">3</sup>/<sub class="denom">4</sub></td>
+<td class="br2">123</td>
+<td>6<sup class="enum">1</sup>/<sub class="denom">4</sub></td>
+<td class="br2">72</td>
+<td>9<sup class="enum">1</sup>/<sub class="denom">2</sub></td>
+<td class="br2">46.0</td>
+<td>14<sup class="enum">1</sup>/<sub class="denom">2</sub></td>
+<td>29.4</td>
+</tr>
+
+<tr>
+<td>1<sup class="enum">1</sup>/<sub class="denom">2</sub></td>
+<td class="br2">325</td>
+<td>4</td>
+<td class="br2">115</td>
+<td>6<sup class="enum">1</sup>/<sub class="denom">2</sub></td>
+<td class="br2">69</td>
+<td>10</td>
+<td class="br2">43.5</td>
+<td>15</td>
+<td>28.3</td>
+</tr>
+
+<tr>
+<td>1<sup class="enum">3</sup>/<sub class="denom">4</sub></td>
+<td class="br2">276</td>
+<td>4<sup class="enum">1</sup>/<sub class="denom">4</sub></td>
+<td class="br2">108</td>
+<td>6<sup class="enum">3</sup>/<sub class="denom">4</sub></td>
+<td class="br2">66</td>
+<td>10<sup class="enum">1</sup>/<sub class="denom">2</sub></td>
+<td class="br2">41.3</td>
+<td>15<sup class="enum">1</sup>/<sub class="denom">2</sub></td>
+<td>27.4</td>
+</tr>
+
+<tr>
+<td>2</td>
+<td class="br2">240</td>
+<td>4<sup class="enum">1</sup>/<sub class="denom">2</sub></td>
+<td class="br2">101</td>
+<td>7</td>
+<td class="br2">64</td>
+<td>11</td>
+<td class="br2">39.3</td>
+<td>16</td>
+<td>26.5</td>
+</tr>
+
+<tr>
+<td>2<sup class="enum">1</sup>/<sub class="denom">4</sub></td>
+<td class="br2">212</td>
+<td>4<sup class="enum">3</sup>/<sub class="denom">4</sub></td>
+<td class="br2">96</td>
+<td>7<sup class="enum">1</sup>/<sub class="denom">4</sub></td>
+<td class="br2">61</td>
+<td>11<sup class="enum">1</sup>/<sub class="denom">2</sub></td>
+<td class="br2">37.5</td>
+<td>16<sup class="enum">1</sup>/<sub class="denom">2</sub></td>
+<td>25.6</td>
+</tr>
+
+<tr>
+<td>2<sup class="enum">1</sup>/<sub class="denom">2</sub></td>
+<td class="br2">189</td>
+<td>5</td>
+<td class="br2">91</td>
+<td>7<sup class="enum">1</sup>/<sub class="denom">2</sub></td>
+<td class="br2">59</td>
+<td>12</td>
+<td class="br2">35.9</td>
+<td>17</td>
+<td>24.8</td>
+</tr>
+
+<tr>
+<td>2<sup class="enum">3</sup>/<sub class="denom">4</sub></td>
+<td class="br2">171</td>
+<td>5<sup class="enum">1</sup>/<sub class="denom">4</sub></td>
+<td class="br2">86</td>
+<td>7<sup class="enum">3</sup>/<sub class="denom">4</sub></td>
+<td class="br2">57</td>
+<td>12<sup class="enum">1</sup>/<sub class="denom">2</sub></td>
+<td class="br2">34.4</td>
+<td>17<sup class="enum">1</sup>/<sub class="denom">2</sub></td>
+<td>24.1</td>
+</tr>
+
+<tr>
+<td>3</td>
+<td class="br2">156</td>
+<td>5<sup class="enum">1</sup>/<sub class="denom">2</sub></td>
+<td class="br2">82</td>
+<td>8</td>
+<td class="br2">55</td>
+<td>13</td>
+<td class="br2">33.0</td>
+<td>18</td>
+<td>23.4</td>
+</tr>
+
+<tr>
+<td>3<sup class="enum">1</sup>/<sub class="denom">4</sub></td>
+<td class="br2">143</td>
+<td>5<sup class="enum">3</sup>/<sub class="denom">4</sub></td>
+<td class="br2">78</td>
+<td>8<sup class="enum">1</sup>/<sub class="denom">2</sub></td>
+<td class="br2">52</td>
+<td>13<sup class="enum">1</sup>/<sub class="denom">2</sub></td>
+<td class="br2">31.7</td>
+<td>....</td>
+<td>....</td>
+</tr>
+
+</table>
+
+<p>Assuming that <i>A</i> = area of fitted surface; <i>a</i> = total allowance
+in inches; <i>P</i> = ultimate pressure required, in tons; <i>F</i> =
+pressure factor based upon assumption that the diameter of the<span class="pagenum"><a name="Pg_133" id="Pg_133">[133]</a></span>
+hub is twice the diameter of the bore, that the shaft is of machine
+steel, and the hub of cast iron, then,</p>
+
+<table class="formula" summary="Formula 133_1">
+<tr><td>&nbsp;</td><td>&nbsp;</td><td><i>A</i>&nbsp;&times;&nbsp;<i>a</i>&nbsp;&times;&nbsp;<i>F</i>&nbsp;</td></tr>
+<tr><td>&nbsp;<i>P</i>&nbsp;</td><td>&nbsp;=&nbsp;</td><td>&nbsp;&mdash;&mdash;&mdash;&mdash;&mdash;&nbsp;</td></tr>
+<tr><td>&nbsp;</td><td>&nbsp;</td><td>&nbsp;2&nbsp;</td></tr>
+</table>
+
+<p><i>Example:</i>&mdash;What will be the approximate pressure required
+for forcing a 4-inch machine steel shaft having an allowance of
+0.0085 inch into a cast-iron hub 6 inches long?</p>
+
+<p class="ind05"><i>A</i> = 4&nbsp;&times;&nbsp;3.1416&nbsp;&times;&nbsp;6 = 75.39 square inches;</p>
+
+<p><i>F</i>, for a diameter of 4 inches, = 115 (see table of &#8220;<a href="#Pg_132">Pressure
+Factors</a>&#8221;). Then,</p>
+
+<p class="ind05"><i>P</i> = (75.39&nbsp;&times;&nbsp;0.0085&nbsp;&times;&nbsp;115)/2 = 37 tons, approximately.</p>
+
+<a name="Secnum_3_33" id="Secnum_3_33"></a><p><b>Allowance for Given Pressure.</b>&mdash;By transposing the preceding
+formula, the approximate allowance for a required ultimate
+tonnage can be determined. Thus, <i>a</i> = 2<i>P</i>&nbsp;&divide;&nbsp;<i>AF</i>. The average
+ultimate pressure in tons commonly used ranges from 7 to 10
+times the diameter in inches. Assuming that the diameter of a
+machine steel shaft is 4 inches and an ultimate pressure of about
+30 tons is desired for forcing it into a cast-iron hub having a
+length of 5<sup class="enum">1</sup>/<sub class="denom">2</sub> inches, what should be the allowance?</p>
+
+<p class="ind05"><i>A</i> = 4&nbsp;&times;&nbsp;3.1416&nbsp;&times;&nbsp;5<sup class="enum">1</sup>/<sub class="denom">2</sub> = 69 square inches,</p>
+
+<p><i>F</i>, for a diameter of 4 inches, = 115. Then,</p>
+
+<table class="formula" summary="Formula 133_2">
+<tr><td>&nbsp;</td><td>&nbsp;</td><td>&nbsp;2&nbsp;&times;&nbsp;30&nbsp;</td><td>&nbsp;</td><td>&nbsp;</td></tr>
+<tr><td>&nbsp;<i>a</i>&nbsp;</td><td>&nbsp;=&nbsp;</td><td>&mdash;&mdash;&mdash;&mdash;&mdash;&nbsp;</td><td>&nbsp;=&nbsp;</td>
+<td>0.0075 inch.&nbsp;</td></tr>
+<tr><td>&nbsp;</td><td>&nbsp;</td><td>&nbsp;69&nbsp;&times;&nbsp;115&nbsp;</td><td>&nbsp;</td><td>&nbsp;</td></tr>
+</table>
+
+<a name="Secnum_3_34" id="Secnum_3_34"></a><p><b>Shrinkage Fits.</b>&mdash;When heat is applied to a piece of metal,
+such as iron or steel, as is commonly known, a certain amount
+of expansion takes place which increases as the temperature
+is increased, and also varies somewhat with different kinds of
+metal, copper and brass expanding more for a given increase in
+temperature than iron and steel. When any part which has
+been expanded by the application of heat is cooled, it contracts
+and resumes its original size. This expansive property of
+metals has been taken advantage of by mechanics in assembling
+various machine details. A cylindrical part which is to be held
+in position by a shrinkage fit is first turned a few thousandths<span class="pagenum"><a name="Pg_134" id="Pg_134">[134]</a></span>
+of an inch larger than the hole; the diameter of the latter is
+then increased by heating, and after the part is inserted, the
+heated outer member is cooled, causing it to grip the pin or
+shaft with tremendous pressure.</p>
+
+<p>General practice seems to favor a smaller allowance for
+shrinkage fits than for forced fits, although in many shops the
+allowances are practically the same in each case, and for some
+classes of work, shrinkage allowances exceed those for forced
+fits. In any case, the shrinkage allowance varies to a great extent
+with the form and construction of the part which has to be
+shrunk into place. The thickness or amount of metal around
+the hole is the most important factor. The way in which the
+metal is distributed also has an influence on the results. Shrinkage
+allowances for locomotive driving wheel tires adopted by the
+American Railway Master Mechanics Association are as follows:</p>
+
+<table class="center" align="center" border="0" summary="Shrinkage allowances">
+<tr><td class="left">Center diameter, inches&nbsp;</td><td>&nbsp;38&nbsp;</td><td>&nbsp;44&nbsp;</td><td>&nbsp;50&nbsp;</td>
+<td>&nbsp;56&nbsp;</td><td>&nbsp;62&nbsp;</td><td>&nbsp;66&nbsp;</td></tr>
+<tr><td class="left">Allowance, inches&nbsp;</td><td>&nbsp;0.040&nbsp;</td><td>&nbsp;0.047&nbsp;</td><td>&nbsp;0.053&nbsp;</td>
+<td>&nbsp;0.060&nbsp;</td><td>&nbsp;0.066&nbsp;</td><td>&nbsp;0.070&nbsp;</td></tr>
+</table>
+
+<p>Whether parts are to be assembled by forced or shrinkage
+fits depends upon conditions. For example, to press a driving
+wheel tire over its wheel center, without heating, would ordinarily
+be a rather awkward and difficult job. On the other
+hand, pins, etc., are easily and quickly forced into place with a
+hydraulic press and there is the additional advantage of knowing
+the exact pressure required in assembling, whereas there is
+more or less uncertainty connected with a shrinkage fit, unless
+the stresses are calculated. Tests to determine the difference
+in the quality of shrinkage and forced fits showed that the resistance
+of a shrinkage fit to slippage was, for an axial pull,
+3.66 times greater than that of a forced fit, and in rotation or
+torsion, 3.2 times greater. In each comparative test, the dimensions
+and allowances were the same.</p>
+
+<p>The most important point to consider when calculating
+shrinkage fits is the stress in the hub at the bore, which depends
+chiefly upon the shrinkage allowance. If the allowance
+is excessive, the elastic limit of the material will be exceeded
+and permanent set will occur, or, in extreme cases, the ultimate
+strength of the metal will be exceeded and the hub will burst.</p>
+
+<hr class="c25" />
+<span class="pagenum"><a name="Pg_135" id="Pg_135">[135]</a></span>
+<h2><a name="Chapnum_4" id="Chapnum_4"></a>CHAPTER IV</h2>
+<h3>THREAD CUTTING IN THE LATHE</h3>
+<hr class="c05" />
+
+<p>When threads are cut in the lathe a tool <i>t</i> is used (see <a href="#Fig_4_2">Fig. 2</a>),
+having a point corresponding to the shape of the thread, and
+the carriage is moved along the bed a certain distance for each
+revolution of the work (the distance depending on the number
+of threads to the inch being cut) by the lead-screw <i>S</i> which is
+rotated by gears <i>a</i>, <i>b</i> and <i>c</i>, which receive their motion from the
+spindle. As the amount that the carriage travels per revolution
+of the work, and, consequently, the number of threads
+per inch that is cut, depends on the size of the gears <i>a</i> and <i>c</i>
+(called change gears) the latter have to be changed for cutting
+different threads. The proper change gears to use for cutting
+a given number of threads to the inch is ordinarily determined
+by referring to a table or &#8220;index plate&#8221; <i>I</i> which shows what the
+size of gears <i>a</i> and <i>c</i> should be, or the number of teeth each
+should have, for cutting any given number of threads per inch.</p>
+
+<a name="Fig_4_1" id="Fig_4_1"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/143sm.png" alt="Measuring Number of Threads per Inch&mdash;Setting Thread Tool" /></div>
+<p class="caption750">Fig. 1. Measuring Number of Threads per Inch&mdash;Setting Thread Tool</p>
+</div>
+
+<a name="Fig_4_2" id="Fig_4_2"></a>
+<span class="pagenum"><a name="Pg_136" id="Pg_136">[136]</a></span>
+<div class="figcenter"><div class="illobox750"><img src="images/144sm.png" alt="Plan and Elevations of Engine Lathe" /></div>
+<p class="center"><span class="caption750">Fig. 2. Plan and Elevations of Engine Lathe</span></p>
+</div>
+
+<a name="Secnum_4_1" id="Secnum_4_1"></a><p><b>Selecting the Change Gears for Thread Cutting.</b>&mdash;Suppose a
+V-thread is to be cut on the end of the bolt <i>B</i>, Fig. 2, having
+a diameter of 1<sup class="enum">1</sup>/<sub class="denom">4</sub> inch and seven threads per inch of length, as
+<span class="pagenum"><a name="Pg_137" id="Pg_137">[137]</a></span>
+shown at <i>A</i> in <a href="#Fig_4_1">Fig. 1</a>, which is the standard number of threads
+per inch for that diameter. First the change gears to use are
+found on plate <i>I</i> which is shown enlarged in <a href="#Fig_4_3">Fig. 3</a>. This plate
+has three columns: The first contains different numbers of
+threads to the inch, the second the size gear to place on the
+&#8220;spindle&#8221; or &#8220;stud&#8221; at <i>a</i> (<a href="#Fig_4_2">Fig. 2</a>) for different threads, and the
+third the size of gear <i>c</i> for the lead-screw.
+As the thread selected as
+an example has 7 threads per inch,
+gear <i>a</i> should have 48 teeth, this
+being the number given in the
+second column opposite figure 7
+in the first. By referring to the
+last column, we find that the
+lead-screw gear should have 84
+teeth. These gears are selected
+from an assortment provided with
+the lathe and they are placed on
+the spindle and lead-screw, respectively.</p>
+
+<p>Intermediate gear <i>b</i> does not
+need to be changed as it is simply
+an &#8220;idler&#8221; for connecting gears <i>a</i>
+and <i>c</i>. Gear <i>b</i> is mounted on a
+swinging yoke <i>Y</i> so that it can
+be adjusted to mesh properly with
+different gear combinations; after
+this adjustment is made, the lathe
+is geared for cutting 7 threads to
+the inch. (The change gears of
+many modern lathes are so arranged that different combinations
+are obtained by simply shifting a lever. A lathe having this
+quick-change gear mechanism is described in the latter part of
+this chapter.) The work <i>B</i> is placed between the centers just
+as it would be for turning, with the end to be threaded turned
+to a diameter of 1<sup class="enum">1</sup>/<sub class="denom">4</sub> inch, which is the outside diameter of the
+thread.</p>
+
+<a name="Fig_4_3" id="Fig_4_3"></a>
+<div class="figcenter"><img src="images/145sm.png" alt="Index Plate showing Gear Changes for Threading" />
+<p class="caption750">Fig. 3. Index Plate showing Gear Changes for Threading</p>
+</div>
+
+<p><span class="pagenum"><a name="Pg_138" id="Pg_138">[138]</a></span>
+<a name="Secnum_4_2" id="Secnum_4_2"></a><b>The Thread Tool.</b>&mdash;The form of tool used for cutting a
+V-thread is shown at <i>A</i>, <a href="#Fig_4_4">Fig. 4</a>. The end is ground V-shaped
+and to an angle of 60 degrees, which corresponds to the angle of
+a standard V-thread. The front or flank, <i>f</i> of the tool is ground
+back at an angle to provide clearance, but the top is left flat or
+without slope. As it is very important to grind the end to exactly
+60 degrees, a gage <i>G</i> is used, having 60-degree notches to
+which the tool-point is fitted. The tool is clamped in the toolpost
+as shown in the plan view, <a href="#Fig_4_2">Fig. 2</a>, square with the work, so
+that both sides of the thread will be cut to the same angle with
+the axis of the work. A very convenient way to set a thread
+tool square is illustrated at <i>B</i>, <a href="#Fig_4_1">Fig. 1</a>. The thread gage is placed
+against the part to be threaded, as shown, and the tool is adjusted
+until the angular sides of the point bear evenly in the
+60-degree notch of the gage. The top of the tool point should
+be at the same height as the lathe centers, as otherwise the
+angle of the thread will not be correct.</p>
+
+<a name="Fig_4_4" id="Fig_4_4"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/146sm.png" alt="Thread Tools and Gage for testing Angle of End" /></div>
+<p class="caption750">Fig. 4. Thread Tools and Gage for testing Angle of End</p>
+</div>
+
+<a name="Secnum_4_3" id="Secnum_4_3"></a><p><b>Cutting the Thread.</b>&mdash;The lathe is now ready for cutting the
+thread. This is done by taking several cuts, as indicated at <i>A</i>,
+<i>B</i>, <i>C</i> and <i>D</i> in <a href="#Fig_4_5">Fig. 5</a>, the tool being fed in a little farther for
+each successive cut until the thread is finished. When these
+cuts are being taken, the carriage is moved along the bed, as
+previously explained, by the lead-screw <i>S</i>, <a href="#Fig_4_2">Fig. 2</a>. The carriage
+is engaged with the lead-screw by turning lever <i>u</i> which causes
+the halves of a split nut to close around the screw. The way a
+lathe is handled when cutting a thread is as follows: After the<span class="pagenum"><a name="Pg_139" id="Pg_139">[139]</a></span>
+lathe is started, the carriage is moved until the tool-point is
+slightly beyond the right end of the work, and the tool is fed
+in far enough to take the first cut which, ordinarily, would be
+about <sup class="enum">1</sup>/<sub class="denom">16</sub> inch deep. The carriage is then engaged with the
+lead-screw, by operating lever <i>u</i>, and the tool moves to the left
+(in this case <sup class="enum">1</sup>/<sub class="denom">7</sub> inch for each revolution of the work) and cuts a
+winding groove as at <i>A</i>, <a href="#Fig_4_5">Fig. 5</a>. When the tool has traveled as
+far as the thread is wanted, it is withdrawn by a quick turn of
+cross-slide handle <i>e</i>, and the carriage is returned to the starting
+point for another cut. The tool is then fed in a little farther
+and a second cut is taken as at <i>B</i>, <a href="#Fig_4_5">Fig. 5</a>, and this operation is
+repeated as at <i>C</i> and <i>D</i> until a &#8220;full&#8221; thread is cut or until the
+top of the thread is sharp. The thread is then tested for size
+but before referring to this part of the work, the way the carriage
+is returned to the starting point after each cut should be
+explained.</p>
+
+<a name="Fig_4_5" id="Fig_4_5"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/147sm.png" alt="Thread is formed by taking a Number of Successive Cuts" /></div>
+<p class="caption750">Fig. 5. Thread is formed by taking a Number of Successive Cuts</p>
+</div>
+
+<p>When the tool is withdrawn at the end of the first cut, if the
+carriage is disengaged from the lead-screw and returned by
+hand, the tool may or may not follow the first cut when the carriage
+is again engaged with the lead-screw. If the number of
+threads to the inch being cut is a multiple of the number on the
+lead-screw <i>S</i>, then the carriage can be returned by hand and<span class="pagenum"><a name="Pg_140" id="Pg_140">[140]</a></span>
+engaged with the lead-screw at random and the tool will follow
+the first cut. For example, if the lead-screw has six threads per
+inch, and 6, 12, 18 or any number of threads is being cut that is
+a multiple of six, the carriage can be engaged at any time and the
+tool will always follow the original cut. This is not the case,
+however, when the number of threads being cut is not a multiple
+of the number on the lead-screw.</p>
+
+<p>One method of bringing the carriage back to the starting point,
+when cutting threads which are not multiples, is to reverse the
+lathe (by shifting the overhead driving belts) in order to bring
+the tool back to the starting point without disengaging the
+carriage; in this way the tool is kept in the same relation to the
+work, and the carriage is not disengaged from the lead-screw
+until the thread is finished. This is a good method when cutting
+short threads having a length of say two or three inches;
+but when they are longer, and especially when the diameter is
+comparatively large (which means a slower speed), it is rather
+slow as considerable time is wasted while the tool is moving
+back to its starting point. This is due to the fact that the
+carriage is moved slowly by the lead-screw, but when disengaged,
+it can be traversed quickly by turning handle <i>d</i>, <a href="#Fig_5_2">Fig. 2</a>.</p>
+
+<p>A method of returning the carriage by hand when the number
+of threads being cut is not a multiple of the number on the
+lead-screw is as follows: The tool is moved a little beyond the
+right end of the work and the carriage or split nut is engaged
+with the lead-screw. The lathe is then turned forward by hand
+to take up any lost motion, and a line is made on the lathe
+bed showing the position of the carriage. The positions of the
+spindle and lead-screw are also marked by chalking a tooth on
+both the spindle and lead-screw gears, which happens to be
+opposite a corner or other point on the bed. After a cut is
+taken, the carriage is returned by hand to the original starting
+point as shown by the line on the bed, and is again engaged
+when the chalk marks show that the spindle and lead-screw are
+in their original position; the tool will then follow the first cut.
+If the body of the tailstock is moved against the bridge of the
+carriage before starting the first cut, the carriage can be located<span class="pagenum"><a name="Pg_141" id="Pg_141">[141]</a></span>
+for each following cut by moving it back against the tailstock,
+and it will not be necessary to have a line on the bed.</p>
+
+<a name="Fig_4_6" id="Fig_4_6"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/149sm.png" alt="Indicator used when Cutting Threads" /></div>
+<p class="caption750">Fig. 6. Indicator used when Cutting Threads</p>
+</div>
+
+<a name="Secnum_4_4" id="Secnum_4_4"></a><p><b>Indicator or Chasing Dial for Catching Threads.</b>&mdash;On some
+lathes there is an indicator for &#8220;catching threads,&#8221; as this is
+called in shop language. This is a simple device attached to
+the carriage and consists
+of a graduated
+dial <i>D</i> and a worm-wheel
+<i>W</i> (see <a href="#Fig_4_2">Figs. 2</a>
+and <a href="#Fig_4_6">6</a>) which meshes
+with the lead-screw,
+so that the dial is
+revolved by the lead-screw
+when the carriage
+is stationary,
+and when the carriage
+is moved by the screw,
+the dial remains stationary.
+The indicator
+is used by engaging
+the carriage when
+one of the graduation
+lines is opposite the
+arrow mark; after a
+cut is taken the carriage
+is returned by
+hand and when one of
+the graduation lines
+again moves opposite
+the arrow, the half-nuts are thrown into mesh, as before, and
+this is repeated for each successive cut, thus causing the tool to
+always come right with the thread. If the number of threads per
+inch is even, engagement can be made when any line is opposite
+the arrow, but for odd numbers such as 3, 7, 9, 11, etc., one of
+the four long or numbered lines must be used. Of course, if the
+thread being cut is a multiple of the number on the lead-screw,
+engagement can be made at any time, as previously mentioned.</p>
+
+<a name="Secnum_4_5" id="Secnum_4_5"></a><p><span class="pagenum"><a name="Pg_142" id="Pg_142">[142]</a></span>
+<b>Principle of the Thread Indicator.</b>&mdash;The principle upon
+which the thread indicator operates is as follows: The number
+of teeth in worm-wheel <i>W</i> is some multiple of the number of
+threads per inch of the lead-screw, and the number of teeth in
+the worm-wheel, divided by the pitch of the screw, equals the
+number of graduations on the dial. For example, if the lead-screw
+has six threads per inch, the worm-wheel could have
+twenty-four teeth, in which case the dial would have four divisions,
+each representing an inch of carriage travel, and by sub-dividing
+the dial into eighths (as shown) each line would correspond
+to <sup class="enum">1</sup>/<sub class="denom">2</sub> inch of travel. The dial, therefore, would enable
+the carriage to be engaged with the lead-screw at points equal
+to a travel of one-half inch. To illustrate the advantage of this
+suppose ten threads per inch are being cut and (with the lathe
+stationary) the carriage is disengaged and moved <sup class="enum">1</sup>/<sub class="denom">6</sub> inch or one
+thread on the lead-screw; the tool point will also have moved
+<sup class="enum">1</sup>/<sub class="denom">6</sub> inch, but it will not be opposite the next thread groove in the
+work as the pitch is <sup class="enum">1</sup>/<sub class="denom">10</sub> inch. If the carriage is moved another
+thread on the lead-screw, or <sup class="enum">2</sup>/<sub class="denom">6</sub> inch, the tool will still be out of
+line with the thread on the work, but when it has moved three
+threads, or <sup class="enum">1</sup>/<sub class="denom">2</sub> inch, the tool will then coincide with the original
+cut because it has passed over exactly five threads. This would
+be true for any number of threads per inch that is divisible by
+2. If the thread being cut had nine threads per inch or any
+other odd number, the tool would only coincide with the thread
+at points 1 inch apart. Therefore, the carriage can only be
+engaged when one of the four graduations representing an inch
+of travel is opposite the arrow, when cutting odd threads;
+whereas even numbers can be &#8220;caught&#8221; by using any one of the
+eight lines.</p>
+
+<p>This indicator can also be used for &#8220;catching&#8221; fractional
+threads. As an illustration, suppose 11<sup class="enum">1</sup>/<sub class="denom">2</sub> threads per inch are
+to be cut, and the carriage is engaged for the first cut when
+graduation line 1 is opposite the arrow; engagement would then
+be made for each successive cut, when either line 1 or 3 were
+opposite the arrow, or in other words at spaces equal to a carriage
+movement of 2 inches. As the use of the indicator when<span class="pagenum"><a name="Pg_143" id="Pg_143">[143]</a></span>
+cutting fractional threads is liable to result in error, it is better
+to keep the half-nuts in engagement and return the carriage by
+reversing the lathe.</p>
+
+<a name="Secnum_4_6" id="Secnum_4_6"></a><p><b>Replacing Sharpened Thread Tool.</b>&mdash;If it is necessary to
+sharpen the thread tool before the thread is finished, it should
+be reset square with the work by testing with the thread gage
+as at <i>B</i>, <a href="#Fig_4_1">Fig. 1</a>. The carriage is then engaged with the lead-screw
+and the lathe is turned forward to bring the tool opposite
+the partly finished thread and also to take up any backlash or
+lost motion in the gears or half-nut. If the tool-point is not
+in line with the thread groove previously cut, it can be shifted
+sidewise by feeding the compound rest <i>E</i> in or out, provided
+the latter is set in an angular position as shown in the plan
+view, <a href="#Fig_4_2">Fig. 2</a>.</p>
+
+<p>If the thread tool is ground flat on the top as at <i>A</i>, <a href="#Fig_4_4">Fig. 4</a>, it
+is not a good tool for removing metal rapidly as neither of its
+two cutting edges has any slope. In order to give each cutting
+edge a backward slope, it would be necessary to grind the
+top surface hollow or concave, which would be impracticable.
+When a course thread is to be cut, a tool shaped as at <i>B</i> can be
+used to advantage for rough turning the thread groove, which
+is afterward finished to the correct depth and angle by tool <i>A</i>.
+This roughing tool is ground with a backward slope from the
+point and the latter is rounded to make it stronger.</p>
+
+<a name="Fig_4_7" id="Fig_4_7"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/152sm.png" alt="Cutting Thread by using Compound Rest" /></div>
+<p class="caption750">Fig. 7. Cutting Thread by using Compound Rest</p>
+</div>
+
+<a name="Secnum_4_7" id="Secnum_4_7"></a><p><b>Use of Compound Rest for Thread Cutting.</b>&mdash;Another form
+of thread tool is shown at <i>A</i>, <a href="#Fig_4_7">Fig. 7</a>, which is very good for
+cutting V-threads especially of coarse pitch. When this tool is
+used, the compound rest <i>E</i> is set to an angle of 30 degrees, as
+shown, and it is fed in for the successive cuts by handle <i>w</i> in the
+direction indicated by the arrow. It will be seen that the point
+a of the tool moves at an angle of 60 degrees with the axis of
+the work, thus forming one side of the thread, and the cutting
+edge <i>a&mdash;b</i>, which can be set as shown at <i>B</i>, forms the opposite
+side and does all the cutting. As this edge is given a backward
+slope, as shown, it cuts easily and enables threading operations
+to be performed quickly. Threads cut in this way are often
+finished by taking a light cut with a regular thread tool. The<span class="pagenum"><a name="Pg_144" id="Pg_144">[144]</a></span>
+cutting edge <i>a&mdash;b</i> is ground to an angle of 60 degrees (or slightly
+less, if anything) with the side, as shown by sketch <i>A</i>.</p>
+
+<p>When cutting threads in steel or wrought iron, some sort of
+lubricant is usually applied to the tool to preserve the cutting
+end and give a smooth finish to the thread. Lard oil or a mixture
+of equal parts of lard oil and paraffin oil are often used for this
+purpose. If the thread is small, the lubricant may be applied
+from an ordinary oil can, but when cutting comparatively large
+threads, it is better to have a stream of oil constantly playing
+upon the tool-point. This constant flow may be obtained by
+mounting a can having a spout leading to the tool, on a bracket
+at the rear of the carriage.</p>
+
+<a name="Fig_4_8" id="Fig_4_8"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/153sm.png" alt="Threads" /></div>
+<p class="caption750">Fig. 8. (A) V-thread.<br />(B) U. S. Standard Thread.<br />(C) Square Thread.<br />(D)
+Left-hand Thread.<br />(E) Double Square Thread.<br />(F) Triple Square Thread</p>
+</div>
+
+<a name="Secnum_4_8" id="Secnum_4_8"></a><p><b>Threads Commonly Used.</b>&mdash;Three forms of threads or screws
+which are in common use are shown in <a href="#Fig_4_8">Fig. 8</a>; these are the
+V-thread (<i>A</i>), the U. S. standard (<i>B</i>), and the square thread
+(<i>C</i>). The shapes of these threads are shown by the sectioned
+parts. The V-thread has straight sides which incline at an<span class="pagenum"><a name="Pg_145" id="Pg_145">[145]</a></span>
+angle of 60 degrees with each other and at the same angle with
+the axis of the screw. The U. S. standard thread is similar
+to the V-thread except that the top of the thread and bottom of
+the groove is left flat, as shown, and the width of these flats is
+made equal to <sup class="enum">1</sup>/<sub class="denom">8</sub> of the pitch. The square thread is square in
+section, the width <i>a</i>, depth <i>b</i> and space <i>c</i> being all equal. All
+of these threads are right-hand, which means that the grooves
+wind around to the right so that a nut will have to be turned<span class="pagenum"><a name="Pg_146" id="Pg_146">[146]</a></span>
+toward the right to enter it on the thread. A left-hand thread
+winds in the other direction, as shown at <i>D</i>, and a nut is screwed
+on by turning it to the left.</p>
+
+<a name="Secnum_4_9" id="Secnum_4_9"></a><p><b>Multiple Threads.</b>&mdash;Threads, in addition to being right-and
+left-handed, are single, as at <i>A</i>, <i>B</i>, <i>C</i> and <i>D</i>, double, as at <i>E</i>,
+and triple, as at <i>F</i>, and for certain purposes quadruple threads
+or those of a higher multiple are employed. A double thread
+is different from a single thread in that it has two grooves,
+starting diametrically opposite, whereas a triple thread has three
+grooves cut as shown at <i>F</i>. The object of these multiple
+threads is to obtain an increase in lead without weakening the
+screw. For example, the threads shown at <i>C</i> and <i>E</i> have the
+same pitch <i>p</i> but the lead <i>l</i> of the double-threaded screw is
+twice that of the one with a single thread so that a nut would
+advance twice as far in one revolution, which is often a very
+desirable feature. To obtain the same lead with a single thread,
+the pitch would have to be double, thus giving a much coarser
+thread, which would weaken the screw, unless its diameter
+were increased. (The lead is the distance <i>l</i> that one thread advances
+in a single turn, or the distance that a nut would advance
+in one turn, and it should not be confused with the pitch <i>p</i>,
+which is the distance between the centers of adjacent threads.
+Obviously the lead and pitch of a single thread are the same.)</p>
+
+<a name="Fig_4_9" id="Fig_4_9"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/155sm.png" alt="U. S. Standard Thread, Thread Tool, and Gage" /></div>
+<p class="caption750">Fig. 9. U. S. Standard Thread, Thread Tool, and Gage</p>
+</div>
+
+<a name="Secnum_4_10" id="Secnum_4_10"></a><p><b>Cutting a U. S. Standard Thread.</b>&mdash;The method of cutting a
+U. S. standard thread is the same as described for a V-thread,
+so far as handling the lathe is concerned. The thread tool
+must correspond, of course, to the shape of a U. S. standard
+thread. This tool is first ground to an angle of 60 degrees, as
+it would be for cutting a V-thread, and then the point is made
+flat as shown in <a href="#Fig_4_9">Fig. 9</a>. As will be recalled, the width of this
+flat should be equal to <sup class="enum">1</sup>/<sub class="denom">8</sub> of the pitch. By using a gage like the
+one shown at <i>G</i>, the tool can easily be ground for any pitch, as
+the notches around the periphery of the gage are marked for
+different pitches and the tool-point is fitted into the notch corresponding
+to the pitch wanted. If such a gage is not available, the
+width of the flat at the point can be tested by using, as a gage,
+a U. S. standard tap of the same pitch as the thread to be cut.</p>
+
+<p><span class="pagenum"><a name="Pg_147" id="Pg_147">[147]</a></span>
+When cutting the thread, the tool is set square with the blank,
+and a number of successive cuts are taken, the tool being fed
+in until the width w of the flat at the top of the thread is equal
+to the width at the bottom. The thread will then be the right
+size provided the outside diameter <i>D</i> is correct and the tool is
+of the correct form. As it would be difficult to measure the
+width of this flat accurately, the thread can be tested by screwing
+a standard nut over it if a standard thread is being cut. If
+it is being fitted to a tapped hole, the tap itself is a very convenient
+gage to use, the method being to caliper the tap and
+then compare its size with the work.</p>
+
+<p>A good method of cutting a U. S. standard thread to a given
+size is as follows: First turn the outside of the blank accurately
+to diameter <i>D</i>, and then turn a small part of the end to diameter
+<i>r</i> of the thread at the root. The finishing cut for the thread
+is then taken with the tool point set to just graze diameter <i>r</i>.
+If ordinary calipers were set to diameter <i>r</i> and measurements
+taken in the thread groove, the size would be incorrect owing to<span class="pagenum"><a name="Pg_148" id="Pg_148">[148]</a></span>
+the angularity of the groove, which makes it necessary to hold
+the calipers at an angle when measuring. To determine the
+root diameter divide 1.299 by the number of threads per inch
+and subtract the quotient from the outside diameter. Expressing
+this rule as a formula,</p>
+
+<table class="formula" summary="Formula 148_1">
+
+<tr>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+<td rowspan="3"><span class="row3">(</span></td>
+<td>1.299</td>
+<td rowspan="3"><span class="row3">)</span></td>
+<td>&nbsp;</td>
+</tr>
+
+<tr>
+<td>&nbsp;<i>r</i>&nbsp;</td>
+<td>&nbsp;=&nbsp;</td>
+<td>&nbsp;<i>D</i>&nbsp;</td>
+<td>&nbsp;-&nbsp;</td>
+<td>&nbsp;</td>
+<td>&mdash;&mdash;&mdash;</td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+<td><i>N</i></td>
+<td>&nbsp;</td>
+</tr>
+
+</table>
+
+<p>in which <i>D</i> equals outside diameter; <i>N</i>, the number of threads
+per inch; and <i>r</i>, the root diameter. The number 1.299 is a constant
+that is always used.</p>
+
+<a name="Fig_4_10" id="Fig_4_10"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/156sm.png" alt="End View of Lathe Headstock" /></div>
+<p class="caption750">Fig. 10. End View of Lathe Headstock</p>
+</div>
+
+<a name="Secnum_4_11" id="Secnum_4_11"></a><p><b>Cutting a Left-hand Thread.</b>&mdash;The only difference between
+cutting left-hand and right-hand threads in the lathe is in the
+movement of the tool with relation to the work. When cutting
+a right-hand thread, the tool moves from right to left, but this
+movement is reversed for left-hand threads because the thread
+winds around in the opposite direction. To make the carriage
+travel from left to right, the lead-screw is rotated backwards
+by means of reversing gears <i>a</i> and <i>b</i> (<a href="#Fig_4_10">Fig. 10</a>) located in the
+<span class="pagenum"><a name="Pg_149" id="Pg_149">[149]</a></span>
+headstock. Either of these gears can be engaged with the
+spindle gear by changing the position of lever <i>R</i>. When gear <i>a</i>
+is in engagement, as shown, the drive from the spindle to gear
+<i>c</i> is through gears <i>a</i> and <i>b</i>, but when lever <i>R</i> is raised thus shifting
+<i>b</i> into mesh, the drive is direct and the direction of rotation
+is reversed. The thread is cut by starting the tool at <i>a</i>, <a href="#Fig_4_8">Fig. 8</a>,
+instead of at the end.</p>
+
+<a name="Fig_4_11" id="Fig_4_11"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/157sm.png" alt="End of Square Thread Tool, and Graphic Method of Determining Helix Angle of Thread" /></div>
+<p class="caption750">Fig. 11. End of Square Thread Tool, and Graphic Method of
+Determining Helix Angle of Thread</p>
+</div>
+
+<a name="Secnum_4_12" id="Secnum_4_12"></a><p><b>Cutting a Square Thread.</b>&mdash;The form of tool used for cutting
+a square thread is shown in <a href="#Fig_4_11">Fig. 11</a>. The width <i>w</i> is made
+equal to one-half the pitch of the thread to be cut and the end <i>E</i>
+is at an angle with the shank, which corresponds to the inclination
+<i>x&mdash;y</i> of the threads. This angle <i>A</i> depends upon the
+diameter of the screw and the lead of the thread; it can be determined
+graphically by drawing a line <i>a&mdash;b</i> equal in length to
+the circumference of the screw to be cut, and a line <i>b&mdash;c</i>, at right
+angles, equal in length to the lead of the thread. The angle &alpha;
+between lines <i>a&mdash;b</i> and <i>a&mdash;c</i> will be the required angle <i>A</i>. (See
+end view of thread tool). It is not necessary to have this angle
+accurate, ordinarily, as it is simply to prevent the tool from
+binding against the sides of the thread. The end of a square
+thread tool is shown in section to the right, to illustrate its
+position with relation to the threads. The sides <i>e</i> and <i>e<sub>1</sub></i> are
+ground to slope inward, as shown, to provide additional clearance.</p>
+
+<p><span class="pagenum"><a name="Pg_150" id="Pg_150">[150]</a></span>
+When cutting multiple threads, which, owing to their increased
+lead, incline considerably with the axis of the screw,
+the angles for each side of the tool can be determined independently
+as follows: Draw line <i>a&mdash;b</i> equal in length to the circumference
+of the thread, as before, to obtain the required
+angle <i>f</i> of the rear or following side <i>e<sub>1</sub></i>; the angle <i>l</i> of the opposite
+or leading side is found by making <i>a&mdash;b</i> equal to the circumference
+at the root of the thread. The tool illustrated is for
+cutting right-hand threads; if it were intended for a left-hand
+thread, the end, of course, would incline in the opposite direction.
+The square thread is cut so that the depth <i>d</i> is equal to
+the width. When threading a nut for a square thread screw, it
+is the usual practice to use a tool having a width slightly greater
+than one-half the pitch, to provide clearance for the screw, and
+the width of a tool for threading square-thread taps to be used
+for tapping nuts is made slightly less than one-half the pitch.</p>
+
+<a name="Fig_4_12" id="Fig_4_12"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/159sm.png" alt="Views illustrating how a Double Square Thread is Cut" /></div>
+<p class="caption750">Fig. 12. Views illustrating how a Double Square Thread is Cut</p>
+</div>
+
+<a name="Secnum_4_13" id="Secnum_4_13"></a><p><b>Cutting Multiple Threads.</b>&mdash;When a multiple thread is to be
+cut, such as a double or triple thread, the lathe is geared with
+reference to the number of single threads to the inch. For example,
+the lead of the double thread, shown at <i>B</i>, <a href="#Fig_4_12">Fig. 12</a>, is
+one-half inch, or twice the pitch, and the number of single
+threads to the inch equals 1&nbsp;&divide;&nbsp;<sup class="enum">1</sup>/<sub class="denom">2</sub> = 2. Therefore, the lathe is
+geared for cutting two threads per inch. The first cut is taken
+just as though a single thread were being cut, leaving the work
+as shown at <i>A</i>. When this cut is finished the work is turned
+one-half a revolution (for a double thread) without disturbing
+the position of the lead-screw or carriage, which brings the tool
+midway between the grooves of the single thread as indicated
+by dotted lines. The second groove is then cut, producing a
+double thread as shown at <i>B</i>. In the case of a triple thread,
+the work would be indexed one-third of a revolution after turning
+the first groove, and then another third revolution to locate
+the tool for cutting the last groove. Similarly, for a quadruple
+thread, it would be turned one-quarter revolution after cutting
+each successive groove or thread.</p>
+
+<p>There are different methods of indexing the work when
+cutting multiple threads, in order to locate the tool in the<span class="pagenum"><a name="Pg_151" id="Pg_151">[151]</a></span>
+proper position for cutting another thread groove. Some machinists,
+when cutting a double thread, simply remove the
+work from the lathe and turn it one-half a revolution by placing
+the tail of the driving dog in the opposite slot of the faceplate.
+This is a very simple method, but if the slots are not
+directly opposite or 180 degrees apart, the last thread will not be
+central with the first. Another and better method is to disengage
+the idler gear from the gear on the stud, turn the spindle
+and work one-half, or one-third, of a revolution, as the case
+might be, and then connect the gears. For example, if the
+stud gear had 96 teeth, the tooth meshing with the idler gear
+would be marked with chalk, the gears disengaged, and the
+spindle turned until the chalked tooth had made the required
+part of a revolution, which could be determined by counting
+the teeth. When this method is used, the number of teeth in
+the stud gear must be evenly divisible by two if a double thread
+is being cut, or by three for a triple thread, etc. If the stud is
+not geared to the spindle so that each makes the same number
+of revolutions, the ratio of the gearing must be considered.</p>
+
+<p><span class="pagenum"><a name="Pg_152" id="Pg_152">[152]</a></span>
+<a name="Secnum_4_14" id="Secnum_4_14"></a><b>Setting Tool When Cutting Multiple Threads.</b>&mdash;Another
+method, which can sometimes be used for setting the tool after
+cutting the first groove of a multiple thread, is to disengage the
+lock-nuts from the lead-screw (while the spindle is stationary)
+and move the carriage back whatever distance is required to
+locate the tool in the proper position for taking the second cut.
+Evidently this distance must not only locate the tool in the right
+place, but be such that the lock-nuts can be re-engaged with
+the lead-screw. Beginning with a simple illustration, suppose a
+double thread is being cut having a lead of 1 inch. After the
+first thread groove is cut, the tool can be set in a central position
+for taking the second cut, by simply moving the carriage back
+<sup class="enum">1</sup>/<sub class="denom">2</sub> inch (one-half the lead), or <sup class="enum">1</sup>/<sub class=
+"denom">2</sub> inch plus the lead or any
+multiple of the lead. If the length of the threaded part were
+5 inches, the tool would be moved back far enough to clear the
+end of the work, or say <sup class="enum">1</sup>/<sub class="denom">2</sub>&nbsp;+&nbsp;5 = 5<sup class=
+"enum">1</sup>/<sub class="denom">2</sub> inches. In order to disengage
+the lock-nuts and re-engage them after moving the carriage
+5<sup class="enum">1</sup>/<sub class="denom">2</sub> inches (or any distance equal, in this case, to one-half
+plus a whole number), the lead-screw must have an even number
+of threads per inch.</p>
+
+<p>Assume that a double thread is being cut having 1<sup class="enum">1</sup>/<sub class="denom">4</sub> single
+threads per inch. The lead then would equal 1&nbsp;&divide;&nbsp;1<sup class="enum">1</sup>/<sub class="denom">4</sub> = 0.8
+inch, and if the carriage is moved back 0.8&nbsp;&divide;&nbsp;2 = 0.4 inch, the
+tool will be properly located for the second cut; but the lock-nuts
+could not be re-engaged unless the lead-screw had ten
+threads per inch, which is finer than the pitch found on the
+lead-screws of ordinary engine lathes. However, if the movement
+were 0.4 + 0.8&nbsp;&times;&nbsp;2 = 2 inches, the lock-nuts could be re-engaged
+regardless of the number of threads per inch on the
+lead-screw. The rule then, is as follows:</p>
+
+<p><i>Divide the lead of the thread by 2 for a double thread, 3 for a
+triple thread, 4 for a quadruple thread, etc., thus obtaining the
+pitch; then add the pitch to any multiple of the lead, which will
+give a movement, in inches, that will enable the lock-nuts to be re-engaged
+with the lead-screw.</i></p>
+
+<p>Whenever the number obtained by this rule is a whole number,
+obviously, the movement can be obtained with a lead-screw<span class="pagenum"><a name="Pg_153" id="Pg_153">[153]</a></span>
+of any pitch. If the number is fractional, the number of threads
+per inch on the lead-screw must be divisible by the denominator
+of the fraction.</p>
+
+<p>To illustrate the application of the foregoing rule, suppose a
+quadruple thread is to be cut having 1<sup class="enum">1</sup>/<sub class="denom">2</sub> single threads per inch
+(which would be the number the lathe would be geared to cut).
+Then the lead of the thread = 1&nbsp;&divide;&nbsp;1<sup class="enum">1</sup>/<sub class="denom">2</sub> = 0.6666 inch and the
+pitch = 0.6666&nbsp;&divide;&nbsp;4 = 0.1666 inch; adding the pitch to twice
+the lead we have 0.1666 + 2&nbsp;&times;&nbsp;0.6666 = 1.499 inch. Hence, if
+the carriage is moved 1<sup class="enum">1</sup>/<sub class="denom">2</sub> inch (which will require a lead-screw
+having an even number of threads per inch), the tool will be
+located accurately enough for practical purposes. When the
+tool is set in this way, if it does not clear the end of the part
+being threaded, the lathe can be turned backward to place the
+tool in the proper position.</p>
+
+<p>The foregoing rule, as applied to triple threads or those of a
+higher number, does not always give the only distance that the
+carriage can be moved. To illustrate, in the preceding example
+the carriage movement could be equal to 0.499, or what is practically
+one-half inch, instead of 1<sup class="enum">1</sup>/<sub class="denom">2</sub> inch, and the tool would be
+properly located. The rule, however, has the merit of simplicity
+and can be used in most cases.</p>
+
+<a name="Fig_4_13" id="Fig_4_13"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/161sm.png" alt="Indexing Faceplate used for Multiple Thread Cutting" /></div>
+<p class="caption750">Fig. 13. Indexing Faceplate used for Multiple Thread Cutting</p>
+</div>
+
+<p>Special faceplates are sometimes used for multiple thread
+cutting, that enable work to be easily and accurately indexed.
+One of these is illustrated in <a href="#Fig_4_13">Fig. 13</a>; it consists of two parts <i>A</i>
+<span class="pagenum"><a name="Pg_154" id="Pg_154">[154]</a></span>
+and <i>B</i>, part <i>A</i> being free to rotate in relation to <i>B</i> when bolts <i>C</i>
+are loosened. The driving pin for the lathe dog is attached to
+plate <i>A</i>. When one groove of a multiple thread is finished,
+bolts <i>C</i> are loosened and plate <i>A</i> is turned around an amount
+corresponding to the type of thread being cut. The periphery
+of plate <i>A</i> is graduated in degrees, as shown, and for a double
+thread it would be turned one-half revolution or 180 degrees,
+for a triple thread, 120 degrees, etc. This is a very good arrangement
+where multiple thread cutting is done frequently.</p>
+
+<a name="Fig_4_14" id="Fig_4_14"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/162sm.png" alt="Correct and Incorrect Positions of Tool for Taper Thread Cutting" /></div>
+<p class="caption750">Fig. 14. Correct and Incorrect Positions of Tool for Taper Thread Cutting</p>
+</div>
+
+<a name="Secnum_4_15" id="Secnum_4_15"></a><p><b>Taper Threading.</b>&mdash;When a taper thread is to be cut, the
+tool should be set square with axis <i>a&mdash;a</i> as at <i>A</i>, <a href="#Fig_4_14">Fig. 14</a>, and
+not by the tapering surface as at <i>B</i>. If there is a cylindrical
+part, the tool can be set as indicated by the dotted lines. All
+taper threads should be cut by the use of taper attachments.
+If the tailstock is set over to get the required taper, and an
+ordinary bent-tail dog is used for driving, the curve of the
+thread will not be true, or in other words the thread will not
+advance at a uniform rate; this is referred to by machinists as
+a &#8220;drunken thread.&#8221; This error in the thread is due to the
+angularity between the driving dog and the faceplate, which
+causes the work to be rotated at a varying velocity. The pitch
+of a taper thread that is cut with the tailstock set over will also
+be slightly finer than the pitch for which the lathe is geared.
+The amount of these errors depends upon the angle of the taper
+and the distance that the center must be offset.</p>
+
+<a name="Fig_4_15" id="Fig_4_15"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/163sm.png" alt="Method of setting and using Inside Thread Tool" /></div>
+<p class="caption750">Fig. 15. Method of setting and using Inside Thread Tool</p>
+</div>
+
+<a name="Secnum_4_16" id="Secnum_4_16"></a><p><b>Internal Threading.</b>&mdash;Internal threading, or cutting threads
+in holes, is an operation performed on work held in the chuck or<span class="pagenum"><a name="Pg_155" id="Pg_155">[155]</a></span>
+on a faceplate, as for boring. The tool used is similar to a
+boring tool except that the working end is shaped to conform
+to the thread to be cut. The method of procedure, when cutting
+an internal thread, is similar to that for outside work, as
+far as handling the lathe is concerned. The hole to be threaded
+is first bored to the root diameter <i>D</i>, <a href="#Fig_4_15">Fig. 15</a>, of the screw that is
+to fit into it. The tool-point (of a tool for a U. S. standard or
+V-thread) is then set square by holding a gage <i>G</i> against the
+true side of the work and adjusting the point to fit the notch in
+the gage as shown. The view to the right shows the tool taking
+the first cut.</p>
+
+<p>Very often the size of a threaded hole can be tested by using
+as a gage the threaded part that is to fit into it. When making
+such a test, the tool is, of course, moved back out of the way.
+It is rather difficult to cut an accurate thread in a small hole,
+especially when the hole is quite deep, owing to the flexibility
+of the tool; for this reason threads are sometimes cut slightly
+under size with the tool, after which a tap with its shank end
+held straight by the tailstock center is run through the hole.
+In such a case, the tap should be calipered and the thread made
+just small enough with the tool to give the tap a light cut.
+Small square-threaded holes are often finished in this way, and
+if a number of pieces are to be threaded, the use of a tap makes
+the holes uniform in size.</p>
+
+<a name="Fig_4_16" id="Fig_4_16"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/164sm.png" alt="Cross-slide equipped with Stop for Regulating Depth of Cut when Threading" /></div>
+<p class="caption750">Fig. 16. Cross-slide equipped with Stop for Regulating Depth
+of Cut when Threading</p>
+</div>
+
+<a name="Secnum_4_17" id="Secnum_4_17"></a><p><b>Stop for Thread Tools.</b>&mdash;When cutting a thread, it is rather
+difficult to feed in the tool just the right amount for each successive
+cut, because the tool is moved in before it feeds up to<span class="pagenum"><a name="Pg_156" id="Pg_156">[156]</a></span>
+the work. A stop is sometimes used for threading which overcomes
+this difficulty. This stop consists of a screw <i>S</i>, <a href="#Fig_4_16">Fig. 16</a>,
+which enters the tool slide and passes through a block <i>B</i> clamped
+in front of the slide. The hole in the block through which the
+stop-screw passes is not threaded, but is large enough to permit
+the screw to move freely. When cutting a thread, the tool is
+set for the first cut and the screw is adjusted until the head is
+against the fixed block. After taking the first cut, the stop-screw
+is backed out, say one-half revolution, which allows the
+tool to be fed in far enough for a second cut. If this cut is
+about right for depth, the screw is again turned about one-half
+revolution for the next cut and this is continued for each successive
+cut until the thread is finished. By using a stop of this
+kind, there is no danger of feeding the tool in too far as is often
+done when the tool is set by guess. If this form of stop is used
+for internal threading, the screw, instead of passing through the
+fixed block, is placed in the slide so that the end or head will
+come against the stop <i>B</i>. This change is made because the tool
+is fed outward when cutting an internal thread.</p>
+
+<a name="Fig_4_17" id="Fig_4_17"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/165sm.png" alt="Gage for grinding and setting Acme Thread Tools" /></div>
+<p class="caption750">Fig. 17. Gage for grinding and setting Acme Thread Tools</p>
+</div>
+
+<a name="Secnum_4_18" id="Secnum_4_18"></a><p><b>The Acme Standard Thread.</b>&mdash;The Acme thread is often
+used, at the present time, in place of a square thread. The
+angle between the sides of the Acme thread is 29 degrees (see
+<a href="#Fig_4_21">Fig. 21</a>) and the depth is made equal to one-half the pitch plus
+<span class="pagenum"><a name="Pg_157" id="Pg_157">[157]</a></span>
+0.010 inch to provide clearance and insure a bearing upon the
+sides. The thread tool is ordinarily ground to fit a gage having
+notches representing different pitches. An improved form of
+Acme thread gage is shown in <a href="#Fig_4_17">Fig. 17</a>. The tool point is first
+ground to the correct angle by fitting it to the 29-degree notch
+in the end of the gage, as at <i>A</i>. The end is then ground to the
+proper width for the pitch to be cut, by testing it, as at <i>B</i>. The
+numbers opposite the shallow notches for gaging the width represent
+the number of threads per inch. With this particular gage,
+the tool can be set square by placing edge <i>D</i> against the turned
+surface to be threaded, and adjusting the tool until the end is in
+line with the gage, as at <i>C</i>. By placing the tool in this position,
+the angle between the side and the end can also be tested.</p>
+
+<a name="Fig_4_18" id="Fig_4_18"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/166sm.png" alt="Measuring Width of Acme Thread Tool with Vernier Gear-tooth Caliper" /></div>
+<p class="caption750">Fig. 18. Measuring Width of Acme Thread Tool with Vernier Gear-tooth
+Caliper</p>
+</div>
+
+<p>In case it should be necessary to measure the end width of
+an Acme thread tool, for a pitch not on the regular gage, this
+can be done by using a vernier gear-tooth caliper, as indicated
+in <a href="#Fig_4_18">Fig. 18</a>. If we assume that the caliper jaws bear on the sides
+of the tool at a distance <i>A</i> from the top, equal to <sup class="enum">1</sup>/<sub class="denom">4</sub> inch, then
+the width of the tool point equals the caliper reading (as shown
+by the horizontal scale) minus 0.1293 inch. For example, if the
+caliper reading was 0.315 inch, the width at the point would
+equal 0.315 - 0.1293 = 0.1857 inch, assuming that the sides
+were ground to the standard angle of 29 degrees. The constant<span class="pagenum"><a name="Pg_158" id="Pg_158">[158]</a></span>
+to be subtracted from the caliper reading equals 2 <i>A</i> tan 14&deg; 30'
+or, in this case, 2&nbsp;&times;&nbsp;0.25&nbsp;&times;&nbsp;0.2586 = 0.1293.</p>
+
+<a name="Secnum_4_19" id="Secnum_4_19"></a><p><b>The Whitworth Thread.</b>&mdash;The Whitworth (or British Standard
+Whitworth) thread, which is used principally in Great
+Britain, has an included angle of 55 degrees, and the threads
+are rounded at the top and at the root, as shown in <a href="#Fig_4_23">Fig. 23</a>.
+The shape of the tool used for cutting this thread is also shown
+in this illustration. The end is rounded to form the fillet at
+the root of the thread, and the round corners on the sides give
+the top of the thread the required curvature. Every pitch requires
+a different tool, and the cutting end is given the curved
+form by milling or hobbing. The hob used for this purpose is
+accurately threaded to correspond with the pitch for which
+the tool is required, and then it is fluted to form cutting edges,
+and is hardened. The hob is then used like a milling cutter
+for forming the end of the thread tool. The tool is sharpened
+by grinding on the top. The method of cutting a Whitworth
+thread is, of course, similar to that followed for a U. S. standard
+or V-thread, in that the tool is set square with the unthreaded
+blank and at the same height as the lathe centers, in order to
+secure a thread of the proper form. Care should be taken to
+turn the blank to the right diameter so that the top of the
+thread will be fully rounded when the screw is the required size.
+</p>
+
+<p class="pagenum"><a name="Pg_159" id="Pg_159">[159]</a></p>
+<a name="Fig_4_19" id="Fig_4_19"></a>
+<a name="Fig_4_20" id="Fig_4_20"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/167asm.png" alt="United States Standard Thread and Standard Sharp V-Thread" /></div>
+<p class="caption750">Fig. 19. United States Standard Thread<br />Fig. 20. Standard Sharp V-thread</p>
+</div>
+
+<a name="Fig_4_21" id="Fig_4_21"></a>
+<a name="Fig_4_22" id="Fig_4_22"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/167bsm.png" alt="Acme Standard and Square Thread" /></div>
+<p class="caption750">Fig. 21. Acme Standard Thread<br />Fig. 22. Square Thread</p>
+</div>
+
+<a name="Fig_4_23" id="Fig_4_23"></a>
+<a name="Fig_4_24" id="Fig_4_24"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/167csm.png" alt="Whitworth Standard and Standard Worm Thread" /></div>
+<p class="caption750">Fig. 23. Whitworth Standard Thread<br />Fig. 24. Standard Worm Thread</p>
+</div>
+
+<a name="Secnum_4_20" id="Secnum_4_20"></a><p><span class="pagenum"><a name="Pg_160" id="Pg_160">[160]</a></span>
+<b>Worm Threads.</b>&mdash;The standard worm thread has an angle
+of 29 degrees between the sides, the same as an Acme thread,
+but the depth of a worm thread and the width of the flat at the
+top and bottom differ from the Acme standard, as will be seen
+by comparing <a href="#Fig_4_21">Figs. 21</a> and <a href="#Fig_4_24">24</a>. The whole depth of the thread
+equals the linear pitch multiplied by 0.6866, and the width of
+the thread tool at the end equals the linear pitch multiplied by
+0.31. Gages notched for threads of different pitch are ordinarily
+used when grinding worm thread tools.</p>
+
+<p>When it is necessary to cut multiple-threaded worms of large
+lead in an ordinary lathe, difficulty is sometimes experienced
+because the lead-screw must be geared to run much faster than
+the spindle, thus imposing excessive strains on the gearing.
+This difficulty is sometimes overcome by mounting a belt pulley
+on the lead-screw, beside the change gear, and connecting
+it to the countershaft by a belt; the spindle is then driven
+through the change gearing from the lead-screw, instead of <i>vice
+versa</i>.</p>
+
+<a name="Secnum_4_21" id="Secnum_4_21"></a><p><b>Coarse Threading Attachment.</b>&mdash;To avoid the difficulties
+connected with cutting threads of large lead, some lathes are
+equipped with a coarse screw-cutting attachment. The arrangement
+of this attachment, as made by the Bradford Machine
+Tool Co., is as follows: On the usual reversing shaft, and inside
+of the headstock, there is a sliding double gear, so arranged as
+to be engaged with either the usual gear on the spindle, or with
+a small pinion at the end of the cone. The gears are so proportioned
+that the ratio of the two engagements is as 10 to 1;
+that is, when engaged with the cone gear (the back-gears being
+thrown in) the mating gear will make ten revolutions to one of
+the spindle, so that when the lathe is ordinarily geared to cut
+one thread per inch, it will, when driven by the cone pinion,
+cut one thread in ten inches. This construction dispenses with
+the extra strain on the reverse gears due to moving the carriage
+at the rapid rate that would be necessary for such a large
+lead, when not using an attachment. These attachments are
+not only extensively used for the cutting of coarse screws but
+for cutting oil grooves on cylindrical parts.</p>
+
+<p><span class="pagenum"><a name="Pg_161" id="Pg_161">[161]</a></span>When cutting a thread
+of large lead or &#8220;steep pitch,&#8221; the top
+of the thread tool should be ground so that it is at right angles
+to the thread; then the thread groove will be cut to the same
+width as the tool.</p>
+
+<a name="Secnum_4_22" id="Secnum_4_22"></a><p><b>Testing the Size of a Thread.</b>&mdash;When the thread tool has
+been fed in far enough to form a complete thread, the screw is
+then tested for size. If we assume that a bolt is being threaded
+for a standard nut, it would be removed from the lathe and the
+test made by screwing a nut on the end. If the thread were
+too large, the nut might screw on very tightly or not at all; in
+either case, the work would again be placed in the lathe and a
+light cut taken over it to reduce the thread to the proper size.
+When replacing a threaded part between the centers, it should
+be put back in the original position, that is, with the &#8220;tail&#8221; of
+the driving dog in the same slot of the faceplate it previously
+occupied.</p>
+
+<a name="Fig_4_25" id="Fig_4_25"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/169sm.png" alt="Testing Diameter of Thread with Calipers and Micrometer" /></div>
+<p class="caption750">Fig. 25. Testing Diameter of Thread with Calipers and Micrometer</p>
+</div>
+
+<p>As it is difficult to tell just when a thread is cut to the exact
+size, special thread calipers having wedge-shaped ends are
+sometimes used for measuring the diameter of a V-thread or a
+U. S. standard thread, at the bottom of the grooves or the root
+diameter, as shown at <i>A</i> in <a href="#Fig_4_25">Fig. 25</a>. These calipers can be set
+from a tap corresponding to the size of the thread being cut, or
+from a previously threaded piece of the right size.</p>
+
+<p><span class="pagenum"><a name="Pg_162" id="Pg_162">[162]</a></span>
+<a name="Secnum_4_23" id="Secnum_4_23"></a><b>The Thread Micrometer.</b>&mdash;Another form of caliper for testing
+threads is shown at <i>B</i>. This is one of the micrometer type
+and is intended for very accurate work. The spindle of this
+micrometer has a conical end and the &#8220;anvil&#8221; is V-shaped,
+and these ends bear on the sides of the thread or the surfaces
+which form the bearing when the screw is inserted in a nut or
+threaded hole. The cone-shaped point is slightly rounded so
+that it will not bear in the bottom of the thread. There is also
+sufficient clearance at the bottom of the V-shaped anvil to prevent
+it from bearing on top of the thread. The diameter as
+indicated by this micrometer is the &#8220;pitch diameter&#8221; of the
+thread and is equal to the outside diameter minus the depth of
+one thread. This depth may be determined as follows:</p>
+
+<p class="ind05">Depth of a V-thread = 0.866&nbsp;&divide;&nbsp;No. of threads per inch;</p>
+
+<p class="ind05">Depth of a U. S. standard thread = 0.6495&nbsp;&divide;&nbsp;No. of threads
+per inch;</p>
+
+<p class="ind05">Depth of Whitworth thread = 0.6403&nbsp;&divide;&nbsp;No. of threads per inch.</p>
+
+<p>The movable point measures all pitches, but the fixed anvil
+is limited in its capacity, for if made large enough to measure a
+thread of, say, <sup class="enum">1</sup>/<sub class="denom">4</sub>-inch pitch, it would be too wide at the top to
+measure a thread of <sup class="enum">1</sup>/<sub class="denom">24</sub>-inch pitch, hence each caliper is limited
+in the range of threads that the anvil can measure. When
+measuring the &#8220;angle diameter&#8221; of a thread, the micrometer
+should be passed back and forth across the thread, in order to
+make sure that the largest dimension or the actual diameter is
+being measured. If the micrometer is placed over what seems
+to be the center of the screw and the reading is taken by simply
+adjusting in the anvil or point against the thread, without moving
+the micrometer back and forth across it, an incorrect reading
+may be obtained.</p>
+
+<a name="Fig_4_26" id="Fig_4_26"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/171sm.png" alt="Testing Thread" /></div>
+<p class="caption750">Fig. 26. (A) Testing Size of Thread with Ball-point Micrometer.<br />(B) Testing Size
+of V-thread by the Three-wire System.<br />(C) Testing the Size of a U. S. Standard Thread</p>
+</div>
+
+<p>If standard threaded reference gages are available, the size
+of the thread being cut can be tested by comparing it with the
+gage. Micrometers having small spherical measuring ends (see
+sketch <i>A</i>, <a href="#Fig_4_26">Fig. 26</a>) are sometimes used for this purpose. The
+ball points are small enough to bear against the sides of the
+thread and the diameter, as compared with the reference gage,
+can be determined with great accuracy.</p>
+
+<p><span class="pagenum"><a name="Pg_163" id="Pg_163">[163]</a></span>
+<a name="Secnum_4_24" id="Secnum_4_24"></a><b>Three-wire System of Measuring Threads.</b>&mdash;A method of
+measuring threads by using an ordinary micrometer and three
+wires of equal diameter is illustrated at <i>B</i> and <i>C</i>, <a href="#Fig_4_26">Fig. 26</a>. Two
+wires are placed between the threads on one side and one on the
+opposite side of the screw. The dimension <i>M</i> over the wires is
+then measured with an ordinary micrometer. When the thread
+is cut to a standard size, the dimension <i>M</i> for different threads
+is as follows:</p>
+
+<p>For a U. S. standard thread:</p>
+
+<p class="ind05"><i>m</i> = <i>d</i> - 1.5155<i>p</i> + 3<i>w</i></p>
+
+<p>For a sharp V-thread:</p>
+
+<p class="ind05"><i>m</i> = <i>d</i> - 1.732<i>p</i> + 3<i>w</i></p>
+
+<p>For a Whitworth standard thread:</p>
+
+<p class="ind05"><i>m</i> = <i>d</i> - 1.6008<i>p</i> + 3.1657<i>w</i></p>
+
+<p>In these formulas, <i>d</i> = standard outside diameter of screw;
+<i>m</i> = measurement over wires; <i>w</i> = diameter of wires; <i>p</i> =
+pitch of thread = 1&nbsp;&divide;&nbsp;number of threads per inch.</p>
+
+<p>To illustrate the use of the formula for the U. S. standard
+thread, let us assume that a screw having 6 threads per inch
+(<sup class="enum">1</sup>/<sub class="denom">6</sub>-inch pitch) is to be cut to a diameter of 1<sup class="enum">1</sup>/<sub
+class="denom">2</sub> inch, and that wires<span class="pagenum"><a name="Pg_164" id="Pg_164">[164]</a></span>
+0.140 inch diameter are to be used in conjunction with a micrometer
+for measurement. Then the micrometer reading <i>m</i> should
+be</p>
+
+<p class="ind05">1<sup class="enum">1</sup>/<sub class="denom">2</sub> - 1.5155&nbsp;&times;&nbsp;<sup class="enum">1</sup>/<sub
+class="denom">6</sub> + 3&nbsp;&times;&nbsp;0.140 = 1.6674 inch</p>
+
+<p>If the micrometer reading were 1.670 inch, it would indicate
+that the pitch diameter of the screw was too large, the error
+being equal to difference between 1.667 and the actual reading.</p>
+
+<a name="Fig_4_27" id="Fig_4_27"></a>
+<div class="figcenter"><img src="images/172sm.jpg" alt="Rivett-Dock Circular Threading Tool in Working Position" />
+<p class="caption750">Fig. 27. Rivett-Dock Circular Threading Tool in Working Position</p>
+</div>
+
+<a name="Secnum_4_25" id="Secnum_4_25"></a><p><b>Rivett-Dock Threading Tool.</b>&mdash;A special form of thread tool,
+which overcomes a number of disadvantages common to an
+ordinary single-point thread tool, is shown in <a href="#Fig_4_27">Fig. 27</a>. This
+tool has a circular-shaped cutter <i>C</i>, having ten teeth around its
+circumference, which, beginning with tooth No. 1, gradually increase
+in height, cutter No. 2 being higher than No. 1, etc.
+This cutter is mounted on a slide <i>S</i>, that is fitted to the frame
+<i>F</i>, and can be moved in or out by lever <i>L</i>. The hub of this lever
+has an eccentric stud which moves slide <i>S</i> and locks it when
+in the forward or cutting position. The action of the lever in
+moving the slide engages the cutter with pawl <i>P</i>, thus rotating
+the cutter one tooth at a time and presenting a different tooth
+to the work for each movement of the lever. When the slide is<span class="pagenum"><a name="Pg_165" id="Pg_165">[165]</a></span>
+moved forward, the heel or underside of the tooth which is in
+the working position rests on a stop that takes the thrust of
+the cut.</p>
+
+<p>When the tool is in use, it is mounted on the tool-block of the
+lathe as shown in the illustration. The cutter is set for height
+by placing a tooth in the working position and setting the top
+level with the lathe center. The cutter is also set square with
+the work by using an ordinary square, and it is tilted slightly
+from the vertical to correspond with the angle of the thread to
+be cut, by adjusting frame <i>F</i>. At first a light cut is taken with
+lever <i>L</i> moved forward and tooth No. 1 on the stop. After
+this cut is completed, the lever is reversed which rotates the
+cutter one tooth, and the return movement places tooth No. 2
+in the working position. This operation is repeated until the
+tenth tooth finishes the thread. It is often necessary, when
+using a single-point thread tool, to re-sharpen it before taking
+the finishing cut, but with a circular tool this is not necessary,
+for by using the different teeth successively, the last tooth,
+which only takes finishing cuts, is kept in good condition.</p>
+
+<a name="Secnum_4_26" id="Secnum_4_26"></a><p><b>Cutting Screws to Compensate for Shrinkage.</b>&mdash;Some tool
+steels are liable to shrink more or less when they are hardened;
+consequently if a very accurate hardened screw is required, it is
+sometimes cut so that the pitch is slightly greater than standard,
+to compensate for the shrinkage due to the hardening
+operation. As the amount of contraction incident to hardening
+is very little, it is not practicable to use change gears that will
+give the exact pitch required. A well-known method of obtaining
+this increase of pitch is by the use of a taper attachment.</p>
+
+<a name="Fig_4_28" id="Fig_4_28"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/174sm.png" alt="Diagram Illustrating Method of Cutting a Thread to Compensate for the Error in Pitch due to Shrinkage in Hardening" /></div>
+<p class="caption750">Fig. 28. Diagram Illustrating Method of Cutting a Thread to<br />Compensate for the Error in Pitch
+due to Shrinkage in Hardening</p>
+</div>
+
+<p>For example, suppose a tap having 8 threads per inch is to be
+threaded, and, owing to the contraction of the steel, the pitch
+must be 0.12502 inch instead of 0.125 inch. The lathe is geared
+to cut 8 threads per inch or 0.125 inch pitch, and then the
+taper attachment is set to an angle <i>a</i>, <a href="#Fig_4_28">Fig. 28</a>, the cosine of
+which equals 0.125&divide;0.12502; that is, the cosine of angle <i>a</i> equals <i>the
+pitch required after hardening</i>, divided by the <i>pitch necessary to
+compensate for shrinkage</i>. The angle is then found by referring<span class="pagenum"><a name="Pg_166" id="Pg_166">[166]</a></span>
+to a table of cosines. The tap blank is also set to the same
+angle a by adjusting the tailstock center, thus locating the axis
+of the work parallel with the slide of the taper attachment.
+When the carriage moves a distance <i>x</i>, the tool point will have
+moved a greater distance <i>y</i> along the work, the difference between
+x and y depending upon angle <i>a</i>; hence the tool will cut
+a thread of slightly greater pitch than the lathe is geared to cut.</p>
+
+<p>To illustrate by using the preceding example, cosine of angle
+<i>a</i> = 0.125&divide;0.12502 = 0.99984. By referring to a table of cosines, we
+find that 0.99984 is the cosine of 1 degree, approximately;
+hence, the taper attachment slide and the work should be set
+to this angle. (The angle <i>a</i> in <a href="#Fig_4_28">Fig. 28</a> has been exaggerated in
+order to more clearly illustrate the principle.)</p>
+
+<p>As is well known, it is objectionable to cut a thread with the
+tailstock center offset, because the work is not rotated at a
+uniform velocity, owing to the fact that the driving dog is at an
+angle with the faceplate. For a small angle such as 1 degree,
+however, the error resulting from this cause would be very
+small.</p>
+
+<p>If a thread having a pitch slightly less than standard is
+needed to fit a threaded part which has contracted in hardening,
+the taper attachment can also be used provided the lathe
+is equipped with special gears to cut a little less than the required
+<span class="pagenum"><a name="Pg_167" id="Pg_167">[167]</a></span>
+pitch. Suppose a screw having a pitch of 0.198 inch is
+required to fit the thread of a nut the pitch of which has been
+reduced from 0.200 inch to 0.198 inch. If gears having 83 and
+84 teeth are available, these can be inserted in a compound
+train, so as to reduce the 0.200 inch pitch that would be obtained
+with the regular gearing, to <sup class="enum">83</sup>/<sub class="denom">84</sub> of 0.200 or 0.19762 inch.
+This pitch, which is less than the 0.198 inch pitch required, is
+then increased by using the taper attachment as previously described.
+(This method was described by Mr. G. H. Gardner
+in <span class="smcap">Machinery</span>, February, 1914.)</p>
+
+<a name="Secnum_4_27" id="Secnum_4_27"></a><p><b>Calculating Change Gears for Thread Cutting.</b>&mdash;As previously
+mentioned, the change gears for cutting threads of various
+pitches are shown by a table or &#8220;index plate&#8221; attached to
+the lathe. The proper gears to be used can be calculated, but
+the use of the table saves time and tends to avoid mistakes.
+Every machinist, however, should know how to determine the
+size of gears used for cutting any number of threads to the
+inch. Before referring to any rules, let us first consider why a
+lathe cuts a certain number of threads to the inch and how this
+number is changed by the use of different gears.</p>
+
+<a name="Fig_4_29" id="Fig_4_29"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/176sm.png" alt="Lathe with Simple Gearing for Thread Cutting, Compound Geared Lathe" /></div>
+<p class="caption750">Fig. 29. (A) Lathe with Simple Gearing for Thread Cutting.<br />(B) Compound Geared Lathe</p>
+</div>
+
+<p>As the carriage <i>C</i> and the tool are moved by the lead-screw
+<i>S</i> (see <a href="#Fig_4_2">Fig. 2</a>), which is geared to the spindle, the number of
+threads to the inch that are cut depends, in every case, upon the
+number of turns the work makes while the lead-screw is moving
+the carriage one inch. If the lead-screw has six threads per
+inch, it will make six revolutions while the carriage and the
+thread tool travel one inch along the piece to be threaded.
+Now if the change gears <i>a</i> and <i>c</i> (see also sketch <i>A</i>, <a href="#Fig_4_29">Fig. 29</a>) are
+so proportioned that the spindle makes the same number of
+revolutions as the lead-screw, in a given time, it is evident that
+the tool will cut six threads per inch. If the spindle revolved
+twice as fast as the lead-screw, it would make twelve turns
+while the tool moved one inch, and, consequently, twelve threads
+per inch would be cut; but to get this difference in speeds it is
+necessary to use a combination of gearing that will cause the
+lead-screw to revolve once while the lathe spindle and work
+make two revolutions.</p>
+
+<p><span class="pagenum"><a name="Pg_168" id="Pg_168">[168]</a></span>Suppose that nine threads to the inch are to be cut and the
+lead-screw has six threads per inch. In this case the work must
+make nine revolutions while the lead-screw makes six and causes
+the carriage and thread tool to move one inch, or in other words,
+one revolution of the lead-screw corresponds to one and one-half
+revolution of the spindle; therefore, if the lead-screw gear
+<i>c</i> has 36 teeth, the gear <i>a</i> on the spindle stud should have
+24 teeth. The spindle will then revolve one and one-half times
+faster than the lead-screw, provided the stud rotates at the
+same rate of speed as the main lathe spindle. The number of
+teeth in the change gears that is required for a certain pitch
+can be found by multiplying the number of threads per inch of
+the lead-screw, and the number of threads per inch to be cut,
+by the same trial multiplier. The formula which expresses the
+relation between threads per inch of lead-screw, threads per<span class="pagenum"><a name="Pg_169" id="Pg_169">[169]</a></span>
+inch to be cut, and the number of teeth in the change gears, is
+as follows:</p>
+
+<table class="formula" summary="Formula 169_1">
+<tr><td>&nbsp;threads per inch of lead-screw</td><td>&nbsp;</td><td>&nbsp;teeth in gear on spindle stud&nbsp;</td></tr>
+<tr><td>&nbsp;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&nbsp;</td><td>&nbsp;=&nbsp;</td><td>&nbsp;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&nbsp;</td></tr>
+<tr><td>&nbsp;threads per inch to be cut&nbsp;</td><td>&nbsp;</td><td>&nbsp;teeth in gear on lead-screw&nbsp;</td></tr>
+</table>
+
+<p>Applying this to the example given, we have 6&divide;9 = 24&divide;36. The
+values of 36 and 24 are obtained by multiplying 6 and 9, respectively,
+by 4, which, of course, does not change the proportion.
+Any other number could be used as a multiplier, and if gears
+having 24 and 36 teeth were not available, this might be necessary.
+For example, if there were no gears of this size, some
+other multiplier as 5 or 6 might be used.</p>
+
+<p>Suppose the number of teeth in the change gears supplied
+with the lathe are 24, 28, 32, 36, etc., increasing by four teeth
+up to 100, and assume that the lead-screw has 6 threads per
+inch and that 10 threads per inch are to be cut. Then,</p>
+
+<table class="formula" summary="Formula 169_2">
+
+<tr>
+<td>&nbsp;6&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;6&nbsp;&times;&nbsp;4&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;24&nbsp;</td>
+</tr>
+
+<tr>
+<td>&nbsp;&mdash;&nbsp;</td>
+<td>&nbsp;=&nbsp;</td>
+<td>&nbsp;&mdash;&mdash;&mdash;&nbsp;</td>
+<td>&nbsp;=&nbsp;</td>
+<td>&nbsp;&mdash;&nbsp;</td>
+</tr>
+
+<tr>
+<td>&nbsp;10&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;10&nbsp;&times;&nbsp;4&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;40&nbsp;</td>
+</tr>
+
+</table>
+
+<p>By multiplying both numerator and denominator by 4, we
+obtain two available gears having 24 and 40 teeth, respectively.
+The 24-tooth gear goes on the spindle stud and, the 40-tooth gear
+on the lead-screw. The number of teeth in the intermediate or
+&#8220;idler&#8221; gear <i>b</i>, which connects the stud and lead-screw gears, is
+not considered as it does not affect the ratios between gears <i>a</i>
+and <i>c</i>, but is used simply to transmit motion from one gear to
+the other.</p>
+
+<p>We have assumed in the foregoing that the spindle stud (on
+which gear <i>a</i> is mounted) and the main spindle of the lathe are
+geared in the ratio of one to one and make the same number of
+revolutions. In some lathes, however, these two members do
+not rotate at the same speed, so that if equal gears were placed
+on the lead-screw and spindle stud, the spindle would not make
+the same number of revolutions as the lead-screw. In that case
+if the actual number of threads per inch in the lead-screw were
+used when calculating the change gears, the result would be
+incorrect; hence, to avoid mistakes, the following general rule<span class="pagenum"><a name="Pg_170" id="Pg_170">[170]</a></span>
+should be used as it gives the correct result, regardless of the
+ratios of the gears which connect the spindle and spindle stud:</p>
+
+<p><i>Rule.&mdash;First find the number of threads per inch that is cut
+when gears of the same size are placed on the lead-screw and spindle,
+either by actual trial or by referring to the index plate. Then
+place this number as the numerator of a fraction and the number
+of threads per inch to be cut, as the denominator; multiply both
+numerator and denominator by some trial number, until numbers
+are obtained which correspond to numbers of teeth in gears that are
+available.</i> The product of the trial number and the numerator
+(or &#8220;lathe screw constant&#8221;) represents the gear <i>a</i> for the spindle
+stud, and the product of the trial number and the denominator,
+the gear for the lead-screw.</p>
+
+<a name="Secnum_4_28" id="Secnum_4_28"></a><p><b>Lathes with Compound Gearing.</b>&mdash;When gearing is arranged
+as shown at <i>A</i>, <a href="#Fig_4_29">Fig. 29</a>, it is referred to as simple gearing, but
+sometimes it is necessary to introduce two gears between the
+stud and screw as at <i>B</i>, which is termed compound gearing.
+The method of figuring compound gearing is practically the same
+as that for simple gearing. To find the change gears used in
+compound gearing, place the &#8220;screw constant&#8221; obtained by the
+foregoing rule, as the numerator, and the number of threads per
+inch to be cut as the denominator of a fraction; resolve both
+numerator and denominator into two factors each, and multiply
+each &#8220;pair&#8221; of factors by the same number, until values are
+obtained representing numbers of teeth in available change
+gears. (One factor in the numerator and one in the denominator
+make a &#8220;pair&#8221; of factors.)</p>
+
+<p>Suppose the lathe cuts 6 threads per inch when gears of equal
+size are used, and that the number of teeth in the gears available
+are 30, 35, 40 and so on, increasing by 5 up to 100. If 24
+threads per inch are to be cut, the screw constant 6 is placed in
+the numerator and 24 in the denominator. The numerator and
+denominator are then divided into factors and each pair of
+factors is multiplied by the same number to find the gears,
+thus:</p>
+
+<table class="formula" summary="Formula 170_1">
+
+<tr>
+<td>&nbsp;6&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;2&nbsp;&times;&nbsp;3&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;(2&nbsp;&times;&nbsp;20)&nbsp;&times;&nbsp;(3&nbsp;&times;&nbsp;10)</td>
+<td>&nbsp;</td>
+<td>&nbsp;40&nbsp;&times;&nbsp;30&nbsp;</td>
+</tr>
+
+<tr>
+<td>&nbsp;&mdash;&nbsp;</td>
+<td>&nbsp;=&nbsp;</td>
+<td>&nbsp;&mdash;&mdash;&mdash;&nbsp;</td>
+<td>&nbsp;=&nbsp;</td>
+<td>&nbsp;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&nbsp;</td>
+<td>&nbsp;=&nbsp;</td>
+<td>&nbsp;&mdash;&mdash;&mdash;&nbsp;</td>
+</tr>
+
+<tr>
+<td>&nbsp;24&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;4&nbsp;&times;&nbsp;6&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;(4&nbsp;&times;&nbsp;20)&nbsp;&times;&nbsp;(6&nbsp;&times;&nbsp;10)</td>
+<td>&nbsp;</td>
+<td>&nbsp;80&nbsp;&times;&nbsp;60&nbsp;</td>
+</tr>
+
+</table>
+
+<p><span class="pagenum"><a name="Pg_171" id="Pg_171">[171]</a></span>The last four numbers indicate the gears which should be used.
+The upper two having 40 and 30 teeth are the <i>driving</i> gears
+and the lower two having 80 and 60 teeth are the <i>driven</i> gears.
+The driving gears are gear <i>a</i> on the spindle stud and gear <i>c</i> on
+the intermediate stud, meshing with the lead-screw gear, and
+the driven gears are gears <i>b</i> and <i>d</i>. It makes no difference which
+of the driving gears is placed on the spindle stud, or which of
+the driven is placed on the lead-screw.</p>
+
+<a name="Secnum_4_29" id="Secnum_4_29"></a><p><b>Fractional Threads.</b>&mdash;Sometimes the lead of a thread is
+given as a fraction of an inch instead of stating the number
+of threads per inch. For example, a thread may be required
+to be cut, having <sup class="enum">3</sup>/<sub class="denom">8</sub>-inch lead. The expression &#8220;<sup
+class="enum">3</sup>/<sub class="denom">8</sub>-inch lead&#8221;
+should first be transformed to &#8220;number of threads per inch.&#8221;
+The number of threads per inch (the thread being single) equals:</p>
+
+<table class="formula2" summary="Formula 171_1">
+
+<tr>
+<td>&nbsp;1&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;3&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;8&nbsp;</td>
+<td>&nbsp;</td>
+</tr>
+
+<tr>
+<td>&nbsp;&mdash;&mdash;&mdash;&nbsp;</td>
+<td>&nbsp;=&nbsp;</td>
+<td>&nbsp;1&nbsp;&nbsp;&divide;&nbsp;</td>
+<td>&nbsp;&mdash;&nbsp;</td>
+<td>&nbsp;=&nbsp;</td>
+<td>&nbsp;&mdash;&nbsp;</td>
+<td>&nbsp;=&nbsp;&nbsp;2<sup class="enum">2</sup>/<sub class="denom">3</sub></td>
+</tr>
+
+<tr>
+<td>&nbsp;3&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;8&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;3&nbsp;</td>
+<td>&nbsp;</td>
+</tr>
+
+<tr>
+<td>&nbsp;&mdash;&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+</tr>
+
+<tr>
+<td>&nbsp;8&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+</tr>
+
+</table>
+
+<p>To find the change gears to cut 2<sup class="enum">2</sup>/<sub class="denom">3</sub> threads per inch in a lathe
+having a screw constant of 8 and change gears varying from 24
+to 100 teeth, increasing by 4, proceed as follows:</p>
+
+<table class="formula2" summary="Formula 171_2">
+
+<tr>
+<td>&nbsp;8&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;2&nbsp;&times;&nbsp;4&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;(2&nbsp;&times;&nbsp;36)&nbsp;&times;&nbsp;(4&nbsp;&times;&nbsp;24)&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;72&nbsp;&times;&nbsp;96&nbsp;</td>
+</tr>
+
+<tr>
+<td>&nbsp;&mdash;&nbsp;</td>
+<td>&nbsp;=&nbsp;</td>
+<td>&nbsp;&mdash;&mdash;&mdash;&nbsp;</td>
+<td>&nbsp;=&nbsp;</td>
+<td>&nbsp;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&nbsp;</td>
+<td>&nbsp;=&nbsp;</td>
+<td>&nbsp;&mdash;&mdash;&mdash;&mdash;&nbsp;</td>
+</tr>
+
+<tr>
+<td>&nbsp;2<sup class="enum">2</sup>/<sub class="denom">3</sub>&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;1&nbsp;&times;&nbsp;2<sup class="enum">2</sup>/<sub class="denom">3</sub>&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;(1&nbsp;&times;&nbsp;36)&nbsp;&times;&nbsp;(2<sup class="enum">2</sup>/<sub class="denom">3</sub>&nbsp;&times;&nbsp;24)&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;36&nbsp;&times;&nbsp;64&nbsp;</td>
+</tr>
+
+</table>
+
+<p>As another illustration, suppose we are to cut 1<sup class="enum">3</sup>/<sub class="denom">4</sub> thread per
+inch on a lathe having a screw constant of 8, and that the gears
+have 24, 28, 32, 36, 40 teeth, etc., increasing by four up to one
+hundred. Following the rule:</p>
+
+<table class="formula2" summary="Formula 171_3">
+
+<tr>
+<td>&nbsp;8&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;2&nbsp;&times;&nbsp;4&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;(2&nbsp;&times;&nbsp;36)&nbsp;&times;&nbsp;(4&nbsp;&times;&nbsp;16)&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;72&nbsp;&times;&nbsp;64&nbsp;</td>
+</tr>
+
+<tr>
+<td>&nbsp;&mdash;&nbsp;</td>
+<td>&nbsp;=&nbsp;</td>
+<td>&nbsp;&mdash;&mdash;&mdash;&nbsp;</td>
+<td>&nbsp;=&nbsp;</td>
+<td>&nbsp;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&nbsp;</td>
+<td>&nbsp;=&nbsp;</td>
+<td>&nbsp;&mdash;&mdash;&mdash;&mdash;&nbsp;</td>
+</tr>
+
+<tr>
+<td>&nbsp;1<sup class="enum">3</sup>/<sub class="denom">4</sub>&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;1&nbsp;&times;&nbsp;1<sup class="enum">3</sup>/<sub class="denom">4</sub>&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;(1&nbsp;&times;&nbsp;36)&nbsp;&times;&nbsp;(1<sup class="enum">3</sup>/<sub class="denom">4</sub>&nbsp;&times;&nbsp;16)&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;36&nbsp;&times;&nbsp;28&nbsp;</td>
+</tr>
+
+</table>
+
+<p>The gears having 72 and 64 teeth are the <i>driving</i> gears, and
+those with 36 and 28 teeth are the <i>driven</i> gears.</p>
+
+<a name="Secnum_4_30" id="Secnum_4_30"></a><p><b>Change Gears for Metric Pitches.</b>&mdash;When screws are cut in
+accordance with the metric system, it is the usual practice to
+give the lead of the thread in millimeters, instead of the number
+of threads per unit of measurement. To find the change
+gears for cutting metric threads, when using a lathe having an
+English lead-screw, first determine the number of threads per<span class="pagenum"><a name="Pg_172" id="Pg_172">[172]</a></span>
+inch corresponding to the given lead in millimeters. Suppose a
+thread of 3 millimeters lead is to be cut in a lathe having an
+English lead-screw and a screw constant of 6. As there are
+25.4 millimeters per inch, the number of threads per inch will
+equal 25.4&nbsp;&divide;&nbsp;3. Place the screw constant as the numerator,
+and the number of threads per inch to be cut as the denominator:</p>
+
+<table class="formula" summary="Formula 172_1">
+
+<tr>
+<td>&nbsp;6&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;25.4&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;6&nbsp;&times;&nbsp;3&nbsp;</td>
+</tr>
+
+<tr>
+<td>&nbsp;&mdash;&mdash;&mdash;&mdash;&nbsp;</td>
+<td>&nbsp;=&nbsp;</td>
+<td>&nbsp;6&nbsp;&nbsp;&divide;&nbsp;</td>
+<td>&nbsp;&mdash;&mdash;&nbsp;</td>
+<td>&nbsp;=&nbsp;</td>
+<td>&nbsp;&mdash;&mdash;&nbsp;</td>
+</tr>
+
+<tr>
+<td>&nbsp;25.4&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;3&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;25.4&nbsp;</td>
+</tr>
+
+<tr>
+<td>&nbsp;&mdash;&mdash;&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+</tr>
+
+<tr>
+<td>&nbsp;3&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+</tr>
+
+</table>
+
+<p>The numerator and denominator of this fractional expression
+of the change-gear ratio are next multiplied by some trial number
+to determine the size of the gears. The first whole number
+by which 25.4 can be multiplied so as to get a whole number as
+the result is 5. Thus, 25.4&nbsp;&times;&nbsp;5 = 127; hence, one gear having
+127 teeth is always used when cutting metric threads with
+an English lead-screw. The other gear required in this case
+has 90 teeth. Thus:</p>
+
+<table class="formula" summary="Formula 172_2">
+
+<tr>
+<td>&nbsp;6&nbsp;&times;&nbsp;3&nbsp;&times;&nbsp;5&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;90&nbsp;</td>
+</tr>
+
+<tr>
+<td>&nbsp;&mdash;&mdash;&mdash;&mdash;</td>
+<td>&nbsp;=&nbsp;</td>
+<td>&nbsp;&mdash;&mdash;</td>
+</tr>
+
+<tr>
+<td>&nbsp;25.4&nbsp;&times;&nbsp;5&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;127&nbsp;</td>
+</tr>
+
+</table>
+
+<p>Therefore, the following rule can be used to find the change
+gears for cutting metric pitches with an English lead-screw:</p>
+
+<p><i>Rule.&mdash;Place the lathe screw constant multiplied by the lead of
+the required thread in millimeters multiplied by 5, as the numerator
+of the fraction, and 127 as the denominator. The product of the
+numbers in the numerator equals the number of teeth for the spindle-stud
+gear, and 127 is the number of teeth for the lead-screw gear.</i></p>
+
+<p>If the lathe has a metric pitch lead-screw, and a screw having
+a given number of threads per inch is to be cut, first find the
+&#8220;metric screw constant&#8221; of the lathe or the lead of thread in
+millimeters that would be cut with change gears of equal size
+on the lead-screw and spindle stud; then the method of determining
+the change gears is simply the reverse of the one already
+explained for cutting a metric thread with an English lead-screw.</p>
+
+<p><i>Rule.&mdash;To find the change gears for cutting English threads
+with a metric lead-screw, place 127 in the numerator and the threads
+per inch to be cut, multiplied by the metric screw constant multiplied</i>
+<span class="pagenum"><a name="Pg_173" id="Pg_173">[173]</a></span>
+<i>by 5, in the denominator; 127 is the number of teeth on the
+spindle-stud gear and the product of the numbers in the denominator
+equals the number of teeth in the lead-screw gear.</i></p>
+
+<a name="Fig_4_30" id="Fig_4_30"></a>
+<div class="figcenter"><img src="images/181sm.jpg" alt="Lathe having Quick Change-gear Mechanism" />
+<p class="caption750">Fig. 30. Lathe having Quick Change-gear Mechanism</p>
+</div>
+
+<a name="Secnum_4_31" id="Secnum_4_31"></a><p><b>Quick Change-gear Type of Lathe.</b>&mdash;A type of lathe that is
+much used at the present time is shown in <a href="#Fig_4_30">Fig. 30</a>. This is
+known as the quick change-gear type, because it has a system
+of gearing which makes it unnecessary to remove the change
+gears and replace them with different sizes for cutting threads
+of various pitches. Changes of feed are also obtained by the
+same mechanism, but the feeding movement is transmitted to
+the carriage by the rod <i>R</i>, whereas the screw <i>S<sub>1</sub></i> is used for screw
+cutting. As previously explained, the idea of using the screw exclusively
+for threading is to prevent it from being worn excessively,
+as it would be if continually used in place of rod <i>R</i>, for
+feeding the carriage when turning.</p>
+
+<a name="Fig_4_31" id="Fig_4_31"></a>
+<span class="pagenum"><a name="Pg_174" id="Pg_174">[174]</a></span>
+<div class="figcenter"><div class="illobox750"><img src="images/182sm.png" alt="End and Side Views of Quick Change-gear Mechanism" /></div>
+<p class="caption750">Fig. 31. End and Side Views of Quick Change-gear Mechanism</p>
+</div>
+
+<p>The general construction of this quick change gear mechanism<span class="pagenum"><a name="Pg_175" id="Pg_175">[175]</a></span>
+and the way the changes are made for cutting threads of different
+pitch, will be explained in connection with <a href="#Fig_4_30">Figs. 30</a>, <a href="#Fig_4_31">31</a> and
+<a href="#Fig_4_32">32</a>, which are marked with the same reference letters for corresponding
+parts. Referring to <a href="#Fig_4_30">Fig. 30</a>, the movement is transmitted
+from gear <i>s</i> on the spindle stud through idler gear <i>I</i>,
+which can be moved sidewise to mesh with either of the three
+gears <i>a</i>, <i>b</i> or <i>c</i>, <a href="#Fig_4_31">Fig. 31</a>. This cone of three gears engages gears
+<i>d</i>, <i>e</i> and <i>f</i>, any one of which can be locked with shaft <i>T</i> (<a href="#Fig_4_32">Fig.
+32</a>) by changing the position of knob <i>K</i>. On shaft <i>T</i> there is
+a gear <i>S</i> which can be moved along the shaft by hand lever <i>L</i>
+and, owing to the spline or key <i>t</i>, both the sliding gear and shaft
+rotate together. Shaft <i>T</i>, carrying gears <i>d</i>, <i>e</i> and <i>f</i> and the
+sliding gear <i>S</i>, is mounted in a yoke <i>Y</i>, which can be turned
+about shaft <i>N</i>, thus making it possible to lower sliding gear <i>S</i>
+into mesh with any one of a cone of eight gears <i>C</i>, <a href="#Fig_4_31">Fig. 31</a>. The
+shaft on which the eight gears are mounted has at the end a
+small gear <i>m</i> meshing with gear <i>n</i> on the feed-rod, and the latter,
+in turn, drives the lead-screw, unless gear <i>o</i> is shifted to the
+right out of engagement, which is its position except when
+cutting threads.</p>
+
+<a name="Fig_4_32" id="Fig_4_32"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/183sm.png" alt="Sectional Views of Quick Change-gear Mechanism" /></div>
+<p class="caption750">Fig. 32. Sectional Views of Quick Change-gear Mechanism</p>
+</div>
+
+<p>With this mechanism, eight changes for different threads or
+feeds are obtained by simply placing gear <i>S</i> into mesh with the
+<span class="pagenum"><a name="Pg_176" id="Pg_176">[176]</a></span>
+various sized gears in cone <i>C</i>. As the speed of shaft <i>T</i> depends
+on which of the three gears <i>d</i>, <i>e</i> and <i>f</i> are locked to it, the eight
+changes are tripled by changing the position of knob <i>K</i>, making
+twenty-four. Now by shifting idler gear <i>I</i>, three speed changes
+may be obtained for gears <i>a</i>, <i>b</i> and <i>c</i>, which rotate together, so
+that the twenty-four changes are also tripled, giving a total of
+seventy-two variations without
+removing any gears, and if a
+different sized gear <i>s</i> were placed
+on the spindle stud, an entirely
+different range could be obtained,
+but such a change would
+rarely be necessary. As shown
+in <a href="#Fig_4_30">Fig. 30</a>, there are eight hardened
+steel buttons <i>B</i>, or one for
+each gear of the cone <i>C</i>, placed
+at different heights in the casing.
