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diff --git a/34030-8.txt b/34030-8.txt new file mode 100644 index 0000000..44bc134 --- /dev/null +++ b/34030-8.txt @@ -0,0 +1,8936 @@ +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. 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