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+The Project Gutenberg EBook of An Introduction to Machine Drawing and
+Design, by David Allan Low
+
+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: An Introduction to Machine Drawing and Design
+
+Author: David Allan Low
+
+Release Date: March 4, 2012 [EBook #39033]
+
+Language: English
+
+Character set encoding: ISO-8859-1
+
+*** START OF THIS PROJECT GUTENBERG EBOOK AN INTRODUCTION TO MACHINE ***
+
+
+
+
+Produced by Juliet Sutherland and the Online Distributed
+Proofreading Team at http://www.pgdp.net
+
+
+
+
+
+
+
+
+  AN INTRODUCTION
+  TO
+  MACHINE DRAWING
+  AND
+  DESIGN
+
+  BY
+
+  DAVID ALLAN LOW
+
+  (WHITWORTH SCHOLAR), M. INST. M.E.
+
+  HEAD MASTER OF THE PEOPLE'S PALACE TECHNICAL SCHOOLS, LONDON
+  AUTHOR OF 'A TEXT-BOOK ON PRACTICAL SOLID OR DESCRIPTIVE GEOMETRY'
+  'AN ELEMENTARY TEXT-BOOK OF APPLIED MECHANICS' ETC.
+
+  [Illustration]
+
+  _FOURTH EDITION_
+
+  LONDON
+  LONGMANS, GREEN, AND CO.
+  AND NEW YORK: 15 EAST 16th STREET
+  1890
+
+
+
+  PRINTED BY
+  SPOTTISWOODE AND CO., NEW-STREET SQUARE
+  LONDON
+
+
+
+
+PREFACE.
+
+
+It is now generally recognised that the old-fashioned method of teaching
+machine drawing is very unsatisfactory. In teaching by this method an
+undimensioned scale drawing, often of a very elaborate description, is
+placed before the student, who is required to _copy_ it. Very often the
+student succeeds in making a good copy of the drawing placed before him
+without learning very much about the object represented by it, and this
+state of matters is sometimes not much improved by the presence of the
+teacher, who is often simply an art master, knowing nothing about
+machine design. It is related of one school that a pupil, after making a
+copy of a particular drawing, had a discussion with his teacher as to
+whether the object represented was a sewing machine or an electrical
+machine. Evidently the publisher of the drawing example in this case did
+not adopt the precaution which a backward student used at an examination
+in machine design: he put on a full title above his drawing, for the
+information of his examiner.
+
+Now, if machine drawing is to be of practical use to any one, he must be
+able to understand the form and arrangement of the parts of a machine
+from an inspection of suitable drawings of them without seeing the parts
+themselves. Also he ought to be able to make suitable drawings of a
+machine or parts of a machine from the machine or the parts themselves.
+
+In producing this work the author has aimed at placing before young
+engineers and others, who wish to acquire the skill and knowledge
+necessary for making the simpler _working drawings_ such as are produced
+in engineers' drawing offices, a number of good exercises in drawing,
+sufficient for one session's work, and at the same time a corresponding
+amount of information on the design of machine details generally.
+
+The exercises set are of various kinds. In the first and simplest
+certain views of some machine detail are given, generally drawn to a
+small scale, which the student is asked to reproduce _to dimensions
+marked on these views_, and he is expected to keep to these dimensions,
+and not to measure anything from the given illustrations. In the second
+kind of exercise the student is asked to reproduce certain views shown
+_to dimensions given in words or in tabular form_. In the third kind of
+exercise the student is required to make, in addition to certain views
+shown to given dimensions, others which he can only draw correctly if he
+thoroughly understands the design before him. In the fourth kind of
+exercise the student is asked to make the necessary working drawings for
+some part of a machine which has been previously described and
+illustrated, _the dimensions to be calculated by rules given in the
+text_.
+
+The illustrations for this work are all new, and have been specially
+prepared by the author from _working drawings_, and he believes that
+they will be found to represent the best modern practice.
+
+As exercises in drawing, those given in this book are not numbered
+exactly in their order of difficulty, but unless on the recommendation
+of a teacher, the student should take them up in the order given,
+omitting the following:--26, 27, 28, 35, 40, 42, 43, 45, 49, 50, 54, 60,
+61, as he comes to them, until he has been right through the book;
+afterwards he should work out those which he omitted on first going over
+the book.
+
+In addition to the exercises given in this work the student should
+practise making freehand sketches of machine details from actual
+machines or good models of them. Upon these sketches he should put the
+proper dimensions, got by direct measurement from the machine or model
+by himself. These sketches should be made in a note-book kept for the
+purpose, and no opportunity should be lost of inserting a sketch of any
+design which may be new to the student, always putting on the dimensions
+if possible. These sketches form excellent examples from which to make
+working drawings. The student should also note any rules which he may
+meet with for proportioning machines, taking care, however, in each case
+to state the source of such information for his future guidance and
+reference.
+
+As machine drawing is simply the application of the principles of
+descriptive geometry to the representation of machines, the student of
+the former subject, if he is not already acquainted with the latter,
+should commence to study it at once.
+
+                                                              D. A. L.
+  GLASGOW: _March_ 1887.
+
+
+_PREFACE TO THE THIRD EDITION._
+
+To this edition another chapter has been added, containing a number of
+miscellaneous exercises, which it is hoped will add to the usefulness of
+the work as a text-book in science classes. The latest examination paper
+in machine drawing by the Science and Art Department has also been added
+to the Appendix.
+
+                                                              D. A. L.
+  LONDON: _August_ 1888.
+
+
+
+
+CONTENTS.
+
+
+                                                    PAGE
+      I.  INTRODUCTION                                 1
+     II.  RIVETED JOINTS                               6
+    III.  SCREWS, BOLTS, AND NUTS                     14
+     IV.  KEYS                                        22
+      V.  SHAFTING                                    24
+     VI.  SHAFT COUPLINGS                             25
+    VII.  BEARINGS FOR SHAFTS                         30
+   VIII.  PULLEYS                                     36
+     IX.  TOOTHED WHEELS                              39
+      X.  CRANKS AND CRANKED SHAFTS                   43
+     XI.  ECCENTRICS                                  47
+    XII.  CONNECTING RODS                             49
+   XIII.  CROSS-HEADS                                 56
+    XIV.  PISTONS                                     57
+     XV.  STUFFING-BOXES                              63
+    XVI.  VALVES                                      68
+   XVII.  MATERIALS USED IN MACHINE CONSTRUCTION      76
+  XVIII.  MISCELLANEOUS EXERCISES                     81
+
+          APPENDIX A                                  99
+          APPENDIX B                                 102
+          INDEX                                      113
+
+
+
+
+AN INTRODUCTION
+
+TO
+
+MACHINE DRAWING AND DESIGN.
+
+
+
+
+I. INTRODUCTION.
+
+
+_Drawing Instruments._--For working the exercises in this book the
+student should be provided with the following:--A well-seasoned yellow
+pine _drawing-board_, 24 inches long, 17 inches wide, and 3/8 inch or
+1/2 inch thick, provided with cross-bars on the back to give it strength
+and to prevent warping. A =T= _square_, with a blade 24 inches long
+attached permanently to the stock, _but not sunk into it_. One 45° and
+one 60° _set square_. The short edges of the former may be about 6
+inches and the short edge of the latter about 5 inches long. A _pair of
+compasses_ with pen and pencil attachments, and having legs from 5
+inches to 6 inches long. A _pair of dividers_, with screw adjustment if
+possible. A _pair of small steel spring pencil bows_ for drawing small
+circles, and a _pair of small steel spring pen bows_ for inking in the
+same. A _drawing pen_ for inking in straight lines. All compasses should
+have _round points_, and if possible _needle_ points. A piece of
+india-rubber will also be required, besides two pencils, one marked H or
+HH and one marked HB or F; the latter to be used for lining in a drawing
+which is not to be inked in, or for freehand work.