+When lever <i>L</i> is shifted sidewise
+to change the position of sliding
+gear <i>S</i>, it is lowered onto one
+of these buttons (which enters a
+pocket on the under side) and in
+this way gear <i>S</i> is brought into
+proper mesh with any gear of the
+cone <i>C</i>. To shift lever <i>L</i>, the
+handle is pulled outward against
+the tension of spring <i>r</i> (<a href="#Fig_4_32">Fig. 32</a>),
+which disengages latch <i>l</i> and enables
+the lever to be lifted clear of the button; yoke <i>Y</i> is then
+raised or lowered, as the case may be, and lever <i>L</i> with the
+sliding gear is shifted laterally to the required position.</p>
+
+<a name="Fig_4_33" id="Fig_4_33"></a>
+<div class="figcenter"><img src="images/184sm.png" alt="Index Plate showing Position of Control Levers for Cutting Threads of Different Pitch" />
+<p class="caption750">Fig. 33. Index Plate showing Position of Control Levers<br />for Cutting Threads of Different Pitch</p>
+</div>
+
+<p>The position of lever <i>L</i> and knob <i>K</i> for cutting threads of
+different pitches is shown by an index plate or table attached
+to the lathe and arranged as shown in <a href="#Fig_4_33">Fig. 33</a>. The upper
+section <i>a</i> of this table shows the different numbers of threads to
+the inch that can be obtained when idler gear <i>I</i> is in the position
+shown by the diagram <i>A</i>. Section <i>b</i> gives the changes when
+<span class="pagenum"><a name="Pg_177" id="Pg_177">[177]</a></span>
+the idler gear is moved, as shown at <i>B</i>, and, similarly, section
+<i>c</i> gives the changes for position <i>C</i> of the idler. The horizontal
+row of figures from 1 to 8 below the word &#8220;stops&#8221; represents
+the eight positions for lever <i>L</i>, which has a plate <i>p</i> (<a href="#Fig_4_30">Fig. 30</a>) just
+beneath it with corresponding numbers, and the column to the
+left shows whether knob <i>K</i> should be out, in a central position,
+or in.</p>
+
+<p>In order to find what the position of lever <i>L</i> and knob <i>K</i>
+should be for cutting any given number of threads to the inch,
+find what &#8220;stop&#8221; number is directly above the number of threads
+to be cut, which will indicate the location of lever <i>L</i>, and also what
+position should be occupied by knob <i>K</i>, as shown in the column
+to the left. For example, suppose the lathe is to be geared for
+cutting eight threads to the inch. By referring to section a we
+see that lever <i>L</i> should be in position 4 and knob <i>K</i> in the center,
+provided the idler gear <i>I</i> were in position <i>A</i>, as it would be
+ordinarily, because all standard numbers of threads per inch
+(U. S. standard) from <sup class="enum">1</sup>/<sub class="denom">4</sub> inch up to and including 4 inches in
+diameter can be cut with the idler gear in that position. As
+another illustration, suppose we want to cut twenty-eight threads
+per inch. This is listed in section <i>c</i>, which shows that lever <i>L</i>
+must be placed in position 3 with knob <i>K</i> pushed in and the
+idler gear shifted to the left as at <i>C</i>.</p>
+
+<p>The simplicity of this method as compared with the time-consuming
+operation of removing and changing gears is apparent.
+The diagram <i>D</i> to the right shows an arrangement of
+gearing for cutting nineteen threads per inch. A 20-tooth gear
+is placed on the spindle stud (in place of the regular one having
+16 teeth) and one with 95 teeth on the lead-screw, thus driving
+the latter direct as with ordinary change gears. Of course it
+will be understood that the arrangement of a quick change-gear
+mechanism varies somewhat on lathes of different make.</p>
+
+<hr class="c25" />
+<span class="pagenum"><a name="Pg_178" id="Pg_178">[178]</a></span>
+<h2><a name="Chapnum_5" id="Chapnum_5">CHAPTER V</a></h2>
+<h3>TURRET LATHE PRACTICE</h3>
+<hr class="c05" />
+
+<p>Turret lathes are adapted for turning duplicate parts in quantity.
+The characteristic feature of a turret lathe is the turret
+which is mounted upon a carriage and contains the tools which
+are successively brought into the working position by indexing
+or rotating the turret. In many instances, all the tools required
+can be held in the turret, although it is often necessary to use
+other tools, held on a cross-slide, for cutting off the finished
+part, facing a radial surface, knurling, or for some other operation.
+After a turret lathe is equipped with the tools needed
+for machining a certain part, it produces the finished work much
+more rapidly than would be possible by using an ordinary engine
+lathe, principally because each tool is carefully set for turning
+or boring to whatever size is required and the turret makes it
+possible to quickly place any tool in the working position. Turret
+lathes also have systems of stops or gages for controlling the
+travel of the turret carriage and cross-slide, in order to regulate
+the depth of a bored hole, the length of a cylindrical part or its
+diameter; hence, turning machines of this type are much more
+efficient than ordinary lathes for turning duplicate parts, unless
+the quantity is small, in which case, the advantage of the turret
+lathe might be much more than offset by the cost of the special
+tool equipment and the time required for &#8220;setting up&#8221; the
+machine. (See &#8220;<a href="#Secnum_5_32">Selecting Type of Turning Machine</a>.&#8221;)</p>
+
+<a name="Fig_5_1" id="Fig_5_1"></a><span class="pagenum"><a name="Pg_179" id="Pg_179">[179]</a></span>
+<div class="figcenter"><img src="images/187sm.jpg" alt="Turret Lathe of Motor-driven Geared-head Type" />
+<p class="caption750">Fig. 1. Bardons &amp; Oliver Turret Lathe of Motor-driven Geared-head Type</p>
+</div>
+
+<a name="Secnum_5_1" id="Secnum_5_1"></a><p><b>General Description of a Turret Lathe.</b>&mdash;The turret lathe
+shown in <a href="#Fig_5_1">Fig. 1</a> has a hexagonal shaped turret <i>A</i> with a hole in
+each side in which the tools are held. This turret is mounted on
+a slide <i>B</i> which is carried by a saddle <i>C</i> that can be moved along
+the bed to locate the turret slide with reference to the length of
+the tools in the turret and the room required for indexing. The
+turret slide can be moved longitudinally by turning the pilot<span class="pagenum"><a name="Pg_180" id="Pg_180">[180]</a></span>
+wheel or turnstile <i>D</i>, or it can be fed by power. Ordinarily,
+the hand adjustment is used for quickly moving the carriage
+when the tools are not cutting, although sometimes the hand
+feed is preferable to a power feed when the tools are at work,
+especially if the cuts are short. After a turret tool has finished
+its cut, the turnstile is used to return the slide to the starting
+point, and at the end of this backward movement the turret
+is automatically indexed or turned one-sixth of a revolution,
+thus bringing the next tool into the working position. The
+turret is accurately located in each of its six positions by a lock
+bolt which engages notches formed in a large index ring at the
+turret base. A binder lever <i>E</i> at the top of the turret stud is
+used to clamp the turret rigidly to the slide when the tools are
+cutting.</p>
+
+<p>The forward movement of the slide for each position of the
+turret is controlled by stops at <i>F</i>, which are set to suit the work
+being turned. When parts are being turned from bar stock, the
+latter passes through the hollow spindle of the headstock and
+extends just far enough beyond the end of the spindle to permit
+turning one of the parts. The bar is held while the turning tools
+are at work, by a chuck of the collet type at <i>G</i>. This chuck is
+opened or closed around the bar by turning handwheel <i>H</i>. After
+a finished part has been cut off by a tool held in cross-slide <i>J</i>,
+the chuck is released and further movement of wheel <i>H</i> causes
+ratchet feed dog <i>K</i>, and the bar which passes through it, to
+be drawn forward. This forward movement is continued until
+the end of the bar comes against a stop gage held in one of the
+turret holes, to insure feeding the bar out just the right amount
+for turning the next piece. On some turret lathes, the lever
+which operates the chuck also controls a power feed for the
+bar stock, the latter being pushed through the spindle against
+the stop.</p>
+
+<p>The machine illustrated has a power feed for the cross-slide
+as well as for the turret. The motion is obtained from the same
+shaft <i>L</i> which actuates the turret slide, but the feed changes
+are independent. The cross-slide feed changes are varied by
+levers <i>M</i> and those for the turret by levers <i>N</i>. For many
+<span class="pagenum"><a name="Pg_181" id="Pg_181">[181]</a></span>
+turret lathe operations, such as turning castings, etc., a jawed
+chuck is screwed onto the spindle and the work is held the same
+as when a chuck is used on an engine lathe. Sometimes chucks
+are used having special jaws for holding castings of irregular
+shape, or special work-holding fixtures which are bolted to the
+faceplate. The small handle at <i>O</i> is for moving the cross-slide
+along the bed when this is necessary in order to feed a tool
+sidewise.</p>
+
+<p>This particular machine is driven by a motor at the rear of
+the headstock, connection being made with the spindle through
+gearing. The necessary speed changes are obtained both by
+varying the speed of the motor and by shifting gears in the
+headstock. The motor is controlled by the turnstile <i>P</i> and the
+gears are shifted by the vertical levers shown.</p>
+
+<p>While many of the features referred to are common to turret
+lathes in general, it will be understood that the details such as
+the control levers, arrangement of stops, etc., vary on turret
+lathes of different make.</p>
+
+<a name="Fig_5_2" id="Fig_5_2"></a><span class="pagenum"><a name="Pg_182" id="Pg_182">[182]</a></span>
+<a name="Fig_5_3" id="Fig_5_3"></a>
+<div class="figcenter"><div class="illobox750"><img src="images/190sm.png" alt="Diagrams showing Turret Lathe Tool Equipment for Machining Automobile Hub Casting" /></div>
+<p class="caption750">Figs. 2 and 3. Diagrams showing Turret Lathe Tool Equipment for Machining Automobile Hub Casting</p>
+</div>
+
+<a name="Secnum_5_2" id="Secnum_5_2"></a><p><b>Example of Turret Lathe Work.</b>&mdash;The diagrams <a href="#Fig_5_2">Figs. 2</a> and
+<a href="#Fig_5_3">3</a> show a turret lathe operation which is typical in many respects.
+The part to be turned is a hub casting for an automobile and it
+is machined in two series of operations. The first series is shown
+by the plan view, <a href="#Fig_5_2">Fig. 2</a>. The casting <i>A</i> is held in a three-jaw
+chuck <i>B</i>. Tool No. 1 on the cross-slide is equipped with two
+cutters and rough faces the flange and end, while the inner and
+outer surfaces of the cylindrical part are rough bored and turned
+by combination boring and turning tool No. 2. This tool has,
+in addition to a regular boring-bar, a bracket or tool-holder
+which projects above the work and carries cutters that operate
+on the top surface. Tools Nos. 3 and 4 next come into action,
+No. 3 finishing the surfaces roughed out by No. 2, and No. 4
+finish-facing the flange and end of the hub. The detailed side
+view of Tool No. 3 (which is practically the same as No. 2),
+shows the arrangement of the cutters <i>C</i> and <i>D</i>, one of which
+turns the cylindrical surface and the other bevels the end of
+the hub. The hole in the hub is next finished by tool No. 5
+which is a stepped reamer that machines the bore and counterbore<span class="pagenum"><a name="Pg_183" id="Pg_183">[183]</a></span>
+to the required size within very close limits. The surfaces
+machined by the different tools referred to are indicated by
+the sectional view <i>E</i> of the hub, which shows by the numbers
+what tools are used on each surface.</p>
+
+<p>For the second series of operations, the position of the hub
+is reversed and it is held in a spring or collet type of chuck as
+shown by the plan view <a href="#Fig_5_3">Fig. 3</a>. The finished cylindrical end
+of the hub is inserted in the split collet <i>F</i> which is drawn back
+into the tapering collet ring by rod <i>G</i> (operated by turnstile <i>H</i>,
+<a href="#Fig_5_1">Fig. 1</a>) thus closing the collet tightly around the casting. The
+first operation is that of facing the side of the flange and end of
+the hub with tool No. 6 on the cross-slide, which is shown in the
+working position. A broad cutter <i>H</i> is used for facing the
+flange and finishing the large fillet, and the end is faced by a
+smaller cutter <i>I</i>. When these tools are withdrawn, tool No. 7
+is moved up for rough turning the outside of the cylindrical end
+(preparatory to cutting a thread) and rough boring the hole.
+These same surfaces are then finished by tool No. 8. The arrangement
+of tools Nos. 7 and 8 is shown by the detailed view.
+Tool <i>J</i> turns the part to be threaded; tool <i>K</i> turns the end beyond
+the threaded part; and tool <i>L</i> bevels the corner or edge.
+The reaming tool No. 9 is next indexed to the working position
+for finishing the hole and beveling the outer edge slightly. At
+the same time, the form tool No. 10, held at the rear of the cross-slide,
+is fed up for beveling the flange to an angle of 60 degrees.
+The final operation is that of threading the end, which is done
+with die No. 11. The boring-bars of tools Nos. 2, 3, 7 and 8
+are all provided with pilots <i>N</i> which enter close fitting bushings
+held in the spindle, to steady the bar while taking the
+cut. This is a common method of supporting turret lathe
+tools.</p>
+
+<p>The feed of the turret for both the first and second series of
+operations is <sup class="enum">1</sup>/<sub class="denom">27</sub> inch per revolution and the speeds 60 revolutions
+per minute for the roughing cuts and 90 revolutions per
+minute for the finishing cuts. The total time for machining
+one of these castings complete is about 7<sup class="enum">1</sup>/<sub class="denom">2</sub> minutes, which includes
+the time required for placing the work in the chuck.</p>
+
+<a name="Fig_5_4" id="Fig_5_4"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/192sm.png" alt="First Cycle of Operations in Finishing Gasoline Engine Flywheels on a Pond Turret Lathe" /></div>
+<p class="caption750">Fig. 4. First Cycle of Operations in Finishing Gasoline Engine<br />Flywheels on a Pond Turret Lathe</p>
+</div>
+
+<p><span class="pagenum"><a name="Pg_184" id="Pg_184">[184]</a></span>
+<a name="Secnum_5_3" id="Secnum_5_3"></a><b>Machining Flywheels in Turret Lathe.</b>&mdash;<a href="#Fig_5_4">Figs. 4</a>
+to <a href="#Fig_5_6">6</a>, inclusive,illustrate how a gasoline engine flywheel is finished all over in
+two cycles of operations. First the flywheel is turned complete
+on one side, the hole bored and reamed, and the outside of the
+rim finished; in the second cycle the other side of the flywheel
+is completed.</p>
+
+<p>During the first operation, the work is held by the inside of
+the rim by means of a four-jaw chuck equipped with hard jaws.
+The side of the rim, the tapering circumference of the recess,
+the web, and the hub are first rough-turned, using tools held in
+the carriage toolpost. The hole is then rough-bored by bar <i>C</i>,
+which is supported in a bushing in the chuck, as shown in <a href="#Fig_5_4">Fig. 4.</a>
+The outside of the wheel rim is rough-turned at the same time
+by a cutter held in the extension turret tool-holder <i>T</i> (<a href="#Fig_5_5">Fig. 5</a>),
+and the taper fit on the inside of the flywheel is turned by means
+of cutter <i>A</i> (<a href="#Fig_5_4">Fig. 4</a>) held in a tool-holder attached to the turret.</p>
+
+<a name="Fig_5_5" id="Fig_5_5"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/193sm.png" alt="Elevation of Turret and Tools for Finishing Flywheels&mdash;First Operation" /></div>
+<p class="caption750">Fig. 5. Elevation of Turret and Tools for Finishing Flywheels&mdash;First Operation</p>
+</div>
+
+<p>The outside of the wheel rim is next finish-turned with cutter
+<i>V</i> (<a href="#Fig_5_5">Fig. 5</a>) held in an extension turret tool-holder the same as
+<span class="pagenum"><a name="Pg_185" id="Pg_185">[185]</a></span>
+the roughing tool <i>T</i>. At the same time, the bore is finished
+by a cutter in boring-bar <i>D</i> (<a href="#Fig_5_4">Fig. 4</a>). The side of the rim and
+the hub of the wheel are also finished at this time by two facing
+cutters <i>H</i> and <i>K</i>, held in tool-holders on the face of the turret.
+When the finishing cuts on the rim and hub are being taken,
+the work is supported by a bushing on the boring-bar which enters
+the bore of the wheel, the boring cutter and facing tools being
+set in such relation to each other that the final boring of the hole
+is completed before the facing cuts are taken.</p>
+
+<p>The web of the wheel is next finish-faced with the facing cutter
+held in the holder <i>E</i>, and the taper surface on the inside of the
+rim is finished by the tool <i>L</i>, at the same time. While these
+last operations are performed, the work is supported by a bushing
+on a supporting arbor <i>J</i>, which enters the bore of the wheel.
+The bore is finally reamed to size by a reamer <i>F</i> held in a &#8220;floating&#8221;
+reamer-holder. When the reaming operation is completed,
+a clearance groove <i>N</i> is cut on the inside of the rim, using a
+tool <i>G</i> held in the carriage toolpost. The first cycle of operations
+on the flywheel is now completed.</p>
+
+<a name="Fig_5_6" id="Fig_5_6"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/194sm.png" alt="Second Cycle of Operations on Flywheel" /></div>
+<p class="caption750">Fig. 6. Second Cycle of Operations on Flywheel</p>
+</div>
+
+<p>The flywheel is then removed from the chuck, turned around,
+and held in &#8220;soft&#8221; jaws for the second cycle of operations, the<span class="pagenum"><a name="Pg_186" id="Pg_186">[186]</a></span>
+jaws fitting the outside of the wheel rim. (Soft unhardened
+jaws are used to prevent marring the finished surface of the
+rim.) The operations on this side are very similar to those performed
+on the other side. First, the side of the rim, the inside
+of the rim, the web, and hub are rough-turned, using tools held
+in the carriage toolpost. The inside of the rim and the web are
+then finished by a cutter held in a tool-holder at <i>P</i>, <a href="#Fig_5_6">Fig. 6</a>, which
+is bolted to the face of the turret. The work is supported
+during this operation by a bushing held on a supporting arbor
+<i>U</i>, having a pilot which enters a bushing in the chuck. Finally,
+the rim and hub are finished, by the facing cutters <i>R</i> and <i>S</i>,
+the work being supported by an arbor, as before.</p>
+
+<p>These operations illustrate the methods employed in automobile
+factories, and other shops where large numbers of engine
+flywheels, etc., must be machined.</p>
+
+<a name="Fig_5_7" id="Fig_5_7"></a><span class="pagenum"><a name="Pg_188" id="Pg_188">[188]</a></span>
+<div class="figcenter"><div class="illobox450"><img src="images/196sm.png" alt="Turret Lathe Tool Equipment for Machining Flywheels" /></div>
+<p class="caption750">Fig. 7. Turret Lathe Tool Equipment for Machining Flywheels</p>
+</div>
+
+<a name="Secnum_5_4" id="Secnum_5_4"></a><p><b>Finishing a Flywheel at One Setting in Turret Lathe.</b>&mdash;The
+plan view <i>A</i>, <a href="#Fig_5_7">Fig. 7</a>, shows an arrangement of tools for finishing
+a flywheel complete at one setting. The hole for the shaft has
+to be bored and reamed and the hub faced on both sides. The
+sides and periphery of the rim also have to be finished and all
+four corners of the rim rounded. The tools for doing this work
+consist of boring-bars, a reamer, facing heads on the main turret,<span class="pagenum"><a name="Pg_187" id="Pg_187">[187]</a></span>
+a turret toolpost on the slide rest (carrying, in this case, three
+tools) and a special supplementary wing rest attached to the
+front of the carriage at the extreme left.</p>
+
+<p>The casting is held by three special hardened jaws <i>b</i> in a universal
+chuck. These jaws grip the work on the inner side of the
+rim, leaving room for a tool to finish the rear face without striking
+the chuck body or jaws. Three rests <i>c</i> are provided between
+the chuck jaws. The work is pressed against these rests while
+being tightened in the chuck, and they serve to locate it so that
+the arms will run true so far as sidewise movement is concerned.
+These rests also locate the casting with relation to the stops for
+the turret and carriage movements. The chuck carries a bushing
+<i>r</i> of suitable diameter to support the boring-bars in the main
+turret, as will be described.</p>
+
+<p>In the first operation, boring-bar <i>m</i> is brought in line with the
+spindle and is entered in bushing <i>r</i> in the chuck. Double-ended
+cutter <i>n</i> is then fed through the hub of the pulley to true up the
+cored hole. While boring the hole, the scale on the front face
+of the rim and hub is removed by tool <i>j</i>. Tool <i>k</i> is then brought
+into action to rough turn the periphery, after which tool <i>e</i>, in
+the wing rest, is fed down to clean up the back face of the rim.
+As soon as the scale is removed, the hole is bored nearly to size
+by cutter <i>n<sub>1</sub></i> in bar <i>m<sub>1</sub></i>, and it is finally finished with reamer <i>q</i>
+mounted on a floating arbor.</p>
+
+<p>The cutters <i>f</i>, <i>g</i> and <i>h</i>, in the facing head, are next brought up
+to rough face the hub and rim, and round the corners of the rim
+on the front side. This operation is all done by broad shaving
+cuts. The facing head in which the tools are held is provided
+with a pilot bar <i>t</i> which fits the finished hole in the flywheel hub,
+and steadies the head during the operation. The cutters <i>f</i>, <i>g</i>
+and <i>h</i> are mounted in holders which may be so adjusted as to
+bring them to the proper setting for the desired dimensions.
+This completes the roughing operations.</p>
+
+<p>The periphery of the rim is now finished by cutter <i>l</i> in the
+turret toolpost which is indexed to the proper position for this
+operation. The rear face of the rim is finished by the same
+tool <i>e</i> with which the roughing was done. Tool <i>e</i> is then removed
+<span class="pagenum"><a name="Pg_189" id="Pg_189">[189]</a></span>
+and replaced with <i>d</i> which rounds the inner corner of the
+rim. Tool <i>d</i> is also replaced with a third tool for rounding the
+outer corner of the rear side. For finishing the front faces of
+the rim and hub and rounding the corners of the rim, a second
+facing head, identical with the first one, is employed. This is
+shown in position in the illustration. Cutters <i>f<sub>1</sub></i>, <i>g<sub>1</sub></i> and <i>h<sub>1</sub></i> correspond
+with the cutters <i>f</i>, <i>g</i> and <i>h</i>, previously referred to, and
+perform the same operations.</p>
+
+<p>The remaining operation of finishing the back of the hub is
+effected by cutter <i>p</i>. This cutter is removed from the bar, which
+is then inserted through the bore; the cutter is then replaced in
+its slot and the rear end of the hub is faced by feeding the carriage
+away from the headstock. This completes the operations, the
+flywheel being finished at one setting.</p>
+
+<a name="Secnum_5_5" id="Secnum_5_5"></a><p><b>Finishing a Webbed Flywheel in Two Settings.</b>&mdash;The plan
+views <i>B</i> and <i>C</i>, <a href="#Fig_5_7">Fig. 7</a>, show the arrangement of tools for finishing
+a webbed flywheel which has to be machined all over. This,
+of course, requires two operations. In the first of these (see
+sketch <i>B</i>) the rough casting is chucked on the inside of the rim
+with regular inside hard chuck jaws <i>b</i>. The cored hole is first
+rough bored with cutter <i>n</i> attached to the end of boring-bar <i>m</i>,
+and guided by the drill support <i>d</i> pivoted to the carriage. Next,
+the boring-bar <i>m<sub>1</sub></i> is brought into position, the drill support
+being swung back out of the way. This bar is steadied by its
+bearing in bushing <i>r</i> in the chuck. Two cutters, <i>n<sub>1</sub></i> and <i>n<sub>2</sub></i>, are
+used to roughly shape the hole to the desired taper, the small
+end being finished to within 0.002 inch of the required diameter.
+While boring with the bar <i>m<sub>1</sub></i>, the scale is broken on the web
+and hub of the casting by the tool <i>k</i> in the turret toolpost. The
+latter is then shifted to bring the tool <i>j</i> into position for removing
+the scale on the periphery of the wheel. Next, the hole is
+reamed with taper reamer <i>q</i>, the pilot of which is supported by
+bushing <i>r</i>.</p>
+
+<p>The first of the facing heads is now brought into action. This
+facing head carries a guide <i>t</i> which is steadied in a taper bushing
+<i>c</i>, driven into the taper hole of the hub for that purpose. The
+top cutter <i>f</i> turns the periphery, cutter <i>g</i> turns the hub and faces
+<span class="pagenum"><a name="Pg_190" id="Pg_190">[190]</a></span>
+the web, and cutter <i>h</i> faces the rim. A fourth cutter <i>e</i> on the
+under side of the head faces the hub. This casting is now
+machined approximately to size.</p>
+
+<p>For finishing, similar cutters, <i>e<sub>1</sub></i>, <i>f<sub>1</sub></i>, <i>g<sub>1</sub></i> and <i>h<sub>1</sub></i>, in the other
+facing head are used, the latter being supported by the taper
+bushing <i>c</i> in the same way. A very light cut is taken for finishing.
+Tool <i>l</i> in the carriage turret is used to round the outer and
+inner corners of the rim, which completes the work on this face
+of the casting.</p>
+
+<p>In the second cycle of operations, shown at <i>C</i>, the casting is
+chucked on the outside with the soft jaws <i>b</i>, which are bored to
+the exact diameter of the finished rim. The work is further
+supported and centered by sliding bushing <i>c</i>, which is tapered
+to fit the finished hole in the hub, and has an accurate bearing
+in bushing <i>r</i> in the chuck. This bushing is provided with a
+threaded collar for forcing it into the work and withdrawing it.
+The scale on the web and the inside and face of the rim is first
+broken with the tool <i>k</i> in the turret toolpost. These surfaces
+are then roughed off with cutters <i>f</i>, <i>g</i> and <i>h</i>, in the facing head.
+This latter is steadied by a pilot <i>t</i> which enters the hole in the
+sliding bushing <i>c</i> on which the work is supported. A light cut
+is next taken with cutters <i>f<sub>1</sub></i>, <i>g<sub>1</sub></i> and <i>h<sub>1</sub></i>, in the finishing facing
+head, which completes the operation.</p>
+
+<a name="Secnum_5_6" id="Secnum_5_6"></a><p><b>Tools for Turret Lathes.</b>&mdash;The operation of a turret lathe after
+the tools have been properly arranged is not particularly difficult,
+but designing and making the tools, determining what
+order of operations will give the most efficient and accurate
+results, and setting the tools on the machine, requires both skill
+and experience. For some classes of work, especially if of a
+rather complicated nature, many of the tools must be specially
+designed, although there are certain standard types used on
+turret lathes which are adapted to general turning operations.
+Some of the principal types are referred to in the following.</p>
+
+<a name="Fig_5_8" id="Fig_5_8"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/199sm.png" alt="Different Types of Box-tools for Turret Lathe" /></div>
+<p class="caption750">Fig. 8. Different Types of Box-tools for Turret Lathe</p>
+</div>
+
+<a name="Secnum_5_7" id="Secnum_5_7"></a><p><b>Box-tools.</b>&mdash;Tools of this type are used for turning bar
+stock. There are many different designs, some of which are
+shown in <a href="#Fig_5_8">Figs. 8</a>, <a href="#Fig_5_9">9</a> and <a href="#Fig_5_10">10</a>. Box-tools are held in the turret and
+they have back-rests opposite the turning tools, for supporting<span class="pagenum"><a name="Pg_191" id="Pg_191">[191]</a></span>
+the part being turned. The box-tool shown at <i>A</i>, <a href="#Fig_5_8">Fig. 8</a>, is for
+roughing. The cutter <i>a</i> is a piece of high-speed steel beveled
+on the cutting end to produce a keen edge. It takes a shearing
+tangent cut on top of the bar and the latter is kept from springing
+away by means of the adjustable, hardened tool-steel back-rest
+<i>b</i>. This tool is considered superior to a hollow mill whenever
+a fair amount of stock must be removed. If considerable
+smoothness and accuracy are necessary, the finishing box-tool
+shown at <i>B</i> should follow the roughing box tool, but in most
+cases, especially if the part is to be threaded by a die, a finishing
+cut is unnecessary.</p>
+
+<p><span class="pagenum"><a name="Pg_192" id="Pg_192">[192]</a></span>
+The finishing box-tool <i>B</i> is also used to follow a hollow mill if
+special accuracy or smoothness is desired. This tool is only
+intended for light finishing cuts, the allowances varying from
+0.005 inch to 0.015 inch in diameter. The cutters are made of
+square tool steel of commercial size, and are ground and set to
+take a scraping end cut. This particular tool has two tool-holders
+which permit finishing two diameters at once. If a
+larger number of sizes must be turned, extra tool-holders can
+be applied.</p>
+
+<p>The single-cutter box-tool shown at <i>C</i> is bolted directly to the
+face of the turret instead of being held by a shank in the turret
+hole, and it is adapted for heavy cuts such as are necessary
+when turning comparatively large bar stock. The tool-holder <i>a</i>
+swivels on a stud, thus allowing the cutter to be withdrawn
+from the work while being returned, which prevents marring the
+turned surface. The high-speed steel cutter is ground to take
+a side cut on the end of the bar. The latter is supported by
+hardened and ground tool-steel rolls <i>b</i> which revolve on hardened
+and ground studs. These rolls are mounted on swinging arms
+which have a screw adjustment for different diameters. They
+can also be adjusted parallel to the bar, thus enabling them to
+be set either in advance of or back of the cutter. The opening
+in the base allows the stock to pass into the turret when it is not
+larger than the turret hole.</p>
+
+<p>The box-tool shown at <i>D</i> is similar to the one just described,
+except that it has two or more cutters and roller back-rests, thus
+enabling different diameters to be turned simultaneously. The
+cutters are ground to take a side cut. Ordinarily this gives a
+satisfactory finish, but if special accuracy and smoothness are
+desired, two tools should be used, one for roughing and one for
+finishing, the latter being ground to take a light scraping end cut.</p>
+
+<p>The taper-turning box-tool shown at <i>E</i> is designed for accurately
+turning tapers on brass or cast-iron parts, when there is a
+small amount of stock to be removed. The taper is obtained by
+cross motion imparted to the cutter slide as the turret advances.
+The taper-turning box-tool shown at <i>F</i>, instead of having a
+single-point cutter, is provided with a wide cutter <i>a</i>. This tool
+<span class="pagenum"><a name="Pg_193" id="Pg_193">[193]</a></span>
+is designed to turn tapering parts of small or medium diameter,
+requiring the use of a support which cannot be provided with a
+straight forming tool and holder mounted on the cut-off slide.
+The cutter is backed up by the screws shown, which also provide
+adjustment for different tapers within a limited range.
+The bar is supported by the three back-rests shown, which also
+have screw adjustment.</p>
+
+<a name="Fig_5_9" id="Fig_5_9"></a><span class="pagenum"><a name="Pg_194" id="Pg_194">[194]</a></span>
+<div class="figcenter"><div class="illobox450"><img src="images/202sm.png" alt="Box-tools and Work for which they are Intended" /></div>
+<p class="caption750">Fig. 9. Box-tools and Work for which they are Intended</p>
+</div>
+
+<a name="Secnum_5_8" id="Secnum_5_8"></a><p><b>Examples of Box-tool Turning.</b>&mdash;Box-tools are not only used
+for cylindrical and taper turning on the end of a bar, but for
+many other operations. <a href="#Fig_5_9">Figs. 9</a> and <a href="#Fig_5_10">10</a> show a number of box-tools
+of different designs, with examples of the work for which
+each is intended. While these tools are designed for some
+specific part, they can, of course, with slight modifications be
+adapted to other work.</p>
+
+<p>A box-tool of the pilot type that is used for finishing, after
+the surplus stock has been removed by roughing tools, is shown
+at <i>A</i>, <a href="#Fig_5_9">Fig. 9</a>. The work, which is the cone for a ball bearing, is
+shown at <i>a</i> by the dotted lines and also by the detail view to the
+right. The pilot <i>b</i> enters the work before either of the cutters
+begins to operate on its respective surface. The inverted cutter
+<i>c</i>, which sizes the flange of the cone, is held in position by a clamp
+<i>d</i>, which is forced down by a collar-head screw. The cutter is
+further secured against a beveled shoulder at <i>g</i> by the set-screws <i>f</i>,
+and it is adjusted forward by the screw <i>e</i>. By loosening the
+screws <i>f</i> and the collar-head screw, the cutter may be removed
+for sharpening. The cutter <i>h</i> is adjusted to cut to the proper
+diameter, by the screws <i>l</i>, after which the clamp <i>k</i> is made level
+by the screw <i>j</i>. The collar-screw <i>m</i> is then used to secure the
+tool in place. The cutter is made from drill rod and it is slightly
+cupped out on the cutting end to give keenness to the cutting
+edge. The adjusting screw <i>o</i>, which passes through plate <i>p</i>, prevents
+the cutter from backing away from the work. This adjusting
+screw plate has its screw holes slotted to avoid removing the
+screws when it becomes necessary to remove the plate and
+cutter for sharpening. Pilot <i>b</i> is held firmly to the tool body
+by set-screw <i>r</i>. The hole <i>s</i> through the shank makes it easy to
+remove the pilot, in case this is necessary.</p>
+
+<p><span class="pagenum"><a name="Pg_195" id="Pg_195">[195]</a></span>
+A pilot box-tool for finishing another type of ball bearing cone
+is shown at <i>B</i>. The shape of the work itself is indicated by the
+dotted lines <i>a</i> and by the detail view. This tool is somewhat
+similar in its construction to the one just described. The cutters
+<i>b</i> and <i>c</i> are inverted and are used to face the flange at <i>d</i> and to
+turn it to the proper diameter. These cutters are held by the
+clamp <i>f</i> and screws <i>g</i> and are adjusted forward by the screw <i>h</i>.
+The cutter <i>j</i>, which operates on top of the stock, rests on a
+bolster, of the proper angle and is adjusted up or down by the
+screws <i>k</i>. The clamp <i>l</i>, which binds against this tool, is beveled
+to correspond with the angle of the tool. This clamp is secured
+by the collar-screw shown and it is leveled by set-screws <i>s</i>. The
+adjusting screw <i>p</i> prevents the cutter from slipping back. The
+holes in the adjusting-screw plate are also slotted in this case so
+that it will not be necessary to remove any screws when the
+cutter has to be taken out of the holder.</p>
+
+<p>A box-tool for finishing a treadle-rod cone for a sewing machine
+is shown at <i>C</i>. This tool is also of the pilot type. The
+cutters in it operate on opposite sides of the cone <i>a</i>. The inverted
+cutter <i>b</i> sizes the cylindrical part of the cone, while the
+front cutter <i>d</i> is set at the proper angle to finish the tapered
+part. The rear cutter <i>b</i> is held in place by the clamp <i>g</i> and a
+collar screw. It is adjusted forward by the screw <i>h</i> in the plate
+<i>i</i> which is held by screws as shown. The pilot is retained by a
+set-screw, and it is easily removed by inserting a small rod in
+the hole <i>l</i> which passes through the shank. The cutter <i>d</i> is held
+by clamp <i>m</i> and is adjusted by screw <i>n</i> which passes through a
+tapped hole in plate <i>o</i>. The screw holes in both the adjusting
+plates <i>i</i> and <i>o</i> are slotted to facilitate their removal.</p>
+
+<a name="Fig_5_10" id="Fig_5_10"></a><span class="pagenum"><a name="Pg_197" id="Pg_197">[197]</a></span>
+<div class="figcenter"><div class="illobox450"><img src="images/205sm.png" alt="Examples of Box-tool Designs" /></div>
+<p class="caption750">Fig. 10. Examples of Box-tool Designs</p>
+</div>
+
+<p>The box-tool illustrated at <i>A</i>, <a href="#Fig_5_10">Fig. 10</a>, is used for finishing
+the bushing of a double-taper cone bearing <i>a</i>. The cutters are
+so arranged that they all cut on the center; that is, the cutting
+edges lie in a horizontal plane. The inverted cutter <i>b</i> at the
+rear forms the short angular surface, and the cutter <i>c</i> in front
+forms the long tapering part of the bearing. The large diameter
+is turned, to size by cutter <i>d</i>. The pilot <i>e</i> has a bearing in the
+bore nearly equal to the length of the work and it is provided<span class="pagenum"><a name="Pg_196" id="Pg_196">[196]</a></span>
+with oil grooves, as shown. The taper shank of this pilot is
+tapped for the screw <i>i</i> which extends the whole length of the
+shank and is used to draw the pilot back to its seat. It is not
+necessary to remove adjusting-screw plate <i>k</i> to take out the cutter
+<i>b</i>, as the latter can be drawn out from the front after the collar-screw
+<i>m</i> is loosened. The cutter <i>c</i> is removed by taking off the
+adjusting-screw plate <i>s</i> after loosening the collar-screw <i>n</i>. The
+cutter <i>d</i> is held in a dove-tailed slot by two headless set-screws <i>q</i>.
+It is also backed up by an adjusting screw in the plate <i>s</i>. These
+adjusting screws should all have fine threads, say from 32 to
+40 per inch, and be nicely fitted so they will not loosen after being
+adjusted.</p>
+
+<p>The box-tools shown at <i>B</i> and <i>C</i>, <a href="#Fig_5_10">Fig. 10</a>, are for turning the
+sides of a loose pulley for a sewing machine. This pulley (shown
+by the dotted lines) is finished in two operations. The box-tool
+for finishing the side of the pulley on which the hub projects
+beyond the rim, is shown at <i>B</i>. The inverted cutter <i>a</i>,
+which faces the end of the hub, is held by a clamp <i>c</i> (clearly
+shown in the end view) from the under side and it has no adjustment.
+The collar-screw <i>d</i> is tapped into this clamp, which
+is prevented from getting out of place by the dowel-pin <i>f</i>. The
+pilot <i>g</i> is made small in the shank, so that tool <i>a</i> can be so placed
+as to insure the removal of all burrs around the bore of the
+hub. The pilot is held by a set-screw and it is provided with oil
+grooves. The cutter <i>j</i> sizes the outside of the hub, and the cutter
+<i>k</i> faces the side of the pulley rim. These cutters are both held
+by the clamp <i>l</i> and the collar-screw <i>m</i>. No side plates are used
+on this tool, and the cutters are all easily removed.</p>
+
+<p>Sketch <i>C</i> shows the box-tool used for the second operation.
+As the hub is flush with the rim on the side for which this tool
+is intended, it needs only one cutter to face both. This is done
+by the wide cutter <i>a</i> which is held in a dove-tailed slot in the
+front of the tool and is fastened by the clamp <i>b</i> and collar-screw
+<i>c</i>. The bushing <i>d</i>, in which the end of the work arbor is supported,
+is held by the collar-screw <i>e</i>, and to obtain the necessary
+compression, the body of the tool is slotted as far back as <i>f</i>. This
+bushing is provided with oil grooves and one side is cut away<span class="pagenum"><a name="Pg_198" id="Pg_198">[198]</a></span>
+to clear the cutter <i>a</i>. The pilot end of the arbor on which the
+work is mounted is <sup class="enum">1</sup>/<sub class="denom">16</sub> inch smaller than the bore of the pulley,
+which allows the cutter to be set in far enough to prevent any
+burr which might form at the edge of the bore. A disk <i>i</i> is inserted
+back of bushing <i>d</i>, so that the latter may be easily removed
+by passing a rod through the hollow shank. The special chuck
+used for this second operation on the loose pulley is screwed
+onto the spindle, and the work is mounted on a projecting arbor
+and driven by the pins engaging holes in the pulley web. The
+arbor is made a driving fit for the work, and the end or pilot is
+a running fit in the bushing of the box-tool. A counterbore
+in the arbor hub provides clearance for the hub of the pulley
+which projects beyond the rim on one side.</p>
+
+<a name="Fig_5_11" id="Fig_5_11"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/206sm.png" alt="Hollow Mill and Holder, Spring Screw-threading Die" /></div>
+<p class="caption750">Fig. 11. (A) Hollow Mill and Holder.<br />(B) Spring Screw-threading Die
+and Releasing Die-holder</p>
+</div>
+
+<a name="Secnum_5_9" id="Secnum_5_9"></a><p><b>Hollow Mills.</b>&mdash;A hollow mill such as is shown at
+<i>A</i> in <a href="#Fig_5_11">Fig. 11</a>
+is sometimes used in place of a box-tool (especially when turning
+brass) for short roughing cuts preceding a threading operation.
+The turning is done by the cutting edges <i>e</i>, and the turned part
+enters the mill and is steadied by it. If this type of tool is used
+for long, straight cuts, especially on square stock and when
+making screws with large heads from the bar, it should always
+be followed by a finishing box-tool to insure accurate work. A<span class="pagenum"><a name="Pg_199" id="Pg_199">[199]</a></span>
+hollow mill can be sharpened readily by grinding the ends without
+materially changing the cutting size. A slight adjustment
+can be obtained by means of the clamp collar shown to the
+left, although this is not generally used. When making these
+mills, they should be reamed out tapering from the rear to give
+clearance to the cutting edges. For turning steel, the cutting
+edge should be about <sup class="enum">1</sup>/<sub class="denom">10</sub> of the diameter ahead of the center,
+whereas for brass, it should be on the center-line.</p>
+
+<a name="Fig_5_12" id="Fig_5_12"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/207sm.png" alt="Geometric Adjustable Hollow Milling Tool" /></div>
+<p class="caption750">Fig. 12. Geometric Adjustable Hollow Milling Tool</p>
+</div>
+
+<p>Hollow mills are also made adjustable. The design shown in
+<a href="#Fig_5_12">Fig. 12</a> is especially adapted for brass finishing. It can also be
+used for taking light cuts on cast iron or steel but its use in
+place of roughing or finishing box-tools for general use is not
+recommended. With the exception of the cutters and screws,
+the complete tool consists of three parts, <i>viz.</i>, the holder, cam,
+and ring. The cam serves to adjust the cutters for different
+diameters. The adjustment is made by the two screws shown,
+the amount being indicated by a micrometer scale. When adjusting
+the cutters for a given diameter, the use of a hardened
+steel plug of the required size is advisable, the cutters being
+adjusted against the plug.</p>
+
+<a name="Secnum_5_10" id="Secnum_5_10"></a><p><b>Releasing Die and Tap Holders.</b>&mdash;Threads are cut in the
+turret lathe by means of dies for external threading, and taps for
+internal threading, the die or tap being held in a holder attached
+to the turret. A simple form of releasing die holder is shown<span class="pagenum"><a name="Pg_200" id="Pg_200">[200]</a></span>
+at <i>B</i>, <a href="#Fig_5_11">Fig. 11</a>. This holder was designed for the spring-screw
+type of threading die shown to the left. The die is clamped in
+the holder <i>a</i> by the set-screw shown, and the shank <i>b</i> of the holder
+is inserted in the turret hole. Holder <i>a</i> has an extension <i>c</i> which
+passes through the hollow shank. When the die is pressed
+against the end of the work, holder <i>a</i> and its extension moves
+back until lug <i>d</i> on the holder engages lug <i>e</i> on the shank. The
+die and holder are then prevented from rotating with the work
+and the die begins to cut a thread. It continues to screw itself
+onto the work with the turret following, until the thread has
+been cut to the required length; the turret is then stopped and
+as the die and holder <i>a</i> are drawn forward, lugs <i>d</i> and <i>e</i> disengage
+so that the die simply rotates with the work without continuing
+to advance. The lathe spindle is then reversed and as the turret
+is moved back by hand, pin <i>f</i> comes around and enters notch <i>g</i>,
+thus holding the die stationary; the die then backs off from the
+threaded end. Some tap holders are also constructed the same
+as this die holder, so far as the releasing mechanism is concerned.
+There are also many other designs in use, some of which
+operate on this same principle.</p>
+
+<a name="Secnum_5_11" id="Secnum_5_11"></a><p><b>Self-opening Die Heads.</b>&mdash;The type of die holder shown at
+<i>B</i> in <a href="#Fig_5_11">Fig. 11</a> is objectionable because of the time required for
+backing the die off the threaded end; hence, self-opening dies
+are extensively used in turret lathe work. As the name implies,<span class="pagenum"><a name="Pg_201" id="Pg_201">[201]</a></span>
+this type of die, instead of being solid, has several chasers
+which are opened automatically when the thread has been cut
+to the required length. The turret can then be returned without
+reversing the lathe spindle. The dies are opened by simply
+stopping the travel of the turret slide, the stop-rod for the feed
+of the turret being adjusted to give the proper amount of travel.</p>
+
+<a name="Fig_5_13" id="Fig_5_13"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/208sm.png" alt="Self-opening and Adjustable Screw-cutting Die Head" /></div>
+<p class="caption750">Fig. 13. Geometric Self-opening and Adjustable Screw-cutting Die Head</p>
+</div>
+
+<p>A well-known die head of the self-opening type is shown in
+<a href="#Fig_5_13">Fig. 13</a>. The dies open automatically as soon as the travel of
+the head is retarded, or they can be opened at any point by simply
+holding back on the turnstile or lever by which the turret slide
+is moved. The die is closed again by means of the small handle
+seen projecting at right-angles from the side of the head. The
+closing may be done by hand or automatically by screwing a pin
+into a threaded hole opposite the handle and attaching a small
+piece of flat steel to the back edge of the turret slide. The latter
+will then engage the pin as the turret revolves, thus closing
+the die head. This die head has a roughing and finishing attachment
+which is operated by handle <i>A</i>. When this handle
+is moved forward, the dies are adjusted outward 0.01 inch for
+the roughing cut, whereas returning the handle closes and locks
+the dies for the finishing cut. The die head has a micrometer
+scale which is used when making slight adjustments to compensate
+for the wear of the chasers or to make either a tight-or
+a loose-fitting thread.</p>
+
+<a name="Fig_5_14" id="Fig_5_14"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/209sm.png" alt="Geometric Collapsing Tap" /></div>
+<p class="caption750">Fig. 14. Geometric Collapsing Tap</p>
+</div>
+
+<p><span class="pagenum"><a name="Pg_202" id="Pg_202">[202]</a></span>
+<a name="Secnum_5_12" id="Secnum_5_12"></a><b>Collapsing Taps.</b>&mdash;The collapsing tap shown in <a href="#Fig_5_14">Fig. 14</a> is one
+of many different designs that are manufactured. They are
+often used in turret lathe practice in place of solid taps. When
+using this particular style of collapsing tap, the adjustable gage
+<i>A</i> is set for the length of thread required. When the tap has
+been fed to this depth, the gage comes into contact with the
+end of the work, which causes the chasers to collapse automatically.
+The tool is then withdrawn, after which the chasers
+are again expanded and locked in position by the handle seen at
+the side of the holder. In all threading operations, whether
+using taps or dies, a suitable lubricant should be used, as a better
+thread is obtained and there is less wear on the tools. Lard oil
+is a good lubricant, although cheaper compounds give satisfactory
+results on many classes of work.</p>
+
+<a name="Fig_5_15" id="Fig_5_15"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/211sm.png" alt="Various Types of Tools for the Turret Lathe" /></div>
+<p class="caption750">Fig. 15. Various Types of Tools for the Turret Lathe</p>
+</div>
+
+<a name="Secnum_5_13" id="Secnum_5_13"></a><p><b>Miscellaneous Turret Lathe Tools.</b>&mdash;The chamfering tool
+shown at <i>A</i>, <a href="#Fig_5_15">Fig. 15</a>, is used for pointing the end of a bar before
+running on a roughing box-tool. This not only finishes the
+end of the bar but provides an even surface for the box-tool to
+start on. The cutter is beveled on the end to form a cutting
+edge and it is held at an angle. The back-rest consists of a
+bell-mouthed, hardened tool-steel bushing which supports the
+bar while the cut is being taken.</p>
+
+<p>The stop gages <i>B</i> and <i>C</i> are used in the turret to govern the
+length of stock that is fed through the spindle. When a finished
+piece has been cut off, the rough bar is fed through the spindle
+and up against the stop gage, thus locating it for another operation.
+This gage may be a plain cylindrical piece of hardened
+steel, as at <i>B</i>, or it may have an adjusting screw as at <i>C</i>; for
+special work, different forms or shapes are also required. The
+stop gages on some machines, instead of being held in the turret,
+are attached to a swinging arm or bracket that is fastened to
+the turret slide and is swung up in line with the spindle when
+the stock is fed forward.</p>
+
+<p>The center drilling tool <i>D</i> is designed to hold a standard combination
+center drill and reamer. This type of tool is often used
+when turning parts that must be finished afterwards by grinding,
+to form a center for the grinding machine. The adjustable turning<span class="pagenum"><a name="Pg_203" id="Pg_203">[203]</a></span>
+tool <i>E</i> is used for turning the outside of gear blanks, pulley
+hubs or the rims of small pulleys. The pilot <i>a</i> enters the finished
+bore to steady the tool, and cutter <i>b</i> is adjusted to turn to the
+required diameter.</p>
+
+<p>The cutting-off tool-holder <i>F</i> (which is held on the cross-slide
+of the turret lathe) is usually more convenient than a regular
+toolpost, as the blade can be set closer to the chuck. The
+blade is held in an inclined position, as shown, to provide rake
+for the cutting edge; the inclined blade can also be adjusted
+vertically, a limited amount, by moving it in or out. The
+multiple cutting-off tool <i>G</i> holds two or more blades and is used
+for cutting off several washers, collars, etc., simultaneously.
+By changing the distance pieces between the cutters, the latter
+are spaced for work of different widths. The flat drill holder<span class="pagenum"><a name="Pg_204" id="Pg_204">[204]</a></span>
+<i>H</i> is used for drilling short holes, and also to form a true &#8220;spot&#8221;
+or starting point for other drills.</p>
+
+<p>Knurling tools are shown at <i>I</i> and <i>J</i>. The former is intended
+for knurling short lengths and is sometimes clamped on
+top of the cut-off tool on the cross-slide, the end being swung
+back after knurling (as shown by the dotted lines) to prevent
+interference with the work when the cutting-off tool is in operation.
+The knurling tool <i>J</i> has a shank and is held in the turret.
+The two knurls are on opposite sides of the work so that the
+pressure of knurling is equalized. By adjusting the arms which
+hold the knurls, the tool can be set for different diameters.</p>
+
+<p>Three styles of drill holders are shown at <i>K</i>, <i>L</i> and <i>M</i>. Holder
+<i>K</i> is provided with a split collet (seen to the left) which is tightened
+on the drill shank by a set-screw in the holder. This
+holder requires a separate collet for each size drill. The taper
+shank drill holder <i>L</i> has a standard taper hole into which the
+shank of the drill is inserted. The adjustable type of holder <i>M</i> is
+extensively used, especially on small and medium sized machines
+when several sizes of drills are necessary. This holder is simply
+a drill chuck fitted with a special shank. For large drills the
+plain style of holder <i>K</i> is recommended, and if only a few sizes
+of drills are required, it is more satisfactory and economical
+than the adjustable type.</p>
+
+<p>The various types of small turret lathe tools referred to in
+the foregoing for turning, threading, tapping, knurling, etc., are
+a few of the many different designs of tools used in turret lathe
+practice. Naturally, the tool equipment for each particular
+job must be changed somewhat to suit the conditions governing
+each case. The tools referred to, however, represent in a general
+way, the principal types used in ordinary practice. Some
+of the more special tools are shown in connection with examples
+of turret lathe work, which are referred to in the following.</p>
+
+<a name="Fig_5_16" id="Fig_5_16"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/213sm.png" alt="Method of Boring and Turning Pistons in Gisholt Lathe, Special Chuck and Tools for Turning, Boring and Cutting Off Eccentric Piston Rings" /></div>
+<p class="caption750">Fig. 16. (A) Method of Boring and Turning Pistons in Gisholt Lathe.<br />(B)
+Special Chuck and Tools for Turning, Boring and Cutting Off Eccentric
+Piston Rings</p>
+</div>
+
+<a name="Secnum_5_14" id="Secnum_5_14"></a><p><b>Turning Gasoline Engine Pistons in Turret Lathe.</b>&mdash;The
+making of pistons for gas engines, especially in automobile factories,
+is done on such a large scale that rapid methods of machining
+them are necessary. The plan view <i>A</i>, <a href="#Fig_5_16">Fig. 16</a>, shows
+the turret lathe tools used in one shop for doing this work. As
+<span class="pagenum"><a name="Pg_205" id="Pg_205">[205]</a></span>
+is often advisable with work done in large quantities, the rough
+castings are made with extra projections so arranged as to assist
+in holding them. These projections are, of course, removed
+when the piece is completed. In this case the piston casting <i>a</i>
+has a ring about 1<sup class="enum">1</sup>/<sub class="denom">4</sub> inch long and a little less in diameter than
+the piston, at the chucking end. The piston is held in suitable
+chuck jaws <i>b</i> which are tightened against the inside of this ring.
+The set-screws in these special jaws are then tightened, thus
+clamping the casting between the points of the screws and the
+jaws. This method of holding permits the whole exterior of
+the piston to be turned, since it projects beyond the chuck jaws.
+This is the object in providing the piston with the projecting
+ring by which it is held.</p>
+
+<p>The first operation consists in rough-boring the front end of
+the piston. The double-ended cutter <i>n</i> is held in boring-bar <i>m</i>,
+which is, in turn, supported by a drill-holder, clamped to one<span class="pagenum"><a name="Pg_206" id="Pg_206">[206]</a></span>
+of the faces of the turret. This bar is steadied by a bushing in
+the drill support <i>c</i> which is attached to the carriage, and may be
+swung into or out of the operating position, as required. After
+this cut is completed, the turret is revolved half way around and
+the casting is finish-bored in a similar manner, with double-ended
+cutter <i>n<sub>1</sub></i> held in bar <i>m<sub>1</sub></i>, the drill support being used as in
+the previous case. The support is then turned back out of the
+way to allow the turning tools in the turret toolpost to be used.</p>
+
+<p>The outside of the piston is next rough-turned with tool <i>k</i>
+in the turret toolpost, which is revolved to bring this cutter into
+action. The toolpost is then turned to the position shown,
+and the outside is finish-turned by tool <i>j</i>, which takes a broad
+shaving cut. The turret tool-holder is again revolved to bring
+form tool <i>l</i> into position. This tool cuts the grooves for the
+piston rings. Suitable positive stops are, of course, provided
+for both the longitudinal and cross movements of the turret
+toolpost.</p>
+
+<p>In the second operation, the piston <i>a</i> is reversed and held in
+soft jaws, which are used in place of the hardened jaws <i>b</i> shown in
+the illustration. These jaws are bored to the outside diameter
+of the piston, so that when closed, they hold the work true or
+concentric with the lathe spindle. In this operation the chucking
+ring by which the piston was previously held is cut off, and
+the end of the piston is faced true. If the crank-pin hole is to
+be finished, a third operation is necessary, a self-centering chuck-plate
+and boring and reaming tools being used. (These are not
+shown in the illustration.)</p>
+
+<a name="Secnum_5_15" id="Secnum_5_15"></a><p><b>Turning Piston Rings in Turret Lathe.</b>&mdash;One method of turning
+piston rings is shown at <i>B</i> in <a href="#Fig_5_16">Fig. 16</a>. The piston rings are
+cut from a cast-iron cylindrical piece which has three lugs <i>b</i>
+cast on one end and so arranged that they may be held in a three-jawed
+chuck. This cylindrical casting is about 10 inches long,
+and when the rings are to have their inside and outside surfaces
+concentric, the casting is held by the lugs in the regular jaws
+furnished with the chuck. (The arrangement used for turning
+and boring eccentric rings, which is that shown in the illustration,
+will be described later.)</p>
+
+<p><span class="pagenum"><a name="Pg_207" id="Pg_207">[207]</a></span>
+The casting <i>a</i>, from which the rings are made, is first rough-bored
+with double-ended cutter <i>n</i> in boring-bar <i>m</i>, after which
+it is finish-bored with cutter <i>n<sub>1</sub></i> in bar <i>m<sub>1</sub></i>. While taking these
+cuts, the bars <i>m</i> and <i>m<sub>1</sub></i> are supported by their extension ends
+which enter bushing <i>r</i> located in the central hole of the chuck.
+This furnishes a rigid support so that a heavy cut can be
+taken.</p>
+
+<p>The outside of the casting is next rough-turned with tool <i>k</i>,
+held in the turret toolpost. This toolpost is then revolved to
+bring tool <i>j</i> into position, by which the outside is turned true to
+size, a broad shaving chip being taken. The toolpost is again
+swung around, to bring the cutting-off tool-holder <i>l</i> into position.
+This holder contains four blades set the proper distance apart
+to give rings of the desired width. Each blade, from right to
+left, is set a little back of the preceding one, so that the rings are
+cut off one after the other, the outer rings being supported until
+they are completely severed. After the first four rings are cut
+off, the carriage is moved ahead to a second stop, and four more
+rings are severed, this operation being continued until the casting
+has been entirely cut up into rings.</p>
+
+<p>When the bore of the ring is to be eccentric with the outside,
+the holding arrangement shown in the illustration is used. The
+casting a is bolted to a sliding chuck-plate <i>c</i>, and the outside is
+rough-turned with tool <i>k</i> in the toolpost. Finishing tool <i>j</i> is
+then brought into action, and the outside diameter is turned
+accurately to size. Then the sliding chuck-plate <i>c</i>, carrying the
+work, is moved over a distance equal to the eccentricity desired,
+and the work is bored with cutters <i>n</i> and <i>n<sub>1</sub></i> as in the previous
+case. The turret toolpost is next revolved and the tools <i>l</i> are
+used for cutting off the rings. The reason for finishing the
+outside first is to secure smooth rings in cutting off, as this
+operation should be done when the work is running concentric
+with the bore, rather than with the exterior surface.</p>
+
+<p>It will be evident that this method gives a far greater output
+of rings than is possible by finishing them in the more primitive
+way on engine lathes. The faces of the rings may be finished in
+a second operation if desired, or they may be ground, depending<span class="pagenum"><a name="Pg_208" id="Pg_208">[208]</a></span>
+on the method used in the shop where the work is being done,
+and the accuracy required.</p>
+
+<a name="Fig_5_17" id="Fig_5_17"></a>
+<div class="figcenter"><img src="images/216sm.jpg" alt="Turning Gasoline Engine Pistons in Pratt &amp; Whitney Turret Lathe" />
+<p class="caption750">Fig. 17. Turning Gasoline Engine Pistons in Pratt &amp; Whitney Turret Lathe</p>
+</div>
+
+<a name="Secnum_5_16" id="Secnum_5_16"></a><p><b>Piston Turning in Pratt and Whitney Turret Lathe.</b>&mdash;A turret
+lathe equipped with tools for turning, facing and grooving automobile
+gasoline engine pistons is shown in <a href="#Fig_5_17">Fig. 17</a>. The piston
+is held on an expanding pin chuck which is so constructed that
+all of the pins are forced outward with equal pressure and automatically
+conform to any irregularities on the inside of the
+piston. Tool <i>A</i> rough-turns the outside, and just as this tool
+completes its cut, a center hole is drilled and reamed in the end
+of the piston by combination drill and reamer <i>B</i>. The turret
+is then indexed one-half a revolution and a finishing cut is taken
+by tool <i>C</i>. After the cylindrical body of the piston has been
+turned, tools held in a special holder <i>E</i> attached to the cut-off
+slide are used to face the ends of the piston and cut the packing-ring
+grooves. While the grooves are being cut, the outer
+end of the piston is supported by center <i>D</i>. The center hole in
+the end also serves to support the piston while being ground to
+the required diameter in a cylindrical grinding machine. The
+edge at the open end of the piston may also be faced square and<span class="pagenum"><a name="Pg_209" id="Pg_209">[209]</a></span>
+the inner corner beveled by a hook tool mounted on the rear
+cross-slide, although this is usually done in a separate operation.
+(This provides a true surface by which to hold this end when
+grinding.)</p>
+
+<p>This illustration (<a href="#Fig_5_17">Fig. 17</a>) shows very clearly the stops which
+automatically disengage the turret feed. A bracket <i>F</i> is bolted
+to the front of the bed and contains six stop-rods <i>G</i> (one for each
+position or side of the turret). When one of these stop-rods
+strikes lever <i>H</i>, the feed is disengaged, the stop being adjusted
+to throw out the feed when the tool has completed its cut.
+Lever <i>H</i> is automatically aligned with the stop-rods for different
+sides of the turret by a cam <i>J</i> on the turret base. A roller
+<i>K</i> bears against this cam and, through the connecting shaft and
+lever shown, causes lever <i>H</i> to move opposite the stop-rod for
+whatever turret face is in the working position. Lever <i>L</i> is
+used for engaging the feed and lever <i>R</i> for disengaging it by
+hand.</p>
+
+<p>The indexing of the turret at the end of the backward movement
+of the slide is controlled by stop <i>M</i> against which rod <i>N</i>
+<span class="pagenum"><a name="Pg_210" id="Pg_210">[210]</a></span>
+strikes, thus disengaging the lock bolt so that the turret can turn.
+This stop <i>M</i> is adjusted along the bed to a position depending
+upon the length of the turret tools and the distance the turret
+must move back to allow the tools to clear as they swing around.</p>
+
+<a name="Fig_5_18" id="Fig_5_18"></a>
+<div class="figcenter"><img src="images/217sm.jpg" alt="Pratt &amp; Whitney Turret Lathe equipped with Special Attachment for Turning Eccentric Piston Rings" />
+<p class="caption750">Fig. 18. Pratt &amp; Whitney Turret Lathe equipped with Special<br />Attachment
+for Turning Eccentric Piston Rings</p>
+</div>
+
+<a name="Secnum_5_17" id="Secnum_5_17"></a><p><b>Attachment for Turning Piston Rings.</b>&mdash;<a href="#Fig_5_18">Fig.
+18</a> shows a special attachment applied to a Pratt &amp; Whitney turret lathe for
+turning eccentric, gas-engine piston rings. The boring of the
+ring casting, turning the outside and cutting off the rings, is
+done simultaneously. The interior of the casting is turned concentric
+with the lathe spindle by a heavy boring-bar, the end of
+which is rigidly supported by a bushing in the spindle. The
+slide which carries the outside turning tool is mounted on a
+heavy casting which straddles the turret. The outside of the
+ring casting is turned eccentric to the bore as a result of an in-and-out
+movement imparted to the tool by a cam on shaft <i>A</i>
+which is rotated from the lathe spindle through the gearing
+shown. For each revolution of the work, the tool recedes from
+the center and advances toward it an amount sufficient to give<span class="pagenum"><a name="Pg_211" id="Pg_211">[211]</a></span>
+the required eccentricity. When the turning and boring tools
+have fed forward about 2 inches, then the cutting-off tools which
+are held in holder <i>B</i> come into action. The end of each cutting-off
+tool, from right to left, is set a little farther away from the
+work than the preceding tool, so that the end rings are always
+severed first as the tools are fed in by the cross-slide. A number
+of the completed rings may be seen in the pan of the machine.</p>
+
+<a name="Fig_5_19" id="Fig_5_19"></a>
+<div class="figcenter"><img src="images/218sm.jpg" alt="Tool Equipment for Worm Gear Blanks&mdash;Davis Turret Lathe" />
+<p class="caption750">Fig. 19. Tool Equipment for Machining Worm Gear Blanks&mdash;Davis Turret Lathe</p>
+</div>
+
+<a name="Secnum_5_18" id="Secnum_5_18"></a><p><b>Turning Worm-gear Blanks in Turret Lathe.</b>&mdash;This is a second
+operation, the hub of worm-gear blank <i>G</i> (<a href="#Fig_5_19">Fig. 19</a>) having
+previously been bored, reamed, and faced on the rear side. The
+casting is mounted upon a close-fitting arbor attached to a
+plate bolted to the faceplate of the lathe, and is driven by two
+pins which engage holes on the rear side. The rim is first rough-turned
+by a tool <i>A</i> which operates on top, and the side is rough-faced
+by a toothed or serrated cutter <i>B</i>. A similar tool-holder<span class="pagenum"><a name="Pg_212" id="Pg_212">[212]</a></span>
+having a tool <i>C</i> and a smooth cutter <i>D</i> is then used to turn the
+rim to the required diameter and finish the side. The end of
+the hub is faced by cutters mounted in the end of bars <i>E</i> and <i>F</i>,
+one being the roughing cutter and the other the finishing cutter.
+The work arbor projects beyond the hub, as will be seen, and
+forms a pilot that steadies these cutter bars. The curved rim
+of the gear is turned to the required radius (preparatory to
+gashing and bobbing the worm-wheel teeth) by a formed tool
+<i>H</i> held on the cross-slide.</p>
+
+<a name="Fig_5_20" id="Fig_5_20"></a>
+<div class="figcenter"><img src="images/219sm.jpg" alt="Turning Bevel Gear Blanks in Davis Turret Lathe&mdash;First Operation" />
+<p class="caption750">Fig. 20. Turning Bevel Gear Blanks in Davis Turret Lathe&mdash;First Operation</p>
+</div>
+
+<a name="Secnum_5_19" id="Secnum_5_19"></a><p><b>Turning Bevel Gear Blanks.</b>&mdash;<a href="#Fig_5_20">Fig. 20</a> shows a plan view of
+the tools used for the first turning operation on bevel gear blanks
+(these gears are used for driving drill press spindles). The cored
+hole is beveled true at the end by flat drill <i>A</i> to form a true starting
+surface for the three-fluted drill <i>B</i> which follows. The hole
+is bored close to the required size by a tool (not shown) held in
+the end of bar <i>C</i>, and it is finished by reamer <i>D</i>. The cylindrical
+end of the gear blank or hub is rough-and finish-turned by<span class="pagenum"><a name="Pg_213" id="Pg_213">[213]</a></span>
+tools held in holders <i>E</i> and <i>F</i>, respectively. (These holders
+were made to set at an angle of 45 degrees, instead of being
+directly over the work, as usual, so that the cutters would be in
+view when setting up the machine.) It will be noted that the
+chuck is equipped with special jaws which fit the beveled part
+of the casting.</p>
+
+<a name="Fig_5_21" id="Fig_5_21"></a>
+<div class="figcenter"><img src="images/220sm.jpg" alt="Second Operation on Bevel Gear Blanks" />
+<p class="caption750">Fig. 21. Second Operation on Bevel Gear Blanks</p>
+</div>
+
+<p>The second and final operation on this blank is shown in <a href="#Fig_5_21">Fig.
+21</a>. The work <i>A</i> is held by a special driver plate attached to
+the faceplate of the machine. This driver plate has two pins
+which engage holes drilled in the gear blank and prevent it from
+rotating. The blank is also held by a bolt <i>B</i> which forces a bushing
+against the cylindrical end. First, the broad beveled side
+which is to be the toothed part of the gear, is rough-turned by
+toothed cutters <i>C</i>, and a recess is formed in the end of the blank,
+by a turning tool in this same tool-holder. A similar tool-holder
+<i>E</i>, having finishing cutters, is then used to finish the bevel face
+and recess. The other tools seen in the turret are not used for
+this second operation. The rear bevel is roughed and finished
+by tools and held on the cross-slide.</p>
+
+<a name="Secnum_5_20" id="Secnum_5_20"></a><p><b>Shell Turning Operation in Flat Turret Lathe.</b>&mdash;The &#8220;flat
+turret lathe&#8221; is so named because the turret is a flat circular
+plate mounted on a low carriage to secure direct and rigid support
+from the lathe bed. The tools, instead of being held by<span class="pagenum"><a name="Pg_214" id="Pg_214">[214]</a></span>
+shanks inserted in holes in the turret, are designed so that they
+can be clamped firmly onto the low circular turret plate.</p>
+
+<a name="Fig_5_22" id="Fig_5_22"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/221sm.png" alt="Sectional View of Tapering Mold Shell which is turned in Hartness Flat Turret Lathe" /></div>
+<p class="caption750">Fig. 22. Sectional View of Tapering Mold Shell which is turned in<br />Hartness
+Flat Turret Lathe, as illustrated in <a href="#Fig_5_23">Figs. 23</a> to <a href="#Fig_5_27">27</a>, Inclusive</p>
+</div>
+
+<p>An interesting example of flat turret lathe work is shown in
+<a href="#Fig_5_22">Fig. 22</a>. This is a steel shell which must be accurately finished
+to a slight taper, both inside and out, threaded and plain recesses
+are required at the ends, and, in addition, one or two minor
+operations are necessary. This work is done in the Hartness
+flat turret lathe, built by the Jones &amp; Lamson Machine Co.
+The shells are turned from cold-drawn seamless steel tubing,
+having a carbon content of 0.20 per cent, and they are finished
+at the rate of one in nine minutes. The tubing comes to the
+machine in 12-foot lengths, and the tube being operated upon
+is, of course, fed forward through the hollow spindle as each
+successive shell is severed.</p>
+
+<a name="Fig_5_23" id="Fig_5_23"></a>
+<div class="figcenter"><img src="images/222sm.jpg" alt="Rough-turning and Boring" />
+<p class="caption750">Fig. 23. First Operation on Shell Illustrated in <a href="#Fig_5_22">Fig. 22</a>&mdash;Rough-turning and Boring</p>
+</div>
+
+<p>In finishing this shell, five different operations are required.
+During the first operation the shell is rough-bored and turned by
+one passage of a box-tool, <a href="#Fig_5_23">Fig. 23</a>, and the recess <i>A</i>, <a href="#Fig_5_22">Fig. 22</a>,
+at the outer end, is finished to size by a second cutter located in
+the boring-bar close to the turret. The turret is then indexed
+to the second station which brings the threading attachment <i>G</i>
+into position, as shown in <a href="#Fig_5_24">Fig. 24</a>. After the thread is finished,
+<span class="pagenum"><a name="Pg_215" id="Pg_215">[215]</a></span>
+the recess <i>B</i>, <a href="#Fig_5_22">Fig. 22</a>, is turned by a flat cutter <i>K</i>, <a href="#Fig_5_25">Fig. 25</a>. The
+inner and outer surfaces are then finished to size by a box-tool
+mounted on the fourth station of the turret and shown in position
+in <a href="#Fig_5_26">Fig. 26</a>. The final operation, <a href="#Fig_5_27">Fig. 27</a>, is performed by three
+tools held on an auxiliary turret cross-slide, and consists in
+rounding the corners at <i>b</i> and <i>c</i>, <a href="#Fig_5_22">Fig. 22</a>, and severing the finished
+shell.</p>
+
+<p>One of the interesting features connected with the machining
+of this shell is the finishing of the inner and outer tapering surfaces.
+The taper on the outside is <sup class="enum">3</sup>/<sub class="denom">32</sub> inch per foot, while the
+bore has a taper of only <sup class="enum">1</sup>/<sub class="denom">64</sub> inch per foot, and these surfaces are
+finished simultaneously. The box-tool employed is of a standard
+type, with the exception of an inserted boring-bar, and the
+taper on the outside is obtained by the regular attachment which
+consists of a templet <i>D</i> (<a href="#Fig_5_23">Fig. 23</a>) of the required taper, that
+causes the turning tool to recede at a uniform rate as it feeds along.
+To secure the internal taper, the headstock of the machine is
+swiveled slightly on its transverse ways by the use of tapering
+gibs. By this simple method, the double taper is finished to
+the required accuracy without special tools or equipment.</p>
+
+<a name="Fig_5_24" id="Fig_5_24"></a>
+<div class="figcenter"><img src="images/223sm.jpg" alt="Cutting Internal Thread" />
+<p class="caption750">Fig. 24. Second Operation&mdash;Cutting Internal Thread</p>
+</div>
+
+<a name="Fig_5_25" id="Fig_5_25"></a>
+<div class="figcenter"><img src="images/224sm.jpg" alt="Turning Recess at Rear End; Tool is shown withdrawn" />
+<p class="caption750">Fig. 25. Third Operation&mdash;Turning Recess at Rear End; Tool is shown withdrawn</p>
+</div>
+
+<a name="Fig_5_26" id="Fig_5_26"></a>
+<div class="figcenter"><img src="images/225sm.jpg" alt="Finishing the Bore and Outside" />
+<p class="caption750">Fig. 26. Fourth Operation&mdash;Finishing the Bore and Outside</p>
+</div>
+
+<a name="Fig_5_27" id="Fig_5_27"></a>
+<div class="figcenter"><img src="images/226sm.jpg" alt="Rounding Ends, Scoring Large End, and Cutting Off" />
+<p class="caption750">Fig. 27. Fifth Operation&mdash;Rounding Ends, Scoring Large End, and Cutting Off</p>
+</div>
+
+<p>As those familiar with this machine know, the longitudinal<span class="pagenum"><a name="Pg_216" id="Pg_216">[216]</a></span>
+movements of the turret as well as the transverse movements
+of the headstock are controlled by positive stops. The headstock
+of this machine has ten stops which are mounted in a revolving
+holder and are brought into position, as required, by
+manipulating a lever at the front. The stops for length, or those
+controlling the turret travel, are divided into two general groups,
+known as &#8220;A&#8221; and &#8220;B&#8221;. Each of these groups has six stops
+so that there are two stops for each of the six positions or stations
+of the turret, and, in addition, five extra stops are available for
+any one tool, by the engagement of a pin at the rear of the turret.
+The change from the &#8220;A&#8221; to the &#8220;B&#8221; stops is made by adjusting
+lever <i>L</i>, <a href="#Fig_5_26">Fig. 26</a>, which also has a neutral position.</p>
+
+<p>After the box-tool for the roughing cut, shown at work in
+<a href="#Fig_5_23">Fig. 23</a>, has reached the end of its travel, further movement is
+arrested by a stop of the &#8220;A&#8221; group. The outside turning tool
+is then withdrawn by operating lever <i>E</i> and the turret is run
+back and indexed to the second station, thus bringing the threading
+attachment into position. The surface speed of 130 feet per
+minute which is used for turning is reduced to about 30 feet per
+minute for threading by manipulating levers <i>H</i>, <a href="#Fig_5_24">Fig. 24</a>. After
+the turret is located by another stop of the &#8220;A&#8221; group,
+the<span class="pagenum"><a name="Pg_217" id="Pg_217">[217]</a></span>
+threading attachment is made operative by depressing a small
+plunger <i>I</i>, which connects a vertical driving shaft from the
+spindle with the splined transmission shaft <i>J</i>. A reciprocating
+movement is then imparted to the thread chaser <i>t</i> which advances
+on the cutting stroke and then automatically retreats to clear
+the thread on the return. This movement is repeated until
+the thread is cut to the proper depth, as determined by one
+of the stops for the headstock. While the thread is being cut,
+the carriage is locked to the bed by the lever <i>N</i>, <a href="#Fig_5_26">Fig. 26</a>. It was
+found necessary to perform the threading operation before taking
+the outside finishing cut, owing to a slight distortion of the
+shell wall, caused by the threading operation.</p>
+
+<p>After the thread is finished, the turret is turned to the third
+station as shown in <a href="#Fig_5_25">Fig. 25</a>, and tool <i>K</i> for the inner recess <i>B</i>,
+<a href="#Fig_5_22">Fig. 22</a>, is brought into position and fed to the proper depth,
+as determined by another cross-stop. The turret is also locked
+in position for this operation. The finishing cuts for the bore
+and the outside are next taken by a box-tool which is shown
+near the end of its cut in <a href="#Fig_5_26">Fig. 26</a>. This box-tool is similar to
+the one used for roughing, but it is equipped with differently
+shaped cutters to obtain the required finish. The outside turning<span class="pagenum"><a name="Pg_218" id="Pg_218">[218]</a></span>
+tool has a straight cutting edge set tangent to the cylindrical
+surface and at an angle, while the boring tool has a cutting
+edge of large radius. An end view of this box-tool is shown in
+<a href="#Fig_5_27">Fig. 27</a>. A reduced feed is employed for the finishing cut, and
+the speed is increased to 130 feet per minute, which is the same
+as that used for roughing.</p>
+
+<p>During the next and final operation, the turret, after being
+indexed to the position shown in <a href="#Fig_5_27">Fig. 27</a>, is first located by a
+stop of the &#8220;A&#8221; group so that the cutting-off tool <i>R</i> in front can
+be used for rounding the corner <i>b</i>, <a href="#Fig_5_22">Fig. 22</a>. The stop lever <i>L</i>
+is then shifted and the turret is moved to a second stop of the
+&#8220;B&#8221; group. The corner <i>c</i> is then rounded and the shell is
+scored at <i>d</i> by two inverted tools <i>S</i> and <i>T</i> at the rear, after which
+the finished work is severed by the cut-off tool at the front.
+The cross-movement of these three tools is controlled by positive
+stops on the cross-slide, and the latter is moved to and fro by
+hand lever <i>O</i>. After the shell is cut off, the stop <i>M</i>, mounted
+on the turret, <a href="#Fig_5_26">Fig. 26</a>, is swung into position, and the tube is
+automatically fed forward to the swinging stop by the roll feed,
+as soon as the chuck is released by operating lever <i>Q</i>. This
+completes the cycle of operations. A copious supply of lubricant<span class="pagenum"><a name="Pg_219" id="Pg_219">[219]</a></span>
+is, of course, furnished to the tools during these operations,
+and the two boring-tool shanks are hollow so that lubricant
+can be forced through them and be made to play directly upon
+the cutters.</p>
+
+<a name="Fig_5_28" id="Fig_5_28"></a>
+<div class="figcenter"><img src="images/227sm.jpg" alt="Tool Equipment for Turning Scroll Gear Blank on Acme Flat Turret Lathe" />
+<p class="caption750">Fig. 28. Tool Equipment for Turning Scroll Gear Blank on Acme Flat Turret Lathe</p>
+</div>
+
+<a name="Secnum_5_21" id="Secnum_5_21"></a><p><b>Chuck Work in Flat Turret Lathe.</b>&mdash;Two examples of chuck
+work on the Acme combination flat turret lathe are shown in
+<a href="#Fig_5_28">Figs. 28</a> and <a href="#Fig_5_29">29</a>. <a href="#Fig_5_28">Fig. 28</a> shows the tool equipment for turning
+a cylindrical part <i>A</i> which is held in a three-jaw universal chuck.
+The front flange is first rough-turned by a bent turning tool <i>B</i>.
+The diameter is regulated by one of the cross-stops at <i>D</i> which
+has been previously set and controls the movement of the turret
+cross-slide. The longitudinal feed is disengaged when the flange
+has been turned, by an independent stop. This machine has twelve
+longitudinal stops, there being one for each turret face and six
+auxiliary stops, in addition to the stops for the cross-slide.</p>
+
+<p>After roughing the flange, the turret carriage is locked or
+clamped rigidly to the bed to prevent any lengthwise movement,
+and the back face of the front flange is rough-turned by tool <i>B</i>
+<span class="pagenum"><a name="Pg_220" id="Pg_220">[220]</a></span>
+in to the diameter of the hub which is indicated by a micrometer
+dial on the cross-feed screw. The carriage is then unlocked
+and auxiliary stop No. 7 is engaged (by turning a knob at the
+front of the slide) and the cylindrical hub is turned back to the
+rear flange, the feed being disengaged by the auxiliary stop just
+as the tool reaches the flange. The cross-slide is now moved
+outward, longitudinal auxiliary stop No. 8 is engaged, the
+turret slide is moved against the stop, the carriage is locked and
+the front sides of both the front and rear flanges are rough-faced
+by tools <i>B</i> and <i>C</i>. The turret is next indexed and the hole
+rough-bored by cutter <i>E</i>. After again indexing the turret, the
+hub and flanges are finish-turned and faced by tools <i>F</i> and <i>G</i>,
+as described for the rough-turning operation. The final operation
+is that of finishing the bore by cutter <i>H</i>.</p>
+
+<a name="Fig_5_29" id="Fig_5_29"></a>
+<div class="figcenter"><img src="images/228sm.jpg" alt="Acme Flat Turret Lathe Arranged for Turning Roller Feed Body" />
+<p class="caption750">Fig. 29. Acme Flat Turret Lathe Arranged for Turning Roller Feed Body</p>
+</div>
+
+<p>The operation shown in <a href="#Fig_5_29">Fig. 29</a> is that of turning the body
+of a roller feed mechanism for a turret lathe. The casting is
+held in a three-jaw universal chuck and it is first rough-bored
+by tool <i>A</i>. The turret is then indexed and the side of the body
+and end of the hub are rough-faced by tools at <i>B</i>. The turret
+is again indexed for rough-turning the outside of the hub and<span class="pagenum"><a name="Pg_221" id="Pg_221">[221]</a></span>
+body, by tools <i>C</i> and <i>D</i>. Similar tools <i>E</i> and <i>F</i> are then used
+to finish these same surfaces, after which the end of the hub
+and side of the body are finished by tools <i>G</i> and <i>H</i> similar to
+those located at <i>B</i>. The final operation is that of finishing
+the bore by tool <i>J</i> and cutting a groove in the outside of the
+hub by the bent tool <i>K</i>.</p>
+
+<a name="Fig_5_30" id="Fig_5_30"></a>
+<div class="figcenter"><img src="images/229sm.jpg" alt="Turret and Head of Jones &amp; Lamson Double-spindle Flat Turret Lathe" />
+<p class="caption750">Fig. 30. Turret and Head of Jones &amp; Lamson Double-spindle Flat Turret Lathe</p>
+</div>
+
+<a name="Secnum_5_22" id="Secnum_5_22"></a><p><b>Double-spindle Flat Turret Lathe.</b>&mdash;The extent to which
+modern turning machines have been developed, especially for
+turning duplicate parts in quantity, is illustrated by the design
+of turret lathe the turret and head of which is shown in <a href="#Fig_5_30">Fig. 30</a>.
+This machine has two spindles and a large flat turret which holds
+a double set of tools, so that two duplicate castings or forgings
+can be turned at the same time. It was designed primarily for
+chuck work and can be used as a single-spindle machine if desirable.
+When two spindles are employed for machining two duplicate
+parts simultaneously, considerably more time is required for
+setting up the machine than is necessary for the regular single-spindle
+type, but it is claimed that the increased rate of production
+obtained with the two-spindle design more than offsets<span class="pagenum"><a name="Pg_222" id="Pg_222">[222]</a></span>
+this initial handicap. The manufacturers consider the single-spindle
+machine the best type for ordinary machine building
+operations, regardless of whether the work is turned from the
+bar or is of the chucking variety. On the other hand, the double-spindle
+type is preferred when work is to be produced in such
+quantities that the time for setting up the machine becomes a
+secondary consideration.</p>
+
+<p>When the double-spindle machine is used as a single-spindle
+type, a chuck 17 inches in diameter is used, and when both
+spindles are in operation, two 9-inch chucks are employed.
+The general outline of the turret is square, and the tools are
+rigidly held, with a minimum amount of overhang, by means
+of tool-blocks and binding screws connected with the clamping
+plates. Two duplicate sets of tools are clamped to each side of
+the turret and these operate simultaneously on the two pieces
+held in the chucks or on faceplates. Primarily the turret is used<span class="pagenum"><a name="Pg_223" id="Pg_223">[223]</a></span>
+in but four positions, but when a 17-inch chuck or faceplate is
+employed, corner blocks may be held by the clamping plates in
+which tools are supported, giving, if necessary, four additional
+operations by indexing the turret to eight positions.</p>
+
+<a name="Fig_5_31" id="Fig_5_31"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/230sm.png" alt="Diagram showing Tool Equipment and Successive Steps in Machining Sprocket Blanks on Double-spindle Flat Turret Lathe" /></div>
+<p class="caption750">Fig. 31. Diagram showing Tool Equipment and Successive Steps<br />in
+Machining Sprocket Blanks on Double-spindle Flat Turret Lathe</p>
+</div>
+
+<p>A typical job to demonstrate the application of the double-spindle
+flat turret lathe is illustrated in <a href="#Fig_5_31">Fig. 31</a>. The parts to
+be turned are sprocket wheels which are held in the two 9-inch
+chucks. At the first position of the turret (which is the one
+illustrated), the inside is rough-bored by tools <i>A</i>. At the second
+position of the turret, tools <i>B</i> rough-face the inner sides of the
+flanges; tools <i>C</i> face the outer sides of the flanges, while tools <i>D</i>
+turn the faces of the flanges. At the third position of the turret,
+tools <i>E</i> finish-turn the inside of the flanges; tools <i>F</i> finish-turn
+the outside of the flanges, while tools <i>G</i> finish the faces of the
+flanges. At the fourth position of the turret, tools <i>H</i> finish-bore
+the sprockets; tools <i>I</i> complete the turning on the outside of the
+flanges, while tools <i>J</i> accurately size the interior of the flanges.</p>
+
+<p>With the double-spindle flat turret lathe, each operation is a
+double operation, and the speeds are varied according to the
+nature of the cut; thus, if at one position of the turret, the tools
+are required to rough out the work, this may be done rapidly,
+for it has no bearing on the other operations that are subsequently
+performed. Furthermore, if the following operation
+has to be performed with great care, this may be done without
+reducing the speed of the less exacting operations.</p>
+
+<a name="Fig_5_32" id="Fig_5_32"></a><span class="pagenum"><a name="Pg_224" id="Pg_224">[224]</a></span>
+<div class="figcenter"><img src="images/232sm.jpg" alt="Potter &amp; Johnston Machine" />
+<p class="caption750">Fig. 32. Potter &amp; Johnston Automatic Chucking and Turning Machine</p>
+</div>
+
+<a name="Secnum_5_23" id="Secnum_5_23"></a><p><b>Automatic Chucking and Turning Machine.</b>&mdash;The chucking
+and turning machine shown in <a href="#Fig_5_32">Fig. 32</a> is automatic in its operation,
+the feeding of the tools, indexing of the turret, etc., being
+done automatically after the machine is properly arranged, and
+the work is placed in the chuck. This machine is adapted to
+turning and boring a great variety of castings, forgings or parts
+from bar stock, and it is often used in preference to the hand-operated
+turret lathe, especially when a great many duplicate
+parts are required. It is provided with mechanism for
+operating the cross-slide, feeding the turret slide forward, returning
+it rapidly, rotating the turret to a new position, and
+feeding it forward quickly for taking a new cut. The cross-slide
+<span class="pagenum"><a name="Pg_225" id="Pg_225">[225]</a></span>
+and turret-slide movements are effected by cams mounted on
+the large drum <i>E</i> seen beneath the turret, while the various
+speed and feed changes are effected by dogs and pins carried on
+disk <i>D</i> which is keyed to the same shaft that the cam drum is
+mounted upon. This shaft with the cam drum and governing
+disk <i>D</i>, makes one revolution for each piece of work completed.
+The cams for operating the turret slide are mounted upon the
+periphery of drum <i>E</i>. The roll which engages the angular faces
+of these cams and imparts movement to the turret is carried
+by an intermediate slide which has rack teeth engaging a pinion
+on the square shaft <i>C</i>. By turning this shaft with a crank, the
+position of the turret-slide, with relation to the cam, may be
+adjusted for long or short work and long or short tools, as may
+be required.</p>
+
+<a name="Fig_5_33" id="Fig_5_33"></a>
+<div class="figcenter"><img src="images/233sm.jpg" alt="Rear View of Machine showing the Cross-slide Mechanism, Driving Gearing, etc." />
+<p class="caption750">Fig. 33. Rear View of Machine showing the Cross-slide Mechanism, Driving Gearing, etc.</p>
+</div>
+
+<p>The cams which operate the cross-slide are mounted on the
+right-hand end of drum <i>E</i> and actuate the yoke <i>A</i> (see <a href="#Fig_5_33">Fig. 33</a>)
+which extends diagonally upward. The rear end of this yoke
+has rack teeth meshing with the teeth of a segmental pinion,<span class="pagenum"><a name="Pg_226" id="Pg_226">[226]</a></span>
+which is fastened to rock-shaft <i>B</i>. At the headstock end, this
+rock-shaft carries another segmental pinion meshing with rack
+teeth formed on the cross-slide. The movement imparted to
+the yoke by the cams is thus transmitted through the pinions
+and rock-shaft to the cross-slide.</p>
+
+<a name="Fig_5_34" id="Fig_5_34"></a>
+<div class="figcenter"><img src="images/234sm.jpg" alt="The Automatic Controlling Mechanism for Feeds and Speeds" />
+<p class="caption750">Fig. 34. The Automatic Controlling Mechanism for Feeds and Speeds</p>
+</div>
+
+<p>The cam drum <i>E</i> is driven by a pinion meshing with a gear
+attached to its front side. This pinion is driven through a train
+of gearing from pulley <i>L</i> (see <a href="#Fig_5_34">Fig. 34</a>) which is belted to the
+spindle. The feeds are thus always dependent on the spindle
+speed. By means of epicyclic gearing and suitable clutches,
+the motion thus derived from the spindle may be made rapid
+for returning the turret to be indexed and then advancing it to
+the cutting position again, or very slow for the forward feed when
+the tools are at work. These changes from slow to fast or <i>vice
+versa</i> are controlled by disk <i>D</i>. This disk carries pins which
+strike a star wheel located back of the disk at the top, and as
+this star wheel is turned, the speeds are changed by operation
+of the gearing and clutches referred to. The first pin <i>M</i> that
+<span class="pagenum"><a name="Pg_227" id="Pg_227">[227]</a></span>
+strikes the star wheel advances it one-sixth of a rotation, changing
+the feed from fast to slow; the next pin that strikes it advances
+it another sixth of a rotation, changing the feed from slow to
+fast and so on. By adjusting the pins for each piece of work,
+the feed changes are made to take place at the proper time.
+Handwheel <i>E</i> is geared with the cam-shaft on which the star
+wheel is mounted, so that the feeds may be changed by hand
+if desired.</p>
+
+<p>In addition to these feed-changing pins, disk <i>D</i> has a dog
+which operates a lever by which the feed movement is stopped
+when the work has been completed. Four rates of feed are
+provided by quick change gearing of the sliding gear type, operated
+by handle <i>K</i>. With this handle set in the central position,
+the feed is disengaged. On the periphery of disk <i>D</i> are also
+clamped dogs or cams <i>N</i>, which operate a horizontal swinging
+lever <i>P</i> connected by a link with vertical lever <i>J</i>, which controls
+the two spindle speeds with which the machine is provided.
+Either one of these speeds can be automatically engaged
+at any time, by adjusting the cams <i>N</i> on disk <i>D</i>.</p>
+
+<p>Lever <i>H</i> connects or disconnects the driving pulley from the
+shaft on which it is mounted, thus starting or stopping the
+machine. The square shaft <i>G</i> serves to operate the drums by
+hand and is turned with a crank. The rotation of the turret,
+which takes place at the rear of its travel, is, of course, effected
+automatically. A dog, which may be seen in <a href="#Fig_5_32">Fig. 32</a> at the side
+of the bed, is set to trip the turret revolving mechanism at the
+proper point in the travel, to avoid interference between the
+tools and the work. The turret is provided with an automatic
+clamping device. The mechanism first withdraws the locking
+pin, unclamps the turret, revolves it, then throws in the locking
+pin and clamps the turret again.</p>
+
+<a name="Fig_5_35" id="Fig_5_35"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/236sm.png" alt="Example of Work done in Automatic Chucking and Turning Machine" /></div>
+<p class="caption750">Fig. 35. Simple Example of Work done in Automatic Chucking and Turning Machine</p>
+</div>
+
+<a name="Secnum_5_24" id="Secnum_5_24"></a><p><b>Example of Work on Automatic Turning Machine.</b>&mdash;The
+piece selected for illustrating the &#8220;setting up&#8221; and operation
+of the automatic chucking and turning machine is shown in
+<a href="#Fig_5_35">Fig. 35</a>. This is a second operation, and a very simple one
+which will clearly illustrate the principles involved. In the first
+operation, the hole was drilled, bored and reamed, the small end<span class="pagenum"><a name="Pg_228" id="Pg_228">[228]</a></span>
+of the bushing faced, and the outside diameter finished, as indicated
+by the sketch to the left. (The enlarged diameter at the
+end was used for holding the work in the chuck.) In the second
+operation (illustrated to the right), the enlarged chucking end
+is cut off and, in order to prevent wasting this piece, it is made
+into a collar for another part of the machine for which the bushing
+is intended; hence, the outside diameter is turned and the
+outside end faced, before cutting off the collar. In addition,
+the bushing is recessed in the second operation, and the outer
+end faced. In order to have the surfaces finished in the second
+operation, concentric with those machined in the first operation,
+the chuck is equipped with a set of soft &#8220;false jaws&#8221; which have
+been carefully bored to exactly the diameter of the work to be
+held.</p>
+
+<p>The first thing to determine when setting up a machine of
+this type is the order of operations. In this particular case,
+the order is as follows: At the first position of the turret, the
+outside collar is rough-turned and the outer end rough-faced.
+At the second position, the collar is turned to the required diameter
+and the outer face is finished. The third face of the turret
+is not equipped with tools, this part of the cycle being taken up
+in cutting off the collar with a cut-off tool on the rear cross-slide.
+The fourth operation is that of recessing the bushing, and the
+fifth operation, facing the end to remove the rough surface left
+by the cutting-off tool.</p>
+
+<a name="Fig_5_36" id="Fig_5_36"></a>
+<div class="figcenter"><img src="images/237sm.jpg" alt="Front View of Machine set up for the Finishing Operation on the Recessed Bushing and Collar shown in the Foreground and in Fig. 35" />
+<p class="caption750">Fig. 36. Front View of Machine set up for the Finishing Operation on the
+Recessed Bushing and Collar shown in the Foreground and in <a href="#Fig_5_35">Fig. 35</a></p>
+</div>
+
+<p>The tools <i>A</i> and <i>B</i>, <a href="#Fig_5_36">Fig. 36</a>, used for turning the outside of
+the flange, are held in brackets <i>C</i> bolted to the face of the turret.
+<span class="pagenum"><a name="Pg_229" id="Pg_229">[229]</a></span>
+These brackets are each provided with three holes for carrying
+turning tool-holders. This arrangement provides for turning a
+number of diameters at different positions, simultaneously, but
+for this particular operation, a single cutting tool for each tool-holder
+is all that is necessary. A special device is used for recessing
+and will be described later.</p>
+
+<a name="Fig_5_37" id="Fig_5_37"></a>
+<div class="figcenter"><img src="images/238sm.png" alt="Plate on the Headstock of Machine Illustrated in Fig. 32" />
+<p class="caption750">Fig. 37. Plate on the Headstock of Machine Illustrated in<br /><a href="#Fig_5_32">Fig. 32</a>
+giving the Speeds and Feeds</p>
+</div>
+
+<a name="Secnum_5_25" id="Secnum_5_25"></a><p><b>Determining Speed and Feed Changes.</b>&mdash;As previously mentioned,
+the particular machine illustrated in <a href="#Fig_5_32">Fig. 32</a> can be
+arranged for two automatic changes of speed to suit different
+diameters on the work. The change gears that will give the
+required spindle speeds should first be selected. These change
+gears for different speeds are listed on a speed and feed plate
+attached to the headstock of the machine (see <a href="#Fig_5_37">Fig. 37</a>). It is
+possible to use one speed from the list given for the fast train
+of gears, and one from the list for the slow train, so long as the
+same gears are not used in each case. The diameter of the
+collar on the work shown in <a href="#Fig_5_35">Fig. 35</a> is 2<sup class="enum">1</sup>/<sub class=
+"denom">2</sub> inches, and the diameter
+of the body is 2 inches. Assuming that the surface speed
+for this job should be about 40 feet per minute, a little calculation
+<span class="pagenum"><a name="Pg_230" id="Pg_230">[230]</a></span>
+shows that the 66 revolutions per minute, given by the fast
+train of gears, is equivalent to a surface speed of 43 feet per
+minute on a diameter of 2<sup class="enum">1</sup>/<sub class="denom">2</sub> inches. Moreover, the 78 revolutions
+per minute obtained from the slow train of gearing, gives
+about 41 feet per minute on a diameter of 2 inches. The spindle
+gearing indicated for these speeds is, therefore, placed in position
+on the proper studs at the back of the machine.</p>
+
+<p>Next we have to determine on which faces of the turret to
+place the different tools. Each turret face is numbered to
+agree with the corresponding feed cam on the drum. The speed
+and feed plate (<a href="#Fig_5_37">Fig. 37</a>) gives the various feeds obtainable per
+revolution of the spindle. As will be seen, the different cams
+give different feeds. Cam No. 1 has a coarse feed suitable for
+roughing; cam No. 2 a finer feed adapted to finishing, and so on.
+Since the first operation consists in rough-turning, cam No. 1
+is used. Cam No. 2, which gives a finer feed, is used for the
+finish-turning operation. Cam No. 4, which is ordinarily used<span class="pagenum"><a name="Pg_231" id="Pg_231">[231]</a></span>
+for reaming, could, in this case, be used for recessing, as this
+recess is for clearance only and may be bored with a coarse feed.</p>
+
+<p>The final operation, which is that of facing, can be done with
+any cam and cam No. 5 may be used. It will be understood
+that for facing operations, the feeds given do not apply. As
+the roll passes over the point of the feed cam at the extreme
+end of the movement, the feed of the turret slide is gradually
+slowed down to zero; since the facing takes place in the last
+eighth or sixteenth inch of this movement, it is done at a feed
+which is gradually reduced to zero. This is, of course, as it
+should be, and it is not necessary to pay any attention to the
+tabulated feeds in facing operations.</p>
+
+<a name="Secnum_5_26" id="Secnum_5_26"></a><p><b>Setting the Turret Slide.</b>&mdash;The next adjustment is that of
+setting the turret slide. In making this adjustment the turret
+is set in such relation to the work that the tools will have but
+a small amount of overhang, the cam-shaft being revolved by
+hand until the cam-roll is at the extreme top of the forward
+feeding cam, so that the turret slide is at the extreme of its forward
+movement. When this adjustment has been made by the
+means provided, set the turret index tripping dog so as to revolve
+the turret at the proper point. After a turning tool-holder and
+tool is attached to the face of the turret, cam No. 1 is placed
+in its operating position and is revolved by hand until the roll
+is on the point of the cam and the turret at the forward extreme
+of its motion. At this point the tool-holder is set so that the
+cutter will be far enough forward to complete its turning operation.
+The feed cam is then turned backward, thus returning
+the turret slide, and the cutter is set to turn the flange to the
+proper diameter for the roughing cut. The turret slide is fed
+forward and back while the cutter is adjusted, and when it is
+properly set, the flange is turned, the cam-drum being fed by
+hand. This is the first trial cut on the piece.</p>
+
+<p>A facing tool, shown in the working position in <a href="#Fig_5_36">Fig. 36</a>, is placed
+at this station of the turret, being held in the turret hole. This
+tool has a pilot bar and a holder which contains a facing blade.
+Feeding by hand, as before, the tool is adjusted lengthwise so
+as to rough-face the work to the dimension desired. In a similar<span class="pagenum"><a name="Pg_232" id="Pg_232">[232]</a></span>
+way the finish-turning and facing tools for the second position
+of the turret are set, the cam-shaft being revolved by hand to
+bring this second face and second cam into the working position.