+
+Pencils for mechanical drawing should be sharpened with a _chisel
+point_, and those for freehand work with a _round point_. _Do not wet
+the pencil_, as the lines afterwards made with it are very difficult to
+rub out.
+
+Drawing-paper for working drawings may be secured to the board by
+_drawing-pins_, but the paper for finished drawings or drawings upon
+which there is to be a large amount of colouring should be _stretched_
+upon the board.
+
+The student should get the best instruments he can afford to buy, and he
+should rather have a few good instruments than a large box of inferior
+ones.
+
+_Drawing-paper._--The names and sizes of the sheets of drawing paper are
+given in the following table:--
+
+                     Inches
+  Demy              20 × 15
+  Medium            22 × 17
+  Royal             24 × 19
+  Imperial          30 × 22
+  Atlas             34 × 26
+  Double Elephant   40 × 27
+  Antiquarian       52 × 31
+
+The above sizes must not be taken as exact. In practice they will be
+found to vary in some cases as much as an inch.
+
+Cartridge-paper is made in sheets of various sizes, and also in rolls.
+
+Hand-made paper is the best, but it is expensive. Good cartridge-paper
+is quite suitable for ordinary drawings.
+
+_Centre Lines._--Drawings of most parts of machines will be found to
+be symmetrical about certain lines called _centre lines_. These lines
+should be drawn first with great care. On a pencil drawing centre
+lines should be thin continuous lines; in this book they are shown
+thus -- - -- - --.
+
+After drawing the centre line of any part the dimensions of that part
+must be marked off from the centre line, so as to insure that it really
+is the centre line of that part: thus in making a drawing of a rivet,
+such as is shown at (_a_) fig. 1, after drawing the centre line, half
+the diameter of the rivet would be marked off on each side of that line,
+in order to determine the lines for the sides of the rivet.
+
+_Inking._--For inking in drawings the best Indian ink should be used,
+and not common writing ink. Common ink does not dry quick enough, and
+rapidly corrodes the drawing pens. The pen should be filled by means of
+a brush or a narrow strip of paper, and not by dipping the pen into the
+ink.
+
+In cases where there are straight lines and arcs of circles touching one
+another _ink in the arcs first_, then the straight lines; in this way it
+is easier to hide the joints.
+
+_Colouring._--Camel's-hair or sable brushes should be used; the latter
+are the best, but are much more expensive than the former. The colour
+should be rubbed down in a dish, and the tint should be light. The
+mistake which a beginner invariably makes is in having the colour of too
+dark a tint.
+
+First go over the part to be coloured with the brush and _clean_ water
+for the purpose of damping it. Next dry with clean blotting-paper to
+take off any superfluous water. Then take another brush with the colour,
+and beginning at the top, work from left to right and downwards. If it
+is necessary to recolour any part let the first coating dry before
+beginning.
+
+Engineers have adopted certain colours to represent particular
+materials; these are given in the following table:--
+
+_Table showing Colours used to represent Different Materials._
+
+  MATERIAL          COLOUR
+
+  Cast iron         Payne's grey or neutral tint.
+  Wrought iron      Prussian blue.
+  Steel             Purple (mixture of Prussian blue and crimson lake).
+  Brass             Gamboge with a little sienna or a very little red
+                         added.
+  Copper            A mixture of crimson lake and gamboge, the former
+                         colour predominating.
+  Lead              Light Indian ink with a very little indigo added.
+  Brickwork         Crimson lake and burnt sienna.
+  Firebrick         Yellow and Vandyke brown.
+  Greystones        Light sepia or pale Indian ink, with a little
+                         Prussian blue added.
+  Brown freestone   Mixture of pale Indian ink, burnt sienna, and
+                         carmine.
+  Soft woods        For ground work, pale tint of sienna.
+  Hard woods        For ground work, pale tint of sienna with a little
+                         red added.
+                    For graining woods use darker tint with a greater
+                         proportion of red.
+
+_Printing._--A good drawing should have its title printed, a plain style
+of letter being used for this purpose, such as the following:--
+
+  [Illustration: ABCDEFGHIJKLMNOPQRST
+                        UVWXYZ
+                      1234567890]
+
+  [Illustration: ABCDEFGHIJKLMNOPQR
+                      STUVWXYZ
+                     1234567890]
+
+The following letters look well _if they are well made_, but they are
+much more difficult to draw.
+
+  [Illustration: ABCDEFGHIJKLMNOP
+                    QRSTUVWXYZ
+                    1234567890]
+
+For remarks on a drawing the following style is most suitable:--
+
+  [Illustration: abcdefghijklmnopqrstuvwxyz]
+
+All printing should be done by freehand.
+
+_Border lines_ are seldom put on engineering drawings.
+
+_Working Drawings._--A good working drawing should be prepared in the
+following manner. It must first be carefully outlined in pencil and then
+inked in. After this all parts cut by planes of section should be
+coloured, the colours used indicating the materials of which the parts
+are made. Parts which are round may also be lightly shaded with the
+brush and colours to suit the materials. The centre lines are now inked
+in with _red_ or _blue ink_. The red ink may be prepared by rubbing down
+the cake of crimson lake, and the blue ink in like manner from the cake
+of Prussian blue. Next come the _distance_ or _dimension_ lines, which
+should be put in with _blue_ or _red ink_, depending on which colour was
+used for the centre lines. Dimension lines and centre lines are best put
+in of different colour. The arrow-heads at the ends of the dimension
+lines are now put in with _black ink_, and so are the figures for the
+dimensions. The arrow-heads and the figures should be made with a common
+writing pen. The dimensions should be put on neatly. Many a good drawing
+has its appearance spoiled through being slovenly dimensioned.
+
+We may here point out the importance of putting the dimensions on a
+working drawing. If the drawing is not dimensioned, the workman must get
+his sizes from the drawing by applying his rule or a suitable scale. Now
+this operation takes time, and is very liable to result in error. Time
+is therefore saved, and the chance of error reduced, by marking the
+sizes in figures.
+
+In practice it is not usual to send original drawings from the drawing
+office to the workshop, but copies only. The copies may be produced by
+various 'processes,' or they may be tracings drawn by hand. Many
+engineers do not ink in their original drawings, but leave them in
+pencil; especially is this the case if the drawings are not likely to be
+much used.
+
+_Scales._--The best scales are made of ivory, and are twelve inches
+long. Boxwood scales are much cheaper, although not so durable as those
+made of ivory. If the student does not care to go to the expense of
+ivory or boxwood scales, he can get paper ones very cheap, which will be
+quite sufficient for his purpose. The divisions of the scale should be
+marked down to its edge, so that measurements may be made by applying
+the scale directly to the drawing. For working such exercises as are in
+this book the student should be provided with the following scales:--
+
+  A scale of  1, or 12 inches to a foot.
+     "       1/2  "  6         "
+     "       1/3  "  4         "
+     "       1/4  "  3         "
+     "       1/6  "  2         "
+
+A scale of 1 is spoken of as 'full size,' and a scale of 1/2 as 'half
+size.'
+
+Engineers in this country state dimensions of machines in feet, inches,
+and fractions of an inch, the latter being the 1/2, 1/4, 1/8, 1/16, &c.
+In making calculations it is generally more convenient to use decimal
+fractions, and then substitute for the results the equivalent fractions
+in eighths, sixteenths, &c. The following table will be found useful for
+this purpose:--
+
+_Decimal Equivalents of Fractions of an Inch._
+
+  +----------+--------------------+
+  | Fraction | Decimal Equivalent |
+  +----------+--------------------+
+  |  1/32    |      .03125        |
+  |  1/16    |      .0625         |
+  |  3/32    |      .09375        |
+  |  1/8     |      .125          |
+  |  5/32    |      .15625        |
+  |  3/16    |      .1875         |
+  |  7/32    |      .21875        |
+  |  1/4     |      .25           |
+  |  9/32    |      .28125        |
+  |  5/16    |      .3125         |
+  | 11/32    |      .34375        |
+  |  3/8     |      .375          |
+  | 13/32    |      .40625        |
+  |  7/16    |      .4375         |
+  | 15/32    |      .46875        |
+  |  1/2     |      .5            |
+  | 17/32    |      .53125        |
+  |  9/16    |      .5625         |
+  | 19/32    |      .59375        |
+  |  5/8     |      .625          |
+  | 21/32    |      .65625        |
+  | 11/16    |      .6875         |
+  | 23/32    |      .71875        |
+  |  3/4     |      .75           |
+  | 25/32    |      .78125        |
+  | 13/16    |      .8125         |
+  | 27/32    |      .84375        |
+  |  7/8     |      .875          |
+  | 29/32    |      .90625        |
+  | 15/16    |      .9375         |
+  | 31/32    |      .96875        |
+  |   1      |     1.0            |
+  +----------+--------------------+
+
+Engineers use a single accent (') to denote _feet_, and a double
+accent (") to denote _inches_. Thus 2' 9" reads two feet nine inches.
+
+
+
+
+II. RIVETED JOINTS.
+
+
+Two plates or pieces to be riveted together have holes punched or
+drilled in them in such a manner that one may be made to overlap the
+other so that the holes in the one may be opposite the holes in the
+other. The rivets, which are round bars of iron, or steel, or other
+metal, are heated to redness and inserted in the holes; the head already
+formed on the rivet, and called the tail, is then held up, and the point
+is hammered or pressed so as to form another head. This process of
+forming the second head on the rivet is known as riveting, and may be
+done by hand-hammering or by a machine.
+
+_Forms of Rivet Heads._--In fig. 1 are shown four different forms of
+rivet heads: (_a_) is a _snap head_, (_b_) a _conical head_ (_c_) a
+_pan head_, and (_d_) _a countersunk head_.
+
+_Proportions of Rivet Heads._--The diameter of the snap head is about
+1.7 times the diameter of the rivet, and its height about .6 of the
+diameter of the rivet. The conical head has a diameter twice and a
+height three quarters of the rivet diameter. The greatest diameter of
+the pan head is about 1.6, and its height .7 of the rivet diameter. The
+greatest diameter of the countersunk head may be one and a half, and its
+depth a half of the diameter of the rivet.
+
+[Illustration: FIG. 1.]
+
+In fig. 1 at (_a_) and (_b_) are shown geometrical constructions devised
+by the author for drawing the snap and conical head for any size of
+rivet, the proportions being nearly the same as those given above.
+
+_Geometrical Construction for Proportioning Snap Heads._--With centre A,
+and radius equal to half diameter of rivet, describe a circle cutting
+the centre line of the rivet at B and C. With centre B and radius BC
+describe the arc CD. Make BE equal to AD. With centre E and radius ED
+describe the arc DFH.
+
+_Construction for Conical Head._--With centre K, and radius equal to
+diameter of rivet, describe the semicircle LMN, cutting the side of the
+rivet at M. With centre M and radius MN describe the arc NP to cut the
+centre line of rivet at P. Join PL and PN.
+
+When a number of rivets of the same diameter have to be shown on the
+same drawing the above constructions need only be performed on one
+rivet. After the point E has been discovered the distance AE may be
+measured off on all the other rivets, and the arcs corresponding to
+DFH drawn with radii equal to ED. In like manner the height KP of the
+conical head may be marked off on all rivets of the same diameter with
+conical heads.
+
+_Caulking._--In order to make riveted joints steam- or water-tight the
+edges of the plates and the edges of the heads of the rivets are burred
+down by a blunt chisel or caulking tool as shown at Q and R.
+
+[Illustration: FIG. 2.]
+
+[Illustration: FIG. 3.]
+
+    EXERCISE 1: _Forms of Rivets._--Draw, full size, the rivets and
+    rivet heads shown in fig. 1. The diameter of the rivet in each
+    case to be 1-1/8 inches, and the thickness of the plates 7/8 inch.
+
+    EXERCISE 2: _Single Riveted Lap Joint._--Draw, full size, the
+    plan and sectional elevation of the _single riveted lap joint_
+    shown in fig. 2.
+
+_Table showing the Proportions of Single Riveted Lap Joints for various
+Thicknesses of Plates._ (_Plates and Rivets Wrought Iron._)
+
+  +--------------+-------------+----------+--------------+
+  | Thickness of | Diameter of | Pitch of | Width of lap |
+  |    plates    |    rivets   |  rivets  |              |
+  +--------------+-------------+----------+--------------+
+  |      1/4     |     9/16    |  1-5/8   |    1-3/4     |
+  |      5/16    |     5/8     |  1-3/4   |    2         |
+  |      3/8     |    11/16    |  1-7/8   |    2-1/4     |
+  |      7/16    |     3/4     |  2       |    2-1/2     |
+  |      1/2     |    13/16    |  2-1/8   |    2-3/4     |
+  |      9/16    |     7/8     |  2-1/4   |    2-7/8     |
+  |      5/8     |    15/16    |  2-5/16  |    3         |
+  |     11/16    |   1         |  2-3/8   |    3-1/8     |
+  |      3/4     |   1-1/16    |  2-1/2   |    3-1/4     |
+  +------------------------------------------------------+
+
+  All the dimensions are in inches.
+
+[Illustration: FIG. 4.]
+
+    EXERCISE 3.--Draw, half size, a plan and section of a single
+    riveted lap joint for plates 3/4" thick to the dimensions given in
+    the above table.
+
+    EXERCISE 4: _Double Riveted Lap Joint._--Draw, full size, the two
+    views of the _double riveted lap joint_ shown in fig. 3.
+
+_Table showing the Proportions of Double Riveted Lap Joints for various
+Thicknesses of Plates._ (_Plates and Rivets Wrought Iron._)
+
+  +-----------+-------------+----------+------------------+----------+
+  | Thickness | Diameter of | Pitch of | Distance between | Width of |
+  | of plates |    rivets   |  rivets  |  rows of rivets  |    lap   |
+  +-----------+-------------+----------+------------------+----------+
+  |   3/8     |    11/16    |  2-1/2   |    1-1/8         |  3-1/2   |
+  |   7/16    |     3/4     |  2-5/8   |    1-1/4         |  3-3/4   |
+  |   1/2     |    13/16    |  2-3/4   |    1-3/8         |  4       |
+  |   9/16    |     7/8     |  2-7/8   |    1-7/16        |  4-1/4   |
+  |   5/8     |    15/16    |  3       |    1-9/16        |  4-1/2   |
+  |  11/16    |   1         |  3-1/8   |    1-3/4         |  4-3/4   |
+  |   3/4     |   1-1/16    |  3-1/4   |    1-7/8         |  5       |
+  |  13/16    |   1-1/16    |  3-3/8   |    1-7/8         |  5       |
+  |   7/8     |   1-1/8     |  3-1/2   |    1-15/16       |  5-1/4   |
+  |  15/16    |   1-1/8     |  3-5/8   |    1-15/16       |  5-1/4   |
+  | 1         |   1-3/16    |  3-3/4   |    2             |  5-1/2   |
+  +-----------+-------------+----------+------------------+----------+
+
+[Illustration: FIG. 5.]
+
+    EXERCISE 5.--Draw, half size, a plan and section of a double
+    riveted lap joint for plates 7/8 inch thick to the dimensions
+    given in the above table.
+
+    EXERCISE 6: _Single Riveted Butt Joints._--In fig. 4 are shown
+    _single riveted butt joints_. One of the sectional views shows a
+    butt joint with one _cover plate_ or _butt strap_; the other
+    sectional view shows the same joint with two cover plates; the
+    third view is a plan of both arrangements. Draw all these views
+    full size.