+(The finish-facing tool is not shown in place in <a href="#Fig_5_36">Fig. 36</a>.)</p>
+
+<a name="Secnum_5_27" id="Secnum_5_27"></a><p><b>Setting the Cross-slide Cam.</b>&mdash;As previously mentioned, the
+third turret face has no tool, the cutting off of the collar being
+done during this part of the cycle of operations. It has been
+taken for granted that in setting the turret slide, room has been
+left between it and the chuck for the cross-slide. The cross-slide
+is clamped in a longitudinal position on the bed, convenient
+for the cutting-off operation, which is done with a tool <i>D</i> (<a href="#Fig_5_36">Fig. 36</a>)
+in the rear toolpost, thus leaving the front unobstructed for the
+operator. When both forming and cutting off are to be done,
+the forming tool is generally held at the front and the cutting-off
+tool at the back because heavier and more accurate forming
+can be done with the work revolving downward toward a tool
+in the front toolpost, than with the tool at the rear where it is
+subjected to a lifting action.</p>
+
+<a name="Fig_5_38" id="Fig_5_38"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/240sm.png" alt="Diagram of Cross-slide Cams and Feeding Mechanism" /></div>
+<p class="caption750">Fig. 38. Diagram of Cross-slide Cams and Feeding Mechanism</p>
+</div>
+
+<p><span class="pagenum"><a name="Pg_233" id="Pg_233">[233]</a></span>
+The arrangement of the cross-slide cams is shown in <a href="#Fig_5_38">Fig. 38</a>,
+which is an end view of the large drum <i>E</i>, <a href="#Fig_5_32">Fig. 32</a>. The rear
+feed cam is the one to be used, and since this cutting-off operation
+is a short one, it may be done during the return of the turret for
+position No. 3. The cam drum is, therefore, rotated by hand
+until the turret face No. 3 has begun to return. The cross-slide
+cams are then loosened and the rear feed cam is swung around
+to just touch the roller <i>R</i> which operates arm <i>A</i>, the cross-slide
+having been adjusted out to nearly the limit of its forward
+travel, leaving approximately enough movement for cutting off
+the collar. The rear feed cam is then clamped in this position.</p>
+
+<p>A cutting-off tool is next placed in the rear toolpost at the
+proper height. The rear toolpost slide is then adjusted to bring
+the point of the cutting-off tool up to the work, and the cam
+drum is revolved by hand until the piece is cut off. The cross-slide
+tool is, of course, set in the proper position to make a collar
+of the required thickness. Feeding by hand is discontinued
+when the roll is on the point of the cam; the cutting-off tool
+slide is then permanently set on the cross-slide so that the point
+of the cutting-off tool enters the bore just far enough to completely
+sever the collar from the bushing. The motion of the
+cam drum is continued, by hand, until the roll is over the point
+of the feed cam. The cross-slide is then pushed back, by hand,
+until the cam and roll are again in contact, when the return
+cam is brought up and clamped in position, so that there is just
+room for the roll between the feed cam and the return cam.
+The rear return cam (as the hand feed of the cam drum is continued)
+brings the cross-slide back to its central position. Since
+there is no front tool used for this series of operations (although
+a tool is shown in the front toolpost, <a href="#Fig_5_36">Fig. 36</a>), the first feed and
+return cams are allowed to remain wherever they happen to be.
+These cam adjustments can all be made from the front of the
+machine.</p>
+
+<a name="Fig_5_39" id="Fig_5_39"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/242sm.png" alt="Flexible Boring Tool used for Recessing a Bushing in Automatic Chucking and Turning Machine" /></div>
+<p class="caption750">Fig. 39. Flexible Boring Tool used for Recessing<br />a Bushing in Automatic
+Chucking and Turning Machine</p>
+</div>
+
+<a name="Secnum_5_28" id="Secnum_5_28"></a><p><b>Setting the Boring Tool for Recessing.</b>&mdash;The feeding of the
+turret slide is now continued to make sure that the cutting-off
+tool is returned to its normal position before the facing tool in
+the next face of the turret begins to work. The facing of the<span class="pagenum"><a name="Pg_234" id="Pg_234">[234]</a></span>
+bushing, so far as the setting of the tool is concerned, is merely
+a repetition of the facing operation at the first position of the
+turret. The recessing tool is next set. This tool, which is
+shown diagrammatically in <a href="#Fig_5_39">Fig. 39</a>, is very simple as compared
+with the somewhat complex operation it has to perform. This
+recess is for clearance only, and accurate dimensions and fine
+finish are not necessary. The recessing tool consists simply of a
+slender boring-bar held in the turret and carrying a cutter suitably
+located about midway the bar. The forward end of the bar
+is small enough to enter a bell-mouthed bushing held in the
+chuck. The boring-bar is bent to one side far enough so that
+the cutter clears the hole as the bar enters, but is forced into
+the work as the rounded hole of the bushing engages the end of
+the bar and deflects it into the working position. The upper
+diagram shows the position of the bar as it enters the hole, and
+the lower one the position after it has entered the bushing and
+is engaged in turning the recess. This bar is set in the turret
+so that at the extreme forward travel of the turret slide, the
+recess will be bored to the required length. The cutter must
+also be adjusted to bore to the desired diameter. This completes
+the setting of the cutting tools.</p>
+
+<a name="Secnum_5_29" id="Secnum_5_29"></a><p><span class="pagenum"><a name="Pg_235" id="Pg_235">[235]</a></span>
+<b>Adjustments for Automatic Feed and Speed Changes.</b>&mdash;The
+machine must now be set to perform automatically the desired
+changes of spindle speed and the fast and slow cam movements
+for the tools. After placing a new piece of work in the machine
+(the first one having been completed in the setting-up operation),
+the cam-shaft is revolved by hand until the turning tool in turret
+face No. 1 is just about to begin its cut. The control wheel <i>D</i>,
+<a href="#Fig_5_34">Fig. 34</a>, is rotated in its normal direction until the next graduation
+marked &#8220;slow&#8221; is in line with an index mark on the base of the
+machine. Then the nearest pin <i>M</i> is moved up until it bears
+against a tooth of the star wheel (previously referred to) and is
+clamped in this position. The pin should now be in the proper
+location, but to test its position, rotate the cam shaft backward
+by hand and throw in the automatic feed; then watch the cut
+to see if the drum slows down just before the tool begins to work.
+If it does not, the pin should be adjusted a little, one way or the
+other, as may be required. (In going over a piece of work for
+the first time, it is best to have the feed set to the smallest rate,
+feed change handle <i>K</i> being in position No. 1.)</p>
+
+<p>After the cut has been completed and the turret feed cam-roll
+is on the high part of the cam, the power feed should again be
+stopped and the handwheel revolved until the next graduation
+marked &#8220;fast&#8221; is opposite the index mark. The next stop pin
+is then moved up until it just touches the star wheel, where it
+is clamped in position. The feed being again thrown in, the
+turret will be returned rapidly, indexed, and moved forward for
+the second operation. After stopping the automatic movement,
+the pins are set for this face, and so on for all the operations,
+including that in which the cross-slide is used for cutting off
+the finished collar.</p>
+
+<p>As the first, second, and third operations are on comparatively
+large diameters, they should be done at the slow speed, handle <i>J</i>,
+<a href="#Fig_5_34">Fig. 34</a>, being set to give that speed. While the turret slide is
+being returned between operations 3 and 4, one of the spindle
+speed-changing dogs <i>N</i> should be clamped to the rim of disk <i>D</i>
+so as to change the spindle speed to the fast movement. This
+speed is continued until the last operation is completed, when a<span class="pagenum"><a name="Pg_236" id="Pg_236">[236]</a></span>
+second dog is clamped in place to again throw in the slow movement.
+The feed knock-off dog should also be clamped in place
+on the disk to stop the machine at the completion of the fifth
+operation, when the turret is in its rear position. This completes
+the setting up of the machine. If the feed is finer than is necessary,
+the feed change handle <i>K</i> may now be moved to a position
+which will give the maximum feed that can be used.</p>
+
+<p>It has taken considerable time to describe the setting up of
+the machine for this simple operation, but in the hands of a
+competent man it can be done quite rapidly. While a simple
+operation has been referred to in the foregoing, it will be understood
+that a great variety of work can be done on a machine of
+this type. It is not unusual to see as many as ten cutting tools
+operating simultaneously on a piece of work, the tools being
+carried by the turret, cross-slide and back facing attachment.
+The latter is operated from a separate cam applied to the cam-shaft
+and acting through levers on a back facing bar which passes
+through a hole in the spindle. In this back facing bar may
+be mounted drills, cutters, facing tools, etc. for machining the
+rear face of a casting held in the chuck jaws. Where extreme
+accuracy is required, a double back facing attachment may be
+used, arranged with cutters for taking both roughing and finishing
+cuts. The use of this attachment often saves a second operation.
+This automatic chucking and turning machine is also adapted
+for bar work, especially in diameters varying from 3 to 6 inches.</p>
+
+<a name="Fig_5_40" id="Fig_5_40"></a>
+<div class="figcenter"><img src="images/245sm.jpg" alt="Machining Flywheels in Potter &amp; Johnston Automatic Chucking and Turning Machine" />
+<p class="caption750">Fig. 40. Machining Flywheels in Potter &amp; Johnston Automatic<br />Chucking
+and Turning Machine</p>
+</div>
+
+<a name="Secnum_5_30" id="Secnum_5_30"></a><p><b>Turning Flywheel in Automatic Chucking and Turning Machine.</b>&mdash;A
+typical operation on the Potter &amp; Johnston automatic
+chucking and turning machine is illustrated in <a href="#Fig_5_40">Fig. 40</a>,
+which shows the machine arranged for turning the cast-iron flywheel
+for the engine of a motor truck. The rim is turned and
+faced on both sides and the hub is bored, reamed and faced on
+both sides. The flywheel casting is held in a chuck by three
+special jaws which grip the inside of the rim. The order of the
+operations is as follows:</p>
+
+<p>The rear end of the hub is faced by the back facing bar; the
+cored hole is started by a four-lipped drill in the turret and
+the front end of the hub is rough-faced. (These tools are on the<span class="pagenum"><a name="Pg_237" id="Pg_237">[237]</a></span>
+rear side of the turret when the latter is in the position shown
+in the illustration.) After the turret indexes, the hole is rough-bored
+by tool <i>A</i> and while this is being done, the outside of the
+rim is rough-turned by tool <i>B</i> held in a special bracket attached
+to the turret. Both sides of the rim are also rough-faced by
+tools <i>C</i> and <i>D</i> held at the front of the cross-slide, this operation
+taking place at the same time that the rim is turned and the
+hole is being bored.</p>
+
+<p>The turret again automatically recedes and indexes, thus locating
+bar <i>E</i> and turning tool <i>G</i> in the working position. The
+hole is then finish-bored by tool <i>E</i> and the hub is finish-faced by
+blade <i>F</i>; at the same time the rim is finish-turned by tool <i>G</i> and
+the sides are finish-faced to the proper width by two tools held
+at the rear of the cross-slide. The turret automatically recedes
+and indexes a third time, thus locating the flat-cutter reamer-bar
+<i>H</i> in the working position and then the hole is reamed to the
+required diameter. This completes the cycle of operations.
+The total time for machining this flywheel is forty minutes.</p>
+
+<a name="Fig_5_41" id="Fig_5_41"></a>
+<div class="figcenter"><img src="images/246sm.jpg" alt="New Britain Multiple-spindle Automatic Chucking Machine of Single-head Type" />
+<p class="caption750">Fig. 41. New Britain Multiple-spindle Automatic<br />Chucking Machine of
+Single-head Type</p>
+</div>
+
+<a name="Secnum_5_31" id="Secnum_5_31"></a><p><span class="pagenum"><a name="Pg_238" id="Pg_238">[238]</a></span>
+<b>Automatic Multiple-spindle Chucking Machine.</b>&mdash;An example
+of the specialized machines now used for producing
+duplicate parts, is shown in <a href="#Fig_5_41">Fig. 41</a>. This is a &#8220;New Britain&#8221;
+automatic multiple-spindle chucking machine of the single-head
+type and it is especially adapted for boring, reaming and facing
+operations on castings or forgings which can readily be held in
+chuck jaws. This particular machine has five spindles, which
+carry and revolve the tools. The work being machined is held
+stationary in the multiple chuck turret <i>A</i> which holds each part
+in line with one of the spindles and automatically indexes, so that
+the work passes from one spindle to another until it is finished.
+The turret then indexes the finished piece to a sixth or &#8220;loading
+position&#8221; which is not opposite a spindle, where the part is removed
+and replaced with a rough casting. Each pair of chuck
+jaws is operated independently of the others by the use of a chuck
+wrench. These jaws are made to suit the shape of the work.</p>
+
+<p>When a single-head machine is in operation, the turret advances
+and feeds the work against the revolving tools so that a number
+of pieces are operated upon at the same time. The turret is fed
+by a cam drum <i>B</i>. Cam strips are bolted to the outside of this<span class="pagenum"><a name="Pg_239" id="Pg_239">[239]</a></span>
+drum and act directly against a roller attached to the yoke <i>C</i>
+which can be clamped in different positions on the spindle <i>D</i>,
+the position depending upon the length of the work. On the
+opposite end of the turret spindle is the indexing mechanism <i>E</i>.
+An automatically spring-operated latch <i>F</i> engages notches in
+the rim of the dividing wheel, thus accurately locating the turret.
+The turret is locked by a steadyrest <i>G</i>, which, for each working
+position, automatically slides into engagement with one of the
+notches in the turret. This relieves the indexing mechanism of
+all strain.</p>
+
+<p>This type of machine is also built with two spindle heads,
+the double-head design being used for work requiring operations
+on both ends. When the double-head machine is in operation,
+the revolving spindles and tools advance on both sides of the
+chuck turret, the latter remaining stationary except when
+indexing. The feed drums on the double-head machine are
+located directly beneath each group of spindles.</p>
+
+<a name="Fig_5_42" id="Fig_5_42"></a>
+<div class="figcenter"><img src="images/247sm.jpg" alt="Detail View of New Britain Double-head Eight-spindle Machine, Boring, Reaming and Facing Castings" />
+<p class="caption750">Fig. 42. Detail View of New Britain Double-head Eight-spindle<br />Machine,
+Boring, Reaming and Facing Castings</p>
+</div>
+
+<p><a href="#Fig_5_42">Fig. 42</a> shows an example of work on a machine of the double-head
+design. This is an eight-spindle machine, there being two
+groups of four spindles on each side of the turret. The castings<span class="pagenum"><a name="Pg_240" id="Pg_240">[240]</a></span>
+<i>E</i> are for the wheel hubs of automobiles. The order of the operations
+on one of the castings, as it indexes around, is as follows:
+The hole in the hub is first rough-reamed by taper reamer <i>A</i>
+and the opposite end of the hub is rough-faced and counterbored
+by a tool in spindle <i>A<sub>1</sub></i>. When the turret indexes, this same
+casting is reamed close to the finished size by reamer <i>B</i> and the
+left end of the hub is rough-faced by cutter <i>F</i>, while a tool in the
+opposite spindle <i>B<sub>1</sub></i> finishes the counterboring and facing operation.
+At the third position, reamer <i>C</i> finishes the hole accurately
+to size, and when the work is indexed to the fourth position,
+the hub on the left side is finish-faced by a tool in spindle <i>D</i>.
+(The third and fourth spindles of the right-hand group are not
+used for this particular operation.) When the turret again
+indexes, the finished casting is removed and replaced with a
+rough one. While the successive operations on a single casting
+have just been described, it will be understood that all of the
+tools operate simultaneously and that a finished casting arrives
+at the unloading and loading position each time the turret indexes.
+Three hundred of these malleable castings are machined
+in nine hours.</p>
+
+<a name="Secnum_5_32" id="Secnum_5_32"></a><p><b>Selecting Type of Turning Machine.</b>&mdash;The variety of machine
+tools now in use is very extensive, and as different types can
+often be employed for the same kind of work, the selection of
+the best and most efficient machine is often a rather difficult
+problem. To illustrate, there are many different types and
+designs of turning machines, such as the ordinary engine lathe,
+the hand-operated turret lathe, the semi-automatic turning
+machine, and the fully automatic type, which, after it is &#8220;set
+up&#8221; and started, is entirely independent. Hence, when a certain
+part must be turned, the question is, what kind of machine
+should be used, assuming that it would be possible to employ
+several different machines? The answer to this question usually
+depends principally upon the number of parts that must be
+turned.</p>
+
+<p>For example, a certain casting or forging might be turned in
+a lathe, which could be finished in some form of automatic or
+semi-automatic turning machine much more quickly. It does<span class="pagenum"><a name="Pg_241" id="Pg_241">[241]</a></span>
+not necessarily follow, however, that the automatic is the best
+machine to use, because the lathe is designed for general work
+and the part referred to could doubtless be turned with the
+regular lathe equipment, whereas the automatic machine would
+require special tools and it would also need to be carefully adjusted.
+Therefore, if only a few parts were needed, the lathe
+might be the best tool to use, but if a large number were required,
+the automatic or semi-automatic machine would doubtless
+be preferable, because the saving in time effected by the latter
+type would more than offset the extra expense for tool equipment
+and setting the machine. It is also necessary, in connection
+with some work, to consider the degree of accuracy required,
+as well as the rate of production, and it is because of these varying
+conditions that work of the same general class is often done
+in machines of different types, in order to secure the most efficient
+results.</p>
+
+<hr class="c25" /><span class="pagenum"><a name="Pg_242" id="Pg_242">[242]</a></span>
+<h2><a name="Chapnum_6" id="Chapnum_6">CHAPTER VI</a></h2>
+<h3>VERTICAL BORING MILL PRACTICE</h3>
+<hr class="c05" />
+
+<p>All the different types of turning machines now in use originated
+from the lathe. Many of these tools, however, do not
+resemble the lathe because, in the process of evolution, there
+have been many changes made in order to develop turning
+machines for handling certain classes of work to the best advantage.
+The machine illustrated in <a href="#Fig_6_1">Fig. 1</a> belongs to the lathe
+family and is known as a vertical boring and turning mill.
+This type, as the name implies, is used for boring and turning
+operations, and it is very efficient for work within its range.
+The part to be machined is held to the table <i>B</i> either by clamps
+or in chuck jaws attached to the table. When the machine is
+in operation, the table revolves and the turning or boring tools
+(which are held in tool-blocks <i>T</i>) remain stationary, except for
+the feeding movement. Very often more than one tool is used
+at a time, as will be shown later by examples of vertical boring
+mill work. The tool-blocks <i>T</i> are inserted in tool-bars <i>T<sub>1</sub></i> carried
+by saddles <i>S</i> which are mounted on cross-rail <i>C</i>. Each
+tool-head (consisting of a saddle and tool-bar) can be moved
+horizontally along cross-rail <i>C</i>, and the tool-bars <i>T<sub>1</sub></i> have a
+vertical movement. These movements can be effected either
+by hand or power.</p>
+
+<a name="Fig_6_1" id="Fig_6_1"></a>
+<div class="figcenter"><img src="images/251sm.jpg" alt="Gisholt Vertical Boring and Turning Mill" />
+<p class="caption750">Fig. 1. Gisholt Vertical Boring and Turning Mill</p>
+</div>
+
+<p>When a surface is being turned parallel to the work table,
+the entire tool-head moves horizontally along the cross-rail, but
+when a cylindrical surface is being turned, the tool-bar moves
+vertically. The tool-heads are moved horizontally by the
+screws <i>H</i> and <i>H<sub>1</sub></i>, and the vertical feed for the tool-bars is obtained
+from the splined shafts <i>V</i> and <i>V<sub>1</sub></i>, there being a separate
+screw and shaft for each head so that the feeding movements
+are independent. These feed shafts are rotated for the power
+feed by vertical shafts <i>A</i> and <i>A<sub>1</sub></i> on each side of the machine.
+<span class="pagenum"><a name="Pg_243" id="Pg_243">[243]</a></span>
+These vertical shafts connect with the feed shafts through bevel
+and spur gears located at the ends of the cross-rail. On most
+boring mills, connection is made with one of the splined shafts
+<i>V</i> or screw <i>H</i>, by a movable gear, which is placed on whichever
+shaft will give the desired direction of feed. The particular
+machine illustrated is so arranged that either the right
+or left screw or feed shaft can be engaged by simply shifting
+levers <i>D<sub>1</sub></i> or <i>D</i>.</p>
+
+<p>The amount of feed per revolution of the table is varied for
+each tool-head by feed-changing mechanisms <i>F</i> on each side of
+the machine. These feed boxes contain gears of different sizes,
+and by changing the combinations of these gears, the amount
+of feed is varied. Five feed changes are obtained on this machine<span class="pagenum"><a name="Pg_244" id="Pg_244">[244]</a></span>
+by shifting lever <i>E</i>, and this number is doubled by shifting
+lever <i>G</i>. By having two feed boxes, the feeding movement
+of each head can be varied independently. The direction of
+either the horizontal or vertical feed can be reversed by lever
+<i>R</i>, which is also used for engaging or disengaging the feeds.
+This machine is equipped with the dials <i>I</i> and <i>I<sub>1</sub></i> which can be
+set to automatically disengage the feed at any predetermined
+point. There are also micrometer dials graduated to thousandths
+of an inch and used for adjusting the tools without the
+use of measuring instruments.</p>
+
+<p>The work table <i>B</i> is driven indirectly from a belt pulley at
+the rear, which transmits the power through gearing. The
+speed of the table can be varied for turning large or small parts,
+by levers <i>J</i> and <i>K</i> and the table can be started, stopped or
+rotated part of a revolution by lever <i>L</i> which connects with a
+friction clutch. There are corresponding feed and speed levers
+on the opposite side, so that the machine can be controlled from
+either position.</p>
+
+<p>The heads can be adjusted along the cross-rail for setting the
+tools by hand-cranks <i>N</i>, and the tool slides can be moved vertically
+by turning shafts <i>V</i> with the same cranks. With this
+machine, however, these adjustments do not have to be made
+by hand, ordinarily, as there are rapid power movements controlled
+by levers <i>M</i>. These levers automatically disengage the
+feeds and enable the tool-heads to be rapidly shifted to the required
+position, the direction of the movement depending upon
+the position of the feed reverse lever <i>R</i> and lever <i>D</i>. This rapid
+traverse, which is a feature applied to modern boring mills of
+medium and large size, saves time and the labor connected with
+hand adjustments. The cross-rail <i>C</i> has a vertical adjustment
+on the faces of the right and left housings which support it, in
+order to locate the tool-heads at the right height for the work.
+This adjustment is effected by power and is controlled by
+levers at the sides of the housings. Normally, the cross-rail is
+bolted to the housings, and these bolts must be loosened before
+making the adjustment, and must always be tightened afterwards.</p>
+
+<p><span class="pagenum"><a name="Pg_245" id="Pg_245">[245]</a></span>The function of these different levers has been explained to
+show, in a general way, how a vertical boring machine is operated.
+It should be understood, however, that the arrangement
+differs considerably on machines of other makes. The construction
+also varies considerably on machines of the same
+make but of different size.</p>
+
+<a name="Fig_6_2" id="Fig_6_2"></a>
+<div class="figcenter"><img src="images/253sm.jpg" alt="Small Boring and Turning Mill with Single Turret-head" />
+<p class="caption750">Fig. 2. Small Boring and Turning Mill<br />with Single Turret-head</p>
+</div>
+
+<p>All modern vertical boring mills of medium and large sizes
+are equipped with two tool-heads, as shown in <a href="#Fig_6_1">Fig. 1</a>, because a
+great deal of work done on a machine of this type can have two
+surfaces machined simultaneously. On the other hand, small<span class="pagenum"><a name="Pg_246" id="Pg_246">[246]</a></span>
+mills of the type illustrated in <a href="#Fig_6_2">Fig. 2</a> have a single head. The
+toolslide of this machine, instead of having a single tool-block,
+carries a five-sided turret <i>T</i> in which different tools can be
+mounted. These tools are shifted to the working position as
+they are needed, by loosening binder lever <i>L</i> and turning or
+&#8220;indexing&#8221; the turret. The turret is located and locked in any
+of its five positions by lever <i>I</i>, which controls a plunger that
+engages notches at the rear. Frequently, all the tools for
+machining a part can be held in the turret, so that little time
+is required for changing from one tool to the next. Some large
+machines having two tool-heads are also equipped with a turret
+on one head.</p>
+
+<a name="Secnum_6_1" id="Secnum_6_1"></a><p><b>Boring and Turning in a Vertical Boring Mill.</b>&mdash;The vertical
+boring mill is, in many respects, like a lathe placed in a vertical
+position, the table of the mill corresponding to the faceplate
+or chuck of the lathe and the tool-head to the lathe carriage.
+Much of the work done by a vertical mill could also be machined
+in a lathe, but the former is much more efficient for work
+within its range. To begin with, it is more convenient to clamp
+work to a horizontal table than to the vertical surface of a lathe
+faceplate, or, as someone has aptly said, &#8220;It is easier to lay a
+piece down than to hang it up.&#8221; This is especially true of the
+heavy parts for which the boring mill is principally used. Very
+deep roughing cuts can also be taken with a vertical mill. This
+type of machine mill is designed for turning and boring work
+which, generally speaking, is quite large in diameter in proportion
+to the width or height. The work varies greatly,
+especially in regard to its diameter, so that boring mills are
+built in a large range of sizes. The small and medium sizes
+will swing work varying from about 30 inches to 6 or 7 feet in
+diameter, whereas large machines, such as are used for turning
+very large flywheels, sheaves, etc., have a swing of 16 or 20 feet,
+and larger sizes are used in some shops. The size of a vertical
+mill, like any other machine tool, should be somewhat in proportion
+to the size of the work for which it is intended, as a
+very large machine is unwieldy, and, therefore, inefficient for
+machining comparatively small parts.</p>
+
+<p><span class="pagenum"><a name="Pg_247" id="Pg_247">[247]</a></span>
+<a name="Secnum_6_2" id="Secnum_6_2"></a><b>Holding and Setting Work on Boring Mill Table.</b>&mdash;There
+are three general methods of holding work to the table of a
+boring mill; namely, by the use of chucks, by ordinary bolts
+and clamps, or in special fixtures. Chucks which are built into
+the table (as illustrated in <a href="#Fig_6_2">Fig. 2</a>) and have both universal and
+independent adjustments for the jaws can be used to advantage
+for holding castings that are either round or irregular in shape.
+The universal adjustment is used for cylindrical parts, such as
+disks, flywheels, gear blanks, etc., and the independent adjustment,
+for castings of irregular shape. Chucks which have
+either an independent or universal movement for the jaws are
+known as a &#8220;combination&#8221; type and usually have three jaws.
+There is also a four-jaw type which has the independent adjustment
+only. This style is preferable for work that is not cylindrical
+and which must be held very securely. Chuck jaws that do
+not form a part of the machine table, but are bolted to it in the
+required position, are also employed extensively, especially on
+comparatively large machines.</p>
+
+<p>Most of the work done in a vertical mill is held in a chuck.
+Occasionally, however, it is preferable to clamp a part directly
+to the table. This may be desirable because of the shape and
+size of the work, or because it is necessary to hold a previously
+machined surface directly against the table in order to secure
+greater accuracy. Sometimes a casting is held in the chuck for
+turning one side, and then the finished side is clamped against
+the table for turning the opposite side. Parts which are to be
+machined in large quantities are often held in special fixtures.
+This method is employed when it enables the work to be set up
+more quickly than would be possible if regular clamps or chuck
+jaws were used.</p>
+
+<a name="Fig_6_3" id="Fig_6_3"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/256sm.png" alt="Plan View showing Flywheel Casting Chucked for Turning" /></div>
+<p class="caption750">Fig. 3. Plan View showing Flywheel Casting Chucked for Turning</p>
+</div>
+
+<p>Work that is to be turned or bored should first be set so that
+the part to be machined is about central with the table. For
+example, the rim of a flywheel should be set to run true so that
+it can be finished by removing about the same amount of metal
+around the entire rim; in other words, the rim should be set
+concentric with the table, as shown in <a href="#Fig_6_3">Fig. 3</a>, and the sides of
+the rim should also be parallel to the table.</p>
+
+<p><span class="pagenum"><a name="Pg_248" id="Pg_248">[248]</a></span>A simple tool that is very useful for testing the position of
+any cylindrical casting consists of a wooden shank into which
+is inserted a piece of wire, having one end bent. This tool is
+clamped in the toolpost and as the work revolves the wire is
+adjusted close to the cylindrical surface being tested. The
+movement of the work with relation to the stationary wire point
+will, of course, show whether or not the part runs true. The
+advantage of using a piece of wire for testing, instead of a rigid
+tool, is that the wire, owing to its flexibility, will simply be
+bent backward if it is moved too close to a surface which is
+considerably out of true. The upper surface of a casting can
+be tested for parallelism with the table by using this same
+wire gage, or by comparing the surface, as the table is revolved
+slowly, with a tool held in the toolpost. An ordinary
+surface gage is also used for this purpose. The proper surface
+to set true, in any case, depends upon the requirements.
+A plain cylindrical disk would be set so that the outside ran
+true and the top surface was parallel with the table. When
+setting a flywheel, if the inside of the rim is to remain rough,
+the casting should be set by this surface rather than by the
+outside, so that the rim, when finished, will be uniform in<span class="pagenum"><a name="Pg_249" id="Pg_249">[249]</a></span>
+thickness.</p>
+
+<p>As far as possible, chucks should be used for holding cylindrical
+parts, owing to their convenience. The jaws should be set
+against an interior cylindrical surface whenever this is feasible.
+To illustrate, the flywheel in <a href="#Fig_6_3">Fig. 3</a> is gripped by the inside of
+the rim which permits the outside to be turned at this setting
+of the work. It is also advisable to set a flywheel casting in
+the chuck so that a spoke rests against one of the jaws as at
+<i>d</i>, if this is possible. This jaw will then act as a driver and prevent
+the casting from slipping or turning in the chuck jaws,
+owing to the tangential pressure of the turning tool. When a
+cut is being taken, the table and work rotate as shown by
+arrow <i>a</i>, and the thrust of the cut (taken by tool <i>t</i>) tends to
+move the wheel backward against the direction of rotation, as
+shown by arrow <i>b</i>. If one of the chuck jaws bears against one
+of the spokes, this movement is prevented. It is not always
+feasible to use a chuck jaw as a driver and then a special driver
+having the form of a small angle-plate or block is sometimes
+bolted directly to the table. Another method of driving is to
+set a brace between a spoke or projection on the work and a
+chuck jaw or strip attached to the table. Drivers are not only
+used when turning flywheels, but in connection with any large
+casting, especially when heavy cuts have to be taken. Of
+course, some castings are so shaped that drivers cannot be
+employed.</p>
+
+<a name="Fig_6_4" id="Fig_6_4"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/258sm.png" alt="Turning Flat and Cylindrical Surfaces" /></div>
+<p class="caption750">Fig. 4. (A) Turning a Flat Surface.<br />(B) Turning a Cylindrical Surface</p>
+</div>
+
+<a name="Secnum_6_3" id="Secnum_6_3"></a><p><b>Turning in a Boring Mill.</b>&mdash;The vertical type of boring mill is
+used more for turning cylindrical surfaces than for actual boring,
+although a large part of the work requires both turning
+and boring. We shall first consider, in a general way, how
+surfaces are turned and then refer to some boring operations.
+The diagram <i>A</i>, <a href="#Fig_6_4">Fig. 4</a>, illustrates how a horizontal surface
+would be turned. The tool <i>t</i> is clamped in tool-block <i>t<sub>1</sub></i>, in a
+vertical position, and it is fed horizontally as the table and
+work rotate. The tool is first adjusted by hand for the proper
+depth of cut and the automatic horizontal feed is then engaged.
+When a cylindrical surface is to be turned, the tool (provided a<span class="pagenum"><a name="Pg_250" id="Pg_250">[250]</a></span>
+straight tool is used) is clamped in a horizontal position and is
+fed downward as indicated at <i>B</i>. The amount that the tool
+should feed per revolution of the work, depends upon the kind
+of material being turned, the diameter of the turned part and
+the depth of the cut.</p>
+
+<p>Most of the parts machined in a vertical boring mill are made
+of cast iron and, ordinarily, at least one roughing and one finishing
+cut is taken. The number of roughing cuts required in any
+case depends, of course, upon the amount of metal to be removed.
+An ordinary roughing cut in soft cast iron might vary
+in depth from <sup class="enum">1</sup>/<sub class="denom">8</sub> or <sup class=
+"enum">3</sup>/<sub class="denom">16</sub> inch to <sup class="enum">3</sup>/<sub class="denom">8</sub> or <sup class=
+"enum">1</sup>/<sub class="denom">2</sub> inch and the tool would
+probably have a feed per revolution of from <sup class="enum">1</sup>/<sub class=
+"denom">16</sub> to <sup class="enum">1</sup>/<sub class="denom">8</sub> inch, although
+deeper cuts and coarser feeds are sometimes taken.
+These figures are merely given to show, in a general way, what
+cuts and feeds are practicable. The tool used for roughing
+usually has a rounded end which leaves a ridged or rough surface.
+To obtain a smooth finish, broad flat tools are used. The
+flat cutting edge is set parallel to the tool's travel and a coarse
+feed is used in order to reduce the time required for taking the
+cut. The finishing feeds for cast iron vary from <sup class="enum">1</sup>/<sub class=
+"denom">4</sub> to <sup class="enum">3</sup>/<sub class="denom">4</sub> inch on
+ordinary work. The different tools used on the vertical mill
+will be referred to more in detail later.</p>
+
+<p>All medium and large sized vertical boring mills are equipped
+with two tool-heads and two tools are frequently used at the<span class="pagenum"><a name="Pg_251" id="Pg_251">[251]</a></span>
+same time, especially on large work. <a href="#Fig_6_9">Fig. 9</a> illustrates the use
+of two tools simultaneously. The casting shown is a flywheel,
+and the tool on the right side turns the upper side of the rim,
+while the tool on the left side turns the outside or cylindrical
+surface. As a boring mill table rotates in a counter-clockwise
+direction, the left-hand tool is reversed to bring the cutting edge
+at the rear. By turning two surfaces at once, the total time
+for machining the casting is, of course, greatly reduced. The
+turning of flywheels is a common vertical boring mill operation,
+and this work will be referred to in detail later on.</p>
+
+<a name="Fig_6_5" id="Fig_6_5"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/259sm.png" alt="Tools for Boring and Reaming Holes" /></div>
+<p class="caption750">Fig. 5. Tools for Boring and Reaming Holes</p>
+</div>
+
+<a name="Secnum_6_4" id="Secnum_6_4"></a><p><b>Boring Operations.</b>&mdash;There are several methods of machining
+holes when using a vertical boring mill. Ordinarily, small holes
+are cored in castings and it is simply necessary to finish the
+rough surface to the required diameter. Some of the tools
+used for boring and finishing comparatively small holes are
+shown in <a href="#Fig_6_5">Fig. 5</a>. Sketch <i>A</i> shows a boring tool consisting of a
+cutter <i>c</i> inserted in a shank, which, in turn, is held in the tool
+slide, or in a turret attached to the tool slide. With a tool of
+this type, a hole is bored by taking one or more cuts down
+through it. The tool shown at <i>B</i> is a four-lipped drill which is
+used for drilling cored holes preparatory to finishing by a cutter
+or reamer. This drill would probably finish a hole to within
+about <sup class="enum">1</sup>/<sub class="denom">32</sub> inch of the finish diameter, thus leaving a small amount
+of metal for the reamer to remove. The tool illustrated at <i>C</i><span class="pagenum"><a name="Pg_252" id="Pg_252">[252]</a></span>
+has a double-ended flat cutter <i>c</i>, which cuts on both sides.
+These cutters are often made in sets for boring duplicate parts.
+Ordinarily, there are two cutters in a set, one being used for
+roughing and the other for finishing. The cutter passes through
+a rectangular slot in the bar and this particular style is centrally
+located by shoulders <i>s</i>, and is held by a taper pin <i>p</i>. Some
+cutter bars have an extension end, or &#8220;pilot&#8221; as it is called,
+which passes through a close-fitting bushing in the table to
+steady the bar. Sketch <i>D</i> shows a finishing reamer. This tool
+takes a very light cut and is intended to finish holes that have
+been previously bored close to the required size. Sometimes a
+flat cutter <i>C</i> is used for roughing and a reamer for finishing.
+The reamer is especially desirable for interchangeable work,
+when all holes must have a smooth finish and be of the same
+diameter. When a reamer is held rigidly to a turret or toolslide,
+it is liable to produce a hole that is either tapering or
+larger than the reamer diameter. To prevent this, the reamer
+should be held in a &#8220;floating&#8221; holder which, by means of a
+slight adjustment, allows the reamer to align itself with the
+hole. There are several methods of securing this &#8220;floating&#8221;
+movement. (See &#8220;<a href="#Secnum_6_11">Floating Reamer Holders</a>.&#8221;)</p>
+
+<a name="Fig_6_6" id="Fig_6_6"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/260sm.png" alt="Boring with Regular Turning Tools" /></div>
+<p class="caption750">Fig. 6. Boring with Regular Turning Tools</p>
+</div>
+
+<p>Large holes or interior cylindrical surfaces are bored by tools
+held in the regular tool-head. The tool is sometimes clamped
+in a horizontal position as shown at <i>A</i>, <a href="#Fig_6_6">Fig. 6</a>, or a bent type is
+used as at <i>B</i>. Cast iron is usually finished by a broad flat tool
+as at <i>C</i>, the same as when turning exterior surfaces. Obviously
+<span class="pagenum"><a name="Pg_253" id="Pg_253">[253]</a></span>
+a hole that is bored in this way must be large enough to admit
+the tool-block.</p>
+
+<a name="Fig_6_7" id="Fig_6_7"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/261sm.png" alt="Set of Boring Mill Tools" /></div>
+<p class="caption750">Fig. 7. Set of Boring Mill Tools</p>
+</div>
+
+<a name="Secnum_6_5" id="Secnum_6_5"></a><p><b>Turning Tools for the Vertical Boring Mill.</b>&mdash;A set of turning
+tools for the vertical boring mill is shown in <a href="#Fig_6_7">Fig. 7</a>. These
+tools can be used for a wide variety of ordinary turning operations.
+When a great many duplicate parts are to be machined,
+special tool equipment can often be used to advantage, but as
+the form of this equipment depends upon the character of the
+work, only standard tools have been shown in this illustration.
+The tool shown at <i>A</i> is a right-hand, roughing tool, and a left-hand
+tool of the same type is shown at <i>B</i>. Tool <i>C</i> is an offset
+or bent, left-hand round nose for roughing, and <i>D</i> is a right-hand
+offset roughing tool. A straight round nose is shown
+at <i>E</i>. Tool <i>F</i> has a flat, broad cutting edge and is used for
+finishing. Left-and right-hand finishing tools of the offset<span class="pagenum"><a name="Pg_254" id="Pg_254">[254]</a></span>
+type are shown at <i>G</i> and <i>H</i>, respectively. Tool <i>I</i> has a square
+end and is used for cutting grooves. Right-and left-hand
+parting tools are shown at <i>J</i> and <i>K</i>, and tool <i>L</i> is a form frequently
+used for rounding corners.</p>
+
+<a name="Fig_6_8" id="Fig_6_8"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/262sm.png" alt="Diagrams Illustrating Use of Different Forms of Tools" /></div>
+<p class="caption750">Fig. 8. Diagrams Illustrating Use of Different Forms of Tools</p>
+</div>
+
+<p>The diagrams in <a href="#Fig_6_8">Fig. 8</a> show, in a general way, how each of
+the tools illustrated in <a href="#Fig_6_7">Fig. 7</a> are used, and corresponding tools
+are marked by the same reference letters in both of these illustrations.
+The right-and left-hand roughing tools <i>A</i> and <i>B</i> are
+especially adapted for taking deep roughing cuts. One feeds
+away from the center of the table, or to the right (when held in
+the right-hand tool-block) and the other tool is ground to feed
+in the opposite direction. Ordinarily, when turning plain flat
+surfaces, the cut is started at the outside and the tool feeds
+toward the center, as at <i>B</i>, although it is sometimes more convenient
+to feed in the opposite direction, as at <i>A</i>, especially when
+there is a rim or other projecting part at the outside edge. The
+tool shown at <i>A</i> could also be used for turning cylindrical
+surfaces, by clamping it in a horizontal position across the bottom
+<span class="pagenum"><a name="Pg_255" id="Pg_255">[255]</a></span>
+of the tool-block. The feeding movement would then be
+downward or at right-angles to the work table.</p>
+
+<p>The offset round-nose tools <i>C</i> and <i>D</i> are for turning exterior
+or interior cylinder surfaces. The shank of this tool is clamped
+in the tool-block in a vertical position and as the bent end extends
+below the tool-block, it can be fed down close to a shoulder.
+The straight type shown at <i>E</i> is commonly used for turning steel
+or iron, and when the point is drawn out narrower, it is also
+used for brass, although the front is then ground without slope.
+Tool <i>F</i> is for light finishing cuts and broad feeds. The amount
+of feed per revolution of the work should always be less than
+the width of the cutting edge as otherwise ridges will be left
+on the turned surface. The offset tools <i>G</i> and <i>H</i> are for finishing
+exterior and interior cylindrical surfaces. These tools also
+have both vertical and horizontal cutting edges and are sometimes
+used for first finishing a cylindrical and then a horizontal
+surface, or <i>vice versa</i>. Tool <i>I</i> is adapted to such work as cutting
+packing-ring grooves in engine pistons, forming square or rectangular
+grooves, and similar work. The parting tools <i>J</i> and
+<i>K</i> can also be used for forming narrow grooves or for cutting
+off rings, etc. The sketch <i>K</i> (<a href="#Fig_6_8">Fig. 8</a>) indicates how a tool of
+this kind might be used for squaring a corner under a shoulder.
+Tool <i>L</i> is frequently used on boring mills for rounding the
+corners of flywheel rims, in order to give them a more finished
+appearance. It has two cutting edges so that either side can
+be used as when rounding the inner and outer corners of a rim.</p>
+
+<p>The turning tools of a vertical boring mill are similar, in
+many respects, to those used in a lathe, although the shanks of
+the former are shorter and more stocky than those of lathe
+tools. The cutting edges of some of the tools also differ somewhat
+in form, but the principles which govern the grinding of
+lathe and boring mill tools are identical, and those who are
+not familiar with tool grinding are referred to <a href="#Chapnum_2">Chapter II</a>, in
+which this subject is treated.</p>
+
+<a name="Fig_6_9" id="Fig_6_9"></a>
+<div class="figcenter"><img src="images/264sm.jpg" alt="Turning the Rim of a Flywheel" />
+<p class="caption750">Fig. 9. Turning the Rim of a Flywheel</p>
+</div>
+
+<a name="Secnum_6_6" id="Secnum_6_6"></a><p><b>Turning a Flywheel on a Vertical Mill.</b>&mdash;The turning of a
+flywheel is a good example of the kind of work for which a vertical
+boring mill is adapted. A flywheel should preferably be<span class="pagenum"><a name="Pg_256" id="Pg_256">[256]</a></span>
+machined on a double-head mill so that one side and the periphery
+of the rim can be turned at the same time. A common method
+of holding a flywheel is shown in <a href="#Fig_6_9">Fig. 9</a>. The rim is gripped by
+four chuck jaws <i>D</i> which, if practicable, should be on the inside
+where they will not interfere with the movement of the tool.
+Two of the jaws, in this case, are set against the spokes on opposite
+sides of the wheel, to act as drivers and prevent any
+backward shifting of work when a heavy cut is being taken.
+The illustration shows the tool to the right rough turning the
+side of the rim, while the left-hand tool turns the periphery.
+Finishing cuts are also taken over the rim, at this setting, and
+the hub is turned on the outside, faced on top, and the hole
+bored.</p>
+
+<a name="Fig_6_10" id="Fig_6_10"></a>
+<div class="figcenter"><img src="images/265sm.jpg" alt="Tool B set for Boring the Hub" />
+<p class="caption750">Fig. 10. Tool B set for Boring the Hub</p>
+</div>
+
+<p>The three tools <i>A</i>, <i>B</i> and <i>C</i>, for finishing the hole, are mounted
+in the turret. Bar <i>A</i>, which carries a cutter at its end, first
+rough bores the hole. The sizing cutter <i>B</i> is then used to
+straighten it before inserting the finishing reamer <i>C</i>. <a href="#Fig_6_10">Fig. 10</a>
+shows the turret moved over to a central position and the sizing
+cutter <i>B</i> set for boring. The head is centrally located (on this
+particular machine) by a positive center-stop. The turret is indexed<span class="pagenum"><a name="Pg_257" id="Pg_257">[257]</a></span>
+for bringing the different tools into the working position,
+by loosening the clamping lever <i>L</i> and pulling down lever <i>I</i>
+which disengages the turret lock-pin. When all the flywheels
+in a lot have been machined as described, the opposite side is
+finished.</p>
+
+<a name="Fig_6_11" id="Fig_6_11"></a><span class="pagenum"><a name="Pg_258" id="Pg_258">[258]</a></span>
+<div class="figcenter"><div class="illobox750"><img src="images/266sm.png" alt="Diagrams showing Method of Turning and Boring a Flywheel on a Double-head Mill having one Turret Head" /></div>
+<p class="caption750">Fig. 11. Diagrams showing Method of Turning and Boring a Flywheel on a Double-head Mill having one Turret Head</p>
+</div>
+
+<p>In order to show more clearly the method of handling work of
+this class, the machining of a flywheel will be explained more in
+detail in connection with <a href="#Fig_6_11">Fig. 11</a>, which illustrates practically
+the same equipment as is shown in <a href="#Fig_6_9">Figs. 9</a> and <a href="#Fig_6_10">10</a>. The successive
+order in which the various operations are performed is
+as follows: Tool <i>a</i> (see sketch <i>A</i>) rough turns the side of the
+rim, while tool <i>b</i>, which is set with its cutting edge toward the
+rear, rough turns the outside. The direction of the feeding
+movement for each tool is indicated by the arrows. When tool
+<i>a</i> has crossed the rim, it is moved over for facing the hub, as
+shown by the dotted lines. The side and periphery of the rim
+are next finished by the broad-nose finishing tools <i>c</i> and <i>d</i> (see
+sketch <i>B</i>). The feed should be increased for finishing, so that
+each tool will have a movement of say <sup class="enum">1</sup>/<sub class="denom">4</sub> or
+<sup class="enum">3</sup>/<sub class="denom">8</sub> inch per revolution
+of the work, and the cuts should, at least, be deep enough to<span class="pagenum"><a name="Pg_259" id="Pg_259">[259]</a></span>
+remove the marks made by the roughing tools. Tool <i>c</i> is also
+used for finishing the hub as indicated by the dotted lines.
+After these cuts are taken, the outside of the hub and inner
+surface of the rim are usually turned down as far as the spokes,
+by using offset tools similar to the ones shown at <i>C</i> and <i>D</i> in
+<a href="#Fig_6_7">Fig. 7</a>. The corners of the rim and hub are also rounded to
+give the work a more finished appearance, by using a tool <i>L</i>.</p>
+
+<p>The next operation is that of finishing the hole through the
+hub. The hard scale is first removed by a roughing cutter <i>r</i>
+(sketch <i>C</i>), which is followed by a &#8220;sizing&#8221; cutter <i>s</i>. The hole
+is then finished smooth and to the right diameter by reamer <i>f</i>.
+The bars carrying cutters <i>r</i> and <i>s</i> have extensions or &#8220;pilots&#8221;
+which enter a close-fitting bushing in the table, in order to
+steady the bar and hold it in alignment.</p>
+
+<p>When the hole is finished, the wheel is turned over, so that
+the lower side of the rim and hub can be faced. The method
+of holding the casting for the final operation is shown at <i>D</i>.
+The chuck jaws are removed, and the finished side of the rim is
+clamped against parallels <i>p</i> resting on the table. The wheel is
+centrally located for turning this side by a plug <i>e</i> which is inserted
+in a hole in the table and fits the bore of the hub. The
+wheel is held by clamps which bear against the spokes. Roughing
+and finishing cuts are next taken over the top surface of the
+rim and hub and the corners are rounded, which completes the
+machining operations. If the rim needs to be a certain width,
+about the same amount of metal should be removed from each
+side, unless sandy spots or &#8220;blow-holes&#8221; in the casting make it
+necessary to take more from one side than from the other. That
+side of the rim which was up in the mold when the casting was
+made should be turned first, because the porous, spongy spots
+usually form on the &#8220;cope&#8221; or top side of a casting.</p>
+
+<a name="Fig_6_12" id="Fig_6_12"></a>
+<div class="figcenter"><img src="images/268sm.jpg" alt="Gisholt Mill equipped with Convex Turning Attachment" />
+<p class="caption750">Fig. 12. Gisholt Mill equipped with Convex Turning Attachment</p>
+</div>
+
+<a name="Secnum_6_7" id="Secnum_6_7"></a><p><b>Convex Turning Attachment for Boring Mills.</b>&mdash;<a href="#Fig_6_12">Fig. 12</a>
+shows a vertical boring mill arranged for turning pulleys having
+convex rims; that is, the rim, instead of being cylindrical, is
+rounded somewhat so that it slopes from the center toward
+either side. (The reason for turning a pulley rim convex is to
+prevent the belt from running off at one side, as it sometimes<span class="pagenum"><a name="Pg_260" id="Pg_260">[260]</a></span>
+tends to do when a cylindrical pulley is used.) The convex
+surface is produced by a special attachment which causes the
+turning tool to gradually move outward as it feeds down, until
+the center of the rim is reached, after which the movement is
+inward.</p>
+
+<p>The particular attachment shown in <a href="#Fig_6_12">Fig. 12</a> consists of a
+special box-shaped tool-head <i>F</i> containing a sliding holder <i>G</i>, in
+which the tool is clamped by set-screws passing through elongated
+slots in the front of the tool-head. In addition, there is
+a radius link <i>L</i> which swivels on a stud at the rear of the tool-head
+and is attached to vertical link <i>H</i>. Link <i>L</i> is so connected
+to the sliding tool-block that any downward movement of the
+tool-bar <i>I</i> causes the tool to move outward until the link is in
+a horizontal position, after which the movement is reversed.
+When the attachment is first set up, the turning tool is placed
+at the center of the rim and then link <i>L</i> is clamped to the vertical
+link while in a horizontal position. The cut is started at
+the top edge of the rim, and the tool is fed downward by power,<span class="pagenum"><a name="Pg_261" id="Pg_261">[261]</a></span>
+the same as when turning a cylindrical surface. The amount of
+curvature or convexity of a rim can be varied by inserting the
+clamp bolt <i>J</i> in different holes in link <i>L</i>.</p>
+
+<p>The tools for machining the hub and sides of the rim are held
+in a turret mounted on the left-hand head, as shown. The
+special tool-holder <i>A</i> contains two bent tools for turning the
+upper and lower edges of the pulley rim at the same time as
+the tool-head is fed horizontally. Roughing and finishing tools
+<i>B</i> are for facing the hub, and the tools <i>C</i>, <i>D</i>, and <i>E</i> rough bore,
+finish bore, and ream the hole for the shaft.</p>
+
+<a name="Fig_6_13" id="Fig_6_13"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/269sm.png" alt="Turning a Taper or Conical Surface" /></div>
+<p class="caption750">Fig. 13. Turning a Taper or Conical Surface</p>
+</div>
+
+<a name="Secnum_6_8" id="Secnum_6_8"></a><p><b>Turning Taper or Conical Surfaces.</b>&mdash;Conical or taper surfaces
+are turned in a vertical boring mill by swiveling the tool-bar
+to the proper angle as shown in <a href="#Fig_6_13">Fig. 13</a>. When the taper is
+given in degrees, the tool-bar can be set by graduations on the
+edge of the circular base <i>B</i>, which show the angle <i>a</i> to which the
+bar is swiveled from a vertical position. The base turns on a
+central stud and is secured to the saddle <i>S</i> by the bolts shown,
+which should be tightened after the tool-bar is set. The vertical
+power feed can be used for taper turning the same as for
+cylindrical work.</p>
+
+<a name="Fig_6_14" id="Fig_6_14"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/270sm.png" alt="Turning a Conical Surface by using the Combined Vertical and Horizontal Feeds" /></div>
+<p class="caption750">Fig. 14. Turning a Conical Surface by using the<br />Combined Vertical
+and Horizontal Feeds</p>
+</div>
+
+<p><span class="pagenum"><a name="Pg_262" id="Pg_262">[262]</a></span>
+Occasionally it is necessary to machine a conical surface which
+has such a large included angle that the tool-bar cannot be
+swiveled far enough around to permit turning by the method
+illustrated in <a href="#Fig_6_13">Fig. 13</a>. Another method, which is sometimes resorted
+to for work of this class, is to use the combined vertical
+and horizontal feeds. Suppose we want to turn the conical
+casting <i>W</i> (<a href="#Fig_6_14">Fig. 14</a>), to an angle of 30 degrees, as shown, and
+that the tool-head of the boring mill moves horizontally <sup class="enum">1</sup>/<sub class="denom">4</sub> inch
+per turn of the feed-screw and has a vertical movement of <sup class="enum">3</sup>/<sub class="denom">16</sub>
+inch per turn of the upper feed-shaft. If the two feeds are
+used simultaneously, the tool will move a distance <i>h</i> of say 8
+inches, while it moves downward a distance <i>v</i> of 6 inches, thus
+turning the surface to an angle <i>y</i>. This angle is greater (as
+measured from a horizontal plane) than the angle required, but,
+if the tool-bar is swiveled to an angle <i>x</i>, the tool, as it moves
+downward, will also be advanced horizontally, in addition to
+the regular horizontal movement. The result is that the angle
+<i>y</i> is diminished and if the tool-bar is set over the right amount,
+<span class="pagenum"><a name="Pg_263" id="Pg_263">[263]</a></span>
+the conical surface can be turned to an angle <i>a</i> of 30 degrees.
+The problem, then, is to determine what the angle <i>x</i> should be
+for turning to a given angle <i>a</i>.</p>
+
+<a name="Fig_6_15" id="Fig_6_15"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/271sm.png" alt="Diagram showing Method of Obtaining Angular Position of Tool-head when Turning Conical Surfaces by using Vertical and Horizontal Feeding Movements" /></div>
+<p class="caption750">Fig. 15. Diagram showing Method of Obtaining Angular Position<br />of Tool-head
+when Turning Conical Surfaces by using Vertical and<br />Horizontal
+Feeding Movements</p>
+</div>
+
+<p>The way angle <i>x</i> is calculated will be explained in connection
+with the enlarged diagram, <a href="#Fig_6_15">Fig. 15</a>, which shows one-half of the
+casting. The sine of the known angle <i>a</i> is first found in a table
+of natural sines. Then the sine of angle <i>b</i>, between the taper
+surface and center-line of the tool-head, is determined as follows:
+sin&nbsp;<i>b</i> = (sin&nbsp;<i>a</i>&nbsp;&times;&nbsp;<i>h</i>)&nbsp;&divide;&nbsp;<i>v</i>, in which <i>h</i> represents the rate
+of horizontal
+feed and <i>v</i> the rate of vertical feed. The angle corresponding
+to sine <i>b</i> is next found in a table of sines. We now
+have angles <i>b</i> and <i>a</i>, and by subtracting the sum of these angles
+from 90 degrees, the desired angle <i>x</i> is obtained. To illustrate:</p>
+
+<p>The sine of 30 degrees is 0.5; then sin <i>b</i> = (0.5&nbsp;&times;&nbsp;<sup class="enum">1</sup>/<sub class=
+"denom">4</sub>)&nbsp;&divide;&nbsp;<sup class="enum">3</sup>/<sub class="denom">16</sub> = 0.6666;
+hence angle <i>b</i> = 41 degrees 49 minutes, and <i>x</i> = 90&deg;&nbsp;- (30&deg;&nbsp;+
+41&deg; 49') = 18 degrees 11 minutes. Hence to turn the casting to
+angle <i>a</i> in a boring mill having the horizontal and vertical feeds
+given, the tool-head would be set over from the vertical 18 degrees
+and 11 minutes which is equivalent to about 18<sup class="enum">1</sup>/<sub class="denom">6</sub> degrees.</p>
+
+<p><span class="pagenum"><a name="Pg_264" id="Pg_264">[264]</a></span>
+If the required angle <i>a</i> were greater than angle <i>y</i> obtained
+from the combined feeds with the tool-bar in a vertical position,
+it would then be necessary to swing the lower end of the bar to
+the left rather than to the right of a vertical plane. When the
+required angle <i>a</i> exceeds angle <i>y</i>, the sum of angles <i>a</i> and <i>b</i> is
+greater than 90 degrees so that angle <i>x</i> for the tool-head =
+(<i>a</i>&nbsp;+ <i>b</i>)&nbsp;- 90 degrees.</p>
+
+<a name="Fig_6_16" id="Fig_6_16"></a>
+<div class="figcenter"><img src="images/273sm.jpg" alt="Bullard Vertical Turret Lathe" />
+<p class="caption750">Fig. 16. Bullard Vertical Turret Lathe</p>
+</div>
+
+<a name="Secnum_6_9" id="Secnum_6_9"></a><p><b>Turret-lathe Type of Vertical Boring Mill.</b>&mdash;The machine
+illustrated in <a href="#Fig_6_16">Fig. 16</a> was designed to combine the advantages of
+the horizontal turret lathe and the vertical boring mill. It is
+known as a &#8220;vertical turret lathe,&#8221; but resembles, in many
+respects, a vertical boring mill. This machine has a turret on
+the cross-rail the same as many vertical boring mills, and, in
+addition, a side-head <i>S</i>. The side-head has a vertical feeding
+movement, and the tool-bar <i>T</i> can be fed horizontally. The
+tool-bar is also equipped with a four-sided turret for holding
+turning tools. This arrangement of the tool-heads makes it
+possible to use two tools simultaneously upon comparatively
+small work. When both heads are mounted on the cross-rail,
+as with a double-head boring mill, it is often impossible to
+machine certain parts to advantage, because one head interferes
+with the other.</p>
+
+<p>The drive to the table (for the particular machine illustrated)
+is from a belt pulley at the rear, and fifteen speed changes are
+available. Five changes are obtained by turning the pilot-wheel
+<i>A</i> and this series of five speeds is compounded three
+times by turning lever <i>B</i>. Each spoke of pilot-wheel <i>A</i> indicates
+a speed which is engaged only when the spoke is in a
+vertical position, and the three positions for <i>B</i> are indicated,
+by slots in the disk shown. The number of table revolutions
+per minute for different positions of pilot-wheel <i>A</i> and lever
+<i>B</i> are shown by figures seen through whichever slot is at <i>C</i>.
+There are five rows of figures corresponding to the five spokes
+of the pilot-wheel and three figures in a row, and the speed
+is shown by arrows on the sides of the slots. The segment
+disk containing these figures also serves as an interlocking
+device which prevents moving more than one speed controlling<span class="pagenum"><a name="Pg_265" id="Pg_265">[265]</a></span>
+lever at a time, in order to avoid damaging the driving
+mechanism.</p>
+
+<p>The feeding movement for each head is independent. Lever
+<i>D</i> controls the engagement or disengagement of the vertical or
+cross feeds for the head on the cross-rail. The feed for the
+side-head is controlled by lever <i>E</i>. When this lever is pushed
+inward, the entire head feeds vertically, but when it is pulled
+out, the tool-bar feeds horizontally. These two feeds can be
+disengaged by placing the lever in a neutral position. The<span class="pagenum"><a name="Pg_266" id="Pg_266">[266]</a></span>
+direction of the feeding movement for either head can be reversed
+by lever <i>R</i>. The amount of feed is varied by feed-wheel
+<i>F</i> and clutch-rod <i>G</i>. When lever <i>E</i> is in the neutral
+position, the side-head or tool-bar can be adjusted by the hand-cranks
+<i>H</i> and <i>I</i>, respectively. The cross-rail head and its
+turret slide have rapid power traverse movements for making
+quick adjustments. This rapid traverse is controlled by the
+key-handles <i>J</i>.</p>
+
+<p>The feed-screws for the vertical head have micrometer dials
+<i>K</i> for making accurate adjustments. There are also large dials
+at <i>L</i> which indicate vertical movements of the side head and
+horizontal movements of the tool slide. All of these dials have
+small adjustable clips <i>c</i> which are numbered to correspond to
+numbers on the faces of the respective turrets. These clips or
+&#8220;observation stops&#8221; are used in the production of duplicate
+parts. For example, suppose a tool in face No. 1 for the main
+turret is set for a given diameter and height of shoulder on a
+part which is to be duplicated. To obtain the same setting of
+the tools for the next piece, clips No. 1, on both the vertical
+feed rod and screw dials, are placed opposite the graduations
+which are intersected by stationary pointers secured to the cross-rail.
+The clips are set in this way after the first part has been
+machined to the required size and before disturbing the final
+position of the tools. For turning a duplicate part, the tools
+are simply brought to the same position by turning the feed
+screws until the clips and stationary pointers again coincide.
+For setting tools on other faces of either turret, this operation
+is repeated, except that clips are used bearing numbers corresponding
+to the turret face in use.</p>
+
+<p>The main turret of this machine has five holes in which are
+inserted the necessary boring and turning tools, drills or reamers,
+as may be required. By having all the tools mounted in the
+turret, they can be quickly and accurately set in the working
+position. When the turret is indexed from one face to the next,
+binder lever <i>N</i> is first loosened. The turret then moves forward,
+away from its seat, thus disengaging the indexing and registering
+pins which accurately locate it in any one of the five positions.<span class="pagenum"><a name="Pg_267" id="Pg_267">[267]</a></span>
+The turret is revolved by turning crank <i>M</i>, one turn of
+this handle moving the turret <sup class="enum">1</sup>/<sub class="denom">5</sub> revolution or from one hole to
+the next. The side-head turret is turned by loosening lever <i>O</i>.
+The turret slide can be locked rigidly in any position by lever
+<i>P</i> and its saddle is clamped to the cross-rail by lever <i>Q</i>. The
+binder levers for the saddle and toolslide of the side-head are
+located at <i>U</i> and <i>V</i>, respectively. A slide that does not require
+feeding movements is locked in order to obtain greater rigidity.
+To illustrate, if the main tool slide were to feed vertically and
+not horizontally, it might be advisable to lock the saddle to the
+cross-rail, while taking the vertical cut.</p>
+
+<p>The vertical slide can be set at an angle for taper turning,
+and the turret is accurately located over the center of the table
+for boring or reaming, by a positive center stop. The machine is
+provided with a brake for stopping the work table quickly, which
+is operated by lifting the shaft of pilot-wheel <i>A</i>. The side-and
+cross-rails are a unit and are adjusted together to accommodate
+work of different heights. This adjustment is effected by power<span class="pagenum"><a name="Pg_268" id="Pg_268">[268]</a></span>
+on the particular machine illustrated, and it is controlled by a
+lever near the left end of the cross-rail. Before making this
+adjustment, all binder bolts which normally hold the rails rigidly
+to the machine column must be released, and care should be
+taken to tighten them after the adjustment is made.</p>
+
+<a name="Fig_6_17" id="Fig_6_17"></a>
+<div class="figcenter"><img src="images/275sm.jpg" alt="Turning a Gear Blank on a Vertical Turret Lathe" />
+<p class="caption750">Fig. 17. Turning a Gear Blank on a Vertical Turret Lathe</p>
+</div>
+
+<a name="Secnum_6_10" id="Secnum_6_10"></a><p><b>Examples of Vertical Turret Lathe Work.</b>&mdash;In order to illustrate
+how a vertical turret lathe is used, one or two examples of
+work will be referred to in detail. These examples also indicate,
+in a general way, the class of work for which this type of machine
+is adapted. <a href="#Fig_6_17">Fig. 17</a> shows how a cast-iron gear blank is machined.
+The work is gripped on the inside of the rim by three
+chuck jaws, and all of the tools required for the various operations
+are mounted in the main and side turrets. The illustration<span class="pagenum"><a name="Pg_269" id="Pg_269">[269]</a></span>
+shows the first operation which is that of rough turning the
+hub, the top side of the blank and its periphery. The tools <i>A</i>
+for facing the hub and upper surface are both held in one tool-block
+on the main turret, and tool <i>A<sub>1</sub></i> for roughing the periphery
+is in the side turret. With this arrangement, the three surfaces
+can be turned simultaneously.</p>
+
+<p>The main turret is next indexed one-sixth of a revolution
+which brings the broad finishing tools <i>B</i> into position, and the
+side turret is also turned to locate finishing tool <i>B<sub>1</sub></i> at the front.
+(The indexing of the main turret on this particular machine is
+effected by loosening binder lever n and raising the turret lock-pin
+by means of lever <i>p</i>.) The hub, side and periphery of the
+blank are then finished. When tools <i>B</i> are clamped in the tool-blocks,
+<span class="pagenum"><a name="Pg_270" id="Pg_270">[270]</a></span>
+they are, of course, set for turning the hub to the required
+height. The third operation is performed by the tools at <i>C</i>, one
+of which &#8220;breaks&#8221; or chamfers the corner of the cored hole in
+the hub, to provide a starting surface for drill <i>D</i>, and the other
+turns the outside of the hub, after the chamfering tool is removed.
+The four-lipped shell-drill <i>D</i> is next used to drill the cored hole
+and then this hole is bored close to the finished size and concentric
+with the circumference of the blank by boring tool <i>E</i>,
+which is followed by the finishing reamer <i>F</i>. When the drill,
+boring tool and reamer are being used, the turret is set over the
+center or axis of the table, by means of a positive center stop
+on the left-side of the turret saddle. If it is necessary to move<span class="pagenum"><a name="Pg_271" id="Pg_271">[271]</a></span>
+the turret beyond the central position, this stop can be swung
+out of the way.</p>
+
+<a name="Fig_6_18" id="Fig_6_18"></a>
+<div class="figcenter"><img src="images/276sm.jpg" alt="Turning Gasoline Engine Flywheel on Vertical Turret Lathe&mdash;First Position" />
+<p class="caption750">Fig. 18. Turning Gasoline Engine Flywheel on Vertical Turret
+Lathe&mdash;First Position</p>
+</div>
+
+<a name="Fig_6_19" id="Fig_6_19"></a>
+<div class="figcenter"><img src="images/277sm.jpg" alt="Turning Gasoline Engine Flywheel&mdash;Second Position" />
+<p class="caption750">Fig. 19. Turning Gasoline Engine Flywheel&mdash;Second Position</p>
+</div>
+
+<p><a href="#Fig_6_18">Figs. 18</a> and <a href="#Fig_6_19">19</a> illustrate the turning of an automobile flywheel,
+which is another typical example of work for a machine
+of this type. The flywheel is finished in two settings. Its
+position for the first series of operations is shown in <a href="#Fig_6_18">Fig. 18</a>, and
+the successive order of the four operations for the first setting
+is shown by the diagrams, <a href="#Fig_6_20">Fig. 20</a>. The first operation requires
+four tools which act simultaneously. The three held in tool-block
+<i>A</i> of the turret, face the hub, the web and the rim of the
+flywheel, while tool <i>a</i> in the side-head rough turns the outside
+diameter. The outside diameter is also finished by broad-nosed
+tool <i>b</i> which is given a coarse feed. In the second operation,
+the under face of the rim is finished by tool <i>c</i>, the outer
+corners are rounded by tool <i>d</i> and the inner surface of the rim
+is rough turned by a bent tool <i>B</i>, which is moved into position
+by indexing the main turret. In the third operation, the side-head
+is moved out of the way and the inside of the rim is finished
+by another bent tool <i>B<sub>1</sub></i>. The final operation at this setting is
+the boring of the central hole, which is done with a bar <i>C</i> having
+interchangeable cutters which make it possible to finish the hole
+at one setting of the turret.</p>
+
+<a name="Fig_6_20" id="Fig_6_20"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/278sm.png" alt="Diagrams showing How Successive Operations are Performed by Different Tools in the Turret" /></div>
+<p class="caption750">Fig. 20. Diagrams showing How Successive Operations<br />are Performed
+by Different Tools in the Turret</p>
+</div>
+
+<p>The remaining operations are performed on the opposite side
+of the work which is held in &#8220;soft&#8221; jaws <i>J</i> accurately bored to
+fit the finished outside diameter as indicated in <a href="#Fig_6_19">Fig. 19</a>. The
+tool in the main turret turns the inside of the rim, and the side-head
+is equipped with two tools for facing the web and hub
+simultaneously. As the tool in the main turret operates on the
+left side of the rim, it is set with the cutting edge toward the
+rear. In order to move the turret to this position, which is beyond
+the center of the table, the center stop previously referred
+to is swung out of the way.</p>
+
+<a name="Secnum_6_11" id="Secnum_6_11"></a><p><b>Floating Reamer Holders.</b>&mdash;If a reamer is held rigidly in the
+turret of a boring mill or turret lathe, it is liable to produce a
+hole which tapers slightly or is too large. When a hole is bored
+with a single-point boring tool, it is concentric with the axis of
+rotation, and if a reamer that is aligned exactly with the bored<span class="pagenum"><a name="Pg_272" id="Pg_272">[272]</a></span>
+hole is fed into the work, the finished hole should be cylindrical
+and the correct size. It is very difficult, however, to locate a
+reamer exactly in line with a bored hole, because of slight variations
+in the indexing of the turret, or errors resulting from wear
+of the guiding ways or other important parts of the machine.</p>
+
+<p>To prevent inaccuracies due to this cause, reamers are often
+held in what is known as a &#8220;floating&#8221; holder. This type of
+holder is so arranged that the reamer, instead of being held
+rigidly, is allowed a slight free or floating movement so that it
+can follow a hole which has been bored true, without restraint.
+In this way the hole is reamed straight and to practically the
+same size as the reamer.</p>
+
+<a name="Fig_6_21" id="Fig_6_21"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/280sm.png" alt="Two Types of Floating Reamer Holders" /></div>
+<p class="caption750">Fig. 21. Two Types of Floating Reamer Holders</p>
+</div>
+
+<p>There are many different designs of floating holders but the
+general principle upon which they are based is illustrated by
+the two types shown in <a href="#Fig_6_21">Fig. 21</a>. The reamer and holder shown
+to the left has a ball-shank <i>A</i> which bears against a backing-up
+screw <i>B</i> inserted in the end of holder <i>C</i> through which the driving
+pin passes. The lower end of the reamer shank is also
+spherical-shaped at <i>D</i>, and screw-pin <i>E</i> secures the shell reamer
+to this end. It will be noted that the hole in the shank for pin
+<i>E</i> is &#8220;bell-mouthed&#8221; on each side of the center and that
+there<span class="pagenum"><a name="Pg_273" id="Pg_273">[273]</a></span>
+is clearance at <i>F</i> between the shank and reamer shell; hence the
+reamer has a free floating action in any direction. This holder
+has given very satisfactory results.</p>
+
+<p>The holder shown to the right is attached to the face of the
+turret by four fillister-head screws. Sleeve <i>C</i> is held in plate <i>A</i>
+by means of two steel pins <i>B</i> which are tight in plate <i>A</i> and made
+to fit freely in bayonet grooves <i>D</i>. Reamer holder <i>E</i> floats on
+sleeve <i>C</i>, the floating motion being obtained through the four
+steel pins <i>G</i> extending into driving ring <i>F</i>. Two of the pins are
+tight in the holder <i>E</i> and two in sleeve <i>C</i>. The faces of sleeve
+<i>C</i>, driving ring <i>F</i>, and reamer holder <i>E</i> are held tightly against
+each other by means of spring <i>H</i> which insures the reamer being
+held perfectly true. Spring <i>H</i> is adjusted by means of nut <i>I</i>
+which is turned with a spanner wrench furnished with each
+holder. The reamer is so held that its axis is always maintained
+parallel to the center of the hole, and, at the same time, it has
+a slight self-adjusting tendency radially, so that the hole and<span class="pagenum"><a name="Pg_274" id="Pg_274">[274]</a></span>
+reamer will automatically keep in perfect alignment with each
+other.</p>
+
+<a name="Fig_6_22" id="Fig_6_22"></a>
+<div class="figcenter"><img src="images/281sm.jpg" alt="Multiple-spindle Cylinder Boring Machine" />
+<p class="caption750">Fig. 22. Multiple-spindle Cylinder Boring Machine</p>
+</div>
+
+<a name="Secnum_6_12" id="Secnum_6_12"></a><p><b>Multiple Cylinder Boring Machine.</b>&mdash;In automobile and
+other factories where a great many gasoline engine cylinders are
+required, multiple-spindle boring machines of the vertical type
+are commonly used. The machine shown in <a href="#Fig_6_22">Fig. 22</a> is a special
+design for boring four cylinders which are cast <i>en bloc</i> or in one
+solid casting. The work is held in a box jig which has a top
+plate equipped with guide bearings for holding the spindles
+rigidly while boring. The lower end of each spindle has attached
+to it a cutter-head and the boring is done by feeding the table
+and casting vertically. This feeding movement is effected by
+power and it is disengaged automatically when the cutters have
+bored to the required depth. The particular machine illustrated
+is used for rough boring only, the cylinders being finished
+by reaming in another similar machine. The cylinders are
+bored to a diameter of 3<sup class="enum">5</sup>/<sub class="denom">8</sub> inches, and about
+<sup class="enum">3</sup>/<sub class="denom">8</sub> inch of metal is
+removed by the roughing cut. The spindles have fixed center-to-center
+distances as the machine is intended for constant use
+on cylinders of one size, so that adjustment is not necessary.
+Of course, a special machine of this kind is only used in shops
+where large numbers of cylinders of one design are required
+continually. Some cylinder boring machines of the vertical type
+have spindles which can be adjusted for different center-to-center
+distances if this should be necessary in order to accommodate
+a cylinder of another size.</p>
+
+<hr class="c25" />
+<span class="pagenum"><a name="Pg_275" id="Pg_275">[275]</a></span>
+<h2><a name="Chapnum_7" id="Chapnum_7">CHAPTER VII</a></h2>
+<h3>HORIZONTAL BORING MACHINES</h3>
+<hr class="c05" />
+
+<p>A boring machine of the horizontal type is shown in <a href="#Fig_7_1">Fig. 1</a>.
+The construction and operation of this machine is very different
+from that of a vertical boring mill and it is also used for an
+entirely different class of work. The horizontal machine is
+employed principally for boring, drilling or milling, whereas the
+vertical design is especially adapted to turning and boring.
+The horizontal type is also used for turning or facing flanges
+or similar surfaces when such an operation can be performed to
+advantage in connection with other machine work on the same
+part.</p>
+
+<a name="Fig_7_1" id="Fig_7_1"></a><span class="pagenum"><a name="Pg_276" id="Pg_276">[276]</a></span>
+<div class="figcenter"><img src="images/284sm.jpg" alt="Lucas Horizontal Boring, Drilling and Milling Machine" />
+<p class="caption750">Fig. 1. Lucas Horizontal Boring, Drilling and Milling Machine</p>
+</div>
+
+<p>The type of machine illustrated in <a href="#Fig_7_1">Fig. 1</a> has a heavy base or
+bed to which is bolted the column <i>C</i> having vertical ways on
+which the spindle-head <i>H</i> is mounted. This head contains a
+sleeve or quill in which the spindle <i>S</i> slides longitudinally.
+The spindle carries cutters for boring, whereas milling cutters
+or the auxiliary facing arm are bolted to the end <i>A</i> of the
+spindle sleeve. The work itself is attached either directly or
+indirectly to the table or platen <i>P</i>. When the machine is in
+operation, the cutter or tool revolves with the spindle sleeve
+or spindle and either the cutter or the part being machined is
+given a feeding movement, depending on the character of the
+work. The spindle can be moved in or out by hand for adjustment,
+or by power for feeding the cutter, as when boring or
+drilling.</p>
+
+<p>The entire spindle-head <i>H</i> can also be moved vertically on
+the face of the column <i>C</i>, by hand, for setting the spindle to the
+proper height, or by power for feeding a milling cutter in a
+vertical direction. When the vertical position of the spindle-head
+is changed, the outboard bearing block <i>B</i> also moves
+up or down a corresponding amount, the two parts being connected<span class="pagenum"><a name="Pg_277" id="Pg_277">[277]</a></span>
+by shafts and gearing. Block <i>B</i> steadies the outer end
+of the boring-bar and the back-rest in which this block is
+mounted can be shifted along the bed to suit the length of the
+work, by turning the squared end of shaft <i>D</i> with a crank.
+The platen <i>P</i> has a cross-feed, and the saddle <i>E</i> on which it is
+mounted can be traversed lengthwise on the bed; both of these
+movements can also be effected by hand or power. There is a
+series of power feeding movements for the cutters and, in addition,
+rapid power movements <i>in a reverse direction from the
+feed</i> for returning a cutter quickly to its starting position, when
+this is desirable.</p>
+
+<p>This machine is driven by a belt connecting pulley <i>G</i> with an
+overhead shaft. When the machine is in operation, this pulley
+is engaged with the main driving shaft by a friction clutch <i>F</i>
+controlled by lever <i>L</i>. This main shaft drives through gearing
+a vertical shaft <i>I</i>, which by means of other gears in the spindle-head
+imparts a rotary movement to the spindle. As a machine
+of this type is used for boring holes of various diameters and
+for a variety of other work, it is necessary to have a number
+of speed changes for the spindle. Nine speeds are obtained by
+changing the position of the sliding gears controlled by levers
+<i>R</i> and this number is doubled by back-gears in the spindle-head
+and controlled by lever <i>J</i>.</p>
+
+<p>The amount of feed for the spindle, spindle-head, platen or
+saddle is varied by two levers <i>K</i> and <i>K<sub>1</sub></i> which control the position
+of sliding gears through which the feeding movements are
+transmitted. The direction of the feed can be reversed by shifting
+lever <i>O</i>. With this particular machine, nine feed changes
+are available for each position of the spindle back-gears, making
+a total of eighteen changes. The feeding movement is transmitted
+to the spindle-head, spindle, platen or saddle, as required,
+by the three distributing levers <i>T</i>, <i>U</i> and <i>V</i>, which control
+clutches connecting with the transmission shafts or feed
+screws. When lever <i>T</i> is turned to the left, the longitudinal
+power feed for the spindle is engaged, whereas turning it to the
+right throws in the vertical feed for the spindle-head. Lever <i>U</i>
+engages the cross-feed for platen <i>P</i> and lever <i>V</i>, the longitudinal
+<span class="pagenum"><a name="Pg_278" id="Pg_278">[278]</a></span>
+feed for saddle <i>E</i>. These levers have a simple but ingenious
+interlocking device which makes it impossible to engage more
+than one feed at a time. For example, if lever <i>T</i> is set for feeding
+the spindle, levers <i>U</i> and <i>V</i> are locked against movement.</p>
+
+<p>The feeds are started and stopped by lever <i>M</i> which also
+engages the rapid power traverse when thrown in the opposite
+direction. This rapid traverse operates for whatever feed is
+engaged by the distributing levers and, as before stated, in a
+reverse direction. For example, if the reverse lever <i>O</i> is set for
+feeding the spindle to the right, the rapid traverse would be to
+the left, and <i>vice versa</i>. The cross-feed for the platen can be
+automatically tripped at any point by setting an adjustable
+stop in the proper position and the feed can also be tripped by
+a hand lever at the side of the platen.</p>
+
+<p>All the different feeding movements can be effected by hand
+as well as by power. By means of handwheel <i>N</i>, the spindle
+can be moved in or out slowly, for feeding a cutter by hand.
+When the friction clamp <i>Q</i> is loosened, the turnstile <i>W</i> can be
+used for traversing the spindle, in case a hand adjustment is desirable.
+The spindle-head can be adjusted vertically by turning
+squared shaft <i>X</i> with a crank, and the saddle can be shifted
+along the bed by turning shaft <i>Y</i>. The hand adjustment of the
+platen is effected by shaft <i>Z</i>. The spindle-head, platen and
+saddle can also be adjusted from the end of the machine, when
+this is more convenient. Shafts <i>X</i>, <i>Y</i> and <i>Z</i> are equipped with
+micrometer dials which are graduated to show movements of
+one-thousandth inch. These dials are used for accurately adjusting
+the spindle or work and for boring holes or milling
+surfaces that must be an exact distance apart.</p>
+
+<a name="Fig_7_2" id="Fig_7_2"></a>
+<div class="figcenter"><img src="images/287sm.jpg" alt="Horizontal Boring and Drilling Machine with Vertical Table Adjustment" />
+<p class="caption750">Fig. 2. Horizontal Boring and Drilling Machine with Vertical Table Adjustment</p>
+</div>
+
+<a name="Secnum_7_1" id="Secnum_7_1"></a><p><b>Horizontal Boring Machine with Vertical Table Adjustment.</b>&mdash;Another
+horizontal boring machine is partly shown in <a href="#Fig_7_2">Fig. 2</a>.
+This machine is of the same type as that illustrated in Fig. 1,
+but its construction is quite different, as will be seen. The spindle
+cannot be adjusted vertically as with the first design described, but
+it is mounted and driven very much like the spindle of a lathe,
+and adjustment for height is obtained by raising or lowering
+the work table. The design is just the reverse, in this respect,<span class="pagenum"><a name="Pg_279" id="Pg_279">[279]</a></span>
+of the machine shown in <a href="#Fig_7_1">Fig. 1</a>, which has a vertical adjustment
+for the spindle, and a work table that remains in the same
+horizontal plane. The raising or lowering of the table is effected
+by shaft <i>E</i>, which rotates large nuts engaging the screws <i>S</i>.
+Shaft <i>E</i> is turned either by hand or power.</p>
+
+<p>The main spindle is driven by a cone pulley <i>P</i>, either directly,
+or indirectly through the back-gears shown. This arrangement
+gives six spindle speeds, and double this number is
+obtained by using a two-speed countershaft overhead. The
+motion for feeding the spindle longitudinally is transmitted
+through a cone of gears, which gives the required changes, to a
+pinion meshing with a rack which traverses the spindle. The
+large handwheel <i>H</i> and a corresponding wheel on the opposite
+side are used for adjusting the spindle rapidly by hand. The
+yoke or outboard bearing <i>B</i> for the boring-bars can be clamped
+in any position along the bed for supporting the bar as close to
+the work as possible.</p>
+
+<p>Horizontal boring machines are built in many other designs,
+but they all have the same general arrangement as the machines
+illustrated and operate on the same principle, with the exception<span class="pagenum"><a name="Pg_280" id="Pg_280">[280]</a></span>
+of special types intended for handling certain classes of
+work exclusively. The horizontal boring, drilling and milling
+machine is very efficient for certain classes of work because it
+enables all the machining operations on some parts to be completed
+at one setting. To illustrate, a casting which requires
+drilling, boring and milling at different places, can often be
+finished without disturbing its position on the platen after it is
+clamped in place. Frequently a comparatively small surface
+needs to be milled after a part has been bored. If this milling
+operation can be performed while the work is set up for boring,
+accurate results will be obtained (provided the machine is in
+good condition) and the time saved that would otherwise be
+required for re-setting the part on another machine. Some
+examples of work on which different operations are performed
+at the same setting will be referred to later. The horizontal
+boring machine also makes it possible to machine duplicate
+parts without the use of jigs, which is important, especially on
+large work, owing to the cost of jigs.</p>
+
+<a name="Secnum_7_2" id="Secnum_7_2"></a><p><b>Drilling and Boring&mdash;Cutters Used.</b>&mdash;Holes are drilled in a
+horizontal machine by simply inserting a drill of required size
+either directly in the spindle <i>S</i> (see <a href="#Fig_7_1">Fig. 1</a>), or in a reducing
+socket, and then feeding the spindle outward either by hand or
+power. When a hole is to be bored, a boring-bar <i>B<sub>1</sub></i> is inserted
+in the spindle and the cutter is attached to this bar. The
+latter is then fed through the hole as the cutter revolves. The
+distinction made by machinists between drilling and boring is as
+follows: A hole is said to be drilled when it is formed by sinking
+a drill into solid metal, whereas boring means the enlargement
+of a drilled or cored hole either by the use of a single boring
+tool, a double-ended cutter which operates on both sides of the
+hole, or a cutter-head having several tools.</p>
+
+<a name="Fig_7_3" id="Fig_7_3"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/289sm.png" alt="Boring-cutters of Different Types" /></div>
+<p class="caption750">Fig. 3. Boring-cutters of Different Types</p>
+</div>
+
+<p>There are various methods of attaching cutters to boring-bars
+and the cutters used vary for different classes of work. A
+simple style of cutter which is used widely for boring small holes
+is shown at <i>A</i> in <a href="#Fig_7_3">Fig. 3</a>. The cutter <i>c</i> is made from flat stock
+and the cutting is done by the front edges <i>e</i> and <i>e<sub>1</sub></i>, which are
+beveled in opposite directions. The cutter is held in the bar<span class="pagenum"><a name="Pg_281" id="Pg_281">[281]</a></span>
+by a taper wedge <i>w</i> and it is centered by shoulders at <i>s</i>, so that
+the diameter of the hole will equal the length across the cutter.
+The outer corners at the front should be slightly rounded, as a
+sharp corner would be dulled quickly. These cutters are made
+in different sizes and also in sets for roughing and finishing.
+The roughing cutter bores holes to within about <sup class="enum">1</sup>/<sub class="denom">32</sub> inch of the
+finish size and it is then replaced by the finishing cutter. A
+cutter having rounded ends, as shown by the detail sketch <i>a</i>, is
+sometimes used for light finishing cuts. These rounded ends
+form the cutting edges and give a smooth finish.</p>
+
+<p>Another method of holding a flat cutter is shown at <i>B</i>. The
+conical end of a screw bears against a conical seat in, the cutter,
+thus binding the latter in its slot. The conical seat also centers
+the cutter. A very simple and inexpensive form of cutter is
+shown at <i>C</i>. This is made from a piece of round steel, and it
+is held in the bar by a taper pin which bears against a circular<span class="pagenum"><a name="Pg_282" id="Pg_282">[282]</a></span>
+recess in the side of the cutter. This form has the advantage
+of only requiring a hole through the boring-bar, whereas it is
+necessary to cut a rectangular slot for the flat cutter.</p>
+
+<a name="Fig_7_4" id="Fig_7_4"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/290sm.png" alt="Boring with a Flat Double-ended Cutter" /></div>
+<p class="caption750">Fig. 4. Boring with a Flat Double-ended Cutter</p>
+</div>
+
+<p><a href="#Fig_7_4">Fig. 4</a> shows how a hole is bored by cutters of the type referred
+to. The bar rotates as indicated by the arrow <i>a</i> and at
+the same time feeds longitudinally as shown by arrow <i>b</i>. The
+speed of rotation depends upon the diameter of the hole and
+the kind of material being bored, and the feed per revolution
+must also be varied to suit conditions. No definite rule can be
+given for speed or feed. On some classes of work a long boring-bar
+is used, which passes through the hole to be bored and is
+steadied at its outer end by the back-rest <i>B</i>, <a href="#Fig_7_1">Figs. 1</a> and <a href="#Fig_7_2">2</a>.
+On other work, a short bar is inserted in the spindle having a
+cutter at the outer end. An inexpensive method of holding a
+cutter at the end of a bar is shown at <i>D</i>, <a href="#Fig_7_3">Fig. 3</a>. The cutter
+passes through a slot and is clamped by a bolt as shown. When
+it is necessary to bore holes that are &#8220;blind&#8221; or closed at the
+bottom, a long boring-bar which passes through the work cannot,
+of course, be used.</p>
+
+<p>Sometimes it is necessary to have a cutter mounted at the
+extreme end of a bar in order to bore close to a shoulder or the
+bottom of a hole. One method of holding a cutter so that it
+projects beyond the end of a bar is indicated at <i>E</i>. A screw
+similar to the one shown at <i>B</i> is used, and the conical end bears
+in a conical hole in the cutter. This hole should be slightly<span class="pagenum"><a name="Pg_283" id="Pg_283">[283]</a></span>
+offset so that the cutter will be forced back against its seat.
+The tool shown at <i>F</i> has adjustable cutters. The inner end of
+each cutter is tapering and bears against a conical-headed screw
+<i>b</i> which gives the required outward adjustment. The cutters
+are held against the central bolt by fillister-head screws <i>f</i> and
+they are clamped by the screws <i>c</i>. Boring tools are made in
+many different designs and the number and form of the cutters
+is varied somewhat for different kinds of work.</p>
+
+<a name="Fig_7_5" id="Fig_7_5"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/291sm.png" alt="Cutter-heads for Boring Large Holes" /></div>
+<p class="caption750">Fig. 5. Cutter-heads for Boring Large Holes</p>
+</div>
+
+<a name="Secnum_7_3" id="Secnum_7_3"></a><p><b>Cutter-heads for Boring Large Holes.</b>&mdash;When large holes are
+to be bored, the cutters are usually held in a cast-iron head
+which is mounted on the boring-bar. One type of cutter-head
+is shown in <a href="#Fig_7_5">Fig. 5</a>. This particular head is double-ended and
+carries two cutters <i>c</i>. The cutter-head is bored to fit the bar
+closely and it is prevented from turning by a key against which
+a set-screw is tightened. By referring to the end view, it will be
+seen that each cutter is offset with relation to the center of the
+bar, in order to locate the front of the tool on a radial line.
+The number of cutters used in a cutter-head varies. By having
+several cutters, the work of removing a given amount of metal in
+boring is distributed, and holes can be bored more quickly with
+a multiple cutter-head, although more power is required to
+drive the boring-bar. The boring-bar is also steadied by a
+multiple cutter-head, because the tendency of any one cutter<span class="pagenum"><a name="Pg_284" id="Pg_284">[284]</a></span>
+to deflect the bar is counteracted by the cutters on the opposite
+side.</p>
+
+<a name="Fig_7_6" id="Fig_7_6"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/292sm.png" alt="Cutter-head with Four Boring Tools" /></div>
+<p class="caption750">Fig. 6. Cutter-head with Four Boring Tools</p>
+</div>
+
+<p>A disk-shaped head having four cutters is illustrated in <a href="#Fig_7_6">Fig.
+6</a>. The cutters are inserted in slots or grooves in the face of
+the disk and they are held by slotted clamping posts. The
+shape of these posts is shown by the sectional view. The tool
+passes through an elongated slot and it is tightly clamped
+against the disk by tightening nut <i>n</i>. This head is also driven
+by a key which engages a keyway in the boring-bar.</p>
+
+<a name="Fig_7_7" id="Fig_7_7"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/293sm.png" alt="Cutter-heads equipped with Adjustable Tools" /></div>
+<p class="caption750">Fig. 7. Cutter-heads equipped with Adjustable Tools</p>
+</div>
+
+<p>Two other designs of cutter-heads are shown in <a href="#Fig_7_7">Fig. 7</a>. The
+one illustrated at <i>A</i> has three equally spaced cutters which are
+held in an inclined position. The cutters are clamped by screws
+<i>c</i> and they can be adjusted within certain limits by screws <i>s</i>.
+The cutters are placed at an angle so that they will extend beyond
+the front of the head, thus permitting the latter to be
+moved up close to a shoulder. The cutter-heads shown in
+<a href="#Fig_7_5">Figs. 5</a> and <a href="#Fig_7_6">6</a> can also be moved up close to a shoulder if bent
+cutters are used as shown in the right-hand view, <a href="#Fig_7_5">Fig. 5</a>. The
+idea in bending the cutters is to bring the cutting edges in
+advance of the clamping posts so that they will reach a shoulder
+before the binding posts strike it. The arrangement of cutter-head
+<i>B</i> (<a href="#Fig_7_7">Fig. 7</a>) is clearly shown by the illustration.</p>
+
+<p><span class="pagenum"><a name="Pg_285" id="Pg_285">[285]</a></span>Cutter-heads are often provided with two sets of cutters, one
+set being used for roughing and the other for finishing. It is a
+good plan to make these cutters so that the ends <i>e</i> (<a href="#Fig_7_6">Fig. 6</a>) will
+rest against the bar or bottom of the slot, when the cutting edge
+is set to the required radius. The cutters can then be easily
+set for boring duplicate work. One method of making cutters
+in sets is to clamp the annealed stock in the cutter-head and
+then turn the ends to the required radius by placing the head
+in the lathe. After both sets of cutters have been turned in
+this way, they are ground to shape and then hardened.</p>
+
+<a name="Fig_7_8" id="Fig_7_8"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/294sm.png" alt="Boring Tools for Roughing and Finishing Cuts" /></div>
+<p class="caption750">Fig. 8. Boring Tools for Roughing and Finishing Cuts</p>
+</div>
+
+<p>Boring cutters intended for roughing and finishing cuts are
+shown in the detail view <a href="#Fig_7_8">Fig. 8</a> at <i>A</i> and <i>B</i>, respectively. The
+side of the roughing cutter <i>A</i> is ground to a slight angle <i>c</i> to
+provide clearance for the cutting edge, and the front has a
+backward slope <i>s</i> to give the tool keenness. This tool is a good
+form to use for roughing cuts in cast iron. The finishing tool
+at <i>B</i> has a broad flat edge <i>e</i> and it is intended for coarse feeds
+and light cuts in cast iron. If a round cutting edge is used for
+finishing, a comparatively fine feed is required in order to obtain
+a smooth surface. The corners of tool <i>B</i> are rounded and they
+should be ground to slope inward as shown in the plan view.
+The top or ends <i>d</i> of both of these tools are &#8220;backed off&#8221; slightly
+<span class="pagenum"><a name="Pg_286" id="Pg_286">[286]</a></span>
+to provide clearance. This clearance should be just enough to
+prevent the surface back of the cutting edge from dragging over
+the work. Excessive end clearance not only weakens the cutting
+edge, but tends to cause chattering. As a finishing tool
+cuts on the upper end instead of on the side, the front should
+slope backward as shown in the side view, rather than sidewise
+as with a roughing cutter. The angle of the slope should
+be somewhat greater for steel than cast iron, unless the steel is
+quite hard, thus requiring a strong blunt tool.</p>
+
+<a name="Fig_7_9" id="Fig_7_9"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/295sm.png" alt="Cylinder mounted on Horizontal Machine for Boring" /></div>
+<p class="caption750">Fig. 9. Cylinder mounted on Horizontal Machine for Boring</p>
+</div>
+
+<a name="Secnum_7_4" id="Secnum_7_4"></a><p><b>Cylinder Boring.</b>&mdash;<a href="#Fig_7_9">Fig. 9</a>
+illustrates the use of a cutter-head for cylinder boring. After the cylinder casting is set on the
+platen of the machine, the boring-bar with the cutter-head
+mounted on it is inserted in the spindle. The bar <i>B</i> has a taper
+shank and a driving tang similar to a drill shank, which fits a
+taper hole in the end of the spindle. The cutter-head <i>C</i> is
+fastened to the bar so that it will be in the position shown when
+the spindle is shifted to the right, as the feeding movement
+(with this particular machine) is to be in the opposite direction.
+The casting <i>A</i> should be set central with the bar by adjusting
+the work-table vertically and laterally, if necessary, and the
+outer support <i>F</i> should be moved close to the work, to make the
+bar as rigid as possible.</p>
+
+<p>The cylinder is now ready to be bored. Ordinarily, one or
+two roughing cuts and one finishing cut would be sufficient, unless
+the rough bore were considerably below the finish diameter.<span class="pagenum"><a name="Pg_287" id="Pg_287">[287]</a></span>
+As previously explained, the speed and feed must be governed
+by the kind of material being bored and the diameter of the
+cut. The power and rigidity of the boring machine and the
+quality of the steel used for making the cutters also affect
+the cutting speed and feed. As the finishing cut is very light, a
+tool having a flat cutting edge set parallel to the bar is ordinarily
+used when boring cast iron. The coarse feed enables the
+cut to be taken in a comparatively short time and the broad-nosed
+tool gives a smooth finish if properly ground.</p>
+
+<p>The coarse finishing feed is not always practicable, especially
+if the boring machine is in poor condition, owing to the chattering
+of the tool, which results in a rough surface. The last or
+finishing cut should invariably be a continuous one, for if the
+machine is stopped before the cut is completed, there will be a
+ridge in the bore at the point where the tool temporarily left off
+cutting. This ridge is caused by the cooling and resulting contraction
+and shortening of the tool during the time that it is
+stationary. For this reason independent drives are desirable
+for boring machines.</p>
+
+<p><span class="pagenum"><a name="Pg_288" id="Pg_288">[288]</a></span>Facing arms are attached to the bar on either side of the
+cylinder for facing the flanges after the boring operation. The
+turning tool of a facing arm is fastened to a slide which is fed
+outward a short distance each revolution, by a star-wheel that
+is caused to turn as it strikes against a stationary pin. By
+facing the flanges in this way, they are finished square with the
+bore.</p>
+
+<p>When setting a cylinder which is to be bored it should, when
+the design will permit, be set true by the outside of the flange,
+or what is even better, by the outside of the cylinder itself,
+rather than by the rough bore, in order that the walls of the
+finished cylinder will have a uniform thickness. The position
+of very large cylinders, while they are being bored, is an important
+consideration. Such cylinders should be bored in the
+position which they will subsequently occupy when assembled.
+For example, the cylinder for a large horizontal engine should
+be bored while in a horizontal position, as the bore is liable to
+spring to a slight oval shape when the cylinder is placed horizontal
+after being bored while standing in a vertical position. If,
+however, the cylinder is bored while in the position in which it
+will be placed in the assembled engine, this trouble is practically
+eliminated.</p>
+
+<p>There is a difference of opinion among machinists as to the
+proper shape of the cutting point of a boring tool for finishing
+cuts, some contending that a wide cutting edge is to be preferred,
+while others advocate the use of a comparatively narrow
+edge with a reduced feed. It is claimed, that the narrow tool
+produces a more perfect bore, as it is not so easily affected by
+hard spots in the iron, and it is also pointed out that the minute
+ridges left by the narrow tool are an advantage rather than a
+disadvantage, as they form pockets for oil and aid in lubricating
+the cylinder. It is the modern practice, however, to use a
+broad tool and a coarse feed for the light finishing cut, provided
+the tool does not chatter.</p>
+
+<p>The type of machine tool used for boring cylinders, and also
+the method of procedure is determined largely by the size of
+the work and the quantity which is to be machined. The<span class="pagenum"><a name="Pg_289" id="Pg_289">[289]</a></span>
+turret lathe, as well as horizontal and vertical boring mills, is
+used for this work, and in automobile factories or other shops
+where a great many cylinders are bored, special machines and
+fixtures are often employed.</p>
+
+<a name="Fig_7_10" id="Fig_7_10"></a>
+<div class="figcenter"><img src="images/297sm.jpg" alt="Boring a Duplex Cylinder on Horizontal Machine" />
+<p class="caption750">Fig. 10. Boring a Duplex Cylinder on a Horizontal Machine</p>
+</div>
+
+<a name="Secnum_7_5" id="Secnum_7_5"></a><p><b>Boring a Duplex Gasoline Engine Cylinder.</b>&mdash;The method of
+holding work on a horizontal boring machine depends on its
+shape. A cylinder or other casting having a flat base can be
+clamped directly to the platen, but pieces of irregular shape are
+usually held in special fixtures. <a href="#Fig_7_10">Fig. 10</a> shows how the cylinder
+casting of a gasoline engine is set up for the boring operation.