+
+    EXERCISE 7.--Fig. 5 shows a plan and sectional elevation of the
+    connection of three plates together, which are in the same plane,
+    by means of single riveted butt joints and single cover plates.
+    The butt straps where they overlap are forged so as to fit one
+    another as shown, and thus form a close joint. Draw these views to
+    the scale of 6 inches to a foot.
+
+    The plates are 1/2 inch thick and the butt straps 9/16 inch thick.
+    All other dimensions must be deduced from the table for single
+    riveted lap joints.
+
+    EXERCISE 8.--The connection of three plates by single riveted lap
+    joints is shown in fig. 6. To make the joint close one plate has a
+    portion of its edge thinned out, and the plate above it is set up
+    at this part so as to lie close to the former.
+
+    Draw the three views shown in fig. 6 to the same scale as the last
+    exercise.
+
+    The plates are 7/16 inch thick. All other dimensions to be
+    obtained from table for single riveted lap joints.
+
+    EXERCISE 9: _Corner of Wrought-iron Tank._--This exercise is to
+    illustrate the connection of plates which are at right angles to
+    one another by means of _angle irons_. Fig. 7 is a plan and
+    elevation of the corner of a wrought-iron tank. The sides of the
+    tank are riveted to a vertical angle iron, the cross section of
+    which is clearly shown in the plan. Another angle iron of the same
+    dimensions is used in the same way to connect the sides with the
+    bottom. The sides do not come quite up to the corner of the
+    vertical angle iron, excepting at the bottom where the horizontal
+    angle iron comes in. At this point the vertical plates meet one
+    another, and the edge formed is rounded over to fit the interior
+    of the bend of the horizontal angle iron so as to make the joint
+    tight. Draw half size.
+
+    The dimensions are as follows: angle irons 2-1/2 inches × 2-1/2
+    inches × 3/8 inch; plates 3/8 inch thick; rivets 11/16 inch
+    diameter and 2 inches pitch.
+
+    EXERCISE 10: _Gusset Stay._--In order that the flat ends of a
+    steam boiler may not be bulged out by the pressure of the steam
+    they are strengthened by means of stays. One form of boiler stay,
+    called a 'gusset stay,' is shown in fig. 8. This stay consists of
+    a strip of wrought-iron plate which passes in a diagonal direction
+    from the flat end of the boiler to the cylindrical shell. One end
+    of this plate is placed between and riveted to two angle irons
+    which are riveted to the shell of the boiler. A similar
+    arrangement connects the other end of the stay plate to the flat
+    end of the boiler. In this example the stay or gusset plate is 3/4
+    of an inch thick; the angle irons are 4 inches broad and 1/2 inch
+    thick. The rivets are 1 inch in diameter. The same figure also
+    illustrates the most common method of connecting the ends of a
+    boiler to the shell. The end plates are _flanged_ or bent over at
+    right angles and riveted to the shell as shown. The radius of the
+    inside curve at the angle of the flange is 1-1/4 inches. Draw this
+    example to a scale of 3 inches to 1 foot.
+
+[Illustration: FIG. 6.]
+
+[Illustration: FIG. 7.]
+
+[Illustration: FIG. 8.]
+
+
+
+
+III. SCREWS, BOLTS, AND NUTS.
+
+
+_Screw Threads._--The various forms of screw threads used in machine
+construction are shown in fig. 9. The _Whitworth_ =V= thread is shown at
+(_a_). This is the standard form of triangular thread used in this
+country. The angle between the sides of the =V= is 55°, and one-sixth of
+the total depth is rounded off both at the top and bottom. At (_b_) is
+shown the _Sellers_ =V= thread, which is the standard triangular thread
+used by engineers in America. In this form of thread the angle between
+the sides of the =V= is 60°, and one-eighth of the total depth is cut
+square off at the top and bottom. The _Square_ thread is shown at (_c_).
+This form is principally used for transmitting motion.
+
+[Illustration: FIG. 9.]
+
+Comparing the triangular and square threads, the former is the stronger
+of the two; but owing to the normal pressure on the =V= thread being
+inclined to the axis of the screw, that pressure must be greater than
+the pressure which is being transmitted by the screw; and therefore,
+seeing that the normal pressure on the square thread is parallel, and
+therefore equal to the pressure transmitted in the direction of the axis
+of the screw, the friction of the =V= thread must be greater than the
+friction of the square thread. In the case of the triangular thread
+there is also a tendency of the pressure to burst the nut. The
+_Buttress_ thread shown at (_e_) is designed to combine the advantages
+of the =V= and square threads, but it only has these advantages when the
+pressure is transmitted in one direction; if the direction of the
+pressure be reversed, the friction and bursting action on the nut are
+even greater than with the =V= thread, because of the greater
+inclination of the slant side of the buttress thread. The angles of the
+square thread are frequently rounded to a greater or less extent to
+render them less easily damaged. If this rounding is carried to excess
+we get the _Knuckle_ thread shown at (_d_). The rounding of the angles
+increases both the strength and the friction.
+
+    EXERCISE 11: _Forms of Screw Threads._--Draw to a scale of three
+    times full size the sections of screw threads as shown in fig. 9.
+    The pitch for the Whitworth, Sellers, and buttress threads to be
+    3/8 inch, and the pitch of the square and knuckle threads to be 1/2
+    inch.
+
+_Dimensions of Whitworth Screws._
+
+  +-----------------------------------+
+  | Diameter |   Number   | Diameter  |
+  | of screw | of threads | at bottom |
+  |          |  per inch  | of thread |
+  +----------+------------+-----------+
+  |  1/8     |    40      |   .093    |
+  |  3/16    |    24      |   .134    |
+  |  1/4     |    20      |   .186    |
+  |  5/16    |    18      |   .241    |
+  |  3/8     |    16      |   .295    |
+  |  7/16    |    14      |   .346    |
+  |  1/2     |    12      |   .393    |
+  |  5/8     |    11      |   .508    |
+  |  3/4     |    10      |   .622    |
+  |  7/8     |     9      |   .733    |
+  |   1      |     8      |   .840    |
+  |  1-1/8   |     7      |   .942    |
+  |  1-1/4   |     7      |  1.067    |
+  |  1-3/8   |     6      |  1.162    |
+  |  1-1/2   |     6      |  1.286    |
+  |  1-5/8   |     5      |  1.369    |
+  |  1-3/4   |     5      |  1.494    |
+  |  1-7/8   |   4-1/2    |  1.590    |
+  |   2      |   4-1/2    |  1.715    |
+  |  2-1/4   |     4      |  1.930    |
+  |  2-1/2   |     4      |  2.180    |
+  |  2-3/4   |   3-1/2    |  2.384    |
+  |   3      |   3-1/2    |  2.634    |
+  |  3-1/4   |   3-1/4    |  2.856    |
+  |  3-1/2   |   3-1/4    |  3.106    |
+  |  3-3/4   |     3      |  3.323    |
+  |   4      |     3      |  3.573    |
+  |  4-1/4   |   2-7/8    |  3.805    |
+  |  4-1/2   |   2-7/8    |  4.055    |
+  |  4-3/4   |   2-3/4    |  4.284    |
+  |   5      |   2-3/4    |  4.534    |
+  |  5-1/4   |   2-5/8    |  4.762    |
+  |  5-1/2   |   2-5/8    |  5.012    |
+  |  5-3/4   |   2-1/2    |  5.238    |
+  |   6      |   2-1/2    |  5.488    |
+  +-----------------------------------+
+
+_Gas Threads_[1] (_Whitworth Standard_).
+
+[1] Used for wrought-iron and brass tubes.