+The casting <i>W</i> is placed in a fixture <i>F</i> which is clamped to the
+machine table. One end of the casting rests on the adjustable
+screws <i>S</i> and it is clamped by set-screws located in the top and
+sides of the fixture. There are two cylinders cast integral and
+these are bored by a short stiff bar mounted in the end of the
+spindle and having cutters at the outer end. A long bar of
+the type which passes through the work and is supported by the
+outboard bearing <i>B</i>, could not be used for this work, because
+the top of each cylinder is closed.</p>
+
+<p>When one cylinder is finished the other is set in line with the<span class="pagenum"><a name="Pg_290" id="Pg_290">[290]</a></span>
+spindle by adjusting the work-table laterally. This adjustment
+is effected by screw <i>C</i>, and the required center-to-center
+distance between the two cylinders can be gaged by the micrometer
+dial <i>M</i> on the cross-feed screw, although positive stops
+are often used in preference. After the first cylinder is bored,
+the dial is set to the zero position by loosening the small knurled
+screw shown, and turning the dial around. The feed screw is
+then rotated until the dial shows that the required lateral
+adjustment is made, which locates the casting for boring the
+second cylinder. The end of the casting is also faced true by a
+milling cutter. Ordinarily, milling cutters are bolted directly
+to the spindle sleeve <i>A</i> on this particular machine, which gives
+a rigid support for the cutter and a powerful drive.</p>
+
+<a name="Fig_7_11" id="Fig_7_11"></a>
+<div class="figcenter"><img src="images/298sm.jpg" alt="Cylinder turned around for Machining Valve Seats" />
+<p class="caption750">Fig. 11. Cylinder turned around for Machining Valve Seats</p>
+</div>
+
+<p>The next operation is that of boring and milling the opposite
+end of the cylinder. This end is turned toward the spindle
+(as shown in <a href="#Fig_7_11">Fig. 11</a>) without unclamping the work or fixture,
+by simply turning the circular table <i>T</i> half way around. This
+table is an attachment which is clamped to the main table for
+holding work that must be turned to different positions for
+machining the various parts. Its position is easily changed, and<span class="pagenum"><a name="Pg_291" id="Pg_291">[291]</a></span>
+as the work remains fixed with relation to the table, the alignment
+between different holes or surfaces is assured, if the table
+is turned the right amount. In this case, the casting needs to
+be rotated one-half a revolution or 180 degrees, and this is done
+by means of angular graduations on the base of the table.
+The illustration shows the casting set for boring the inlet and
+exhaust valve chambers. The different cutters required for
+boring are mounted on one bar as shown, and the casting is
+adjusted crosswise to bring each valve chamber in position, by
+using the micrometer dial. The single-ended cutter <i>c</i> forms a
+shallow circular recess or seat in the raised pad which surrounds
+the opening. The cover joint directly back of the cylinders is
+finished by milling.</p>
+
+<a name="Fig_7_12" id="Fig_7_12"></a>
+<div class="figcenter"><img src="images/299sm.jpg" alt="Boring Differential Gear Casing" />
+<p class="caption750">Fig. 12. Boring Differential Gear Casing</p>
+</div>
+
+<a name="Secnum_7_6" id="Secnum_7_6"></a><p><b>Examples of Boring, Radial Facing and Milling.</b>&mdash;Another
+example of boring, in which the circular table is used, is shown
+in <a href="#Fig_7_12">Fig. 12</a>. The work <i>W</i> is a casing for the differential gears of
+an automobile. It is mounted in a fixture <i>F</i> which is bolted to
+the table. The casting has round ends, which are clamped in
+V-blocks, thus aligning the work. This fixture has a guide-bushing<span class="pagenum"><a name="Pg_292" id="Pg_292">[292]</a></span>
+<i>G</i> which is centered with the bar and cutter in order to
+properly locate the casting. There is a bearing at each end of
+the casing, and two larger ones in the center. These are bored
+by flat cutters similar to the style illustrated at <i>A</i> in <a href="#Fig_7_3">Fig. 3</a>.
+The cutter for the inner bearings is shown at <i>c</i>.</p>
+
+<a name="Fig_7_13" id="Fig_7_13"></a>
+<div class="figcenter"><img src="images/300sm.jpg" alt="Facing and Turning Flange of Differential Gear Casing" />
+<p class="caption750">Fig. 13. Facing and Turning Flange of Differential Gear Casing</p>
+</div>
+
+<p>After the bearings are bored, the circular table is turned 90
+degrees and the work is moved closer to the spindle (as shown
+in <a href="#Fig_7_13">Fig. 13</a>) for facing flange <i>F</i> at right angles to the bearings.
+Circular flanges of this kind are faced in a horizontal boring
+machine by a special facing-arm or head <i>H</i>. For this particular
+job this head is clamped directly to the spindle sleeve,
+but it can also be clamped to the spindle if necessary. The
+turning tool is held in a slotted toolpost, and it is fed radially
+for turning the side or face of the flange, by the well-known
+star feed at <i>S</i>. When this feed is in operation the bent finger
+<i>E</i> is turned downward so that it strikes one of the star wheel
+arms for each revolution; this turns the wheel slightly, and<span class="pagenum"><a name="Pg_293" id="Pg_293">[293]</a></span>
+the movement is transmitted to the tool-block by a feed-screw.
+The illustration shows the tool set for turning the outside or
+periphery of the flange. This is done by setting the tool to the
+proper radius and then feeding the work horizontally by shifting
+the work-table along the bed. By referring to <a href="#Fig_7_12">Fig. 12</a> it will be
+seen that the facing head does not need to be removed for boring,
+as it is attached to the spindle driving quill and does not interfere
+with the longitudinal adjustment of the spindle. This
+facing head is also used frequently for truing the flanges of
+cylinders which are to be bored, and for similar work.</p>
+
+<a name="Fig_7_14" id="Fig_7_14"></a>
+<div class="figcenter"><img src="images/301sm.jpg" alt="Example of Work requiring Boring and Milling" />
+<p class="caption750">Fig. 14. Example of Work requiring Boring and Milling</p>
+</div>
+
+<p><a href="#Fig_7_14">Fig. 14</a> shows another example of work which requires boring
+and milling. This casting is mounted on a fixture which is
+bolted to the main table. In this case the circular table is not
+necessary, because the work can be finished without swiveling
+it around. After the boring is completed the edge <i>E</i> is trued
+by the large-face milling cutter <i>M</i> bolted to the spindle sleeve.
+The irregular outline of the edge is followed by moving the table
+crosswise and the spindle vertically, as required.</p>
+
+<a name="Fig_7_15" id="Fig_7_15"></a>
+<div class="figcenter"><div class="illobox450"><img src="images/302sm.png" alt="Cylinder Lining mounted in Fixture for Boring" /></div>
+<p class="caption750">Fig. 15. Cylinder Lining mounted in Fixture for Boring</p>
+</div>
+
+<a name="Secnum_7_7" id="Secnum_7_7"></a><p><b>Fixture for Cylinder Lining or Bushing.</b>&mdash;A method of holding
+a cylinder lining or bushing while it is being bored is shown<span class="pagenum"><a name="Pg_294" id="Pg_294">[294]</a></span>
+in <a href="#Fig_7_15">Fig. 15</a>. The lining <i>L</i> is mounted in two cast-iron ring-shaped
+fixtures <i>F</i>. These fixtures are circular in shape and have
+flat bases which are bolted to the table of the machine. On the
+inside of each fixture, there are four equally spaced wedges <i>W</i>
+which fit into grooves as shown in the end view. These wedges
+are drawn in against the work by bolts, and they prevent the
+lining from rotating when a cut is being taken. This form of
+fixture is especially adapted for holding thin bronze linings,
+such as are used in pump cylinders, because only a light pressure
+against the wedges is required, and thin work can be
+held without distorting it. If a very thin lining is being
+bored, it is well to loosen the wedges slightly before taking the
+finishing cut, so that the work can spring back to its normal
+shape.</p>
+
+<a name="Fig_7_16" id="Fig_7_16"></a><span class="pagenum"><a name="Pg_295" id="Pg_295">[295]</a></span>
+<div class="figcenter"><img src="images/303sm.jpg" alt="Detrick &amp; Harvey Horizontal Boring Machine of the Floor Type Boring Engine Bed Casting" />
+<p class="caption750">Fig. 16. Detrick &amp; Harvey Horizontal Boring Machine of the Floor Type Boring Engine Bed Casting</p>
+</div>
+
+<a name="Secnum_7_8" id="Secnum_7_8"></a><p><b>Horizontal Boring Machine of Floor Type.</b>&mdash;The type of
+horizontal boring, drilling and milling machine, shown in <a href="#Fig_7_16">Fig. 16</a>,
+is intended for boring heavy parts such as the cylinders of large
+engines or pumps, the bearings of heavy machine beds and
+similar work. This machine can also be used for drilling and
+milling, although it is intended primarily for boring, and the
+other operations are usually secondary. This design is ordinarily
+referred to as the &#8220;floor type,&#8221; because the work-table
+is low for accommodating large heavy castings. The spindle <i>S</i>
+which drives the boring-bar, and the spindle feeding mechanism,
+are carried by a saddle. This saddle is free to move vertically<span class="pagenum"><a name="Pg_296" id="Pg_296">[296]</a></span>
+on the face of column <i>C</i> which is mounted on transverse ways
+extending across the right-hand end of the main bed. This
+construction permits the spindle to move vertically or laterally
+(by traversing the column) either for adjusting it to the required
+position or for milling operations. The spindle also
+has a longitudinal movement for boring. There is an outer
+bearing <i>B</i> for supporting the boring-bar, which also has lateral
+and vertical adjustments, so that it can be aligned with the
+bar.</p>
+
+<p>The work done on a machine of this type is either clamped
+directly to the large bed-plate <i>A</i> (which has a number of T-slots
+for receiving the heads of the clamping bolts) or, in some cases,
+a special fixture may be used or an auxiliary table. Boring
+machines of this same general construction are built in many
+different sizes. The main spindle of the machine illustrated is
+driven by a motor located at the rear of the vertical column
+<i>C</i>, the motion being transmitted to the spindle through shafts
+and gearing. The casting <i>D</i>, shown in this particular illustration,
+is for a steam engine of the horizontal type, and the operation
+is that of boring the cylindrical guides or bearings for the
+crosshead. These bearings have a diameter of 15<sup class="enum">3</sup>/<sub class="denom">4</sub> inches and
+are 37<sup class="enum">3</sup>/<sub class="denom">4</sub> inches long. In boring them, two roughing cuts and one
+finishing cut are taken. The end of the casting, which in the
+assembled engine bears against the cylinder, is then faced by
+means of a regular facing arm.</p>
+
+<p>After removing the boring-bar the table <i>E</i> of the special
+fixture on which the casting is mounted is turned one quarter
+of a revolution. A large milling cutter 24 inches in diameter is
+next mounted on the spindle of the machine, and one side of
+the main bearing, as well as the pads for the valve-rod guide-bar
+brackets, are milled. The table is then revolved and the opposite
+side of the main bearing is milled in the same way, the
+table being accurately located in the different positions by an
+index plunger <i>F</i> which engages holes on the under side. The
+spindle is now moved upward to allow the table to be turned so
+as to locate the bearing end of the frame next to the headstock
+of the machine. The milling cutter is then used to machine<span class="pagenum"><a name="Pg_297" id="Pg_297">[297]</a></span>
+the inside and top surfaces of the main bearing. By turning the
+fixture and not changing the position of the casting after it is
+bolted into place, the various surfaces are machined in the correct
+relation to one another without difficulty. This is a good
+example of the work done on horizontal boring machines of the
+floor type.</p>
+<hr class="c25" />
+
+<p class="pagenum"><a name="Pg_299" id="Pg_299">[299]</a></p>
+
+<h2>INDEX</h2>
+<hr class="c05" />
+
+<table align="center" class="center" width="50%" cellpadding="0" cellspacing="0" summary="Index">
+
+<tr>
+<td width="1%">&nbsp;</td>
+<td width="10%">&nbsp;</td>
+<td width="2%" class="right"><span class="smcap">Page</span></td>
+</tr>
+
+<tr><td colspan="3">&nbsp;</td></tr>
+
+<tr>
+<td colspan="2" class="left" valign="bottom"><span class="dropcap">A</span>cme flat turret lathe, examples of chuck work</td>
+<td class="right" valign="bottom"><a href="#Pg_219">219</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Acme standard thread and tool for cutting</td>
+<td class="right"><a href="#Pg_159">159</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Acme standard thread gage</td>
+<td class="right"><a href="#Pg_157">157</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Acme thread tool, measuring width with vernier caliper</td>
+<td class="right"><a href="#Pg_157">157</a>, <a href="#Pg_158">158</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Accumulation of errors</td>
+<td class="right"><a href="#Pg_105">105</a>, <a href="#Pg_106">106</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Aligning lathe centers for cylindrical turning</td>
+<td class="right"><a href="#Pg_16">16</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Allowances, average, for forced fits</td>
+<td class="right"><a href="#Pg_130">130</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">for different classes of fits</td>
+<td class="right"><a href="#Pg_131">131</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">for driving fits</td>
+<td class="right"><a href="#Pg_131">131</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">for forced fits of given pressure</td>
+<td class="right"><a href="#Pg_133">133</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">for push fits</td>
+<td class="right"><a href="#Pg_131">131</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">for running fits</td>
+<td class="right"><a href="#Pg_131">131</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">for shrinkage fits</td>
+<td class="right"><a href="#Pg_133">133</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Aluminum, lubricant for machining</td>
+<td class="right"><a href="#Pg_53">53</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">shape of tools for turning</td>
+<td class="right"><a href="#Pg_53">53</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">speed and feed for machining</td>
+<td class="right"><a href="#Pg_53">53</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Angle-plate applied to lathe faceplate</td>
+<td class="right"><a href="#Pg_48">48</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Angles, gage for accurate measurement of</td>
+<td class="right"><a href="#Pg_97">97</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Apron of lathe</td>
+<td class="right"><a href="#Pg_4">4</a>, <a href="#Pg_5">5</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Arbor or mandrel press</td>
+<td class="right"><a href="#Pg_22">22</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Arbors or mandrels for lathe work, types of</td>
+<td class="right"><a href="#Pg_49">19</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">use of</td>
+<td class="right"><a href="#Pg_17">17</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Attachment, application of Hendey relieving</td>
+<td class="right"><a href="#Pg_125">125</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">convex turning for vertical boring mill</td>
+<td class="right"><a href="#Pg_259">259</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">for coarse threading in lathe</td>
+<td class="right"><a href="#Pg_160">160</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">for spherical turning</td>
+<td class="right"><a href="#Pg_113">113</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">for taper turning in lathe</td>
+<td class="right"><a href="#Pg_88">88</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">Hendey relieving</td>
+<td class="right"><a href="#Pg_123">123</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Automatic chucking and turning machine, Potter &amp; Johnston</td>
+<td class="right"><a href="#Pg_223">223</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">Potter &amp; Johnston, method of &#8220;setting-up&#8221;</td>
+<td class="right"><a href="#Pg_227">227</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">Potter &amp; Johnston, turning flywheel in</td>
+<td class="right"><a href="#Pg_236">236</a></td>
+</tr>
+
+<tr>
+<td colspan="3">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="left" valign="bottom"><span class="dropcap">B</span>ack-gears of lathe</td>
+<td class="right" valign="bottom"><a href="#Pg_3">3</a>, <a href="#Pg_4">4</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Bardons &amp; Oliver turret lathe, general description</td>
+<td class="right"><a href="#Pg_178">178</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Bored holes, measuring diameter of</td>
+<td class="right"><a href="#Pg_41">41</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Boring and reaming tools for vertical mill</td>
+<td class="right"><a href="#Pg_251">251</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Boring and turning mill, vertical, general description</td>
+<td class="right"><a href="#Pg_242">242</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">vertical, holding and setting work</td>
+<td class="right"><a href="#Pg_247">247</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">vertical, turning in</td>
+<td class="right"><a href="#Pg_249">249</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">turning tools for
+<span class="pagenum"><a name="Pg_300" id="Pg_300">[300]</a></span>
+</td>
+<td class="right"><a href="#Pg_253">253</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Boring-bar cutters and methods of holding</td>
+<td class="right"><a href="#Pg_280">280</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Boring cutters for roughing and finishing cuts</td>
+<td class="right"><a href="#Pg_285">285</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Boring cylinders on horizontal machine</td>
+<td class="right"><a href="#Pg_286">286</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Boring holes to given center distance in lathe</td>
+<td class="right"><a href="#Pg_51">51</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Boring in lathe, example of</td>
+<td class="right"><a href="#Pg_39">39</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Boring large castings in lathe</td>
+<td class="right"><a href="#Pg_49">49</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Boring large holes, cutter-heads used for</td>
+<td class="right"><a href="#Pg_283">283</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Boring machine, horizontal</td>
+<td class="right"><a href="#Pg_275">275</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">horizontal, examples of work on</td>
+<td class="right"><a href="#Pg_289">289-297</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">horizontal, floor type</td>
+<td class="right"><a href="#Pg_294">294</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">vertical, multiple-spindle type</td>
+<td class="right"><a href="#Pg_274">274</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Boring tool, lathe</td>
+<td class="right"><a href="#Pg_40">40</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Box-tools, different designs and examples of work</td>
+<td class="right"><a href="#Pg_193">193</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">for general turret lathe work</td>
+<td class="right"><a href="#Pg_190">190</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Bradford belt-driven lathe, general description</td>
+<td class="right"><a href="#Pg_1">1</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Bradford quick change-gear type of lathe</td>
+<td class="right"><a href="#Pg_173">173</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Brass, speed for turning</td>
+<td class="right"><a href="#Pg_52">52</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">tool for turning in lathe</td>
+<td class="right"><a href="#Pg_52">52</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">&#8220;Bridle&#8221; or &#8220;hold-back&#8221; for lathe</td>
+<td class="right"><a href="#Pg_26">26</a>, <a href="#Pg_27">27</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Bullard vertical turret lathe</td>
+<td class="right"><a href="#Pg_264">264</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">examples of work</td>
+<td class="right"><a href="#Pg_268">268</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Button method of locating work</td>
+<td class="right"><a href="#Pg_101">101</a></td>
+</tr>
+
+<tr>
+<td colspan="3">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="left" valign="bottom"><span class="dropcap">C</span>aliper tool for taper turning</td>
+<td class="right" valign="bottom"><a href="#Pg_85">85</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Calipers, methods of setting</td>
+<td class="right"><a href="#Pg_10">10</a>, <a href="#Pg_11">11</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">&#8220;Cat-head,&#8221; application in lathe work</td>
+<td class="right"><a href="#Pg_25">25</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Center holes, incorrect and correct forms</td>
+<td class="right"><a href="#Pg_32">32</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Center indicator, use of</td>
+<td class="right"><a href="#Pg_100">100</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Centered stock, methods of facing ends</td>
+<td class="right"><a href="#Pg_34">34</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Centers, lathe, aligning for cylindrical turning</td>
+<td class="right"><a href="#Pg_16">16</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">lathe, grinder for truing</td>
+<td class="right"><a href="#Pg_34">34</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Centering machine</td>
+<td class="right"><a href="#Pg_30">30</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Centering parts to be turned</td>
+<td class="right"><a href="#Pg_28">28</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Centering, precaution for tool steel</td>
+<td class="right"><a href="#Pg_33">33</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Change gears, calculating for thread cutting</td>
+<td class="right"><a href="#Pg_167">167</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">compound, for thread cutting</td>
+<td class="right"><a href="#Pg_170">170</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">for cutting fractional threads</td>
+<td class="right"><a href="#Pg_171">171</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">for cutting metric pitches</td>
+<td class="right"><a href="#Pg_171">171</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">for thread cutting</td>
+<td class="right"><a href="#Pg_135">135</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Chasing dial for &#8220;catching threads&#8221; when screw cutting</td>
+<td class="right"><a href="#Pg_141">141</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Chuck, inaccuracy from pressure of jaws</td>
+<td class="right"><a href="#Pg_42">42</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">lathe, application of</td>
+<td class="right"><a href="#Pg_37">37</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">setting work in</td>
+<td class="right"><a href="#Pg_42">42</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">universal, independent and combination</td>
+<td class="right"><a href="#Pg_36">36</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Chucking and turning machine, Potter &amp; Johnston automatic</td>
+<td class="right"><a href="#Pg_223">223</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">Potter &amp; Johnston automatic, method of &#8220;setting-up&#8221;</td>
+<td class="right"><a href="#Pg_227">227</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">Potter &amp; Johnston automatic, turning flywheel in</td>
+<td class="right"><a href="#Pg_236">236</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Chucking machine, New Britain, multiple-spindle type</td>
+<td class="right"><a href="#Pg_238">238</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Clearance angle for turning tools
+<span class="pagenum"><a name="Pg_301" id="Pg_301">[301]</a></span></td>
+<td class="right"><a href="#Pg_66">66</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Clearance of turning tools, meaning of</td>
+<td class="right"><a href="#Pg_62">62</a>, <a href="#Pg_63">63</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Coarse threading attachment for lathe</td>
+<td class="right"><a href="#Pg_160">160</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Collapsing tap, Geometric</td>
+<td class="right"><a href="#Pg_202">202</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Combination chuck for lathe</td>
+<td class="right"><a href="#Pg_36">36</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Compound rest, applied to screw or thread cutting</td>
+<td class="right"><a href="#Pg_143">143</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">applied to taper turning</td>
+<td class="right"><a href="#Pg_95">95</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Convex turning attachment for vertical boring mills</td>
+<td class="right"><a href="#Pg_259">259</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Copper, tool for turning in lathe</td>
+<td class="right"><a href="#Pg_52">52</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Crankshaft lathe, description of R. K. LeBlond special</td>
+<td class="right"><a href="#Pg_108">108</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">operation of R. K. LeBlond</td>
+<td class="right"><a href="#Pg_110">110</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Crankshaft turning in engine lathe</td>
+<td class="right"><a href="#Pg_107">107</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Cross-slide stop for threading</td>
+<td class="right"><a href="#Pg_155">155</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Cuts, average depth for turning</td>
+<td class="right"><a href="#Pg_75">75</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">roughing and finishing in lathe</td>
+<td class="right"><a href="#Pg_12">12</a>, <a href="#Pg_75">75</a>, <a href="#Pg_76">76</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Cutter-heads, for boring, equipped with adjustable tools</td>
+<td class="right"><a href="#Pg_284">284</a>, <a href="#Pg_285">285</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">for horizontal boring machine</td>
+<td class="right"><a href="#Pg_283">283</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Cutters, boring, roughing and finishing types</td>
+<td class="right"><a href="#Pg_285">285</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">for boring-bars</td>
+<td class="right"><a href="#Pg_280">280</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Cutting lubricants for turning tools</td>
+<td class="right"><a href="#Pg_77">77</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Cutting speeds, average for turning</td>
+<td class="right"><a href="#Pg_72">72</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">based on Taylor's experiments</td>
+<td class="right"><a href="#Pg_71">71</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">effect of lubricant on</td>
+<td class="right"><a href="#Pg_76">76</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">factors which limit speeds for turning</td>
+<td class="right"><a href="#Pg_72">72</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">rules for calculating</td>
+<td class="right"><a href="#Pg_74">74</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Cylinder boring machine, multiple-spindle type</td>
+<td class="right"><a href="#Pg_274">274</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Cylinder boring on horizontal machine</td>
+<td class="right"><a href="#Pg_286">286</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Cylinder lining, fixture for holding when boring</td>
+<td class="right"><a href="#Pg_293">293</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Cylindrical turning, simple example of</td>
+<td class="right"><a href="#Pg_6">6</a></td>
+</tr>
+
+<tr>
+<td colspan="3">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="left" valign="bottom"><span class="dropcap">D</span>avis turret lathe, turning bevel gear blanks</td>
+<td class="right" valign="bottom"><a href="#Pg_212">212</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">turning worm-gear blanks</td>
+<td class="right"><a href="#Pg_211">211</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Depth of cut for turning, average</td>
+<td class="right"><a href="#Pg_75">75</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Detrick &amp; Harvey horizontal boring machine, floor type</td>
+<td class="right"><a href="#Pg_294">294</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Dial for &#8220;catching threads&#8221; when screw cutting</td>
+<td class="right"><a href="#Pg_141">141</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Dial gage, testing concentricity of button with</td>
+<td class="right"><a href="#Pg_103">103</a>, <a href="#Pg_104">104</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Die and tap holders, releasing</td>
+<td class="right"><a href="#Pg_199">199</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Die-heads, self-opening type</td>
+<td class="right"><a href="#Pg_200">200</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Disk gage, for angles and tapers</td>
+<td class="right"><a href="#Pg_97">97</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">rules for setting</td>
+<td class="right"><a href="#Pg_98">98</a>, <a href="#Pg_99">99</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Dogs or drivers, lathe, application of</td>
+<td class="right"><a href="#Pg_16">16</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Drill, flat, for lathe</td>
+<td class="right"><a href="#Pg_44">44</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Drilling and reaming in lathe</td>
+<td class="right"><a href="#Pg_43">43</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Drivers or dogs, lathe, application of</td>
+<td class="right"><a href="#Pg_16">16</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Driving fits, allowances for</td>
+<td class="right"><a href="#Pg_131">131</a></td>
+</tr>
+
+<tr>
+<td colspan="3">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="left" valign="bottom"><span class="dropcap">E</span>ccentric turning in lathe</td>
+<td class="right" valign="bottom"><a href="#Pg_106">106</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Engine lathe, general description</td>
+<td class="right"><a href="#Pg_1">1</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Errors, accumulation of</td>
+<td class="right"><a href="#Pg_105">105</a>, <a href="#Pg_106">106</a></td>
+</tr>
+
+<tr>
+<td colspan="3">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="left" valign="bottom"><span class="dropcap">F</span>aceplate, indexing for multiple-thread cutting
+<span class="pagenum"><a name="Pg_302" id="Pg_302">[302]</a></span></td>
+<td class="right" valign="bottom"><a href="#Pg_153">153</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">lathe, application of angle-plate to</td>
+<td class="right"><a href="#Pg_48">48</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">lathe, holding work on</td>
+<td class="right"><a href="#Pg_45">45</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Facing ends of centered stock, different methods</td>
+<td class="right"><a href="#Pg_34">34</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Feed and depth of cut for turning, average</td>
+<td class="right"><a href="#Pg_75">75</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Feeds and speeds for turning based on Taylor's experiments</td>
+<td class="right"><a href="#Pg_71">71</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Filing and polishing in lathe</td>
+<td class="right"><a href="#Pg_13">13</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Finishing and roughing cuts in lathe</td>
+<td class="right"><a href="#Pg_75">75</a>, <a href="#Pg_76">76</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Fits, allowances for different classes</td>
+<td class="right"><a href="#Pg_131">131</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">different classes used in machine construction</td>
+<td class="right"><a href="#Pg_129">129</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">driving, allowances for</td>
+<td class="right"><a href="#Pg_131">131</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">forced, allowances for given pressure</td>
+<td class="right"><a href="#Pg_133">133</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">forced, average allowance for</td>
+<td class="right"><a href="#Pg_130">130</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">forced, pressure for</td>
+<td class="right"><a href="#Pg_132">132</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">push, allowances for</td>
+<td class="right"><a href="#Pg_131">131</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">running, allowances for</td>
+<td class="right"><a href="#Pg_131">131</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">shrinkage, allowances for</td>
+<td class="right"><a href="#Pg_133">133</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Fixture for holding thin lining when boring</td>
+<td class="right"><a href="#Pg_293">293</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Flat drill and holder for lathe</td>
+<td class="right"><a href="#Pg_44">44</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Flat turret lathe, Acme, examples of chuck work</td>
+<td class="right"><a href="#Pg_219">219</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">Hartness, example of turning</td>
+<td class="right"><a href="#Pg_213">213</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">Jones &amp; Lamson double-spindle type</td>
+<td class="right"><a href="#Pg_221">221</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Floating reamer holders</td>
+<td class="right"><a href="#Pg_271">271</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Flywheel, finishing in one setting in turret lathe</td>
+<td class="right"><a href="#Pg_186">186</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">finishing in two settings in turret lathe</td>
+<td class="right"><a href="#Pg_189">189</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">machining in turret lathe</td>
+<td class="right"><a href="#Pg_184">184</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">turning in Potter &amp; Johnston automatic</td>
+<td class="right"><a href="#Pg_236">236</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">turning in vertical boring mill</td>
+<td class="right"><a href="#Pg_255">255</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Follow-rest for lathe</td>
+<td class="right"><a href="#Pg_27">27</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Forced fits, allowances for given pressure</td>
+<td class="right"><a href="#Pg_133">133</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">average allowance for</td>
+<td class="right"><a href="#Pg_130">130</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">pressure generally used in assembling</td>
+<td class="right"><a href="#Pg_132">132</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Fractional threads, change gears for cutting</td>
+<td class="right"><a href="#Pg_171">171</a></td>
+</tr>
+
+<tr>
+<td colspan="3">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="left" valign="bottom"><span class="dropcap">G</span>age, disk, for angles and tapers</td>
+<td class="right" valign="bottom"><a href="#Pg_97">97</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">disk, rules for setting</td>
+<td class="right"><a href="#Pg_98">98</a>, <a href="#Pg_99">99</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">for testing V-thread tool</td>
+<td class="right"><a href="#Pg_138">138</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">standard plug, for holes</td>
+<td class="right"><a href="#Pg_42">42</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">thread, Acme standard</td>
+<td class="right"><a href="#Pg_157">157</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Geometric collapsing tap</td>
+<td class="right"><a href="#Pg_202">202</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Geometric self-opening die-head</td>
+<td class="right"><a href="#Pg_200">200</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Gisholt convex attachment for vertical mill</td>
+<td class="right"><a href="#Pg_259">259</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Gisholt vertical boring mill, general description</td>
+<td class="right"><a href="#Pg_242">242</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Grinder for truing lathe centers</td>
+<td class="right"><a href="#Pg_34">34</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Grinding lathe tools</td>
+<td class="right"><a href="#Pg_62">62</a></td>
+</tr>
+
+<tr>
+<td colspan="3">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="left" valign="bottom"><span class="dropcap">H</span>artness flat turret lathe, example of turning</td>
+<td class="right" valign="bottom"><a href="#Pg_213">213</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Hendey relieving attachment</td>
+<td class="right"><a href="#Pg_123">123</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">application of, for relieving taps, cutters and hobs</td>
+<td class="right"><a href="#Pg_125">125</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">&#8220;Hold-back&#8221; or &#8220;bridle&#8221; for lathe</td>
+<td class="right"><a href="#Pg_26">26</a>, <a href="#Pg_27">27</a>
+<span class="pagenum"><a name="Pg_303" id="Pg_303">[303]</a></span></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Hollow mills for turret lathe</td>
+<td class="right"><a href="#Pg_198">198</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Horizontal boring machine</td>
+<td class="right"><a href="#Pg_275">275</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">Detrick &amp; Harvey floor type</td>
+<td class="right"><a href="#Pg_294">294</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">examples of work</td>
+<td class="right"><a href="#Pg_289">289-297</a></td>
+</tr>
+
+<tr>
+<td colspan="3">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="left" valign="bottom"><span class="dropcap">I</span>ndependent chuck for lathe</td>
+<td class="right" valign="bottom"><a href="#Pg_36">36</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Index plate, change gear, for lathe</td>
+<td class="right"><a href="#Pg_137">137</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Indicator, center, use on lathe</td>
+<td class="right"><a href="#Pg_100">100</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">for &#8220;catching threads&#8221; when screw cutting</td>
+<td class="right"><a href="#Pg_141">141</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">test, truing buttons with</td>
+<td class="right"><a href="#Pg_102">102</a>, <a href="#Pg_103">103</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">thread, for lathe apron, principle of</td>
+<td class="right"><a href="#Pg_142">142</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Inserted cutter turning tools for lathe</td>
+<td class="right"><a href="#Pg_58">58</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Internal threading</td>
+<td class="right"><a href="#Pg_154">154</a></td>
+</tr>
+
+<tr>
+<td colspan="3">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="left" valign="bottom"><span class="dropcap">J</span>ones &amp; Lamson double-spindle flat turret lathe</td>
+<td class="right" valign="bottom"><a href="#Pg_221">221</a></td>
+</tr>
+
+<tr>
+<td colspan="3">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="left" valign="bottom"><span class="dropcap">K</span>nurling in lathe and tool used</td>
+<td class="right" valign="bottom"><a href="#Pg_122">122</a></td>
+</tr>
+
+<tr>
+<td colspan="3">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="left" valign="bottom"><span class="dropcap">L</span>ard oil as a cutting lubricant</td>
+<td class="right" valign="bottom"><a href="#Pg_78">78</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Lathe, boring holes to given center distance in</td>
+<td class="right"><a href="#Pg_51">51</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">boring large castings in</td>
+<td class="right"><a href="#Pg_49">49</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">boring small hole with</td>
+<td class="right"><a href="#Pg_104">104</a>, <a href="#Pg_105">105</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">cutting threads in</td>
+<td class="right"><a href="#Pg_135">135</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">drilling small hole with</td>
+<td class="right"><a href="#Pg_104">104</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">general description of Bradford</td>
+<td class="right"><a href="#Pg_1">1</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">LeBlond crankshaft, operation of</td>
+<td class="right"><a href="#Pg_110">110</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">Lo-swing, general description</td>
+<td class="right"><a href="#Pg_115">115</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">method of handling when cutting threads</td>
+<td class="right"><a href="#Pg_138">138</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">quick change-gear type</td>
+<td class="right"><a href="#Pg_173">173</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">R. K. LeBlond special crankshaft</td>
+<td class="right"><a href="#Pg_108">108</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">turret type, general description</td>
+<td class="right"><a href="#Pg_178">178</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Lathe centers, grinder for truing</td>
+<td class="right"><a href="#Pg_34">34</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Lathe chucks, application of</td>
+<td class="right"><a href="#Pg_37">37</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">universal, independent and combination</td>
+<td class="right"><a href="#Pg_36">36</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Lathe faceplate, holding work on</td>
+<td class="right"><a href="#Pg_45">45</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Lathe follow-rest</td>
+<td class="right"><a href="#Pg_27">27</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Lathe steadyrest</td>
+<td class="right"><a href="#Pg_23">23</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">application of, when boring</td>
+<td class="right"><a href="#Pg_25">25</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Lathe taper attachment</td>
+<td class="right"><a href="#Pg_88">88</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">practical application of</td>
+<td class="right"><a href="#Pg_90">90</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Lathe tool grinding</td>
+<td class="right"><a href="#Pg_62">62</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Lathe tools, angle of clearance</td>
+<td class="right"><a href="#Pg_66">66</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">angle of keenness</td>
+<td class="right"><a href="#Pg_67">67</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">application of various types</td>
+<td class="right"><a href="#Pg_56">56</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">slope of cutting edge</td>
+<td class="right"><a href="#Pg_66">66</a>, <a href="#Pg_67">67</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Lathe turning tools, inserted-cutter type</td>
+<td class="right"><a href="#Pg_58">58</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">set of tools for general work</td>
+<td class="right"><a href="#Pg_54">54</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Lead of thread, definition of</td>
+<td class="right"><a href="#Pg_146">146</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">LeBlond, R. K., lathe for crankshaft turning</td>
+<td class="right"><a href="#Pg_108">108</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Left-hand thread, method of cutting
+<span class="pagenum"><a name="Pg_304" id="Pg_304">[304]</a></span></td>
+<td class="right"><a href="#Pg_148">148</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Lining, fixture for holding when boring</td>
+<td class="right"><a href="#Pg_293">293</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Lo-swing lathe, general description</td>
+<td class="right"><a href="#Pg_115">115</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">example of multiple-turning</td>
+<td class="right"><a href="#Pg_117">117</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Lubricant, effect on cutting speed</td>
+<td class="right"><a href="#Pg_76">76</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">for cooling turning tools</td>
+<td class="right"><a href="#Pg_77">77</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">for machining aluminum</td>
+<td class="right"><a href="#Pg_53">53</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">lard oil as a cutting</td>
+<td class="right"><a href="#Pg_78">78</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Lucas horizontal boring machine</td>
+<td class="right"><a href="#Pg_275">275</a></td>
+</tr>
+
+<tr>
+<td colspan="3">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="left" valign="bottom"><span class="dropcap">M</span>andrel or arbor press</td>
+<td class="right" valign="bottom"><a href="#Pg_22">22</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">Mandrels or arbors for lathe work, types of</td>
+<td class="right"><a href="#Pg_19">19</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">for lathe work, use of</td>
+<td class="right"><a href="#Pg_17">17</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Metric pitches, change gears for cutting</td>
+<td class="right"><a href="#Pg_171">171</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Micrometer for measuring threads</td>
+<td class="right"><a href="#Pg_162">162</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Mills, hollow, for turret lathe</td>
+<td class="right"><a href="#Pg_198">198</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Multiple-spindle chucking machine, New Britain</td>
+<td class="right"><a href="#Pg_238">238</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Multiple-thread cutting, indexing faceplate for</td>
+<td class="right"><a href="#Pg_153">153</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Multiple threads</td>
+<td class="right"><a href="#Pg_146">146</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">method of cutting</td>
+<td class="right"><a href="#Pg_150">150</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">setting tool when cutting</td>
+<td class="right"><a href="#Pg_152">152</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Multiple-turning in Lo-swing lathe</td>
+<td class="right"><a href="#Pg_117">117</a></td>
+</tr>
+
+<tr>
+<td colspan="3">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="left" valign="bottom"><span class="dropcap">N</span>ew Britain multiple-spindle chucking machine</td>
+<td class="right" valign="bottom"><a href="#Pg_238">238</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">Newall Engineering Co's fit allowances</td>
+<td class="right"><a href="#Pg_131">131</a></td>
+</tr>
+
+<tr>
+<td colspan="3">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="left" valign="bottom"><span class="dropcap">P</span>istons, gasoline engine, turning in turret lathe</td>
+<td class="right" valign="bottom"><a href="#Pg_204">204</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">Piston rings, attachment for turning in turret lathe</td>
+<td class="right"><a href="#Pg_210">210</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">turning in turret lathe</td>
+<td class="right"><a href="#Pg_206">206</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Piston turning in Pratt &amp; Whitney turret lathe</td>
+<td class="right"><a href="#Pg_208">208</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Pitch, metric, change gears for cutting</td>
+<td class="right"><a href="#Pg_171">171</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Pitch of thread, definition of</td>
+<td class="right"><a href="#Pg_146">146</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Plug gage, standard</td>
+<td class="right"><a href="#Pg_42">42</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Polishing and filing in lathe</td>
+<td class="right"><a href="#Pg_13">13</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Potter &amp; Johnston automatic chucking and turning machine</td>
+<td class="right"><a href="#Pg_223">223</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">method of &#8220;setting-up&#8221;</td>
+<td class="right"><a href="#Pg_227">227</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">turning flywheel in</td>
+<td class="right"><a href="#Pg_236">236</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Pratt &amp; Whitney turret lathe, arranged for piston turning</td>
+<td class="right"><a href="#Pg_208">208</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">equipped with piston ring turning attachment</td>
+<td class="right"><a href="#Pg_210">210</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Press for arbors or mandrels</td>
+<td class="right"><a href="#Pg_22">22</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Pressure generally used in assembling forced fits</td>
+<td class="right"><a href="#Pg_132">132</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Push fits, allowances for</td>
+<td class="right"><a href="#Pg_131">131</a></td>
+</tr>
+
+<tr>
+<td colspan="3">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="left" valign="bottom"><span class="dropcap">Q</span>uick change-gear type of lathe</td>
+<td class="right" valign="bottom"><a href="#Pg_173">173</a></td>
+</tr>
+
+<tr>
+<td colspan="3">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="left" valign="bottom"><span class="dropcap">R</span>eamer holders, floating type</td>
+<td class="right" valign="bottom"><a href="#Pg_271">271</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">Reaming and drilling in lathe</td>
+<td class="right"><a href="#Pg_43">43</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Releasing die and tap holders</td>
+<td class="right"><a href="#Pg_199">199</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Relieving attachment, Hendey</td>
+<td class="right"><a href="#Pg_123">123</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">application of
+<span class="pagenum"><a name="Pg_305" id="Pg_305">[305]</a></span></td>
+<td class="right"><a href="#Pg_125">125</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Relieving hobs or taps having spiral flutes</td>
+<td class="right"><a href="#Pg_128">128</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Rivett-Dock threading tool</td>
+<td class="right"><a href="#Pg_164">164</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Roughing and finishing cuts in lathe</td>
+<td class="right"><a href="#Pg_75">75</a>, <a href="#Pg_76">76</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Running fits, allowances for</td>
+<td class="right"><a href="#Pg_131">131</a></td>
+</tr>
+
+<tr>
+<td colspan="3">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="left" valign="bottom"><span class="dropcap">S</span>crew cutting, calculating change gears for</td>
+<td class="right" valign="bottom"><a href="#Pg_167">167</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">compound gearing for</td>
+<td class="right"><a href="#Pg_170">170</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">in engine lathe</td>
+<td class="right"><a href="#Pg_135">135</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">method of handling lathe</td>
+<td class="right"><a href="#Pg_138">138</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">selecting change gears for</td>
+<td class="right"><a href="#Pg_135">135</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">with compound rest</td>
+<td class="right"><a href="#Pg_143">143</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Screws, cutting to compensate for shrinkage</td>
+<td class="right"><a href="#Pg_165">165</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">metric, change gears for cutting</td>
+<td class="right"><a href="#Pg_171">171</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">testing size of</td>
+<td class="right"><a href="#Pg_161">161</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Selecting type of turning machine</td>
+<td class="right"><a href="#Pg_240">240</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Shrinkage, cutting screws to compensate for</td>
+<td class="right"><a href="#Pg_165">165</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Shrinkage fits, allowances for</td>
+<td class="right"><a href="#Pg_133">133</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Side-tool, facing with</td>
+<td class="right"><a href="#Pg_7">7</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Speeds for turning, average</td>
+<td class="right"><a href="#Pg_72">72</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">based on Taylor's experiments</td>
+<td class="right"><a href="#Pg_71">71</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">effect of lubricant</td>
+<td class="right"><a href="#Pg_76">76</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">factors which limit</td>
+<td class="right"><a href="#Pg_72">72</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">rules for calculating</td>
+<td class="right"><a href="#Pg_74">74</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Spherical turning</td>
+<td class="right"><a href="#Pg_111">111</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">attachments for</td>
+<td class="right"><a href="#Pg_113">113</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">&#8220;Spider&#8221; for supporting bushing while turning</td>
+<td class="right"><a href="#Pg_48">48</a>, <a href="#Pg_49">49</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Spiral flutes, method of relieving hobs or taps with</td>
+<td class="right"><a href="#Pg_128">128</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Square thread and method of cutting</td>
+<td class="right"><a href="#Pg_149">149</a>, <a href="#Pg_159">159</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Steadyrest, application of when boring</td>
+<td class="right"><a href="#Pg_25">25</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">for engine lathe</td>
+<td class="right"><a href="#Pg_23">23</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Stop for lathe cross-slide when threading</td>
+<td class="right"><a href="#Pg_155">155</a></td>
+</tr>
+
+<tr>
+<td colspan="3">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="left" valign="bottom"><span class="dropcap">T</span>ap and die holders, releasing type</td>
+<td class="right" valign="bottom"><a href="#Pg_199">199</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Taper attachment for lathe</td>
+<td class="right"><a href="#Pg_88">88</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">practical application of</td>
+<td class="right"><a href="#Pg_90">90</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Taper boring with taper attachment</td>
+<td class="right"><a href="#Pg_90">90</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Taper threading, position of tool for</td>
+<td class="right"><a href="#Pg_154">154</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Taper turning, adjustment of tailstock center for</td>
+<td class="right"><a href="#Pg_82">82</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">by offset-center method</td>
+<td class="right"><a href="#Pg_80">80</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">examples of</td>
+<td class="right"><a href="#Pg_83">83</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">height of tool for</td>
+<td class="right"><a href="#Pg_94">94</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">in vertical boring mill</td>
+<td class="right"><a href="#Pg_261">261</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">in vertical mill with horizontal and vertical feeds</td>
+<td class="right"><a href="#Pg_262">262</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">setting tailstock center with caliper tool</td>
+<td class="right"><a href="#Pg_85">85</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">setting tailstock center with square</td>
+<td class="right"><a href="#Pg_87">87</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">with compound rest</td>
+<td class="right"><a href="#Pg_95">95</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">with taper attachment</td>
+<td class="right"><a href="#Pg_92">92</a>, <a href="#Pg_93">93</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Tapers, gage for accurate measurement of</td>
+<td class="right"><a href="#Pg_97">97</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">rules for figuring
+<span class="pagenum"><a name="Pg_306" id="Pg_306">[306]</a></span></td>
+<td class="right"><a href="#Pg_97">97</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Test indicator, truing buttons with</td>
+<td class="right"><a href="#Pg_102">102</a>, <a href="#Pg_103">103</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Test or center indicator for use on lathe</td>
+<td class="right"><a href="#Pg_100">100</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Thread cutting, calculating change gears for</td>
+<td class="right"><a href="#Pg_167">167</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">compound gearing for</td>
+<td class="right"><a href="#Pg_170">170</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">cross-slide stop used for</td>
+<td class="right"><a href="#Pg_155">155</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">indexing faceplate for multiple threads</td>
+<td class="right"><a href="#Pg_153">153</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">in engine lathe</td>
+<td class="right"><a href="#Pg_135">135</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">internal</td>
+<td class="right"><a href="#Pg_154">154</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">method of handling lathe</td>
+<td class="right"><a href="#Pg_138">138</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">selecting change gears for</td>
+<td class="right"><a href="#Pg_135">135</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">taper, position of tool for</td>
+<td class="right"><a href="#Pg_154">154</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">with compound rest</td>
+<td class="right"><a href="#Pg_143">143</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Thread gage, Acme standard</td>
+<td class="right"><a href="#Pg_157">157</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Thread indicator for lathe apron</td>
+<td class="right"><a href="#Pg_141">141</a>, <a href="#Pg_142">142</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Thread micrometer</td>
+<td class="right"><a href="#Pg_162">162</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Thread tool, Acme, measuring width with vernier caliper</td>
+<td class="right"><a href="#Pg_157">157</a>, <a href="#Pg_158">158</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">for cutting V-thread</td>
+<td class="right"><a href="#Pg_138">138</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Thread tools for standard threads</td>
+<td class="right"><a href="#Pg_159">159</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Threads, Acme standard, and tool for cutting</td>
+<td class="right"><a href="#Pg_159">159</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">change gears for fractional</td>
+<td class="right"><a href="#Pg_171">171</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">cutting to compensate for shrinkage</td>
+<td class="right"><a href="#Pg_165">165</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">different forms of</td>
+<td class="right"><a href="#Pg_144">144</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">left-hand, method of cutting</td>
+<td class="right"><a href="#Pg_148">148</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">metric, change gears for cutting</td>
+<td class="right"><a href="#Pg_171">171</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">multiple</td>
+<td class="right"><a href="#Pg_146">146</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">multiple, method of cutting</td>
+<td class="right"><a href="#Pg_150">150</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">multiple, setting tool when cutting</td>
+<td class="right"><a href="#Pg_152">152</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">sharp V, and tool for cutting</td>
+<td class="right"><a href="#Pg_159">159</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">square, and method of cutting</td>
+<td class="right"><a href="#Pg_149">149</a>, <a href="#Pg_159">159</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">testing size of</td>
+<td class="right"><a href="#Pg_161">161</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">three-wire system for measuring</td>
+<td class="right"><a href="#Pg_163">163</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">U. S. standard, and tool for cutting</td>
+<td class="right"><a href="#Pg_146">146</a>, <a href="#Pg_159">159</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">Whitworth standard, and tool for cutting</td>
+<td class="right"><a href="#Pg_158">158</a>, <a href="#Pg_159">159</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">worm, and tool for cutting</td>
+<td class="right"><a href="#Pg_159">159</a>, <a href="#Pg_160">160</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Threading attachment, lathe, for coarse threads</td>
+<td class="right"><a href="#Pg_160">160</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Threading tool, Rivett-Dock</td>
+<td class="right"><a href="#Pg_164">164</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Tool grinding</td>
+<td class="right"><a href="#Pg_62">62</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Tools for lathe, set for general turning</td>
+<td class="right"><a href="#Pg_54">54</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Tools for turning, angle of clearance</td>
+<td class="right"><a href="#Pg_66">66</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">angle of keenness</td>
+<td class="right"><a href="#Pg_67">67</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">inserted-cutter type</td>
+<td class="right"><a href="#Pg_58">58</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">slope of cutting edge</td>
+<td class="right"><a href="#Pg_66">66</a>, <a href="#Pg_67">67</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Tools for turret lathe</td>
+<td class="right"><a href="#Pg_190">190</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Tools, lathe, application of various types</td>
+<td class="right"><a href="#Pg_56">56</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Turning, cylindrical, simple example of</td>
+<td class="right"><a href="#Pg_6">6</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">eccentric</td>
+<td class="right"><a href="#Pg_106">106</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">multiple, in Lo-swing lathe</td>
+<td class="right"><a href="#Pg_117">117</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">with front and rear tools</td>
+<td class="right"><a href="#Pg_114">114</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Turning speeds, average for lathe
+<span class="pagenum"><a name="Pg_307" id="Pg_307">[307]</a></span></td>
+<td class="right"><a href="#Pg_72">72</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">based on Taylor's experiments</td>
+<td class="right"><a href="#Pg_71">71</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">factors which limit</td>
+<td class="right"><a href="#Pg_72">72</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">rules for calculating</td>
+<td class="right"><a href="#Pg_74">74</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Turning tools, angle of clearance</td>
+<td class="right"><a href="#Pg_66">66</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">angle of keenness</td>
+<td class="right"><a href="#Pg_67">67</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">for aluminum</td>
+<td class="right"><a href="#Pg_53">53</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">for brass</td>
+<td class="right"><a href="#Pg_52">52</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">for copper</td>
+<td class="right"><a href="#Pg_52">52</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">for lathe, position of</td>
+<td class="right"><a href="#Pg_60">60</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">for lathe, set of, for general work</td>
+<td class="right"><a href="#Pg_54">54</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">inserted-cutter type for lathe</td>
+<td class="right"><a href="#Pg_58">58</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">slope of cutting edge</td>
+<td class="right"><a href="#Pg_66">66</a>, <a href="#Pg_67">67</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Turret lathe, Bardons &amp; Oliver, general description</td>
+<td class="right"><a href="#Pg_178">178</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">examples of chuck work in Acme flat</td>
+<td class="right"><a href="#Pg_219">219</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">Hartness flat, example of turning</td>
+<td class="right"><a href="#Pg_213">213</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">Jones &amp; Lamson double-spindle type</td>
+<td class="right"><a href="#Pg_221">221</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">machining flywheels in</td>
+<td class="right"><a href="#Pg_184">184</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">Pratt &amp; Whitney arranged for piston turning</td>
+<td class="right"><a href="#Pg_208">208</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">piston ring turning attachment for</td>
+<td class="right"><a href="#Pg_210">210</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">tools for general work</td>
+<td class="right"><a href="#Pg_190">190</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">turning bevel gear blanks in Davis</td>
+<td class="right"><a href="#Pg_212">212</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">turning gasoline engine pistons in</td>
+<td class="right"><a href="#Pg_204">204</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">turning piston rings in</td>
+<td class="right"><a href="#Pg_206">206</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">turning worm-gear blanks in Davis</td>
+<td class="right"><a href="#Pg_211">211</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">typical example of turret lathe work</td>
+<td class="right"><a href="#Pg_181">181</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Turret lathe tools, miscellaneous types</td>
+<td class="right"><a href="#Pg_202">202</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Turret lathe type of vertical boring mill</td><td class="right"><a href="#Pg_264">264</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Type of turning machine, factors which govern selection</td>
+<td class="right"><a href="#Pg_240">240</a></td>
+</tr>
+
+<tr>
+<td colspan="3">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="left" valign="bottom"><span class="dropcap">U</span>. S. standard thread</td>
+<td class="right" valign="bottom"><a href="#Pg_159">159</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">method of cutting</td>
+<td class="right"><a href="#Pg_146">146</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Universal chuck for lathe</td>
+<td class="right"><a href="#Pg_36">36</a></td>
+</tr>
+
+<tr>
+<td colspan="3">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="left" valign="bottom"><span class="dropcap">V</span>-thread and tool for cutting</td>
+<td class="right" valign="bottom"><a href="#Pg_159">159</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Vertical boring mill, Bullard turret lathe type</td>
+<td class="right"><a href="#Pg_264">264</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">convex turning attachment</td>
+<td class="right"><a href="#Pg_259">259</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">general description</td>
+<td class="right"><a href="#Pg_242">242</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">holding and setting work</td>
+<td class="right"><a href="#Pg_247">247</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">taper turning in</td>
+<td class="right"><a href="#Pg_261">261</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">taper turning with horizontal and vertical feeds</td>
+<td class="right"><a href="#Pg_262">262</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">tools for boring and reaming</td>
+<td class="right"><a href="#Pg_251">251</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">turning flywheel in</td>
+<td class="right"><a href="#Pg_255">255</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="left">turning tools for</td>
+<td class="right"><a href="#Pg_253">253</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Vertical turret lathe, Bullard, examples of work</td>
+<td class="right"><a href="#Pg_268">268</a></td>
+</tr>
+
+<tr>
+<td colspan="3">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="left" valign="bottom"><span class="dropcap">W</span>hitworth standard thread and tool for cutting</td>
+<td class="right" valign="bottom"><a href="#Pg_158">158</a>, <a href="#Pg_159">159</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Wire system for measuring threads</td>
+<td class="right"><a href="#Pg_163">163</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="left">Worm thread and tool for cutting</td>
+<td class="right"><a href="#Pg_159">159</a>, <a href="#Pg_160">160</a></td>
+</tr>
+
+</table>
+
+<p>&nbsp;</p>
+<hr class="c25" />
+<p>&nbsp;</p>
+
+<div class="tnbox">
+
+<p class="center"><b>Transcriber's notes:</b></p>
+
+<ul>
+
+  <li>Inconsistencies encountered:
+
+    <ul>
+      <li>Left as in original:
+        <ul>
+          <li>use of degree, deg. and &deg;;</li>
+          <li>use of minute, min. and '.</li>
+        </ul>
+      </li>
+    </ul>
+
+    <ul>
+      <li>Standardised to the most commonly used in the book:
+        <ul>
+          <li>backgear(s) to back-gear(s);</li>
+          <li>camshaft to cam-shaft;</li>
+          <li>crankpin to crank-pin;</li>
+          <li>face-plate to faceplate;</li>
+          <li>out-board to outboard;</li>
+          <li>over-hang to overhang;</li>
+          <li>setscrew to set-screw;</li>
+          <li>steady-rest to steadyrest;</li>
+          <li>subdivision(s) to sub-division(s);</li>
+          <li>tail-stock to tailstock;</li>
+          <li>thumbscrew to thumb-screw;</li>
+          <li>tool-post to toolpost;</li>
+          <li>tool-slide to toolslide;</li>
+          <li>hand-wheel to handwheel;</li>
+          <li>U.S. to U. S.</li>
+        </ul>
+      </li>
+    </ul>
+  </li>
+  <li>Page 64 had a blotched (illegible) word, this has been replaced by (large and rigid) <i>work</i>.</li>
+  <li>Table of Contents: largely re-compiled to create one-to-one links with named paragraphs and sections in text.</li>
+  <li>Illustrations: generally moved to the paragraph they refer to.</li>
+</ul>
+
+</div>
+
+
+
+
+
+
+
+
+<pre>
+
+
+
+
+
+End of the Project Gutenberg EBook of Turning and Boring, by Franklin D. Jones
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+</body>
+</html>
+
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+The Project Gutenberg EBook of Turning and Boring, by Franklin D. Jones
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: Turning and Boring
+       A specialized treatise for machinists, students in the
+       industrial and engineering schools, and apprentices, on
+       turning and boring methods, etc.
+
+Author: Franklin D. Jones
+
+Release Date: October 4, 2010 [EBook #34030]
+
+Language: English
+
+Character set encoding: ASCII
+
+*** START OF THIS PROJECT GUTENBERG EBOOK TURNING AND BORING ***
+
+
+
+
+Produced by Juliet Sutherland, Harry Lame and the Online
+Distributed Proofreading Team at https://www.pgdp.net
+
+
+
+
+
+
+
+
+
+    Transcriber's notes:
+    words in bold and italics have been transcribed as =word= and
+    _word_, respectively; superscripts are indicated by ^, subscripts
+    by _.
+    Greek letters have been transliterated as [alpha], [beta], etc.
+    Spelling and hyphenation have been standardised (see list at end
+    of text).
+
+
+
+
+                  TURNING AND
+                    BORING
+
+      A SPECIALIZED TREATISE FOR MACHINISTS,
+      STUDENTS IN INDUSTRIAL AND ENGINEERING
+          SCHOOLS, AND APPRENTICES, ON
+      TURNING AND BORING METHODS, INCLUDING
+          MODERN PRACTICE WITH ENGINE
+       LATHES, TURRET LATHES, VERTICAL AND
+          HORIZONTAL BORING MACHINES
+
+             BY FRANKLIN D. JONES
+
+        ASSOCIATE EDITOR OF MACHINERY
+       AUTHOR OF "PLANING AND MILLING"
+
+              _FIRST EDITION_
+              FIFTH PRINTING
+
+                 NEW YORK
+           THE INDUSTRIAL PRESS
+   LONDON: THE MACHINERY PUBLISHING CO., LTD.
+                   1919
+
+
+
+
+  COPYRIGHT, 1914
+  BY
+  THE INDUSTRIAL PRESS
+  NEW YORK
+
+
+
+
+PREFACE
+
+
+Specialization in machine-tool manufacture has been developed to such a
+degree that there is need also for treatises which specialize on
+different classes of tools and their application in modern practice.
+This book deals exclusively with the use of various types of turning and
+boring machines and their attachments, and is believed to be unusually
+complete. In addition to standard practice, it describes many special
+operations seldom or never presented in text-books. Very little space is
+given to mere descriptions of different types of machine tools, the
+principal purpose being to explain the use of the machine and the
+practical problems connected with its operation, rather than the
+constructional details. No attempt has been made to describe every
+machine or tool which might properly be included, but rather to deal
+with the more important and useful operations, especially those which
+illustrate general principles.
+
+Readers of mechanical literature are familiar with MACHINERY'S 25-cent
+Reference Books, of which one hundred and twenty-five different titles
+have been published during the past six years. Many subjects, however,
+cannot be adequately covered in all their phases in books of this size,
+and in response to a demand for more comprehensive and detailed
+treatments on the more important mechanical subjects, it has been deemed
+advisable to bring out a number of larger volumes, of which this is one.
+This work includes much of the material published in MACHINERY'S
+Reference Books Nos. 91, 92 and 95, together with a great amount of
+additional information on modern boring and turning methods.
+
+It is a pleasure to acknowledge our indebtedness to the manufacturers
+who generously supplied illustrations and data, including many
+interesting operations from actual practice. Much valuable information
+was also obtained from MACHINERY.
+
+  F. D. J.
+
+  NEW YORK, _May, 1914_.
+
+
+
+
+CONTENTS
+
+                                                                  PAGES
+
+
+  CHAPTER I
+
+  THE ENGINE LATHE--TURNING AND BORING OPERATIONS
+
+  General Description of an Engine Lathe--Example of Cylindrical
+  Turning--Facing the Ends Square with a Side-tool--Turning
+  Tool--Turning Work Cylindrical--Roughing and Finishing
+  Cuts--Filing and Finishing--Aligning Centers for Cylindrical
+  Turning--Application of Drivers or Dogs--Lathe Arbors or
+  Mandrels--Different Types of Lathe Arbors--Mandrel or Arbor
+  Press--Steadyrest for Supporting Flexible Parts--Application of
+  Steadyrest when Boring--The Follow-rest--Centering Parts to be
+  Turned--Centering Machine--Different Forms of Centers--Precaution
+  When Centering Tool Steel--Facing the Ends of Centered
+  Stock--Truing Lathe Centers--Universal, Independent and
+  Combination Chucks--Application of Chucks--Example of
+  Boring--Measuring Bored Holes--Setting Work in the
+  Chuck--Inaccuracy from Pressure of Chuck Jaws--Drilling and
+  Reaming--Holding Work on Faceplate--Application of Angle-plate to
+  Faceplate--Supporting Outer End of Chucked Work--Boring Large
+  Castings in the Lathe--Boring Holes to a Given Center
+  Distance--Turning Brass, Bronze and Copper--Machining Aluminum   1-53
+
+
+  CHAPTER II
+
+  LATHE TURNING TOOLS AND CUTTING SPEEDS
+
+  Turning Tools for General Work--Tool-holders with Inserted
+  Cutters--The Position of Turning Tools--Tool Grinding--Shape or
+  Contour of Cutting Edge--Direction of Top Slope for Turning
+  Tools--Clearance for the Cutting Edge--Angle of Tool-point and
+  Amount of Top Slope--Grinding a Lathe Tool--Cutting Speeds and
+  Feeds--Average Cutting Speeds for Turning--Factors which Limit
+  the Cutting Speed--Rules for Calculating Cutting Speeds--Feed of
+  Tool and Depth of Cut--Effect of Lubricant on Cutting
+  Speed--Lubricants Used for Turning--Lard Oil as a Cutting
+  Lubricant                                                       54-79
+
+
+  CHAPTER III
+
+  TAPER TURNING--SPECIAL OPERATIONS--FITTING
+
+  Setting Tailstock Center for Taper Turning--Example of Taper
+  Turning--Setting the Tailstock Center with a Caliper
+  Tool--Setting the Tailstock Center with a Square--The Taper
+  Attachment--Application of Taper Attachment--Height of Tool
+  when Turning Tapers--Taper Turning with the Compound
+  Rest--Accurate Measurement of Angles and Tapers--To Find
+  Center Distance for a Given Taper--To Find Center Distance
+  for a Given Angle--To Find Angle for Given Taper per Foot--To
+  Find Angle for Given Disk Dimensions--Use of the Center
+  Indicator--Locating Work by the Button Method--Eccentric
+  Turning--Turning a Crankshaft in a Lathe--Special Crankshaft
+  Lathe--Operation of Special Crankshaft Lathe--Spherical
+  Turning--Spherical Turning Attachments--Turning with Front
+  and Rear Tools--A Multiple-tool Lathe--Examples of Multiple
+  Turning--Knurling in the Lathe--Relieving
+  Attachment--Application of Relieving Attachment--Relieving
+  Hobs or Taps Having Spiral Flutes--Classes of Fits Used in
+  Machine Construction--Forced Fits--Allowance for Forced
+  Fits--Pressure for Forced Fits--Allowance for Given
+  Pressure-Shrinkage Fits                                        80-134
+
+
+  CHAPTER IV
+
+  THREAD CUTTING IN THE LATHE
+
+  Selecting the Change Gears for Thread Cutting--The Thread
+  Tool--Cutting the Thread--Indicator or Chasing Dial for
+  Catching Threads--Principle of the Thread
+  Indicator--Replacing Sharpened Thread Tool--Use of Compound
+  Rest for Thread Cutting--Threads Commonly Used--Multiple
+  Threads--Cutting a U. S. Standard Thread--Cutting a Left-hand
+  Thread--Cutting a Square Thread--Cutting Multiple
+  Threads--Setting Tool When Cutting Multiple Threads--Taper
+  Threading--Internal Threading--Stop for Thread Tools--The
+  Acme Standard Thread--The Whitworth Thread--Worm
+  Threads--Coarse Threading Attachment--Testing the Size of a
+  Thread--The Thread Micrometer--Three-wire System of Measuring
+  Threads--Rivett-Dock Threading Tool--Cutting Screws to
+  Compensate for Shrinkage--Calculating Change Gears for Thread
+  Cutting--Lathes with Compound Gearing--Fractional
+  Threads--Change Gears for Metric Pitches--Quick Change-gear
+  Type of Lathe                                                 135-177
+
+
+  CHAPTER V
+
+  TURRET LATHE PRACTICE
+
+  General Description of a Turret Lathe--Example of Turret
+  Lathe Work--Machining Flywheels in Turret Lathe--Finishing a
+  Flywheel at One Setting in Turret Lathe--Finishing a Webbed
+  Flywheel in Two Settings--Tools for Turret
+  Lathes--Box-tools--Examples of Box-tool Turning--Hollow
+  Mills--Releasing Die and Tap Holders--Self-opening Die
+  Heads--Collapsing Taps--Miscellaneous Turret Lathe
+  Tools--Turning Gasoline Engine Pistons in Turret
+  Lathe--Turning Piston Rings in Turret Lathe--Piston Turning
+  in Pratt and Whitney Turret Lathe--Attachment for Turning
+  Piston Rings--Turning Worm-gear Blanks in Turret
+  Lathe--Turning Bevel Gear Blanks--Shell Turning Operation in
+  Flat Turret Lathe--Chuck Work in Flat Turret
+  Lathe--Double-spindle Flat Turret Lathe--Automatic Chucking
+  and Turning Machine--Example of Work on Automatic Turning
+  Machine--Determining Speed and Feed Changes--Setting the
+  Turret Slide--Setting the Cross-slide Cam--Setting the Boring
+  Tool for Recessing--Adjustments for Automatic Feed and Speed
+  Changes--Turning Flywheel in Automatic Chucking and Turning
+  Machine--Automatic Multiple-spindle Chucking
+  Machine--Selecting Type of Turning Machine                    178-241
+
+
+  CHAPTER VI
+
+  VERTICAL BORING MILL PRACTICE
+
+  Boring and Turning in a Vertical Boring Mill--Holding and
+  Setting Work on Boring Mill Table--Turning in a Boring
+  Mill--Boring Operations--Turning Tools for the Vertical
+  Boring Mill--Turning a Flywheel on a Vertical Mill--Convex
+  Turning Attachment for Boring Mills--Turning Taper or Conical
+  Surfaces--Turret-lathe Type of Vertical Boring Mill--Examples
+  of Vertical Turret Lathe Work--Floating Reamer
+  Holders--Multiple Cylinder Boring Machine                     242-274
+
+
+  CHAPTER VII
+
+  HORIZONTAL BORING MACHINES
+
+  Horizontal Boring Machine with Vertical Table
+  Adjustment--Drilling and Boring--Cutters Used--Cutter-heads
+  for Boring Large Holes--Cylinder Boring--Boring a Duplex
+  Gasoline Engine Cylinder--Examples of Boring, Radial Facing
+  and Milling--Fixture for Cylinder Lining or
+  Bushing--Horizontal Boring Machine of Floor Type              275-297
+
+  INDEX                                                         299-307
+
+
+
+
+TURNING AND BORING
+
+
+
+
+CHAPTER I
+
+THE ENGINE LATHE--TURNING AND BORING OPERATIONS
+
+
+The standard "engine" lathe, which is the type commonly used by
+machinists for doing general work, is one of the most important tools in
+a machine shop, because it is adapted to a great variety of operations,
+such as turning all sorts of cylindrical and taper parts, boring holes,
+cutting threads, etc. The illustration Fig. 1 shows a lathe which, in
+many respects, represents a typical design, and while some of the parts
+are arranged differently on other makes, the general construction is
+practically the same as on the machine illustrated.
+
+The principal parts are the bed _B_, the headstock _H_, the tailstock
+_T_, and the carriage _C_. The headstock contains a spindle which is
+rotated by a belt that passes over the cone-pulley _P_, and this spindle
+rotates the work, which is usually held between pointed or conical
+centers _h_ and _h_{1}_ in the headstock and tailstock, or in a chuck
+screwed onto the spindle instead of the faceplate _F_. The carriage _C_
+can be moved lengthwise along the bed by turning handle _d_, and it can
+also be moved by power, the movement being transmitted from the
+headstock spindle either through gears _a_, _b_, _c_, and lead-screw
+_S_, or by a belt operating on pulleys _p_ and _p_{1}_, which drive the
+feed-rod _R_. The lead-screw _S_ is used when cutting threads, and the
+feed-rod _R_ for ordinary turning operations; in this way the wear on
+the lead-screw is reduced and its accuracy is preserved.
+
+[Illustration: Fig. 1. Bradford Belt-driven Lathe--View of Front or
+Operating Side]
+
+On the carriage, there is a cross-slide _D_ which can be moved at right
+angles to the lathe bed by handle _e_, and on _D_ there is an upper or
+compound slide _E_ which can be swiveled to different positions. The
+tool _t_, that does the turning, is clamped to the upper slide, as
+shown, and it can be moved with relation to the work by the movement of
+the carriage _C_ along the bed, or by moving slide _D_ crosswise. The
+lengthwise movement is used to feed the tool along the work when
+turning, boring or cutting a screw, and the crosswise movement for
+facing the ends of shafts, etc., or for radial turning. When the tool is
+to be fed at an angle, other than at right angles to the bed, slide _E_,
+which can be set to the required angle, is used. The lengthwise and
+crosswise feeding movements can be effected by power, the lengthwise
+feed being engaged by tightening knob _k_, and the cross-feed by
+tightening knob _l_. The direction of either of these movements can also
+be reversed by shifting lever _r_. Ordinarily the carriage and slide are
+adjusted by hand to bring the tool into the proper position for turning
+to the required diameter, and then the power feed (operating in the
+desired direction) is engaged. The tailstock _T_ can be clamped in
+different positions along the bed, to suit the length of the work, and
+its center _h_{1}_ can be moved in or out for a short distance, when
+adjusting it to the work, by turning handle _n_.
+
+[Illustration: Fig. 2. Plan View of Lathe Headstock showing Back-gears]
+
+[Illustration: Fig. 3. Feed Mechanism of Lathe Apron]
+
+As some metals are much harder than others, and as the diameters of
+parts to be turned also vary considerably, speed changes are necessary,
+because if the speed is excessive, the turning tool will become dull in
+too short a time. These speed changes (with a belt-driven lathe) are
+obtained by placing the driving belt on different steps of cone-pulley
+_P_, and also by the use of back-gears. The cone-pulley can be connected
+directly with the spindle or be disengaged from it by means of bolt _m_.
+When the pulley and spindle are connected, five speeds (with this
+particular lathe) are obtained by simply shifting the driving belt to
+different steps of the cone. When a slower speed is required than can be
+obtained with the belt on the largest step of the cone, the latter is
+disconnected from the spindle, and the back-gears _G_ and _G_{1}_ (shown
+in the plan view Fig. 2) are moved forward into mesh by turning handle
+_O_; the drive is then from cone-pulley _P_ and gear _L_ to gear _G_,
+and from gear _G_{1}_ to the large gear _J_ on the spindle. When driving
+through the back-gears, five more speed changes are obtained by shifting
+the position of the driving belt, as before. The fastest speed with the
+back-gears in mesh is somewhat slower than the slowest speed when
+driving direct or with the back-gears out of mesh; hence, with this
+particular lathe, a series of ten gradually increasing speeds is
+obtained. Changes of feed for the turning tool are also required, and
+these are obtained by shifting the belt operating on pulleys _p_ and
+_p_{1}_ to different-sized steps. On some lathes these feed changes are
+obtained through gears which can be shifted to give different ratios.
+Many lathes also have gears in the headstock for changing the speeds.
+
+[Illustration: Fig. 4. Rear View of Lathe Apron]
+
+Front and rear views of the carriage apron, which contains the feeding
+mechanism, are shown in Figs. 3 and 4, to indicate how the feeds are
+engaged and reversed. The feed-rod _R_ (Fig. 1) drives the small bevel
+gears _A_ and _A_{1}_ (Figs. 3 and 4), which are mounted on a slide _S_
+that can be moved by lever _r_ to bring either bevel gear into mesh with
+gear _B_. Gear _B_ is attached to pinion _b_ (see Fig. 3) meshing with
+gear _C_, which, when knob _k_ (Fig. 1) is tightened, is locked by a
+friction clutch to pinion _c_. The latter pinion drives gear _D_ which
+rotates shaft _E_. A pinion cut on the end of shaft _E_ engages rack _K_
+(Fig. 1) attached to the bed, so that the rotation of _E_ (which is
+controlled by knob _k_) moves the carriage along the bed. To reverse the
+direction of the movement, it is only necessary to throw gear _A_ into
+mesh and gear _A_{1}_ out, or _vice versa_, by operating lever _r_. When
+the carriage is traversed by hand, shaft _E_ and gear _D_ are rotated by
+pinion _d_{1}_ connected with handle _d_ (Fig. 1).
+
+The drive for the cross-feed is from gear _C_ to gear _F_ which can be
+engaged through a friction clutch (operated by knob _l_, Fig. 1) with
+gear _G_ meshing with a pinion _H_. The latter rotates the cross-feed
+screw, which passes through a nut attached to slide _D_ (Fig. 1), thus
+moving the latter at right angles to the ways of the bed. The cross-feed
+is also reversed by means of lever _r_. As previously explained,
+lead-screw _S_ is only used for feeding the carriage when cutting
+threads. The carriage is engaged with this screw by means of two
+half-nuts _N_ (Fig. 4) that are free to slide vertically and are closed
+around the screw by operating lever _u_. These half-nuts can only be
+closed when lever _r_ is in a central or neutral position, so that the
+screw feed and the regular turning feed cannot be engaged at the same
+time. As previously mentioned, lead-screw _S_, Fig. 1, is rotated from
+the lathe spindle, through gears _a_, _b_ and _c_, called change gears.
+An assortment of these gears, of various sizes, is provided with the
+lathe, for cutting screws of different pitch. The gears to use for any
+pitch within the range of the lathe are given on the plate _I_.
+
+=Example of Cylindrical Turning.=--Having now considered the principal
+features of what might be called a standard lathe, the method of using
+it in the production of machine parts will be explained. To begin with a
+simple example of work, suppose a steel shaft is to be turned to a
+diameter of 2-1/4 inches and a length of 14-1/2 inches, these being the
+finished dimensions. We will assume that the rough stock is cut off to a
+length of 14-5/8 inches and has a diameter of 2-5/8 inches. The first
+step in this operation is to form conically shaped center-holes in each
+end of the piece as indicated at _c_ in Fig. 5. As all work of this kind
+is held, while being turned, between the centers _h_ and _h_{1}_, holes
+corresponding in shape to these centers are necessary to keep the work
+in place. There are several methods of forming these center-holes, as
+explained later.
+
+After the work is centered, a dog _A_ is clamped to one end by
+tightening screw _s_; it is then placed between the centers of the
+lathe. The dog has a projecting end or "tail," as it is commonly called,
+which enters a slot in the faceplate _F_ and thereby drives or rotates
+the work, when power is applied to the lathe spindle onto which the
+faceplate is screwed. The tailstock center _h_1_, after being oiled,
+should be set up just tight enough to eliminate all play, without
+interfering with a free rotary movement of the work. This is done by
+turning handle _n_, and when the center is properly adjusted, the
+tailstock spindle containing the center is locked by tightening handle
+_p_. (Ordinary machine oil is commonly used for lubricating lathe
+centers, but a lubricant having more "body" should be used, especially
+when turning heavy parts. The following mixtures are recommended: 1. Dry
+or powdered red lead mixed with a good grade of mineral oil to the
+consistency of cream. 2. White lead mixed with sperm oil with enough
+graphite added to give the mixture a dark lead color.)
+
+[Illustration: Fig. 5. Plan View showing Work Mounted between Centers of
+Lathe]
+
+=Facing the Ends Square with a Side-tool.=--Everything is now ready for
+the turning operation. The ends of the piece should be faced square
+before turning the body to size, and the tool for this squaring
+operation is shown in Fig. 6; this is known as a side-tool. It has a
+cutting edge _e_ which shaves off the metal as indicated in the end view
+by the dotted lines. The side _f_ is ground to an angle so that when
+the tool is moved in the direction shown by the arrow, the cutting edge
+will come in contact with the part to be turned; in other words, side
+_f_ is ground so as to provide clearance for the cutting edge. In
+addition, the top surface against which the chip bears, is beveled to
+give the tool keenness so that it will cut easily. As the principles of
+tool grinding are treated separately in Chapter II we shall for the
+present consider the tool's use rather than its form.
+
+[Illustration: Fig. 6. Lathe Side-tool for Facing Ends of Shafts, etc.]
+
+For facing the end, the side tool is clamped in the toolpost by
+tightening the screw _u_, Fig. 5, and it should be set with the cutting
+edge slightly inclined from a right-angled position, the point being in
+advance so that it will first come into contact with the work. The
+cutting edge should also be about the same height as the center of the
+work. When the tool is set, the lathe (if belt-driven) is started by
+shifting an overhead belt and the tool is then moved in until the point
+is in the position shown at _A_, Fig. 7. The tool-point is then fed
+against the end by handle _d_, Fig. 5, until a light chip is being
+turned off, and then it is moved outward by handle _e_ (as indicated by
+the arrow at _B_, Fig. 7), the carriage remaining stationary. As the
+movement of the tool-point is guided by the cross-slide _D_, which is at
+right angles with the axis of the work, the end will be faced square.
+For short turning operations of this kind, the power feeds ordinarily
+are not used as they are intended for comparatively long cuts. If it
+were necessary to remove much metal from the end, a number of cuts would
+be taken across it; in this case, however, the rough stock is only 1/8
+inch too long so that this end need only be made true.
+
+[Illustration: Fig. 7. Facing End with Side-tool and Turning Work
+Cylindrical]
+
+After taking a cut as described, the surface, if left rough by the
+tool-point, should be made smooth by a second or finishing cut. If the
+tool is ground slightly round at the point and the cutting edge is set
+almost square, as at _C_, Fig. 7, a smooth finish can be obtained; the
+cut, however, should be light and the outward feed uniform. The work is
+next reversed in the centers and the driving dog is placed on the end
+just finished; the other end is then faced, enough metal being removed
+to make the piece 14-1/2 inches long, as required in this particular
+case. This completes the facing operation. If the end of the work does
+not need to be perfectly square, the facing operation can be performed
+by setting the tool in a right-angled position and then feeding it
+sidewise, thus removing a chip equal to the width of one side. Evidently
+this method is confined to comparatively small diameters and the
+squareness of the turned end will be determined by the position of the
+tool's cutting edge.
+
+=Turning Tool--Turning Work Cylindrical.=--The tool used to turn the
+body to the required diameter is shaped differently from the side-tool,
+the cutting edge _E_ of most tools used for plain cylindrical turning
+being curved as shown in Fig. 8. A tool of this shape can be used for a
+variety of cylindrical turning operations. As most of the work is done
+by that part of the edge marked by arrow _a_, the top of the tool is
+ground to slope back from this part to give it keenness. The end _F_, or
+the flank, is also ground to an angle to provide clearance for the
+cutting edge. If the tool did not have this clearance, the flank would
+rub against the work and prevent the cutting edge from entering the
+metal. This type of tool is placed about square with the work, for
+turning, and with the cutting end a little above the center.
+
+[Illustration: Fig. 8. Tool used for Cylindrical Turning]
+
+Before beginning to turn, a pair of outside calipers or a micrometer
+should be set to 2-1/4 inches, which, in this case, is the finished
+diameter of the work. Calipers are sometimes set by using a graduated
+scale as at _A_, Fig. 9, or they can be adjusted to fit a standard
+cylindrical gage of the required size as at _B_. Very often fixed
+caliper gages _C_ are used instead of the adjustable spring calipers.
+These fixed gages, sometimes called "snap" gages, are accurately made to
+different sizes, and they are particularly useful when a number of
+pieces have to be turned to exactly the same size.
+
+The turning tool is started at the right-hand end of the work and the
+tool should be adjusted with the left hand when beginning a cut, as
+shown in Fig. 10, in order to have the right hand free for calipering. A
+short space is first turned by hand feeding, as at _D_, Fig. 7, and when
+the calipers show that the diameter is slightly greater than the
+finished size (to allow for a light finishing cut, either in the lathe
+or grinding machine) the power feed for the carriage is engaged; the
+tool then moves along the work, reducing it as at _E_. Evidently, if the
+movement is along a line _b--b_, parallel with the axis _a--a_, the
+diameter _d_ will be the same at all points, and a true cylindrical
+piece will be turned. On the other hand, if the axis _a--a_ is inclined
+one way or the other, the work will be made tapering; in fact, the
+tailstock center _h_1_ can be adjusted laterally for turning tapers, but
+for straight turning, both centers must be in alignment with the
+carriage travel. Most lathes have lines on the stationary and movable
+parts of the tailstock base which show when the centers are set for
+straight turning. These lines, however, may not be absolutely correct,
+and it is good practice to test the alignment of the centers before
+beginning to turn. This can be done by taking trial cuts, at each end of
+the work (without disturbing the tool's crosswise position), and then
+comparing the diameters, or by testing the carriage travel with a true
+cylindrical piece held between the centers as explained later.
+
+[Illustration: Fig. 9. Setting Calipers by Scale--Setting by Gage--Fixed
+Gage]
+
+If the relative positions of the lathe centers are not known, the work
+should be calipered as the cut progresses to see if the diameter _d_ is
+the same at all points. In case the diameter gradually increases, the
+tailstock center should be shifted slightly to the rear before taking
+the next cut, but if the diameter gradually diminishes, the adjustment
+would, of course, be made in the opposite direction. The diameter is
+tested by attempting to pass the calipers over the work. When the
+measuring points just touch the work as they are gently passed across
+it, the diameter being turned is evidently the same as the size to which
+the calipers are set.
+
+[Illustration: Fig. 10. Views showing how the Cross-slide and Carriage
+are Manipulated by Hand when Starting a Cut--View to Left, Feeding Tool
+Laterally; View to Right, Feeding Tool in a Lengthwise Direction]
+
+As the driving dog is on one end, the cut cannot be taken over the
+entire length, and when the tool has arrived at say position _x_, Fig.
+5, it is returned to the starting point and the work is reversed in the
+centers, the dog being placed upon the other end. The unfinished part is
+then turned, and if the cross-slide is not moved, the tool will meet the
+first cut. It is not likely that the two cuts will be joined or blended
+together perfectly, however, and for this reason a cut should be
+continuous when this is possible.
+
+=Roughing and Finishing Cuts.=--Ordinarily in lathe work, as well as in
+other machine work, there are two classes of cuts, known as "roughing"
+and "finishing" cuts. Roughing cuts are for reducing the work as
+quickly as possible almost to the required size, whereas finishing cuts,
+as the name implies, are intended to leave the part smooth and of the
+proper size. When the rough stock is only a little larger than the
+finished diameter, a single cut is sufficient, but if there is
+considerable metal to turn away, one or more deep roughing cuts would
+have to be taken, and, finally, a light cut for finishing. In this
+particular case, one roughing and one finishing cut would doubtless be
+taken, as the diameter has to be reduced 3/8 inch. Ordinarily the
+roughing cut would be deep enough to leave the work about 1/32 or
+perhaps 1/16 inch above the finished size. When there is considerable
+metal to remove and a number of roughing cuts have to be taken, the
+depth of each cut and the feed of the tool are governed largely by the
+pulling power of the lathe and the strength of the work to withstand the
+strain of a heavy cut. The depth of roughing cuts often has to be
+reduced considerably because the part being turned is so flexible that a
+heavy cut would spring the work and cause the tool to gouge in. Of
+course, just as few cuts as possible should be taken in order to save
+time. The speed of the work should also be as fast as the conditions
+will allow for the same reason, but as there are many things which
+govern the speed, the feed of the tool, and the depth of the cut, these
+important points are referred to separately in Chapter II.
+
+=Filing and Finishing.=--In many cases the last or finishing cut does
+not leave as smooth a surface as is required and it is necessary to
+resort to other means. The method commonly employed for finishing in the
+lathe is by the use of a file and emery cloth. The work is rotated
+considerably faster for filing than for turning, and the entire surface
+is filed by a flat, single-cut file, held as shown in Fig. 11. The file
+is passed across the work and advanced sidewise for each forward stroke,
+until the entire surface is finished. The file should be kept in contact
+with the work continually, but on the return stroke the pressure should
+be relieved. The movement of the file during the forward or cutting
+stroke should be much slower than when filing in a vise. By moving the
+file slowly, the work can make a number of revolutions for each stroke,
+which tends to keep it round, as practically the same amount of metal is
+removed from the entire circumference. On the other hand, short rapid
+strokes tend to produce flat spots, or at least an irregular surface,
+especially if the work can only make part of a revolution for each
+cutting stroke. The pressure on the file during the forward stroke
+should also be kept as nearly uniform as possible.
+
+[Illustration: Fig. 11. Filing Work after Finishing Cut is taken]
+
+It is very difficult to file a part smooth and at the same time to keep
+it round and cylindrical, and the more filing that has to be done, the
+greater the chance of error. For this reason, the amount left for filing
+should be very small; in fact, the metal removed by filing should be
+just enough to take out the tool marks and give a smooth finish. Very
+often a satisfactory finish can be obtained with a turning tool, and
+filing is not necessary at all. The file generally used for lathe work
+is a "single-cut bastard" of "mill" section, having a length of from 12
+to 14 inches.
+
+Sometimes particles of metal collect between the teeth of a file and
+make deep scratches as the file is passed across the work. When this
+occurs, the teeth should be cleaned by using a wire brush or a file
+card, which is drawn across the file in the direction of the teeth. This
+forming of tiny particles between the teeth is known as "pinning" and it
+can sometimes be avoided by rubbing chalk on the file. Filing is not
+only done to obtain a smooth finish, but also to reduce the work to an
+exact diameter, as a very slight reduction can be made in this way.
+
+[Illustration: Fig. 12. Two Methods of Aligning Centers for Cylindrical
+Turning]
+
+If a polish is desired, this can be obtained by holding a piece of emery
+cloth tightly around the work as it revolves. The coarseness of emery
+cloth is indicated by letters and numbers corresponding to the grain
+number of loose emery. The letters and numbers for grits ranging from
+fine to coarse are as follows: _FF_, _F_, 120, 100, 90, 80, 70, 60, 54,
+46, 40. For large work roughly filed, use coarse cloth such as Nos. 46
+or 54, and then finer grades to obtain the required polish. If the work
+has been carefully filed, a good polish can be obtained with Nos. 60 and
+90 cloth, and a brilliant polish by finishing with No. 120 and
+flour-emery.
+
+Most cylindrical parts can be finished more quickly and accurately in
+the grinder than in the lathe, and many classes of work are, at the
+present time, simply rough-turned in the lathe and then ground to size
+in a cylindrical grinding machine.
+
+=Aligning Centers for Cylindrical Turning.=--When a rod or shaft must be
+turned cylindrical or to the same diameter throughout its entire length,
+it is good practice to test the alignment of the centers, before
+inserting the work. The position of the tailstock center for cylindrical
+turning may be indicated by the coincidence of graduation marks on the
+base, but if accuracy is necessary, the relative position of the two
+centers should be determined in a more positive way. A very simple and
+convenient method of testing the alignment is shown at _A_ in Fig. 12.
+The work is first turned for a short distance, near the dogged end, as
+shown, and the tool is left as set for this cut; then the tailstock
+center is withdrawn and the work is moved sufficiently to permit running
+the tool back to the tailstock end without changing its original
+setting. A short cut is then taken at this end and the diameters _d_ and
+_d_{1}_ are carefully compared. In case there is any variation, the
+tailstock center is adjusted laterally, other trial cuts are taken, and
+the test repeated.
+
+Another method is illustrated at _B_, which requires the use of a
+test-bar _t_. This bar should have accurately made centers and the ends
+finished to exactly the same diameter. The lathe centers are aligned by
+placing the bar between them and then testing the position of the ends.
+This can be done by comparing each end with a tool held in the toolpost
+and moved from one to the other by shifting the carriage, but a better
+method is to clamp a test indicator _i_ in the toolpost and bring it in
+contact with first one end of the bar and then the other. If the dial
+does not register the same at each end, it shows that the lathe centers
+are not in line. Even when centers are correctly set, lathes that have
+been in use a long time do not always turn cylindrical or straight,
+because if the ways that guide the carriage are worn unevenly, the tool
+as it moves along does not remain in the same plane and this causes a
+variation in the diameter of the part being turned.
+
+=Application of Drivers or Dogs.=--Work that is turned between centers
+is sometimes driven by a dog which is so short for the faceplate that
+the bent driving end bears against the bottom _a_ of the faceplate slot,
+as shown at _A_, Fig. 13. If the dog is nearly the right length, it may
+allow the headstock center to enter the center in the work part way,
+with the result that the turned surface is not true with the centers.
+When a driving dog of this type is used, care should be taken to see
+that it moves freely in the faceplate slot and does not bind against the
+bottom. By using a straight dog (_B_), which is driven by a pin _b_
+bolted to the faceplate, all danger from this source is eliminated. The
+straight dog, however, is used more particularly to do away with the
+leverage _l_ of a bent dog, as this leverage tends to spring a flexible
+part when a cut is being taken.
+
+[Illustration: Fig. 13. (A) Dog that is too Short for Faceplate. (B)
+Straight Driving Dog]
+
+Straight dogs are also made with two driving ends which engage pins on
+opposite sides of the faceplate. This type is preferable because it
+applies the power required for turning, evenly to the work, which still
+further reduces the tendency to spring it out of shape. The principal
+objection to the double-ended type lies in the difficulty of adjusting
+the driving pins so that each bears with equal pressure against the dog.
+The double-ended driver is often used for large work especially if deep
+roughing cuts are necessary.
+
+=Lathe Arbors or Mandrels.=--When it is necessary to turn the outside of
+a part having a hole through it, centers cannot, of course, be drilled
+in the ends and other means must be resorted to. We shall assume that
+the bushing _B_, Fig. 14, has a finished hole through the center, and
+it is desired to turn the outside cylindrical and concentric with the
+hole. This could be done by forcing a tightly-fitted arbor _M_, having
+accurately-centered ends, into the bushing and inserting the mandrel and
+work between the lathe centers _h_ and _h_{1}_ as shown. Evidently, if
+the arbor runs true on its centers, the hole in the bushing will also
+run true and the outside can be turned the same as though the arbor and
+bushing were a solid piece. From this it will be seen that an arbor
+simply forms a temporary support for parts that are bored and therefore
+cannot be centered.
+
+[Illustration: Fig. 14. Bushing mounted on Arbor for Turning]
+
+Another example of work that would be turned on an arbor is shown in
+Fig. 15. This is a small cast-iron wheel having a finished hole through
+the hub, and the outer surface and sides of the rim are to be turned
+true with this hole. In this case, the casting would also be held by
+pressing a mandrel through the hub; as shown. This method, however,
+would only apply to comparatively small wheels because it would be
+difficult, if not impossible, to prevent a large wheel from turning on
+the arbor when taking a cut, and even if it could be driven, large work
+could be done to better advantage on another type of machine. (The
+vertical boring mill is used extensively for turning large wheels, as
+explained in Chapter VI.) When turning the outside of the rim, a tool
+similar to that shown at _t_ should be used, but for facing or turning
+the sides, it might be better, if not necessary, to use tools having
+bent ends as shown by the dotted lines; in fact, turning tools of
+various kinds are made with the ends bent to the right or left, as this
+enables them to be used on surfaces that could not be reached very well
+with a straight tool. If a comparatively large pulley is mounted near
+the end of the arbor, it can be driven directly by pins attached to the
+faceplate and engaging the pulley arms. This method of driving is often
+employed when the diameter to be turned is large and the hole for the
+arbor is so small that there will not be sufficient friction for
+driving.
+
+[Illustration: Fig. 15. Turning Pulley Held on an Arbor]
+
+=Different Types of Lathe Arbors.=--Three different types of lathe
+arbors are shown in Fig. 16. The kind shown at _A_ is usually made of
+tool steel and the body is finished to a standard size. The ends are
+somewhat reduced and flat spots are milled, as shown, to give the
+clamping screw of the dog a good grip. The body of the arbor is usually
+tapered about 0.006 inch per foot. This taper makes it easier to insert
+the arbor in a close-fitting hole, and it also permits slight variations
+in the diameter of different holes. As to hardening, the practice at the
+present time among manufacturers is to harden arbors all over, but for
+extremely accurate work, an arbor having hardened ends and a soft body
+is generally considered superior, as there is less tendency of
+distortion from internal stresses. Hardened arbors are "seasoned" before
+finish-grinding to relieve these internal stresses.
+
+The solid type _A_, Fig. 16, is used very extensively, but in shops
+where a great variety of work is being done and there are many odd-sized
+holes, some form of expanding arbor _B_ can be used to advantage. This
+type, instead of being solid, consists of a tapering inner arbor _M_ on
+which is placed a split bushing that can be expanded, within certain
+limits, by driving in the tapering member. The advantage of this type is
+that a comparatively small stock of arbors is required, as
+different-sized bushings can be used. This type can also be fitted to
+holes of odd sizes, whereas a solid arbor must be provided for each
+different size hole, unless the variation is very slight. The latter
+are, however, more accurate than the expanding type.
+
+[Illustration: Fig. 16. Different Types of Lathe Arbors]
+
+Another form of expanding arbor is shown at _C_. This type has a
+straight body _N_ in which four tapering grooves are cut lengthwise, as
+shown, and there is a sleeve _S_, containing four slots that are located
+to correspond with the tapering grooves. Strips s are fitted into these
+slots, and as the part _N_ is driven in, the strips are moved outward as
+they ascend the tapering grooves. By having different sets of these
+strips of various heights, one arbor of this type can be made to cover
+quite a range of sizes. It is not suited, however, to thin work, as the
+pressure, being concentrated in four places, would spring a flexible
+part out of shape.
+
+The cone arbor or mandrel shown at _A_, in Fig. 17, is convenient for
+holding parts having comparatively large holes, as it can be adjusted
+for quite a range of diameters. The work is gripped between the two
+cones _c_ and _c_{1}_ which are forced together by nut _n_. The cones
+are prevented from turning upon the arbor by keys. This style of arbor
+should not be used for accurate work. The threaded arbor _B_ is used for
+facing the sides of nuts square with the tapped hole. When a nut is
+first put upon the arbor, the rough side comes against an equalizing
+washer _w_. This washer rests against a spherical seat so that it can
+shift to provide a uniform bearing for the rough side of the nut, even
+though it is not square with the tapped hole. This feature prevents the
+nut from being canted on the arbor and insures an accurately faced nut.
+The revolving conical center shown at _C_ is often used for holding a
+pipe or tube while turning the outside. The cone is adjusted to fit into
+the hole of the pipe, by means of the tailstock spindle, and the
+opposite end is usually held in a chuck.
+
+[Illustration: Fig. 17. (A) Cone Arbor. (B) Nut Arbor. (C) Pipe Center]
+
+Particular care should be taken to preserve the accuracy of the centers
+of lathe arbors by keeping them clean and well-oiled while in use.
+
+=Mandrel or Arbor Press.=--The best method of inserting an arbor of the
+solid type in a hole is by using a press, Fig. 18, designed for that
+purpose, but if such a press is not available and it is necessary to
+drive the mandrel in, a "soft" hammer, made of copper, lead or other
+soft material, should be used to protect the centered end of the arbor.
+In either case, the arbor should not be forced in too tightly, for if it
+fits properly, this will not be necessary in order to hold the work
+securely. On the other hand, the work might easily be broken by
+attempting to force the arbor in as far and as tightly as possible. In
+using the arbor press, the work is placed on the base _B_ with the hole
+in a vertical position, and the arbor (which should be oiled slightly)
+is forced down into it by ram _R_, operated by lever _L_. Slots are
+provided in the base, as shown, so that the end of the arbor can come
+through at the bottom of the hole. The lever of this particular press is
+counter-weighted so that it rises to a vertical position when released.
+The ram can then be adjusted quickly to any required height by the
+handwheel seen at the left.
+
+[Illustration: Fig. 18. Press for Forcing Arbors into Work]
+
+Some shops are equipped with power-driven mandrel or arbor presses.
+This type is particularly desirable for large work, owing to the greater
+pressure required for inserting mandrels that are comparatively large in
+diameter. One well-known type of power press is driven by a belt, and
+the downward pressure of the ram is controlled by a handwheel. The ram
+is raised or lowered by turning this handwheel in one direction or the
+other, and a gage shows how much pressure is being applied. This type of
+press can also be used for other purposes, such as forcing bushings or
+pins into or out of holes, bending or straightening parts, or for
+similar work.
+
+[Illustration: Fig. 19. Steadyrest and Follow-rest for Supporting
+Flexible Parts]
+
+=Steadyrest for Supporting Flexible Parts.=--Occasionally long slender
+shafts, rods, etc., which have to be turned, are so flexible that it is
+necessary to support them at some point between the lathe centers. An
+attachment for the lathe known as a steadyrest is often used for this
+purpose. A steadyrest is composed of a frame containing three jaws _J_
+(Fig. 19), that can be adjusted in or out radially by turning screws
+_S_. The frame is hinged at _h_, thus allowing the upper half to be
+swung back (as shown by the dotted lines) for inserting or removing the
+work. The bolt-clamp _c_ holds the hinged part in the closed position.
+The base of the frame has V-grooves in it that fit the ways of the lathe
+bed. When the steadyrest is in use, it is secured to the bed by clamp
+_C_, and the jaws _J_ are set in against the work, thus supporting or
+steadying it during the turning operation. The steadyrest must, of
+course, be located at a point where it will not interfere with the
+turning tool.
+
+[Illustration: Fig. 20. Application of Steadyrest to a Flexible Rod]
+
+Fig. 20 shows the application of the steadyrest to a long forged rod,
+having one small end, which makes it too flexible to be turned without
+support. As this forging is rough, a true surface _n_ a little wider
+than the jaws _J_ (Fig. 19) is first turned as a bearing for the jaws.
+This should be done very carefully to prevent the work from mounting the
+tool. A sharp pointed tool should be used and very light cuts taken. The
+steadyrest is next clamped to the lathe bed opposite the turned surface,
+and the jaws are adjusted in against this surface, thus forming a
+bearing. Care should be taken not to set up the jaws too tightly, as the
+work should turn freely but without play. The large part of the rod and
+central collar are then turned to size, this half being machined while
+the small part is in the rough and as stiff as possible. The rod is then
+reversed and the steadyrest is applied to the part just finished, as
+shown at _B_, thus supporting the work while the small end is being
+turned. That part against which the jaws bear should be kept well oiled,
+and if the surface is finished it should be protected by placing a strip
+of emery cloth beneath the jaws with the emery side out; a strip of
+belt leather is also used for this purpose, the object in each case
+being to prevent the jaws from scratching and marring the finished
+surface, as they tend to do, especially if at all rough.
+
+If the work were too flexible to permit turning a spot at _n_, this
+could be done by first "spotting" it at some point _o_, and placing the
+steadyrest at that point while turning another spot at _n_.
+
+Sometimes it is desirable to apply a steadyrest to a surface that does
+not run true and one which is not to be turned; in such a case a device
+called a "cat-head" is used. This is simply a sleeve _S_ (Fig. 21) which
+is placed over the untrue surface to serve as a bearing for the
+steadyrest. The sleeve is made to run true by adjusting the four
+set-screws at each end, and the jaws of the steadyrest are set against
+it, thus supporting the work.
+
+[Illustration: Fig. 21. Cat-head which is sometimes used as Bearing for
+Steadyrest]
+
+=Application of Steadyrest when Boring.=--Another example illustrating
+the use of the steadyrest is shown in Fig. 22. The rod _R_ is turned on
+the outside and a hole is to be bored in the end (as shown by dotted
+lines) true with the outer surface. If the centers used for turning the
+rod are still in the ends, as they would be ordinarily, this work could
+be done very accurately by the following method: The rod is first placed
+between the centers as for turning, with a driving dog _D_ attached, and
+the steadyrest jaws _J_ are set against it near the outer end, as shown.
+
+Before any machine work is done, means must be provided for holding the
+rod back against the headstock center _h_, because, for an operation of
+this kind, the outer end cannot be supported by the tailstock center;
+consequently the work tends to shift to the right. One method of
+accomplishing this is shown in the illustration. A hardwood piece _w_,
+having a hole somewhat larger than the work, is clamped against the dog,
+in a crosswise position, by the swinging bolts and thumb-screws shown.
+If the dog is not square with the work, the wood piece should be canted
+so that the bearing will not be all on one side. For large heavy parts a
+similar "bridle" or "hold-back"--as this is commonly called--is made by
+using steel instead of wood for the part _w_. Another very common method
+which requires no special equipment is illustrated in Fig. 23. An
+ordinary leather belt lacing _L_ is attached to the work and faceplate
+while the latter is screwed off a few turns as shown. Then the lacing is
+drawn up by hand and tied, and the faceplate is screwed onto the
+spindle, thus tightening the lacing and drawing the work against the
+headstock center. The method of applying the lacing is quite clearly
+indicated in the illustration. If a small driving faceplate is used, it
+may be necessary to drill holes for the belt lacing, as shown.
+
+[Illustration: Fig. 22. Shaft supported by Steadyrest for Drilling and
+Boring End]
+
+A hole is next drilled in the end of the rod by using a twist drill in
+the tailstock. If the hole is finished by boring, a depth mark should
+be made on the tool shank that will warn the workman of the cutting
+end's approach to the bottom. A chuck can also be used in connection
+with a steadyrest for doing work of this kind, as shown in Fig. 24, the
+end of the rod being held and driven by the chuck _C_. If the piece is
+centered, it can be held on these centers while setting the steadyrest
+and adjusting the chuck, but if the ends are without centers, a very
+good way is to make light centers in the ends with a punch; after these
+are properly located they are used for holding the work until the
+steadyrest and chuck jaws have been adjusted. In case it is necessary to
+have the end hole very accurate with the outside of the finished rod, a
+test indicator _I_ should be applied to the shaft as shown. This is an
+instrument which shows with great accuracy whether a rotating part runs
+true and it is also used for many other purposes in machine shops. The
+indicator is held in the lathe toolpost and the contact point beneath
+the dial is brought against the work. If the latter does not run true,
+the hand of the indicator vibrates and the graduations on the dial show
+how much the work is out in thousandths of an inch.
+
+[Illustration: Fig. 23. Hold-back used when Outer End of Work is held in
+Steadyrest]
+
+=The Follow-rest.=--When turning long slender parts, such as shafts,
+etc., a follow-rest is often used for supporting the work. The
+follow-rest differs from the steadyrest in that it is attached to and
+travels with the lathe carriage. The type illustrated to the right in
+Fig. 19 has two adjustable jaws which are located nearly opposite the
+turning tool, thus providing support where it is most needed. In using
+this rest, a cut is started at the end and the jaws are adjusted to this
+turned part. The tool is then fed across the shaft, which cannot spring
+away from the cut because of the supporting jaws. Some follow-rests
+have, instead of jaws, a bushing bored to fit the diameter being turned,
+different bushings being used for different diameters. The bushing forms
+a bearing for the work and holds it rigidly. Whether a bushing or jaws
+are used, the turning tool is slightly in advance of the supporting
+member.
+
+[Illustration: Fig. 24. Testing Work with Dial Indicator]
+
+=Centering Parts to be Turned.=--As previously mentioned, there are a
+number of different methods of forming center-holes in the ends of parts
+that have to be turned while held between lathe centers. A method of
+centering light work, and one that requires few special tools, is first
+to locate a central point on the end and then drill and ream the
+center-hole by using the lathe itself. Hermaphrodite dividers are useful
+for finding the center, as illustrated at _A_, Fig. 25, but if the work
+is fairly round, a center-square _B_ is preferable. A line is scribed
+across the end and then another line at right angles to the first by
+changing the position of the square; the intersection of these two lines
+will be the center, which should be marked by striking a pointed punch
+_C_ with a hammer. If a cup or bell center-punch _D_ is available, it
+will not be necessary to first make center lines, as the conical part
+shown locates the punch in a central position. This style of punch
+should only be used on work which is fairly round.
+
+[Illustration: Fig. 25. Centering End with Punch preparatory to
+Drilling]
+
+After small centers have been located in both ends, their position can
+be tested by placing the work between the lathe centers and rotating it
+rapidly by drawing the hand quickly across it. By holding a piece of
+chalk close to the work as it spins around, a mark will be made on the
+"high" side if the centers are not accurate; the centers are then
+shifted toward these marks. If the work is close to the finished
+diameter, the centers should, of course, be located quite accurately in
+order that the entire surface of the work will be turned true when it is
+reduced to the finished size.
+
+One method of forming these center-holes is indicated in Fig. 26. A
+chuck _C_ is screwed onto the spindle in place of the faceplate, and a
+combination center drill and reamer _R_ is gripped by the chuck jaws and
+set to run true. The center is then drilled and reamed at one end by
+pressing the work against the revolving drill with the tailstock
+spindle, which is fed out by turning handle _n_. The piece is then
+reversed for drilling the opposite end. The work may be kept from
+revolving while the centers are being drilled and reamed, by attaching a
+dog to it close to the tailstock end and then adjusting the cross-slide
+until the dog rests upon the slide. Many parts can be held by simply
+gripping them with one hand. From the foregoing it will be seen that the
+small centers made by punch _C_, Fig. 25, serve as a starting point for
+the drill and also as a support for the outer end of the work while the
+first hole is being drilled.
+
+[Illustration: Fig. 26. Drilling Centers in the Lathe]
+
+The form of center-hole produced by a combination drill and reamer is
+shown by the lower left-hand view in Fig. 27. A small straight hole a in
+the bottom prevents the point of the lathe center from coming in contact
+with the work and insures a good bearing on the conical surface _c_. The
+standard angle for lathe centers is sixty degrees, as the illustration
+shows, and the tapering part of all center-holes should be made to this
+angle.
+
+[Illustration: Fig. 27. Centers of Incorrect and Correct Form]
+
+[Illustration: Fig. 28. Special Machine for Centering Parts to be
+Turned]
+
+=Centering Machine.=--Many shops have a special machine for forming
+centers which enables the operation to be performed quickly. One type
+of centering machine is shown in Fig. 28. The work is gripped in a chuck
+_C_ that automatically locates it in a central position so that it is
+not necessary to lay out the end before drilling. There are two spindles
+_s_, one of which holds the drill and the other the countersink, and
+these are rotated by a belt passing over pulley _P_. Each of these
+spindles is advanced by lever _L_ and either of them can be moved to a
+position central with the work, as they are mounted in a swiveling
+frame. In operating this machine, a small straight hole is first made by
+a twist drill held in one of the spindles; the other spindle is then
+moved over to the center and the hole is reamed tapering. The
+arrangement is such that neither spindle can be advanced by the feeding
+lever except when in a central position. The amount that each spindle
+can be advanced is limited by a fixed collar inside the head, and there
+is also a swinging adjustable stop against which the end of the work
+should be placed before tightening the chuck. These two features make it
+possible to ream center holes of the same size or depth in any number of
+pieces.
+
+[Illustration: Fig. 29. The Imperfect Center Bearing is the Result of
+Centering before Straightening]
+
+=Different Forms of Centers.=--In some poorly equipped shops it is
+necessary to form centers by the use of a center-punch only, as there is
+no better tool. If the end of the punch has a sixty-degree taper, a fair
+center can be formed in this way, but it is not a method to be
+recommended, especially when accurate work is required. Sometimes
+centers are made with punches that are too blunt, producing a shallow
+center, such as the one shown in the upper left-hand view, Fig. 27. In
+this case all the bearing is on the point of the lathe center, which is
+the worst possible place for it. Another way is to simply drill a
+straight hole as in the upper view to the right; this is also bad
+practice in more than one respect. The lower view to the right shows a
+form of center which is often found in the ends of lathe arbors, the
+mouth of the center being rounded, at _r_, and the arbor end recessed as
+shown. The rounded corner prevents the point of the lathe center from
+catching when it is moved rapidly towards work which is not being held
+quite centrally (as shown by the illustration), and the end is recessed
+to protect the center against bruises. Stock that is bent should always
+be straightened before the centers are drilled and reamed. If the work
+is first centered and then straightened the bearing on the lathe center
+would be as shown in Fig. 29. The center will then wear unevenly with
+the result that the surfaces last turned will not be concentric with
+those which were finished first.
+
+[Illustration: Fig. 30. Tool Steel should be centered Concentric, in
+order to remove the Decarbonized Outer Surface]
+
+=Precaution When Centering Tool Steel.=--Ordinarily centers are so
+located that the stock runs approximately true before being turned, but
+when centering tool steel to be used in making tools, such as reamers,
+mills, etc., which need to be hardened, particular care should be taken
+to have the rough surface run fairly true. This is not merely to insure
+that the piece will "true-up," as there is a more important
+consideration, the disregard of which often affects the quality of the
+finished tool. As is well known, the degree of hardness of a piece of
+tool steel that has been heated and then suddenly cooled depends upon
+the amount of carbon that it contains, steel that is high in carbon
+becoming much harder than that which contains less carbon. Furthermore,
+the amount of carbon found at the surface, and to some little depth
+below the surface of a bar of steel, is less than the carbon content in
+the rest of the bar. This is illustrated diagrammatically in Fig. 30 by
+the shaded area in the view to the left. (This decarbonization is
+probably due to the action of the oxygen of the air on the bar during
+the process of manufacture.) If stock for a reamer is so centered that
+the tool removes the decarbonized surface only on one side, as
+illustrated to the right, evidently when the reamer is finished and
+hardened the teeth on the side _A_ will be harder than those on the
+opposite side, which would not have been the case if the rough bar had
+been centered true. To avoid any trouble of this kind, stock that is to
+be used for hardened tools should be enough larger than the finished
+diameter and so centered that this decarbonized surface will be entirely
+removed in turning.
+
+[Illustration: Fig. 31. Three Methods of Facing the Ends Square]
+
+=Facing the Ends of Centered Stock.=--As a piece of work is not properly
+centered until the ends are faced square, we will consider this
+operation in connection with centering. Some machinists prefer lathe
+centers that are cut away as shown at _A_, Fig. 31, so that the point of
+the side tool can be fed in far enough to face the end right up to the
+center hole. Others, instead of using a special center, simply loosen
+the regular one slightly and then, with the tool in a position as at
+_B_, face the projecting teat by feeding both tool and center inward as
+shown by the arrow. Whenever this method is employed, care should be
+taken to remove any chips from the center hole which may have entered. A
+method which makes it unnecessary to loosen the regular center, or to
+use a special one, is to provide clearance for the tool-point by
+grinding it to an angle of approximately forty-five degrees, as shown at
+_C_. If the tool is not set too high, it can then be fed right up to the
+lathe center and the end squared without difficulty. As for the special
+center _A_, the use of special tools and appliances should always be
+avoided unless they effect a saving in time or their use makes it
+possible to accomplish the same end with less work.
+
+=Truing Lathe Centers.=--The lathe centers should receive careful
+attention especially when accurate work must be turned. If the headstock
+center does not run true as it revolves with the work, a round surface
+may be turned, but if the position of the driving dog with reference to
+the faceplate is changed, the turned surface will not run true because
+the turned surface is not true with the work centers. Furthermore, if
+it is necessary to reverse the work for finishing the dogged or driving
+end, the last part turned will be eccentric to the first. Therefore, the
+lathe centers should be kept true in order to produce turned surfaces
+that are true or concentric with the centered ends, as it is often
+necessary to change the part being turned "end for end" for finishing,
+and any eccentricity between the different surfaces would, in many
+cases, spoil the work.
+
+[Illustration: Fig. 32. Grinder for Truing Lathe Centers]
+
+Some lathes are equipped with hardened centers in both the head-and
+tailstock and others have only one hardened center which is in the
+tailstock. The object in having a soft or unhardened headstock center is
+to permit its being trued by turning, but as a soft center is quite
+easily bruised and requires truing oftener than one that is hard, it is
+better to have both centers hardened. Special grinders are used for
+truing these hardened centers. One type that is very simple and easily
+applied to a lathe is shown in Fig. 32. This grinder is held in the
+lathe toolpost and is driven by a wheel _A_ that is held in contact with
+the cone-pulley. The emery wheel _B_ is moved to a position for grinding
+by adjusting the carriage and cross-slide, and it is traversed across
+the conical surface of the center by handle _C_. As the grinding
+proceeds, the wheel is fed inward slightly by manipulating the
+cross-slide.
+
+This grinder is set to the proper angle by placing the two centered ends
+_D_ and _D_{1}_ between the lathe centers, which should be aligned as
+for straight turning. The grinding spindle will then be 30 degrees from
+the axis of the lathe spindle. The grinder should be carefully clamped
+in the toolpost so that it will remain as located by the centered ends.
+After the tailstock center is withdrawn, the emery wheel is adjusted for
+grinding. As the wheel spindle is 30 degrees from the axis of the lathe
+spindle, the lathe center is not only ground true but to an included
+angle of 60 degrees, which is the standard angle for lathe centers.
+There are many other styles of center grinders on the market, some of
+which are driven by a small belt from the cone-pulley and others by
+electric motors which are connected with ordinary lighting circuits. The
+tailstock center is ground by inserting it in the spindle in place of
+the headstock center. Before a center is replaced in its spindle, the
+hole should be perfectly clean as even a small particle of dirt may
+affect the alignment. The center in the headstock is usually referred to
+as the "live center" because it turns around when the lathe is in use,
+and the center in the tailstock as the "dead center," because it remains
+stationary.
+
+=Universal, Independent and Combination Chucks.=--Many parts that are
+turned in the lathe are so shaped that they cannot be held between the
+lathe centers like shafts and other similar pieces and it is often
+necessary to hold them in a chuck _A_, Fig. 33, which is screwed onto
+the lathe spindle instead of the faceplate. The work is gripped by the
+jaws _J_ which can be moved in or out to accommodate various diameters.
+There are three classes of chucks ordinarily used on the lathe, known as
+the independent, universal and combination types. The independent chuck
+is so named because each jaw can be adjusted in or out independently of
+the others by turning the jaw screws S with a wrench. The jaws of the
+universal chuck all move together and keep the same distance from the
+center, and they can be adjusted by turning any one of the screws _S_,
+whereas with the independent type the chuck wrench must be applied to
+each jaw screw. The combination chuck, as the name implies, may be
+changed to operate either as an independent or universal type. The
+advantage of the universal chuck is that round and other parts of a
+uniform shape are located in a central position for turning without any
+adjustment. The independent type is, however, preferable in some
+respects as it is usually stronger and adapted for holding odd-shaped
+pieces because each jaw can be set to any required position.
+
+[Illustration: Fig. 33. (A) Lathe Chuck. (B) Faceplate Jaw]
+
+=Application of Chucks.=--As an example of chuck work, we shall assume
+that the sides of disk _D_, Fig. 34, are to be turned flat and parallel
+with each other and that an independent chuck is to be used. First the
+chuck is screwed onto the lathe spindle after removing the faceplate.
+The chuck jaws are then moved out or in, as the case may be, far enough
+to receive the disk and each jaw is set about the same distance from the
+center by the aid of concentric circles on the face of the chuck. The
+jaws are then tightened while the disk is held back against them to
+bring the rough inner surface in a vertical plane. If the work is quite
+heavy, it can be held against the chuck, before the jaws are tightened,
+by inserting a piece of wood between it and the tailstock center; the
+latter is then run out far enough to force the work back. The outside
+or periphery of the disk should run nearly true and it may be necessary
+to move the jaws in on one side and out on the other to bring the disk
+to a central position. To test its location, the lathe is run at a
+moderate speed and a piece of chalk is held near the outer surface. If
+the latter runs out, the "high" side will be marked by the chalk, and
+this mark can be used as a guide in adjusting the jaws. It should be
+remembered that the jaws are moved only one-half the amount that the
+work runs out.
+
+[Illustration: Fig. 34. (A) Radial Facing. (B) Boring Pulley Held in
+Chuck]
+
+A round-nosed tool _t_ of the shape shown can be used for radial facing
+or turning operations of the kind illustrated. This tool is similar to
+the form used when turning between centers, the principal difference
+being in the direction of the top slope. The radial facing tool should
+be ground to slope downward toward _a_ (see Fig. 35) whereas the regular
+turning tool slopes toward _b_, the inclination in each case being away
+from that part of the cutting edge which does the work. The cutting edge
+should be the same height as the lathe centers, and the cut is taken by
+feeding the tool from the outside in to the center. The cut is started
+by hand and then the power feed is engaged, except for small surfaces.
+The first cut should, if possible, be deep enough to get beneath the
+scale, especially if turning cast iron, as a tool which just grazes the
+hard outer surface will be dulled in a comparatively short time.
+
+If it were simply necessary to turn a true flat surface and the
+thickness of the disk were immaterial, two cuts would be sufficient,
+unless the surface were very uneven, the first or roughing cut being
+followed by a light finishing cut. For a finishing cut, the same tool
+could be used, but if there were a number of disks to be faced, a
+square-nosed tool _F_, Fig. 35, could probably be used to better
+advantage. This type has a broad flat cutting edge that is set parallel
+with the rough-turned surface and this broad edge enables a coarse feed
+to be taken, thus reducing the time required for the finishing cut. If a
+coarse feed were taken with the round tool, the turned surface would
+have spiral grooves in it, whereas with the broad cutting edge, a smooth
+surface is obtained even though the feed is coarse. The amount of feed
+per revolution of the work, however, should always be less than the
+width _w_ of the cutting edge. Very often broad tools cannot be used for
+finishing cuts, especially when turning steel, because their greater
+contact causes chattering and results in a rough surface. An old and
+worn lathe is more liable to chatter than one that is heavy and
+well-built, and as the diameter of the work also makes a difference, a
+broad tool cannot always be used for finishing, even though,
+theoretically, it would be preferable. After one side of the disk is
+finished, it is reversed in the chuck, the finished surface being placed
+against the jaws. The remaining rough side is then turned, care being
+taken when starting the first cut to caliper the width of the disk at
+several points to make sure that the two sides are parallel.
+
+[Illustration: Fig. 35. Tools Ground so that Top Slopes away from
+Working Part of Cutting Edge]
+
+=Example of Boring.=--Another example of chuck work is shown at _B_,
+Fig. 34. In this case a cast-iron pulley is to have a true hole _h_
+bored through the hub. (The finishing of internal cylindrical surfaces
+in a lathe is referred to as boring rather than turning.) The casting
+should be set true by the rim instead of by the rough-cored hole in the
+hub; this can be done by the use of chalk as previously explained. Even
+though a universal type of chuck were used, the jaws of which, as will
+be recalled, are self-centering, it might be necessary to turn the
+pulley relative to the chuck as a casting sometimes runs out because of
+rough spots or lumps which happen to come beneath one or more of the
+jaws.
+
+[Illustration: Fig. 36. Boring Tool]
+
+The shape of tool _t_ for boring is quite different from one used for
+outside turning, as shown by Fig. 36. The cutting end of a solid type of
+tool is forged approximately at right angles to the body or shank, and
+the top surface is ground to slope away from the working part _w_ of the
+cutting edge, as with practically all turning tools. The front part or
+flank, _f_ is also ground away to give the edge clearance. This type of
+tool is clamped in the toolpost with the body about parallel with the
+lathe spindle, and ordinarily the cutting edge would be about as high as
+the center of the hole, or a little below, if anything. When starting a
+cut, the tool is brought up to the work by moving the carriage and it is
+then adjusted radially to get the right depth of cut, by shifting the
+cross-slide. The power feed for the carriage is then used, the tool
+feeding back through the hole as indicated by the arrow, Fig. 34. In
+this case, as with all turning operations, the first cut should be deep
+enough to remove the hard outer scale at every part of the hole. Usually
+a rough-cored hole is so much smaller than the finished size that
+several cuts are necessary; in any case, the last or finishing cut
+should be very light to prevent the tool from springing away from the
+work, so that the hole will be as true as possible. Boring tools,
+particularly for small holes, are not as rigid as those used for outside
+turning, as the tool has to be small enough to enter the hole and for
+this reason comparatively light cuts have to be taken. When boring a
+small hole, the largest tool that will enter it without interference
+should be used to get the greatest rigidity possible.
+
+[Illustration: Fig. 37 (A) Setting Outside Calipers. (B) Transferring
+Measurements to Inside Calipers. (C) Micrometer Gage]
+
+=Measuring Bored Holes.=--The diameters of small holes that are being
+bored are usually measured with inside calipers or standard gages. If
+the pulley were being bored to fit over some shaft, the diameter of the
+shaft would first be measured by using outside calipers, as shown at
+_A_, Fig. 37, the measuring points of the calipers being adjusted until
+they just made contact with the shaft when passed over it. The inside
+calipers are then set as at _B_ to correspond with the size of the
+shaft, and the hole is bored just large enough to admit the inside
+calipers easily. Very accurate measurements can be made with calipers,
+but to become expert in their use requires experience. Some mechanics
+never become proficient in the art of calipering because their hands are
+"heavy" and they lack the sensitiveness and delicacy of touch that is
+necessary. For large holes, a gage _C_ is often used, the length _l_
+being adjusted to the diameter desired. Small holes are often bored to
+fit hardened steel plug gages (Fig. 38), the cylindrical measuring ends
+of which are made with great accuracy to standard sizes. This type of
+gage is particularly useful when a number of holes have to be bored to
+the same size, all holes being made just large enough to fit the gage
+without any perceptible play.
+
+[Illustration: Fig. 38. Standard Plug Gage]
+
+_Setting Work in the Chuck._--When setting a part in a chuck, care
+should be taken to so locate it that every surface to be turned will be
+true when machined to the finished size. As a simple illustration, let
+us assume that the hole through the cast-iron disk, Fig. 39, has been
+cored considerably out of center, as shown. If the work is set by the
+outside surface _S_, as it would be ordinarily, the hole is so much out
+of center that it will not be true when bored to the finished size, as
+indicated by the dotted lines. On the other hand, if the rough hole is
+set true, the outside cannot be finished all over, without making the
+diameter too small, when it is finally turned. In such a case, the
+casting should be shifted, as shown by the arrow, to divide the error
+between the two surfaces, both of which can then be turned as shown by
+the dotted lines in the view to the right. This principle of dividing
+the error when setting work can often be applied in connection with
+turning and boring. After a casting or other part has been set true by
+the most important surface, all other surfaces which require machining
+should be tested to make sure that they all can be finished to the
+proper size.
+
+=Inaccuracy from Pressure of Chuck Jaws.=--Work that is held in a chuck
+is sometimes sprung out of shape by the pressure of the chuck jaws so
+that when the part is bored or turned, the finished surfaces are untrue
+after the jaws are released and the work has resumed its normal shape.
+This applies more particularly to frail parts, such as rings, thin
+cylindrical parts, etc. Occasionally the distortion can be prevented by
+so locating the work with relation to the chuck jaws that the latter
+bear against a rigid part. When the work cannot be held tightly enough
+for the roughing cuts without springing it, the jaws should be released
+somewhat before taking the finishing cut, to permit the part to spring
+back to its natural shape.
+
+[Illustration: Fig. 39. Diagram Illustrating Importance of Setting Work
+with Reference to Surfaces to be Turned]
+
+[Illustration: Fig. 40. Drilling in the Lathe]
+
+=Drilling and Reaming.=--When a hole is to be bored from the solid, it
+is necessary to drill a hole before a boring tool can be used. One
+method of drilling in the lathe is to insert an ordinary twist drill in
+a holder or socket _S_, Fig. 40, which is inserted in the tailstock
+spindle in place of the center. The drill is then fed through the work
+by turning the handle _n_ and feeding the spindle outward as shown by
+the arrow. Before beginning to drill, it is well to turn a conical spot
+or center for the drill point so the latter will start true. This is
+often done by using a special tool having a point like a flat drill.
+This tool is clamped in the toolpost with the point at the same height
+as the lathe centers. It is then fed against the center of the work and
+a conical center is turned. If the drill were not given this true
+starting point, it probably would enter the work more or less off
+center. Drills can also be started without turning a center by bringing
+the square end or butt of a tool-shank held in the toolpost in contact
+with the drill near the cutting end. If the point starts off center,
+thus causing the drill to wobble, the stationary tool-shank will
+gradually force or bump it over to the center.
+
+[Illustration: Fig. 41. Flat Drill and Holder]
+
+Small holes are often finished in the lathe by drilling and reaming
+without the use of a boring tool. The form of drill that is used quite
+extensively for drilling cored holes in castings is shown in Fig. 41, at
+_A_. This drill is flat and the right end has a large center hole for
+receiving the center of the tailstock. To prevent the drill from
+turning, a holder _B_, having a slot _s_ in its end through which the
+drill passes, is clamped in the toolpost, as at _C_. This slot should be
+set central with the lathe centers, and the drill, when being started,
+should be held tightly in the slot by turning or twisting it with a
+wrench as indicated in the end view at _D_; this steadies the drill and
+causes it to start fairly true even though the cored hole runs out
+considerably.
+
+Another style of tool for enlarging cored holes is shown in Fig. 42, at
+_A_. This is a rose chucking reamer, having beveled cutting edges on the
+end and a cylindrical body, which fits closely in the reamed hole, thus
+supporting and guiding the cutting end. The reamer shown at _B_ is a
+fluted type with cutting edges that extend from _a_ to _b_; it is used
+for finishing holes and the drill or rose reamer preceding it should
+leave the hole very close to the required size. These reamers are held
+while in use in a socket inserted in the tailstock spindle, as when
+using a twist drill.
+
+[Illustration: Fig. 42. Rose and Fluted Reamers]
+
+=Holding Work on Faceplate.=--Some castings or forgings are so shaped
+that they cannot be held in a chuck very well, or perhaps not at all,
+and work of this kind is often clamped to a faceplate which is usually
+larger than the faceplate used for driving parts that are turned between
+the centers. An example of faceplate work is shown in Fig. 43. This is a
+rectangular-shaped casting having a round boss or projection, the end
+_e_ of which is to be turned parallel with the back face of the casting
+previously finished on a planer. A rough cored hole through the center
+of the boss also needs to be bored true.
+
+The best way to perform this operation in the lathe would be to clamp
+the finished surface of the casting directly against the faceplate by
+bolts and clamps _a_, _b_, _c_, and _d_, as shown; the work would then
+be turned just as though it were held in a chuck. By holding the casting
+in this way, face _e_ will be finished parallel with the back surface
+because the latter is clamped directly against the true-running surface
+of the faceplate. If a casting of this shape were small enough it could
+also be held in the jaws of an independent chuck, but if the surface e
+needs to be exactly parallel with the back face, it is better to clamp
+the work to the faceplate. Most lathes have two faceplates: One of small
+diameter used principally for driving work turned between centers, and a
+large one for holding heavy or irregularly shaped pieces; either of
+these can be screwed onto the spindle, and the large faceplate has a
+number of slots through which clamping bolts can be inserted.
+
+[Illustration: Fig. 43. Casting Clamped to Faceplate for Turning and
+Boring]
+
+The proper way to clamp a piece to the faceplate depends, of course,
+largely on its shape and the location of the surface to be machined, but
+in any case it is necessary to hold it securely to prevent any shifting
+after a cut is started. Sometimes castings can be held by inserting
+bolts through previously drilled holes, but when clamps are used in
+connection with the bolts, their outer ends are supported by hardwood or
+metal blocks which should be just high enough to make the clamp bear
+evenly on the work. When deep roughing cuts have to be taken,
+especially on large diameters, it is well to bolt a piece to the
+faceplate and against one side of the casting, as at _D_, to act as a
+driver and prevent the work from shifting; but a driver would not be
+needed in this particular case. Of course a faceplate driver is always
+placed to the rear, as determined by the direction of rotation, because
+the work tends to shift backward when a cut is being taken. If the
+surface which is clamped against the faceplate is finished as in this
+case, the work will be less likely to shift if a piece of paper is
+placed between it and the faceplate.
+
+[Illustration: Fig. 44. Cast Elbow held on Angle-plate attached to
+Faceplate]
+
+Work mounted on the faceplate is generally set true by some surface
+before turning. As the hole in this casting should be true with the
+round boss, the casting is shifted on the faceplate until the rough
+outer surface of the boss runs true; the clamps which were previously
+set up lightly are then tightened. The face e is first turned by using a
+round-nosed tool. This tool is then replaced by a boring tool and the
+hole is finished to the required diameter. If the hole being bored is
+larger than the central hole in the faceplate, the casting should be
+clamped against parallel pieces, and not directly against the faceplate,
+to provide clearance for the tool when it reaches the inner end of the
+hole and prevent it from cutting the faceplate. The parallel pieces
+should be of the same thickness and be located near the clamps to
+prevent springing the casting.
+
+=Application of Angle-plate to Faceplate.=--Another example of faceplate
+work is shown in Fig. 44. This is a cast-iron elbow _E_, the two flanges
+of which are to be faced true and square with each other. The shape of
+this casting is such that it would be very difficult to clamp it
+directly to the faceplate, but it is easily held on an angle-plate _P_,
+which is bolted to the faceplate. The two surfaces of this angle-plate
+are square with each other so that when one flange of the elbow is
+finished and bolted against the angle-plate, the other will be faced
+square. When setting up an angle-plate for work of this kind, the
+distance from its work-holding side to the center of the faceplate is
+made equal to the distance _d_ between the center of one flange and the
+face of the other, so that the flange to be faced will run about true
+when bolted in place. As the angle-plate and work are almost entirely on
+one side of the faceplate, a weight _W_ is attached to the opposite side
+for counterbalancing. Very often weights are also needed to
+counterbalance offset parts that are bolted directly to the faceplate.
+The necessity of counterbalancing depends somewhat upon the speed to be
+used for turning. If the surface to be machined is small in diameter so
+that the lathe can be run quite rapidly, any unbalanced part should
+always be counterbalanced.
+
+Sometimes it is rather difficult to hold heavy pieces against the
+vertical surface of the faceplate while applying the clamps, and
+occasionally the faceplate is removed and placed in a horizontal
+position on the bench; the work can then be located about right, and
+after it is clamped, the faceplate is placed on the lathe spindle by the
+assistance of a crane.
+
+Special faceplate jaws, such as the one shown to the right in Fig. 33,
+can often be used to advantage for holding work on large faceplates.
+Three or four of these jaws are bolted to the faceplate which is
+converted into a kind of independent chuck. These faceplate jaws are
+especially useful for holding irregularly shaped parts, as the different
+jaws can be located in any position.
+
+=Supporting Outer End of Chucked Work.=--Fig. 45 shows how the tailstock
+center is sometimes used for supporting the outer end of a long casting,
+the opposite end of which is held in a chuck. This particular casting
+is to be turned and bored to make a lining for the cylinder of a
+locomotive in order to reduce the diameter of the cylinder which has
+been considerably enlarged by re-boring a number of times. These
+bushings are rough-turned on the outside while the outer end is
+supported by the cross-shaped piece or "spider" which forms a
+center-bearing for the tailstock. This spider has set screws in the
+flanged ends of the arms, which are tightened against the inner surface
+of the casting and are adjusted one way or the other in order to locate
+it in a concentric position. After roughing the outside, the inside is
+bored to the finish size; then centered disks, which fit into the bore,
+are placed in the ends of the bushing and the latter is finish-turned.
+The object in rough turning the outside prior to boring is to avoid the
+distortion which might occur if this hard outer surface were removed
+last.
+
+[Illustration: Fig. 45. Rough Turning a Cylinder Lining--Note Method of
+Supporting Outer End]
+
+=Boring Large Castings in the Lathe.=--An ordinary engine lathe is
+sometimes used for boring engine or pump cylinders, linings, etc., which
+are too large to be held in the chuck or on a faceplate, and must be
+attached to the lathe carriage. As a rule, work of this class is done in
+a special boring machine (see "Horizontal Boring Machines"), but if
+such a machine is not available, it may be necessary to use a lathe.
+There are two general methods of boring.
+
+Fig. 46 shows how the lining illustrated in Fig. 45 is bored in a large
+engine lathe. The casting is held in special fixtures which are attached
+to the lathe carriage, and the boring-bar is rotated by the lathe
+spindle. The tool-head of this boring-bar carries two tools located 180
+degrees apart and it is fed along the bar by a star-feed mechanism shown
+attached to the bar and the tailstock spindle. Each time the bar
+revolves, the star wheel strikes a stationary pin and turns the
+feed-screw which, as the illustration shows, extends along a groove cut
+in one side of the bar. This feed-screw passes through a nut attached to
+the tool-head so that the latter is slowly fed through the bore. When
+using a bar of this type, the carriage, of course, remains stationary.
+
+[Illustration: Fig. 46. Boring a Cylinder Lining in an Ordinary Engine
+Lathe]
+
+Cylindrical parts attached to the carriage can also be bored by using a
+plain solid bar mounted between the centers. The bar must be provided
+with a cutter for small holes or a tool-head for larger diameters
+(preferably holding two or more tools) and the boring is done by
+feeding the carriage along the bed by using the regular power feed of
+the lathe. A symmetrically shaped casting like a bushing or lining is
+often held upon wooden blocks bolted across the carriage. These are
+first cut away to form a circular seat of the required radius, by using
+the boring-bar and a special tool having a thin curved edge. The casting
+is then clamped upon these blocks by the use of straps and bolts, and if
+the curved seats were cut to the correct radius, the work will be
+located concentric with the boring-bar. When using a boring-bar of this
+type, the bar must be long enough to allow the part being bored to feed
+from one side of the cutter-head to the other, the cutter-head being
+approximately in a central location.
+
+[Illustration: Fig. 47. Method of Setting Circle on Work Concentric with
+Lathe Spindle]
+
+=Boring Holes to a Given Center Distance.=--In connection with faceplate
+work, it is often necessary to bore two or more holes at a given
+distance apart. The best method of doing this may depend upon the
+accuracy required. For ordinary work sometimes two or more circles _A_
+and _B_ (Fig. 47) are drawn upon the part to be bored, in the position
+for the holes; the piece is then clamped to the faceplate and one of the
+circles is centered with the lathe spindle by testing it with a pointer
+C held in the toolpost; that is, when the pointer follows the circle as
+the work is turned, evidently the circle is concentric with the spindle.
+The hole is then drilled and bored. The other circle is then centered
+in the same way for boring the second hole. As will be seen, the
+accuracy of this method depends first, upon the accuracy with which the
+circles were laid out, and second; upon the care taken in setting them
+concentric. For a more accurate way of locating parts for boring, see
+"Use of Center Indicator" and "Locating Work by the Button Method."
+
+=Turning Brass, Bronze and Copper.=--When turning soft yellow brass, a
+tool should be used having very little or no slope or rake on the top
+surface against which the chip bears, and for plain cylindrical turning,
+the point of the tool is drawn out quite thin and rounded, by grinding,
+to a radius of about 1/8 or 3/16 inch. If a tool having very much top
+slope is used for brass, there is danger of its gouging into the metal,
+especially if the part being turned is at all flexible. The clearance
+angle of a brass tool is usually about 12 or 14 degrees, which is 3 or 4
+degrees greater than the clearance for steel turning tools. Most brass
+is easily turned, as compared with steel, and for that reason this
+increase in clearance is desirable, because it facilitates feeding the
+tool into the metal, especially when the carriage and cross-slide
+movements are being controlled by hand as when turning irregular shapes.
+
+The speed for turning soft brass is much higher than for steel, being
+ordinarily between 150 and 200 feet per minute. When turning phosphor,
+tobin or other tough bronze compositions, the tool should be ground with
+rake the same as for turning steel, and lard oil is sometimes used as a
+lubricant. The cutting speed for bronzes varies from 35 or 40 to 80 feet
+per minute, owing to the difference in the composition of bronze alloys.
+
+Turning tools for copper are ground with a little more top rake than is
+given steel turning tools, and the point should be slightly rounded. It
+is important to have a keen edge, and a grindstone is recommended for
+sharpening copper turning tools. Milk is generally considered the best
+lubricant to use when turning copper. The speed can be nearly as fast as
+for brass.
+
+=Machining Aluminum.=--Tools for turning aluminum should have acute
+cutting angles. After rough-grinding the tool, it is advisable to finish
+sharpening the cutting edge on a grindstone or with an oilstone for fine
+work, as a keen edge is very essential. High speeds and comparatively
+light cuts are recommended. The principal difficulty in the machining of
+aluminum and aluminum alloys is caused by the clogging of the chips,
+especially when using such tools as counterbores and milling cutters.
+This difficulty can be avoided largely by using the right kind of
+cutting lubricant. Soap-water and kerosene are commonly employed. The
+latter enables a fine finish to be obtained, provided the cutting tool
+is properly ground.
+
+The following information on this subject represents the experience of
+the Brown-Lipe Gear Co., where aluminum parts are machined in large
+quantities: For finishing bored holes, a bar equipped with cutters has
+been found more practicable than reamers. The cutters used for machining
+4-inch holes have a clearance of from 20 to 22 degrees and no rake or
+slope on the front faces against which the chips bear. The roughing
+cutters for this work have a rather sharp nose, being ground on the
+point to a radius of about 3/32 inch, but for securing a smooth surface,
+the finishing tools are rounded to a radius of about 3/4 inch. The
+cutting speed, as well as the feed, for machining aluminum is from 50 to
+60 per cent faster than the speeds and feeds for cast iron. The
+lubricant used by this company is composed of one part "aqualine" and 20
+parts water. This lubricant not only gives a smooth finish but preserves
+a keen cutting edge and enables tools to be used much longer without
+grinding. Formerly, a lubricant composed of one part of high-grade lard
+oil and one part of kerosene was used. This mixture costs approximately
+30 cents per gallon, whereas the aqualine and water mixture now being
+used costs less than 4 cents per gallon, and has proved more effective
+than the lubricant formerly employed.
+
+
+
+
+CHAPTER II
+
+LATHE TURNING TOOLS AND CUTTING SPEEDS
+
+
+Notwithstanding the fact that a great variety of work can be done in the
+lathe, the number of turning tools required is comparatively small. Fig.
+1 shows the forms of tools that are used principally, and typical
+examples of the application of these various tools are indicated in Fig.
+2. The reference letters used in these two illustrations correspond for
+tools of the same type, and both views should be referred to in
+connection with the following description.
+
+=Turning Tools for General Work.=--The tool shown at _A_ is the form
+generally used for rough turning, that is for taking deep cuts when
+considerable metal has to be removed. At _B_ a tool of the same type is
+shown, having a bent end which enables it to be used close up to a
+shoulder or surface _s_ that might come in contact with the tool-rest if
+the straight form were employed. Tool _C_, which has a straight cutting
+end, is used on certain classes of work for taking light finishing cuts,
+with a coarse feed. This type of tool has a flat or straight cutting
+edge at the end, and will leave a smooth finish even though the feed is
+coarse, provided the cutting edge is set parallel with the tool's travel
+so as to avoid ridges. Broad-nosed tools and wide feeds are better
+adapted for finishing cast iron than steel. When turning steel, if the
+work is at all flexible, a broad tool tends to gouge into it and for
+this reason round-nosed tools and finer feeds are generally necessary. A
+little experience in turning will teach more on this point than a whole
+chapter on the subject.
+
+[Illustration: Fig. 1. Set of Lathe Turning Tools for General Work]
+
+[Illustration: Fig. 2. Views illustrating Use of Various Types of Lathe
+Tools]
+
+The side-tools shown at _D_ and _E_ are for facing the ends of shafts,
+collars, etc. The first tool is known as a right side-tool because it
+operates on the right end or side of a shaft or collar, whereas the left
+side-tool _E_ is used on the opposite side, as shown in Fig. 2.
+Side-tools are also bent to the right or left because the cutting edge
+of a straight tool cannot always be located properly for facing certain
+surfaces. A bent right side-tool is shown at _F_. A form of tool that is
+frequently used is shown at _G_; this is known as a parting tool and is
+used for severing pieces and for cutting grooves, squaring corners, etc.
+The same type of tool having a bent end is shown at _H_ (Fig. 2)
+severing a piece held in the chuck. Work that is held between centers
+should not be entirely severed with a parting tool unless a steadyrest
+is placed between the tool and faceplate, as otherwise the tool may be
+broken by the springing of the work just before the piece is cut in two.
+It should be noted that the sides of this tool slope inward back of the
+cutting edge to provide clearance when cutting in a narrow groove.
+
+At _I_ a thread tool is shown for cutting a U. S. standard thread. This
+thread is the form most commonly used in this country at the present
+time. A tool for cutting a square thread is shown at _J_. This is shaped
+very much like a parting tool except that the cutting end is inclined
+slightly to correspond with the helix angle of the thread, as explained
+in Chapter IV, which contains descriptions of different thread forms and
+methods of cutting them. Internal thread tools are shown at _K_ and _L_
+for cutting U. S. standard and square threads in holes. It will be seen
+that these tools are somewhat like boring tools excepting the ends which
+are shaped to correspond with the thread which they are intended to cut.
+
+[Illustration: Fig. 3. Turning Tool with Inserted Cutter]
+
+A tool for turning brass is shown at _M_. Brass tools intended for
+general work are drawn out quite thin and they are given a narrow
+rounded point. The top of the brass tool is usually ground flat or
+without slope as otherwise it tends to gouge into the work, especially
+if the latter is at all flexible. The end of a brass tool is sometimes
+ground with a straight cutting edge for turning large rigid work, such
+as brass pump linings, etc., so that a coarse feed can be used without
+leaving a rough surface. The tools at _N_ and _O_ are for boring or
+finishing drilled or cored holes. Two sizes are shown, which are
+intended for small and large holes, respectively.
+
+The different tools referred to in the foregoing might be called the
+standard types because they are the ones generally used, and as Fig. 2
+indicates, they make it possible to turn an almost endless variety of
+forms. Occasionally some special form of tool is needed for doing odd
+jobs, having, perhaps, an end bent differently or a cutting edge shaped
+to some particular form. Tools of the latter type, which are known as
+"form tools," are sometimes used for finishing surfaces that are either
+convex, concave, or irregular in shape. The cutting edges of these tools
+are carefully filed or ground to the required shape, and the form given
+the tool is reproduced in the part turned. Ornamental or other irregular
+surfaces can be finished very neatly by the use of such tools. It is
+very difficult, of course, to turn convex or concave surfaces with a
+regular tool; in fact, it would not be possible to form a true spherical
+surface, for instance, without special equipment, because the tool could
+not be moved along a true curve by simply using the longitudinal and
+cross feeds. Form tools should be sharpened by grinding entirely on the
+top surface, as any grinding on the end or flank would alter the shape
+of the tool.
+
+[Illustration: Fig. 4. Heavy Inserted-cutter Turning Tool]
+
+=Tool-holders with Inserted Cutters.=--All of the tools shown in Fig. 1
+are forged from the bar, and when the cutting ends have been ground down
+considerably it is necessary to forge a new end. To eliminate the
+expense of this continual dressing of tools and also to effect a great
+reduction in the amount of tool steel required, tool-holders having
+small inserted cutters are used in many shops. A tool-holder of this
+type, for outside turning, is shown in Fig. 3. The cutter _C_ is held in
+a fixed position by the set-screw shown, and it is sharpened,
+principally, by grinding the end, except when it is desired to give the
+top of the cutter a different slope from that due to its angular
+position. Another inserted-cutter turning tool is shown in Fig. 4, which
+is a heavy type intended for roughing. The cutter in this case has teeth
+on the rear side engaging with corresponding teeth cut in the clamping
+block which is tightened by a set-screw on the side opposite that shown.
+With this arrangement, the cutter can be adjusted upward as the top is
+ground away.
+
+[Illustration: Fig. 5. Parting Tool with Inserted Blade]
+
+[Illustration: Fig. 6. Boring Tool with Inserted Cutter and Adjustable
+Bar]
+
+A parting tool of the inserted blade type is shown in Fig. 5. The blade
+_B_ is clamped by screw _S_ and also by the spring of the holder when
+the latter is clamped in the toolpost. The blade can, of course, be
+moved outward when necessary. Fig. 6 shows a boring tool consisting of a
+holder _H_, a bar _B_ that can be clamped in any position, and an
+inserted cutter _C_. With this type of boring tool, the bar can be
+extended beyond the holder just far enough to reach through the hole to
+be bored, which makes the tool very rigid. A thread tool of the holder
+type is shown in Fig. 7. The angular edge of the cutter _C_ is
+accurately ground by the manufacturers, so that the tool is sharpened
+by simply grinding it flat on the top. As the top is ground away, the
+cutter is raised by turning screw _S_, which can also be used for
+setting the tool to the proper height.
+
+=The Position of Turning Tools.=--The production of accurate lathe work
+depends partly on the condition of the lathe used and also on the care
+and judgment exercised by the man operating it. Even though a lathe is
+properly adjusted and in good condition otherwise, errors are often made
+which are due to other causes which should be carefully avoided. If the
+turning tool is clamped so that the cutting end extends too far from the
+supporting block, the downward spring of the tool, owing to the thrust
+of the cut, sometimes results in spoiled work, especially when an
+attempt is made to turn close to the finished size by taking a heavy
+roughing cut. Suppose the end of a cylindrical part is first reduced for
+a short distance by taking several trial cuts until the diameter _d_,
+Fig. 8, is slightly above the finished size and the power feed is then
+engaged. When the tool begins to take the full depth _e_ of the cut, the
+point, which ordinarily would be set a little above the center, tends to
+spring downward into the work, and if there were considerable springing
+action, the part would probably be turned below the finished size, the
+increased reduction beginning at the point where the full cut started.
+
+[Illustration: Fig. 7. Threading Tool]
+
+This springing action, as far as the tool is concerned, can be
+practically eliminated by locating the tool so that the distance _A_
+between the tool-block and cutting end, or the "overhang," is as short
+as possible. Even though the tool has little overhang it may tilt
+downward because the toolslide is loose on its ways, and for this reason
+the slide should have a snug adjustment that will permit an easy
+movement without unnecessary play. The toolslides of all lathes are
+provided with gibs which can be adjusted by screws to compensate for
+wear, or to secure a more rigid bearing.
+
+[Illustration: Fig. 8. To avoid springing, Overhang A of Tool should not
+be Excessive]
+
+When roughing cuts are to be taken, the tool should be located so that
+any change in its position which might be caused by the pressure of the
+cut will not spoil the work. This point is illustrated at _A_ in Fig. 9.
+Suppose the end of a rod has been reduced by taking a number of trial
+cuts, until it is 1/32 inch above the finished size. If the power feed
+is then engaged with the tool clamped in an oblique position, as shown,
+when the full cut is encountered at _c_, the tool, unless very tightly
+clamped, may be shifted backward by the lateral thrust of the cut, as
+indicated by the dotted lines. The point will then begin turning smaller
+than the finished size and the work will be spoiled. To prevent any
+change of position, it is good practice, especially when roughing, to
+clamp the tool square with the surface being turned, or in other words,
+at right angles to its direction of movement. Occasionally, however,
+there is a decided advantage in having the tool set at an angle. For
+example, if it is held about as shown at _B_, when turning the flange
+casting _C_, the surfaces _s_ and _s_{1}_ can be finished without
+changing the tool's position. Cylindrical and radial surfaces are often
+turned in this way in order to avoid shifting the tool, especially when
+machining parts in quantity.
+
+=Tool Grinding.=--In the grinding of lathe tools there are three things
+of importance to be considered: First, the cutting edge of the tool (as
+viewed from the top) needs to be given a certain shape; second, there
+must be a sufficient amount of clearance for the cutting edge; and
+third, tools, with certain exceptions, are ground with a backward slope
+or a side slope, or with a combination of these two slopes on that part
+against which the chip bears when the tool is in use.
+
+[Illustration: Fig. 9. (A) The Way in which Tool is sometimes displaced
+by Thrust of Cut, when set at an Angle. (B) Tool Set for Finishing both
+Cylindrical and Radial Surfaces]
+
+In Fig. 10 a few of the different types of tools which are used in
+connection with lathe work are shown. This illustration also indicates
+the meaning of the various terms used in tool grinding. As shown, the
+clearance of the tool is represented by the angle [alpha], the back
+slope is represented by the angle [beta], and the side slope by the
+angle [gamma]. The angle [delta] for a tool without side slope is known
+as the lip angle or the angle of keenness. When, however, the tool has
+both back and side slopes, this lip angle would more properly be the
+angle between the flank _f_ and the top of the tool, measured diagonally
+along a line _z--z_. It will be seen that the lines _A--B_ and _A--C_
+from which the angles of clearance and back slope are measured are
+parallel with the top and sides of the tool shank, respectively. For
+lathe tools, however, these lines are not necessarily located in this
+way when the tool is in use, as the height of the tool point with
+relation to the work center determines the position of these lines, so
+that the _effective_ angles of back slope, clearance and keenness are
+changed as the tool point is lowered or raised. The way the position of
+the tool affects these angles will be explained later.
+
+[Illustration: Fig. 10. Illustration showing the Meaning of Terms used
+in Tool Grinding as applied to Tools of Different Types]
+
+While tools must, of necessity, be varied considerably in shape to adapt
+them to various purposes, there are certain underlying principles
+governing their shape which apply generally; so in what follows we shall
+not attempt to explain in detail just what the form of each tool used on
+the lathe should be, as it is more important to understand how the
+cutting action of the tool and its efficiency is affected when it is
+improperly ground. When the principle is understood, the grinding of
+tools of various types and shapes is comparatively easy.
+
+[Illustration: Fig. 11. Plan View of Lathe Turning and Threading Tools]
+
+=Shape or Contour of Cutting Edge.=--In the first place we shall
+consider the shape or contour of the cutting edge of the tool as viewed
+from the top, and then take up the question of clearance and slope, the
+different elements being considered separately to avoid confusion. The
+contour of the cutting edge depends primarily upon the purpose for which
+the tool is intended. For example, the tool _A_, in Fig. 11, where a
+plan view of a number of different lathe tools is shown, has a very
+different shape from that of, say, tool _D_, as the first tool is used
+for rough turning, while tool _D_ is intended for cutting grooves or
+severing a turned part. Similarly, tool _E_ is V-shaped because it is
+used for cutting V-threads. Tools _A_, _B_ and _C_, however, are regular
+turning tools; that is, they are all intended for turning plain
+cylindrical surfaces, but the contour of the cutting edges varies
+considerably, as shown. In this case it is the characteristics of the
+work and the cut that are the factors which determine the shape. To
+illustrate, tool _A_ is of a shape suitable for rough-turning large and
+rigid work, while tool _B_ is adapted for smaller and more flexible
+parts. The first tool is well shaped for roughing because experiments
+have shown that a cutting edge of a large radius is capable of higher
+cutting speed than could be used with a tool like _B_, which has a
+smaller point. This increase in the cutting speed is due to the fact
+that the tool _A_ removes a thinner chip for a given feed than tool _B_;
+therefore, the speed may be increased without injuring the cutting edge
+to the same extent. If, however, tool _A_ were to be used for turning a
+long and flexible part, chattering might result; consequently, a tool
+_B_ having a point with a smaller radius would be preferable, if not
+absolutely necessary.
+
+The character of the work also affects the shape of tools. The tool
+shown at _C_ is used for taking light finishing cuts with a wide feed.
+Obviously, if the straight or flat part of the cutting edge is in line
+with the travel of the tool, the cut will be smooth and free from
+ridges, even though the feed is coarse, and by using a coarse feed the
+cut is taken in less time; but such a tool cannot be used on work that
+is not rigid, as chattering would result. Therefore, a smaller cutting
+point and a reduced feed would have to be employed. Tools with broad
+flat cutting edges and coarse feeds are often used for taking finishing
+cuts in cast iron, as this metal offers less resistance to cutting than
+steel, and is less conducive to chattering.
+
+The shape of a tool (as viewed from the top) which is intended for a
+more specific purpose than regular turning, can be largely determined by
+simply considering the tool under working conditions. This point may be
+illustrated by the parting tool _D_ which, as previously stated, is used
+for cutting grooves, squaring corners, etc. Evidently this tool should
+be widest at the cutting edge; that is, the sides _d_ should have a
+slight amount of clearance so that they will not bind as the tool is fed
+into a groove. As the tool at _E_ is for cutting a V-thread, the angle
+[alpha] between its cutting edges must equal the angle between the sides
+of a V-thread, or 60 degrees. The tool illustrated at _F_ is for cutting
+inside square threads. In this case the width _w_ should be made equal
+to one-half the pitch of the thread (or slightly greater to provide
+clearance for the screw), and the sides should be given a slight amount
+of side clearance, the same as with the parting tool _D_. So we see that
+the outline of the tool, as viewed from the top, must conform to and be
+governed by its use.
+
+=Direction of Top Slope for Turning Tools.=--Aside from the question of
+the shape of the cutting edge as viewed from the top, there remains to
+be determined the amount of clearance that the tool shall have, and also
+the slope (and its direction) of the top of the tool. By the top is
+meant that surface against which the chip bears while it is being
+severed. It may be stated, in a general way, that the direction in which
+the top of the tool should slope should be away from what is to be the
+_working part_ of the cutting edge. For example, the working edge of a
+roughing tool _A_ (Fig. 11), which is used for heavy cuts, would be,
+practically speaking, between points _a_ and _b_, or, in other words,
+most of the work would be done by this part of the cutting edge;
+therefore the top should slope back from this part of the edge.
+Obviously, a tool ground in this way will have both a back and a side
+slope.
+
+When most of the work is done on the point or nose of the tool, as, for
+example, with the lathe finishing tool _C_ which takes light cuts, the
+slope should be straight back from the point or cutting edge _a--b_. As
+the side tool shown in Fig. 10 does its cutting along the edge _a--b_,
+the top is given a slope back from this edge as shown in the end view.
+This point should be remembered, for when the top slopes in the right
+direction, less power is required for cutting. Tools for certain classes
+of work, such as thread tools, or those for turning brass or chilled
+iron, are ground flat on top, that is, without back or side slope.
+
+=Clearance for the Cutting Edge.=--In order that the cutting edge may
+work without interference, it must have clearance; that is, the flank
+_f_ (Fig. 10) must be ground to a certain angle [alpha] so that it will
+not rub against the work and prevent the cutting edge from entering the
+metal. This clearance should be just enough to permit the tool to cut
+freely. A clearance angle of eight or ten degrees is about right for
+lathe turning tools.
+
+The back slope of a tool is measured from a line _A--B_ which is
+parallel to the shank, and the clearance angle, from a line _A--C_ at
+right angles to line _A--B_. These lines do not, however, always occupy
+this position with relation to the tool shank when the tool is in use.
+As shown to the left in Fig. 12, the base line _A--B_ for a turning
+tool in use intersects with the point of the tool and center of the
+work, while the line _A--C_ remains at right angles to the first. It
+will be seen, then, that by raising the tool, as shown to the right, the
+_effective_ clearance angle [alpha] will be diminished, whereas lowering
+it, as shown by the dotted lines, will have the opposite effect.
+
+A turning tool for brass or other soft metal, particularly where
+considerable hand manipulation is required, could advantageously have a
+clearance of twelve or fourteen degrees, as it would then be easier to
+feed the tool into the metal; but, generally speaking, the clearance for
+turning tools should be just enough to permit them to cut freely.
+Excessive clearance weakens the cutting edge and may cause it to crumble
+under the pressure of the cut.
+
+[Illustration: Fig. 12. Illustrations showing how Effective Angles of
+Slope and Clearance change as Tool is raised or lowered]
+
+=Angle of Tool-point and Amount of Top Slope.=--The lip angle or the
+angle of keenness [delta] (Fig. 10) is another important consideration
+in connection with tool grinding, for it is upon this angle that the
+efficiency of the tool largely depends. By referring to the illustration
+it will be seen that this angle is governed by the clearance and the
+slope [beta], and as the clearance remains practically the same, it is
+the slope which is varied to meet different conditions. Now, the amount
+of slope a tool should have depends on the work for which it is
+intended. If, for example, a turning tool is to be used for roughing
+medium or soft steel, it should have a back slope of about eight degrees
+and a side slope ranging from fourteen to twenty degrees, while a tool
+for cutting very hard steel should have a back slope of about five
+degrees and a side slope of nine degrees.
+
+[Illustration: Fig. 13. (A) Blunt Tool for Turning Hard Steel. (B)
+Tool-point Ground to give Keenness]
+
+The reason for decreasing the slope and thus increasing the lip angle
+for harder metals is to give the necessary increased strength to the
+cutting edge to prevent it from crumbling under the pressure of the cut.
+The tool illustrated at _A_, Fig. 13, is much stronger than it would be
+if ground as shown at _B_, as the former is more blunt. If a tool ground
+as at _A_, however, were used for cutting very soft steel, there would
+be a greater chip pressure on the top and, consequently, a greater
+resistance to cutting, than if a keener tool had been employed;
+furthermore the cutting speed would have to be lower, which is of even
+greater importance than the chip pressure; therefore, the lip angle, as
+a general rule, should be as small as possible without weakening the
+tool so that it cannot do the required work. In order to secure a strong
+and well-supported cutting edge, tools used for turning very hard metal,
+such as chilled rolls, etc., are ground with practically no slope and
+with very little clearance. Brass tools, while given considerable
+clearance, as previously stated, are ground flat on top or without
+slope; this is not done, however, to give strength to the cutting edge,
+but rather to prevent the tool from gouging into the work, which it is
+likely to do if the part being turned is at all flexible and the tool
+has top slope.
+
+Experiments conducted by Mr. F. W. Taylor to determine the most
+efficient form for lathe roughing tools showed that the nearer the lip
+angle approached sixty-one degrees, the higher the cutting speed. This,
+however, does not apply to tools for turning cast iron, as the latter
+will work more efficiently with a lip angle of about sixty-eight
+degrees. This is doubtless because the chip pressure, when turning cast
+iron, comes closer to the cutting edge which should, therefore, be more
+blunt to withstand the abrasive action and heat. Of course, the
+foregoing remarks concerning lip angles apply more particularly to tools
+used for roughing.
+
+[Illustration: Fig. 14. Grinding the Top and Flank of a Turning Tool]
+
+=Grinding a Lathe Tool.=--The way a turning tool is held while the top
+surface is being ground is shown to the left in Fig. 14. By inclining
+the tool with the wheel face, it will be seen that both the back and
+side slopes may be ground at the same time. When grinding the flank of
+the tool it should be held on the tool-rest of the emery wheel or
+grindstone, as shown by the view to the right. In order to form a curved
+cutting edge, the tool is turned about the face of the stone while it is
+being ground. This rotary movement can be effected by supporting the
+inner end of the tool with one hand while the shank is moved to and fro
+with the other.
+
+Often a tool which has been ground properly in the first place is
+greatly misshapen after it has been sharpened a few times. This is
+usually the result of attempts on the part of the workman to re-sharpen
+it hurriedly; for example, it is easier to secure a sharp edge on the
+turning tool shown to the left in Fig. 12, by grinding the flank as
+indicated by the dotted line, than by grinding the entire flank. The
+clearance is, however, reduced and the lip angle changed.
+
+There is great danger when grinding a tool of burning it or drawing the
+temper from the fine cutting edge, and, aside from the actual shape of
+the cutting end, this is the most important point in connection with
+tool grinding. If a tool is pressed hard against an emery or other
+abrasive wheel, even though the latter has a copious supply of water,
+the temper will sometimes be drawn. When grinding a flat surface, to
+avoid burning, the tool should frequently be withdrawn from the stone so
+that the cooling water (a copious supply of which should be provided)
+can reach the surface being ground. A moderate pressure should also be
+applied, as it is better to spend an extra minute or two in grinding
+than to ruin the tool by burning, in an attempt to sharpen it quickly.
+Of course, what has been said about burning applies more particularly to
+carbon steel, but even self-hardening steels are not improved by being
+over-heated at the stone. In some shops, tools are ground to the
+theoretically correct shape in special machines instead of by hand. The
+sharpened tools are then kept in the tool-room and are given out as they
+are needed.
+
+=Cutting Speeds and Feeds.=--The term cutting speed as applied to
+turning operations is the speed in feet per minute of the surface being
+turned, or, practically speaking, it is equivalent to the length of a
+chip, in feet, which would be turned in one minute. The term cutting
+speed should not be confused with revolutions per minute, because the
+cutting speed depends not only upon the speed of the work but also upon
+its diameter. The feed of a tool is the amount it moves across the
+surface being turned for each revolution; that is, when turning a
+cylindrical piece, the feed is the amount that the tool moves sidewise
+for each revolution of the work. Evidently the time required for turning
+is governed largely by the cutting speed, the feed, and the depth of the
+cut; therefore, these elements should be carefully considered.
+
+Cutting Speeds and Feeds for Turning Tools[1]
+
+  +---------------------------------++---------------------------------+
+  |  Steel--Standard 7/8-inch Tool  ||Cast Iron--Standard 7/8-inch Tool|
+  +-----+-----+---------------------++-----+-----+---------------------+
+  |     |     |  Speed in Feet per  ||     |     |  Speed in Feet per  |
+  |Depth|Feed |  Minute for a Tool  ||Depth|Feed |  Minute for a Tool  |
+  | of  | in  |  which is to last   || of  | in  |  which is to last   |
+  | Cut | In- |  1-1/2 Hour before  || Cut | In- |  1-1/2 Hour before  |
+  | in  |ches |     Re-grinding     || in  |ches |     Re-grinding     |
+  | In- |     +------+------+-------++ In- |     +-------+------+------+
+  |ches |     | Soft |Medium| Hard  ||ches |     | Soft  |Medium| Hard |
+  |     |     |Steel |Steel |Steel  ||     |     | Cast  | Cast | Cast |
+  |     |     |      |      |       ||     |     | Iron  | Iron | Iron |
+  +-----+-----+------+------+-------++-----+-----+-------+------+------+
+  |     | 1/64| 476  | 238  | 108   ||     | 1/16| 122   | 61.2 | 35.7 |
+  |3/32 | 1/32| 325  | 162  |  73.8 ||3/32 | 1/8 |  86.4 | 43.2 | 25.2 |
+  |     | 1/16| 222  | 111  |  50.4 ||     | 3/16|  70.1 | 35.1 | 20.5 |
+  |     | 3/32| 177  |  88.4|  40.2 ++-----+-----+-------+------+------+
+  +-----+-----+------+------+-------++     | 1/32| 156   | 77.8 | 45.4 |
+  |     | 1/64| 420  | 210  |  95.5 || 1/8 | 1/16| 112   | 56.2 | 32.8 |
+  | 1/8 | 1/32| 286  | 143  |  65.0 ||     | 1/8 |  79.3 | 39.7 | 23.2 |
+  |     | 1/16| 195  |  97.6|  44.4 ||     | 3/16|  64.3 | 32.2 | 18.8 |
+  |     | 1/8 | 133  |  66.4|  30.2 ++-----+-----+-------+------+------+
+  +-----+-----+------+------+-------++     | 1/32| 137   | 68.6 | 40.1 |
+  |     | 1/64| 352  | 176  |  80.0 ||3/16 | 1/16|  99.4 | 49.7 | 29.0 |
+  |3/16 | 1/32| 240  | 120  |  54.5 ||     | 1/8 |  70.1 | 35.0 | 20.5 |
+  |     | 1/16| 164  |  82  |  37.3 ||     | 3/16|  56.8 | 28.4 | 16.6 |
+  |     | 1/8 | 112  |  56  |  25.5 ++-----+-----+-------+------+------+
+  +-----+-----+------+------+-------++     | 1/32| 126   | 62.9 | 36.7 |
+  |     | 1/64| 312  | 156  |  70.9 || 1/4 | 1/16|  90.8 | 45.4 | 26.5 |
+  | 1/4 | 1/32| 213  | 107  |  48.4 ||     | 1/8 |  64.1 | 32.0 | 18.7 |
+  |     | 1/16| 145  |  72.6|  33.0 ||     | 3/16|  52   | 26.0 | 15.2 |
+  |     | 3/32| 116  |  58.1|  26.4 ++-----+-----+-------+------+------+
+  +-----+-----+------+------+-------++     | 1/32| 111   | 55.4 | 32.3 |
+  |     | 1/64| 264  | 132  |  60.0 || 3/8 | 1/16|  80   | 40.0 | 23.4 |
+  | 3/8 | 1/32| 180  |  90.2|  41.0 ||     | 1/8 |  56.4 | 28.2 | 16.5 |
+  |     | 1/16| 122  |  61.1|  27.8 ++-----+-----+-------+------+------+
+  +-----+-----+------+------+-------++     | 1/32| 104   | 52.1 | 30.4 |
+  | 1/2 | 1/64| 237  | 118  |  53.8 || 1/2 | 1/16|  75.2 | 37.6 | 22.0 |
+  |     | 1/32| 162  |  80.8|  36.7 ||     | 1/8 |  43.1 | 21.6 | 12.6 |
+  +-----+-----+------+------+-------++-----+-----+-------+------+------+
+  |Steel--Standard 5/8-inch Tool    ||Cast Iron--Standard 5/8-inch Tool|
+  +-----+-----+------+------+-------++-----+-----+-------+------+------+
+  |Depth|Feed | Soft |Medium| Hard  ||Depth|Feed | Soft  |Medium| Hard |
+  | of  |     |Steel |Steel |Steel  || of  |     | Cast  | Cast | Cast |
+  | Cut |     |      |      |       || Cut |     | Iron  | Iron | Iron |
+  +-----+-----+------+------+-------++-----+-----+-------+------+------+
+  |     | 1/64| 548  | 274  | 125   ||     | 1/32| 160   | 80.0 | 46.6 |
+  |1/16 | 1/32| 358  | 179  |  81.6 ||3/32 | 1/16| 110   | 55.0 | 32.2 |
+  |     | 1/16| 235  | 117  |  53.3 ||     | 1/8 |  75.4 | 37.7 | 22.0 |
+  +-----+-----+------+------+-------++-----+-----+-------+------+------+
+  |     | 1/64| 467  | 234  | 106   ||     | 1/32| 148   | 74.0 | 43.3 |
+  |3/32 | 1/32| 306  | 153  |  69.5 || 1/8 | 1/16| 104   | 51.8 | 32.0 |
+  |     | 1/16| 200  | 100  |  45.5 ||     | 1/8 |  69.6 | 34.8 | 20.3 |
+  |     | 3/32| 156  |  78  |  35.5 ++-----+-----+-------+------+------+
+  +-----+-----+------+------+-------++     | 1/64| 183   | 91.6 | 68.0 |
+  |     | 1/64| 417  | 209  |  94.8 ||3/16 | 1/32| 135   | 67.5 | 39.4 |
+  | 1/8 | 1/32| 273  | 136  |  62.0 ||     | 1/16|  94   | 47.0 | 27.4 |
+  |     | 1/16| 179  |  89.3|  40.6 ||     | 1/8 |  64.3 | 32.2 | 18.8 |
+  |     | 3/32| 140  |  69.8|  31.7 ++-----+-----+-------+------+------+
+  +-----+-----+------+------+-------++     | 1/64| 171   | 85.7 | 50.1 |
+  |     | 1/64| 362  | 181  |  82.2 || 1/4 | 1/32| 126   | 63.2 | 36.9 |
+  |3/16 | 1/32| 236  | 118  |  53.8 ||     | 1/16|  87.8 | 43.9 | 25.6 |
+  |     | 1/16| 155  |  77.4|  35.2 ||     | 3/32|  70.4 | 35.2 | 20.6 |
+  +-----+-----+------+------+-------++-----+-----+-------+------+------+
+  | 1/4 | 1/64| 328  | 164  |  74.5 || 3/8 | 1/64| 156   | 77.8 | 45.4 |
+  |     | 1/32| 215  | 107  |  48.8 ||     | 1/32| 116   | 57.8 | 33.8 |
+  +-----+-----+------+------+-------++     | 1/16|  79.7 | 39.9 | 23.3 |
+  | 3/8 | 1/64| 286  | 143  |  65.0 ||     |     |       |      |      |
+  +-----+-----+------+------+-------++-----+-----+-------+------+------+
+
+[1] Cutting speeds for tools of a good grade of high-speed steel,
+properly ground and heat-treated.--From MACHINERY'S HANDBOOK.
+
+=Average Cutting Speeds for Turning.=--The cutting speed is governed
+principally by the hardness of the metal to be turned; the kind of steel
+of which the turning tool is made; the shape of the tool and its
+heat-treatment; the feed and depth of cut; whether or not a cooling
+lubricant is used on the tool; the power of the lathe and also its
+construction; hence it is impossible to give any definite rule for
+determining either the speed, feed, or depth of cut, because these must
+be varied to suit existing conditions. A general idea of the speeds used
+in ordinary machine shop practice may be obtained from the following
+figures:
+
+Ordinary machine steel is generally turned at a speed varying between 45
+and 65 feet per minute. For ordinary gray cast iron, the speed usually
+varies from 40 to 50 feet per minute; for annealed tool steel, from 25
+to 35 feet per minute; for soft yellow brass, from 150 to 200 feet per
+minute; for hard bronze, from 35 to 80 feet per minute, the speed
+depending upon the composition of the alloy. While these speeds
+correspond closely to general practice, they can be exceeded for many
+machining operations.
+
+The most economical speeds for a given feed and depth of cut, as
+determined by the experiments conducted by Mr. F. W. Taylor, are given
+in the table, "Cutting Speeds and Feeds for Turning Tools." The speeds
+given in this table represent results obtained with tools made of a good
+grade of high-speed steel properly heat-treated and correctly ground. It
+will be noted that the cutting speed is much slower for cast iron than
+for steel. Cast iron is cut with less pressure or resistance than soft
+steel, but the slower speed required for cast iron is probably due to
+the fact that the pressure of the chip is concentrated closer to the
+cutting edge, combined with the fact that cast iron wears the tool
+faster than steel. The speeds given are higher than those ordinarily
+used, and, in many cases, a slower rate would be necessary to prevent
+chattering or because of some other limiting condition.
+
+=Factors which limit the Cutting Speed.=--It is the durability of the
+turning tool or the length of time that it will turn effectively
+without grinding, that limits the cutting speed; and the hardness of the
+metal being turned combined with the quality of the tool are the two
+factors which largely govern the time that a tool can be used before
+grinding is necessary. The cutting speed for very soft steel or cast
+iron can be three or four times faster than the speed for hard steel or
+hard castings, but whether the material is hard or soft, the kind and
+quality of the tool used must also be considered, as the speed for a
+tool made of ordinary carbon steel will have to be much slower than for
+a tool made of modern "high-speed" steel.
+
+When the cutting speed is too high, even though high-speed steel is
+used, the point of the tool is softened to such an extent by the heat
+resulting from the pressure and friction of the chip, that the cutting
+edge is ruined in too short a time. On the other hand, when the speed is
+too slow, the heat generated is so slight as to have little effect and
+the tool point is dulled by being slowly worn or ground away by the
+action of the chip. While a tool operating at such a low speed can be
+used a comparatively long time without re-sharpening, this advantage is
+more than offset by the fact that too much time is required for removing
+a given amount of metal when the work is revolving so slowly.
+
+Generally speaking, the speed should be such that a fair amount of work
+can be done before the tool requires re-grinding. Evidently, it would
+not pay to grind a tool every few minutes in order to maintain a high
+cutting speed; neither would it be economical to use a very slow speed
+and waste considerable time in turning, just to save the few minutes
+required for grinding. For example, if a number of roughing cuts had to
+be taken over a heavy rod or shaft, time might be saved by running at
+such a speed that the tool would have to be sharpened (or be replaced by
+a tool previously sharpened) when it had traversed half-way across the
+work; that is, the time required for sharpening or changing the tool
+would be short as compared with the gain effected by the higher work
+speed. On the other hand, it might be more economical to run a little
+slower and take a continuous cut across the work with one tool.
+
+The experiments of Mr. Taylor led to the conclusion that, as a rule, it
+is not economical to use roughing tools at a speed so slow as to cause
+them to last more than 1-1/2 hour without being re-ground; hence the
+speeds given in the table previously referred to are based upon this
+length of time between grindings. Sometimes the work speed cannot be as
+high as the tool will permit, because of the chattering that often
+results when the lathe is old and not massive enough to absorb the
+vibrations, or when there is unnecessary play in the working parts. The
+shape of the tool used also affects the work speed, and as there are so
+many things to be considered, the proper cutting speed is best
+determined by experiment.
+
+=Rules for Calculating Cutting Speeds.=--The number of revolutions
+required to give any desired cutting speed can be found by multiplying
+the cutting speed, in feet per minute, by 12 and dividing the product by
+the circumference of the work in inches. Expressing this as a formula we
+have
+
+        _C_ x 12
+  _R_ = --------
+         [pi]_d_
+
+in which
+
+  _R_  = revolutions per minute;
+  _C_  = the cutting speed in feet per minute;
+  [pi] = 3.1416;
+  _d_  = the diameter in inches.
+
+For example if a cutting speed of 60 feet per minute is wanted and the
+diameter of the work is 5 inches, the required speed would be found as
+follows:
+
+         60 x 12
+  _R_ = ---------- = 46 revolutions per minute.
+        3.1416 x 5
+
+If the diameter is simply multiplied by 3 and the fractional part is
+omitted, the calculation can easily be made, and the result will be
+close enough for practical purposes. In case the cutting speed, for a
+given number of revolutions and diameter, is wanted, the following
+formula can be used:
+
+        _R_[pi]_d_
+  _C_ = ----------
+            12
+
+Machinists who operate lathes do not know, ordinarily, what cutting
+speeds, in feet per minute, are used for different classes of work, but
+are guided entirely by past experience.
+
+=Feed of Tool and Depth of Cut.=--The amount of feed and depth of cut
+also vary like the cutting speed, for different conditions. When turning
+soft machine steel the feed under ordinary conditions would vary between
+1/32 and 1/16 inch per revolution. For turning soft cast iron the feed
+might be increased to from 1/16 to 1/8 inch per revolution. These feeds
+apply to fairly deep roughing cuts. Coarser feeds might be used in many
+cases especially when turning large rigid parts in a powerful lathe. The
+depth of a roughing cut in machine steel might vary from 1/8 to 3/8
+inch, and in cast iron from 3/16 to 1/2 inch. These figures are intended
+simply to give the reader a general idea of feeds and cuts that are
+feasible under average conditions.
+
+Ordinarily coarser feeds and a greater depth of cut can be used for cast
+iron than for soft steel, because cast iron offers less resistance to
+turning, but in any case, with a given depth of cut, metal can be
+removed more quickly by using a coarse feed and the necessary slower
+speed, than by using a fine feed and the higher speed which is possible
+when the feed is reduced. When the turning operation is simply to remove
+metal, the feed should be coarse, and the cut as deep as practicable.
+Sometimes the cut must be comparatively light, either because the work
+is too fragile and springy to withstand the strain of a heavy cut, or
+the lathe has not sufficient pulling power. The difficulty with light
+slender work is that a heavy cut may cause the part being turned to bend
+under the strain, thus causing the tool to gouge in, which would
+probably result in spoiling the work. Steadyrests can often be used to
+prevent flexible parts from springing, as previously explained, but
+there are many kinds of light work to which the steadyrest cannot be
+applied to advantage.
+
+The amount of feed to use for a finishing cut might, properly, be either
+fine or coarse. Ordinarily, fine feeds are used for finishing steel,
+especially if the work is at all flexible, whereas finishing cuts in
+cast iron are often accompanied by a coarse feed. Fig. 15 illustrates
+the feeds that are often used when turning cast iron. The view to the
+left shows a deep roughing cut and the one to the right, a finishing
+cut. By using a broad flat cutting edge set parallel to the tool's
+travel, and a coarse feed for finishing, a smooth cut can be taken in a
+comparatively short time. Castings which are close to the finished size
+in the rough can often be finished to advantage by taking a single cut
+with a broad tool, provided the work is sufficiently rigid. It is not
+always practicable to use these broad tools and coarse feeds, as they
+sometimes cause chattering, and when used on steel, a broad tool tends
+to gouge or "dig in" unless the part being turned is rigid. Heavy steel
+parts, however, are sometimes finished in this way. The modern method of
+finishing many steel parts is to simply rough them out in a lathe to
+within, say, 1/32 inch of the required diameter and take the finishing
+cut in a cylindrical grinding machine.
+
+[Illustration: Fig. 15. Roughing Cut--Light Finishing Cut and Coarse
+Feed]
+
+=Effect of Lubricant on Cutting Speed.=--When turning iron or steel a
+higher cutting speed can be used, if a stream of soda water or other
+cooling lubricant falls upon the chip at the point where it is being
+removed by the tool. In fact, experiments have shown that the cutting
+speed, when using a large stream of cooling water and a high-speed steel
+tool, can be about 40 percent higher than when turning dry or without a
+cooling lubricant. For ordinary carbon steel tools, the gain was about
+25 per cent. The most satisfactory results were obtained from a stream
+falling at a rather slow velocity but in large volume. The gain in
+cutting speed, by the use of soda water or other suitable fluids, was
+found to be practically the same for all qualities of steel from the
+softest to the hardest.
+
+Cast iron is usually turned dry or without a cutting lubricant.
+Experiments, however, made to determine the effect of applying a heavy
+stream of cooling water to a tool turning cast iron, showed the
+following results: Cutting speed without water, 47 feet per minute;
+cutting speed with a heavy stream of water, nearly 54 feet per minute;
+increase in speed, 15 per cent. The dirt caused by mixing the fine
+cast-iron turnings with a cutting lubricant is an objectionable feature
+which, in the opinion of many, more than offsets the increase in cutting
+speed that might be obtained.
+
+Turret lathes and automatic turning machines are equipped with a pump
+and piping for supplying cooling lubricant to the tools in a continuous
+stream. Engine lathes used for general work, however, are rarely
+provided with such equipment and a lubricant, when used, is often
+supplied by a can mounted at the rear of the carriage, having a spout
+which extends above the tool. Owing to the inconvenience in using a
+lubricant on an engine lathe, steel, as well as cast iron, is often
+turned dry especially when the work is small and the cuts light and
+comparatively short.
+
+=Lubricants Used for Turning.=--A good grade of lard oil is an excellent
+lubricant for use when turning steel or wrought iron and it is
+extensively used on automatic screw machines, especially those which
+operate on comparatively small work. For some classes of work,
+especially when high-cutting speeds are used, lard oil is not as
+satisfactory as soda water or some of the commercial lubricants, because
+the oil is more sluggish and does not penetrate to the cutting point
+with sufficient rapidity. Many lubricants which are cheaper than oil are
+extensively used on "automatics" for general machining operations. These
+usually consist of a mixture of sal-soda (carbonate of soda) and water,
+to which is added some ingredient such as lard oil or soft soap to
+thicken or give body to the lubricant.
+
+A cheap lubricant for turning, milling, etc., and one that has been
+extensively used, is made in the following proportions: 1 pound of
+sal-soda, 1 quart of lard oil, 1 quart of soft soap, and enough water to
+make 10 or 12 gallons. This mixture is boiled for one-half hour,
+preferably by passing a steam coil through it. If the solution should
+have an objectionable odor, this can be eliminated by adding 2 pounds of
+unslaked lime. The soap and soda in this solution improve the
+lubricating quality and also prevent the surfaces from rusting. For
+turning and threading operations, plain milling, deep-hole drilling,
+etc., a mixture of equal parts of lard oil and paraffin oil will be
+found very satisfactory, the paraffin being added to lessen the expense.
+
+Brass or bronze is usually machined dry, although lard oil is sometimes
+used for automatic screw machine work. Babbitt metal is also worked dry,
+ordinarily, although kerosene or turpentine is sometimes used when
+boring or reaming. If babbitt is bored dry, balls of metal tend to form
+on the tool point and score the work. Milk is generally considered the
+best lubricant for machining copper. A mixture of lard oil and
+turpentine is also used for copper. For aluminum, the following
+lubricants can be used: Kerosene, a mixture of kerosene and gasoline,
+soap-water, or "aqualine" one part, water 20 parts.
+
+=Lard Oil as a Cutting Lubricant.=--After being used for a considerable
+time, lard oil seems to lose some of its good qualities as a cooling
+compound. There are several reasons for this: Some manufacturers use the
+same oil over and over again on different materials, such as brass,
+steel, etc. This is objectionable, for when lard oil has been used on
+brass it is practically impossible to get the fine dust separated from
+it in a centrifugal separator. When this impure oil is used on steel,
+especially where high-speed steels are employed, it does not give
+satisfactory results, owing to the fact that when the cutting tool
+becomes dull, the small brass particles "freeze" to the cutting tool and
+thus produce rough work. The best results are obtained from lard oil by
+keeping it thin, and by using it on the same materials--that is, not
+transferring the oil from a machine in which brass is being cut to one
+where it would be employed on steel. If the oil is always used on the
+same class of material, it will not lose any of its good qualities.
+
+Prime lard oil is nearly colorless, having a pale yellow or greenish
+tinge. The solidifying point and other characteristics of the oil depend
+upon the temperature at which it was expressed, winter-pressed lard oil
+containing less solid constituents of the lard than that expressed in
+warm weather. The specific gravity should not exceed 0.916; it is
+sometimes increased by adulterants, such as cotton-seed and maize oils.
+
+
+
+
+CHAPTER III
+
+TAPER TURNING--SPECIAL OPERATIONS--FITTING
+
+
+It is often necessary, in connection with lathe work, to turn parts
+tapering instead of straight or cylindrical. If the work is mounted
+between the centers, one method of turning a taper is to set the
+tailstock center out of alignment with the headstock center. When both
+of these centers are in line, the movement of the tool is parallel to
+the axis of the work and, consequently, a cylindrical surface is
+produced; but if the tailstock _h_{1}_ is set out of alignment, as shown
+in Fig. 1, the work will then be turned tapering as the tool is
+traversed from _a_ to _b_, because the axis _x--x_ is at an angle with
+the movement of the tool. Furthermore the amount of taper or the
+difference between the diameters at the ends for a given length, will
+depend on how much center _h_{1}_ is set over from the central position.
+
+[Illustration: Fig. 1. Taper Turning by the Offset-center Method]
+
+[Illustration: Fig. 2. Examples of Taper Work]
+
+The amount of taper is usually given on drawings in inches per foot, or
+the difference in the diameter at points twelve inches apart. For
+example, the taper of the piece shown at _A_, Fig. 2, is 1 inch per
+foot, as the length of the tapering surface is just twelve inches and
+the difference between the diameters at the ends is 1 inch. The conical
+roller shown at _B_ has a total length of 9 inches and a tapering
+surface 6 inches long, and in this case the taper per foot is also 1
+inch, there being a difference of 1/2 inch in a length of 6 inches or 1
+inch in twice that length. When the taper per foot is known, the amount
+that the tailstock center should be set over for turning that taper can
+easily be estimated, but it should be remembered that the setting
+obtained in this way is not absolutely correct, and is only intended to
+locate the center approximately. When a taper needs to be at all
+accurate, it is tested with a gage, or by other means, after taking a
+trial cut, as will be explained later, and the tailstock center is
+readjusted accordingly. There are also more accurate methods of setting
+the center, than by figuring the amount of offset, but as the latter is
+often convenient this will be referred to first.
+
+=Setting Tailstock Center for Taper Turning.=--Suppose the tailstock
+center is to be set for turning part _C_, Fig. 2, to a taper of
+approximately 1 inch per foot. In this case the center would simply be
+moved toward the front of the machine 1/2 inch, or one-half the required
+taper per foot, because the total length of the work happens to be just
+12 inches. This setting, however, would not be correct for all work
+requiring a taper of 1 inch per foot, as the adjustment depends not only
+on the _amount_ of the taper but on the _total length_ of the piece.
+
+[Illustration: Fig. 3. Detail View of Lathe Tailstock]
+
+For example, the taper roller _B_ has a taper of 1 inch per foot, but
+the center, in this case, would be offset less than one-half the taper
+per foot, because the total length is only 9 inches. For lengths longer
+or shorter than twelve inches, the taper per inch should be found first;
+this is then multiplied by the _total_ length of the work (not the
+length of the taper) which gives the taper for that length, and one-half
+this taper is the amount to set over the center. For example, the taper
+per inch of part _B_ equals 1 inch divided by 12 = 1/12 inch. The total
+length of 9 inches multiplied by 1/12 inch = 3/4 inch, and 1/2 of 3/4 =
+3/8, which is the distance that the tailstock center should be offset.
+In this example if the taper per foot were not known, and only the
+diameters of the large and small ends of the tapered part were given,
+the difference between these diameters should first be found (2-1/2-2 =
+1/2); this difference should then be divided by the length of the taper
+(1/2 / 6 = 1/12 inch) to obtain the taper per inch. The taper per inch
+times the _total_ length represents what the taper would be if it
+extended throughout the entire length, and one-half of this equals the
+offset, which is 3/8 inch.
+
+=Example of Taper Turning.=--As a practical example of taper turning let
+us assume that the piece A, Fig. 4, which has been centered and
+rough-turned as shown, is to be made into a taper plug, as indicated at
+_B_, to fit a ring gage as at _C_. If the required taper is 1-1/2 inch
+per foot and the total length is 8 inches, the tailstock center would be
+offset 1/2 inch.
+
+[Illustration: Fig. 4. Taper Plug and Gage]
+
+To adjust the tailstock, the nuts _N_ (Fig. 3) are first loosened and
+then the upper part _A_ is shifted sidewise by turning screw _S_. Scales
+are provided on some tailstocks for measuring the amount of this
+adjustment; if there is no scale, draw a line across the movable and
+stationary parts _A_ and _B_, when the tailstock is set for straight
+turning. The movement of the upper line in relation to the lower will
+then show the offset, which can be measured with a scale.
+
+When the adjustment has been made, nuts _N_ are tightened and the part
+to be turned, with a dog attached, is placed between the centers the
+same as for straight turning. The taper end is then reduced by turning,
+but before it is near the finished size, the work is removed and the
+taper tested by inserting it in the gage. If it is much out, this can be
+felt, as the end that is too small can be shaken in the hole. Suppose
+the plug did not taper enough and only the small end came into contact
+with the gage, as shown somewhat exaggerated at _D_; in that case the
+center would be shifted a little more towards the front, whereas if the
+taper were too steep, the adjustment would, of course, be in the
+opposite direction. A light cut would then be taken, to be followed by
+another test. If the plug should fit the gage so well that there was no
+perceptible shake, it could be tested more closely as follows: Draw
+three or four chalk lines along the tapering surface, place the work in
+the gage and turn it a few times. The chalk marks will then show whether
+the taper of the plug corresponds to that of the gage; for example, if
+the taper is too great, the marks will be rubbed out on the large end,
+but if the taper is correct, the lines throughout their length will be
+partially erased.
+
+[Illustration: Fig. 5. Setting Work for Taper Turning by use of Caliper
+Gage]
+
+Another and more accurate method of testing tapers is to apply a thin
+coat of Prussian-blue to one-half of the tapering surface, in a
+lengthwise direction. The work is then inserted in the hole or gage and
+turned to mark the bearing. If the taper is correct, the bearing marks
+will be evenly distributed, whereas if the taper is incorrect, they will
+appear at one end. Tapering pieces that have to be driven tightly into a
+hole, such as a piston-rod, can be tested by the location of the bearing
+marks produced by actual contact.
+
+After the taper is found to be correct, the plug is reduced in size
+until it just enters the gage as at _C_. The final cut should leave it
+slightly above the required size, so that a smooth surface can be
+obtained by filing. It should be mentioned that on work of this kind,
+especially if great accuracy is required, the final finish is often
+obtained by grinding in a regular grinding machine, instead of by
+filing. When this method is employed, a lathe is used merely to
+rough-turn the part close to size.
+
+[Illustration: Fig. 6. Side View showing Relative Positions of Gage and
+Work]
+
+When the amount that the tailstock center should be offset is determined
+by calculating, as in the foregoing example, it is usually necessary to
+make slight changes afterward, and the work should be tested before it
+is too near the finished size so that in case one or more trial cuts are
+necessary, there will be material enough to permit this. When there are
+a number of tapered pieces to be turned to the same taper, the
+adjustment of the tailstock center will have to be changed unless the
+total length of each piece and the depth of the center holes are the
+same in each case.
+
+=Setting the Tailstock Center with a Caliper Tool.=--Another method of
+setting the tailstock center for taper turning is illustrated in Fig. 5.
+The end of an engine piston-rod is to be made tapering as at A and to
+dimensions _a_, _b_, _c_ and _d_. It is first turned with the centers in
+line as at _B_. The end _d_ is reduced to diameter _b_ up to the
+beginning of the taper and it is then turned to diameter _a_ as far as
+the taper part _c_ extends. The tailstock center is next set over by
+guess and a caliper tool is clamped in the toolpost. This tool, a side
+view of which is shown in Fig. 6, has a pointer _p_ that is free to
+swing about pivot _r_, which should be set to about the same height as
+the center of the work. The tailstock center is adjusted until this
+pointer just touches the work when in the positions shown by the full
+and dotted lines at _C_, Fig. 5; that is, until the pointer makes
+contact at the beginning and end of the taper part. The travel of the
+carriage will then be parallel to a line _x--x_, representing the taper;
+consequently, if a tool is started at the small end, as shown by the
+dotted lines at _D_, with the nose just grazing the work, it will also
+just graze it when fed to the extreme left as shown. Of course, if the
+taper were at all steep, more than one cut would be taken.
+
+[Illustration: Fig. 7. Obtaining Tailstock Center Adjustment by use of
+Square]
+
+If these various operations are carefully performed, a fairly accurate
+taper can be produced. The straight end _d_ is reduced to size after the
+tail-center is set back to the central position. Some mechanics turn
+notches or grooves at the beginning and end of the tapering part, having
+diameters equal to the largest and smallest part of the taper; the work
+is then set by these grooves with a caliper tool. The advantage of the
+first method is that most of the metal is removed while the centers are
+in alignment.
+
+[Illustration: Fig. 8. Second Step in Adjusting Tailstock Center by use
+of Square]
+
+=Setting the Tailstock Center with a Square.=--Still another method of
+adjusting the tailstock for taper turning, which is very simple and
+eliminates all figuring, is as follows: The part to be made tapering is
+first turned cylindrical or straight for 3 or 4 inches of its length,
+after the ends have been properly centered and faced square. The work is
+then removed and the tailstock is shifted along the bed until the
+distance _a--b_ between the extreme points of the centers is exactly 1
+foot. The center is next offset a distance _b--c_ equal to one-half the
+required taper per foot, after which a parallel strip _D_, having true
+sides, is clamped in the toolpost. Part _D_ is then set at right angles
+to a line passing from one center point to the other. This can be done
+conveniently by holding a 1-foot square (preferably with a sliding head)
+against one side of _D_ and adjusting the latter in the toolpost until
+edge _E_ of the square blade is exactly in line with both center points.
+After part _D_ is set, it should be clamped carefully to prevent
+changing the position. The angle between the side of _D_ and an
+imaginary line which is perpendicular to axis _a--b_ is now equal to
+one-half the angle of the required taper.
+
+The axis of the part to be turned should be set parallel with line _E_,
+which can be done by setting the cylindrical surface which was
+previously finished, at right angles to the side of _D_. In order to do
+this the work is first placed between centers, the tailstock being
+shifted along the bed if necessary; the tail-center is then adjusted
+laterally until the finished cylindrical surface is square with the side
+of _D_. A small try-square can be used for testing the position of the
+work, as indicated in Fig. 8. If the length of the work is less than 1
+foot, it will be necessary to move the center toward the rear of the
+machine, and if the length is greater than 1 foot, the adjustment is, of
+course, in the opposite direction.
+
+[Illustration: Fig. 9. A Lathe Taper Attachment]
+
+=The Taper Attachment.=--Turning tapers by setting over the tailstock
+center has some objectionable features. When the lathe centers are not
+in alignment, as when set for taper turning, they bear unevenly in the
+work centers because the axis of the work is at an angle with them; this
+causes the work centers to wear unevenly and results in inaccuracy.
+Furthermore, the adjustment of the tailstock center must be changed when
+turning duplicate tapers, unless the length of each piece and the depth
+of the center holes are the same. To overcome these objections, many
+modern lathes are equipped with a special device for turning tapers,
+known as a taper attachment, which permits the lathe centers to be kept
+in alignment, as for cylindrical turning, and enables more accurate work
+to be done.
+
+[Illustration: Fig. 10. Sectional View of Taper Attachment]
+
+Taper attachments, like lathes, vary some in their construction, but all
+operate on the same principle. An improved form of taper attachment is
+illustrated in Figs. 9 and 10. Fig. 9 shows a plan view of a lathe
+carriage with an attachment fitted to it, and Fig. 10 a sectional view.
+This attachment has an arm _A_ on which is mounted a slide _S_ that can
+be turned about a central pivot by adjusting screw _D_. The arm _A_ is
+supported by, and is free to slide on, a bracket _B_ (see also sectional
+view) that is fastened to the carriage, and on one end of the arm there
+is a clamp _C_ that is attached to the lathe bed when turning tapers. On
+the slide _S_ there is a shoe _F_ that is connected to bar _E_ which
+passes beneath the toolslide. The rear end of the cross-feed screw is
+connected to this bar, and the latter is clamped to the toolslide when
+the attachment is in use.
+
+When a taper is to be turned, the carriage is moved opposite the taper
+part and clamp _C_ is fastened to the bed; this holds arm _A_ and slide
+_S_ stationary so that the carriage, with bracket _B_ and shoe _F_, can
+be moved with relation to the slide. If this slide _S_ is set at an
+angle, as shown, the shoe as it moves along causes the toolslide and
+tool to move in or out, but if the slide is set parallel to the carriage
+travel, the toolslide remains stationary. Now if the tool, as it feeds
+lengthwise of the work, is also gradually moved crosswise, it will turn
+a taper, and as this crosswise movement is caused by the angularity of
+slide _S_, different tapers are obtained by setting the slide to
+different positions.
+
+By means of a graduated scale _G_ at the end of slide _S_, the taper
+that will be obtained for any angular position of the slide is shown. On
+some attachments there are two sets of graduations, one giving the taper
+in inches per foot and the other in degrees. While tapers are ordinarily
+given in inches per foot on drawings, sometimes the taper is given in
+degrees instead. The attachment is set for turning tapers by adjusting
+slide _S_ until pointer _p_ is opposite the division or fractional part
+of a division representing the taper. The whole divisions on the scale
+represent taper in inches per foot, and by means of the sub-divisions,
+the slide can be set for turning fractional parts of an inch per foot.
+When slide _S_ is properly set, it is clamped to arm _A_ by the nuts
+_N_. Bar _E_ is also clamped to the toolslide by bolt _H_, as previously
+stated. The attachment is disconnected for straight turning by simply
+loosening clamp _C_ and the bolt _H_.
+
+=Application of Taper Attachment.=--Practical examples of lathe work,
+which illustrate the use of the taper attachment, are shown in Figs, 11
+and 12. Fig. 11 shows how a taper hole is bored in an engine
+piston-head, preparatory to reaming. The casting must be held either in
+a chuck _C_ or on a faceplate if too large for the chuck. The side of
+the casting (after it has been "chucked") should run true, and also the
+circumference, unless the cored hole for the rod is considerably out of
+center, in which case the work should be shifted to divide the error.
+The side of the casting for a short space around the hole is faced true
+with a round nose turning tool, after which the rough-cored hole is
+bored with an ordinary boring tool _t_, and then it is finished with a
+reamer to exactly the right size and taper.
+
+This particular taper attachment is set to whatever taper is given on
+the drawing, by loosening nuts _N_ and turning slide _S_ until pointer
+_P_ is opposite that division on the scale which represents the taper.
+The attachment is then ready, after bolt _H_ and nuts _N_ are tightened,
+and clamp _C_ is fastened to the lathe bed. The hole is bored just as
+though it were straight, and as the carriage advances, the tool is
+gradually moved inward by the attachment. If the lathe did not have a
+taper attachment, the taper hole could be bored by using the compound
+rest.
+
+[Illustration: Fig. 11. Lathe with Taper Attachment arranged for Boring
+Taper Hole in Engine Piston]
+
+The hole should be bored slightly less than the finish size to allow for
+reaming. When a reamer is used in the lathe, the outer end is supported
+by the tailstock center and should have a deep center-hole. The lathe is
+run very slowly for reaming and the reamer is fed into the work by
+feeding out the tailstock spindle. The reamer can be kept from
+revolving, either by attaching a heavy dog to the end or, if the end is
+squared, by the use of a wrench long enough to rest against the lathe
+carriage. A common method is to clamp a dog to the reamer shank, and
+then place the tool-rest beneath it to prevent rotation. If the shank
+of a tool is clamped to the toolpost so that the dog rests against it,
+the reamer will be prevented from slipping off the center as it tends to
+do; with this arrangement, the carriage is gradually moved along as the
+tailstock spindle is fed outward. Some reamers are provided with
+stop-collars which come against the finished side of the casting when
+the hole has been reamed to size.
+
+After the reaming operation, the casting is removed from the chuck and a
+taper mandrel is driven into the hole for turning the outside of the
+piston. This mandrel should run true on its centers, as otherwise the
+outside surface of the piston will not be true with the bored hole. The
+driving dog, especially for large work of this kind, should be heavy and
+stiff, because light flexible clamps or dogs vibrate and frequently
+cause chattering. For such heavy work it is also preferable to drive at
+two points on opposite sides of the faceplate, but the driving pins
+should be carefully adjusted to secure a uniform bearing on both sides.
+
+The foregoing method of machining a piston is one that would ordinarily
+be followed when using a standard engine lathe, and it would, perhaps,
+be as economical as any if only one piston were being made; but where
+such work is done in large quantities, time could be saved by proceeding
+in a different way. For example, the boring and reaming operation could
+be performed much faster in a turret lathe, which is a type designed for
+just such work, but a turret lathe cannot be used for as great a variety
+of turning operations as a lathe of the regular type. There are also
+many other classes of work that can be turned more quickly in special
+types of machines, but as more or less time is required for arranging
+these special machines and often special tools have to be made, the
+ordinary lathe is frequently indispensable when only a few parts are
+needed; in addition, it is better adapted to some turning operations
+than any other machine.
+
+Fig. 12 illustrates how a taper attachment would be used for turning the
+taper fitting for the crosshead end of an engine piston-rod. Even though
+this taper corresponds to the taper of the hole in the piston, slide _S_
+would have to be reset to the corresponding division on the opposite
+side of the central zero mark, because the taper of the hole decreased
+in size during the boring operation, whereas the rod is smallest at the
+beginning of the cut, so that the tool must move outward rather than
+inward as it advances. The taper part is turned practically the same as
+a cylindrical part; that is, the power feed is used and, as the carriage
+moves along the bed, the tool is gradually moved outward by the taper
+attachment.