+
+  +-------------------------------------------------------------+
+  | Diameter of Screw | 1/8 | 1/4 | 3/8 | 1/2 | 5/8 | 3/4 |  1  |
+  +-------------------+-----+-----+-----+-----+-----+-----+------
+  | Number of threads |     |     |     |     |     |     |     |
+  |     per inch      | 28  | 19  | 19  |  14 |  14 |  14 | 11  |
+  +-------------------------------------------------------------+
+
+  +-------------------------------------------------+
+  | Diameter of Screw | 1-1/4 | 1-1/2 | 1-3/4 |  2  |
+  +-------------------+-------+-------+-------+-----+
+  | Number of threads |       |       |       |     |
+  |     per inch      |  11   |  11   |  11   |  11 |
+  +-------------------------------------------------+
+
+_Representation of Screws._--The correct method of representing screw
+threads involves considerable trouble, and is seldom adopted by
+engineers for working drawings. For an explanation of the method see the
+author's Text-book on Practical Solid Geometry, Part II., problem 134. A
+method very often adopted on working drawings is shown in fig. 15; here
+the thin lines represent the points, and the thick lines the roots of
+the threads. At fig. 16 is shown a more complete method. The simplest
+method is illustrated by figs. 10, 11, 13, and 14.
+
+Here dotted lines are drawn parallel to the axis of the screw as far as
+it extends, and at a distance from one another equal to the diameter of
+the screw at the bottom of the thread.
+
+[Illustration: FIG. 10.]
+
+[Illustration: FIG. 11.]
+
+_Forms of Nuts._--The most common form of nut is the hexagonal shown in
+figs. 10, 13, 14, 15, and 16; next to this comes the square nut shown in
+fig. 11. The method of drawing these nuts will be understood by
+reference to the figures; the small circles indicate the centres, and
+the inclined lines passing through them the radii of the curves which
+represent the chamfered or bevelled edge of the nut. In all the figures
+but the first the chamfer is just sufficient to touch the middle points
+of the sides, and in these cases the drawing of the nut is simpler.
+
+[Illustration: FIG. 12.]
+
+[Illustration: FIG. 13.]
+
+[Illustration: FIG. 14.]
+
+_Forms of Bolts._--At (_a_), fig. 12, is shown a bolt with a square head
+and a square neck. If this form of bolt is passed through a square hole
+the square neck prevents the bolt from turning when the nut is being
+screwed up. Instead of a square neck a snug may be used for the same
+purpose, as shown on the cup-headed bolt at (_b_). The snug fits into a
+short groove cut in the side of the hole through which the bolt passes.
+At (_a_) the diagonal lines are used to distinguish the flat side of the
+neck from the round part of the bolt above it. At (_c_) is shown a
+tee-headed bolt, and at (_d_) an eye-bolt. Fig. 13 represents a hook
+bolt. A bolt with a countersunk head is shown in fig. 11. If the
+countersunk head be lengthened so as to take up the whole of the
+unscrewed part of the bolt, we get the taper bolt shown in fig. 14,
+which is often used in the couplings of the screw shafts of steamships.
+The taper bolt has the advantage of having no projecting head, and it
+may also be made a tight fit in the hole with less trouble than a
+parallel bolt. Bolts may also have hexagonal heads.
+
+[Illustration: FIG. 15]
+
+[Illustration: FIG. 16]
+
+_Studs_, or _stud bolts_, are shown in figs. 15 and 16; that in fig. 15
+is a _plain stud_, while that in fig. 16 has an intermediate collar
+forged upon it, and is therefore called a _collared stud_.
+
+_Proportions of Nuts and Bolt-heads._--In the hexagonal nut the diameter
+D across the flats is 1-1/2_d_ + 1/8, where _d_ is the diameter of the
+bolt. The same rule gives the width of a square nut across the flats. A
+rule very commonly used in making drawings of hexagonal nuts is to make
+the diameter D, across the angles equal to 2_d_. H, the height of the
+nut, is equal to the diameter of the bolt. In square and hexagonal
+headed bolts the height of the head varies from _d_ to 2/3_d_; the other
+dimensions are the same as for the corresponding nuts.
+
+_Washers_ are flat, circular, wrought-iron plates, having holes in their
+centres of the same diameter as the bolts on which they are used. The
+object of the washer is to give a smooth bearing surface for the nut to
+turn upon, and it is used when the surfaces of the pieces to be
+connected are rough, or when the bolt passes through a hole larger than
+itself, as shown in fig. 10. The diameter of the washer is a little more
+than the diameter of the nut across the angles, and its thickness about
+1/8 of the diameter of the bolt.
+
+    EXERCISE 12.--Draw, full size, the views shown in fig. 10 of an
+    hexagonal nut and washer for a bolt 1-1/4 inches in diameter. The
+    bolt passes through a hole 1-3/4 × 1-1/4. All the dimensions are
+    to be calculated from the rules which have just been given.
+
+    EXERCISE 13.--Draw, full size, the plan and elevation of the
+    square nut and bolt with countersunk head shown in fig. 11, to the
+    dimensions given.
+
+    EXERCISE 14.--Draw, full size, the elevation of the hook bolt with
+    hexagonal nut shown in fig. 13 to the dimensions given, and show
+    also a plan.
+
+    EXERCISE 15.--Draw, to a scale of 4 inches to a foot, the conical
+    bolt for a marine shaft coupling shown in fig. 14. All the parts
+    are of wrought iron.
+
+    EXERCISE 16.--Fig. 15 is a section of the mouth of a small
+    steam-engine cylinder, showing how the cover is attached; draw
+    this full size.
+
+    EXERCISE 17.--Fig. 16 shows the central portion of the
+    india-rubber disc valve which is described on page 68. A is the
+    central boss of the grating, into which is screwed the stud B,
+    upon which is forged the collar C. The upper part of the stud is
+    screwed, and carries the guard D and an hexagonal nut E. F is the
+    india-rubber. The grating and guard are of brass. The stud and nut
+    are of wrought iron. Draw full size the view shown.
+
+_Lock Nuts._--In order that a nut may turn freely upon a bolt, there is
+always a very small clearance space between the threads of the nut and
+those of the bolt. This clearance is shown exaggerated at (_a_), fig.
+17, where A is a portion of a bolt within a nut B. Suppose that the bolt
+is stretched by a force W. When the nut B is screwed up, the upper
+surfaces of the projecting threads of the nut will press on the under
+surfaces of the threads of the bolt with a force P equal and opposite
+to W, as shown at (_b_), fig. 17. When in this condition the nut has no
+tendency to slacken back, because of the friction due to the pressure on
+the nut. Now suppose that the tension W on the bolt is momentarily
+diminished, then the friction which opposes the turning of the nut may
+be so much diminished that a vibration may cause it to slacken back
+through a small angle. If this is repeated a great many times the nut
+may slacken back so far as to become useless.
+
+[Illustration: FIG. 17.]
+
+[Illustration: FIG. 18.]
+
+A very common arrangement for locking a nut is shown at (_a_), fig. 18.
+C is an ordinary nut, and B one having half the thickness of C. B is
+first screwed up tight so as to act on the bolt, as shown at (_b_), fig.
+17. C is then screwed on top of B. When C is almost as tight as it can
+be made, it is held by one spanner, while B is turned back through a
+small angle with another. The action of the nuts upon the bolt and upon
+one another is now as shown at (_b_), fig. 18. It will be seen that the
+nuts are wedged tight on to the bolt, and that this action is
+independent of the tension W in the bolt. The nuts will, therefore,
+remain tight after the tension in the bolt is removed.
+
+It is evident that if the nuts are screwed up in the manner explained,
+the outer nut C will carry the whole load on the bolt; hence C should be
+the thicker of the two nuts. In practice, the thin nut, called the lock
+nut, is often placed on the outside, for the reason that ordinary
+spanners are too thick to act on the thin nut when placed under the
+other.
+
+Another very common arrangement for locking a nut is shown in fig. 19. A
+is the bolt and B the nut, the lower part of which is turned circular. A
+groove C is also turned on the nut at this part. The circular part of
+the nut fits into a circular recess in one of the parts connected by the
+bolt. Through this part passes a set screw D, the point of which can be
+made to press on the nut at the bottom of the groove C. D is turned back
+when the nut B is being moved, and when B is tightened up, the set screw
+is screwed up so as to press hard on the bottom of the groove C. The nut
+B is thus prevented from slackening back. The screw thread is turned off
+the set screw at the point where it enters the groove on the nut.
+
+[Illustration: FIG. 19]
+
+The use of the groove for receiving the point of the set screw is this:
+The point of the set screw indents the nut and raises a bur which would
+interfere with the free turning of the nut in the recess if the bur was
+not at the bottom of a groove. Additional security is obtained by
+drilling a hole through the point of the bolt, and fitting it with a
+split pin E.
+
+Locking arrangements for nuts are exceedingly numerous, and many of them
+are very ingenious, but want of space prevents us describing them. We
+may point out, however, that many very good locking arrangements have
+the defect of only locking the nut at certain points of a revolution,
+say at every 30°. It will be noticed that the two arrangements which we
+have described are not open to this objection.
+
+    EXERCISE 18.--Draw, full size, a plan, front elevation, and side
+    elevation of the arrangement of nuts shown in fig. 18, for a bolt
+    7/8 inch diameter.
+
+    EXERCISE 19.--Draw the plan and elevation of the nut and locking
+    arrangement shown in fig. 19. Make also an elevation looking in
+    the direction of the arrow. Scale 6 inches to a foot.
+
+
+
+
+IV. KEYS.
+
+
+_Keys_ are wedges, generally rectangular in section, but sometimes
+circular; they are made of wrought iron or steel, and are used for
+securing wheels, pulleys, cranks, &c., to shafts.
+
+[Illustration: Fig. 20.]
+
+Various sections of keys are shown in fig. 20. At (_a_) is the _hollow_
+or _saddle key_. With this form of key it is not necessary to cut the
+shaft in any way, but its holding power is small, and it is therefore
+only used for light work. At (_b_) is the _key on a flat_, sometimes
+called a _flat key_. The holding power of this key is much greater than
+that of the saddle key. At (_c_) is the _sunk key_, a very secure and
+very common form.
+
+The part of the shaft upon which a key rests is called the _key bed_ or
+_key way_, and the recess in the boss of the wheel or pulley into which
+the key fits is called the _key way_; both are also called _key seats_.
+With saddle, flat, and sunk keys the key bed is parallel to the axis of
+the shaft; but the key way is deeper at one end than the other to
+accommodate the taper of the key. The sides of the key are parallel.
+
+The _round key_ or taper pin shown at (_d_) is in general only used for
+wheels or cranks which have been previously shrunk on to their shafts or
+forced on by great pressure. After the wheel or crank has been shrunk
+on, a hole is drilled, half into the shaft and half into the wheel or
+crank, to receive the pin.
+
+When the point of a key is inaccessible the other end is provided with a
+_gib head_ as shown at (_e_), to enable the key to be withdrawn.
+
+A _sliding_ or _feather key_ secures a piece to a shaft so far as to
+prevent the one from rotating without the other, but allows of relative
+motion in the direction of the axis of the shaft. This form of key has
+no taper, and it is secured to the piece carried by the shaft, but is
+made a _sliding fit_ in the key way of the shaft. In one form of feather
+key the part within the piece carried by the shaft is dovetailed as
+shown at (_f_). In another form the key has a round projecting pin
+forged upon it, which enters a corresponding hole as shown at (_g_). The
+feather key may also be secured to the piece carried by the shaft by
+means of one or more screws as shown at (_h_). The key way in the shaft
+is made long enough to permit of the necessary sliding motion.
+
+_Cone Keys._--These are sometimes fitted to pulleys, and are shown in
+fig. 32, page 38. In this case the eye of the pulley is tapered and is
+larger than the shaft. The space between the shaft and the boss of the
+pulley is filled with three _saddle_ or _cone keys_. These keys are made
+of cast iron and are all cast together, and before being divided the
+casting is bored to fit the shaft and turned to fit the eye of the
+pulley. By this arrangement of keys the same pulley may be fixed on
+shafts of different diameters by using keys of different thicknesses;
+also the pulley may be bored out large enough to pass over any boss
+which may be forged on the shaft.
+
+_Proportions of Keys._--The following rules are taken from Unwin's
+'Machine Design,' pp. 142-43.
+
+  Diameter of eye of wheel, or boss of shaft = _d_.
+  Width of key                               = 3/4_d_ + 1/8.
+  Mean thickness of sunk key                 = 1/8_d_ + 1/8.
+         "          key on flat              = 1/16_d_ + 1/16.
+
+The following table gives dimensions agreeing with average practice.
+
+_Dimensions of Keys._
+
+  D   = diameter of shaft.
+  B   = breadth of key.
+  T   = thickness of sunk key.
+  T_{1} = thickness of flat key, also = thickness of saddle key. Taper
+  of key 1/8 inch per foot of length, _i.e._ 1 in 96.
+
+  +---------------------------------------------------------------+
+  |  D  | 3/4 |  1  | 1-1/4 | 1-1/2 | 1-3/4 |  2  | 2-1/4 | 2-1/2 |
+  +-----+-----+-----+-------+-------+-------+-----+-------+-------+
+  |  B  | 5/16| 3/8 | 7/16  |  1/2  | 9/16  | 5/8 | 11/16 | 11/16 |
+  |  T  | 1/4 | 1/4 |  1/4  | 5/16  | 5/16  | 5/16|  3/8  |  3/8  |
+  |T_{1}| 3/16| 3/16|  3/16 | 3/16  |  1/4  | 1/4 |  1/4  | 5/16  |
+  +---------------------------------------------------------------+
+
+  +-------------------------------------------------------------------+
+  |  D  | 2-3/4 |  3  | 3-1/2 |   4   | 4-1/2 |   5   | 5-1/2 |   6   |
+  +-----+-------+-----+-------+-------+-------+-------+-------+-------+
+  |  B  |  3/4  | 7/8 |   1   | 1-1/8 | 1-1/4 | 1-3/8 | 1-1/2 | 1-5/8 |
+  |  T  |  3/8  | 7/16|  1/2  |  1/2  | 9/16  |  5/8  | 11/16 |  3/4  |
+  |T_{1}|  5/16 | 5/16|  3/8  | 7/16  |  1/2  |  1/2  |  9/16 |  5/8  |
+  +-------------------------------------------------------------------+
+
+  +-------------------------------------------------------+
+  |  D  |   7   |   8   |   9   |   10   |   11   |   12  |
+  +-----+-------+-------+-------+--------+--------+-------+
+  |  B  | 1-7/8 | 2-1/8 | 2-3/8 | 2-5/8  | 2-7/8  | 3-1/8 |
+  |  T  | 13/16 | 15/16 |   1   | 1-1/16 | 1-3/16 | 1-1/4 |
+  |T_{1}| 11/16 |  3/4  |  7/8  | 15/16  | 1-1/16 | 1-1/8 |
+  +-------------------------------------------------------+
+
+
+
+
+V. SHAFTING.
+
+
+Shafting is nearly always cylindrical and made of wrought iron or steel.
+Cast iron is rarely used for shafting.
+
+_Axles_ are shafts which are subjected to bending without twisting.
+
+The parts of a shaft or axle which rest upon the bearings or supports
+are called _journals_, _pivots_, or _collars_.
+
+In journals the supporting pressure is at right angles to the axis of
+the shaft, while in pivots and collars the pressure is parallel to that
+axis.
+
+Shafts may be solid or hollow. Hollow shafts are stronger than solid
+shafts for the same weight of material. Thus a hollow shaft having an
+external diameter of 10-1/4 inches and an internal diameter of 7 inches
+would have about the same weight as a solid shaft of the same material
+7-1/2 inches in diameter, but the former would have about double the
+strength of the latter. Hollow shafts are also stiffer and yield less to
+bending action than solid shafts, which in some cases, as in propeller
+shafts, is an objection.