+
+[Illustration: Fig. 12. Taper Attachment Set for Turning Taper End of
+Piston-rod]
+
+If the rod is being fitted directly to the crosshead (as is usually the
+case), the approximate size of the small end of the taper could be
+determined by calipering, the calipers being set to the size of the hole
+at a distance from the shoulder or face side of the crosshead, equal to
+the length of the taper fitting on the rod. If the crosshead were bored
+originally to fit a standard plug gage, the taper on the rod could be
+turned with reference to this gage, but, whatever the method, the taper
+should be tested before turning too close to the finished size. The test
+is made by removing the rod from the lathe and driving it tightly into
+the crosshead. This shows how near the taper is to size, and when the
+rod is driven out, the bearing marks show whether the taper is exactly
+right or not. If the rod could be driven in until the shoulder is, say,
+1/8 inch from the crosshead face, it would then be near enough to finish
+to size by filing. When filing, the lathe is run much faster than for
+turning, and most of the filing should be done where the bearing marks
+are the heaviest, to distribute the bearing throughout the length of the
+taper. Care should be taken when driving the rod in or out, to protect
+the center-holes in the ends by using a "soft" hammer or holding a piece
+of soft metal against the driving end.
+
+[Illustration: Fig. 13. Tool Point should be in same Horizontal Plane as
+Axis of Work for Taper Turning]
+
+After the crosshead end is finished, the rod is reversed in the lathe
+for turning the piston end. The dog is clamped to the finished end,
+preferably over a piece of sheet copper to prevent the surface from
+being marred. When turning this end, either the piston reamer or the
+finished hole in the piston can be calipered. The size and angle of the
+taper are tested by driving the rod into the piston, and the end should
+be fitted so that by driving tightly, the shoulder will just come up
+against the finished face of the piston. When the taper is finished, the
+attachment is disengaged and a finishing cut is taken over the body of
+the rod, unless it is to be finished by grinding, which is the modern
+and most economical method.
+
+=Height of Tool when Turning Tapers.=--The cutting edge of the tool,
+when turning tapers, should be at the same height as the center or axis
+of the work, whether an attachment is used or not. The importance of
+this will be apparent by referring to Fig. 13. To turn the taper shown,
+the tool _T_ would be moved back a distance _x_ (assuming that an
+attachment is used) while traversing the length _l_. As an illustration,
+if the tool could be placed as high as point _a_, the setting of the
+attachment remaining as before, the tool would again move back a
+distance _x_, while traversing a distance _l_, but the large end would
+be under-sized (as shown by the dotted line) if the diameters of the
+small ends were the same in each case. Of course, if the tool point were
+only slightly above or below the center, the resulting error would also
+be small. The tool can easily be set central by comparing the height of
+the cutting edge at the point of the tool with one of the lathe centers
+before placing the work in the lathe.
+
+[Illustration: Fig. 14. Plan View showing Method of Turning a Taper with
+the Compound Rest]
+
+=Taper Turning with the Compound Rest.=--The amount of taper that can be
+turned by setting over the tailstock center and by the taper attachment
+is limited, as the centers can only be offset a certain distance, and
+the slide _S_ (Fig. 9) of the attachment cannot be swiveled beyond a
+certain position. For steep tapers, the compound rest _E_ is swiveled to
+the required angle and used as indicated in Fig. 14, which shows a plan
+view of a rest set for turning the valve _V_. This compound rest is an
+upper slide mounted on the lower or main cross-slide _D_, and it can be
+turned to any angular position so that the tool, which ordinarily is
+moved either lengthwise or crosswise of the bed, can be fed at an angle.
+The base of the compound rest is graduated in degrees and the position
+of these graduations shows to what angle the upper slide is set. Suppose
+the seat of valve _V_ is to be turned to an angle of 45 degrees with the
+axis or center, as shown on the drawing at _A_, Fig. 15. To set the
+compound rest, nuts _n_ on either side, which hold it rigidly to the
+lower slide, are first loosened and the slide is then turned until the
+45-degree graduation is exactly opposite the zero line; the slide is
+then tightened in this position. A cut is next taken across the valve by
+operating handle _w_ and feeding the tool in the direction of the arrow.
+
+[Illustration: Fig. 15. Example of Taper Work Turned by using Compound
+Rest]
+
+In this particular instance the compound rest is set to the same angle
+given on the drawing, but this is not always the case. If the draftsman
+had given the included angle of 90 degrees, as shown at _B_, which would
+be another way of expressing it, the setting of the compound rest would,
+of course, be the same as before, or to 45 degrees, but the number of
+degrees marked on the drawing does not correspond with the angle to
+which the rest must be set. As another illustration, suppose the valve
+were to be turned to an angle of 30 degrees with the axis as shown at
+_C_. In this case the compound rest would not be set to 30 degrees but
+to 60 degrees, because in order to turn the work to an angle of 30
+degrees, the rest must be 60 degrees from its zero position, as shown.
+From this it will be seen that the number of degrees marked on the
+drawing does not necessarily correspond to the angle to which the rest
+must be set, as the graduations on the rest show the number of degrees
+that it is moved from its zero position, which corresponds to the line
+_a--b_. The angle to which the compound rest should be set can be found,
+when the drawing is marked as at _A_ or _C_, by subtracting the angle
+given from 90 degrees. When the included angle is given, as at _B_,
+subtract one-half the included angle from 90 degrees to obtain the
+required setting. Of course, when using a compound rest, the lathe
+centers are set in line as for straight turning, as otherwise the angle
+will be incorrect.
+
+Rules for Figuring Tapers
+
++---------------------+---------------------+--------------------------+
+|      Given          |     To Find         |         Rule             |
++---------------------+---------------------+--------------------------+
+|The taper per foot.  |The taper per inch.  |Divide the taper per foot |
+|                     |                     |  by 12.                  |
+|                     |                     |                          |
+|The taper per inch.  |The taper per foot.  |Multiply the taper per    |
+|                     |                     |  inch by 12.             |
+|                     |                     |                          |
+|End diameters and    |The taper per foot.  |Subtract small diameter   |
+|  length of taper in |                     |  from large; divide by   |
+|  inches.            |                     |  length of taper, and    |
+|                     |                     |  multiply quotient by 12.|
+|                     |                     |                          |
+|Large diameter and   |Diameter at small    |Divide taper per foot by  |
+|  length of taper in |  end in inches.     |  12; multiply by length  |
+|  inches and taper   |                     |  of length of taper, and |
+|  per foot.          |                     |  subtract result from    |
+|                     |                     |  large diameter.         |
+|                     |                     |                          |
+|Small diameter and   |Diameter at large    |Divide taper per foot by  |
+|  length of taper in |  end in inches.     |  12; multiply by length  |
+|  inches, and taper  |                     |  of taper, and add result|
+|  per foot.          |                     |  to small diameter.      |
+|                     |                     |                          |
+|The taper per foot   |Distance between     | Subtract small diameter  |
+|  and two diameters  |  two given diameters|   from large; divide re- |
+|  in inches.         |  in inches.         |   mainder by taper per   |
+|                     |                     |   foot, and multiply     |
+|                     |                     |   quotient by 12.        |
+|                     |                     |                          |
+|The taper per foot.  |Amount of taper in   | Divide taper per foot by |
+|                     |  a certain length   |   12; multiply by given  |
+|                     |  given in inches.   |   length of tapered part.|
++---------------------+---------------------+--------------------------+
+
+=Accurate Measurement of Angles and Tapers.=--When great accuracy is
+required in the measurement of angles, or when originating tapers,
+disks are commonly used. The principle of the disk method of taper
+measurement is that if two disks of unequal diameters are placed either
+in contact or a certain distance apart, lines tangent to their
+peripheries will represent an angle or taper, the degree of which
+depends upon the diameters of the two disks and the distance between
+them. The gage shown in Fig. 16, which is a form commonly used for
+originating tapers or measuring angles accurately, is set by means of
+disks. This gage consists of two adjustable straight-edges _A_ and
+_A_{1}_, which are in contact with disks _B_ and _B_{1}_. The angle
+[alpha] or the taper between the straight-edges depends, of course, upon
+the diameters of the disks and the center distance _C_, and as these
+three dimensions can be measured accurately, it is possible to set the
+gage to a given angle within very close limits. Moreover, if a record of
+the three dimensions is kept, the exact setting of the gage can be
+reproduced quickly at any time. The following rules may be used for
+adjusting a gage of this type.
+
+[Illustration: Fig. 16. Disk Gage for Accurate Measurement of Angles and
+Tapers]
+
+=To Find Center Distance for a Given Taper.=--When the taper, in inches
+per foot, is given, to determine center distance _C_. _Rule:_ Divide the
+taper by 24 and find the angle corresponding to the quotient in a table
+of tangents; then find the sine corresponding to this angle and divide
+the difference between the disk diameters by twice the sine.
+
+_Example:_ Gage is to be set to 3/4 inch per foot, and disk diameters
+are 1.25 and 1.5 inch, respectively. Find the required center distance
+for the disks.
+
+  0.75
+  ---- = 0.03125.
+   24
+
+The angle whose tangent is 0.03125 equals 1 degree 47.4 minutes; sin 1 deg.
+47.4' = 0.03123; 1.50 - 1.25 = 0.25 inch;
+
+  0.25
+  ----------- = 4.002 inches = center distance C.
+  2 x 0.03123
+
+=To Find Center Distance for a Given Angle.=--When straight-edges must
+be set to a given angle [alpha], to determine center distance _C_
+between disks of known diameter. _Rule:_ Find the sine of half the angle
+[alpha] in a table of sines; divide the difference between the disk
+diameters by double this sine.
+
+_Example:_ If an angle [alpha] of 20 degrees is required, and the disks
+are 1 and 3 inches in diameter, respectively, find the required center
+distance _C_.
+
+   20
+  ---- = 10 degrees; sin 10 deg. = 0.17365;
+    2
+
+     3 - 1
+  ----------- = 5.759 inches = center distance _C_.
+  2 x 0.17365
+
+=To Find Angle for Given Taper per Foot.=--When the taper in inches per
+foot is known, and the corresponding angle [alpha] is required. _Rule:_
+Divide the taper in inches per foot by 24; find the angle corresponding
+to the quotient, in a table of tangents, and double this angle.
+
+_Example:_ What angle [alpha] is equivalent to a taper of 1-1/2 inch per
+foot?
+
+  1.5
+  --- = 0.0625.
+  24
+
+The angle whose tangent is 0.0625 equals 3 degrees 35 minutes, nearly;
+then, 3 deg. 35 min. x 2 = 7 deg. 10 min.
+
+=To Find Angle for Given Disk Dimensions.=--When the diameters of the
+large and small disks and the center distance are given, to determine
+the angle [alpha]. _Rule:_ Divide the difference between the disk
+diameters by twice the center distance; find the angle corresponding to
+the quotient, in a table of sines, and double the angle.
+
+_Example:_ If the disk diameters are 1 and 1.5 inch, respectively, and
+the center distance is 5 inches, find the included angle [alpha].
+
+  1.5 - 1
+  -------  = 0.05.
+   2 x 5
+
+The angle whose sine is 0.05 equals 2 degrees 52 minutes; then, 2 deg.
+52 min. x 2 = 5 deg. 44 min. = angle [alpha].
+
+[Illustration: Fig. 17. Setting Center Mark in Line with Axis of Lathe
+Spindle by use of Test Indicator]
+
+[Illustration: Fig. 18. Jig-plate with Buttons attached, ready for
+Boring]
+
+=Use of the Center Indicator.--=The center test indicator is used for
+setting a center-punch mark, the position of which corresponds with the
+center or axis of the hole to be bored, in alignment with the axis of
+the lathe spindle. To illustrate, if two holes are to be bored, say 5
+inches apart, small punch marks having that center-to-center distance
+would be laid out as accurately as possible. One of these marks would
+then be set central with the lathe spindle by using a center test
+indicator as shown in Fig. 17. This indicator has a pointer _A_ the end
+of which is conical and enters the punch mark. The pointer is held by
+shank _B_ which is fastened in the toolpost. The joint _C_ by means of
+which the pointer is held to the shank is universal; that is, it allows
+the pointer to move in any direction. Now when the part being tested is
+rotated by running the lathe, if the center-punch mark is not in line
+with the axes of the lathe spindle, obviously the outer end of pointer
+_A_ will vibrate, and as joint _C_ is quite close to the inner end, a
+very slight error in the location of the center-punch mark will cause a
+perceptible movement of the outer end, as indicated by the dotted lines.
+When the work has been adjusted until the pointer remains practically
+stationary, the punch mark is central, and the hole is bored. The other
+center-punch mark is then set in the same way for boring the second
+hole. The accuracy of this method depends, of course, upon the location
+of the center-punch marks. A still more accurate way of setting parts
+for boring holes to a given center-to-center distance is described in
+the following:
+
+=Locating Work by the Button Method.=--Among the different methods
+employed by machinists and toolmakers for accurately locating work such
+as jigs, etc., on the faceplate of a lathe, the one most commonly used
+is known as the button method. This scheme is so named because
+cylindrical bushings or buttons are attached to the work in positions
+corresponding to the holes to be bored, after which they are used in
+locating the work. These buttons, which are ordinarily about 1/2 inch in
+diameter, are ground and lapped to the same size and the ends squared.
+The diameter should, preferably, be such that the radius can be
+determined easily, and the hole through the center should be about 1/8
+inch larger than the retaining screw, so that the button can be shifted.
+
+As an illustration of the practical application of the button method, we
+shall consider, briefly, the way the holes would be accurately machined
+in the jig-plate in Fig. 18. First the centers of the seven holes should
+be laid off approximately correct by the usual methods, after which
+small holes should be drilled and tapped for the clamping screws _S_.
+After the buttons _B_ are clamped lightly in place, they are all set in
+correct relation with each other and with the jig-plate. The proper
+location of the buttons is very important as their positions largely
+determine the accuracy of the work. A definite method of procedure that
+would be applicable in all cases cannot, of course, be given, as the
+nature of the work as well as the tools available make it necessary to
+employ different methods.
+
+[Illustration: Fig. 19. Setting a Button True Preparatory to Boring, by
+use of Test Indicator]
+
+In this particular case, the three buttons _a_, _b_ and _c_ should be
+set first, beginning with the one in the center. As this central hole
+must be 2.30 and 2.65 inches from the finished sides _A_ and _A_{1}_,
+respectively, the work is first placed on an accurate surface-plate as
+shown; by resting it first on one of these sides and then on the other,
+and measuring with a vernier height gage, the central button can be
+accurately set. The buttons _a_ and _c_ are also set to the correct
+height from side _A_{1}_ by using the height gage, and in proper
+relation to the central button by using a micrometer or a vernier
+caliper and measuring the over-all dimension _x_. When measuring in this
+way, the diameter of one button would be deducted to obtain the correct
+center-to-center distance. After buttons _a_, _b_ and _c_ are set
+equidistant from side A_{1} and in proper relation to each other, the
+remaining buttons should be set radially from the central button _b_ and
+the right distance apart. By having two micrometers or gages, one set
+for the radial dimension _x_ and the other for the chordal distance _y_,
+the work may be done in a comparatively short time.
+
+[Illustration: Fig. 20. Testing Concentricity of Button with Dial Gage]
+
+After the buttons have been tightened, all measurements should be
+carefully checked; the work is then mounted on the faceplate of the
+lathe, and one of the buttons, say _b_, is set true by the use of a test
+indicator as shown in Fig. 19. When the end of this indicator (which is
+one of a number of types on the market) is brought into contact with the
+revolving button, the vibration of the pointer _I_ shows how much the
+button runs out of true. When the pointer remains practically
+stationary, thus showing that the button runs true, the latter should be
+removed. The hole is then drilled nearly to the required size, after
+which it is bored to the finish diameter. In a similar manner the other
+buttons are indicated and the holes bored, one at a time. It is evident
+that if each button is correctly located and set perfectly true in the
+lathe, the various holes will be located at the required
+center-to-center dimensions within very close limits.
+
+[Illustration: Fig. 21. Drilling a Bushing Hole]
+
+Fig. 20 shows how one of the buttons attached to a plate in which three
+holes are to be bored is set true or concentric. The particular
+indicator illustrated is of the dial type, any error in the location of
+the button being shown by a hand over a dial having graduations
+representing thousandths of an inch. Fig. 21 shows how the hole is
+drilled after the button is removed. It will be noted that the drill is
+held in a chuck, the taper shank of which fits into the tailstock
+spindle, this being the method of holding small drills. After drilling,
+the hole is bored as shown in Fig. 22. The boring tool should have a
+keen edge to avoid springing, and if the work when clamped in position,
+throws the faceplate out of balance, it is advisable to restore the
+balance, before boring, by the use of a counter-weight, because the
+lathe can be rotated quite rapidly when boring such a small hole.
+
+[Illustration: Fig. 22. Boring a Bushing Hole]
+
+When doing precision work of this kind, the degree of accuracy will
+depend upon the instruments used, the judgment and skill of the workman
+and the care exercised. A good general rule to follow when locating
+bushings or buttons is to use the method which is the most direct and
+which requires the least number of measurements. As an illustration of
+how errors may accumulate, let us assume that seven holes are to be
+bored in the jig-plate shown in Fig. 23, so that they are the same
+distance from each other and in a straight line. The buttons may be
+brought into alignment by the use of a straight-edge, and to simplify
+matters, it will be taken for granted that they have been ground and
+lapped to the same size. If the diameter of the buttons is first
+determined by measuring with a micrometer, and then this diameter is
+deducted from the center distance _x_, the difference will be the
+distance _y_ between adjacent buttons. Now if a temporary gage is made
+to length _y_, all the buttons can be set practically the same distance
+apart, the error between any two adjacent ones being very slight. If,
+however, the total length _z_ over the end buttons is measured by some
+accurate means, the chances are that this distance will not equal six
+times dimension _x_ plus the diameter of one button, as it should,
+because even a very slight error in the gage for distance _y_ would
+gradually accumulate as each button was set. If a micrometer were
+available that would span two of the buttons, the measurements could be
+taken direct and greater accuracy would doubtless be obtained. On work
+of this kind where there are a number of holes that need to have
+accurate over-all dimensions, the long measurements should first be
+taken when setting the buttons, providing, of course, there are proper
+facilities for so doing, and then the short ones. For example, the end
+buttons in this case should first be set, then the central one and
+finally those for the sub-divisions.
+
+[Illustration: Fig. 23. Example of Work illustrating Accumulation of
+Errors]
+
+=Eccentric Turning.=--When one cylindrical surface must be turned
+eccentric to another, as when turning the eccentric of a steam engine,
+an arbor having two sets of centers is commonly used, as shown in Fig.
+24. The distance _x_ between the centers must equal one-half the total
+"throw" or stroke of the eccentric. The hub of the eccentric is turned
+upon the centers _a--a_, and the tongued eccentric surface, upon the
+offset centers, as indicated by the illustration. Sometimes eccentrics
+are turned while held upon special fixtures attached to the faceplate.
+
+[Illustration: Fig. 24. Special Arbor for Turning Eccentrics]
+
+When making an eccentric arbor, the offset center in each end should be
+laid out upon radial lines which can be drawn across the arbor ends by
+means of a surface gage. Each center is then drilled and reamed to the
+same radius _x_ as near as possible. The uniformity of the distance _x_
+at each end is then tested by placing the mandrel upon the offset
+centers and rotating it, by hand, with a dial indicator in contact at
+first one end and then the other. The amount of offset can also be
+tested either by measuring from the point of a tool held in the
+toolpost, or by setting the tool to just graze the mandrel at extreme
+inner and outer positions, and noting the movement of the cross-slide by
+referring to the dial gage of the cross-feed screw.
+
+[Illustration: Fig. 25. Turning an Engine Crank-pin in an Ordinary
+Lathe]
+
+=Turning a Crankshaft in a Lathe.=--Another example of eccentric turning
+is shown in Fig. 25. The operation is that of turning the crank-pin of
+an engine crankshaft, in an ordinary lathe. The main shaft is first
+rough-turned while the forging revolves upon its centers _C_ and _C_{1}_
+and the ends are turned to fit closely the center-arms _A_ and _A_{1}_.
+After the sides _B_ and _B_{1}_ of the crank webs have been rough-faced,
+the center-arms are attached to the ends of the shaft as shown in the
+illustration. These arms have centers at _D_ and _D_{1}_ (located at the
+required crank radius) which should be aligned with the rough pin, when
+attaching the arms, and it is advisable to insert braces _E_ between the
+arms and crank to take the thrust of the lathe centers. With the forging
+supported in this way, the crank-pin and inner sides of the webs are
+turned and faced, the work revolving about the axis of the pin. The
+turning tools must extend beyond the tool-holder far enough to allow the
+crank to clear as it swings around. Owing to this overhang, the tool
+should be as heavy as possible to make it rigid and it is necessary to
+take comparatively light cuts and proceed rather cautiously. After
+finishing the crank-pin and inside of the crank, the center-arms are
+removed and the main body of the shaft and the sides _B_ and _B_{1}_ are
+finished. This method of turning crankshafts is often used in general
+repair shops, etc., especially where new shafts do not have to be turned
+very often. It is slow and inefficient, however, and where crankshafts
+are frequently turned, special machines or attachments are used.
+
+[Illustration: Fig. 26. LeBlond Lathe with Special Equipment for
+Crankshaft Turning]
+
+=Special Crankshaft Lathe.=--A lathe having special equipment for
+rough-turning gas engine crankshaft pins is shown in Fig. 26. This
+lathe is a heavy-duty type built by the R. K. LeBlond Machine Tool Co.
+It is equipped with special adjustable headstock and tailstock fixtures
+designed to take crankshafts having strokes up to about 6 inches. The
+tools are held in a three-tool turret type of toolpost and there are
+individual cross-stops for each tool. This lathe also has a roller
+steadyrest for supporting the crankshaft; automatic stops for the
+longitudinal feed, and a pump for supplying cutting lubricant. The
+headstock fixture is carried on a faceplate mounted on the spindle and
+so arranged as to be adjustable for cranks of different throw. When the
+proper adjustment for a given throw has been made, the slide is secured
+by four T-bolts. A graduated scale and adjusting screw permit of
+accurate adjustments.
+
+The revolving fixture is accurately indexed for locating different
+crank-pins in line with the lathe centers, by a hardened steel plunger
+in the slide which engages with hardened bushings in the fixture. The
+index is so divided that the fixture may be rotated 120 or 180 degrees,
+making it adjustable for 2-, 4- and 6-throw cranks. After indexing, the
+fixture is clamped by two T-bolts which engage a circular T-slot. The
+revolving fixture is equipped with removable split bushings which can be
+replaced to fit the line bearings of different sized crankshafts. The
+work is driven by a V-shaped dovetail piece having a hand-nut
+adjustment, which also centers the pin by the cheek or web. The crank is
+held in position by a hinged clamp on the fixture. The tailstock fixture
+is also adjustable and it is mounted on a spindle which revolves in a
+bushing in the tailstock barrel. The adjustment is obtained in the same
+manner as on the headstock fixture, and removable split bushings as well
+as a hinged clamp are also employed.
+
+The method of chucking a four-throw crank is as follows: The two
+fixtures are brought into alignment by two locking pins. One of these is
+located in the head and enters a bushing in the large faceplate and the
+other is in the tailstock and engages the tailstock fixture. The
+crankshaft is delivered to the machine with the line bearings
+rough-turned and it is clamped by the hinged clamp previously referred
+to and centered by the V-shaped driver. The locking pins for both
+fixtures are then withdrawn and the machine is ready to turn two of the
+pins. After these have been machined, the fixtures are again aligned by
+the locking pins, the two T-bolts of the headstock fixture and the
+hinged clamp at the tailstock are released, the indexing plunger is
+withdrawn and the headstock fixture and crank are turned 180 degrees or
+until the index plunger drops into place. The crank is then clamped at
+the tailstock end and the revolving fixture is secured by the two
+T-bolts previously referred to. After the locking pins are withdrawn,
+the lathe is ready to turn the two opposite pins.
+
+[Illustration: Fig. 27. Diagrams showing Arrangements of Tools on
+LeBlond Lathe]
+
+=Operation of Special Crankshaft Lathe.=--The total equipment of this
+machine (see Fig. 27) is carried on a three-tool turret tool-block. The
+method of turning a crankshaft is as follows: A round-nosed turning tool
+is first fed into a cross stop as illustrated in the plan view at _A_,
+which gives the proper diameter. The feed is then engaged and the tool
+feeds across the pin until the automatic stop lever engages the first
+stop, which throws out the feed automatically. The carriage is then
+moved against a positive stop by means of the handwheel. The roller
+back-rest is next adjusted against the work by the cross-feed handwheel
+operating through a telescopic screw, and the filleting tools are
+brought into position as at _B_. These are run in against a stop,
+removing the part left by the turning tool and giving the pin the proper
+width and fillets of the correct radius. If the crankshaft has straight
+webs which must be finished, two tools seen at _b_ are used for facing
+the webs to the correct width. During these last two operations, the
+crank is supported by the roller back-rest, thus eliminating any
+tendency of the work to spring.
+
+[Illustration: Fig. 28. (A) Spherical Turning with Compound Rest. (B)
+Concave Turning]
+
+After one pin is finished in the manner described, the back-rest is
+moved out of the way, the automatic stop lever raised, the carriage
+shifted to the next pin, and the operation repeated. The tools are held
+in position on the turret by studs, and they can be moved and other
+tools quickly substituted for pins of different widths. This machine is
+used for rough-turning the pins close to the required size, the
+finishing operation being done in a grinder. It should be mentioned, in
+passing, that many crankshafts, especially the lighter designs used in
+agricultural machinery, etc., are not turned at all but are ground from
+the rough.
+
+=Spherical Turning.=--Occasionally it may be necessary to turn a
+spherical surface in the lathe. Sketch _A_, Fig. 28, shows how a small
+ball-shaped end can be turned on a piece held in a chuck. The lathe
+carriage is adjusted so that the pin around which the compound rest
+swivels is directly under the center a. The bolts which hold the swivel
+are slightly loosened to allow the top slide to be turned, as indicated
+by the dotted lines; this causes the tool point to move in an arc about
+center _a_, and a spherical surface is turned. Light cuts must be taken
+as otherwise it would be difficult to turn the slide around by hand.
+
+[Illustration: Fig. 29. Spherical Turning Attachment for Engine Lathe]
+
+Sketch _B_ illustrates how a concave surface can be turned. The
+cross-slide is adjusted until swivel pin is in line with the lathe
+centers, and the carriage is moved along the bed until the horizontal
+distance between center _b_ of the swivel, and the face of the work,
+equals the desired radius of the concave surface. The turning is then
+done by swinging the compound rest as indicated by the dotted lines. The
+slide can be turned more evenly by using the tailstock center to force
+it around. A projecting bar is clamped across the end of the slide at
+_d_, to act as a lever, and a centered bar is placed between this lever
+and the tailstock center; then by screwing out the tailstock spindle,
+the slide is turned about pivot _b_. The alignment between the swivel
+pin and the lathe centers can be tested by taking a trial cut; if the
+swivel pin is too far forward, the tool will not touch the turned
+surface if moved past center _c_, and if the pin is too far back, the
+tool will cut in on the rear side.
+
+=Spherical Turning Attachments.=--When spherical turning must be done
+repeatedly, special attachments are sometimes used. Fig. 29 shows an
+attachment applied to a lathe for turning the spherical ends of
+ball-and-socket joints. The height or radius of the cutting tool and,
+consequently, the diameter of the turned ball, is regulated by adjusting
+screw _A_. The tool is swung around in an arc, by turning handle _B_
+which revolves a worm meshing with an enclosed worm-wheel. As will be
+seen, the work is held in a special chuck, owing to its irregular shape.
+
+[Illustration: Fig. 30. Attachment for Turning Spherical End of Gasoline
+Engine Piston]
+
+Another spherical turning attachment is shown in Fig. 30. This is used
+for machining the ends of gasoline engine pistons. The cross-slide has
+bolted to it a bar _A_ carrying a roller which is pressed against a
+forming plate _B_ by a heavy spring _C_. The forming plate _B_, which is
+attached to a cross-piece fastened to the ways of the lathe bed, is
+curved to correspond with the radius required on the piston end, and
+when the tool is fed laterally by moving the cross-slide, it follows the
+curve of plate _B_. The piston is held in a special hollow chuck which
+locates it in a central position and holds it rigidly.
+
+In connection with lathe work, special attachments and tools are often
+used, especially when considerable work of one class must be turned;
+however, if a certain part is required in large quantities, it is
+usually more economical to use some semi-automatic or automatic turning
+machine, especially designed for repetition work.
+
+=Turning with Front and Rear Tools.=--In ordinary engine lathe practice,
+one tool is used at a time, but some lathes are equipped with
+tool-holders at the front and rear of the carriage so that two tools can
+be used simultaneously. Fig. 31 shows a detail view of a lathe in which
+front and rear tools are being used. These tools are of the inserted
+cutter type and the one at the rear is inverted, as the rotary movement
+of the work is, of course, upward on the rear side. This particular
+lathe was designed for taking heavy roughing cuts and has considerable
+driving power.
+
+[Illustration: Fig. 31. Front and Rear Tools used for Roughing]
+
+The part shown in this illustration is a chrome-nickel steel bar which
+is being roughed out to form a milling machine spindle. It is necessary
+to reduce the diameter of the bar from 5-7/16 inches to 3-3/4 inches for
+a length of 27 inches, because of a collar on one end. This reduction is
+made in one passage of the two tools, with a feed of 1/32 inch per
+revolution and a speed of 60 revolutions per minute. The use of two
+tools for such heavy roughing cuts is desirable, especially when the
+parts are required in large quantities, because the thrust of the cut on
+one side, which tends to deflect the work, is counteracted by the thrust
+on the opposite side.
+
+[Illustration: Fig. 32. Lo-swing Lathe for Multiple Turning]
+
+Sometimes special tool-holders are made for the lathe, so that more than
+one tool can be used for turning different surfaces or diameters at the
+same time, the tools being set in the proper relation to each other. The
+advantage of this method has resulted in the design of a special lathe
+for multiple-tool turning.
+
+=A Multiple-tool Lathe.=--The lathe shown in Fig. 32 (which is built by
+the Fitchburg Machine Works and is known as the Lo-swing) is designed
+especially for turning shafts, pins and forgings not exceeding 3-1/2
+inches in diameter. It has two carriages _A_ and _B_ which, in
+conjunction with special tool-holders, make it possible to turn several
+different diameters simultaneously. At the front of this lathe there is
+an automatic stop-rod _C_ for disengaging the feed when the tools have
+turned a surface to the required length. This stop-rod carries
+adjustable stops _D_ which are set to correspond with shoulders, etc.,
+on the work. The rod itself is also adjustable axially, so that the
+tools, which are usually arranged in groups of two or more (depending
+upon the nature of the work), can be disengaged at a point nearer or
+farther from the headstock as may be required, owing to a variation in
+the depth of center holes. For example, if it were necessary to feed a
+group of tools farther toward the headstock after they had been
+automatically disengaged, the entire rod with its stops would be
+adjusted the required amount in that direction.
+
+[Illustration: Fig. 33. Lo-swing Lathe arranged for Turning a Steering
+Knuckle]
+
+The gage _G_, which is attached to a swinging arm, is used to set the
+stop bar with reference to a shoulder near the end of the work, when it
+is necessary to finish other parts to a given distance from such a
+shoulder or other surface. The use of this gage will be explained more
+fully later. Cooling lubricant for the tools is supplied through the
+tubes _E_. The lathe shown in the illustration is arranged for turning
+Krupp steel bars. A rough bar and also one that has been turned may be
+seen to the right. The plain cylindrical bar is turned to five different
+diameters, by groups of tools held on both carriages.
+
+[Illustration: Fig. 34. Plan View showing Method of driving Steering
+Knuckle and Arrangement of Tools]
+
+=Examples of Multiple Turning.=--Figs. 33 and 34 show how a Lo-swing
+lathe is used for turning the steering knuckle of an automobile. Four
+tools are used in this case, three cylindrical surfaces and one tapering
+surface being turned at the same time. For this job, the four tools are
+mounted on one carriage. The taper part is turned by the second tool
+from the headstock, which is caused to feed outward as the carriage
+advances by a taper attachment. This tool is held in a special holder
+and bears against a templet at the rear, which is tapered to correspond
+with the taper to be turned. This templet is attached to a bar which, in
+turn, is fastened to a stationary bracket seen to the extreme left in
+Fig. 33. This part is finished in two operations, the tool setting being
+identical for each operation, except for diameter adjustments. As the
+illustrations show, three of the four tools employed are used for
+straight turning on different diameters, while the fourth finishes the
+taper.
+
+These pieces, which are rough drop forgings, are first reduced to the
+approximate size. When it becomes necessary to grind the tools, they are
+reset and those parts which have been roughed out are turned to the
+finished size. The average time for the first operation, which includes
+starting, stopping, turning and replacing the piece, is one minute,
+while for the second operation with the finer feed, an average time of
+two minutes is required. The work is driven by sleeve _S_, which fits
+over the spindle and is held in position by the regular driver, as
+shown. This sleeve is notched to fit the knuckle, so that the latter can
+easily and quickly be replaced when finished.
+
+One of the interesting features of this job lies in the method of
+locating the shoulders on each knuckle, at the same distance from the
+hole _H_ which is drilled previously, and which receives the bolt on
+which the knuckle swivels when assembled in a car. As soon as the
+knuckle has been placed between the centers, a close-fitting plug _P_
+(Fig. 33) is inserted in this hole and the indicator arm with its
+attached gage or caliper _G_ is swung up to the position shown. The
+stop-rod on which the stops have been previously set for the correct
+distance between the shoulders is next adjusted axially until the gage
+_G_ just touches the plug _P_. The indicator is then swung out of the
+way, and the piece turned. If the next knuckle were centered, say,
+deeper than the previous one which would, of course, cause it to be
+located nearer the headstock, obviously all the shoulders would be
+located farther from the finished hole, provided the position of the
+stops remained the same as before. In such a case their position would,
+however, be changed by shifting the stop-rod until the gage _G_ again
+touched the plug thus locating all the stops with reference to the hole.
+As the adjustment of the stop-rod changes the position of the taper
+templet as well as the stops, it is evident that both the shoulders and
+the taper are finished the same distance from the hole in each case. The
+connection of the bracket (to which the templet arm is attached) with
+the stop-rod is clearly shown in Fig. 33. This bracket can either be
+locked to the ways or adjusted to slide when the stop-rod is moved.
+
+[Illustration: Fig. 35. First and Second Operations on Automobile
+Transmission Shaft--Lo-swing Lathe]
+
+The part illustrated in Fig. 35 is an automobile transmission shaft. In
+this particular case, cylindrical, tapering and spherical surfaces are
+turned. The upper view shows, diagrammatically, the arrangement of the
+tools and work for the first operation. After the shaft is "spotted" at
+_A_ for the steadyrest, the straight part _C_ and the collar _B_ are
+sized with tools _S_ and _R_ which are mounted on the left-hand
+carriage. A concave groove is then cut in collar _B_ by tool _R_, after
+which spherical end _D_ is formed by a special attachment mounted on the
+right-hand carriage. This attachment is the same, in principle, as the
+regular taper-turning attachment, the substitution of a circular templet
+_T_ for the straight kind used on taper work being the only practical
+difference.
+
+[Illustration: Fig. 36. Axle End turned in One Traverse of the Five
+Tools shown]
+
+After the surfaces mentioned have been finished on a number of pieces,
+the work is reversed and the tools changed as shown by the lower view.
+The first step in the second operation is to turn the body _E_ of the
+shaft with the tool _T_ on the left-hand carriage. The taper _F_ and the
+straight part _G_ are then finished, which completes the turning. It
+will be noted that in setting up the machine for this second operation,
+it is arranged for taper turning by simply replacing the circular
+templet with the straight one shown. When this taper attachment is not
+in use, the swiveling arm _M_, which is attached to a bracket, is swung
+out of the way.
+
+The method of driving this shaft is worthy of note. A dog having two
+driving arms each of which bears against a pin _N_ that passes through a
+hole in the spindle is used. As the ends of this pin, against which the
+dog bears, are beveled in opposite directions, the pin turns in its hole
+when the dog makes contact with it and automatically adjusts itself
+against the two driving members of the dog. The advantage of driving by
+a two-tailed dog, as most mechanics know, is in equalizing the tendency
+to spring slender parts while they are being turned.
+
+[Illustration: Fig. 37. Lathe Knurling Tool having Three Pairs of
+Knurls--Coarse, Medium and Fine]
+
+In Fig. 36 another turning operation on a lathe of this type is shown,
+the work in this case being a rear axle for a motor truck. The turning
+of this part is a good example of that class of work where the rapid
+removal of metal is the important feature. As the engraving shows, the
+stock, prior to turning, is 3-1/2 inches in diameter and it is reduced
+to a minimum diameter of 1-1/16 inch. This metal is turned off with one
+traverse of the carriage or by one passage of the five tools, and the
+weight of the chips removed from each end of the axle is approximately
+12 pounds. The time required for the actual turning is about 9 minutes,
+while the total time for the operation, which includes placing the heavy
+piece in the machine, turning, and removing the work from the lathe, is
+12 minutes. The axle revolves, while being turned, at 110 revolutions
+per minute and a feed equivalent to 1 inch of tool travel to 60
+revolutions of the work is used. It will be noticed that the taper
+attachment is also employed on this part, the taper being turned by the
+second tool from the left. As the axle is equipped with roller bearings,
+it was found desirable to finish the bearing part by a separate
+operation; therefore, in the operation shown the axle is simply roughed
+down rather close to the finished dimensions, leaving enough material
+for a light finishing cut.
+
+=Knurling in the Lathe.=--Knurling is done either to provide a rough
+surface which can be firmly gripped by the hand or for producing an
+ornamental effect. The handles of gages and other tools are often
+knurled, and the thumb-screws used on instruments, etc., usually have
+knurled edges. A knurled surface consists of a series of small ridges or
+diamond-shaped projections, and is produced in the lathe by the use of a
+tool similar to the one shown in Fig. 37, this being one of several
+different designs in common use. The knurling is done by two knurls _A_
+and _B_ having teeth or ridges which incline to the right on one knurl
+and to the left on the opposite knurl, as shown by the end view. When
+these two knurls are pressed against the work as the latter revolves,
+one knurl forms a series of left-hand ridges and the other knurl
+right-hand ridges, which cross and form the diamond-shaped knurling
+which is generally used.
+
+If the surface to be knurled is wider than the knurls, the power feed of
+the lathe should be engaged and the knurling tool be traversed back and
+forth until the diamond-shaped projections are well formed. To prevent
+forming a double set of projections, feed the knurl in with considerable
+pressure at the start, then partially relieve the pressure before
+engaging the power feed. Use oil when knurling.
+
+The knurls commonly used for lathe work have spiral teeth and ordinarily
+there are three classes, known as coarse, medium and fine. The medium
+pitch is generally used. The teeth of coarse knurls have a spiral angle
+of 36 degrees and the pitch of the knurled cut (measured parallel to the
+axis of the work) should be about 8 per inch. For medium knurls, the
+spiral angle is 29-1/2 degrees and the pitch, measured as before, is 12
+per inch. For fine knurls, the spiral angle is 25-3/4 degrees and the
+pitch 20 per inch. The knurls should be about 3/4 inch in diameter and
+3/8 inch wide. When made to these dimensions, coarse knurls have 34
+teeth; medium, 50 teeth; and fine knurls, 80 teeth.
+
+[Illustration: Fig. 38. Hendey Relieving Attachment applied to a Lathe]
+
+The particular tool illustrated in Fig. 37 has three pairs of knurls of
+coarse, medium and fine pitch. These are mounted in a revolving holder
+which not only serves to locate the required set of knurls in the
+working position, but enables each knurl to bear against the surface
+with equal pressure. Concave knurls are sometimes used for knurling
+rounded edges on screw heads, etc.
+
+=Relieving Attachment.=--Some lathes, particularly those used in
+toolrooms, are provided with relieving attachments which are used for
+"backing off" the teeth of milling cutters, taps, hobs, etc. If a
+milling cutter of special shape is to be made, the cutter blank is first
+turned to the required form with a special tool having a cutting edge
+that corresponds with the shape or profile of the cutter to be made. The
+blank is then fluted or gashed to form the teeth, after which the tops
+of the teeth are relieved or backed off to provide clearance for the
+cutting edges. The forming tool used for turning the blank is set to
+match the turned surface, and the teeth are backed off as the result of
+a reciprocating action imparted to the toolslide by the relieving
+attachment. The motion of the toolslide is so adjusted that the tool
+will meet the front of each tooth and the return movement begin promptly
+after the tool leaves the back end of the tooth.
+
+[Illustration: Fig. 39. Relieving a Formed Cutter]
+
+These attachments differ somewhat in their construction and arrangement
+but the principle of their operation is similar. Fig. 38 shows a Hendey
+relieving attachment applied to a lathe. A bracket carrying the gearing
+_A_ through which the attachment is driven is mounted upon the main gear
+box of the lathe, and the special slide _B_, which is used when
+relieving, is placed on the cross-slide after removing the regular
+compound rest. The gears at _A_ are changed to suit the number of flutes
+or gashes in the cutter, tap or whatever is to be relieved. If we assume
+that the work is a formed milling cutter having nine teeth, then with
+this particular attachment, a gear having 90 teeth would be placed on
+the "stud" and a 40-tooth gear on the cam-shaft, the two gears being
+connected by a 60-tooth intermediate gear. With this combination of
+gearing, the toolslide would move in and out nine times for each
+revolution of the work, so that the tool could back off the top of each
+tooth. (The gearing to use for various numbers of flutes is shown by an
+index plate on the attachment.) The amount of relief is varied to suit
+the work being done, by means of a toothed coupling which makes it
+possible to change the relative position between the eccentric which
+actuates the toolslide and the cam lever, thereby lengthening or
+shortening the reciprocating travel of the tool.
+
+[Illustration: Fig. 40. Relieving Side of Angular Milling Cutter]
+
+=Application of Relieving Attachment.=--Some typical examples of the
+kind of work for which the relieving attachment is used are shown in
+Figs. 39 to 42, inclusive. Fig. 39 shows how a formed milling cutter is
+relieved. The toolslide is set at right angles to the axis of the work,
+and the tool moves in as each tooth passes, and out while crossing the
+spaces or flutes between the teeth. As the result of this movement, the
+tops of the teeth are backed off eccentrically but the form or shape is
+the same from the front to the back of the tooth; hence, a cutter that
+has been relieved in this way can be ground repeatedly without changing
+the profile of the teeth, provided the faces are ground so as to lie in
+a radial plane.
+
+When relieving, the cutting speed should be much less than when turning
+in order to give the toolslide time to operate properly. A maximum of
+180 teeth per minute is recommended, and, if wide forming tools are
+used, it might be advisable to reduce the speed so low that only 8 teeth
+per minute would be relieved. It is also essential to use a tool having
+a keen edge, and the toolslide should work freely but be closely
+adjusted to the dovetail of the lower slide. Before beginning to back
+off the teeth, it is a good plan to color the work either by heating it
+or dipping into a strong solution of copper sulphate. This will enable
+one to see plainly the cutting action of the tool in order to stop
+relieving at the proper time.
+
+[Illustration: Fig. 41. Relieving a Right-hand Tap]
+
+Fig. 40 shows a method of relieving the teeth of an angular cutter. For
+an operation of this kind the toolslide is swiveled around at right
+angles to the side that is to be relieved. By the use of an additional
+universal joint and bearing to permit the toolslide to be swung to a
+90-degree angle, the teeth of counterbores, etc., can be relieved on the
+ends. When the attachment is used for relieving inside work, such as
+hollow mills and threading dies, the eccentric which controls the travel
+of the toolslide is set so that the relieving movement is away from the
+axis of the cutter instead of toward it. This change is made by the
+toothed coupling previously referred to, which connects the cam lever
+and oscillating shaft, the latter being turned beyond the zero mark in a
+clockwise direction as far as is necessary to obtain the desired amount
+of travel. For internal work it is also necessary to change the position
+of the opposing spring of the toolslide, so that it will press against
+the end of the slide and prevent the tool from jumping into the work.
+
+[Illustration: Fig. 42. Relieving a Hob having Spiral Flutes]
+
+Fig. 41 shows how a right-hand tap is relieved. The ordinary practice is
+to first set the tool the same as for cutting a thread. The motion of
+the toolslide is then adjusted so that the tool on the forward stroke
+will meet the front of each tooth, and start back as soon as the tool
+leaves the end of the land or top of the tooth. Taps having a left-hand
+thread can be relieved by two different methods. With the first method
+the cut starts at the cutting edge of each tooth, and ends at the
+"heel," the tool moving in toward the center of the work. With the
+second method, the cut begins at the heel and discontinues at the
+cutting edge, the tool being drawn away from the work during the cut.
+When using the first method the tap must be placed with the point toward
+the headstock, the shank end being supported by the tailstock center.
+This is done by providing an extension or blank end at the point of the
+tap long enough to hold the driving dog. With the second method, the tap
+is held between centers the same as one having a right-hand thread, but
+the travel of the toolslide is set the same as for inside relief.
+
+=Relieving Hobs or Taps Having Spiral Flutes.=--With this attachment,
+taps or hobs having "spiral" or helical flutes can also be relieved. (A
+spiral flute is preferable to one that is parallel to the axis, because
+with the former the tool has cutting edges which are square with the
+teeth; this is of especial importance when the lead of the hob or tap
+thread is considerable.) When relieving work having spiral flutes (as
+illustrated in Fig. 42), the lead of the spiral and the gears necessary
+to drive the attachment are first determined. After the attachment is
+geared for the number of flutes and to compensate for the spiral, the
+lead-screw is engaged and the backing-off operation is performed the
+same as though the flutes were straight. The carriage should not be
+disengaged from the lead-screw after starting the cut, the tool being
+returned by reversing the lathe.
+
+When gearing the attachment for relieving a tap or hob having spiral
+flutes, the gears are not selected for the actual number of flutes
+around the circumference but for a somewhat larger number which depends
+upon the lead of the hob thread and the lead of the spiral flutes. Let
+us assume that a hob has 6 spiral flutes and that the attachment is
+geared for that number. The result would be that as the tool advanced
+along the thread, it would not keep "in step" with the teeth because the
+faces of the teeth lie along a spiral (or helix which is the correct
+name for this curve); in other words, the tool would soon be moving in
+too late to begin cutting at the proper time, and to compensate for
+this, the attachment is geared so that the tool will make a greater
+number of strokes per revolution of the work than the actual number of
+flutes around the circumference.
+
+With this attachment, the two gears listed on the index plate for the
+actual number of flutes are selected, and then two compensating gears
+are added, thus forming a compound train of gearing. The ratio _R_ of
+these compensating gears is determined as follows:
+
+      _r_ + 1
+  R = -------
+        _r_
+
+in which
+
+  _r_ = _L_ / _l_;
+  _L_ = lead of spiral;
+  _l_ = lead of hob thread.
+
+For example, if a hob has a pitch circumference of 3.25, a single thread
+of 0.75 inch lead, and 6 spiral flutes, what compensating gears would be
+required?
+
+The lead _L_ of the spiral flutes is first determined by dividing the
+square of the circumference _C_ of the hob at the pitch line by the lead
+_l_ of the hob thread. Thus lead _L_ = _C^2_/_l_, or, in this case, _L_
+= 3.25^2/0.75 = 14 inches, approximately. Then _r_ = 14 / 0.75 = 18-2/3.
+Inserting these values in the formula for ratio R,
+
+        18-2/3 + 1   19-2/3   19-2/3 x 3   59
+  _R_ = ---------- = ------ = ---------- = --
+          18-2/3     18-2/3   18-2/3 x 3   56
+
+Hence, the compensating gears will have 56 and 59 teeth, respectively,
+the latter being the driver. As the gears for 6 flutes listed on the
+regular index plate are, stud-gear 60 teeth, cam-shaft gear 40 teeth,
+the entire train of gears would be as follows: Gear on stud, 60;
+_driven_ intermediate gear, 56; _driving_ intermediate gear, 59;
+cam-shaft gear, 40. It will be understood that the position of the
+driving gears or the driven gears can be transposed without affecting
+the ratio.
+
+=Classes of Fits Used in Machine Construction.=--In assembling machine
+parts it is necessary to have some members fit together tightly, whereas
+other parts such as shafts, etc., must be free to move or revolve with
+relation to each other. The accuracy required for a fitting varies for
+different classes of work. A shaft that revolves in its bearing must be
+slightly smaller than the bearing so that there will be room for a film
+of lubricant. A crank-pin that must be forced into the crank-disk is
+made a little larger in diameter than the hole, to secure a tight fit.
+When a very accurate fitting between two cylindrical parts that must be
+assembled without pressure is required, the diameter of the inner member
+is made as close to the diameter of the outer member as is possible. In
+ordinary machine construction, five classes of fits are used, _viz_;
+running fit, push fit, driving fit, forced fit and shrinkage fit. The
+running fit, as the name implies, is employed when parts must rotate;
+the push fit is not sufficiently free to rotate; the other classes
+referred to are used for assembling parts that must be held in fixed
+positions.
+
+=Forced Fits.=--This is the term used when a pin, shaft or other
+cylindrical part is forced into a hole of slightly smaller diameter, by
+the use of a hydraulic press or other means. As a rule, forced fits are
+restricted to parts of small and medium size, while shrinkage fits have
+no such limitations and are especially applicable when a maximum "grip"
+is desired, or when (as in the construction of ordnance) accurate
+results as to the intensity of stresses produced in the parts united are
+required. The proper allowance for a forced fit depends upon the mass of
+metal surrounding the hole, the size of the work, the kind and quality
+of the material of which the parts are composed and the smoothness and
+accuracy of the pin and bore. When a pin or other part is pressed into a
+hole a second time, the allowance for a given tonnage should be
+diminished somewhat because the surface of the bore is smoother and the
+metal more compact. The pressure required in assembling a forced fit
+will also vary for cast hubs of the same size, if they are not uniform
+in hardness. Then there is the personal factor which is much in evidence
+in work of this kind; hence, data and formulas for forced fit allowances
+must be general in their application.
+
+=Allowance for Forced Fits.=--The allowance per inch of diameter usually
+ranges from 0.001 inch to 0.0025 inch, 0.0015 being a fair average.
+Ordinarily, the allowance per inch decreases as the diameter increases;
+thus the total allowance for a diameter of 2 inches might be 0.004 inch,
+whereas for a diameter of 8 inches the total allowance might not be over
+0.009 or 0.010 inch. In some shops the allowance is made practically the
+same for all diameters, the increased surface area of the larger sizes
+giving sufficient increase in pressure. The parts to be assembled by
+forced fits are usually made cylindrical, although sometimes they are
+slightly tapered. The advantages of the taper form are that the
+possibility of abrasion of the fitted surfaces is reduced; that less
+pressure is required in assembling; and that the parts are more readily
+separated when renewal is required. On the other hand, the taper fit is
+less reliable, because if it loosens, the entire fit is free with but
+little axial movement. Some lubricant, such as white lead and lard oil
+mixed to the consistency of paint, should be applied to the pin and bore
+before assembling, to reduce the tendency of abrasion.
+
+Allowances for Different Classes of Fits
+
+(Newall Engineering Co.)
+
+  +-----+--------------------------------------------------------------+
+  |     |               Tolerances in Standard Holes[1]                |
+  |Class+------------+---------+---------+---------+---------+---------+
+  |     | Nominal    |  Up to  | 9/16"-1"| 1-1/16"-| 2-1/16"-| 3-1/16"-|
+  |     | Diameters  |   1/2"  |         |    2"   |    3"   |    4"   |
+  +-----+------------+---------+---------+---------+---------+---------+
+  |     | High Limit | +0.0002 | +0.0005 | +0.0007 | +0.0010 | +0.0010 |
+  |  A  | Low Limit  | -0.0002 | -0.0002 | -0.0002 | -0.0005 | -0.0005 |
+  |     | Tolerance  |  0.0004 |  0.0007 |  0.0009 |  0.0015 |  0.0015 |
+  +-----+------------+---------+---------+---------+---------+---------+
+  |     | High Limit | +0.0005 | +0.0007 | +0.0010 | +0.0012 | +0.0015 |
+  |  B  | Low Limit  | -0.0005 | -0.0005 | -0.0005 | -0.0007 | -0.0007 |
+  |     | Tolerance  |  0.0010 |  0.0012 |  0.0015 |  0.0019 |  0.0022 |
+  +-----+------------+---------+---------+---------+---------+---------+
+  |                       Allowances for Forced Fits                   |
+  +-----+------------+---------+---------+---------+---------+---------+
+  |     | High Limit | +0.0010 | +0.0020 | +0.0040 | +0.0060 | +0.0080 |
+  |  F  | Low Limit  | +0.0005 | +0.0015 | +0.0030 | +0.0045 | +0.0060 |
+  |     | Tolerance  |  0.0005 |  0.0005 |  0.0010 |  0.0015 |  0.0020 |
+  +-----+------------+---------+---------+---------+---------+---------+
+  |                      Allowances for Driving Fits                   |
+  +-----+------------+---------+---------+---------+---------+---------+
+  |     | High Limit | +0.0005 | +0.0010 | +0.0015 | +0.0025 | +0.0030 |
+  |  D  | Low Limit  | +0.0002 | +0.0007 | +0.0010 | +0.0015 | +0.0020 |
+  |     | Tolerance  |  0.0003 |  0.0003 |  0.0005 |  0.0010 |  0.0010 |
+  +-----+------------+---------+---------+---------+---------+---------+
+  |                       Allowances for Push Fits                     |
+  +-----+------------+---------+---------+---------+---------+---------+
+  |     | High Limit | -0.0002 | -0.0002 | -0.0002 | -0.0005 | -0.0005 |
+  |  P  | Low Limit  | -0.0007 | -0.0007 | -0.0007 | -0.0010 | -0.0010 |
+  |     | Tolerance  |  0.0005 |  0.0005 |  0.0005 |  0.0005 |  0.0005 |
+  +-----+------------+---------+---------+---------+---------+---------+
+  |                   Allowances for Running Fits[2]                   |
+  +-----+------------+---------+---------+---------+---------+---------+
+  |     | High Limit | -0.0010 | -0.0012 | -0.0017 | -0.0020 | -0.0025 |
+  |  X  | Low Limit  | -0.0020 | -0.0027 | -0.0035 | -0.0042 | -0.0050 |
+  |     | Tolerance  |  0.0010 |  0.0015 |  0.0018 |  0.0022 |  0.0025 |
+  |     | High Limit | -0.0007 | -0.0010 | -0.0012 | -0.0015 | -0.0020 |
+  |  Y  | Low Limit  | -0.0012 | -0.0020 | -0.0025 | -0.0030 | -0.0035 |
+  |     | Tolerance  |  0.0005 |  0.0010 |  0.0013 |  0.0015 |  0.0015 |
+  |     | High Limit | -0.0005 | -0.0007 | -0.0007 | -0.0010 | -0.0010 |
+  |  Z  | Low Limit  | -0.0007 | -0.0012 | -0.0015 | -0.0020 | -0.0022 |
+  |     | Tolerance  |  0.0002 |  0.0005 |  0.0008 |  0.0010 |  0.0012 |
+  +-----+------------+---------+---------+---------+---------+---------+
+
+[1] Tolerance is provided for holes, which ordinary standard reamers can
+produce, in two grades, Classes A and B, the selection of which is a
+question for the user's decision and dependent upon the quality of the
+work required; some prefer to use Class A as working limits and Class B
+as inspection limits.
+
+[2] Running fits, which are the most commonly required, are divided into
+three grades: Class X for engine and other work where easy fits are
+wanted; Class Y for high speeds and good average machine work; Class Z
+for fine tool work.
+
+=Pressure for Forced Fits.=--The pressure required for assembling
+cylindrical parts depends not only upon the allowance for the fit, but
+also upon the area of the fitted surfaces, the pressure increasing in
+proportion to the distance that the inner member is forced in. The
+approximate ultimate pressure in pounds can be determined by the use of
+the following formula in conjunction with the accompanying table of
+"Pressure Factors."
+
+=Pressure Factors=
+
+  +-----+-----++-----+-----++-----+-----++------+------++------+------+
+  |Diam-|Pres-||Diam-|Pres-||Diam-|Pres-||Diam- |Pres- ||Diam- |Pres- |
+  |eter,|sure ||eter,|sure ||eter,|sure ||eter, |sure  ||eter, |sure  |
+  |In-  |Fac- ||In-  |Fac- ||In-  |Fac- ||In-   |Fac-  ||In-   |Fac-  |
+  |ches | tor ||ches | tor ||ches | tor ||ches  |tor   ||ches  |tor   |
+  +-----+-----++-----+-----++-----+-----++------+------++------+------+
+  |1    | 500 ||3-1/2| 132 ||6    | 75  || 9    | 48.7 ||14    | 30.5 |
+  |1-1/4| 395 ||3-3/4| 123 ||6-1/4| 72  || 9-1/2| 46.0 ||14-1/2| 29.4 |
+  |1-1/2| 325 ||4    | 115 ||6-1/2| 69  ||10    | 43.5 ||15    | 28.3 |
+  |1-3/4| 276 ||4-1/4| 108 ||6-3/4| 66  ||10-1/2| 41.3 ||15-1/2| 27.4 |
+  |2    | 240 ||4-1/2| 101 ||7    | 64  ||11    | 39.3 ||16    | 26.5 |
+  |2-1/4| 212 ||4-3/4|  96 ||7-1/4| 61  ||11-1/2| 37.5 ||16-1/2| 25.6 |
+  |2-1/2| 189 ||5    |  91 ||7-1/2| 59  ||12    | 35.9 ||17    | 24.8 |
+  |2-3/4| 171 ||5-1/4|  86 ||7-3/4| 57  ||12-1/2| 34.4 ||17-1/2| 24.1 |
+  |3    | 156 ||5-1/2|  82 ||8    | 55  ||13    | 33.0 ||18    | 23.4 |
+  |3-1/4| 143 ||5-3/4|  78 ||8-1/2| 52  ||13-1/2| 31.7 ||....  | .... |
+  +-----+-----++-----+-----++-----+-----++------+------++------+------+
+
+Assuming that _A_ = area of fitted surface; _a_ = total allowance in
+inches; _P_ = ultimate pressure required, in tons; _F_ = pressure factor
+based upon assumption that the diameter of the hub is twice the
+diameter of the bore, that the shaft is of machine steel, and the hub of
+cast iron, then,
+
+        _A_ x _a_ x _F_
+  _P_ = ---------------
+               2
+
+_Example:_--What will be the approximate pressure required for forcing a
+4-inch machine steel shaft having an allowance of 0.0085 inch into a
+cast-iron hub 6 inches long?
+
+_A_ = 4 x 3.1416 x 6 = 75.39 square inches;
+
+_F_, for a diameter of 4 inches, = 115 (see table of "Pressure
+Factors"). Then,
+
+_P_ = (75.39 x 0.0085 x 115)/2 = 37 tons, approximately.
+
+=Allowance for Given Pressure.=--By transposing the preceding formula,
+the approximate allowance for a required ultimate tonnage can be
+determined. Thus, _a_ = 2_P_ / _AF_. The average ultimate pressure in
+tons commonly used ranges from 7 to 10 times the diameter in inches.
+Assuming that the diameter of a machine steel shaft is 4 inches and an
+ultimate pressure of about 30 tons is desired for forcing it into a
+cast-iron hub having a length of 5-1/2 inches, what should be the
+allowance?
+
+_A_ = 4 x 3.1416 x 5-1/2 = 69 square inches,
+
+_F_, for a diameter of 4 inches, = 115. Then,
+
+          2 x 30
+  _a_ =  -------- = 0.0075 inch.
+         69 x 115
+
+=Shrinkage Fits.=--When heat is applied to a piece of metal, such as
+iron or steel, as is commonly known, a certain amount of expansion takes
+place which increases as the temperature is increased, and also varies
+somewhat with different kinds of metal, copper and brass expanding more
+for a given increase in temperature than iron and steel. When any part
+which has been expanded by the application of heat is cooled, it
+contracts and resumes its original size. This expansive property of
+metals has been taken advantage of by mechanics in assembling various
+machine details. A cylindrical part which is to be held in position by a
+shrinkage fit is first turned a few thousandths of an inch larger than
+the hole; the diameter of the latter is then increased by heating, and
+after the part is inserted, the heated outer member is cooled, causing
+it to grip the pin or shaft with tremendous pressure.
+
+General practice seems to favor a smaller allowance for shrinkage fits
+than for forced fits, although in many shops the allowances are
+practically the same in each case, and for some classes of work,
+shrinkage allowances exceed those for forced fits. In any case, the
+shrinkage allowance varies to a great extent with the form and
+construction of the part which has to be shrunk into place. The
+thickness or amount of metal around the hole is the most important
+factor. The way in which the metal is distributed also has an influence
+on the results. Shrinkage allowances for locomotive driving wheel tires
+adopted by the American Railway Master Mechanics Association are as
+follows:
+
+  Center diameter, inches      38    44    50    56    62    66
+  Allowance, inches          0.040 0.047 0.053 0.060 0.066 0.070
+
+Whether parts are to be assembled by forced or shrinkage fits depends
+upon conditions. For example, to press a driving wheel tire over its
+wheel center, without heating, would ordinarily be a rather awkward and
+difficult job. On the other hand, pins, etc., are easily and quickly
+forced into place with a hydraulic press and there is the additional
+advantage of knowing the exact pressure required in assembling, whereas
+there is more or less uncertainty connected with a shrinkage fit, unless
+the stresses are calculated. Tests to determine the difference in the
+quality of shrinkage and forced fits showed that the resistance of a
+shrinkage fit to slippage was, for an axial pull, 3.66 times greater
+than that of a forced fit, and in rotation or torsion, 3.2 times
+greater. In each comparative test, the dimensions and allowances were
+the same.
+
+The most important point to consider when calculating shrinkage fits is
+the stress in the hub at the bore, which depends chiefly upon the
+shrinkage allowance. If the allowance is excessive, the elastic limit of
+the material will be exceeded and permanent set will occur, or, in
+extreme cases, the ultimate strength of the metal will be exceeded and
+the hub will burst.
+
+
+
+
+CHAPTER IV
+
+THREAD CUTTING IN THE LATHE
+
+
+When threads are cut in the lathe a tool _t_ is used (see Fig. 2),
+having a point corresponding to the shape of the thread, and the
+carriage is moved along the bed a certain distance for each revolution
+of the work (the distance depending on the number of threads to the inch
+being cut) by the lead-screw _S_ which is rotated by gears _a_, _b_ and
+_c_, which receive their motion from the spindle. As the amount that the
+carriage travels per revolution of the work, and, consequently, the
+number of threads per inch that is cut, depends on the size of the gears
+_a_ and _c_ (called change gears) the latter have to be changed for
+cutting different threads. The proper change gears to use for cutting a
+given number of threads to the inch is ordinarily determined by
+referring to a table or "index plate" _I_ which shows what the size of
+gears _a_ and _c_ should be, or the number of teeth each should have,
+for cutting any given number of threads per inch.
+
+[Illustration: Fig. 1. Measuring Number of Threads per Inch--Setting
+Thread Tool]
+
+[Illustration: Fig. 2. Plan and Elevations of Engine Lathe]
+
+=Selecting the Change Gears for Thread Cutting.=--Suppose a V-thread is
+to be cut on the end of the bolt _B_, Fig. 2, having a diameter of 1-1/4
+inch and seven threads per inch of length, as shown at _A_ in Fig. 1,
+which is the standard number of threads per inch for that diameter.
+First the change gears to use are found on plate _I_ which is shown
+enlarged in Fig. 3. This plate has three columns: The first contains
+different numbers of threads to the inch, the second the size gear to
+place on the "spindle" or "stud" at _a_ (Fig. 2) for different threads,
+and the third the size of gear _c_ for the lead-screw. As the thread
+selected as an example has 7 threads per inch, gear _a_ should have 48
+teeth, this being the number given in the second column opposite figure
+7 in the first. By referring to the last column, we find that the
+lead-screw gear should have 84 teeth. These gears are selected from an
+assortment provided with the lathe and they are placed on the spindle
+and lead-screw, respectively.
+
+[Illustration: Fig. 3. Index Plate showing Gear Changes for Threading]
+
+Intermediate gear _b_ does not need to be changed as it is simply an
+"idler" for connecting gears _a_ and _c_. Gear _b_ is mounted on a
+swinging yoke _Y_ so that it can be adjusted to mesh properly with
+different gear combinations; after this adjustment is made, the lathe is
+geared for cutting 7 threads to the inch. (The change gears of many
+modern lathes are so arranged that different combinations are obtained
+by simply shifting a lever. A lathe having this quick-change gear
+mechanism is described in the latter part of this chapter.) The work _B_
+is placed between the centers just as it would be for turning, with the
+end to be threaded turned to a diameter of 1-1/4 inch, which is the
+outside diameter of the thread.
+
+=The Thread Tool.=--The form of tool used for cutting a V-thread is
+shown at _A_, Fig. 4. The end is ground V-shaped and to an angle of 60
+degrees, which corresponds to the angle of a standard V-thread. The
+front or flank, _f_ of the tool is ground back at an angle to provide
+clearance, but the top is left flat or without slope. As it is very
+important to grind the end to exactly 60 degrees, a gage _G_ is used,
+having 60-degree notches to which the tool-point is fitted. The tool is
+clamped in the toolpost as shown in the plan view, Fig. 2, square with
+the work, so that both sides of the thread will be cut to the same angle
+with the axis of the work. A very convenient way to set a thread tool
+square is illustrated at _B_, Fig. 1. The thread gage is placed against
+the part to be threaded, as shown, and the tool is adjusted until the
+angular sides of the point bear evenly in the 60-degree notch of the
+gage. The top of the tool point should be at the same height as the
+lathe centers, as otherwise the angle of the thread will not be correct.
+
+[Illustration: Fig. 4. Thread Tools and Gage for testing Angle of End]
+
+=Cutting the Thread.=--The lathe is now ready for cutting the thread.
+This is done by taking several cuts, as indicated at _A_, _B_, _C_ and
+_D_ in Fig. 5, the tool being fed in a little farther for each
+successive cut until the thread is finished. When these cuts are being
+taken, the carriage is moved along the bed, as previously explained, by
+the lead-screw _S_, Fig. 2. The carriage is engaged with the lead-screw
+by turning lever _u_ which causes the halves of a split nut to close
+around the screw. The way a lathe is handled when cutting a thread is as
+follows: After the lathe is started, the carriage is moved until the
+tool-point is slightly beyond the right end of the work, and the tool is
+fed in far enough to take the first cut which, ordinarily, would be
+about 1/16 inch deep. The carriage is then engaged with the lead-screw,
+by operating lever _u_, and the tool moves to the left (in this case 1/7
+inch for each revolution of the work) and cuts a winding groove as at
+_A_, Fig. 5. When the tool has traveled as far as the thread is wanted,
+it is withdrawn by a quick turn of cross-slide handle _e_, and the
+carriage is returned to the starting point for another cut. The tool is
+then fed in a little farther and a second cut is taken as at _B_, Fig.
+5, and this operation is repeated as at _C_ and _D_ until a "full"
+thread is cut or until the top of the thread is sharp. The thread is
+then tested for size but before referring to this part of the work, the
+way the carriage is returned to the starting point after each cut should
+be explained.
+
+[Illustration: Fig. 5. Thread is formed by taking a Number of Successive
+Cuts]
+
+When the tool is withdrawn at the end of the first cut, if the carriage
+is disengaged from the lead-screw and returned by hand, the tool may or
+may not follow the first cut when the carriage is again engaged with the
+lead-screw. If the number of threads to the inch being cut is a multiple
+of the number on the lead-screw _S_, then the carriage can be returned
+by hand and engaged with the lead-screw at random and the tool will
+follow the first cut. For example, if the lead-screw has six threads per
+inch, and 6, 12, 18 or any number of threads is being cut that is a
+multiple of six, the carriage can be engaged at any time and the tool
+will always follow the original cut. This is not the case, however, when
+the number of threads being cut is not a multiple of the number on the
+lead-screw.
+
+One method of bringing the carriage back to the starting point, when
+cutting threads which are not multiples, is to reverse the lathe (by
+shifting the overhead driving belts) in order to bring the tool back to
+the starting point without disengaging the carriage; in this way the
+tool is kept in the same relation to the work, and the carriage is not
+disengaged from the lead-screw until the thread is finished. This is a
+good method when cutting short threads having a length of say two or
+three inches; but when they are longer, and especially when the diameter
+is comparatively large (which means a slower speed), it is rather slow
+as considerable time is wasted while the tool is moving back to its
+starting point. This is due to the fact that the carriage is moved
+slowly by the lead-screw, but when disengaged, it can be traversed
+quickly by turning handle _d_, Fig. 2.
+
+A method of returning the carriage by hand when the number of threads
+being cut is not a multiple of the number on the lead-screw is as
+follows: The tool is moved a little beyond the right end of the work and
+the carriage or split nut is engaged with the lead-screw. The lathe is
+then turned forward by hand to take up any lost motion, and a line is
+made on the lathe bed showing the position of the carriage. The
+positions of the spindle and lead-screw are also marked by chalking a
+tooth on both the spindle and lead-screw gears, which happens to be
+opposite a corner or other point on the bed. After a cut is taken, the
+carriage is returned by hand to the original starting point as shown by
+the line on the bed, and is again engaged when the chalk marks show that
+the spindle and lead-screw are in their original position; the tool will
+then follow the first cut. If the body of the tailstock is moved against
+the bridge of the carriage before starting the first cut, the carriage
+can be located for each following cut by moving it back against the
+tailstock, and it will not be necessary to have a line on the bed.
+
+[Illustration: Fig. 6. Indicator used when Cutting Threads]
+
+=Indicator or Chasing Dial for Catching Threads.=--On some lathes there
+is an indicator for "catching threads," as this is called in shop
+language. This is a simple device attached to the carriage and consists
+of a graduated dial _D_ and a worm-wheel _W_ (see Figs. 2 and 6) which
+meshes with the lead-screw, so that the dial is revolved by the
+lead-screw when the carriage is stationary, and when the carriage is
+moved by the screw, the dial remains stationary. The indicator is used
+by engaging the carriage when one of the graduation lines is opposite
+the arrow mark; after a cut is taken the carriage is returned by hand
+and when one of the graduation lines again moves opposite the arrow, the
+half-nuts are thrown into mesh, as before, and this is repeated for each
+successive cut, thus causing the tool to always come right with the
+thread. If the number of threads per inch is even, engagement can be
+made when any line is opposite the arrow, but for odd numbers such as 3,
+7, 9, 11, etc., one of the four long or numbered lines must be used. Of
+course, if the thread being cut is a multiple of the number on the
+lead-screw, engagement can be made at any time, as previously
+mentioned.
+
+=Principle of the Thread Indicator.=--The principle upon which the
+thread indicator operates is as follows: The number of teeth in
+worm-wheel _W_ is some multiple of the number of threads per inch of the
+lead-screw, and the number of teeth in the worm-wheel, divided by the
+pitch of the screw, equals the number of graduations on the dial. For
+example, if the lead-screw has six threads per inch, the worm-wheel
+could have twenty-four teeth, in which case the dial would have four
+divisions, each representing an inch of carriage travel, and by
+sub-dividing the dial into eighths (as shown) each line would correspond
+to 1/2 inch of travel. The dial, therefore, would enable the carriage to
+be engaged with the lead-screw at points equal to a travel of one-half
+inch. To illustrate the advantage of this suppose ten threads per inch
+are being cut and (with the lathe stationary) the carriage is disengaged
+and moved 1/6 inch or one thread on the lead-screw; the tool point will
+also have moved 1/6 inch, but it will not be opposite the next thread
+groove in the work as the pitch is 1/10 inch. If the carriage is moved
+another thread on the lead-screw, or 2/6 inch, the tool will still be
+out of line with the thread on the work, but when it has moved three
+threads, or 1/2 inch, the tool will then coincide with the original cut
+because it has passed over exactly five threads. This would be true for
+any number of threads per inch that is divisible by 2. If the thread
+being cut had nine threads per inch or any other odd number, the tool
+would only coincide with the thread at points 1 inch apart. Therefore,
+the carriage can only be engaged when one of the four graduations
+representing an inch of travel is opposite the arrow, when cutting odd
+threads; whereas even numbers can be "caught" by using any one of the
+eight lines.
+
+This indicator can also be used for "catching" fractional threads. As an
+illustration, suppose 11-1/2 threads per inch are to be cut, and the
+carriage is engaged for the first cut when graduation line 1 is opposite
+the arrow; engagement would then be made for each successive cut, when
+either line 1 or 3 were opposite the arrow, or in other words at spaces
+equal to a carriage movement of 2 inches. As the use of the indicator
+when cutting fractional threads is liable to result in error, it is
+better to keep the half-nuts in engagement and return the carriage by
+reversing the lathe.
+
+=Replacing Sharpened Thread Tool.=--If it is necessary to sharpen the
+thread tool before the thread is finished, it should be reset square
+with the work by testing with the thread gage as at _B_, Fig. 1. The
+carriage is then engaged with the lead-screw and the lathe is turned
+forward to bring the tool opposite the partly finished thread and also
+to take up any backlash or lost motion in the gears or half-nut. If the
+tool-point is not in line with the thread groove previously cut, it can
+be shifted sidewise by feeding the compound rest _E_ in or out, provided
+the latter is set in an angular position as shown in the plan view, Fig.
+2.
+
+If the thread tool is ground flat on the top as at _A_, Fig. 4, it is
+not a good tool for removing metal rapidly as neither of its two cutting
+edges has any slope. In order to give each cutting edge a backward
+slope, it would be necessary to grind the top surface hollow or concave,
+which would be impracticable. When a course thread is to be cut, a tool
+shaped as at _B_ can be used to advantage for rough turning the thread
+groove, which is afterward finished to the correct depth and angle by
+tool _A_. This roughing tool is ground with a backward slope from the
+point and the latter is rounded to make it stronger.
+
+=Use of Compound Rest for Thread Cutting.=--Another form of thread tool
+is shown at _A_, Fig. 7, which is very good for cutting V-threads
+especially of coarse pitch. When this tool is used, the compound rest
+_E_ is set to an angle of 30 degrees, as shown, and it is fed in for the
+successive cuts by handle _w_ in the direction indicated by the arrow.
+It will be seen that the point a of the tool moves at an angle of 60
+degrees with the axis of the work, thus forming one side of the thread,
+and the cutting edge _a--b_, which can be set as shown at _B_, forms the
+opposite side and does all the cutting. As this edge is given a backward
+slope, as shown, it cuts easily and enables threading operations to be
+performed quickly. Threads cut in this way are often finished by taking
+a light cut with a regular thread tool. The cutting edge _a--b_ is
+ground to an angle of 60 degrees (or slightly less, if anything) with
+the side, as shown by sketch _A_.
+
+When cutting threads in steel or wrought iron, some sort of lubricant is
+usually applied to the tool to preserve the cutting end and give a
+smooth finish to the thread. Lard oil or a mixture of equal parts of
+lard oil and paraffin oil are often used for this purpose. If the thread
+is small, the lubricant may be applied from an ordinary oil can, but
+when cutting comparatively large threads, it is better to have a stream
+of oil constantly playing upon the tool-point. This constant flow may be
+obtained by mounting a can having a spout leading to the tool, on a
+bracket at the rear of the carriage.
+
+[Illustration: Fig. 7. Cutting Thread by using Compound Rest]
+
+[Illustration: Fig. 8. (A) V-thread. (B) U. S. Standard Thread. (C)
+Square Thread. (D) Left-hand Thread. (E) Double Square Thread. (F)
+Triple Square Thread]
+
+=Threads Commonly Used.=--Three forms of threads or screws which are in
+common use are shown in Fig. 8; these are the V-thread (_A_), the U. S.
+standard (_B_), and the square thread (_C_). The shapes of these threads
+are shown by the sectioned parts. The V-thread has straight sides which
+incline at an angle of 60 degrees with each other and at the same angle
+with the axis of the screw. The U. S. standard thread is similar to the
+V-thread except that the top of the thread and bottom of the groove is
+left flat, as shown, and the width of these flats is made equal to 1/8
+of the pitch. The square thread is square in section, the width _a_,
+depth _b_ and space _c_ being all equal. All of these threads are
+right-hand, which means that the grooves wind around to the right so
+that a nut will have to be turned toward the right to enter it on the
+thread. A left-hand thread winds in the other direction, as shown at
+_D_, and a nut is screwed on by turning it to the left.
+
+=Multiple Threads.=--Threads, in addition to being right-and
+left-handed, are single, as at _A_, _B_, _C_ and _D_, double, as at _E_,
+and triple, as at _F_, and for certain purposes quadruple threads or
+those of a higher multiple are employed. A double thread is different
+from a single thread in that it has two grooves, starting diametrically
+opposite, whereas a triple thread has three grooves cut as shown at _F_.
+The object of these multiple threads is to obtain an increase in lead
+without weakening the screw. For example, the threads shown at _C_ and
+_E_ have the same pitch _p_ but the lead _l_ of the double-threaded
+screw is twice that of the one with a single thread so that a nut would
+advance twice as far in one revolution, which is often a very desirable
+feature. To obtain the same lead with a single thread, the pitch would
+have to be double, thus giving a much coarser thread, which would weaken
+the screw, unless its diameter were increased. (The lead is the distance
+_l_ that one thread advances in a single turn, or the distance that a
+nut would advance in one turn, and it should not be confused with the
+pitch _p_, which is the distance between the centers of adjacent
+threads. Obviously the lead and pitch of a single thread are the same.)
+
+=Cutting a U. S. Standard Thread.=--The method of cutting a U. S.
+standard thread is the same as described for a V-thread, so far as
+handling the lathe is concerned. The thread tool must correspond, of
+course, to the shape of a U. S. standard thread. This tool is first
+ground to an angle of 60 degrees, as it would be for cutting a V-thread,
+and then the point is made flat as shown in Fig. 9. As will be recalled,
+the width of this flat should be equal to 1/8 of the pitch. By using a
+gage like the one shown at _G_, the tool can easily be ground for any
+pitch, as the notches around the periphery of the gage are marked for
+different pitches and the tool-point is fitted into the notch
+corresponding to the pitch wanted. If such a gage is not available, the
+width of the flat at the point can be tested by using, as a gage, a U.
+S. standard tap of the same pitch as the thread to be cut.
+
+When cutting the thread, the tool is set square with the blank, and a
+number of successive cuts are taken, the tool being fed in until the
+width w of the flat at the top of the thread is equal to the width at
+the bottom. The thread will then be the right size provided the outside
+diameter _D_ is correct and the tool is of the correct form. As it would
+be difficult to measure the width of this flat accurately, the thread
+can be tested by screwing a standard nut over it if a standard thread is
+being cut. If it is being fitted to a tapped hole, the tap itself is a
+very convenient gage to use, the method being to caliper the tap and
+then compare its size with the work.
+
+[Illustration: Fig. 9. U. S. Standard Thread, Thread Tool, and Gage]
+
+A good method of cutting a U. S. standard thread to a given size is as
+follows: First turn the outside of the blank accurately to diameter _D_,
+and then turn a small part of the end to diameter _r_ of the thread at
+the root. The finishing cut for the thread is then taken with the tool
+point set to just graze diameter _r_. If ordinary calipers were set to
+diameter _r_ and measurements taken in the thread groove, the size would
+be incorrect owing to the angularity of the groove, which makes it
+necessary to hold the calipers at an angle when measuring. To determine
+the root diameter divide 1.299 by the number of threads per inch and
+subtract the quotient from the outside diameter. Expressing this rule as
+a formula,
+
+               /1.299\
+  _r_ = _D_ - ( ----- )
+               \ _N_ /
+
+in which _D_ equals outside diameter; _N_, the number of threads per
+inch; and _r_, the root diameter. The number 1.299 is a constant that is
+always used.
+
+[Illustration: Fig. 10. End View of Lathe Headstock]
+
+=Cutting a Left-hand Thread.=--The only difference between cutting
+left-hand and right-hand threads in the lathe is in the movement of the
+tool with relation to the work. When cutting a right-hand thread, the
+tool moves from right to left, but this movement is reversed for
+left-hand threads because the thread winds around in the opposite
+direction. To make the carriage travel from left to right, the
+lead-screw is rotated backwards by means of reversing gears _a_ and _b_
+(Fig. 10) located in the headstock. Either of these gears can be
+engaged with the spindle gear by changing the position of lever _R_.
+When gear _a_ is in engagement, as shown, the drive from the spindle to
+gear _c_ is through gears _a_ and _b_, but when lever _R_ is raised thus
+shifting _b_ into mesh, the drive is direct and the direction of
+rotation is reversed. The thread is cut by starting the tool at _a_,
+Fig. 8, instead of at the end.
+
+[Illustration: Fig. 11. End of Square Thread Tool, and Graphic Method of
+Determining Helix Angle of Thread]
+
+=Cutting a Square Thread.=--The form of tool used for cutting a square
+thread is shown in Fig. 11. The width _w_ is made equal to one-half the
+pitch of the thread to be cut and the end _E_ is at an angle with the
+shank, which corresponds to the inclination _x--y_ of the threads. This
+angle _A_ depends upon the diameter of the screw and the lead of the
+thread; it can be determined graphically by drawing a line _a--b_ equal
+in length to the circumference of the screw to be cut, and a line
+_b--c_, at right angles, equal in length to the lead of the thread. The
+angle [alpha] between lines _a--b_ and _a--c_ will be the required angle
+_A_. (See end view of thread tool). It is not necessary to have this
+angle accurate, ordinarily, as it is simply to prevent the tool from
+binding against the sides of the thread. The end of a square thread tool
+is shown in section to the right, to illustrate its position with
+relation to the threads. The sides _e_ and _e_{1}_ are ground to slope
+inward, as shown, to provide additional clearance.
+
+When cutting multiple threads, which, owing to their increased lead,
+incline considerably with the axis of the screw, the angles for each
+side of the tool can be determined independently as follows: Draw line
+_a--b_ equal in length to the circumference of the thread, as before, to
+obtain the required angle _f_ of the rear or following side _e_{1}_; the
+angle _l_ of the opposite or leading side is found by making _a--b_
+equal to the circumference at the root of the thread. The tool
+illustrated is for cutting right-hand threads; if it were intended for a
+left-hand thread, the end, of course, would incline in the opposite
+direction. The square thread is cut so that the depth _d_ is equal to
+the width. When threading a nut for a square thread screw, it is the
+usual practice to use a tool having a width slightly greater than
+one-half the pitch, to provide clearance for the screw, and the width of
+a tool for threading square-thread taps to be used for tapping nuts is
+made slightly less than one-half the pitch.
+
+=Cutting Multiple Threads.=--When a multiple thread is to be cut, such
+as a double or triple thread, the lathe is geared with reference to the
+number of single threads to the inch. For example, the lead of the
+double thread, shown at _B_, Fig. 12, is one-half inch, or twice the
+pitch, and the number of single threads to the inch equals 1 / 1/2 = 2.
+Therefore, the lathe is geared for cutting two threads per inch. The
+first cut is taken just as though a single thread were being cut,
+leaving the work as shown at _A_. When this cut is finished the work is
+turned one-half a revolution (for a double thread) without disturbing
+the position of the lead-screw or carriage, which brings the tool midway
+between the grooves of the single thread as indicated by dotted lines.
+The second groove is then cut, producing a double thread as shown at
+_B_. In the case of a triple thread, the work would be indexed one-third
+of a revolution after turning the first groove, and then another third
+revolution to locate the tool for cutting the last groove. Similarly,
+for a quadruple thread, it would be turned one-quarter revolution after
+cutting each successive groove or thread.
+
+There are different methods of indexing the work when cutting multiple
+threads, in order to locate the tool in the proper position for cutting
+another thread groove. Some machinists, when cutting a double thread,
+simply remove the work from the lathe and turn it one-half a revolution
+by placing the tail of the driving dog in the opposite slot of the
+faceplate. This is a very simple method, but if the slots are not
+directly opposite or 180 degrees apart, the last thread will not be
+central with the first. Another and better method is to disengage the
+idler gear from the gear on the stud, turn the spindle and work
+one-half, or one-third, of a revolution, as the case might be, and then
+connect the gears. For example, if the stud gear had 96 teeth, the tooth
+meshing with the idler gear would be marked with chalk, the gears
+disengaged, and the spindle turned until the chalked tooth had made the
+required part of a revolution, which could be determined by counting the
+teeth. When this method is used, the number of teeth in the stud gear
+must be evenly divisible by two if a double thread is being cut, or by
+three for a triple thread, etc. If the stud is not geared to the spindle
+so that each makes the same number of revolutions, the ratio of the
+gearing must be considered.
+
+[Illustration: Fig. 12. Views illustrating how a Double Square Thread is
+Cut]
+
+=Setting Tool When Cutting Multiple Threads.=--Another method, which can
+sometimes be used for setting the tool after cutting the first groove of
+a multiple thread, is to disengage the lock-nuts from the lead-screw
+(while the spindle is stationary) and move the carriage back whatever
+distance is required to locate the tool in the proper position for
+taking the second cut. Evidently this distance must not only locate the
+tool in the right place, but be such that the lock-nuts can be
+re-engaged with the lead-screw. Beginning with a simple illustration,
+suppose a double thread is being cut having a lead of 1 inch. After the
+first thread groove is cut, the tool can be set in a central position
+for taking the second cut, by simply moving the carriage back 1/2 inch
+(one-half the lead), or 1/2 inch plus the lead or any multiple of the
+lead. If the length of the threaded part were 5 inches, the tool would
+be moved back far enough to clear the end of the work, or say 1/2 + 5 =
+5-1/2 inches. In order to disengage the lock-nuts and re-engage them
+after moving the carriage 5-1/2 inches (or any distance equal, in this
+case, to one-half plus a whole number), the lead-screw must have an even
+number of threads per inch.
+
+Assume that a double thread is being cut having 1-1/4 single threads per
+inch. The lead then would equal 1 / 1-1/4 = 0.8 inch, and if the
+carriage is moved back 0.8 / 2 = 0.4 inch, the tool will be properly
+located for the second cut; but the lock-nuts could not be re-engaged
+unless the lead-screw had ten threads per inch, which is finer than the
+pitch found on the lead-screws of ordinary engine lathes. However, if
+the movement were 0.4 + 0.8 x 2 = 2 inches, the lock-nuts could be
+re-engaged regardless of the number of threads per inch on the
+lead-screw. The rule then, is as follows:
+
+_Divide the lead of the thread by 2 for a double thread, 3 for a triple
+thread, 4 for a quadruple thread, etc., thus obtaining the pitch; then
+add the pitch to any multiple of the lead, which will give a movement,
+in inches, that will enable the lock-nuts to be re-engaged with the
+lead-screw._
+
+Whenever the number obtained by this rule is a whole number, obviously,
+the movement can be obtained with a lead-screw of any pitch. If the
+number is fractional, the number of threads per inch on the lead-screw
+must be divisible by the denominator of the fraction.
+
+To illustrate the application of the foregoing rule, suppose a quadruple
+thread is to be cut having 1-1/2 single threads per inch (which would be
+the number the lathe would be geared to cut). Then the lead of the
+thread = 1 / 1-1/2 = 0.6666 inch and the pitch = 0.6666 / 4 = 0.1666
+inch; adding the pitch to twice the lead we have 0.1666 + 2 x 0.6666 =
+1.499 inch. Hence, if the carriage is moved 1-1/2 inch (which will
+require a lead-screw having an even number of threads per inch), the
+tool will be located accurately enough for practical purposes. When the
+tool is set in this way, if it does not clear the end of the part being
+threaded, the lathe can be turned backward to place the tool in the
+proper position.
+
+[Illustration: Fig. 13. Indexing Faceplate used for Multiple Thread
+Cutting]
+
+The foregoing rule, as applied to triple threads or those of a higher
+number, does not always give the only distance that the carriage can be
+moved. To illustrate, in the preceding example the carriage movement
+could be equal to 0.499, or what is practically one-half inch, instead
+of 1-1/2 inch, and the tool would be properly located. The rule,
+however, has the merit of simplicity and can be used in most cases.
+
+Special faceplates are sometimes used for multiple thread cutting, that
+enable work to be easily and accurately indexed. One of these is
+illustrated in Fig. 13; it consists of two parts _A_ and _B_, part _A_
+being free to rotate in relation to _B_ when bolts _C_ are loosened. The
+driving pin for the lathe dog is attached to plate _A_. When one groove
+of a multiple thread is finished, bolts _C_ are loosened and plate _A_
+is turned around an amount corresponding to the type of thread being
+cut. The periphery of plate _A_ is graduated in degrees, as shown, and
+for a double thread it would be turned one-half revolution or 180
+degrees, for a triple thread, 120 degrees, etc. This is a very good
+arrangement where multiple thread cutting is done frequently.
+
+[Illustration: Fig. 14. Correct and Incorrect Positions of Tool for
+Taper Thread Cutting]
+
+=Taper Threading.=--When a taper thread is to be cut, the tool should be
+set square with axis _a--a_ as at _A_, Fig. 14, and not by the tapering
+surface as at _B_. If there is a cylindrical part, the tool can be set
+as indicated by the dotted lines. All taper threads should be cut by the
+use of taper attachments. If the tailstock is set over to get the
+required taper, and an ordinary bent-tail dog is used for driving, the
+curve of the thread will not be true, or in other words the thread will
+not advance at a uniform rate; this is referred to by machinists as a
+"drunken thread." This error in the thread is due to the angularity
+between the driving dog and the faceplate, which causes the work to be
+rotated at a varying velocity. The pitch of a taper thread that is cut
+with the tailstock set over will also be slightly finer than the pitch
+for which the lathe is geared. The amount of these errors depends upon
+the angle of the taper and the distance that the center must be offset.
+
+=Internal Threading.=--Internal threading, or cutting threads in holes,
+is an operation performed on work held in the chuck or on a faceplate,
+as for boring. The tool used is similar to a boring tool except that the
+working end is shaped to conform to the thread to be cut. The method of
+procedure, when cutting an internal thread, is similar to that for
+outside work, as far as handling the lathe is concerned. The hole to be
+threaded is first bored to the root diameter _D_, Fig. 15, of the screw
+that is to fit into it. The tool-point (of a tool for a U. S. standard
+or V-thread) is then set square by holding a gage _G_ against the true
+side of the work and adjusting the point to fit the notch in the gage as
+shown. The view to the right shows the tool taking the first cut.
+
+[Illustration: Fig. 15. Method of setting and using Inside Thread Tool]
+
+Very often the size of a threaded hole can be tested by using as a gage
+the threaded part that is to fit into it. When making such a test, the
+tool is, of course, moved back out of the way. It is rather difficult to
+cut an accurate thread in a small hole, especially when the hole is
+quite deep, owing to the flexibility of the tool; for this reason
+threads are sometimes cut slightly under size with the tool, after which
+a tap with its shank end held straight by the tailstock center is run
+through the hole. In such a case, the tap should be calipered and the
+thread made just small enough with the tool to give the tap a light cut.
+Small square-threaded holes are often finished in this way, and if a
+number of pieces are to be threaded, the use of a tap makes the holes
+uniform in size.
+
+=Stop for Thread Tools.=--When cutting a thread, it is rather difficult
+to feed in the tool just the right amount for each successive cut,
+because the tool is moved in before it feeds up to the work. A stop is
+sometimes used for threading which overcomes this difficulty. This stop
+consists of a screw _S_, Fig. 16, which enters the tool slide and passes
+through a block _B_ clamped in front of the slide. The hole in the block
+through which the stop-screw passes is not threaded, but is large enough
+to permit the screw to move freely. When cutting a thread, the tool is
+set for the first cut and the screw is adjusted until the head is
+against the fixed block. After taking the first cut, the stop-screw is
+backed out, say one-half revolution, which allows the tool to be fed in
+far enough for a second cut. If this cut is about right for depth, the
+screw is again turned about one-half revolution for the next cut and
+this is continued for each successive cut until the thread is finished.
+By using a stop of this kind, there is no danger of feeding the tool in
+too far as is often done when the tool is set by guess. If this form of
+stop is used for internal threading, the screw, instead of passing
+through the fixed block, is placed in the slide so that the end or head
+will come against the stop _B_. This change is made because the tool is
+fed outward when cutting an internal thread.
+
+[Illustration: Fig. 16. Cross-slide equipped with Stop for Regulating
+Depth of Cut when Threading]
+
+=The Acme Standard Thread.=--The Acme thread is often used, at the
+present time, in place of a square thread. The angle between the sides
+of the Acme thread is 29 degrees (see Fig. 21) and the depth is made
+equal to one-half the pitch plus 0.010 inch to provide clearance and
+insure a bearing upon the sides. The thread tool is ordinarily ground to
+fit a gage having notches representing different pitches. An improved
+form of Acme thread gage is shown in Fig. 17. The tool point is first
+ground to the correct angle by fitting it to the 29-degree notch in the
+end of the gage, as at _A_. The end is then ground to the proper width
+for the pitch to be cut, by testing it, as at _B_. The numbers opposite
+the shallow notches for gaging the width represent the number of threads
+per inch. With this particular gage, the tool can be set square by
+placing edge _D_ against the turned surface to be threaded, and
+adjusting the tool until the end is in line with the gage, as at _C_. By
+placing the tool in this position, the angle between the side and the
+end can also be tested.
+
+[Illustration: Fig. 17. Gage for grinding and setting Acme Thread Tools]
+
+In case it should be necessary to measure the end width of an Acme
+thread tool, for a pitch not on the regular gage, this can be done by
+using a vernier gear-tooth caliper, as indicated in Fig. 18. If we
+assume that the caliper jaws bear on the sides of the tool at a distance
+_A_ from the top, equal to 1/4 inch, then the width of the tool point
+equals the caliper reading (as shown by the horizontal scale) minus
+0.1293 inch. For example, if the caliper reading was 0.315 inch, the
+width at the point would equal 0.315 - 0.1293 = 0.1857 inch, assuming that
+the sides were ground to the standard angle of 29 degrees. The constant
+to be subtracted from the caliper reading equals 2 _A_ tan 14 deg. 30' or,
+in this case, 2 x 0.25 x 0.2586 = 0.1293.
+
+[Illustration: Fig. 18. Measuring Width of Acme Thread Tool with Vernier
+Gear-tooth Caliper]
+
+=The Whitworth Thread.=--The Whitworth (or British Standard Whitworth)
+thread, which is used principally in Great Britain, has an included
+angle of 55 degrees, and the threads are rounded at the top and at the
+root, as shown in Fig. 23. The shape of the tool used for cutting this
+thread is also shown in this illustration. The end is rounded to form
+the fillet at the root of the thread, and the round corners on the sides
+give the top of the thread the required curvature. Every pitch requires
+a different tool, and the cutting end is given the curved form by
+milling or hobbing. The hob used for this purpose is accurately threaded
+to correspond with the pitch for which the tool is required, and then it
+is fluted to form cutting edges, and is hardened. The hob is then used
+like a milling cutter for forming the end of the thread tool. The tool
+is sharpened by grinding on the top. The method of cutting a Whitworth
+thread is, of course, similar to that followed for a U. S. standard or
+V-thread, in that the tool is set square with the unthreaded blank and
+at the same height as the lathe centers, in order to secure a thread of
+the proper form. Care should be taken to turn the blank to the right
+diameter so that the top of the thread will be fully rounded when the
+screw is the required size.
+
+[Illustration: Fig. 19. United States Standard Thread]
+
+[Illustration: Fig. 20. Standard Sharp V-thread]
+
+[Illustration: Fig. 21. Acme Standard Thread]
+
+[Illustration: Fig. 22. Square Thread]
+
+[Illustration: Fig. 23. Whitworth Standard Thread]
+
+[Illustration: Fig. 24. Standard Worm Thread]
+
+=Worm Threads.=--The standard worm thread has an angle of 29 degrees
+between the sides, the same as an Acme thread, but the depth of a worm
+thread and the width of the flat at the top and bottom differ from the
+Acme standard, as will be seen by comparing Figs. 21 and 24. The whole
+depth of the thread equals the linear pitch multiplied by 0.6866, and
+the width of the thread tool at the end equals the linear pitch
+multiplied by 0.31. Gages notched for threads of different pitch are
+ordinarily used when grinding worm thread tools.
+
+When it is necessary to cut multiple-threaded worms of large lead in an
+ordinary lathe, difficulty is sometimes experienced because the
+lead-screw must be geared to run much faster than the spindle, thus
+imposing excessive strains on the gearing. This difficulty is sometimes
+overcome by mounting a belt pulley on the lead-screw, beside the change
+gear, and connecting it to the countershaft by a belt; the spindle is
+then driven through the change gearing from the lead-screw, instead of
+_vice versa_.
+
+=Coarse Threading Attachment.=--To avoid the difficulties connected with
+cutting threads of large lead, some lathes are equipped with a coarse
+screw-cutting attachment. The arrangement of this attachment, as made by
+the Bradford Machine Tool Co., is as follows: On the usual reversing
+shaft, and inside of the headstock, there is a sliding double gear, so
+arranged as to be engaged with either the usual gear on the spindle, or
+with a small pinion at the end of the cone. The gears are so
+proportioned that the ratio of the two engagements is as 10 to 1; that
+is, when engaged with the cone gear (the back-gears being thrown in) the
+mating gear will make ten revolutions to one of the spindle, so that
+when the lathe is ordinarily geared to cut one thread per inch, it will,
+when driven by the cone pinion, cut one thread in ten inches. This
+construction dispenses with the extra strain on the reverse gears due to
+moving the carriage at the rapid rate that would be necessary for such a
+large lead, when not using an attachment. These attachments are not only
+extensively used for the cutting of coarse screws but for cutting oil
+grooves on cylindrical parts.
+
+When cutting a thread of large lead or "steep pitch," the top of the
+thread tool should be ground so that it is at right angles to the
+thread; then the thread groove will be cut to the same width as the
+tool.
+
+=Testing the Size of a Thread.=--When the thread tool has been fed in
+far enough to form a complete thread, the screw is then tested for size.
+If we assume that a bolt is being threaded for a standard nut, it would
+be removed from the lathe and the test made by screwing a nut on the
+end. If the thread were too large, the nut might screw on very tightly
+or not at all; in either case, the work would again be placed in the
+lathe and a light cut taken over it to reduce the thread to the proper
+size. When replacing a threaded part between the centers, it should be
+put back in the original position, that is, with the "tail" of the
+driving dog in the same slot of the faceplate it previously occupied.
+
+[Illustration: Fig. 25. Testing Diameter of Thread with Calipers and
+Micrometer]
+
+As it is difficult to tell just when a thread is cut to the exact size,
+special thread calipers having wedge-shaped ends are sometimes used for
+measuring the diameter of a V-thread or a U. S. standard thread, at the
+bottom of the grooves or the root diameter, as shown at _A_ in Fig. 25.
+These calipers can be set from a tap corresponding to the size of the
+thread being cut, or from a previously threaded piece of the right
+size.
+
+=The Thread Micrometer.=--Another form of caliper for testing threads is
+shown at _B_. This is one of the micrometer type and is intended for
+very accurate work. The spindle of this micrometer has a conical end and
+the "anvil" is V-shaped, and these ends bear on the sides of the thread
+or the surfaces which form the bearing when the screw is inserted in a
+nut or threaded hole. The cone-shaped point is slightly rounded so that
+it will not bear in the bottom of the thread. There is also sufficient
+clearance at the bottom of the V-shaped anvil to prevent it from bearing
+on top of the thread. The diameter as indicated by this micrometer is
+the "pitch diameter" of the thread and is equal to the outside diameter
+minus the depth of one thread. This depth may be determined as follows:
+
+Depth of a V-thread = 0.866 / No. of threads per inch;
+
+Depth of a U. S. standard thread = 0.6495 / No. of threads per inch;
+
+Depth of Whitworth thread = 0.6403 / No. of threads per inch.
+
+The movable point measures all pitches, but the fixed anvil is limited
+in its capacity, for if made large enough to measure a thread of, say,
+1/4-inch pitch, it would be too wide at the top to measure a thread of
+1/24-inch pitch, hence each caliper is limited in the range of threads
+that the anvil can measure. When measuring the "angle diameter" of a
+thread, the micrometer should be passed back and forth across the
+thread, in order to make sure that the largest dimension or the actual
+diameter is being measured. If the micrometer is placed over what seems
+to be the center of the screw and the reading is taken by simply
+adjusting in the anvil or point against the thread, without moving the
+micrometer back and forth across it, an incorrect reading may be
+obtained.
+
+If standard threaded reference gages are available, the size of the
+thread being cut can be tested by comparing it with the gage.
+Micrometers having small spherical measuring ends (see sketch _A_, Fig.
+26) are sometimes used for this purpose. The ball points are small
+enough to bear against the sides of the thread and the diameter, as
+compared with the reference gage, can be determined with great
+accuracy.
+
+[Illustration: Fig. 26. (A) Testing Size of Thread with Ball-point
+Micrometer. (B) Testing Size of V-thread by the Three-wire System. (C)
+Testing the Size of a U. S. Standard Thread]
+
+=Three-wire System of Measuring Threads.=--A method of measuring threads
+by using an ordinary micrometer and three wires of equal diameter is
+illustrated at _B_ and _C_, Fig. 26. Two wires are placed between the
+threads on one side and one on the opposite side of the screw. The
+dimension _M_ over the wires is then measured with an ordinary
+micrometer. When the thread is cut to a standard size, the dimension _M_
+for different threads is as follows:
+
+For a U. S. standard thread:
+
+_m_ = _d_ - 1.5155_p_ + 3_w_
+
+For a sharp V-thread:
+
+_m_ = _d_ - 1.732_p_ + 3_w_
+
+For a Whitworth standard thread:
+
+_m_ = _d_ - 1.6008_p_ + 3.1657_w_
+
+In these formulas, _d_ = standard outside diameter of screw; _m_ =
+measurement over wires; _w_ = diameter of wires; _p_ = pitch of thread =
+1 / number of threads per inch.
+
+To illustrate the use of the formula for the U. S. standard thread, let
+us assume that a screw having 6 threads per inch (1/6-inch pitch) is to
+be cut to a diameter of 1-1/2 inch, and that wires 0.140 inch diameter
+are to be used in conjunction with a micrometer for measurement. Then
+the micrometer reading _m_ should be
+
+1-1/2 - 1.5155 x 1/6 + 3 x 0.140 = 1.6674 inch
+
+If the micrometer reading were 1.670 inch, it would indicate that the
+pitch diameter of the screw was too large, the error being equal to
+difference between 1.667 and the actual reading.
+
+[Illustration: Fig. 27. Rivett-Dock Circular Threading Tool in Working
+Position]
+
+=Rivett-Dock Threading Tool.=--A special form of thread tool, which
+overcomes a number of disadvantages common to an ordinary single-point
+thread tool, is shown in Fig. 27. This tool has a circular-shaped cutter
+_C_, having ten teeth around its circumference, which, beginning with
+tooth No. 1, gradually increase in height, cutter No. 2 being higher
+than No. 1, etc. This cutter is mounted on a slide _S_, that is fitted
+to the frame _F_, and can be moved in or out by lever _L_. The hub of
+this lever has an eccentric stud which moves slide _S_ and locks it when
+in the forward or cutting position. The action of the lever in moving
+the slide engages the cutter with pawl _P_, thus rotating the cutter one
+tooth at a time and presenting a different tooth to the work for each
+movement of the lever. When the slide is moved forward, the heel or
+underside of the tooth which is in the working position rests on a stop
+that takes the thrust of the cut.
+
+When the tool is in use, it is mounted on the tool-block of the lathe as
+shown in the illustration. The cutter is set for height by placing a
+tooth in the working position and setting the top level with the lathe
+center. The cutter is also set square with the work by using an ordinary
+square, and it is tilted slightly from the vertical to correspond with
+the angle of the thread to be cut, by adjusting frame _F_. At first a
+light cut is taken with lever _L_ moved forward and tooth No. 1 on the
+stop. After this cut is completed, the lever is reversed which rotates
+the cutter one tooth, and the return movement places tooth No. 2 in the
+working position. This operation is repeated until the tenth tooth
+finishes the thread. It is often necessary, when using a single-point
+thread tool, to re-sharpen it before taking the finishing cut, but with
+a circular tool this is not necessary, for by using the different teeth
+successively, the last tooth, which only takes finishing cuts, is kept
+in good condition.
+
+=Cutting Screws to Compensate for Shrinkage.=--Some tool steels are
+liable to shrink more or less when they are hardened; consequently if a
+very accurate hardened screw is required, it is sometimes cut so that
+the pitch is slightly greater than standard, to compensate for the
+shrinkage due to the hardening operation. As the amount of contraction
+incident to hardening is very little, it is not practicable to use
+change gears that will give the exact pitch required. A well-known
+method of obtaining this increase of pitch is by the use of a taper
+attachment.
+
+For example, suppose a tap having 8 threads per inch is to be threaded,
+and, owing to the contraction of the steel, the pitch must be 0.12502
+inch instead of 0.125 inch. The lathe is geared to cut 8 threads per
+inch or 0.125 inch pitch, and then the taper attachment is set to an
+angle _a_, Fig. 28, the cosine of which equals 0.125/0.12502; that is,
+the cosine of angle _a_ equals _the pitch required after hardening_,
+divided by the _pitch necessary to compensate for shrinkage_. The angle
+is then found by referring to a table of cosines. The tap blank is also
+set to the same angle a by adjusting the tailstock center, thus locating
+the axis of the work parallel with the slide of the taper attachment.
+When the carriage moves a distance _x_, the tool point will have moved a
+greater distance _y_ along the work, the difference between x and y
+depending upon angle _a_; hence the tool will cut a thread of slightly
+greater pitch than the lathe is geared to cut.
+
+To illustrate by using the preceding example, cosine of angle _a_ =
+0.125/0.12502 = 0.99984. By referring to a table of cosines, we find
+that 0.99984 is the cosine of 1 degree, approximately; hence, the taper
+attachment slide and the work should be set to this angle. (The angle
+_a_ in Fig. 28 has been exaggerated in order to more clearly illustrate
+the principle.)
+
+[Illustration: Fig. 28. Diagram Illustrating Method of Cutting a Thread
+to Compensate for the Error in Pitch due to Shrinkage in Hardening]
+
+As is well known, it is objectionable to cut a thread with the tailstock
+center offset, because the work is not rotated at a uniform velocity,
+owing to the fact that the driving dog is at an angle with the
+faceplate. For a small angle such as 1 degree, however, the error
+resulting from this cause would be very small.
+
+If a thread having a pitch slightly less than standard is needed to fit
+a threaded part which has contracted in hardening, the taper attachment
+can also be used provided the lathe is equipped with special gears to
+cut a little less than the required pitch. Suppose a screw having a
+pitch of 0.198 inch is required to fit the thread of a nut the pitch of
+which has been reduced from 0.200 inch to 0.198 inch. If gears having 83
+and 84 teeth are available, these can be inserted in a compound train,
+so as to reduce the 0.200 inch pitch that would be obtained with the
+regular gearing, to 83/84 of 0.200 or 0.19762 inch. This pitch, which is
+less than the 0.198 inch pitch required, is then increased by using the
+taper attachment as previously described. (This method was described by
+Mr. G. H. Gardner in MACHINERY, February, 1914.)
+
+=Calculating Change Gears for Thread Cutting.=--As previously mentioned,
+the change gears for cutting threads of various pitches are shown by a
+table or "index plate" attached to the lathe. The proper gears to be
+used can be calculated, but the use of the table saves time and tends to
+avoid mistakes. Every machinist, however, should know how to determine
+the size of gears used for cutting any number of threads to the inch.
+Before referring to any rules, let us first consider why a lathe cuts a
+certain number of threads to the inch and how this number is changed by
+the use of different gears.
+
+As the carriage _C_ and the tool are moved by the lead-screw _S_ (see
+Fig. 2), which is geared to the spindle, the number of threads to the
+inch that are cut depends, in every case, upon the number of turns the
+work makes while the lead-screw is moving the carriage one inch. If the
+lead-screw has six threads per inch, it will make six revolutions while
+the carriage and the thread tool travel one inch along the piece to be
+threaded. Now if the change gears _a_ and _c_ (see also sketch _A_, Fig.
+29) are so proportioned that the spindle makes the same number of
+revolutions as the lead-screw, in a given time, it is evident that the
+tool will cut six threads per inch. If the spindle revolved twice as
+fast as the lead-screw, it would make twelve turns while the tool moved
+one inch, and, consequently, twelve threads per inch would be cut; but
+to get this difference in speeds it is necessary to use a combination of
+gearing that will cause the lead-screw to revolve once while the lathe
+spindle and work make two revolutions.
+
+[Illustration: Fig. 29. (A) Lathe with Simple Gearing for Thread
+Cutting. (B) Compound Geared Lathe]
+
+Suppose that nine threads to the inch are to be cut and the lead-screw
+has six threads per inch. In this case the work must make nine
+revolutions while the lead-screw makes six and causes the carriage and
+thread tool to move one inch, or in other words, one revolution of the
+lead-screw corresponds to one and one-half revolution of the spindle;
+therefore, if the lead-screw gear _c_ has 36 teeth, the gear _a_ on the
+spindle stud should have 24 teeth. The spindle will then revolve one and
+one-half times faster than the lead-screw, provided the stud rotates at
+the same rate of speed as the main lathe spindle. The number of teeth in
+the change gears that is required for a certain pitch can be found by
+multiplying the number of threads per inch of the lead-screw, and the
+number of threads per inch to be cut, by the same trial multiplier. The
+formula which expresses the relation between threads per inch of
+lead-screw, threads per inch to be cut, and the number of teeth in the
+change gears, is as follows:
+
+  threads per inch of lead-screw   teeth in gear on spindle stud
+  ------------------------------ = -----------------------------
+    threads per inch to be cut      teeth in gear on lead-screw
+
+Applying this to the example given, we have 6/9 = 24/36. The values of
+36 and 24 are obtained by multiplying 6 and 9, respectively, by 4,
+which, of course, does not change the proportion. Any other number could
+be used as a multiplier, and if gears having 24 and 36 teeth were not
+available, this might be necessary. For example, if there were no gears
+of this size, some other multiplier as 5 or 6 might be used.
+
+Suppose the number of teeth in the change gears supplied with the lathe
+are 24, 28, 32, 36, etc., increasing by four teeth up to 100, and assume
+that the lead-screw has 6 threads per inch and that 10 threads per inch
+are to be cut. Then,
+
+   6    6 x 4   24
+  -- = ------ = --
+  10   10 x 4   40
+
+By multiplying both numerator and denominator by 4, we obtain two
+available gears having 24 and 40 teeth, respectively. The 24-tooth gear
+goes on the spindle stud and, the 40-tooth gear on the lead-screw. The
+number of teeth in the intermediate or "idler" gear _b_, which connects
+the stud and lead-screw gears, is not considered as it does not affect
+the ratios between gears _a_ and _c_, but is used simply to transmit
+motion from one gear to the other.
+
+We have assumed in the foregoing that the spindle stud (on which gear
+_a_ is mounted) and the main spindle of the lathe are geared in the
+ratio of one to one and make the same number of revolutions. In some
+lathes, however, these two members do not rotate at the same speed, so
+that if equal gears were placed on the lead-screw and spindle stud, the
+spindle would not make the same number of revolutions as the lead-screw.
+In that case if the actual number of threads per inch in the lead-screw
+were used when calculating the change gears, the result would be
+incorrect; hence, to avoid mistakes, the following general rule should
+be used as it gives the correct result, regardless of the ratios of the
+gears which connect the spindle and spindle stud:
+
+_Rule.--First find the number of threads per inch that is cut when gears
+of the same size are placed on the lead-screw and spindle, either by
+actual trial or by referring to the index plate. Then place this number
+as the numerator of a fraction and the number of threads per inch to be
+cut, as the denominator; multiply both numerator and denominator by some
+trial number, until numbers are obtained which correspond to numbers of
+teeth in gears that are available._ The product of the trial number and
+the numerator (or "lathe screw constant") represents the gear _a_ for
+the spindle stud, and the product of the trial number and the
+denominator, the gear for the lead-screw.
+
+=Lathes with Compound Gearing.=--When gearing is arranged as shown at
+_A_, Fig. 29, it is referred to as simple gearing, but sometimes it is
+necessary to introduce two gears between the stud and screw as at _B_,
+which is termed compound gearing. The method of figuring compound
+gearing is practically the same as that for simple gearing. To find the
+change gears used in compound gearing, place the "screw constant"
+obtained by the foregoing rule, as the numerator, and the number of
+threads per inch to be cut as the denominator of a fraction; resolve
+both numerator and denominator into two factors each, and multiply each
+"pair" of factors by the same number, until values are obtained
+representing numbers of teeth in available change gears. (One factor in
+the numerator and one in the denominator make a "pair" of factors.)
+
+Suppose the lathe cuts 6 threads per inch when gears of equal size are
+used, and that the number of teeth in the gears available are 30, 35, 40
+and so on, increasing by 5 up to 100. If 24 threads per inch are to be
+cut, the screw constant 6 is placed in the numerator and 24 in the
+denominator. The numerator and denominator are then divided into factors
+and each pair of factors is multiplied by the same number to find the
+gears, thus:
+
+   6   2 x 3   (2 x 20) x (3 x 10)   40 x 30
+  -- = ----- = ------------------- = -------
+  24   4 x 6   (4 x 20) x (6 x 10)   80 x 60
+
+The last four numbers indicate the gears which should be used. The upper
+two having 40 and 30 teeth are the _driving_ gears and the lower two
+having 80 and 60 teeth are the _driven_ gears. The driving gears are
+gear _a_ on the spindle stud and gear _c_ on the intermediate stud,
+meshing with the lead-screw gear, and the driven gears are gears _b_ and
+_d_. It makes no difference which of the driving gears is placed on the
+spindle stud, or which of the driven is placed on the lead-screw.
+
+=Fractional Threads.=--Sometimes the lead of a thread is given as a
+fraction of an inch instead of stating the number of threads per inch.
+For example, a thread may be required to be cut, having 3/8-inch lead.
+The expression "3/8-inch lead" should first be transformed to "number of
+threads per inch." The number of threads per inch (the thread being
+single) equals:
+
+   1        3   8
+  --- = 1 / - = - = 2-2/3
+  3/8       8   3
+
+To find the change gears to cut 2-2/3 threads per inch in a lathe having
+a screw constant of 8 and change gears varying from 24 to 100 teeth,
+increasing by 4, proceed as follows:
+
+    8       2 x 4       (2 x 36) x (4 x 24)     72 x 96
+  ----- = --------- = ----------------------- = -------
+  2-2/3   1 x 2-2/3   (1 x 36) x (2-2/3 x 24)   36 x 64
+
+As another illustration, suppose we are to cut 1-3/4 thread per inch on
+a lathe having a screw constant of 8, and that the gears have 24, 28,
+32, 36, 40 teeth, etc., increasing by four up to one hundred. Following
+the rule:
+
+    8       2 x 4       (2 x 36) x (4 x 16)     72 x 64
+  ----- = --------- = ----------------------- = -------
+  1-3/4   1 x 1-3/4   (1 x 36) x (1-3/4 x 16)   36 x 28
+
+The gears having 72 and 64 teeth are the _driving_ gears, and those with
+36 and 28 teeth are the _driven_ gears.
+
+=Change Gears for Metric Pitches.=--When screws are cut in accordance
+with the metric system, it is the usual practice to give the lead of the
+thread in millimeters, instead of the number of threads per unit of
+measurement. To find the change gears for cutting metric threads, when
+using a lathe having an English lead-screw, first determine the number
+of threads per inch corresponding to the given lead in millimeters.
+Suppose a thread of 3 millimeters lead is to be cut in a lathe having an
+English lead-screw and a screw constant of 6. As there are 25.4
+millimeters per inch, the number of threads per inch will equal 25.4 /
+3. Place the screw constant as the numerator, and the number of threads
+per inch to be cut as the denominator:
+
+     6          25.4   6 x 3
+  ------- = 6 / ---- = -----
+   25.4          3     25.4
+   ----
+    3
+
+The numerator and denominator of this fractional expression of the
+change-gear ratio are next multiplied by some trial number to determine
+the size of the gears. The first whole number by which 25.4 can be
+multiplied so as to get a whole number as the result is 5. Thus, 25.4 x
+5 = 127; hence, one gear having 127 teeth is always used when cutting
+metric threads with an English lead-screw. The other gear required in
+this case has 90 teeth. Thus:
+
+  6 x 3 x 5   90
+  --------- = ---
+  25.4 x 5    127
+
+Therefore, the following rule can be used to find the change gears for
+cutting metric pitches with an English lead-screw:
+
+_Rule.--Place the lathe screw constant multiplied by the lead of the
+required thread in millimeters multiplied by 5, as the numerator of the
+fraction, and 127 as the denominator. The product of the numbers in the
+numerator equals the number of teeth for the spindle-stud gear, and 127
+is the number of teeth for the lead-screw gear._
+
+If the lathe has a metric pitch lead-screw, and a screw having a given
+number of threads per inch is to be cut, first find the "metric screw
+constant" of the lathe or the lead of thread in millimeters that would
+be cut with change gears of equal size on the lead-screw and spindle
+stud; then the method of determining the change gears is simply the
+reverse of the one already explained for cutting a metric thread with an
+English lead-screw.
+
+_Rule.--To find the change gears for cutting English threads with a
+metric lead-screw, place 127 in the numerator and the threads per inch
+to be cut, multiplied by the metric screw constant multiplied by 5, in
+the denominator; 127 is the number of teeth on the spindle-stud gear and
+the product of the numbers in the denominator equals the number of teeth
+in the lead-screw gear._
+
+=Quick Change-gear Type of Lathe.=--A type of lathe that is much used at
+the present time is shown in Fig. 30. This is known as the quick
+change-gear type, because it has a system of gearing which makes it
+unnecessary to remove the change gears and replace them with different
+sizes for cutting threads of various pitches. Changes of feed are also
+obtained by the same mechanism, but the feeding movement is transmitted
+to the carriage by the rod _R_, whereas the screw _S_{1}_ is used for
+screw cutting. As previously explained, the idea of using the screw
+exclusively for threading is to prevent it from being worn excessively,
+as it would be if continually used in place of rod _R_, for feeding the
+carriage when turning.
+
+[Illustration: Fig. 30. Lathe having Quick Change-gear Mechanism]
+
+[Illustration: Fig. 31. End and Side Views of Quick Change-gear
+Mechanism]
+
+The general construction of this quick change gear mechanism and the
+way the changes are made for cutting threads of different pitch, will be
+explained in connection with Figs. 30, 31 and 32, which are marked with
+the same reference letters for corresponding parts. Referring to Fig.
+30, the movement is transmitted from gear _s_ on the spindle stud
+through idler gear _I_, which can be moved sidewise to mesh with either
+of the three gears _a_, _b_ or _c_, Fig. 31. This cone of three gears
+engages gears _d_, _e_ and _f_, any one of which can be locked with
+shaft _T_ (Fig. 32) by changing the position of knob _K_. On shaft _T_
+there is a gear _S_ which can be moved along the shaft by hand lever _L_
+and, owing to the spline or key _t_, both the sliding gear and shaft
+rotate together. Shaft _T_, carrying gears _d_, _e_ and _f_ and the
+sliding gear _S_, is mounted in a yoke _Y_, which can be turned about
+shaft _N_, thus making it possible to lower sliding gear _S_ into mesh
+with any one of a cone of eight gears _C_, Fig. 31. The shaft on which
+the eight gears are mounted has at the end a small gear _m_ meshing with
+gear _n_ on the feed-rod, and the latter, in turn, drives the
+lead-screw, unless gear _o_ is shifted to the right out of engagement,
+which is its position except when cutting threads.
+
+[Illustration: Fig. 32. Sectional Views of Quick Change-gear Mechanism]
+
+With this mechanism, eight changes for different threads or feeds are
+obtained by simply placing gear _S_ into mesh with the various sized
+gears in cone _C_. As the speed of shaft _T_ depends on which of the
+three gears _d_, _e_ and _f_ are locked to it, the eight changes are
+tripled by changing the position of knob _K_, making twenty-four. Now by
+shifting idler gear _I_, three speed changes may be obtained for gears
+_a_, _b_ and _c_, which rotate together, so that the twenty-four changes
+are also tripled, giving a total of seventy-two variations without
+removing any gears, and if a different sized gear _s_ were placed on the
+spindle stud, an entirely different range could be obtained, but such a
+change would rarely be necessary. As shown in Fig. 30, there are eight
+hardened steel buttons _B_, or one for each gear of the cone _C_, placed
+at different heights in the casing. When lever _L_ is shifted sidewise
+to change the position of sliding gear _S_, it is lowered onto one of
+these buttons (which enters a pocket on the under side) and in this way
+gear _S_ is brought into proper mesh with any gear of the cone _C_. To
+shift lever _L_, the handle is pulled outward against the tension of
+spring _r_ (Fig. 32), which disengages latch _l_ and enables the lever
+to be lifted clear of the button; yoke _Y_ is then raised or lowered, as
+the case may be, and lever _L_ with the sliding gear is shifted
+laterally to the required position.
+
+[Illustration: Fig. 33. Index Plate showing Position of Control Levers
+for Cutting Threads of Different Pitch]
+
+The position of lever _L_ and knob _K_ for cutting threads of different
+pitches is shown by an index plate or table attached to the lathe and
+arranged as shown in Fig. 33. The upper section _a_ of this table shows
+the different numbers of threads to the inch that can be obtained when
+idler gear _I_ is in the position shown by the diagram _A_. Section _b_
+gives the changes when the idler gear is moved, as shown at _B_, and,
+similarly, section _c_ gives the changes for position _C_ of the idler.
+The horizontal row of figures from 1 to 8 below the word "stops"
+represents the eight positions for lever _L_, which has a plate _p_
+(Fig. 30) just beneath it with corresponding numbers, and the column to
+the left shows whether knob _K_ should be out, in a central position, or
+in.
+
+In order to find what the position of lever _L_ and knob _K_ should be
+for cutting any given number of threads to the inch, find what "stop"
+number is directly above the number of threads to be cut, which will
+indicate the location of lever _L_, and also what position should be
+occupied by knob _K_, as shown in the column to the left. For example,
+suppose the lathe is to be geared for cutting eight threads to the inch.
+By referring to section a we see that lever _L_ should be in position 4
+and knob _K_ in the center, provided the idler gear _I_ were in position
+_A_, as it would be ordinarily, because all standard numbers of threads
+per inch (U. S. standard) from 1/4 inch up to and including 4 inches in
+diameter can be cut with the idler gear in that position. As another
+illustration, suppose we want to cut twenty-eight threads per inch. This
+is listed in section _c_, which shows that lever _L_ must be placed in
+position 3 with knob _K_ pushed in and the idler gear shifted to the
+left as at _C_.
+
+The simplicity of this method as compared with the time-consuming
+operation of removing and changing gears is apparent. The diagram _D_ to
+the right shows an arrangement of gearing for cutting nineteen threads
+per inch. A 20-tooth gear is placed on the spindle stud (in place of the
+regular one having 16 teeth) and one with 95 teeth on the lead-screw,
+thus driving the latter direct as with ordinary change gears. Of course
+it will be understood that the arrangement of a quick change-gear
+mechanism varies somewhat on lathes of different make.
+
+
+
+
+CHAPTER V
+
+TURRET LATHE PRACTICE
+
+
+Turret lathes are adapted for turning duplicate parts in quantity. The
+characteristic feature of a turret lathe is the turret which is mounted
+upon a carriage and contains the tools which are successively brought
+into the working position by indexing or rotating the turret. In many
+instances, all the tools required can be held in the turret, although it
+is often necessary to use other tools, held on a cross-slide, for
+cutting off the finished part, facing a radial surface, knurling, or for
+some other operation. After a turret lathe is equipped with the tools
+needed for machining a certain part, it produces the finished work much
+more rapidly than would be possible by using an ordinary engine lathe,
+principally because each tool is carefully set for turning or boring to
+whatever size is required and the turret makes it possible to quickly
+place any tool in the working position. Turret lathes also have systems
+of stops or gages for controlling the travel of the turret carriage and
+cross-slide, in order to regulate the depth of a bored hole, the length
+of a cylindrical part or its diameter; hence, turning machines of this
+type are much more efficient than ordinary lathes for turning duplicate
+parts, unless the quantity is small, in which case, the advantage of the
+turret lathe might be much more than offset by the cost of the special
+tool equipment and the time required for "setting up" the machine. (See
+"Selecting Type of Turning Machine.")
+
+[Illustration: Fig. 1. Bardons & Oliver Turret Lathe of Motor-driven
+Geared-head Type]
+
+=General Description of a Turret Lathe.=--The turret lathe shown in Fig.
+1 has a hexagonal shaped turret _A_ with a hole in each side in which
+the tools are held. This turret is mounted on a slide _B_ which is
+carried by a saddle _C_ that can be moved along the bed to locate the
+turret slide with reference to the length of the tools in the turret and
+the room required for indexing. The turret slide can be moved
+longitudinally by turning the pilot wheel or turnstile _D_, or it can
+be fed by power. Ordinarily, the hand adjustment is used for quickly
+moving the carriage when the tools are not cutting, although sometimes
+the hand feed is preferable to a power feed when the tools are at work,
+especially if the cuts are short. After a turret tool has finished its
+cut, the turnstile is used to return the slide to the starting point,
+and at the end of this backward movement the turret is automatically
+indexed or turned one-sixth of a revolution, thus bringing the next tool
+into the working position. The turret is accurately located in each of
+its six positions by a lock bolt which engages notches formed in a large
+index ring at the turret base. A binder lever _E_ at the top of the
+turret stud is used to clamp the turret rigidly to the slide when the
+tools are cutting.
+
+The forward movement of the slide for each position of the turret is
+controlled by stops at _F_, which are set to suit the work being turned.
+When parts are being turned from bar stock, the latter passes through
+the hollow spindle of the headstock and extends just far enough beyond
+the end of the spindle to permit turning one of the parts. The bar is
+held while the turning tools are at work, by a chuck of the collet type
+at _G_. This chuck is opened or closed around the bar by turning
+handwheel _H_. After a finished part has been cut off by a tool held in
+cross-slide _J_, the chuck is released and further movement of wheel _H_
+causes ratchet feed dog _K_, and the bar which passes through it, to be
+drawn forward. This forward movement is continued until the end of the
+bar comes against a stop gage held in one of the turret holes, to insure
+feeding the bar out just the right amount for turning the next piece. On
+some turret lathes, the lever which operates the chuck also controls a
+power feed for the bar stock, the latter being pushed through the
+spindle against the stop.
+
+The machine illustrated has a power feed for the cross-slide as well as
+for the turret. The motion is obtained from the same shaft _L_ which
+actuates the turret slide, but the feed changes are independent. The
+cross-slide feed changes are varied by levers _M_ and those for the
+turret by levers _N_. For many turret lathe operations, such as turning
+castings, etc., a jawed chuck is screwed onto the spindle and the work
+is held the same as when a chuck is used on an engine lathe. Sometimes
+chucks are used having special jaws for holding castings of irregular
+shape, or special work-holding fixtures which are bolted to the
+faceplate. The small handle at _O_ is for moving the cross-slide along
+the bed when this is necessary in order to feed a tool sidewise.
+
+This particular machine is driven by a motor at the rear of the
+headstock, connection being made with the spindle through gearing. The
+necessary speed changes are obtained both by varying the speed of the
+motor and by shifting gears in the headstock. The motor is controlled by
+the turnstile _P_ and the gears are shifted by the vertical levers
+shown.
+
+While many of the features referred to are common to turret lathes in
+general, it will be understood that the details such as the control
+levers, arrangement of stops, etc., vary on turret lathes of different
+make.
+
+[Illustration: Figs. 2 and 3. Diagrams showing Turret Lathe Tool
+Equipment for Machining Automobile Hub Casting]
+
+=Example of Turret Lathe Work.=--The diagrams Figs. 2 and 3 show a
+turret lathe operation which is typical in many respects. The part to be
+turned is a hub casting for an automobile and it is machined in two
+series of operations. The first series is shown by the plan view, Fig.
+2. The casting _A_ is held in a three-jaw chuck _B_. Tool No. 1 on the
+cross-slide is equipped with two cutters and rough faces the flange and
+end, while the inner and outer surfaces of the cylindrical part are
+rough bored and turned by combination boring and turning tool No. 2.
+This tool has, in addition to a regular boring-bar, a bracket or
+tool-holder which projects above the work and carries cutters that
+operate on the top surface. Tools Nos. 3 and 4 next come into action,
+No. 3 finishing the surfaces roughed out by No. 2, and No. 4
+finish-facing the flange and end of the hub. The detailed side view of
+Tool No. 3 (which is practically the same as No. 2), shows the
+arrangement of the cutters _C_ and _D_, one of which turns the
+cylindrical surface and the other bevels the end of the hub. The hole in
+the hub is next finished by tool No. 5 which is a stepped reamer that
+machines the bore and counterbore to the required size within very
+close limits. The surfaces machined by the different tools referred to
+are indicated by the sectional view _E_ of the hub, which shows by the
+numbers what tools are used on each surface.
+
+For the second series of operations, the position of the hub is reversed
+and it is held in a spring or collet type of chuck as shown by the plan
+view Fig. 3. The finished cylindrical end of the hub is inserted in the
+split collet _F_ which is drawn back into the tapering collet ring by
+rod _G_ (operated by turnstile _H_, Fig. 1) thus closing the collet
+tightly around the casting. The first operation is that of facing the
+side of the flange and end of the hub with tool No. 6 on the
+cross-slide, which is shown in the working position. A broad cutter _H_
+is used for facing the flange and finishing the large fillet, and the
+end is faced by a smaller cutter _I_. When these tools are withdrawn,
+tool No. 7 is moved up for rough turning the outside of the cylindrical
+end (preparatory to cutting a thread) and rough boring the hole. These
+same surfaces are then finished by tool No. 8. The arrangement of tools
+Nos. 7 and 8 is shown by the detailed view. Tool _J_ turns the part to
+be threaded; tool _K_ turns the end beyond the threaded part; and tool
+_L_ bevels the corner or edge. The reaming tool No. 9 is next indexed to
+the working position for finishing the hole and beveling the outer edge
+slightly. At the same time, the form tool No. 10, held at the rear of
+the cross-slide, is fed up for beveling the flange to an angle of 60
+degrees. The final operation is that of threading the end, which is done
+with die No. 11. The boring-bars of tools Nos. 2, 3, 7 and 8 are all
+provided with pilots _N_ which enter close fitting bushings held in the
+spindle, to steady the bar while taking the cut. This is a common method
+of supporting turret lathe tools.
+
+The feed of the turret for both the first and second series of
+operations is 1/27 inch per revolution and the speeds 60 revolutions per
+minute for the roughing cuts and 90 revolutions per minute for the
+finishing cuts. The total time for machining one of these castings
+complete is about 7-1/2 minutes, which includes the time required for
+placing the work in the chuck.
+
+=Machining Flywheels in Turret Lathe.=--Figs. 4 to 6, inclusive,
+illustrate how a gasoline engine flywheel is finished all over in two
+cycles of operations. First the flywheel is turned complete on one side,
+the hole bored and reamed, and the outside of the rim finished; in the
+second cycle the other side of the flywheel is completed.
+
+[Illustration: Fig. 4. First Cycle of Operations in Finishing Gasoline
+Engine Flywheels on a Pond Turret Lathe]
+
+During the first operation, the work is held by the inside of the rim by
+means of a four-jaw chuck equipped with hard jaws. The side of the rim,
+the tapering circumference of the recess, the web, and the hub are first
+rough-turned, using tools held in the carriage toolpost. The hole is
+then rough-bored by bar _C_, which is supported in a bushing in the
+chuck, as shown in Fig. 4. The outside of the wheel rim is rough-turned
+at the same time by a cutter held in the extension turret tool-holder
+_T_ (Fig. 5), and the taper fit on the inside of the flywheel is turned
+by means of cutter _A_ (Fig. 4) held in a tool-holder attached to the
+turret.
+
+The outside of the wheel rim is next finish-turned with cutter _V_ (Fig.
+5) held in an extension turret tool-holder the same as the roughing
+tool _T_. At the same time, the bore is finished by a cutter in
+boring-bar _D_ (Fig. 4). The side of the rim and the hub of the wheel
+are also finished at this time by two facing cutters _H_ and _K_, held
+in tool-holders on the face of the turret. When the finishing cuts on
+the rim and hub are being taken, the work is supported by a bushing on
+the boring-bar which enters the bore of the wheel, the boring cutter and
+facing tools being set in such relation to each other that the final
+boring of the hole is completed before the facing cuts are taken.
+
+[Illustration: Fig. 5. Elevation of Turret and Tools for Finishing
+Flywheels--First Operation]
+
+The web of the wheel is next finish-faced with the facing cutter held in
+the holder _E_, and the taper surface on the inside of the rim is
+finished by the tool _L_, at the same time. While these last operations
+are performed, the work is supported by a bushing on a supporting arbor
+_J_, which enters the bore of the wheel. The bore is finally reamed to
+size by a reamer _F_ held in a "floating" reamer-holder. When the
+reaming operation is completed, a clearance groove _N_ is cut on the
+inside of the rim, using a tool _G_ held in the carriage toolpost. The
+first cycle of operations on the flywheel is now completed.
+
+The flywheel is then removed from the chuck, turned around, and held in
+"soft" jaws for the second cycle of operations, the jaws fitting the
+outside of the wheel rim. (Soft unhardened jaws are used to prevent
+marring the finished surface of the rim.) The operations on this side
+are very similar to those performed on the other side. First, the side
+of the rim, the inside of the rim, the web, and hub are rough-turned,
+using tools held in the carriage toolpost. The inside of the rim and the
+web are then finished by a cutter held in a tool-holder at _P_, Fig. 6,
+which is bolted to the face of the turret. The work is supported during
+this operation by a bushing held on a supporting arbor _U_, having a
+pilot which enters a bushing in the chuck. Finally, the rim and hub are
+finished, by the facing cutters _R_ and _S_, the work being supported by
+an arbor, as before.
+
+[Illustration: Fig. 6. Second Cycle of Operations on Flywheel]
+
+These operations illustrate the methods employed in automobile
+factories, and other shops where large numbers of engine flywheels,
+etc., must be machined.
+
+=Finishing a Flywheel at One Setting in Turret Lathe.=--The plan view
+_A_, Fig. 7, shows an arrangement of tools for finishing a flywheel
+complete at one setting. The hole for the shaft has to be bored and
+reamed and the hub faced on both sides. The sides and periphery of the
+rim also have to be finished and all four corners of the rim rounded.
+The tools for doing this work consist of boring-bars, a reamer, facing
+heads on the main turret, a turret toolpost on the slide rest
+(carrying, in this case, three tools) and a special supplementary wing
+rest attached to the front of the carriage at the extreme left.
+
+The casting is held by three special hardened jaws _b_ in a universal
+chuck. These jaws grip the work on the inner side of the rim, leaving
+room for a tool to finish the rear face without striking the chuck body
+or jaws. Three rests _c_ are provided between the chuck jaws. The work
+is pressed against these rests while being tightened in the chuck, and
+they serve to locate it so that the arms will run true so far as
+sidewise movement is concerned. These rests also locate the casting with
+relation to the stops for the turret and carriage movements. The chuck
+carries a bushing _r_ of suitable diameter to support the boring-bars in
+the main turret, as will be described.
+
+In the first operation, boring-bar _m_ is brought in line with the
+spindle and is entered in bushing _r_ in the chuck. Double-ended cutter
+_n_ is then fed through the hub of the pulley to true up the cored hole.
+While boring the hole, the scale on the front face of the rim and hub is
+removed by tool _j_. Tool _k_ is then brought into action to rough turn
+the periphery, after which tool _e_, in the wing rest, is fed down to
+clean up the back face of the rim. As soon as the scale is removed, the
+hole is bored nearly to size by cutter _n_{1}_ in bar _m_{1}_, and it is
+finally finished with reamer _q_ mounted on a floating arbor.
+
+The cutters _f_, _g_ and _h_, in the facing head, are next brought up to
+rough face the hub and rim, and round the corners of the rim on the
+front side. This operation is all done by broad shaving cuts. The facing
+head in which the tools are held is provided with a pilot bar _t_ which
+fits the finished hole in the flywheel hub, and steadies the head during
+the operation. The cutters _f_, _g_ and _h_ are mounted in holders which
+may be so adjusted as to bring them to the proper setting for the
+desired dimensions. This completes the roughing operations.
+
+[Illustration: Fig. 7. Turret Lathe Tool Equipment for Machining
+Flywheels]
+
+The periphery of the rim is now finished by cutter _l_ in the turret
+toolpost which is indexed to the proper position for this operation. The
+rear face of the rim is finished by the same tool _e_ with which the
+roughing was done. Tool _e_ is then removed and replaced with _d_
+which rounds the inner corner of the rim. Tool _d_ is also replaced with
+a third tool for rounding the outer corner of the rear side. For
+finishing the front faces of the rim and hub and rounding the corners of
+the rim, a second facing head, identical with the first one, is
+employed. This is shown in position in the illustration. Cutters
+_f_{1}_, _g_{1}_ and _h_{1}_ correspond with the cutters _f_, _g_ and
+_h_, previously referred to, and perform the same operations.
+
+The remaining operation of finishing the back of the hub is effected by
+cutter _p_. This cutter is removed from the bar, which is then inserted
+through the bore; the cutter is then replaced in its slot and the rear
+end of the hub is faced by feeding the carriage away from the headstock.
+This completes the operations, the flywheel being finished at one
+setting.
+
+=Finishing a Webbed Flywheel in Two Settings.=--The plan views _B_ and
+_C_, Fig. 7, show the arrangement of tools for finishing a webbed
+flywheel which has to be machined all over. This, of course, requires
+two operations. In the first of these (see sketch _B_) the rough casting
+is chucked on the inside of the rim with regular inside hard chuck jaws
+_b_. The cored hole is first rough bored with cutter _n_ attached to the
+end of boring-bar _m_, and guided by the drill support _d_ pivoted to
+the carriage. Next, the boring-bar _m_{1}_ is brought into position, the
+drill support being swung back out of the way. This bar is steadied by
+its bearing in bushing _r_ in the chuck. Two cutters, _n_{1}_ and
+_n_{2}_, are used to roughly shape the hole to the desired taper, the
+small end being finished to within 0.002 inch of the required diameter.
+While boring with the bar _m_{1}_, the scale is broken on the web and
+hub of the casting by the tool _k_ in the turret toolpost. The latter is
+then shifted to bring the tool _j_ into position for removing the scale
+on the periphery of the wheel. Next, the hole is reamed with taper
+reamer _q_, the pilot of which is supported by bushing _r_.
+
+The first of the facing heads is now brought into action. This facing
+head carries a guide _t_ which is steadied in a taper bushing _c_,
+driven into the taper hole of the hub for that purpose. The top cutter
+_f_ turns the periphery, cutter _g_ turns the hub and faces the web,
+and cutter _h_ faces the rim. A fourth cutter _e_ on the under side of
+the head faces the hub. This casting is now machined approximately to
+size.
+
+For finishing, similar cutters, _e_{1}_, _f_{1}_, _g_{1}_ and _h_{1}_,
+in the other facing head are used, the latter being supported by the
+taper bushing _c_ in the same way. A very light cut is taken for
+finishing. Tool _l_ in the carriage turret is used to round the outer
+and inner corners of the rim, which completes the work on this face of
+the casting.
+
+In the second cycle of operations, shown at _C_, the casting is chucked
+on the outside with the soft jaws _b_, which are bored to the exact
+diameter of the finished rim. The work is further supported and centered
+by sliding bushing _c_, which is tapered to fit the finished hole in the
+hub, and has an accurate bearing in bushing _r_ in the chuck. This
+bushing is provided with a threaded collar for forcing it into the work
+and withdrawing it. The scale on the web and the inside and face of the
+rim is first broken with the tool _k_ in the turret toolpost. These
+surfaces are then roughed off with cutters _f_, _g_ and _h_, in the
+facing head. This latter is steadied by a pilot _t_ which enters the
+hole in the sliding bushing _c_ on which the work is supported. A light
+cut is next taken with cutters _f_{1}_, _g_{1}_ and _h_{1}_, in the
+finishing facing head, which completes the operation.
+
+=Tools for Turret Lathes.=--The operation of a turret lathe after the
+tools have been properly arranged is not particularly difficult, but
+designing and making the tools, determining what order of operations
+will give the most efficient and accurate results, and setting the tools
+on the machine, requires both skill and experience. For some classes of
+work, especially if of a rather complicated nature, many of the tools
+must be specially designed, although there are certain standard types
+used on turret lathes which are adapted to general turning operations.
+Some of the principal types are referred to in the following.
+
+=Box-tools.=--Tools of this type are used for turning bar stock. There
+are many different designs, some of which are shown in Figs. 8, 9 and
+10. Box-tools are held in the turret and they have back-rests opposite
+the turning tools, for supporting the part being turned. The box-tool
+shown at _A_, Fig. 8, is for roughing. The cutter _a_ is a piece of
+high-speed steel beveled on the cutting end to produce a keen edge. It
+takes a shearing tangent cut on top of the bar and the latter is kept
+from springing away by means of the adjustable, hardened tool-steel
+back-rest _b_. This tool is considered superior to a hollow mill
+whenever a fair amount of stock must be removed. If considerable
+smoothness and accuracy are necessary, the finishing box-tool shown at
+_B_ should follow the roughing box tool, but in most cases, especially
+if the part is to be threaded by a die, a finishing cut is unnecessary.
+
+[Illustration: Fig. 8. Different Types of Box-tools for Turret Lathe]
+
+The finishing box-tool _B_ is also used to follow a hollow mill if
+special accuracy or smoothness is desired. This tool is only intended
+for light finishing cuts, the allowances varying from 0.005 inch to
+0.015 inch in diameter. The cutters are made of square tool steel of
+commercial size, and are ground and set to take a scraping end cut. This
+particular tool has two tool-holders which permit finishing two
+diameters at once. If a larger number of sizes must be turned, extra
+tool-holders can be applied.
+
+The single-cutter box-tool shown at _C_ is bolted directly to the face
+of the turret instead of being held by a shank in the turret hole, and
+it is adapted for heavy cuts such as are necessary when turning
+comparatively large bar stock. The tool-holder _a_ swivels on a stud,
+thus allowing the cutter to be withdrawn from the work while being
+returned, which prevents marring the turned surface. The high-speed
+steel cutter is ground to take a side cut on the end of the bar. The
+latter is supported by hardened and ground tool-steel rolls _b_ which
+revolve on hardened and ground studs. These rolls are mounted on
+swinging arms which have a screw adjustment for different diameters.
+They can also be adjusted parallel to the bar, thus enabling them to be
+set either in advance of or back of the cutter. The opening in the base
+allows the stock to pass into the turret when it is not larger than the
+turret hole.
+
+The box-tool shown at _D_ is similar to the one just described, except
+that it has two or more cutters and roller back-rests, thus enabling
+different diameters to be turned simultaneously. The cutters are ground
+to take a side cut. Ordinarily this gives a satisfactory finish, but if
+special accuracy and smoothness are desired, two tools should be used,
+one for roughing and one for finishing, the latter being ground to take
+a light scraping end cut.
+
+The taper-turning box-tool shown at _E_ is designed for accurately
+turning tapers on brass or cast-iron parts, when there is a small amount
+of stock to be removed. The taper is obtained by cross motion imparted
+to the cutter slide as the turret advances. The taper-turning box-tool
+shown at _F_, instead of having a single-point cutter, is provided with
+a wide cutter _a_. This tool is designed to turn tapering parts of
+small or medium diameter, requiring the use of a support which cannot be
+provided with a straight forming tool and holder mounted on the cut-off
+slide. The cutter is backed up by the screws shown, which also provide
+adjustment for different tapers within a limited range. The bar is
+supported by the three back-rests shown, which also have screw
+adjustment.
+
+=Examples of Box-tool Turning.=--Box-tools are not only used for
+cylindrical and taper turning on the end of a bar, but for many other
+operations. Figs. 9 and 10 show a number of box-tools of different
+designs, with examples of the work for which each is intended. While
+these tools are designed for some specific part, they can, of course,
+with slight modifications be adapted to other work.
+
+[Illustration: Fig. 9. Box-tools and Work for which they are Intended]
+
+A box-tool of the pilot type that is used for finishing, after the
+surplus stock has been removed by roughing tools, is shown at _A_, Fig.
+9. The work, which is the cone for a ball bearing, is shown at _a_ by
+the dotted lines and also by the detail view to the right. The pilot _b_
+enters the work before either of the cutters begins to operate on its
+respective surface. The inverted cutter _c_, which sizes the flange of
+the cone, is held in position by a clamp _d_, which is forced down by a
+collar-head screw. The cutter is further secured against a beveled
+shoulder at _g_ by the set-screws _f_, and it is adjusted forward by the
+screw _e_. By loosening the screws _f_ and the collar-head screw, the
+cutter may be removed for sharpening. The cutter _h_ is adjusted to cut
+to the proper diameter, by the screws _l_, after which the clamp _k_ is
+made level by the screw _j_. The collar-screw _m_ is then used to secure
+the tool in place. The cutter is made from drill rod and it is slightly
+cupped out on the cutting end to give keenness to the cutting edge. The
+adjusting screw _o_, which passes through plate _p_, prevents the cutter
+from backing away from the work. This adjusting screw plate has its
+screw holes slotted to avoid removing the screws when it becomes
+necessary to remove the plate and cutter for sharpening. Pilot _b_ is
+held firmly to the tool body by set-screw _r_. The hole _s_ through the
+shank makes it easy to remove the pilot, in case this is necessary.
+
+A pilot box-tool for finishing another type of ball bearing cone is
+shown at _B_. The shape of the work itself is indicated by the dotted
+lines _a_ and by the detail view. This tool is somewhat similar in its
+construction to the one just described. The cutters _b_ and _c_ are
+inverted and are used to face the flange at _d_ and to turn it to the
+proper diameter. These cutters are held by the clamp _f_ and screws _g_
+and are adjusted forward by the screw _h_. The cutter _j_, which
+operates on top of the stock, rests on a bolster, of the proper angle
+and is adjusted up or down by the screws _k_. The clamp _l_, which binds
+against this tool, is beveled to correspond with the angle of the tool.
+This clamp is secured by the collar-screw shown and it is leveled by
+set-screws _s_. The adjusting screw _p_ prevents the cutter from
+slipping back. The holes in the adjusting-screw plate are also slotted
+in this case so that it will not be necessary to remove any screws when
+the cutter has to be taken out of the holder.
+
+A box-tool for finishing a treadle-rod cone for a sewing machine is
+shown at _C_. This tool is also of the pilot type. The cutters in it
+operate on opposite sides of the cone _a_. The inverted cutter _b_ sizes
+the cylindrical part of the cone, while the front cutter _d_ is set at
+the proper angle to finish the tapered part. The rear cutter _b_ is held
+in place by the clamp _g_ and a collar screw. It is adjusted forward by
+the screw _h_ in the plate _i_ which is held by screws as shown. The
+pilot is retained by a set-screw, and it is easily removed by inserting
+a small rod in the hole _l_ which passes through the shank. The cutter
+_d_ is held by clamp _m_ and is adjusted by screw _n_ which passes
+through a tapped hole in plate _o_. The screw holes in both the
+adjusting plates _i_ and _o_ are slotted to facilitate their removal.
+
+The box-tool illustrated at _A_, Fig. 10, is used for finishing the
+bushing of a double-taper cone bearing _a_. The cutters are so arranged
+that they all cut on the center; that is, the cutting edges lie in a
+horizontal plane. The inverted cutter _b_ at the rear forms the short
+angular surface, and the cutter _c_ in front forms the long tapering
+part of the bearing. The large diameter is turned, to size by cutter
+_d_. The pilot _e_ has a bearing in the bore nearly equal to the length
+of the work and it is provided with oil grooves, as shown. The taper
+shank of this pilot is tapped for the screw _i_ which extends the whole
+length of the shank and is used to draw the pilot back to its seat. It
+is not necessary to remove adjusting-screw plate _k_ to take out the
+cutter _b_, as the latter can be drawn out from the front after the
+collar-screw _m_ is loosened. The cutter _c_ is removed by taking off
+the adjusting-screw plate _s_ after loosening the collar-screw _n_. The
+cutter _d_ is held in a dove-tailed slot by two headless set-screws _q_.
+It is also backed up by an adjusting screw in the plate _s_. These
+adjusting screws should all have fine threads, say from 32 to 40 per
+inch, and be nicely fitted so they will not loosen after being adjusted.
+
+The box-tools shown at _B_ and _C_, Fig. 10, are for turning the sides
+of a loose pulley for a sewing machine. This pulley (shown by the dotted
+lines) is finished in two operations. The box-tool for finishing the
+side of the pulley on which the hub projects beyond the rim, is shown at
+_B_. The inverted cutter _a_, which faces the end of the hub, is held by
+a clamp _c_ (clearly shown in the end view) from the under side and it
+has no adjustment. The collar-screw _d_ is tapped into this clamp, which
+is prevented from getting out of place by the dowel-pin _f_. The pilot
+_g_ is made small in the shank, so that tool _a_ can be so placed as to
+insure the removal of all burrs around the bore of the hub. The pilot is
+held by a set-screw and it is provided with oil grooves. The cutter _j_
+sizes the outside of the hub, and the cutter _k_ faces the side of the
+pulley rim. These cutters are both held by the clamp _l_ and the
+collar-screw _m_. No side plates are used on this tool, and the cutters
+are all easily removed.
+
+[Illustration: Fig. 10. Examples of Box-tool Designs]
+
+Sketch _C_ shows the box-tool used for the second operation. As the hub
+is flush with the rim on the side for which this tool is intended, it
+needs only one cutter to face both. This is done by the wide cutter _a_
+which is held in a dove-tailed slot in the front of the tool and is
+fastened by the clamp _b_ and collar-screw _c_. The bushing _d_, in
+which the end of the work arbor is supported, is held by the
+collar-screw _e_, and to obtain the necessary compression, the body of
+the tool is slotted as far back as _f_. This bushing is provided with
+oil grooves and one side is cut away to clear the cutter _a_. The
+pilot end of the arbor on which the work is mounted is 1/16 inch smaller
+than the bore of the pulley, which allows the cutter to be set in far
+enough to prevent any burr which might form at the edge of the bore. A
+disk _i_ is inserted back of bushing _d_, so that the latter may be
+easily removed by passing a rod through the hollow shank. The special
+chuck used for this second operation on the loose pulley is screwed onto
+the spindle, and the work is mounted on a projecting arbor and driven by
+the pins engaging holes in the pulley web. The arbor is made a driving
+fit for the work, and the end or pilot is a running fit in the bushing
+of the box-tool. A counterbore in the arbor hub provides clearance for
+the hub of the pulley which projects beyond the rim on one side.
+
+[Illustration: Fig. 11. (A) Hollow Mill and Holder. (B) Spring
+Screw-threading Die and Releasing Die-holder]
+
+=Hollow Mills.=--A hollow mill such as is shown at _A_ in Fig. 11 is
+sometimes used in place of a box-tool (especially when turning brass)
+for short roughing cuts preceding a threading operation. The turning is
+done by the cutting edges _e_, and the turned part enters the mill and
+is steadied by it. If this type of tool is used for long, straight cuts,
+especially on square stock and when making screws with large heads from
+the bar, it should always be followed by a finishing box-tool to insure
+accurate work. A hollow mill can be sharpened readily by grinding the
+ends without materially changing the cutting size. A slight adjustment
+can be obtained by means of the clamp collar shown to the left, although
+this is not generally used. When making these mills, they should be
+reamed out tapering from the rear to give clearance to the cutting
+edges. For turning steel, the cutting edge should be about 1/10 of the
+diameter ahead of the center, whereas for brass, it should be on the
+center-line.
+
+[Illustration: Fig. 12. Geometric Adjustable Hollow Milling Tool]
+
+Hollow mills are also made adjustable. The design shown in Fig. 12 is
+especially adapted for brass finishing. It can also be used for taking
+light cuts on cast iron or steel but its use in place of roughing or
+finishing box-tools for general use is not recommended. With the
+exception of the cutters and screws, the complete tool consists of three
+parts, _viz._, the holder, cam, and ring. The cam serves to adjust the
+cutters for different diameters. The adjustment is made by the two
+screws shown, the amount being indicated by a micrometer scale. When
+adjusting the cutters for a given diameter, the use of a hardened steel
+plug of the required size is advisable, the cutters being adjusted
+against the plug.
+
+=Releasing Die and Tap Holders.=--Threads are cut in the turret lathe by
+means of dies for external threading, and taps for internal threading,
+the die or tap being held in a holder attached to the turret. A simple
+form of releasing die holder is shown at _B_, Fig. 11. This holder was
+designed for the spring-screw type of threading die shown to the left.
+The die is clamped in the holder _a_ by the set-screw shown, and the
+shank _b_ of the holder is inserted in the turret hole. Holder _a_ has
+an extension _c_ which passes through the hollow shank. When the die is
+pressed against the end of the work, holder _a_ and its extension moves
+back until lug _d_ on the holder engages lug _e_ on the shank. The die
+and holder are then prevented from rotating with the work and the die
+begins to cut a thread. It continues to screw itself onto the work with
+the turret following, until the thread has been cut to the required
+length; the turret is then stopped and as the die and holder _a_ are
+drawn forward, lugs _d_ and _e_ disengage so that the die simply rotates
+with the work without continuing to advance. The lathe spindle is then
+reversed and as the turret is moved back by hand, pin _f_ comes around
+and enters notch _g_, thus holding the die stationary; the die then
+backs off from the threaded end. Some tap holders are also constructed
+the same as this die holder, so far as the releasing mechanism is
+concerned. There are also many other designs in use, some of which
+operate on this same principle.
+
+[Illustration: Fig. 13. Geometric Self-opening and Adjustable
+Screw-cutting Die Head]
+
+=Self-opening Die Heads.=--The type of die holder shown at _B_ in Fig.
+11 is objectionable because of the time required for backing the die off
+the threaded end; hence, self-opening dies are extensively used in
+turret lathe work. As the name implies, this type of die, instead of
+being solid, has several chasers which are opened automatically when the
+thread has been cut to the required length. The turret can then be
+returned without reversing the lathe spindle. The dies are opened by
+simply stopping the travel of the turret slide, the stop-rod for the
+feed of the turret being adjusted to give the proper amount of travel.
+
+[Illustration: Fig. 14. Geometric Collapsing Tap]
+
+A well-known die head of the self-opening type is shown in Fig. 13. The
+dies open automatically as soon as the travel of the head is retarded,
+or they can be opened at any point by simply holding back on the
+turnstile or lever by which the turret slide is moved. The die is closed
+again by means of the small handle seen projecting at right-angles from
+the side of the head. The closing may be done by hand or automatically
+by screwing a pin into a threaded hole opposite the handle and attaching
+a small piece of flat steel to the back edge of the turret slide. The
+latter will then engage the pin as the turret revolves, thus closing the
+die head. This die head has a roughing and finishing attachment which is
+operated by handle _A_. When this handle is moved forward, the dies are
+adjusted outward 0.01 inch for the roughing cut, whereas returning the
+handle closes and locks the dies for the finishing cut. The die head has
+a micrometer scale which is used when making slight adjustments to
+compensate for the wear of the chasers or to make either a tight-or a
+loose-fitting thread.
+
+=Collapsing Taps.=--The collapsing tap shown in Fig. 14 is one of many
+different designs that are manufactured. They are often used in turret
+lathe practice in place of solid taps. When using this particular style
+of collapsing tap, the adjustable gage _A_ is set for the length of
+thread required. When the tap has been fed to this depth, the gage comes
+into contact with the end of the work, which causes the chasers to
+collapse automatically. The tool is then withdrawn, after which the
+chasers are again expanded and locked in position by the handle seen at
+the side of the holder. In all threading operations, whether using taps
+or dies, a suitable lubricant should be used, as a better thread is
+obtained and there is less wear on the tools. Lard oil is a good
+lubricant, although cheaper compounds give satisfactory results on many
+classes of work.
+
+=Miscellaneous Turret Lathe Tools.=--The chamfering tool shown at _A_,
+Fig. 15, is used for pointing the end of a bar before running on a
+roughing box-tool. This not only finishes the end of the bar but
+provides an even surface for the box-tool to start on. The cutter is
+beveled on the end to form a cutting edge and it is held at an angle.
+The back-rest consists of a bell-mouthed, hardened tool-steel bushing
+which supports the bar while the cut is being taken.
+
+The stop gages _B_ and _C_ are used in the turret to govern the length
+of stock that is fed through the spindle. When a finished piece has been
+cut off, the rough bar is fed through the spindle and up against the
+stop gage, thus locating it for another operation. This gage may be a
+plain cylindrical piece of hardened steel, as at _B_, or it may have an
+adjusting screw as at _C_; for special work, different forms or shapes
+are also required. The stop gages on some machines, instead of being
+held in the turret, are attached to a swinging arm or bracket that is
+fastened to the turret slide and is swung up in line with the spindle
+when the stock is fed forward.
+
+The center drilling tool _D_ is designed to hold a standard combination
+center drill and reamer. This type of tool is often used when turning
+parts that must be finished afterwards by grinding, to form a center for
+the grinding machine. The adjustable turning tool _E_ is used for
+turning the outside of gear blanks, pulley hubs or the rims of small
+pulleys. The pilot _a_ enters the finished bore to steady the tool, and
+cutter _b_ is adjusted to turn to the required diameter.
+
+[Illustration: Fig. 15. Various Types of Tools for the Turret Lathe]
+
+The cutting-off tool-holder _F_ (which is held on the cross-slide of the
+turret lathe) is usually more convenient than a regular toolpost, as the
+blade can be set closer to the chuck. The blade is held in an inclined
+position, as shown, to provide rake for the cutting edge; the inclined
+blade can also be adjusted vertically, a limited amount, by moving it in
+or out. The multiple cutting-off tool _G_ holds two or more blades and
+is used for cutting off several washers, collars, etc., simultaneously.
+By changing the distance pieces between the cutters, the latter are
+spaced for work of different widths. The flat drill holder _H_ is used
+for drilling short holes, and also to form a true "spot" or starting
+point for other drills.
+
+Knurling tools are shown at _I_ and _J_. The former is intended for
+knurling short lengths and is sometimes clamped on top of the cut-off
+tool on the cross-slide, the end being swung back after knurling (as
+shown by the dotted lines) to prevent interference with the work when
+the cutting-off tool is in operation. The knurling tool _J_ has a shank
+and is held in the turret. The two knurls are on opposite sides of the
+work so that the pressure of knurling is equalized. By adjusting the
+arms which hold the knurls, the tool can be set for different diameters.
+
+Three styles of drill holders are shown at _K_, _L_ and _M_. Holder _K_
+is provided with a split collet (seen to the left) which is tightened on
+the drill shank by a set-screw in the holder. This holder requires a
+separate collet for each size drill. The taper shank drill holder _L_
+has a standard taper hole into which the shank of the drill is inserted.
+The adjustable type of holder _M_ is extensively used, especially on
+small and medium sized machines when several sizes of drills are
+necessary. This holder is simply a drill chuck fitted with a special
+shank. For large drills the plain style of holder _K_ is recommended,
+and if only a few sizes of drills are required, it is more satisfactory
+and economical than the adjustable type.
+
+The various types of small turret lathe tools referred to in the
+foregoing for turning, threading, tapping, knurling, etc., are a few of
+the many different designs of tools used in turret lathe practice.
+Naturally, the tool equipment for each particular job must be changed
+somewhat to suit the conditions governing each case. The tools referred
+to, however, represent in a general way, the principal types used in
+ordinary practice. Some of the more special tools are shown in
+connection with examples of turret lathe work, which are referred to in
+the following.
+
+=Turning Gasoline Engine Pistons in Turret Lathe.=--The making of
+pistons for gas engines, especially in automobile factories, is done on
+such a large scale that rapid methods of machining them are necessary.
+The plan view _A_, Fig. 16, shows the turret lathe tools used in one
+shop for doing this work. As is often advisable with work done in large
+quantities, the rough castings are made with extra projections so
+arranged as to assist in holding them. These projections are, of course,
+removed when the piece is completed. In this case the piston casting _a_
+has a ring about 1-1/4 inch long and a little less in diameter than the
+piston, at the chucking end. The piston is held in suitable chuck jaws
+_b_ which are tightened against the inside of this ring. The set-screws
+in these special jaws are then tightened, thus clamping the casting
+between the points of the screws and the jaws. This method of holding
+permits the whole exterior of the piston to be turned, since it projects
+beyond the chuck jaws. This is the object in providing the piston with
+the projecting ring by which it is held.
+
+[Illustration: Fig. 16. (A) Method of Boring and Turning Pistons in
+Gisholt Lathe. (B) Special Chuck and Tools for Turning, Boring and
+Cutting Off Eccentric Piston Rings]
+
+The first operation consists in rough-boring the front end of the
+piston. The double-ended cutter _n_ is held in boring-bar _m_, which is,
+in turn, supported by a drill-holder, clamped to one of the faces of
+the turret. This bar is steadied by a bushing in the drill support _c_
+which is attached to the carriage, and may be swung into or out of the
+operating position, as required. After this cut is completed, the turret
+is revolved half way around and the casting is finish-bored in a similar
+manner, with double-ended cutter _n_{1}_ held in bar _m_{1}_, the drill
+support being used as in the previous case. The support is then turned
+back out of the way to allow the turning tools in the turret toolpost to
+be used.
+
+The outside of the piston is next rough-turned with tool _k_ in the
+turret toolpost, which is revolved to bring this cutter into action. The
+toolpost is then turned to the position shown, and the outside is
+finish-turned by tool _j_, which takes a broad shaving cut. The turret
+tool-holder is again revolved to bring form tool _l_ into position. This
+tool cuts the grooves for the piston rings. Suitable positive stops are,
+of course, provided for both the longitudinal and cross movements of the
+turret toolpost.
+
+In the second operation, the piston _a_ is reversed and held in soft
+jaws, which are used in place of the hardened jaws _b_ shown in the
+illustration. These jaws are bored to the outside diameter of the
+piston, so that when closed, they hold the work true or concentric with
+the lathe spindle. In this operation the chucking ring by which the
+piston was previously held is cut off, and the end of the piston is
+faced true. If the crank-pin hole is to be finished, a third operation
+is necessary, a self-centering chuck-plate and boring and reaming tools
+being used. (These are not shown in the illustration.)
+
+=Turning Piston Rings in Turret Lathe.=--One method of turning piston
+rings is shown at _B_ in Fig. 16. The piston rings are cut from a
+cast-iron cylindrical piece which has three lugs _b_ cast on one end and
+so arranged that they may be held in a three-jawed chuck. This
+cylindrical casting is about 10 inches long, and when the rings are to
+have their inside and outside surfaces concentric, the casting is held
+by the lugs in the regular jaws furnished with the chuck. (The
+arrangement used for turning and boring eccentric rings, which is that
+shown in the illustration, will be described later.)
+
+The casting _a_, from which the rings are made, is first rough-bored
+with double-ended cutter _n_ in boring-bar _m_, after which it is
+finish-bored with cutter _n_{1}_ in bar _m_{1}_. While taking these
+cuts, the bars _m_ and _m_{1}_ are supported by their extension ends
+which enter bushing _r_ located in the central hole of the chuck. This
+furnishes a rigid support so that a heavy cut can be taken.
+
+The outside of the casting is next rough-turned with tool _k_, held in
+the turret toolpost. This toolpost is then revolved to bring tool _j_
+into position, by which the outside is turned true to size, a broad
+shaving chip being taken. The toolpost is again swung around, to bring
+the cutting-off tool-holder _l_ into position. This holder contains four
+blades set the proper distance apart to give rings of the desired width.
+Each blade, from right to left, is set a little back of the preceding
+one, so that the rings are cut off one after the other, the outer rings
+being supported until they are completely severed. After the first four
+rings are cut off, the carriage is moved ahead to a second stop, and
+four more rings are severed, this operation being continued until the
+casting has been entirely cut up into rings.
+
+When the bore of the ring is to be eccentric with the outside, the
+holding arrangement shown in the illustration is used. The casting a is
+bolted to a sliding chuck-plate _c_, and the outside is rough-turned
+with tool _k_ in the toolpost. Finishing tool _j_ is then brought into
+action, and the outside diameter is turned accurately to size. Then the
+sliding chuck-plate _c_, carrying the work, is moved over a distance
+equal to the eccentricity desired, and the work is bored with cutters
+_n_ and _n_{1}_ as in the previous case. The turret toolpost is next
+revolved and the tools _l_ are used for cutting off the rings. The
+reason for finishing the outside first is to secure smooth rings in
+cutting off, as this operation should be done when the work is running
+concentric with the bore, rather than with the exterior surface.
+
+It will be evident that this method gives a far greater output of rings
+than is possible by finishing them in the more primitive way on engine
+lathes. The faces of the rings may be finished in a second operation if
+desired, or they may be ground, depending on the method used in the
+shop where the work is being done, and the accuracy required.
+
+[Illustration: Fig. 17. Turning Gasoline Engine Pistons in Pratt &
+Whitney Turret Lathe]
+
+=Piston Turning in Pratt and Whitney Turret Lathe.=--A turret lathe
+equipped with tools for turning, facing and grooving automobile gasoline
+engine pistons is shown in Fig. 17. The piston is held on an expanding
+pin chuck which is so constructed that all of the pins are forced
+outward with equal pressure and automatically conform to any
+irregularities on the inside of the piston. Tool _A_ rough-turns the
+outside, and just as this tool completes its cut, a center hole is
+drilled and reamed in the end of the piston by combination drill and
+reamer _B_. The turret is then indexed one-half a revolution and a
+finishing cut is taken by tool _C_. After the cylindrical body of the
+piston has been turned, tools held in a special holder _E_ attached to
+the cut-off slide are used to face the ends of the piston and cut the
+packing-ring grooves. While the grooves are being cut, the outer end of
+the piston is supported by center _D_. The center hole in the end also
+serves to support the piston while being ground to the required diameter
+in a cylindrical grinding machine. The edge at the open end of the
+piston may also be faced square and the inner corner beveled by a hook
+tool mounted on the rear cross-slide, although this is usually done in a
+separate operation. (This provides a true surface by which to hold this
+end when grinding.)
+
+[Illustration: Fig. 18. Pratt & Whitney Turret Lathe equipped with
+Special Attachment for Turning Eccentric Piston Rings]
+
+This illustration (Fig. 17) shows very clearly the stops which
+automatically disengage the turret feed. A bracket _F_ is bolted to the
+front of the bed and contains six stop-rods _G_ (one for each position
+or side of the turret). When one of these stop-rods strikes lever _H_,
+the feed is disengaged, the stop being adjusted to throw out the feed
+when the tool has completed its cut. Lever _H_ is automatically aligned
+with the stop-rods for different sides of the turret by a cam _J_ on the
+turret base. A roller _K_ bears against this cam and, through the
+connecting shaft and lever shown, causes lever _H_ to move opposite the
+stop-rod for whatever turret face is in the working position. Lever _L_
+is used for engaging the feed and lever _R_ for disengaging it by hand.
+
+The indexing of the turret at the end of the backward movement of the
+slide is controlled by stop _M_ against which rod _N_ strikes, thus
+disengaging the lock bolt so that the turret can turn. This stop _M_ is
+adjusted along the bed to a position depending upon the length of the
+turret tools and the distance the turret must move back to allow the
+tools to clear as they swing around.
+
+[Illustration: Fig. 19. Tool Equipment for Machining Worm Gear
+Blanks--Davis Turret Lathe]
+
+=Attachment for Turning Piston Rings.=--Fig. 18 shows a special
+attachment applied to a Pratt & Whitney turret lathe for turning
+eccentric, gas-engine piston rings. The boring of the ring casting,
+turning the outside and cutting off the rings, is done simultaneously.
+The interior of the casting is turned concentric with the lathe spindle
+by a heavy boring-bar, the end of which is rigidly supported by a
+bushing in the spindle. The slide which carries the outside turning tool
+is mounted on a heavy casting which straddles the turret. The outside of
+the ring casting is turned eccentric to the bore as a result of an
+in-and-out movement imparted to the tool by a cam on shaft _A_ which is
+rotated from the lathe spindle through the gearing shown. For each
+revolution of the work, the tool recedes from the center and advances
+toward it an amount sufficient to give the required eccentricity. When
+the turning and boring tools have fed forward about 2 inches, then the
+cutting-off tools which are held in holder _B_ come into action. The end
+of each cutting-off tool, from right to left, is set a little farther
+away from the work than the preceding tool, so that the end rings are
+always severed first as the tools are fed in by the cross-slide. A
+number of the completed rings may be seen in the pan of the machine.
+
+[Illustration: Fig. 20. Turning Bevel Gear Blanks in Davis Turret
+Lathe--First Operation]
+
+=Turning Worm-gear Blanks in Turret Lathe.=--This is a second operation,
+the hub of worm-gear blank _G_ (Fig. 19) having previously been bored,
+reamed, and faced on the rear side. The casting is mounted upon a
+close-fitting arbor attached to a plate bolted to the faceplate of the
+lathe, and is driven by two pins which engage holes on the rear side.
+The rim is first rough-turned by a tool _A_ which operates on top, and
+the side is rough-faced by a toothed or serrated cutter _B_. A similar
+tool-holder having a tool _C_ and a smooth cutter _D_ is then used to
+turn the rim to the required diameter and finish the side. The end of
+the hub is faced by cutters mounted in the end of bars _E_ and _F_, one
+being the roughing cutter and the other the finishing cutter. The work
+arbor projects beyond the hub, as will be seen, and forms a pilot that
+steadies these cutter bars. The curved rim of the gear is turned to the
+required radius (preparatory to gashing and bobbing the worm-wheel
+teeth) by a formed tool _H_ held on the cross-slide.
+
+[Illustration: Fig. 21. Second Operation on Bevel Gear Blanks]
+
+=Turning Bevel Gear Blanks.=--Fig. 20 shows a plan view of the tools
+used for the first turning operation on bevel gear blanks (these gears
+are used for driving drill press spindles). The cored hole is beveled
+true at the end by flat drill _A_ to form a true starting surface for
+the three-fluted drill _B_ which follows. The hole is bored close to the
+required size by a tool (not shown) held in the end of bar _C_, and it
+is finished by reamer _D_. The cylindrical end of the gear blank or hub
+is rough-and finish-turned by tools held in holders _E_ and _F_,
+respectively. (These holders were made to set at an angle of 45 degrees,
+instead of being directly over the work, as usual, so that the cutters
+would be in view when setting up the machine.) It will be noted that the
+chuck is equipped with special jaws which fit the beveled part of the
+casting.
+
+[Illustration: Fig. 22. Sectional View of Tapering Mold Shell which is
+turned in Hartness Flat Turret Lathe, as illustrated in Figs. 23 to 27,
+Inclusive]
+
+The second and final operation on this blank is shown in Fig. 21. The
+work _A_ is held by a special driver plate attached to the faceplate of
+the machine. This driver plate has two pins which engage holes drilled
+in the gear blank and prevent it from rotating. The blank is also held
+by a bolt _B_ which forces a bushing against the cylindrical end. First,
+the broad beveled side which is to be the toothed part of the gear, is
+rough-turned by toothed cutters _C_, and a recess is formed in the end
+of the blank, by a turning tool in this same tool-holder. A similar
+tool-holder _E_, having finishing cutters, is then used to finish the
+bevel face and recess. The other tools seen in the turret are not used
+for this second operation. The rear bevel is roughed and finished by
+tools and held on the cross-slide.
+
+=Shell Turning Operation in Flat Turret Lathe.=--The "flat turret lathe"
+is so named because the turret is a flat circular plate mounted on a low
+carriage to secure direct and rigid support from the lathe bed. The
+tools, instead of being held by shanks inserted in holes in the turret,
+are designed so that they can be clamped firmly onto the low circular
+turret plate.
+
+An interesting example of flat turret lathe work is shown in Fig. 22.
+This is a steel shell which must be accurately finished to a slight
+taper, both inside and out, threaded and plain recesses are required at
+the ends, and, in addition, one or two minor operations are necessary.
+This work is done in the Hartness flat turret lathe, built by the Jones
+& Lamson Machine Co. The shells are turned from cold-drawn seamless
+steel tubing, having a carbon content of 0.20 per cent, and they are
+finished at the rate of one in nine minutes. The tubing comes to the
+machine in 12-foot lengths, and the tube being operated upon is, of
+course, fed forward through the hollow spindle as each successive shell
+is severed.
+
+[Illustration: Fig. 23. First Operation on Shell Illustrated in Fig.
+22--Rough-turning and Boring]
+
+In finishing this shell, five different operations are required. During
+the first operation the shell is rough-bored and turned by one passage
+of a box-tool, Fig. 23, and the recess _A_, Fig. 22, at the outer end,
+is finished to size by a second cutter located in the boring-bar close
+to the turret. The turret is then indexed to the second station which
+brings the threading attachment _G_ into position, as shown in Fig. 24.
+After the thread is finished, the recess _B_, Fig. 22, is turned by a
+flat cutter _K_, Fig. 25. The inner and outer surfaces are then finished
+to size by a box-tool mounted on the fourth station of the turret and
+shown in position in Fig. 26. The final operation, Fig. 27, is performed
+by three tools held on an auxiliary turret cross-slide, and consists in
+rounding the corners at _b_ and _c_, Fig. 22, and severing the finished
+shell.
+
+[Illustration: Fig. 24. Second Operation--Cutting Internal Thread]
+
+One of the interesting features connected with the machining of this
+shell is the finishing of the inner and outer tapering surfaces. The
+taper on the outside is 3/32 inch Per foot, while the bore has a taper
+of only 1/64 inch per foot, and these surfaces are finished
+simultaneously. The box-tool employed is of a standard type, with the
+exception of an inserted boring-bar, and the taper on the outside is
+obtained by the regular attachment which consists of a templet _D_ (Fig.
+23) of the required taper, that causes the turning tool to recede at a
+uniform rate as it feeds along. To secure the internal taper, the
+headstock of the machine is swiveled slightly on its transverse ways by
+the use of tapering gibs. By this simple method, the double taper is
+finished to the required accuracy without special tools or equipment.
+
+As those familiar with this machine know, the longitudinal movements of
+the turret as well as the transverse movements of the headstock are
+controlled by positive stops. The headstock of this machine has ten
+stops which are mounted in a revolving holder and are brought into
+position, as required, by manipulating a lever at the front. The stops
+for length, or those controlling the turret travel, are divided into two
+general groups, known as "A" and "B". Each of these groups has six stops
+so that there are two stops for each of the six positions or stations of
+the turret, and, in addition, five extra stops are available for any one
+tool, by the engagement of a pin at the rear of the turret. The change
+from the "A" to the "B" stops is made by adjusting lever _L_, Fig. 26,
+which also has a neutral position.
+
+[Illustration: Fig. 25. Third Operation--Turning Recess at Rear End;
+Tool is shown withdrawn]
+
+After the box-tool for the roughing cut, shown at work in Fig. 23, has
+reached the end of its travel, further movement is arrested by a stop of
+the "A" group. The outside turning tool is then withdrawn by operating
+lever _E_ and the turret is run back and indexed to the second station,
+thus bringing the threading attachment into position. The surface speed
+of 130 feet per minute which is used for turning is reduced to about 30
+feet per minute for threading by manipulating levers _H_, Fig. 24. After
+the turret is located by another stop of the "A" group, the threading
+attachment is made operative by depressing a small plunger _I_, which
+connects a vertical driving shaft from the spindle with the splined
+transmission shaft _J_. A reciprocating movement is then imparted to the
+thread chaser _t_ which advances on the cutting stroke and then
+automatically retreats to clear the thread on the return. This movement
+is repeated until the thread is cut to the proper depth, as determined
+by one of the stops for the headstock. While the thread is being cut,
+the carriage is locked to the bed by the lever _N_, Fig. 26. It was
+found necessary to perform the threading operation before taking the
+outside finishing cut, owing to a slight distortion of the shell wall,
+caused by the threading operation.
+
+[Illustration: Fig. 26. Fourth Operation--Finishing the Bore and
+Outside]
+
+After the thread is finished, the turret is turned to the third station
+as shown in Fig. 25, and tool _K_ for the inner recess _B_, Fig. 22, is
+brought into position and fed to the proper depth, as determined by
+another cross-stop. The turret is also locked in position for this
+operation. The finishing cuts for the bore and the outside are next
+taken by a box-tool which is shown near the end of its cut in Fig. 26.
+This box-tool is similar to the one used for roughing, but it is
+equipped with differently shaped cutters to obtain the required finish.
+The outside turning tool has a straight cutting edge set tangent to the
+cylindrical surface and at an angle, while the boring tool has a cutting
+edge of large radius. An end view of this box-tool is shown in Fig. 27.
+A reduced feed is employed for the finishing cut, and the speed is
+increased to 130 feet per minute, which is the same as that used for
+roughing.
+
+[Illustration: Fig. 27. Fifth Operation--Rounding Ends, Scoring Large
+End, and Cutting Off]
+
+During the next and final operation, the turret, after being indexed to
+the position shown in Fig. 27, is first located by a stop of the "A"
+group so that the cutting-off tool _R_ in front can be used for rounding
+the corner _b_, Fig. 22. The stop lever _L_ is then shifted and the
+turret is moved to a second stop of the "B" group. The corner _c_ is
+then rounded and the shell is scored at _d_ by two inverted tools _S_
+and _T_ at the rear, after which the finished work is severed by the
+cut-off tool at the front. The cross-movement of these three tools is
+controlled by positive stops on the cross-slide, and the latter is moved
+to and fro by hand lever _O_. After the shell is cut off, the stop _M_,
+mounted on the turret, Fig. 26, is swung into position, and the tube is
+automatically fed forward to the swinging stop by the roll feed, as soon
+as the chuck is released by operating lever _Q_. This completes the
+cycle of operations. A copious supply of lubricant is, of course,
+furnished to the tools during these operations, and the two boring-tool
+shanks are hollow so that lubricant can be forced through them and be
+made to play directly upon the cutters.
+
+=Chuck Work in Flat Turret Lathe.=--Two examples of chuck work on the
+Acme combination flat turret lathe are shown in Figs. 28 and 29. Fig. 28
+shows the tool equipment for turning a cylindrical part _A_ which is
+held in a three-jaw universal chuck. The front flange is first
+rough-turned by a bent turning tool _B_. The diameter is regulated by
+one of the cross-stops at _D_ which has been previously set and controls
+the movement of the turret cross-slide. The longitudinal feed is
+disengaged when the flange has been turned, by an independent stop. This
+machine has twelve longitudinal stops, there being one for each turret
+face and six auxiliary stops, in addition to the stops for the
+cross-slide.
+
+[Illustration: Fig. 28. Tool Equipment for Turning Scroll Gear Blank on
+Acme Flat Turret Lathe]
+
+After roughing the flange, the turret carriage is locked or clamped
+rigidly to the bed to prevent any lengthwise movement, and the back face
+of the front flange is rough-turned by tool _B_ in to the diameter of
+the hub which is indicated by a micrometer dial on the cross-feed screw.
+The carriage is then unlocked and auxiliary stop No. 7 is engaged (by
+turning a knob at the front of the slide) and the cylindrical hub is
+turned back to the rear flange, the feed being disengaged by the
+auxiliary stop just as the tool reaches the flange. The cross-slide is
+now moved outward, longitudinal auxiliary stop No. 8 is engaged, the
+turret slide is moved against the stop, the carriage is locked and the
+front sides of both the front and rear flanges are rough-faced by tools
+_B_ and _C_. The turret is next indexed and the hole rough-bored by
+cutter _E_. After again indexing the turret, the hub and flanges are
+finish-turned and faced by tools _F_ and _G_, as described for the
+rough-turning operation. The final operation is that of finishing the
+bore by cutter _H_.
+
+[Illustration: Fig. 29. Acme Flat Turret Lathe Arranged for Turning
+Roller Feed Body]
+
+The operation shown in Fig. 29 is that of turning the body of a roller
+feed mechanism for a turret lathe. The casting is held in a three-jaw
+universal chuck and it is first rough-bored by tool _A_. The turret is
+then indexed and the side of the body and end of the hub are rough-faced
+by tools at _B_. The turret is again indexed for rough-turning the
+outside of the hub and body, by tools _C_ and _D_. Similar tools _E_
+and _F_ are then used to finish these same surfaces, after which the end
+of the hub and side of the body are finished by tools _G_ and _H_
+similar to those located at _B_. The final operation is that of
+finishing the bore by tool _J_ and cutting a groove in the outside of
+the hub by the bent tool _K_.
+
+[Illustration: Fig. 30. Turret and Head of Jones & Lamson Double-spindle
+Flat Turret Lathe]
+
+=Double-spindle Flat Turret Lathe.=--The extent to which modern turning
+machines have been developed, especially for turning duplicate parts in
+quantity, is illustrated by the design of turret lathe the turret and
+head of which is shown in Fig. 30. This machine has two spindles and a
+large flat turret which holds a double set of tools, so that two
+duplicate castings or forgings can be turned at the same time. It was
+designed primarily for chuck work and can be used as a single-spindle
+machine if desirable. When two spindles are employed for machining two
+duplicate parts simultaneously, considerably more time is required for
+setting up the machine than is necessary for the regular single-spindle
+type, but it is claimed that the increased rate of production obtained
+with the two-spindle design more than offsets this initial handicap.
+The manufacturers consider the single-spindle machine the best type for
+ordinary machine building operations, regardless of whether the work is
+turned from the bar or is of the chucking variety. On the other hand,
+the double-spindle type is preferred when work is to be produced in such
+quantities that the time for setting up the machine becomes a secondary
+consideration.
+
+[Illustration: Fig. 31. Diagram showing Tool Equipment and Successive
+Steps in Machining Sprocket Blanks on Double-spindle Flat Turret Lathe]
+
+When the double-spindle machine is used as a single-spindle type, a
+chuck 17 inches in diameter is used, and when both spindles are in
+operation, two 9-inch chucks are employed. The general outline of the
+turret is square, and the tools are rigidly held, with a minimum amount
+of overhang, by means of tool-blocks and binding screws connected with
+the clamping plates. Two duplicate sets of tools are clamped to each
+side of the turret and these operate simultaneously on the two pieces
+held in the chucks or on faceplates. Primarily the turret is used in
+but four positions, but when a 17-inch chuck or faceplate is employed,
+corner blocks may be held by the clamping plates in which tools are
+supported, giving, if necessary, four additional operations by indexing
+the turret to eight positions.
+
+A typical job to demonstrate the application of the double-spindle flat
+turret lathe is illustrated in Fig. 31. The parts to be turned are
+sprocket wheels which are held in the two 9-inch chucks. At the first
+position of the turret (which is the one illustrated), the inside is
+rough-bored by tools _A_. At the second position of the turret, tools
+_B_ rough-face the inner sides of the flanges; tools _C_ face the outer
+sides of the flanges, while tools _D_ turn the faces of the flanges. At
+the third position of the turret, tools _E_ finish-turn the inside of
+the flanges; tools _F_ finish-turn the outside of the flanges, while
+tools _G_ finish the faces of the flanges. At the fourth position of the
+turret, tools _H_ finish-bore the sprockets; tools _I_ complete the
+turning on the outside of the flanges, while tools _J_ accurately size
+the interior of the flanges.
+
+With the double-spindle flat turret lathe, each operation is a double
+operation, and the speeds are varied according to the nature of the cut;
+thus, if at one position of the turret, the tools are required to rough
+out the work, this may be done rapidly, for it has no bearing on the
+other operations that are subsequently performed. Furthermore, if the
+following operation has to be performed with great care, this may be
+done without reducing the speed of the less exacting operations.
+
+[Illustration: Fig. 32. Potter & Johnston Automatic Chucking and Turning
+Machine]
+
+=Automatic Chucking and Turning Machine.=--The chucking and turning
+machine shown in Fig. 32 is automatic in its operation, the feeding of
+the tools, indexing of the turret, etc., being done automatically after
+the machine is properly arranged, and the work is placed in the chuck.
+This machine is adapted to turning and boring a great variety of
+castings, forgings or parts from bar stock, and it is often used in
+preference to the hand-operated turret lathe, especially when a great
+many duplicate parts are required. It is provided with mechanism for
+operating the cross-slide, feeding the turret slide forward, returning
+it rapidly, rotating the turret to a new position, and feeding it
+forward quickly for taking a new cut. The cross-slide and turret-slide
+movements are effected by cams mounted on the large drum _E_ seen
+beneath the turret, while the various speed and feed changes are
+effected by dogs and pins carried on disk _D_ which is keyed to the same
+shaft that the cam drum is mounted upon. This shaft with the cam drum
+and governing disk _D_, makes one revolution for each piece of work
+completed. The cams for operating the turret slide are mounted upon the
+periphery of drum _E_. The roll which engages the angular faces of these
+cams and imparts movement to the turret is carried by an intermediate
+slide which has rack teeth engaging a pinion on the square shaft _C_. By
+turning this shaft with a crank, the position of the turret-slide, with
+relation to the cam, may be adjusted for long or short work and long or
+short tools, as may be required.
+
+[Illustration: Fig. 33. Rear View of Machine showing the Cross-slide
+Mechanism, Driving Gearing, etc.]
+
+The cams which operate the cross-slide are mounted on the right-hand end
+of drum _E_ and actuate the yoke _A_ (see Fig. 33) which extends
+diagonally upward. The rear end of this yoke has rack teeth meshing with
+the teeth of a segmental pinion, which is fastened to rock-shaft _B_.
+At the headstock end, this rock-shaft carries another segmental pinion
+meshing with rack teeth formed on the cross-slide. The movement imparted
+to the yoke by the cams is thus transmitted through the pinions and
+rock-shaft to the cross-slide.
+
+[Illustration: Fig. 34. The Automatic Controlling Mechanism for Feeds
+and Speeds]
+
+The cam drum _E_ is driven by a pinion meshing with a gear attached to
+its front side. This pinion is driven through a train of gearing from
+pulley _L_ (see Fig. 34) which is belted to the spindle. The feeds are
+thus always dependent on the spindle speed. By means of epicyclic
+gearing and suitable clutches, the motion thus derived from the spindle
+may be made rapid for returning the turret to be indexed and then
+advancing it to the cutting position again, or very slow for the forward
+feed when the tools are at work. These changes from slow to fast or
+_vice versa_ are controlled by disk _D_. This disk carries pins which
+strike a star wheel located back of the disk at the top, and as this
+star wheel is turned, the speeds are changed by operation of the gearing
+and clutches referred to. The first pin _M_ that strikes the star wheel
+advances it one-sixth of a rotation, changing the feed from fast to
+slow; the next pin that strikes it advances it another sixth of a
+rotation, changing the feed from slow to fast and so on. By adjusting
+the pins for each piece of work, the feed changes are made to take place
+at the proper time. Handwheel _E_ is geared with the cam-shaft on which
+the star wheel is mounted, so that the feeds may be changed by hand if
+desired.
+
+In addition to these feed-changing pins, disk _D_ has a dog which
+operates a lever by which the feed movement is stopped when the work has
+been completed. Four rates of feed are provided by quick change gearing
+of the sliding gear type, operated by handle _K_. With this handle set
+in the central position, the feed is disengaged. On the periphery of
+disk _D_ are also clamped dogs or cams _N_, which operate a horizontal
+swinging lever _P_ connected by a link with vertical lever _J_, which
+controls the two spindle speeds with which the machine is provided.
+Either one of these speeds can be automatically engaged at any time, by
+adjusting the cams _N_ on disk _D_.
+
+Lever _H_ connects or disconnects the driving pulley from the shaft on
+which it is mounted, thus starting or stopping the machine. The square
+shaft _G_ serves to operate the drums by hand and is turned with a
+crank. The rotation of the turret, which takes place at the rear of its
+travel, is, of course, effected automatically. A dog, which may be seen
+in Fig. 32 at the side of the bed, is set to trip the turret revolving
+mechanism at the proper point in the travel, to avoid interference
+between the tools and the work. The turret is provided with an automatic
+clamping device. The mechanism first withdraws the locking pin, unclamps
+the turret, revolves it, then throws in the locking pin and clamps the
+turret again.
+
+=Example of Work on Automatic Turning Machine.=--The piece selected for
+illustrating the "setting up" and operation of the automatic chucking
+and turning machine is shown in Fig. 35. This is a second operation, and
+a very simple one which will clearly illustrate the principles involved.
+In the first operation, the hole was drilled, bored and reamed, the
+small end of the bushing faced, and the outside diameter finished, as
+indicated by the sketch to the left. (The enlarged diameter at the end
+was used for holding the work in the chuck.) In the second operation
+(illustrated to the right), the enlarged chucking end is cut off and, in
+order to prevent wasting this piece, it is made into a collar for
+another part of the machine for which the bushing is intended; hence,
+the outside diameter is turned and the outside end faced, before cutting
+off the collar. In addition, the bushing is recessed in the second
+operation, and the outer end faced. In order to have the surfaces
+finished in the second operation, concentric with those machined in the
+first operation, the chuck is equipped with a set of soft "false jaws"
+which have been carefully bored to exactly the diameter of the work to
+be held.
+
+[Illustration: Fig. 35. Simple Example of Work done in Automatic
+Chucking and Turning Machine]
+
+The first thing to determine when setting up a machine of this type is
+the order of operations. In this particular case, the order is as
+follows: At the first position of the turret, the outside collar is
+rough-turned and the outer end rough-faced. At the second position, the
+collar is turned to the required diameter and the outer face is
+finished. The third face of the turret is not equipped with tools, this
+part of the cycle being taken up in cutting off the collar with a
+cut-off tool on the rear cross-slide. The fourth operation is that of
+recessing the bushing, and the fifth operation, facing the end to remove
+the rough surface left by the cutting-off tool.
+
+The tools _A_ and _B_, Fig. 36, used for turning the outside of the
+flange, are held in brackets _C_ bolted to the face of the turret.
+These brackets are each provided with three holes for carrying turning
+tool-holders. This arrangement provides for turning a number of
+diameters at different positions, simultaneously, but for this
+particular operation, a single cutting tool for each tool-holder is all
+that is necessary. A special device is used for recessing and will be
+described later.
+
+[Illustration: Fig. 36. Front View of Machine set up for the Finishing
+Operation on the Recessed Bushing and Collar shown in the Foreground and
+in Fig. 35]
+
+=Determining Speed and Feed Changes.=--As previously mentioned, the
+particular machine illustrated in Fig. 32 can be arranged for two
+automatic changes of speed to suit different diameters on the work. The
+change gears that will give the required spindle speeds should first be
+selected. These change gears for different speeds are listed on a speed
+and feed plate attached to the headstock of the machine (see Fig. 37).
+It is possible to use one speed from the list given for the fast train
+of gears, and one from the list for the slow train, so long as the same
+gears are not used in each case. The diameter of the collar on the work
+shown in Fig. 35 is 2-1/2 inches, and the diameter of the body is 2
+inches. Assuming that the surface speed for this job should be about 40
+feet per minute, a little calculation shows that the 66 revolutions per
+minute, given by the fast train of gears, is equivalent to a surface
+speed of 43 feet per minute on a diameter of 2-1/2 inches. Moreover, the
+78 revolutions per minute obtained from the slow train of gearing, gives
+about 41 feet per minute on a diameter of 2 inches. The spindle gearing
+indicated for these speeds is, therefore, placed in position on the
+proper studs at the back of the machine.
+
+[Illustration: Fig. 37. Plate on the Headstock of Machine Illustrated in
+Fig. 32 giving the Speeds and Feeds]
+
+Next we have to determine on which faces of the turret to place the
+different tools. Each turret face is numbered to agree with the
+corresponding feed cam on the drum. The speed and feed plate (Fig. 37)
+gives the various feeds obtainable per revolution of the spindle. As
+will be seen, the different cams give different feeds. Cam No. 1 has a
+coarse feed suitable for roughing; cam No. 2 a finer feed adapted to
+finishing, and so on. Since the first operation consists in
+rough-turning, cam No. 1 is used. Cam No. 2, which gives a finer feed,
+is used for the finish-turning operation. Cam No. 4, which is ordinarily
+used for reaming, could, in this case, be used for recessing, as this
+recess is for clearance only and may be bored with a coarse feed.
+
+The final operation, which is that of facing, can be done with any cam
+and cam No. 5 may be used. It will be understood that for facing
+operations, the feeds given do not apply. As the roll passes over the
+point of the feed cam at the extreme end of the movement, the feed of
+the turret slide is gradually slowed down to zero; since the facing
+takes place in the last eighth or sixteenth inch of this movement, it is
+done at a feed which is gradually reduced to zero. This is, of course,
+as it should be, and it is not necessary to pay any attention to the
+tabulated feeds in facing operations.
+
+=Setting the Turret Slide.=--The next adjustment is that of setting the
+turret slide. In making this adjustment the turret is set in such
+relation to the work that the tools will have but a small amount of
+overhang, the cam-shaft being revolved by hand until the cam-roll is at
+the extreme top of the forward feeding cam, so that the turret slide is
+at the extreme of its forward movement. When this adjustment has been
+made by the means provided, set the turret index tripping dog so as to
+revolve the turret at the proper point. After a turning tool-holder and
+tool is attached to the face of the turret, cam No. 1 is placed in its
+operating position and is revolved by hand until the roll is on the
+point of the cam and the turret at the forward extreme of its motion. At
+this point the tool-holder is set so that the cutter will be far enough
+forward to complete its turning operation. The feed cam is then turned
+backward, thus returning the turret slide, and the cutter is set to turn
+the flange to the proper diameter for the roughing cut. The turret slide
+is fed forward and back while the cutter is adjusted, and when it is
+properly set, the flange is turned, the cam-drum being fed by hand. This
+is the first trial cut on the piece.
+
+A facing tool, shown in the working position in Fig. 36, is placed at
+this station of the turret, being held in the turret hole. This tool has
+a pilot bar and a holder which contains a facing blade. Feeding by hand,
+as before, the tool is adjusted lengthwise so as to rough-face the work
+to the dimension desired. In a similar way the finish-turning and
+facing tools for the second position of the turret are set, the
+cam-shaft being revolved by hand to bring this second face and second
+cam into the working position. (The finish-facing tool is not shown in
+place in Fig. 36.)
+
+[Illustration: Fig. 38. Diagram of Cross-slide Cams and Feeding
+Mechanism]
+
+=Setting the Cross-slide Cam.=--As previously mentioned, the third
+turret face has no tool, the cutting off of the collar being done during
+this part of the cycle of operations. It has been taken for granted that
+in setting the turret slide, room has been left between it and the chuck
+for the cross-slide. The cross-slide is clamped in a longitudinal
+position on the bed, convenient for the cutting-off operation, which is
+done with a tool _D_ (Fig. 36) in the rear toolpost, thus leaving the
+front unobstructed for the operator. When both forming and cutting off
+are to be done, the forming tool is generally held at the front and the
+cutting-off tool at the back because heavier and more accurate forming
+can be done with the work revolving downward toward a tool in the front
+toolpost, than with the tool at the rear where it is subjected to a
+lifting action.
+
+The arrangement of the cross-slide cams is shown in Fig. 38, which is an
+end view of the large drum _E_, Fig. 32. The rear feed cam is the one to
+be used, and since this cutting-off operation is a short one, it may be
+done during the return of the turret for position No. 3. The cam drum
+is, therefore, rotated by hand until the turret face No. 3 has begun to
+return. The cross-slide cams are then loosened and the rear feed cam is
+swung around to just touch the roller _R_ which operates arm _A_, the
+cross-slide having been adjusted out to nearly the limit of its forward
+travel, leaving approximately enough movement for cutting off the
+collar. The rear feed cam is then clamped in this position.
+
+A cutting-off tool is next placed in the rear toolpost at the proper
+height. The rear toolpost slide is then adjusted to bring the point of
+the cutting-off tool up to the work, and the cam drum is revolved by
+hand until the piece is cut off. The cross-slide tool is, of course, set
+in the proper position to make a collar of the required thickness.
+Feeding by hand is discontinued when the roll is on the point of the
+cam; the cutting-off tool slide is then permanently set on the
+cross-slide so that the point of the cutting-off tool enters the bore
+just far enough to completely sever the collar from the bushing. The
+motion of the cam drum is continued, by hand, until the roll is over the
+point of the feed cam. The cross-slide is then pushed back, by hand,
+until the cam and roll are again in contact, when the return cam is
+brought up and clamped in position, so that there is just room for the
+roll between the feed cam and the return cam. The rear return cam (as
+the hand feed of the cam drum is continued) brings the cross-slide back
+to its central position. Since there is no front tool used for this
+series of operations (although a tool is shown in the front toolpost,
+Fig. 36), the first feed and return cams are allowed to remain wherever
+they happen to be. These cam adjustments can all be made from the front
+of the machine.
+
+=Setting the Boring Tool for Recessing.=--The feeding of the turret
+slide is now continued to make sure that the cutting-off tool is
+returned to its normal position before the facing tool in the next face
+of the turret begins to work. The facing of the bushing, so far as the
+setting of the tool is concerned, is merely a repetition of the facing
+operation at the first position of the turret. The recessing tool is
+next set. This tool, which is shown diagrammatically in Fig. 39, is very
+simple as compared with the somewhat complex operation it has to
+perform. This recess is for clearance only, and accurate dimensions and
+fine finish are not necessary. The recessing tool consists simply of a
+slender boring-bar held in the turret and carrying a cutter suitably
+located about midway the bar. The forward end of the bar is small enough
+to enter a bell-mouthed bushing held in the chuck. The boring-bar is
+bent to one side far enough so that the cutter clears the hole as the
+bar enters, but is forced into the work as the rounded hole of the
+bushing engages the end of the bar and deflects it into the working
+position. The upper diagram shows the position of the bar as it enters
+the hole, and the lower one the position after it has entered the
+bushing and is engaged in turning the recess. This bar is set in the
+turret so that at the extreme forward travel of the turret slide, the
+recess will be bored to the required length. The cutter must also be
+adjusted to bore to the desired diameter. This completes the setting of
+the cutting tools.