+
+
+
+
+VI. SHAFT COUPLINGS.
+
+
+For convenience of making and handling, shafts used for transmitting
+power are generally made in lengths not exceeding 30 feet. These lengths
+are connected by couplings, of which we give several examples.
+
+[Illustration: FIGS. 21 and 22.]
+
+_Solid_, _Box_, or _Muff Couplings._--One form of box coupling is shown
+in fig. 21. Here the ends of the shafts to be connected butt against one
+another, meeting at the centre of the box, which is made of cast iron.
+The shafts are made to rotate as one by being secured to the box by two
+wrought-iron or steel keys, both driven from the same end of the box. A
+clearance space is left between the head of the forward key and the
+point of the hind one, to facilitate the driving of them out, as then
+only one key needs to be started at a time. Sometimes a single key the
+whole length of the box is used, in which case it is necessary that the
+key ways in the shafts be of exactly the same depth.
+
+The half-lap coupling, introduced by Sir William Fairbairn, is shown in
+fig. 22. In this form of box coupling the ends of the shafts overlap
+within the box. It is evident that one shaft cannot rotate without the
+other as long as the box remains over the lap. To keep the box in its
+place it is fitted with a saddle key.
+
+It will be noticed that the lap joint is sloped in such a way as to
+prevent the two lengths of shaft from being pulled asunder by forces
+acting in the direction of their length.
+
+Half-lap couplings are not used for shafts above 5 inches in diameter.
+
+It may here be pointed out that the half-lap coupling is expensive to
+make, and is now not much used.
+
+As shafts are weakened by cutting key ways in them, very often the ends
+which carry couplings are enlarged in diameter, as shown in fig. 21, by
+an amount equal to the thickness of the key. An objection to this
+enlargement is that wheels and pulleys require either that their bosses
+be bored out large enough to pass over it, or that they be split into
+halves, which are bolted together after being placed on the shaft.
+
+_Dimensions of Box Couplings._
+
+  D     = diameter of shaft.
+  T     = thickness of metal in box.
+  L     = length of box for butt coupling.
+  L_{1} = length of box for lap coupling.
+  _l_   = length of lap.
+  D_{1} = diameter of shaft at lap.
+
+  +---------------------------------------------------------------+
+  |   D   | 1-1/2  |    2   |  2-1/2  |   3   |   3-1/2  |   4    |
+  +-------+--------+--------+---------+-------+----------+--------+
+  | T     | 1-1/8  | 1-5/16 | 1-1/2   | 1-3/4 |  1-15/16 |  2-1/8 |
+  | L     | 5-3/4  | 7      | 8-1/4   | 9-1/2 | 10-3/4   | 12     |
+  | L_{1} | 4-1/8  | 5-1/4  | 6-3/8   | 7-1/2 |  8-5/8   |  9-3/4 |
+  | _l_   | 1-7/16 | 1-7/8  | 2-5/16  | 2-3/4 |  3-3/16  |  3-5/8 |
+  | D_{2} | 2-5/16 | 3      | 3-11/16 | 4-3/8 |  5-1/16  |  5-3/4 |
+  +---------------------------------------------------------------+
+
+  +----------------------------------------------+
+  |   D   |  4-1/2  |   5    |  5-1/2 |     6    |
+  +-------+---------+--------+--------+----------+
+  | T     |  2-5/16 |  2-1/2 |  2-3/4 |  2-15/16 |
+  | L     | 13-1/4  | 14-1/2 | 15-3/4 | 17       |
+  | L_{1} | 10-7/8  | 12     |  --    |   --     |
+  | _l_   |  4-1/16 |  4-1/2 |  --    |   --     |
+  | D_{2} |  6-7/16 |  7-1/8 |  --    |   --     |
+  +----------------------------------------------+
+
+  Slope of lap 1 in 12.
+
+    EXERCISE 20: _Solid Butt Coupling._--From the above table of
+    dimensions make a longitudinal and a transverse section of a solid
+    butt coupling for a shaft 2-1/2 inches in diameter. Scale 6 inches
+    to a foot.
+
+    EXERCISE 21: _Fairbairn's Half-Lap Coupling._--Make the same views
+    as in the last exercise of a half-lap coupling for a 3-inch shaft
+    to the dimensions in the above table. Scale 6 inches to a foot.
+
+_Flange Couplings._--The form of coupling used for the shafts of marine
+engines is shown in fig. 23. The ends of the different lengths of shaft
+have flanges forged on them, which are turned along with the shaft.
+These flanges butt against one another, and are connected by bolts.
+These bolts may be parallel or tapered; generally they are tapered. A
+parallel bolt must have a head, but a tapered bolt will act without one.
+In fig. 23 the bolts are tapered, and also provided with heads. In fig.
+14, page 17, is shown a tapered bolt without a head. The variation of
+diameter in tapered bolts is 3/8 of an inch per foot of length.
+
+[Illustration: FIG. 23.]
+
+Sometimes a projection is formed on the centre of one flange which fits
+into a corresponding recess in the centre of the other, for the purpose
+of ensuring the shafts being in line.
+
+Occasionally a cross-key is fitted in between the flanges, being sunk
+half into each, for the purpose of diminishing the shearing action on
+the bolts.
+
+    EXERCISE 22: _Marine Coupling._--Draw the elevation and section of
+    the coupling shown in fig. 23; also an elevation looking in the
+    direction of the arrow. Scale 3 inches to a foot.
+
+The following table gives the dimensions of a few marine couplings taken
+from actual practice.
+
+_Examples of Marine Couplings._
+
+  +--------------------------------------------------------------------+
+  | Diameter of shaft  |2-3/8 | 9-3/4 | 12-7/8 |16-1/2 | 22-1/2 |  23  |
+  +--------------------+------+-------+--------+-------+--------+------+
+  |Diameter of flange  |  6   |  19   |   24   |  32   |   35   |  38  |
+  |Thickness of flange |  1   | 2-3/4 |  3-1/8 | 4-1/4 |    6   |   5  |
+  |Diameter of bolts   | 3/4  | 2-3/4 | 2-11/16| 3-1/2 |  4-1/4 | 4-1/4|
+  |Number of bolts     |  3   |   6   |    6   |   8   |    9   |   8  |
+  |Diameter of bolt    |      |       |        |       |        |      |
+  |  circle            |4-1/8 | 14-1/8|18-13/16|  25   | 28-3/4 |30-3/8|
+  +--------------------------------------------------------------------+
+
+  All the above dimensions are in inches.
+
+    EXERCISE 23.--Select one of the couplings from the above table, and
+    make the necessary working drawings for it to a suitable scale.
+
+The cast-iron flange coupling is shown in fig. 24. In this kind of
+coupling a cast-iron centre or boss provided with a flange is secured to
+the end of each shaft by a sunk key driven from the face of the flange.
+These flanges are then connected by bolts and nuts as in the marine
+coupling.
+
+To ensure the shafts being in line the end of one projects into the
+flange of the other.
+
+In order that the face of each flange may be exactly perpendicular to
+the axis of the shaft they should be 'faced' in the lathe, after being
+keyed on to the shaft.
+
+If the coupling is in an exposed position, where the nuts and bolt-heads
+would be liable to catch the clothes of workmen or an idle driving band
+which might come in the way, the flanges should be made thicker, and be
+provided with recesses for the nuts and bolt-heads.
+
+[Illustration: FIG. 24.]