+
+[Illustration: Fig. 39. Flexible Boring Tool used for Recessing a
+Bushing in Automatic Chucking and Turning Machine]
+
+=Adjustments for Automatic Feed and Speed Changes.=--The machine must
+now be set to perform automatically the desired changes of spindle speed
+and the fast and slow cam movements for the tools. After placing a new
+piece of work in the machine (the first one having been completed in the
+setting-up operation), the cam-shaft is revolved by hand until the
+turning tool in turret face No. 1 is just about to begin its cut. The
+control wheel _D_, Fig. 34, is rotated in its normal direction until the
+next graduation marked "slow" is in line with an index mark on the base
+of the machine. Then the nearest pin _M_ is moved up until it bears
+against a tooth of the star wheel (previously referred to) and is
+clamped in this position. The pin should now be in the proper location,
+but to test its position, rotate the cam shaft backward by hand and
+throw in the automatic feed; then watch the cut to see if the drum slows
+down just before the tool begins to work. If it does not, the pin should
+be adjusted a little, one way or the other, as may be required. (In
+going over a piece of work for the first time, it is best to have the
+feed set to the smallest rate, feed change handle _K_ being in position
+No. 1.)
+
+After the cut has been completed and the turret feed cam-roll is on the
+high part of the cam, the power feed should again be stopped and the
+handwheel revolved until the next graduation marked "fast" is opposite
+the index mark. The next stop pin is then moved up until it just touches
+the star wheel, where it is clamped in position. The feed being again
+thrown in, the turret will be returned rapidly, indexed, and moved
+forward for the second operation. After stopping the automatic movement,
+the pins are set for this face, and so on for all the operations,
+including that in which the cross-slide is used for cutting off the
+finished collar.
+
+As the first, second, and third operations are on comparatively large
+diameters, they should be done at the slow speed, handle _J_, Fig. 34,
+being set to give that speed. While the turret slide is being returned
+between operations 3 and 4, one of the spindle speed-changing dogs _N_
+should be clamped to the rim of disk _D_ so as to change the spindle
+speed to the fast movement. This speed is continued until the last
+operation is completed, when a second dog is clamped in place to again
+throw in the slow movement. The feed knock-off dog should also be
+clamped in place on the disk to stop the machine at the completion of
+the fifth operation, when the turret is in its rear position. This
+completes the setting up of the machine. If the feed is finer than is
+necessary, the feed change handle _K_ may now be moved to a position
+which will give the maximum feed that can be used.
+
+It has taken considerable time to describe the setting up of the machine
+for this simple operation, but in the hands of a competent man it can be
+done quite rapidly. While a simple operation has been referred to in the
+foregoing, it will be understood that a great variety of work can be
+done on a machine of this type. It is not unusual to see as many as ten
+cutting tools operating simultaneously on a piece of work, the tools
+being carried by the turret, cross-slide and back facing attachment. The
+latter is operated from a separate cam applied to the cam-shaft and
+acting through levers on a back facing bar which passes through a hole
+in the spindle. In this back facing bar may be mounted drills, cutters,
+facing tools, etc. for machining the rear face of a casting held in the
+chuck jaws. Where extreme accuracy is required, a double back facing
+attachment may be used, arranged with cutters for taking both roughing
+and finishing cuts. The use of this attachment often saves a second
+operation. This automatic chucking and turning machine is also adapted
+for bar work, especially in diameters varying from 3 to 6 inches.
+
+=Turning Flywheel in Automatic Chucking and Turning Machine.=--A typical
+operation on the Potter & Johnston automatic chucking and turning
+machine is illustrated in Fig. 40, which shows the machine arranged for
+turning the cast-iron flywheel for the engine of a motor truck. The rim
+is turned and faced on both sides and the hub is bored, reamed and faced
+on both sides. The flywheel casting is held in a chuck by three special
+jaws which grip the inside of the rim. The order of the operations is as
+follows:
+
+The rear end of the hub is faced by the back facing bar; the cored hole
+is started by a four-lipped drill in the turret and the front end of the
+hub is rough-faced. (These tools are on the rear side of the turret
+when the latter is in the position shown in the illustration.) After the
+turret indexes, the hole is rough-bored by tool _A_ and while this is
+being done, the outside of the rim is rough-turned by tool _B_ held in a
+special bracket attached to the turret. Both sides of the rim are also
+rough-faced by tools _C_ and _D_ held at the front of the cross-slide,
+this operation taking place at the same time that the rim is turned and
+the hole is being bored.
+
+[Illustration: Fig. 40. Machining Flywheels in Potter & Johnston
+Automatic Chucking and Turning Machine]
+
+The turret again automatically recedes and indexes, thus locating bar
+_E_ and turning tool _G_ in the working position. The hole is then
+finish-bored by tool _E_ and the hub is finish-faced by blade _F_; at
+the same time the rim is finish-turned by tool _G_ and the sides are
+finish-faced to the proper width by two tools held at the rear of the
+cross-slide. The turret automatically recedes and indexes a third time,
+thus locating the flat-cutter reamer-bar _H_ in the working position and
+then the hole is reamed to the required diameter. This completes the
+cycle of operations. The total time for machining this flywheel is forty
+minutes.
+
+=Automatic Multiple-spindle Chucking Machine.=--An example of the
+specialized machines now used for producing duplicate parts, is shown in
+Fig. 41. This is a "New Britain" automatic multiple-spindle chucking
+machine of the single-head type and it is especially adapted for boring,
+reaming and facing operations on castings or forgings which can readily
+be held in chuck jaws. This particular machine has five spindles, which
+carry and revolve the tools. The work being machined is held stationary
+in the multiple chuck turret _A_ which holds each part in line with one
+of the spindles and automatically indexes, so that the work passes from
+one spindle to another until it is finished. The turret then indexes the
+finished piece to a sixth or "loading position" which is not opposite a
+spindle, where the part is removed and replaced with a rough casting.
+Each pair of chuck jaws is operated independently of the others by the
+use of a chuck wrench. These jaws are made to suit the shape of the
+work.
+
+[Illustration: Fig. 41. New Britain Multiple-spindle Automatic Chucking
+Machine of Single-head Type]
+
+When a single-head machine is in operation, the turret advances and
+feeds the work against the revolving tools so that a number of pieces
+are operated upon at the same time. The turret is fed by a cam drum _B_.
+Cam strips are bolted to the outside of this drum and act directly
+against a roller attached to the yoke _C_ which can be clamped in
+different positions on the spindle _D_, the position depending upon the
+length of the work. On the opposite end of the turret spindle is the
+indexing mechanism _E_. An automatically spring-operated latch _F_
+engages notches in the rim of the dividing wheel, thus accurately
+locating the turret. The turret is locked by a steadyrest _G_, which,
+for each working position, automatically slides into engagement with one
+of the notches in the turret. This relieves the indexing mechanism of
+all strain.
+
+[Illustration: Fig. 42. Detail View of New Britain Double-head
+Eight-spindle Machine, Boring, Reaming and Facing Castings]
+
+This type of machine is also built with two spindle heads, the
+double-head design being used for work requiring operations on both
+ends. When the double-head machine is in operation, the revolving
+spindles and tools advance on both sides of the chuck turret, the latter
+remaining stationary except when indexing. The feed drums on the
+double-head machine are located directly beneath each group of spindles.
+
+Fig. 42 shows an example of work on a machine of the double-head design.
+This is an eight-spindle machine, there being two groups of four
+spindles on each side of the turret. The castings _E_ are for the wheel
+hubs of automobiles. The order of the operations on one of the castings,
+as it indexes around, is as follows: The hole in the hub is first
+rough-reamed by taper reamer _A_ and the opposite end of the hub is
+rough-faced and counterbored by a tool in spindle _A_{1}_. When the
+turret indexes, this same casting is reamed close to the finished size
+by reamer _B_ and the left end of the hub is rough-faced by cutter _F_,
+while a tool in the opposite spindle _B_{1}_ finishes the counterboring
+and facing operation. At the third position, reamer _C_ finishes the
+hole accurately to size, and when the work is indexed to the fourth
+position, the hub on the left side is finish-faced by a tool in spindle
+_D_. (The third and fourth spindles of the right-hand group are not used
+for this particular operation.) When the turret again indexes, the
+finished casting is removed and replaced with a rough one. While the
+successive operations on a single casting have just been described, it
+will be understood that all of the tools operate simultaneously and that
+a finished casting arrives at the unloading and loading position each
+time the turret indexes. Three hundred of these malleable castings are
+machined in nine hours.
+
+=Selecting Type of Turning Machine.=--The variety of machine tools now
+in use is very extensive, and as different types can often be employed
+for the same kind of work, the selection of the best and most efficient
+machine is often a rather difficult problem. To illustrate, there are
+many different types and designs of turning machines, such as the
+ordinary engine lathe, the hand-operated turret lathe, the
+semi-automatic turning machine, and the fully automatic type, which,
+after it is "set up" and started, is entirely independent. Hence, when a
+certain part must be turned, the question is, what kind of machine
+should be used, assuming that it would be possible to employ several
+different machines? The answer to this question usually depends
+principally upon the number of parts that must be turned.
+
+For example, a certain casting or forging might be turned in a lathe,
+which could be finished in some form of automatic or semi-automatic
+turning machine much more quickly. It does not necessarily follow,
+however, that the automatic is the best machine to use, because the
+lathe is designed for general work and the part referred to could
+doubtless be turned with the regular lathe equipment, whereas the
+automatic machine would require special tools and it would also need to
+be carefully adjusted. Therefore, if only a few parts were needed, the
+lathe might be the best tool to use, but if a large number were
+required, the automatic or semi-automatic machine would doubtless be
+preferable, because the saving in time effected by the latter type would
+more than offset the extra expense for tool equipment and setting the
+machine. It is also necessary, in connection with some work, to consider
+the degree of accuracy required, as well as the rate of production, and
+it is because of these varying conditions that work of the same general
+class is often done in machines of different types, in order to secure
+the most efficient results.
+
+
+
+
+CHAPTER VI
+
+VERTICAL BORING MILL PRACTICE
+
+
+All the different types of turning machines now in use originated from
+the lathe. Many of these tools, however, do not resemble the lathe
+because, in the process of evolution, there have been many changes made
+in order to develop turning machines for handling certain classes of
+work to the best advantage. The machine illustrated in Fig. 1 belongs to
+the lathe family and is known as a vertical boring and turning mill.
+This type, as the name implies, is used for boring and turning
+operations, and it is very efficient for work within its range. The part
+to be machined is held to the table _B_ either by clamps or in chuck
+jaws attached to the table. When the machine is in operation, the table
+revolves and the turning or boring tools (which are held in tool-blocks
+_T_) remain stationary, except for the feeding movement. Very often more
+than one tool is used at a time, as will be shown later by examples of
+vertical boring mill work. The tool-blocks _T_ are inserted in tool-bars
+_T_{1}_ carried by saddles _S_ which are mounted on cross-rail _C_. Each
+tool-head (consisting of a saddle and tool-bar) can be moved
+horizontally along cross-rail _C_, and the tool-bars _T_{1}_ have a
+vertical movement. These movements can be effected either by hand or
+power.
+
+When a surface is being turned parallel to the work table, the entire
+tool-head moves horizontally along the cross-rail, but when a
+cylindrical surface is being turned, the tool-bar moves vertically. The
+tool-heads are moved horizontally by the screws _H_ and _H_{1}_, and the
+vertical feed for the tool-bars is obtained from the splined shafts _V_
+and _V_{1}_, there being a separate screw and shaft for each head so
+that the feeding movements are independent. These feed shafts are
+rotated for the power feed by vertical shafts _A_ and _A_{1}_ on each
+side of the machine.
+
+These vertical shafts connect with the feed shafts through bevel and
+spur gears located at the ends of the cross-rail. On most boring mills,
+connection is made with one of the splined shafts _V_ or screw _H_, by a
+movable gear, which is placed on whichever shaft will give the desired
+direction of feed. The particular machine illustrated is so arranged
+that either the right or left screw or feed shaft can be engaged by
+simply shifting levers _D_{1}_ or _D_.
+
+[Illustration: Fig. 1. Gisholt Vertical Boring and Turning Mill]
+
+The amount of feed per revolution of the table is varied for each
+tool-head by feed-changing mechanisms _F_ on each side of the machine.
+These feed boxes contain gears of different sizes, and by changing the
+combinations of these gears, the amount of feed is varied. Five feed
+changes are obtained on this machine by shifting lever _E_, and this
+number is doubled by shifting lever _G_. By having two feed boxes, the
+feeding movement of each head can be varied independently. The direction
+of either the horizontal or vertical feed can be reversed by lever _R_,
+which is also used for engaging or disengaging the feeds. This machine
+is equipped with the dials _I_ and _I_{1}_ which can be set to
+automatically disengage the feed at any predetermined point. There are
+also micrometer dials graduated to thousandths of an inch and used for
+adjusting the tools without the use of measuring instruments.
+
+The work table _B_ is driven indirectly from a belt pulley at the rear,
+which transmits the power through gearing. The speed of the table can be
+varied for turning large or small parts, by levers _J_ and _K_ and the
+table can be started, stopped or rotated part of a revolution by lever
+_L_ which connects with a friction clutch. There are corresponding feed
+and speed levers on the opposite side, so that the machine can be
+controlled from either position.
+
+The heads can be adjusted along the cross-rail for setting the tools by
+hand-cranks _N_, and the tool slides can be moved vertically by turning
+shafts _V_ with the same cranks. With this machine, however, these
+adjustments do not have to be made by hand, ordinarily, as there are
+rapid power movements controlled by levers _M_. These levers
+automatically disengage the feeds and enable the tool-heads to be
+rapidly shifted to the required position, the direction of the movement
+depending upon the position of the feed reverse lever _R_ and lever _D_.
+This rapid traverse, which is a feature applied to modern boring mills
+of medium and large size, saves time and the labor connected with hand
+adjustments. The cross-rail _C_ has a vertical adjustment on the faces
+of the right and left housings which support it, in order to locate the
+tool-heads at the right height for the work. This adjustment is effected
+by power and is controlled by levers at the sides of the housings.
+Normally, the cross-rail is bolted to the housings, and these bolts must
+be loosened before making the adjustment, and must always be tightened
+afterwards.
+
+The function of these different levers has been explained to show, in a
+general way, how a vertical boring machine is operated. It should be
+understood, however, that the arrangement differs considerably on
+machines of other makes. The construction also varies considerably on
+machines of the same make but of different size.
+
+[Illustration: Fig. 2. Small Boring and Turning Mill with Single
+Turret-head]
+
+All modern vertical boring mills of medium and large sizes are equipped
+with two tool-heads, as shown in Fig. 1, because a great deal of work
+done on a machine of this type can have two surfaces machined
+simultaneously. On the other hand, small mills of the type illustrated
+in Fig. 2 have a single head. The toolslide of this machine, instead of
+having a single tool-block, carries a five-sided turret _T_ in which
+different tools can be mounted. These tools are shifted to the working
+position as they are needed, by loosening binder lever _L_ and turning
+or "indexing" the turret. The turret is located and locked in any of its
+five positions by lever _I_, which controls a plunger that engages
+notches at the rear. Frequently, all the tools for machining a part can
+be held in the turret, so that little time is required for changing from
+one tool to the next. Some large machines having two tool-heads are also
+equipped with a turret on one head.
+
+=Boring and Turning in a Vertical Boring Mill.=--The vertical boring
+mill is, in many respects, like a lathe placed in a vertical position,
+the table of the mill corresponding to the faceplate or chuck of the
+lathe and the tool-head to the lathe carriage. Much of the work done by
+a vertical mill could also be machined in a lathe, but the former is
+much more efficient for work within its range. To begin with, it is more
+convenient to clamp work to a horizontal table than to the vertical
+surface of a lathe faceplate, or, as someone has aptly said, "It is
+easier to lay a piece down than to hang it up." This is especially true
+of the heavy parts for which the boring mill is principally used. Very
+deep roughing cuts can also be taken with a vertical mill. This type of
+machine mill is designed for turning and boring work which, generally
+speaking, is quite large in diameter in proportion to the width or
+height. The work varies greatly, especially in regard to its diameter,
+so that boring mills are built in a large range of sizes. The small and
+medium sizes will swing work varying from about 30 inches to 6 or 7 feet
+in diameter, whereas large machines, such as are used for turning very
+large flywheels, sheaves, etc., have a swing of 16 or 20 feet, and
+larger sizes are used in some shops. The size of a vertical mill, like
+any other machine tool, should be somewhat in proportion to the size of
+the work for which it is intended, as a very large machine is unwieldy,
+and, therefore, inefficient for machining comparatively small parts.
+
+=Holding and Setting Work on Boring Mill Table.=--There are three
+general methods of holding work to the table of a boring mill; namely,
+by the use of chucks, by ordinary bolts and clamps, or in special
+fixtures. Chucks which are built into the table (as illustrated in Fig.
+2) and have both universal and independent adjustments for the jaws can
+be used to advantage for holding castings that are either round or
+irregular in shape. The universal adjustment is used for cylindrical
+parts, such as disks, flywheels, gear blanks, etc., and the independent
+adjustment, for castings of irregular shape. Chucks which have either an
+independent or universal movement for the jaws are known as a
+"combination" type and usually have three jaws. There is also a four-jaw
+type which has the independent adjustment only. This style is preferable
+for work that is not cylindrical and which must be held very securely.
+Chuck jaws that do not form a part of the machine table, but are bolted
+to it in the required position, are also employed extensively,
+especially on comparatively large machines.
+
+Most of the work done in a vertical mill is held in a chuck.
+Occasionally, however, it is preferable to clamp a part directly to the
+table. This may be desirable because of the shape and size of the work,
+or because it is necessary to hold a previously machined surface
+directly against the table in order to secure greater accuracy.
+Sometimes a casting is held in the chuck for turning one side, and then
+the finished side is clamped against the table for turning the opposite
+side. Parts which are to be machined in large quantities are often held
+in special fixtures. This method is employed when it enables the work to
+be set up more quickly than would be possible if regular clamps or chuck
+jaws were used.
+
+Work that is to be turned or bored should first be set so that the part
+to be machined is about central with the table. For example, the rim of
+a flywheel should be set to run true so that it can be finished by
+removing about the same amount of metal around the entire rim; in other
+words, the rim should be set concentric with the table, as shown in Fig.
+3, and the sides of the rim should also be parallel to the table.
+
+[Illustration: Fig. 3. Plan View showing Flywheel Casting Chucked for
+Turning]
+
+A simple tool that is very useful for testing the position of any
+cylindrical casting consists of a wooden shank into which is inserted a
+piece of wire, having one end bent. This tool is clamped in the toolpost
+and as the work revolves the wire is adjusted close to the cylindrical
+surface being tested. The movement of the work with relation to the
+stationary wire point will, of course, show whether or not the part runs
+true. The advantage of using a piece of wire for testing, instead of a
+rigid tool, is that the wire, owing to its flexibility, will simply be
+bent backward if it is moved too close to a surface which is
+considerably out of true. The upper surface of a casting can be tested
+for parallelism with the table by using this same wire gage, or by
+comparing the surface, as the table is revolved slowly, with a tool held
+in the toolpost. An ordinary surface gage is also used for this purpose.
+The proper surface to set true, in any case, depends upon the
+requirements. A plain cylindrical disk would be set so that the outside
+ran true and the top surface was parallel with the table. When setting a
+flywheel, if the inside of the rim is to remain rough, the casting
+should be set by this surface rather than by the outside, so that the
+rim, when finished, will be uniform in thickness.
+
+As far as possible, chucks should be used for holding cylindrical parts,
+owing to their convenience. The jaws should be set against an interior
+cylindrical surface whenever this is feasible. To illustrate, the
+flywheel in Fig. 3 is gripped by the inside of the rim which permits the
+outside to be turned at this setting of the work. It is also advisable
+to set a flywheel casting in the chuck so that a spoke rests against one
+of the jaws as at _d_, if this is possible. This jaw will then act as a
+driver and prevent the casting from slipping or turning in the chuck
+jaws, owing to the tangential pressure of the turning tool. When a cut
+is being taken, the table and work rotate as shown by arrow _a_, and the
+thrust of the cut (taken by tool _t_) tends to move the wheel backward
+against the direction of rotation, as shown by arrow _b_. If one of the
+chuck jaws bears against one of the spokes, this movement is prevented.
+It is not always feasible to use a chuck jaw as a driver and then a
+special driver having the form of a small angle-plate or block is
+sometimes bolted directly to the table. Another method of driving is to
+set a brace between a spoke or projection on the work and a chuck jaw or
+strip attached to the table. Drivers are not only used when turning
+flywheels, but in connection with any large casting, especially when
+heavy cuts have to be taken. Of course, some castings are so shaped that
+drivers cannot be employed.
+
+=Turning in a Boring Mill.=--The vertical type of boring mill is used
+more for turning cylindrical surfaces than for actual boring, although a
+large part of the work requires both turning and boring. We shall first
+consider, in a general way, how surfaces are turned and then refer to
+some boring operations. The diagram _A_, Fig. 4, illustrates how a
+horizontal surface would be turned. The tool _t_ is clamped in
+tool-block _t_{1}_, in a vertical position, and it is fed horizontally
+as the table and work rotate. The tool is first adjusted by hand for the
+proper depth of cut and the automatic horizontal feed is then engaged.
+When a cylindrical surface is to be turned, the tool (provided a
+straight tool is used) is clamped in a horizontal position and is fed
+downward as indicated at _B_. The amount that the tool should feed per
+revolution of the work, depends upon the kind of material being turned,
+the diameter of the turned part and the depth of the cut.
+
+[Illustration: Fig. 4. (A) Turning a Flat Surface. (B) Turning a
+Cylindrical Surface]
+
+Most of the parts machined in a vertical boring mill are made of cast
+iron and, ordinarily, at least one roughing and one finishing cut is
+taken. The number of roughing cuts required in any case depends, of
+course, upon the amount of metal to be removed. An ordinary roughing cut
+in soft cast iron might vary in depth from 1/8 or 3/16 inch to 3/8 or
+1/2 inch and the tool would probably have a feed per revolution of from
+1/16 to 1/8 inch, although deeper cuts and coarser feeds are sometimes
+taken. These figures are merely given to show, in a general way, what
+cuts and feeds are practicable. The tool used for roughing usually has a
+rounded end which leaves a ridged or rough surface. To obtain a smooth
+finish, broad flat tools are used. The flat cutting edge is set parallel
+to the tool's travel and a coarse feed is used in order to reduce the
+time required for taking the cut. The finishing feeds for cast iron vary
+from 1/4 to 3/4 inch on ordinary work. The different tools used on the
+vertical mill will be referred to more in detail later.
+
+All medium and large sized vertical boring mills are equipped with two
+tool-heads and two tools are frequently used at the same time,
+especially on large work. Fig. 9 illustrates the use of two tools
+simultaneously. The casting shown is a flywheel, and the tool on the
+right side turns the upper side of the rim, while the tool on the left
+side turns the outside or cylindrical surface. As a boring mill table
+rotates in a counter-clockwise direction, the left-hand tool is reversed
+to bring the cutting edge at the rear. By turning two surfaces at once,
+the total time for machining the casting is, of course, greatly reduced.
+The turning of flywheels is a common vertical boring mill operation, and
+this work will be referred to in detail later on.
+
+[Illustration: Fig. 5. Tools for Boring and Reaming Holes]
+
+=Boring Operations.=--There are several methods of machining holes when
+using a vertical boring mill. Ordinarily, small holes are cored in
+castings and it is simply necessary to finish the rough surface to the
+required diameter. Some of the tools used for boring and finishing
+comparatively small holes are shown in Fig. 5. Sketch _A_ shows a boring
+tool consisting of a cutter _c_ inserted in a shank, which, in turn, is
+held in the tool slide, or in a turret attached to the tool slide. With
+a tool of this type, a hole is bored by taking one or more cuts down
+through it. The tool shown at _B_ is a four-lipped drill which is used
+for drilling cored holes preparatory to finishing by a cutter or reamer.
+This drill would probably finish a hole to within about 1/32 inch of the
+finish diameter, thus leaving a small amount of metal for the reamer to
+remove. The tool illustrated at _C_ has a double-ended flat cutter _c_,
+which cuts on both sides. These cutters are often made in sets for
+boring duplicate parts. Ordinarily, there are two cutters in a set, one
+being used for roughing and the other for finishing. The cutter passes
+through a rectangular slot in the bar and this particular style is
+centrally located by shoulders _s_, and is held by a taper pin _p_. Some
+cutter bars have an extension end, or "pilot" as it is called, which
+passes through a close-fitting bushing in the table to steady the bar.
+Sketch _D_ shows a finishing reamer. This tool takes a very light cut
+and is intended to finish holes that have been previously bored close to
+the required size. Sometimes a flat cutter _C_ is used for roughing and
+a reamer for finishing. The reamer is especially desirable for
+interchangeable work, when all holes must have a smooth finish and be of
+the same diameter. When a reamer is held rigidly to a turret or
+toolslide, it is liable to produce a hole that is either tapering or
+larger than the reamer diameter. To prevent this, the reamer should be
+held in a "floating" holder which, by means of a slight adjustment,
+allows the reamer to align itself with the hole. There are several
+methods of securing this "floating" movement. (See "Floating Reamer
+Holders.")
+
+[Illustration: Fig. 6. Boring with Regular Turning Tools]
+
+Large holes or interior cylindrical surfaces are bored by tools held in
+the regular tool-head. The tool is sometimes clamped in a horizontal
+position as shown at _A_, Fig. 6, or a bent type is used as at _B_. Cast
+iron is usually finished by a broad flat tool as at _C_, the same as
+when turning exterior surfaces. Obviously a hole that is bored in this
+way must be large enough to admit the tool-block.
+
+[Illustration: Fig. 7. Set of Boring Mill Tools]
+
+=Turning Tools for the Vertical Boring Mill.=--A set of turning tools
+for the vertical boring mill is shown in Fig. 7. These tools can be used
+for a wide variety of ordinary turning operations. When a great many
+duplicate parts are to be machined, special tool equipment can often be
+used to advantage, but as the form of this equipment depends upon the
+character of the work, only standard tools have been shown in this
+illustration. The tool shown at _A_ is a right-hand, roughing tool, and
+a left-hand tool of the same type is shown at _B_. Tool _C_ is an offset
+or bent, left-hand round nose for roughing, and _D_ is a right-hand
+offset roughing tool. A straight round nose is shown at _E_. Tool _F_
+has a flat, broad cutting edge and is used for finishing. Left-and
+right-hand finishing tools of the offset type are shown at _G_ and _H_,
+respectively. Tool _I_ has a square end and is used for cutting grooves.
+Right-and left-hand parting tools are shown at _J_ and _K_, and tool _L_
+is a form frequently used for rounding corners.
+
+[Illustration: Fig. 8. Diagrams Illustrating Use of Different Forms of
+Tools]
+
+The diagrams in Fig. 8 show, in a general way, how each of the tools
+illustrated in Fig. 7 are used, and corresponding tools are marked by
+the same reference letters in both of these illustrations. The right-and
+left-hand roughing tools _A_ and _B_ are especially adapted for taking
+deep roughing cuts. One feeds away from the center of the table, or to
+the right (when held in the right-hand tool-block) and the other tool is
+ground to feed in the opposite direction. Ordinarily, when turning plain
+flat surfaces, the cut is started at the outside and the tool feeds
+toward the center, as at _B_, although it is sometimes more convenient
+to feed in the opposite direction, as at _A_, especially when there is a
+rim or other projecting part at the outside edge. The tool shown at _A_
+could also be used for turning cylindrical surfaces, by clamping it in a
+horizontal position across the bottom of the tool-block. The feeding
+movement would then be downward or at right-angles to the work table.
+
+The offset round-nose tools _C_ and _D_ are for turning exterior or
+interior cylinder surfaces. The shank of this tool is clamped in the
+tool-block in a vertical position and as the bent end extends below the
+tool-block, it can be fed down close to a shoulder. The straight type
+shown at _E_ is commonly used for turning steel or iron, and when the
+point is drawn out narrower, it is also used for brass, although the
+front is then ground without slope. Tool _F_ is for light finishing cuts
+and broad feeds. The amount of feed per revolution of the work should
+always be less than the width of the cutting edge as otherwise ridges
+will be left on the turned surface. The offset tools _G_ and _H_ are for
+finishing exterior and interior cylindrical surfaces. These tools also
+have both vertical and horizontal cutting edges and are sometimes used
+for first finishing a cylindrical and then a horizontal surface, or
+_vice versa_. Tool _I_ is adapted to such work as cutting packing-ring
+grooves in engine pistons, forming square or rectangular grooves, and
+similar work. The parting tools _J_ and _K_ can also be used for forming
+narrow grooves or for cutting off rings, etc. The sketch _K_ (Fig. 8)
+indicates how a tool of this kind might be used for squaring a corner
+under a shoulder. Tool _L_ is frequently used on boring mills for
+rounding the corners of flywheel rims, in order to give them a more
+finished appearance. It has two cutting edges so that either side can be
+used as when rounding the inner and outer corners of a rim.
+
+The turning tools of a vertical boring mill are similar, in many
+respects, to those used in a lathe, although the shanks of the former
+are shorter and more stocky than those of lathe tools. The cutting edges
+of some of the tools also differ somewhat in form, but the principles
+which govern the grinding of lathe and boring mill tools are identical,
+and those who are not familiar with tool grinding are referred to
+Chapter II, in which this subject is treated.
+
+=Turning a Flywheel on a Vertical Mill.=--The turning of a flywheel is a
+good example of the kind of work for which a vertical boring mill is
+adapted. A flywheel should preferably be machined on a double-head mill
+so that one side and the periphery of the rim can be turned at the same
+time. A common method of holding a flywheel is shown in Fig. 9. The rim
+is gripped by four chuck jaws _D_ which, if practicable, should be on
+the inside where they will not interfere with the movement of the tool.
+Two of the jaws, in this case, are set against the spokes on opposite
+sides of the wheel, to act as drivers and prevent any backward shifting
+of work when a heavy cut is being taken. The illustration shows the tool
+to the right rough turning the side of the rim, while the left-hand tool
+turns the periphery. Finishing cuts are also taken over the rim, at this
+setting, and the hub is turned on the outside, faced on top, and the
+hole bored.
+
+[Illustration: Fig. 9. Turning the Rim of a Flywheel]
+
+The three tools _A_, _B_ and _C_, for finishing the hole, are mounted in
+the turret. Bar _A_, which carries a cutter at its end, first rough
+bores the hole. The sizing cutter _B_ is then used to straighten it
+before inserting the finishing reamer _C_. Fig. 10 shows the turret
+moved over to a central position and the sizing cutter _B_ set for
+boring. The head is centrally located (on this particular machine) by a
+positive center-stop. The turret is indexed for bringing the different
+tools into the working position, by loosening the clamping lever _L_ and
+pulling down lever _I_ which disengages the turret lock-pin. When all
+the flywheels in a lot have been machined as described, the opposite
+side is finished.
+
+[Illustration: Fig. 10. Tool B set for Boring the Hub]
+
+[Illustration: Fig. 11. Diagrams showing Method of Turning and Boring a
+Flywheel on a Double-head Mill having one Turret Head]
+
+In order to show more clearly the method of handling work of this class,
+the machining of a flywheel will be explained more in detail in
+connection with Fig. 11, which illustrates practically the same
+equipment as is shown in Figs. 9 and 10. The successive order in which
+the various operations are performed is as follows: Tool _a_ (see sketch
+_A_) rough turns the side of the rim, while tool _b_, which is set with
+its cutting edge toward the rear, rough turns the outside. The direction
+of the feeding movement for each tool is indicated by the arrows. When
+tool _a_ has crossed the rim, it is moved over for facing the hub, as
+shown by the dotted lines. The side and periphery of the rim are next
+finished by the broad-nose finishing tools _c_ and _d_ (see sketch _B_).
+The feed should be increased for finishing, so that each tool will have
+a movement of say 1/4 or 3/8 inch per revolution of the work, and the
+cuts should, at least, be deep enough to remove the marks made by the
+roughing tools. Tool _c_ is also used for finishing the hub as indicated
+by the dotted lines. After these cuts are taken, the outside of the hub
+and inner surface of the rim are usually turned down as far as the
+spokes, by using offset tools similar to the ones shown at _C_ and _D_
+in Fig. 7. The corners of the rim and hub are also rounded to give the
+work a more finished appearance, by using a tool _L_.
+
+The next operation is that of finishing the hole through the hub. The
+hard scale is first removed by a roughing cutter _r_ (sketch _C_), which
+is followed by a "sizing" cutter _s_. The hole is then finished smooth
+and to the right diameter by reamer _f_. The bars carrying cutters _r_
+and _s_ have extensions or "pilots" which enter a close-fitting bushing
+in the table, in order to steady the bar and hold it in alignment.
+
+When the hole is finished, the wheel is turned over, so that the lower
+side of the rim and hub can be faced. The method of holding the casting
+for the final operation is shown at _D_. The chuck jaws are removed, and
+the finished side of the rim is clamped against parallels _p_ resting on
+the table. The wheel is centrally located for turning this side by a
+plug _e_ which is inserted in a hole in the table and fits the bore of
+the hub. The wheel is held by clamps which bear against the spokes.
+Roughing and finishing cuts are next taken over the top surface of the
+rim and hub and the corners are rounded, which completes the machining
+operations. If the rim needs to be a certain width, about the same
+amount of metal should be removed from each side, unless sandy spots or
+"blow-holes" in the casting make it necessary to take more from one side
+than from the other. That side of the rim which was up in the mold when
+the casting was made should be turned first, because the porous, spongy
+spots usually form on the "cope" or top side of a casting.
+
+=Convex Turning Attachment for Boring Mills.=--Fig. 12 shows a vertical
+boring mill arranged for turning pulleys having convex rims; that is,
+the rim, instead of being cylindrical, is rounded somewhat so that it
+slopes from the center toward either side. (The reason for turning a
+pulley rim convex is to prevent the belt from running off at one side,
+as it sometimes tends to do when a cylindrical pulley is used.) The
+convex surface is produced by a special attachment which causes the
+turning tool to gradually move outward as it feeds down, until the
+center of the rim is reached, after which the movement is inward.
+
+[Illustration: Fig. 12. Gisholt Mill equipped with Convex Turning
+Attachment]
+
+The particular attachment shown in Fig. 12 consists of a special
+box-shaped tool-head _F_ containing a sliding holder _G_, in which the
+tool is clamped by set-screws passing through elongated slots in the
+front of the tool-head. In addition, there is a radius link _L_ which
+swivels on a stud at the rear of the tool-head and is attached to
+vertical link _H_. Link _L_ is so connected to the sliding tool-block
+that any downward movement of the tool-bar _I_ causes the tool to move
+outward until the link is in a horizontal position, after which the
+movement is reversed. When the attachment is first set up, the turning
+tool is placed at the center of the rim and then link _L_ is clamped to
+the vertical link while in a horizontal position. The cut is started at
+the top edge of the rim, and the tool is fed downward by power, the
+same as when turning a cylindrical surface. The amount of curvature or
+convexity of a rim can be varied by inserting the clamp bolt _J_ in
+different holes in link _L_.
+
+[Illustration: Fig. 13. Turning a Taper or Conical Surface]
+
+The tools for machining the hub and sides of the rim are held in a
+turret mounted on the left-hand head, as shown. The special tool-holder
+_A_ contains two bent tools for turning the upper and lower edges of the
+pulley rim at the same time as the tool-head is fed horizontally.
+Roughing and finishing tools _B_ are for facing the hub, and the tools
+_C_, _D_, and _E_ rough bore, finish bore, and ream the hole for the
+shaft.
+
+=Turning Taper or Conical Surfaces.=--Conical or taper surfaces are
+turned in a vertical boring mill by swiveling the tool-bar to the proper
+angle as shown in Fig. 13. When the taper is given in degrees, the
+tool-bar can be set by graduations on the edge of the circular base _B_,
+which show the angle _a_ to which the bar is swiveled from a vertical
+position. The base turns on a central stud and is secured to the saddle
+_S_ by the bolts shown, which should be tightened after the tool-bar is
+set. The vertical power feed can be used for taper turning the same as
+for cylindrical work.
+
+[Illustration: Fig. 14. Turning a Conical Surface by using the Combined
+Vertical and Horizontal Feeds]
+
+Occasionally it is necessary to machine a conical surface which has such
+a large included angle that the tool-bar cannot be swiveled far enough
+around to permit turning by the method illustrated in Fig. 13. Another
+method, which is sometimes resorted to for work of this class, is to use
+the combined vertical and horizontal feeds. Suppose we want to turn the
+conical casting _W_ (Fig. 14), to an angle of 30 degrees, as shown, and
+that the tool-head of the boring mill moves horizontally 1/4 inch per
+turn of the feed-screw and has a vertical movement of 3/16 inch per turn
+of the upper feed-shaft. If the two feeds are used simultaneously, the
+tool will move a distance _h_ of say 8 inches, while it moves downward a
+distance _v_ of 6 inches, thus turning the surface to an angle _y_. This
+angle is greater (as measured from a horizontal plane) than the angle
+required, but, if the tool-bar is swiveled to an angle _x_, the tool, as
+it moves downward, will also be advanced horizontally, in addition to
+the regular horizontal movement. The result is that the angle _y_ is
+diminished and if the tool-bar is set over the right amount, the
+conical surface can be turned to an angle _a_ of 30 degrees. The
+problem, then, is to determine what the angle _x_ should be for turning
+to a given angle _a_.
+
+[Illustration: Fig. 15. Diagram showing Method of Obtaining Angular
+Position of Tool-head when Turning Conical Surfaces by using Vertical
+and Horizontal Feeding Movements]
+
+The way angle _x_ is calculated will be explained in connection with the
+enlarged diagram, Fig. 15, which shows one-half of the casting. The sine
+of the known angle _a_ is first found in a table of natural sines. Then
+the sine of angle _b_, between the taper surface and center-line of the
+tool-head, is determined as follows: sin_b_ = (sin_a_ x _h_) / _v_, in
+which _h_ represents the rate of horizontal feed and _v_ the rate of
+vertical feed. The angle corresponding to sine _b_ is next found in a
+table of sines. We now have angles _b_ and _a_, and by subtracting the
+sum of these angles from 90 degrees, the desired angle _x_ is obtained.
+To illustrate: The sine of 30 degrees is 0.5; then sin _b_ = (0.5 x 1/4)
+/ 3/16 = 0.6666; hence angle _b_ = 41 degrees 49 minutes, and _x_ =
+90 deg.-(30 deg. + 41 deg. 49') = 18 degrees 11 minutes. Hence to turn
+the casting to angle _a_ in a boring mill having the horizontal and
+vertical feeds given, the tool-head would be set over from the vertical
+18 degrees and 11 minutes which is equivalent to about 18-1/6 degrees.
+
+If the required angle _a_ were greater than angle _y_ obtained from the
+combined feeds with the tool-bar in a vertical position, it would then
+be necessary to swing the lower end of the bar to the left rather than
+to the right of a vertical plane. When the required angle _a_ exceeds
+angle _y_, the sum of angles _a_ and _b_ is greater than 90 degrees so
+that angle _x_ for the tool-head = (_a_ + _b_) - 90 degrees.
+
+=Turret-lathe Type of Vertical Boring Mill.=--The machine illustrated in
+Fig. 16 was designed to combine the advantages of the horizontal turret
+lathe and the vertical boring mill. It is known as a "vertical turret
+lathe," but resembles, in many respects, a vertical boring mill. This
+machine has a turret on the cross-rail the same as many vertical boring
+mills, and, in addition, a side-head _S_. The side-head has a vertical
+feeding movement, and the tool-bar _T_ can be fed horizontally. The
+tool-bar is also equipped with a four-sided turret for holding turning
+tools. This arrangement of the tool-heads makes it possible to use two
+tools simultaneously upon comparatively small work. When both heads are
+mounted on the cross-rail, as with a double-head boring mill, it is
+often impossible to machine certain parts to advantage, because one head
+interferes with the other.
+
+The drive to the table (for the particular machine illustrated) is from
+a belt pulley at the rear, and fifteen speed changes are available. Five
+changes are obtained by turning the pilot-wheel _A_ and this series of
+five speeds is compounded three times by turning lever _B_. Each spoke
+of pilot-wheel _A_ indicates a speed which is engaged only when the
+spoke is in a vertical position, and the three positions for _B_ are
+indicated, by slots in the disk shown. The number of table revolutions
+per minute for different positions of pilot-wheel _A_ and lever _B_ are
+shown by figures seen through whichever slot is at _C_. There are five
+rows of figures corresponding to the five spokes of the pilot-wheel and
+three figures in a row, and the speed is shown by arrows on the sides of
+the slots. The segment disk containing these figures also serves as an
+interlocking device which prevents moving more than one speed
+controlling lever at a time, in order to avoid damaging the driving
+mechanism.
+
+[Illustration: Fig. 16. Bullard Vertical Turret Lathe]
+
+The feeding movement for each head is independent. Lever _D_ controls
+the engagement or disengagement of the vertical or cross feeds for the
+head on the cross-rail. The feed for the side-head is controlled by
+lever _E_. When this lever is pushed inward, the entire head feeds
+vertically, but when it is pulled out, the tool-bar feeds horizontally.
+These two feeds can be disengaged by placing the lever in a neutral
+position. The direction of the feeding movement for either head can be
+reversed by lever _R_. The amount of feed is varied by feed-wheel _F_
+and clutch-rod _G_. When lever _E_ is in the neutral position, the
+side-head or tool-bar can be adjusted by the hand-cranks _H_ and _I_,
+respectively. The cross-rail head and its turret slide have rapid power
+traverse movements for making quick adjustments. This rapid traverse is
+controlled by the key-handles _J_.
+
+The feed-screws for the vertical head have micrometer dials _K_ for
+making accurate adjustments. There are also large dials at _L_ which
+indicate vertical movements of the side head and horizontal movements of
+the tool slide. All of these dials have small adjustable clips _c_ which
+are numbered to correspond to numbers on the faces of the respective
+turrets. These clips or "observation stops" are used in the production
+of duplicate parts. For example, suppose a tool in face No. 1 for the
+main turret is set for a given diameter and height of shoulder on a part
+which is to be duplicated. To obtain the same setting of the tools for
+the next piece, clips No. 1, on both the vertical feed rod and screw
+dials, are placed opposite the graduations which are intersected by
+stationary pointers secured to the cross-rail. The clips are set in this
+way after the first part has been machined to the required size and
+before disturbing the final position of the tools. For turning a
+duplicate part, the tools are simply brought to the same position by
+turning the feed screws until the clips and stationary pointers again
+coincide. For setting tools on other faces of either turret, this
+operation is repeated, except that clips are used bearing numbers
+corresponding to the turret face in use.
+
+The main turret of this machine has five holes in which are inserted the
+necessary boring and turning tools, drills or reamers, as may be
+required. By having all the tools mounted in the turret, they can be
+quickly and accurately set in the working position. When the turret is
+indexed from one face to the next, binder lever _N_ is first loosened.
+The turret then moves forward, away from its seat, thus disengaging the
+indexing and registering pins which accurately locate it in any one of
+the five positions. The turret is revolved by turning crank _M_, one
+turn of this handle moving the turret 1/5 revolution or from one hole to
+the next. The side-head turret is turned by loosening lever _O_. The
+turret slide can be locked rigidly in any position by lever _P_ and its
+saddle is clamped to the cross-rail by lever _Q_. The binder levers for
+the saddle and toolslide of the side-head are located at _U_ and _V_,
+respectively. A slide that does not require feeding movements is locked
+in order to obtain greater rigidity. To illustrate, if the main tool
+slide were to feed vertically and not horizontally, it might be
+advisable to lock the saddle to the cross-rail, while taking the
+vertical cut.
+
+[Illustration: Fig. 17. Turning a Gear Blank on a Vertical Turret Lathe]
+
+The vertical slide can be set at an angle for taper turning, and the
+turret is accurately located over the center of the table for boring or
+reaming, by a positive center stop. The machine is provided with a brake
+for stopping the work table quickly, which is operated by lifting the
+shaft of pilot-wheel _A_. The side-and cross-rails are a unit and are
+adjusted together to accommodate work of different heights. This
+adjustment is effected by power on the particular machine illustrated,
+and it is controlled by a lever near the left end of the cross-rail.
+Before making this adjustment, all binder bolts which normally hold the
+rails rigidly to the machine column must be released, and care should be
+taken to tighten them after the adjustment is made.
+
+[Illustration: Fig. 18. Turning Gasoline Engine Flywheel on Vertical
+Turret Lathe--First Position]
+
+=Examples of Vertical Turret Lathe Work.=--In order to illustrate how a
+vertical turret lathe is used, one or two examples of work will be
+referred to in detail. These examples also indicate, in a general way,
+the class of work for which this type of machine is adapted. Fig. 17
+shows how a cast-iron gear blank is machined. The work is gripped on the
+inside of the rim by three chuck jaws, and all of the tools required for
+the various operations are mounted in the main and side turrets. The
+illustration shows the first operation which is that of rough turning
+the hub, the top side of the blank and its periphery. The tools _A_ for
+facing the hub and upper surface are both held in one tool-block on the
+main turret, and tool _A_{1}_ for roughing the periphery is in the side
+turret. With this arrangement, the three surfaces can be turned
+simultaneously.
+
+[Illustration: Fig. 19. Turning Gasoline Engine Flywheel--Second
+Position]
+
+[Illustration: Fig. 20. Diagrams showing How Successive Operations are
+Performed by Different Tools in the Turret]
+
+The main turret is next indexed one-sixth of a revolution which brings
+the broad finishing tools _B_ into position, and the side turret is also
+turned to locate finishing tool _B_{1}_ at the front. (The indexing of
+the main turret on this particular machine is effected by loosening
+binder lever n and raising the turret lock-pin by means of lever _p_.)
+The hub, side and periphery of the blank are then finished. When tools
+_B_ are clamped in the tool-blocks, they are, of course, set for
+turning the hub to the required height. The third operation is performed
+by the tools at _C_, one of which "breaks" or chamfers the corner of the
+cored hole in the hub, to provide a starting surface for drill _D_, and
+the other turns the outside of the hub, after the chamfering tool is
+removed. The four-lipped shell-drill _D_ is next used to drill the cored
+hole and then this hole is bored close to the finished size and
+concentric with the circumference of the blank by boring tool _E_, which
+is followed by the finishing reamer _F_. When the drill, boring tool and
+reamer are being used, the turret is set over the center or axis of the
+table, by means of a positive center stop on the left-side of the turret
+saddle. If it is necessary to move the turret beyond the central
+position, this stop can be swung out of the way.
+
+Figs. 18 and 19 illustrate the turning of an automobile flywheel, which
+is another typical example of work for a machine of this type. The
+flywheel is finished in two settings. Its position for the first series
+of operations is shown in Fig. 18, and the successive order of the four
+operations for the first setting is shown by the diagrams, Fig. 20. The
+first operation requires four tools which act simultaneously. The three
+held in tool-block _A_ of the turret, face the hub, the web and the rim
+of the flywheel, while tool _a_ in the side-head rough turns the outside
+diameter. The outside diameter is also finished by broad-nosed tool _b_
+which is given a coarse feed. In the second operation, the under face of
+the rim is finished by tool _c_, the outer corners are rounded by tool
+_d_ and the inner surface of the rim is rough turned by a bent tool _B_,
+which is moved into position by indexing the main turret. In the third
+operation, the side-head is moved out of the way and the inside of the
+rim is finished by another bent tool _B_{1}_. The final operation at
+this setting is the boring of the central hole, which is done with a bar
+_C_ having interchangeable cutters which make it possible to finish the
+hole at one setting of the turret.
+
+The remaining operations are performed on the opposite side of the work
+which is held in "soft" jaws _J_ accurately bored to fit the finished
+outside diameter as indicated in Fig. 19. The tool in the main turret
+turns the inside of the rim, and the side-head is equipped with two
+tools for facing the web and hub simultaneously. As the tool in the main
+turret operates on the left side of the rim, it is set with the cutting
+edge toward the rear. In order to move the turret to this position,
+which is beyond the center of the table, the center stop previously
+referred to is swung out of the way.
+
+=Floating Reamer Holders.=--If a reamer is held rigidly in the turret of
+a boring mill or turret lathe, it is liable to produce a hole which
+tapers slightly or is too large. When a hole is bored with a
+single-point boring tool, it is concentric with the axis of rotation,
+and if a reamer that is aligned exactly with the bored hole is fed into
+the work, the finished hole should be cylindrical and the correct size.
+It is very difficult, however, to locate a reamer exactly in line with a
+bored hole, because of slight variations in the indexing of the turret,
+or errors resulting from wear of the guiding ways or other important
+parts of the machine.
+
+To prevent inaccuracies due to this cause, reamers are often held in
+what is known as a "floating" holder. This type of holder is so arranged
+that the reamer, instead of being held rigidly, is allowed a slight free
+or floating movement so that it can follow a hole which has been bored
+true, without restraint. In this way the hole is reamed straight and to
+practically the same size as the reamer.
+
+[Illustration: Fig. 21. Two Types of Floating Reamer Holders]
+
+There are many different designs of floating holders but the general
+principle upon which they are based is illustrated by the two types
+shown in Fig. 21. The reamer and holder shown to the left has a
+ball-shank _A_ which bears against a backing-up screw _B_ inserted in
+the end of holder _C_ through which the driving pin passes. The lower
+end of the reamer shank is also spherical-shaped at _D_, and screw-pin
+_E_ secures the shell reamer to this end. It will be noted that the hole
+in the shank for pin _E_ is "bell-mouthed" on each side of the center
+and that there is clearance at _F_ between the shank and reamer shell;
+hence the reamer has a free floating action in any direction. This
+holder has given very satisfactory results.
+
+[Illustration: Fig. 22. Multiple-spindle Cylinder Boring Machine]
+
+The holder shown to the right is attached to the face of the turret by
+four fillister-head screws. Sleeve _C_ is held in plate _A_ by means of
+two steel pins _B_ which are tight in plate _A_ and made to fit freely
+in bayonet grooves _D_. Reamer holder _E_ floats on sleeve _C_, the
+floating motion being obtained through the four steel pins _G_ extending
+into driving ring _F_. Two of the pins are tight in the holder _E_ and
+two in sleeve _C_. The faces of sleeve _C_, driving ring _F_, and reamer
+holder _E_ are held tightly against each other by means of spring _H_
+which insures the reamer being held perfectly true. Spring _H_ is
+adjusted by means of nut _I_ which is turned with a spanner wrench
+furnished with each holder. The reamer is so held that its axis is
+always maintained parallel to the center of the hole, and, at the same
+time, it has a slight self-adjusting tendency radially, so that the hole
+and reamer will automatically keep in perfect alignment with each
+other.
+
+=Multiple Cylinder Boring Machine.=--In automobile and other factories
+where a great many gasoline engine cylinders are required,
+multiple-spindle boring machines of the vertical type are commonly used.
+The machine shown in Fig. 22 is a special design for boring four
+cylinders which are cast _en bloc_ or in one solid casting. The work is
+held in a box jig which has a top plate equipped with guide bearings for
+holding the spindles rigidly while boring. The lower end of each spindle
+has attached to it a cutter-head and the boring is done by feeding the
+table and casting vertically. This feeding movement is effected by power
+and it is disengaged automatically when the cutters have bored to the
+required depth. The particular machine illustrated is used for rough
+boring only, the cylinders being finished by reaming in another similar
+machine. The cylinders are bored to a diameter of 3-5/8 inches, and
+about 3/8 inch of metal is removed by the roughing cut. The spindles
+have fixed center-to-center distances as the machine is intended for
+constant use on cylinders of one size, so that adjustment is not
+necessary. Of course, a special machine of this kind is only used in
+shops where large numbers of cylinders of one design are required
+continually. Some cylinder boring machines of the vertical type have
+spindles which can be adjusted for different center-to-center distances
+if this should be necessary in order to accommodate a cylinder of
+another size.
+
+
+
+
+CHAPTER VII
+
+HORIZONTAL BORING MACHINES
+
+
+A boring machine of the horizontal type is shown in Fig. 1. The
+construction and operation of this machine is very different from that
+of a vertical boring mill and it is also used for an entirely different
+class of work. The horizontal machine is employed principally for
+boring, drilling or milling, whereas the vertical design is especially
+adapted to turning and boring. The horizontal type is also used for
+turning or facing flanges or similar surfaces when such an operation can
+be performed to advantage in connection with other machine work on the
+same part.
+
+The type of machine illustrated in Fig. 1 has a heavy base or bed to
+which is bolted the column _C_ having vertical ways on which the
+spindle-head _H_ is mounted. This head contains a sleeve or quill in
+which the spindle _S_ slides longitudinally. The spindle carries cutters
+for boring, whereas milling cutters or the auxiliary facing arm are
+bolted to the end _A_ of the spindle sleeve. The work itself is attached
+either directly or indirectly to the table or platen _P_. When the
+machine is in operation, the cutter or tool revolves with the spindle
+sleeve or spindle and either the cutter or the part being machined is
+given a feeding movement, depending on the character of the work. The
+spindle can be moved in or out by hand for adjustment, or by power for
+feeding the cutter, as when boring or drilling.
+
+[Illustration: Fig. 1. Lucas Horizontal Boring, Drilling and Milling
+Machine]
+
+The entire spindle-head _H_ can also be moved vertically on the face of
+the column _C_, by hand, for setting the spindle to the proper height,
+or by power for feeding a milling cutter in a vertical direction. When
+the vertical position of the spindle-head is changed, the outboard
+bearing block _B_ also moves up or down a corresponding amount, the two
+parts being connected by shafts and gearing. Block _B_ steadies the
+outer end of the boring-bar and the back-rest in which this block is
+mounted can be shifted along the bed to suit the length of the work, by
+turning the squared end of shaft _D_ with a crank. The platen _P_ has a
+cross-feed, and the saddle _E_ on which it is mounted can be traversed
+lengthwise on the bed; both of these movements can also be effected by
+hand or power. There is a series of power feeding movements for the
+cutters and, in addition, rapid power movements _in a reverse direction
+from the feed_ for returning a cutter quickly to its starting position,
+when this is desirable.
+
+This machine is driven by a belt connecting pulley _G_ with an overhead
+shaft. When the machine is in operation, this pulley is engaged with the
+main driving shaft by a friction clutch _F_ controlled by lever _L_.
+This main shaft drives through gearing a vertical shaft _I_, which by
+means of other gears in the spindle-head imparts a rotary movement to
+the spindle. As a machine of this type is used for boring holes of
+various diameters and for a variety of other work, it is necessary to
+have a number of speed changes for the spindle. Nine speeds are obtained
+by changing the position of the sliding gears controlled by levers _R_
+and this number is doubled by back-gears in the spindle-head and
+controlled by lever _J_.
+
+The amount of feed for the spindle, spindle-head, platen or saddle is
+varied by two levers _K_ and _K_{1}_ which control the position of
+sliding gears through which the feeding movements are transmitted. The
+direction of the feed can be reversed by shifting lever _O_. With this
+particular machine, nine feed changes are available for each position of
+the spindle back-gears, making a total of eighteen changes. The feeding
+movement is transmitted to the spindle-head, spindle, platen or saddle,
+as required, by the three distributing levers _T_, _U_ and _V_, which
+control clutches connecting with the transmission shafts or feed screws.
+When lever _T_ is turned to the left, the longitudinal power feed for
+the spindle is engaged, whereas turning it to the right throws in the
+vertical feed for the spindle-head. Lever _U_ engages the cross-feed for
+platen _P_ and lever _V_, the longitudinal feed for saddle _E_. These
+levers have a simple but ingenious interlocking device which makes it
+impossible to engage more than one feed at a time. For example, if lever
+_T_ is set for feeding the spindle, levers _U_ and _V_ are locked
+against movement.
+
+The feeds are started and stopped by lever _M_ which also engages the
+rapid power traverse when thrown in the opposite direction. This rapid
+traverse operates for whatever feed is engaged by the distributing
+levers and, as before stated, in a reverse direction. For example, if
+the reverse lever _O_ is set for feeding the spindle to the right, the
+rapid traverse would be to the left, and _vice versa_. The cross-feed
+for the platen can be automatically tripped at any point by setting an
+adjustable stop in the proper position and the feed can also be tripped
+by a hand lever at the side of the platen.
+
+All the different feeding movements can be effected by hand as well as
+by power. By means of handwheel _N_, the spindle can be moved in or out
+slowly, for feeding a cutter by hand. When the friction clamp _Q_ is
+loosened, the turnstile _W_ can be used for traversing the spindle, in
+case a hand adjustment is desirable. The spindle-head can be adjusted
+vertically by turning squared shaft _X_ with a crank, and the saddle can
+be shifted along the bed by turning shaft _Y_. The hand adjustment of
+the platen is effected by shaft _Z_. The spindle-head, platen and saddle
+can also be adjusted from the end of the machine, when this is more
+convenient. Shafts _X_, _Y_ and _Z_ are equipped with micrometer dials
+which are graduated to show movements of one-thousandth inch. These
+dials are used for accurately adjusting the spindle or work and for
+boring holes or milling surfaces that must be an exact distance apart.
+
+=Horizontal Boring Machine with Vertical Table Adjustment.=--Another
+horizontal boring machine is partly shown in Fig. 2. This machine is of
+the same type as that illustrated in Fig. 1, but its construction is
+quite different, as will be seen. The spindle cannot be adjusted
+vertically as with the first design described, but it is mounted and
+driven very much like the spindle of a lathe, and adjustment for height
+is obtained by raising or lowering the work table. The design is just
+the reverse, in this respect, of the machine shown in Fig. 1, which has
+a vertical adjustment for the spindle, and a work table that remains in
+the same horizontal plane. The raising or lowering of the table is
+effected by shaft _E_, which rotates large nuts engaging the screws _S_.
+Shaft _E_ is turned either by hand or power.
+
+[Illustration: Fig. 2. Horizontal Boring and Drilling Machine with
+Vertical Table Adjustment]
+
+The main spindle is driven by a cone pulley _P_, either directly, or
+indirectly through the back-gears shown. This arrangement gives six
+spindle speeds, and double this number is obtained by using a two-speed
+countershaft overhead. The motion for feeding the spindle longitudinally
+is transmitted through a cone of gears, which gives the required
+changes, to a pinion meshing with a rack which traverses the spindle.
+The large handwheel _H_ and a corresponding wheel on the opposite side
+are used for adjusting the spindle rapidly by hand. The yoke or outboard
+bearing _B_ for the boring-bars can be clamped in any position along the
+bed for supporting the bar as close to the work as possible.
+
+Horizontal boring machines are built in many other designs, but they all
+have the same general arrangement as the machines illustrated and
+operate on the same principle, with the exception of special types
+intended for handling certain classes of work exclusively. The
+horizontal boring, drilling and milling machine is very efficient for
+certain classes of work because it enables all the machining operations
+on some parts to be completed at one setting. To illustrate, a casting
+which requires drilling, boring and milling at different places, can
+often be finished without disturbing its position on the platen after it
+is clamped in place. Frequently a comparatively small surface needs to
+be milled after a part has been bored. If this milling operation can be
+performed while the work is set up for boring, accurate results will be
+obtained (provided the machine is in good condition) and the time saved
+that would otherwise be required for re-setting the part on another
+machine. Some examples of work on which different operations are
+performed at the same setting will be referred to later. The horizontal
+boring machine also makes it possible to machine duplicate parts without
+the use of jigs, which is important, especially on large work, owing to
+the cost of jigs.
+
+=Drilling and Boring--Cutters Used.=--Holes are drilled in a horizontal
+machine by simply inserting a drill of required size either directly in
+the spindle _S_ (see Fig. 1), or in a reducing socket, and then feeding
+the spindle outward either by hand or power. When a hole is to be bored,
+a boring-bar _B_{1}_ is inserted in the spindle and the cutter is
+attached to this bar. The latter is then fed through the hole as the
+cutter revolves. The distinction made by machinists between drilling and
+boring is as follows: A hole is said to be drilled when it is formed by
+sinking a drill into solid metal, whereas boring means the enlargement
+of a drilled or cored hole either by the use of a single boring tool, a
+double-ended cutter which operates on both sides of the hole, or a
+cutter-head having several tools.
+
+There are various methods of attaching cutters to boring-bars and the
+cutters used vary for different classes of work. A simple style of
+cutter which is used widely for boring small holes is shown at _A_ in
+Fig. 3. The cutter _c_ is made from flat stock and the cutting is done
+by the front edges _e_ and _e_{1}_, which are beveled in opposite
+directions. The cutter is held in the bar by a taper wedge _w_ and it
+is centered by shoulders at _s_, so that the diameter of the hole will
+equal the length across the cutter. The outer corners at the front
+should be slightly rounded, as a sharp corner would be dulled quickly.
+These cutters are made in different sizes and also in sets for roughing
+and finishing. The roughing cutter bores holes to within about 1/32 inch
+of the finish size and it is then replaced by the finishing cutter. A
+cutter having rounded ends, as shown by the detail sketch _a_, is
+sometimes used for light finishing cuts. These rounded ends form the
+cutting edges and give a smooth finish.
+
+[Illustration: Fig. 3. Boring-cutters of Different Types]
+
+Another method of holding a flat cutter is shown at _B_. The conical end
+of a screw bears against a conical seat in, the cutter, thus binding the
+latter in its slot. The conical seat also centers the cutter. A very
+simple and inexpensive form of cutter is shown at _C_. This is made from
+a piece of round steel, and it is held in the bar by a taper pin which
+bears against a circular recess in the side of the cutter. This form
+has the advantage of only requiring a hole through the boring-bar,
+whereas it is necessary to cut a rectangular slot for the flat cutter.
+
+[Illustration: Fig. 4. Boring with a Flat Double-ended Cutter]
+
+Fig. 4 shows how a hole is bored by cutters of the type referred to. The
+bar rotates as indicated by the arrow _a_ and at the same time feeds
+longitudinally as shown by arrow _b_. The speed of rotation depends upon
+the diameter of the hole and the kind of material being bored, and the
+feed per revolution must also be varied to suit conditions. No definite
+rule can be given for speed or feed. On some classes of work a long
+boring-bar is used, which passes through the hole to be bored and is
+steadied at its outer end by the back-rest _B_, Figs, 1 and 2. On other
+work, a short bar is inserted in the spindle having a cutter at the
+outer end. An inexpensive method of holding a cutter at the end of a bar
+is shown at _D_, Fig. 3. The cutter passes through a slot and is clamped
+by a bolt as shown. When it is necessary to bore holes that are "blind"
+or closed at the bottom, a long boring-bar which passes through the work
+cannot, of course, be used.
+
+Sometimes it is necessary to have a cutter mounted at the extreme end of
+a bar in order to bore close to a shoulder or the bottom of a hole. One
+method of holding a cutter so that it projects beyond the end of a bar
+is indicated at _E_. A screw similar to the one shown at _B_ is used,
+and the conical end bears in a conical hole in the cutter. This hole
+should be slightly offset so that the cutter will be forced back
+against its seat. The tool shown at _F_ has adjustable cutters. The
+inner end of each cutter is tapering and bears against a conical-headed
+screw _b_ which gives the required outward adjustment. The cutters are
+held against the central bolt by fillister-head screws _f_ and they are
+clamped by the screws _c_. Boring tools are made in many different
+designs and the number and form of the cutters is varied somewhat for
+different kinds of work.
+
+[Illustration: Fig. 5. Cutter-heads for Boring Large Holes]
+
+=Cutter-heads for Boring Large Holes.=--When large holes are to be
+bored, the cutters are usually held in a cast-iron head which is mounted
+on the boring-bar. One type of cutter-head is shown in Fig. 5. This
+particular head is double-ended and carries two cutters _c_. The
+cutter-head is bored to fit the bar closely and it is prevented from
+turning by a key against which a set-screw is tightened. By referring to
+the end view, it will be seen that each cutter is offset with relation
+to the center of the bar, in order to locate the front of the tool on a
+radial line. The number of cutters used in a cutter-head varies. By
+having several cutters, the work of removing a given amount of metal in
+boring is distributed, and holes can be bored more quickly with a
+multiple cutter-head, although more power is required to drive the
+boring-bar. The boring-bar is also steadied by a multiple cutter-head,
+because the tendency of any one cutter to deflect the bar is
+counteracted by the cutters on the opposite side.
+
+A disk-shaped head having four cutters is illustrated in Fig. 6. The
+cutters are inserted in slots or grooves in the face of the disk and
+they are held by slotted clamping posts. The shape of these posts is
+shown by the sectional view. The tool passes through an elongated slot
+and it is tightly clamped against the disk by tightening nut _n_. This
+head is also driven by a key which engages a keyway in the boring-bar.
+
+[Illustration: Fig. 6. Cutter-head with Four Boring Tools]
+
+Two other designs of cutter-heads are shown in Fig. 7. The one
+illustrated at _A_ has three equally spaced cutters which are held in an
+inclined position. The cutters are clamped by screws _c_ and they can be
+adjusted within certain limits by screws _s_. The cutters are placed at
+an angle so that they will extend beyond the front of the head, thus
+permitting the latter to be moved up close to a shoulder. The
+cutter-heads shown in Figs. 5 and 6 can also be moved up close to a
+shoulder if bent cutters are used as shown in the right-hand view, Fig.
+5. The idea in bending the cutters is to bring the cutting edges in
+advance of the clamping posts so that they will reach a shoulder before
+the binding posts strike it. The arrangement of cutter-head _B_ (Fig. 7)
+is clearly shown by the illustration.
+
+Cutter-heads are often provided with two sets of cutters, one set being
+used for roughing and the other for finishing. It is a good plan to make
+these cutters so that the ends _e_ (Fig. 6) will rest against the bar or
+bottom of the slot, when the cutting edge is set to the required radius.
+The cutters can then be easily set for boring duplicate work. One method
+of making cutters in sets is to clamp the annealed stock in the
+cutter-head and then turn the ends to the required radius by placing the
+head in the lathe. After both sets of cutters have been turned in this
+way, they are ground to shape and then hardened.
+
+[Illustration: Fig. 7. Cutter-heads equipped with Adjustable Tools]
+
+Boring cutters intended for roughing and finishing cuts are shown in the
+detail view Fig. 8 at _A_ and _B_, respectively. The side of the
+roughing cutter _A_ is ground to a slight angle _c_ to provide clearance
+for the cutting edge, and the front has a backward slope _s_ to give the
+tool keenness. This tool is a good form to use for roughing cuts in cast
+iron. The finishing tool at _B_ has a broad flat edge _e_ and it is
+intended for coarse feeds and light cuts in cast iron. If a round
+cutting edge is used for finishing, a comparatively fine feed is
+required in order to obtain a smooth surface. The corners of tool _B_
+are rounded and they should be ground to slope inward as shown in the
+plan view. The top or ends _d_ of both of these tools are "backed off"
+slightly to provide clearance. This clearance should be just enough to
+prevent the surface back of the cutting edge from dragging over the
+work. Excessive end clearance not only weakens the cutting edge, but
+tends to cause chattering. As a finishing tool cuts on the upper end
+instead of on the side, the front should slope backward as shown in the
+side view, rather than sidewise as with a roughing cutter. The angle of
+the slope should be somewhat greater for steel than cast iron, unless
+the steel is quite hard, thus requiring a strong blunt tool.
+
+[Illustration: Fig. 8. Boring Tools for Roughing and Finishing Cuts]
+
+=Cylinder Boring.=--Fig. 9 illustrates the use of a cutter-head for
+cylinder boring. After the cylinder casting is set on the platen of the
+machine, the boring-bar with the cutter-head mounted on it is inserted
+in the spindle. The bar _B_ has a taper shank and a driving tang similar
+to a drill shank, which fits a taper hole in the end of the spindle. The
+cutter-head _C_ is fastened to the bar so that it will be in the
+position shown when the spindle is shifted to the right, as the feeding
+movement (with this particular machine) is to be in the opposite
+direction. The casting _A_ should be set central with the bar by
+adjusting the work-table vertically and laterally, if necessary, and the
+outer support _F_ should be moved close to the work, to make the bar as
+rigid as possible.
+
+The cylinder is now ready to be bored. Ordinarily, one or two roughing
+cuts and one finishing cut would be sufficient, unless the rough bore
+were considerably below the finish diameter. As previously explained,
+the speed and feed must be governed by the kind of material being bored
+and the diameter of the cut. The power and rigidity of the boring
+machine and the quality of the steel used for making the cutters also
+affect the cutting speed and feed. As the finishing cut is very light, a
+tool having a flat cutting edge set parallel to the bar is ordinarily
+used when boring cast iron. The coarse feed enables the cut to be taken
+in a comparatively short time and the broad-nosed tool gives a smooth
+finish if properly ground.
+
+[Illustration: Fig. 9. Cylinder mounted on Horizontal Machine for
+Boring]
+
+The coarse finishing feed is not always practicable, especially if the
+boring machine is in poor condition, owing to the chattering of the
+tool, which results in a rough surface. The last or finishing cut should
+invariably be a continuous one, for if the machine is stopped before the
+cut is completed, there will be a ridge in the bore at the point where
+the tool temporarily left off cutting. This ridge is caused by the
+cooling and resulting contraction and shortening of the tool during the
+time that it is stationary. For this reason independent drives are
+desirable for boring machines.
+
+Facing arms are attached to the bar on either side of the cylinder for
+facing the flanges after the boring operation. The turning tool of a
+facing arm is fastened to a slide which is fed outward a short distance
+each revolution, by a star-wheel that is caused to turn as it strikes
+against a stationary pin. By facing the flanges in this way, they are
+finished square with the bore.
+
+When setting a cylinder which is to be bored it should, when the design
+will permit, be set true by the outside of the flange, or what is even
+better, by the outside of the cylinder itself, rather than by the rough
+bore, in order that the walls of the finished cylinder will have a
+uniform thickness. The position of very large cylinders, while they are
+being bored, is an important consideration. Such cylinders should be
+bored in the position which they will subsequently occupy when
+assembled. For example, the cylinder for a large horizontal engine
+should be bored while in a horizontal position, as the bore is liable to
+spring to a slight oval shape when the cylinder is placed horizontal
+after being bored while standing in a vertical position. If, however,
+the cylinder is bored while in the position in which it will be placed
+in the assembled engine, this trouble is practically eliminated.
+
+There is a difference of opinion among machinists as to the proper shape
+of the cutting point of a boring tool for finishing cuts, some
+contending that a wide cutting edge is to be preferred, while others
+advocate the use of a comparatively narrow edge with a reduced feed. It
+is claimed, that the narrow tool produces a more perfect bore, as it is
+not so easily affected by hard spots in the iron, and it is also pointed
+out that the minute ridges left by the narrow tool are an advantage
+rather than a disadvantage, as they form pockets for oil and aid in
+lubricating the cylinder. It is the modern practice, however, to use a
+broad tool and a coarse feed for the light finishing cut, provided the
+tool does not chatter.
+
+The type of machine tool used for boring cylinders, and also the method
+of procedure is determined largely by the size of the work and the
+quantity which is to be machined. The turret lathe, as well as
+horizontal and vertical boring mills, is used for this work, and in
+automobile factories or other shops where a great many cylinders are
+bored, special machines and fixtures are often employed.
+
+[Illustration: Fig. 10. Boring a Duplex Cylinder on a Horizontal
+Machine]
+
+=Boring a Duplex Gasoline Engine Cylinder.=--The method of holding work
+on a horizontal boring machine depends on its shape. A cylinder or other
+casting having a flat base can be clamped directly to the platen, but
+pieces of irregular shape are usually held in special fixtures. Fig. 10
+shows how the cylinder casting of a gasoline engine is set up for the
+boring operation. The casting _W_ is placed in a fixture _F_ which is
+clamped to the machine table. One end of the casting rests on the
+adjustable screws _S_ and it is clamped by set-screws located in the top
+and sides of the fixture. There are two cylinders cast integral and
+these are bored by a short stiff bar mounted in the end of the spindle
+and having cutters at the outer end. A long bar of the type which passes
+through the work and is supported by the outboard bearing _B_, could not
+be used for this work, because the top of each cylinder is closed.
+
+When one cylinder is finished the other is set in line with the spindle
+by adjusting the work-table laterally. This adjustment is effected by
+screw _C_, and the required center-to-center distance between the two
+cylinders can be gaged by the micrometer dial _M_ on the cross-feed
+screw, although positive stops are often used in preference. After the
+first cylinder is bored, the dial is set to the zero position by
+loosening the small knurled screw shown, and turning the dial around.
+The feed screw is then rotated until the dial shows that the required
+lateral adjustment is made, which locates the casting for boring the
+second cylinder. The end of the casting is also faced true by a milling
+cutter. Ordinarily, milling cutters are bolted directly to the spindle
+sleeve _A_ on this particular machine, which gives a rigid support for
+the cutter and a powerful drive.
+
+[Illustration: Fig. 11. Cylinder turned around for Machining Valve
+Seats]
+
+The next operation is that of boring and milling the opposite end of the
+cylinder. This end is turned toward the spindle (as shown in Fig. 11)
+without unclamping the work or fixture, by simply turning the circular
+table _T_ half way around. This table is an attachment which is clamped
+to the main table for holding work that must be turned to different
+positions for machining the various parts. Its position is easily
+changed, and as the work remains fixed with relation to the table, the
+alignment between different holes or surfaces is assured, if the table
+is turned the right amount. In this case, the casting needs to be
+rotated one-half a revolution or 180 degrees, and this is done by means
+of angular graduations on the base of the table. The illustration shows
+the casting set for boring the inlet and exhaust valve chambers. The
+different cutters required for boring are mounted on one bar as shown,
+and the casting is adjusted crosswise to bring each valve chamber in
+position, by using the micrometer dial. The single-ended cutter _c_
+forms a shallow circular recess or seat in the raised pad which
+surrounds the opening. The cover joint directly back of the cylinders is
+finished by milling.
+
+[Illustration: Fig. 12. Boring Differential Gear Casing]
+
+=Examples of Boring, Radial Facing and Milling.=--Another example of
+boring, in which the circular table is used, is shown in Fig. 12. The
+work _W_ is a casing for the differential gears of an automobile. It is
+mounted in a fixture _F_ which is bolted to the table. The casting has
+round ends, which are clamped in V-blocks, thus aligning the work. This
+fixture has a guide-bushing _G_ which is centered with the bar and
+cutter in order to properly locate the casting. There is a bearing at
+each end of the casing, and two larger ones in the center. These are
+bored by flat cutters similar to the style illustrated at _A_ in Fig. 3.
+The cutter for the inner bearings is shown at _c_.
+
+[Illustration: Fig. 13. Facing and Turning Flange of Differential Gear
+Casing]
+
+After the bearings are bored, the circular table is turned 90 degrees
+and the work is moved closer to the spindle (as shown in Fig. 13) for
+facing flange _F_ at right angles to the bearings. Circular flanges of
+this kind are faced in a horizontal boring machine by a special
+facing-arm or head _H_. For this particular job this head is clamped
+directly to the spindle sleeve, but it can also be clamped to the
+spindle if necessary. The turning tool is held in a slotted toolpost,
+and it is fed radially for turning the side or face of the flange, by
+the well-known star feed at _S_. When this feed is in operation the bent
+finger _E_ is turned downward so that it strikes one of the star wheel
+arms for each revolution; this turns the wheel slightly, and the
+movement is transmitted to the tool-block by a feed-screw. The
+illustration shows the tool set for turning the outside or periphery of
+the flange. This is done by setting the tool to the proper radius and
+then feeding the work horizontally by shifting the work-table along the
+bed. By referring to Fig. 12 it will be seen that the facing head does
+not need to be removed for boring, as it is attached to the spindle
+driving quill and does not interfere with the longitudinal adjustment of
+the spindle. This facing head is also used frequently for truing the
+flanges of cylinders which are to be bored, and for similar work.
+
+[Illustration: Fig. 14. Example of Work requiring Boring and Milling]
+
+Fig. 14 shows another example of work which requires boring and milling.
+This casting is mounted on a fixture which is bolted to the main table.
+In this case the circular table is not necessary, because the work can
+be finished without swiveling it around. After the boring is completed
+the edge _E_ is trued by the large-face milling cutter _M_ bolted to the
+spindle sleeve. The irregular outline of the edge is followed by moving
+the table crosswise and the spindle vertically, as required.
+
+=Fixture for Cylinder Lining or Bushing.=--A method of holding a
+cylinder lining or bushing while it is being bored is shown in Fig. 15.
+The lining _L_ is mounted in two cast-iron ring-shaped fixtures _F_.
+These fixtures are circular in shape and have flat bases which are
+bolted to the table of the machine. On the inside of each fixture, there
+are four equally spaced wedges _W_ which fit into grooves as shown in
+the end view. These wedges are drawn in against the work by bolts, and
+they prevent the lining from rotating when a cut is being taken. This
+form of fixture is especially adapted for holding thin bronze linings,
+such as are used in pump cylinders, because only a light pressure
+against the wedges is required, and thin work can be held without
+distorting it. If a very thin lining is being bored, it is well to
+loosen the wedges slightly before taking the finishing cut, so that the
+work can spring back to its normal shape.
+
+[Illustration: Fig. 15. Cylinder Lining mounted in Fixture for Boring]
+
+[Illustration: Fig. 16. Detrick & Harvey Horizontal Boring Machine of
+the Floor Type Boring Engine Bed Casting]
+
+=Horizontal Boring Machine of Floor Type.=--The type of horizontal
+boring, drilling and milling machine, shown in Fig. 16, is intended for
+boring heavy parts such as the cylinders of large engines or pumps, the
+bearings of heavy machine beds and similar work. This machine can also
+be used for drilling and milling, although it is intended primarily for
+boring, and the other operations are usually secondary. This design is
+ordinarily referred to as the "floor type," because the work-table is
+low for accommodating large heavy castings. The spindle _S_ which drives
+the boring-bar, and the spindle feeding mechanism, are carried by a
+saddle. This saddle is free to move vertically on the face of column
+_C_ which is mounted on transverse ways extending across the right-hand
+end of the main bed. This construction permits the spindle to move
+vertically or laterally (by traversing the column) either for adjusting
+it to the required position or for milling operations. The spindle also
+has a longitudinal movement for boring. There is an outer bearing _B_
+for supporting the boring-bar, which also has lateral and vertical
+adjustments, so that it can be aligned with the bar.
+
+The work done on a machine of this type is either clamped directly to
+the large bed-plate _A_ (which has a number of T-slots for receiving the
+heads of the clamping bolts) or, in some cases, a special fixture may be
+used or an auxiliary table. Boring machines of this same general
+construction are built in many different sizes. The main spindle of the
+machine illustrated is driven by a motor located at the rear of the
+vertical column _C_, the motion being transmitted to the spindle through
+shafts and gearing. The casting _D_, shown in this particular
+illustration, is for a steam engine of the horizontal type, and the
+operation is that of boring the cylindrical guides or bearings for the
+crosshead. These bearings have a diameter of 15-3/4 inches and are
+37-3/4 inches long. In boring them, two roughing cuts and one finishing
+cut are taken. The end of the casting, which in the assembled engine
+bears against the cylinder, is then faced by means of a regular facing
+arm.
+
+After removing the boring-bar the table _E_ of the special fixture on
+which the casting is mounted is turned one quarter of a revolution. A
+large milling cutter 24 inches in diameter is next mounted on the
+spindle of the machine, and one side of the main bearing, as well as the
+pads for the valve-rod guide-bar brackets, are milled. The table is then
+revolved and the opposite side of the main bearing is milled in the same
+way, the table being accurately located in the different positions by an
+index plunger _F_ which engages holes on the under side. The spindle is
+now moved upward to allow the table to be turned so as to locate the
+bearing end of the frame next to the headstock of the machine. The
+milling cutter is then used to machine the inside and top surfaces of
+the main bearing. By turning the fixture and not changing the position
+of the casting after it is bolted into place, the various surfaces are
+machined in the correct relation to one another without difficulty. This
+is a good example of the work done on horizontal boring machines of the
+floor type.
+
+
+
+
+INDEX
+
+
+                                                                 PAGE
+
+  Acme flat turret lathe, examples of chuck work                  219
+  Acme standard thread and tool for cutting                       159
+  Acme standard thread gage                                       157
+  Acme thread tool, measuring width with vernier caliper     157, 158
+  Accumulation of errors                                     105, 106
+  Aligning lathe centers for cylindrical turning                   16
+  Allowances, average, for forced fits                            130
+    for different classes of fits                                 131
+    for driving fits                                              131
+    for forced fits of given pressure                             133
+    for push fits                                                 131
+    for running fits                                              131
+    for shrinkage fits                                            133
+  Aluminum, lubricant for machining                                53
+    shape of tools for turning                                     53
+    speed and feed for machining                                   53
+  Angle-plate applied to lathe faceplate                           48
+  Angles, gage for accurate measurement of                         97
+  Apron of lathe                                                 4, 5
+  Arbor or mandrel press                                           22
+  Arbors or mandrels for lathe work, types of                      19
+    use of                                                         17
+  Attachment, application of Hendey relieving                     125
+    convex turning for vertical boring mill                       259
+    for coarse threading in lathe                                 160
+    for spherical turning                                         113
+    for taper turning in lathe                                     88
+    Hendey relieving                                              123
+  Automatic chucking and turning machine, Potter & Johnston       223
+    Potter & Johnston, method of "setting-up"                     227
+    Potter & Johnston, turning flywheel in                        236
+
+  Back-gears of lathe                                            3, 4
+  Bardons & Oliver turret lathe, general description              178
+  Bored holes, measuring diameter of                               41
+  Boring and reaming tools for vertical mill                      251
+  Boring and turning mill, vertical, general description          242
+    vertical, holding and setting work                            247
+    vertical, turning in                                          249
+  Boring and turning mill, vertical, turning tools for            253
+  Boring-bar cutters and methods of holding                       280
+  Boring cutters for roughing and finishing cuts                  285
+  Boring cylinders on horizontal machine                          286
+  Boring holes to given center distance in lathe                   51
+  Boring in lathe, example of                                      39
+  Boring large castings in lathe                                   49
+  Boring large holes, cutter-heads used for                       283
+  Boring machine, horizontal                                      275
+    horizontal, examples of work on                           289-297
+    horizontal, floor type                                        294
+    vertical, multiple-spindle type                               274
+  Boring tool, lathe                                               40
+  Box-tools, different designs and examples of work               193
+    for general turret lathe work                                 190
+  Bradford belt-driven lathe, general description                   1
+  Bradford quick change-gear type of lathe                        173
+  Brass, speed for turning                                         52
+    tool for turning in lathe                                      52
+  "Bridle" or "hold-back" for lathe                            26, 27
+  Bullard vertical turret lathe                                   264
+    examples of work                                              268
+  Button method of locating work                                  101
+
+  Caliper tool for taper turning                                   85
+  Calipers, methods of setting                                 10, 11
+  "Cat-head," application in lathe work                            25
+  Center holes, incorrect and correct forms                        32
+  Center indicator, use of                                        100
+  Centered stock, methods of facing ends                           34
+  Centers, lathe, aligning for cylindrical turning                 16
+    lathe, grinder for truing                                      34
+  Centering machine                                                30
+  Centering parts to be turned                                     28
+  Centering, precaution for tool steel                             33
+  Change gears, calculating for thread cutting                    167
+    compound, for thread cutting                                  170
+    for cutting fractional threads                                171
+    for cutting metric pitches                                    171
+    for thread cutting                                            135
+  Chasing dial for "catching threads" when screw cutting          141
+  Chuck, inaccuracy from pressure of jaws                          42
+    lathe, application of                                          37
+    setting work in                                                42
+    universal, independent and combination                         36
+  Chucking and turning machine, Potter & Johnston automatic       223
+    Potter & Johnston automatic, method of "setting-up"           227
+    Potter & Johnston automatic, turning flywheel in              236
+  Chucking machine, New Britain, multiple-spindle type            238
+  Clearance angle for turning tools                                66
+  Clearance of turning tools, meaning of                       62, 63
+  Coarse threading attachment for lathe                           160
+  Collapsing tap, Geometric                                       202
+  Combination chuck for lathe                                      36
+  Compound rest, applied to screw or thread cutting               143
+    applied to taper turning                                       95
+  Convex turning attachment for vertical boring mills             259
+  Copper, tool for turning in lathe                                52
+  Crankshaft lathe, description of R. K. LeBlond special          108
+    operation of R. K. LeBlond                                    110
+  Crankshaft turning in engine lathe                              107
+  Cross-slide stop for threading                                  155
+  Cuts, average depth for turning                                  75
+    roughing and finishing in lathe                        12, 75, 76
+  Cutter-heads, for boring, equipped with adjustable tools   284, 285
+    for horizontal boring machine                                 283
+  Cutters, boring, roughing and finishing types                   285
+    for boring-bars                                               280
+  Cutting lubricants for turning tools                             77
+  Cutting speeds, average for turning                              72
+    based on Taylor's experiments                                  71
+    effect of lubricant on                                         76
+    factors which limit speeds for turning                         72
+    rules for calculating                                          74
+  Cylinder boring machine, multiple-spindle type                  274
+  Cylinder boring on horizontal machine                           286
+  Cylinder lining, fixture for holding when boring                293
+  Cylindrical turning, simple example of                            6
+
+  Davis turret lathe, turning bevel gear blanks                   212
+    turning worm-gear blanks                                      211
+  Depth of cut for turning, average                                75
+  Detrick & Harvey horizontal boring machine, floor type          294
+  Dial for "catching threads" when screw cutting                  141
+  Dial gage, testing concentricity of button with            103, 104
+  Die and tap holders, releasing                                  199
+  Die-heads, self-opening type                                    200
+  Disk gage, for angles and tapers                                 97
+    rules for setting                                          98, 99
+  Dogs or drivers, lathe, application of                           16
+  Drill, flat, for lathe                                           44
+  Drilling and reaming in lathe                                    43
+  Drivers or dogs, lathe, application of                           16
+  Driving fits, allowances for                                    131
+
+  Eccentric turning in lathe                                      106
+  Engine lathe, general description                                 1
+  Errors, accumulation of                                    105, 106
+
+  Faceplate, indexing for multiple-thread cutting                 153
+    lathe, application of angle-plate to                           48
+    lathe, holding work on                                         45
+  Facing ends of centered stock, different methods                 34
+  Feed and depth of cut for turning, average                       75
+  Feeds and speeds for turning based on Taylor's experiments       71
+  Filing and polishing in lathe                                    13
+  Finishing and roughing cuts in lathe                         75, 76
+  Fits, allowances for different classes                          131
+    different classes used in machine construction                129
+    driving, allowances for                                       131
+    forced, allowances for given pressure                         133
+    forced, average allowance for                                 130
+    forced, pressure for                                          132
+    push, allowances for                                          131
+    running, allowances for                                       131
+    shrinkage, allowances for                                     133
+  Fixture for holding thin lining when boring                     293
+  Flat drill and holder for lathe                                  44
+  Flat turret lathe, Acme, examples of chuck work                 219
+    Hartness, example of turning                                  213
+    Jones & Lamson double-spindle type                            221
+  Floating reamer holders                                         271
+  Flywheel, finishing in one setting in turret lathe              186
+    finishing in two settings in turret lathe                     189
+    machining in turret lathe                                     184
+    turning in Potter & Johnston automatic                        236
+    turning in vertical boring mill                               255
+  Follow-rest for lathe                                            27
+  Forced fits, allowances for given pressure                      133
+    average allowance for                                         130
+    pressure generally used in assembling                         132
+  Fractional threads, change gears for cutting                    171
+
+  Gage, disk, for angles and tapers                                97
+    disk, rules for setting                                    98, 99
+    for testing V-thread tool                                     138
+    standard plug, for holes                                       42
+    thread, Acme standard                                         157
+  Geometric collapsing tap                                        202
+  Geometric self-opening die-head                                 200
+  Gisholt convex attachment for vertical mill                     259
+  Gisholt vertical boring mill, general description               242
+  Grinder for truing lathe centers                                 34
+  Grinding lathe tools                                             62
+
+  Hartness flat turret lathe, example of turning                  213
+  Hendey relieving attachment                                     123
+    application of, for relieving taps, cutters and hobs          125
+  "Hold-back" or "bridle" for lathe                            26, 27
+  Hollow mills for turret lathe                                   198
+  Horizontal boring machine                                       275
+    Detrick & Harvey floor type                                   294
+    examples of work                                          289-297
+
+  Independent chuck for lathe                                      36
+  Index plate, change gear, for lathe                             137
+  Indicator, center, use on lathe                                 100
+    for "catching threads" when screw cutting                     141
+    test, truing buttons with                                102, 103
+    thread, for lathe apron, principle of                         142
+  Inserted cutter turning tools for lathe                          58
+  Internal threading                                              154
+
+  Jones & Lamson double-spindle flat turret lathe                 221
+
+  Knurling in lathe and tool used                                 122
+
+  Lard oil as a cutting lubricant                                  78
+  Lathe, boring holes to given center distance in                  51
+    boring large castings in                                       49
+    boring small hole with                                   104, 105
+    cutting threads in                                            135
+    drilling small hole with                                      104
+    general description of Bradford                                 1
+    LeBlond crankshaft, operation of                              110
+    Lo-swing, general description                                 115
+    method of handling when cutting threads                       138
+    quick change-gear type                                        173
+    R. K. LeBlond special crankshaft                              108
+    turret type, general description                              178
+  Lathe centers, grinder for truing                                34
+  Lathe chucks, application of                                     37
+    universal, independent and combination                         36
+  Lathe faceplate, holding work on                                 45
+  Lathe follow-rest                                                27
+  Lathe steadyrest                                                 23
+    application of, when boring                                    25
+  Lathe taper attachment                                           88
+    practical application of                                       90
+  Lathe tool grinding                                              62
+  Lathe tools, angle of clearance                                  66
+    angle of keenness                                              67
+    application of various types                                   56
+    slope of cutting edge                                      66, 67
+  Lathe turning tools, inserted-cutter type                        58
+    set of tools for general work                                  54
+  Lead of thread, definition of                                   146
+  LeBlond, R. K., lathe for crankshaft turning                    108
+  Left-hand thread, method of cutting                             148
+  Lining, fixture for holding when boring                         293
+  Lo-swing lathe, general description                             115
+    example of multiple-turning                                   117
+  Lubricant, effect on cutting speed                               76
+    for cooling turning tools                                      77
+    for machining aluminum                                         53
+    lard oil as a cutting                                          78
+  Lucas horizontal boring machine                                 275
+
+  Mandrel or arbor press                                           22
+  Mandrels or arbors for lathe work, types of                      19
+    for lathe work, use of                                         17
+  Metric pitches, change gears for cutting                        171
+  Micrometer for measuring threads                                162
+  Mills, hollow, for turret lathe                                 198
+  Multiple-spindle chucking machine, New Britain                  238
+  Multiple-thread cutting, indexing faceplate for                 153
+  Multiple threads                                                146
+    method of cutting                                             150
+    setting tool when cutting                                     152
+  Multiple-turning in Lo-swing lathe                              117
+
+  New Britain multiple-spindle chucking machine                   238
+  Newall Engineering Co's fit allowances                          131
+
+  Pistons, gasoline engine, turning in turret lathe               204
+  Piston rings, attachment for turning in turret lathe            210
+    turning in turret lathe                                       206
+  Piston turning in Pratt & Whitney turret lathe                  208
+  Pitch, metric, change gears for cutting                         171
+  Pitch of thread, definition of                                  146
+  Plug gage, standard                                              42
+  Polishing and filing in lathe                                    13
+  Potter & Johnston automatic chucking and turning machine        223
+    method of "setting-up"                                        227
+    turning flywheel in                                           236
+  Pratt & Whitney turret lathe, arranged for piston turning       208
+    equipped with piston ring turning attachment                  210
+  Press for arbors or mandrels                                     22
+  Pressure generally used in assembling forced fits               132
+  Push fits, allowances for                                       131
+
+  Quick change-gear type of lathe                                 173
+
+  Reamer holders, floating type                                   271
+  Reaming and drilling in lathe                                    43
+  Releasing die and tap holders                                   199
+  Relieving attachment, Hendey                                    123
+  Relieving attachment, Hendey, application of                    125
+  Relieving hobs or taps having spiral flutes                     128
+  Rivett-Dock threading tool                                      164
+  Roughing and finishing cuts in lathe                         75, 76
+  Running fits, allowances for                                    131
+
+  Screw cutting, calculating change gears for                     167
+    compound gearing for                                          170
+    in engine lathe                                               135
+    method of handling lathe                                      138
+    selecting change gears for                                    135
+    with compound rest                                            143
+  Screws, cutting to compensate for shrinkage                     165
+    metric, change gears for cutting                              171
+    testing size of                                               161
+  Selecting type of turning machine                               240
+  Shrinkage, cutting screws to compensate for                     165
+  Shrinkage fits, allowances for                                  133
+  Side-tool, facing with                                            7
+  Speeds for turning, average                                      72
+    based on Taylor's experiments                                  71
+    effect of lubricant                                            76
+    factors which limit                                            72
+    rules for calculating                                          74
+  Spherical turning                                               111
+    attachments for                                               113
+  "Spider" for supporting bushing while turning                48, 49
+  Spiral flutes, method of relieving hobs or taps with            128
+  Square thread and method of cutting                        149, 159
+  Steadyrest, application of when boring                           25
+    for engine lathe                                               23
+  Stop for lathe cross-slide when threading                       155
+
+  Tap and die holders, releasing type                             199
+  Taper attachment for lathe                                       88
+    practical application of                                       90
+  Taper boring with taper attachment                               90
+  Taper threading, position of tool for                           154
+  Taper turning, adjustment of tailstock center for                82
+    by offset-center method                                        80
+    examples of                                                    83
+    height of tool for                                             94
+    in vertical boring mill                                       261
+    in vertical mill with horizontal and vertical feeds           262
+    setting tailstock center with caliper tool                     85
+    setting tailstock center with square                           87
+    with compound rest                                             95
+    with taper attachment                                      92, 93
+  Tapers, gage for accurate measurement of                         97
+  Tapers, rules for figuring                                       97
+  Test indicator, truing buttons with                        102, 103
+  Test or center indicator for use on lathe                       100
+  Thread cutting, calculating change gears for                    167
+    compound gearing for                                          170
+    cross-slide stop used for                                     155
+    indexing faceplate for multiple threads                       153
+    in engine lathe                                               135
+    internal                                                      154
+    method of handling lathe                                      138
+    selecting change gears for                                    135
+    taper, position of tool for                                   154
+    with compound rest                                            143
+  Thread gage, Acme standard                                      157
+  Thread indicator for lathe apron                           141, 142
+  Thread micrometer                                               162
+  Thread tool, Acme, measuring width with vernier caliper    157, 158
+    for cutting V-thread                                          138
+  Thread tools for standard threads                               159
+  Threads, Acme standard, and tool for cutting                    159
+    change gears for fractional                                   171
+    cutting to compensate for shrinkage                           165
+    different forms of                                            144
+    left-hand, method of cutting                                  148
+    metric, change gears for cutting                              171
+    multiple                                                      146
+    multiple, method of cutting                                   150
+    multiple, setting tool when cutting                           152
+    sharp V, and tool for cutting                                 159
+    square, and method of cutting                            149, 159
+    testing size of                                               161
+    three-wire system for measuring                               163
+    U. S. standard, and tool for cutting                     146, 159
+    Whitworth standard, and tool for cutting                 158, 159
+    worm, and tool for cutting                               159, 160
+  Threading attachment, lathe, for coarse threads                 160
+  Threading tool, Rivett-Dock                                     164
+  Tool grinding                                                    62
+  Tools for lathe, set for general turning                         54
+  Tools for turning, angle of clearance                            66
+    angle of keenness                                              67
+    inserted-cutter type                                           58
+    slope of cutting edge                                      66, 67
+  Tools for turret lathe                                          190
+  Tools, lathe, application of various types                       56
+  Turning, cylindrical, simple example of                           6
+    eccentric                                                     106
+    multiple, in Lo-swing lathe                                   117
+    with front and rear tools                                     114
+  Turning speeds, average for lathe                                72
+    based on Taylor's experiments                                  71
+    factors which limit                                            72
+    rules for calculating                                          74
+  Turning tools, angle of clearance                                66
+    angle of keenness                                              67
+    for aluminum                                                   53
+    for brass                                                      52
+    for copper                                                     52
+    for lathe, position of                                         60
+    for lathe, set of, for general work                            54
+    inserted-cutter type for lathe                                 58
+    slope of cutting edge                                      66, 67
+  Turret lathe, Bardons & Oliver, general description             178
+    examples of chuck work in Acme flat                           219
+    Hartness flat, example of turning                             213
+    Jones & Lamson double-spindle type                            221
+    machining flywheels in                                        184
+    Pratt & Whitney arranged for piston turning                   208
+    piston ring turning attachment for                            210
+    tools for general work                                        190
+    turning bevel gear blanks in Davis                            212
+    turning gasoline engine pistons in                            204
+    turning piston rings in                                       206
+    turning worm-gear blanks in Davis                             211
+    typical example of turret lathe work                          181
+  Turret lathe tools, miscellaneous types                         202
+  Turret lathe type of vertical boring mill                       264
+  Type of turning machine, factors which govern selection         240
+
+  U. S. standard thread                                           159
+    method of cutting                                             146
+  Universal chuck for lathe                                        36
+
+  V-thread and tool for cutting                                   159
+  Vertical boring mill, Bullard turret lathe type                 264
+    convex turning attachment                                     259
+    general description                                           242
+    holding and setting work                                      247
+    taper turning in                                              261
+    taper turning with horizontal and vertical feeds              262
+    tools for boring and reaming                                  251
+    turning flywheel in                                           255
+    turning tools for                                             253
+  Vertical turret lathe, Bullard, examples of work                268
+
+  Whitworth standard thread and tool for cutting             158, 159
+  Wire system for measuring threads                               163
+  Worm thread and tool for cutting                           159, 160
+
+
+
+
+  Transcriber's notes on changes made to text:
+    Left as in original:
+      use of degree, deg. and  deg.; use of minute, min. and '.
+
+    Standardised to the most commonly used in the book:
+      backgear to back-gear; camshaft to cam-shaft; crankpin to
+      crank-pin; face-plate to faceplate; out-board to outboard;
+      over-hang to overhang; setscrew to set-screw; steady-rest
+      to steadyrest; subdivision(s) to sub-division(s); tail-stock
+      to tailstock; thumbscrew to thumb-screw; tool-post to toolpost;
+      tool-slide to toolslide; hand-wheel to handwheel; U.S. to U. S.
+
+    Page 64 had a blotched (illegible) word, this has been replaced by
+    (large and rigid) work.
+
+    Table of Contents: largely re-compiled to create one-to-one links
+    with named paragraphs and sections in text.
+
+
+
+
+
+End of the Project Gutenberg EBook of Turning and Boring, by Franklin D. Jones
+
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