+
+_Dimensions of Cast-iron Flange Couplings._
+
+  +--------------------------------------------------------------------+
+  |        |Diameter|         |        |Depth |      |Diameter|Diameter|
+  |Diameter|  of    |Thickness|Diameter|  at  |Number|   of   | of bolt|
+  |of shaft| flange |of flange| of boss| boss |  of  | bolts  | circle |
+  |   D    |    F   |    T    |   B    |   L  | bolts|   d    |    C   |
+  +--------|--------|---------|--------|------|------|--------|--------+
+  | 1-1/2  |  7-1/4 |    7/8  | 3-1/2  |2-5/8 |   3  |5/8     | 5-1/2  |
+  | 2      |  8-7/8 |  1-1/16 | 4-3/8  |3-3/16|   4  |     3/4| 6-3/4  |
+  | 2-1/2  | 10-5/8 |  1-1/4  | 5-5/16 |3-3/4 |   4  |7/8     | 8-1/8  |
+  | 3      | 12-3/8 |  1-7/16 | 6-1/4  |4-5/16|   4  |      1 | 9-1/2  |
+  | 3-1/2  | 13-1/8 |  1-5/8  | 7-1/8  |4-7/8 |   4  | 1      |10-5/16 |
+  | 4      | 14     |  1-3/4  | 8      |5-7/16|   6  |      1 |11-1/4  |
+  | 4-1/2  | 15-5/8 |  2      | 8-7/8  |6     |   6  |1-1/8   |12-1/2  |
+  | 5      | 17-3/8 |  2-1/8  | 9-13/16|6-5/8 |   6  |   1-1/4|13-13/16|
+  | 5-1/2  | 18-1/4 |  2-5/16 |10-3/4  |7-1/4 |   6  |1-1/4   |14-3/4  |
+  | 6      | 19-7/8 |  2-1/2  |11-5/8  |7-3/4 |   6  |   1-3/8|   16   |
+  +--------------------------------------------------------------------+
+
+The projection of the shaft _p_ varies from 1/4 inch in the small shafts
+to 1/2 inch in the large ones.
+
+    EXERCISE 24: _Cast-iron Flange Coupling._--Draw the views shown in
+    fig. 24 of a cast-iron flange coupling, for a shaft 4-1/2 inches in
+    diameter, to the dimensions given in the above table. Scale 4 inches
+    to a foot.
+
+
+
+
+VII. BEARINGS  FOR  SHAFTS.
+
+
+An example of a very simple form of bearing is shown in fig. 25, which
+represents a brake shaft carrier of a locomotive tender. The bearing in
+this example is made of cast iron and in one piece. Through the
+oval-shaped flange two bolts pass for attaching the bearing to the
+wrought-iron framing of the tender. With this form of bearing there is
+no adjustment for wear, so that when it becomes worn it must be renewed.
+
+[Illustration: FIG. 25.]
+
+    EXERCISE 25: _Brake Shaft Carrier._--Draw the elevation and
+    sectional plan of the bearing shown in fig. 25. Draw also a
+    vertical section through the axis. The latter view to be projected
+    from the first elevation. Scale 6 inches to a foot.
+
+_Pillow Block_, _Plummer Block_, or _Pedestal_.--The ordinary form of
+plummer block is represented in fig. 26. A is the block proper, B the
+sole through which pass the holding-down bolts. C is the cap. Between
+the block and the cap is the brass bush, which is in halves, called
+_brasses_ or _steps_. The bed for the steps in this example is
+cylindrical, and is prepared by the easy process of boring. The steps
+are not supported throughout their whole length, but at their ends only
+where fitting strips are provided as shown. As the wear on a step is
+generally greatest at the bottom, it is made thicker there than at the
+sides, except where the fitting strips come in. To prevent the steps
+turning within the block they are generally furnished with lugs, which
+enter corresponding recesses in the block and cover.
+
+[Illustration: FIG. 26]
+
+In the block illustrated the journal is lubricated by a _needle
+lubricator_; this consists of an inverted glass bottle fitted with a
+wood stopper, through a hole in which passes a piece of wire, which has
+one end in the oil within the bottle, and the other resting on the
+journal of the shaft. The wire or needle does not fill the hole in the
+stopper, but if the needle is kept from vibrating the oil does not
+escape owing to capillary attraction. When, however, the shaft rotates,
+the needle begins to vibrate, and the oil runs down slowly on to the
+journal; oil is therefore only used when the shaft is running.
+
+    EXERCISE 26: _Pillow Block for a Four-inch Shaft._--Draw the views
+    shown of this block in fig. 26. Make also separate drawings, full
+    size, of one of the steps. Scale 6 inches to a foot.
+
+_Proportions of Pillow Blocks._--The following rules may be used for
+proportioning pillow blocks for shafts up to 8 inches diameter. It
+should be remembered that the proportions used by different makers vary
+considerably, but the following rules represent average practice.
+
+  Diameter of journal                     = _d_.
+  Length of journal                       = _l_.
+  Height to centre                        = 1.05_d_ + .5.
+  Length of base                          = 3.6_d_ + 5.
+  Width of base                           = .8_l_.
+      "    block                          = .7_l_.
+  Thickness of base                       = .3_d_ + .3.
+      "        cap                        = .3_d_ + .4.
+  Diameter of bolts                       = .25_d_ + .25.
+  Distance between centres of cap bolts   = 1.6_d_ + 1.5.
+      "         "             base bolts  = 2.7_d_ + 4.2.
+  Thickness of step at bottom             = _t_ = .09_d_ + .15.
+      "         "      sides              = 3/4 _t_.
+
+The length of the journal varies very much in different cases, and
+depends upon the speed of the shaft, the load which it carries, the
+workmanship of the journal and bearing, and the method of lubrication.
+For ordinary shafting one rule is to make _l_ = _d_ + 1. Some makers use
+the rule _l_ = 1.5_d_; others make _l_ = 2_d_.
+
+    EXERCISE 27: _Design for Pillow Block._--Make the necessary
+    working drawings for a pillow block for a shaft 5 inches in
+    diameter, and having a journal 7 inches long.
+
+[Illustration: FIG. 27.]
+
+_Brackets._--When a pillow block has to be fixed to a wall or column a
+bracket such as that shown in figs. 27 and 28 may be used. The pillow
+block rests between the _joggles_ A A, and is bolted down to the bracket
+and secured in addition with keys at the ends of the base of the block,
+in the same manner as is shown, for the attachment of the bracket to
+the column.
+
+    EXERCISE 28: _Pillar Bracket._--Fig. 27 shows a side elevation and
+    part horizontal section, and fig. 28 shows an end elevation of a
+    pillar bracket for carrying a pillow block for a 3-inch shaft.
+    Draw these views _properly projected from one another_, showing
+    the pillow block, which is to be proportioned by the rules given
+    on page 32. Draw also a plan of the whole. Scale 4 inches to a
+    foot.
+
+[Illustration: FIG. 28.]
+
+_Hangers._--When a shaft is suspended from a ceiling it is carried by
+hangers, one form of which is shown in fig. 29, and which will be
+readily understood. The cap of the bearing, it will be noticed, is
+secured by means of a bolt, and also by a square key.
+
+    EXERCISE 29: _Shaft Hanger._--Draw the two elevations shown in
+    fig. 29, and also a sectional plan. The section to be taken at a
+    point 5 inches above the centre of the shaft. Scale 6 inches to a
+    foot.
+
+_Wall Boxes._--In passing from one part of a building to another a shaft
+may have to pass through a wall. In that case a neat appearance is given
+to the opening and a suitable support obtained for a pillow block by
+building into the wall a _wall box_, one form of which is shown in fig.
+30.
+
+    EXERCISE 30: _Wall Box._--Draw the views of the wall box shown in
+    fig. 30, and also a sectional plan; the plane of section to pass
+    through the box a little above the joggles for the pillow block.
+    Scale 3 inches to a foot.
+
+[Illustration: FIG. 29.]
+
+[Illustration: FIG. 30.]
+
+
+
+
+VIII. PULLEYS.
+
+
+_Velocity Ratio in Belt Gearing._--Let two pulleys A and B be connected
+by a belt, and let their diameters be D_{1} and D_{2}; and let their
+speeds, in revolutions per minute, be N_{1} and N_{2} respectively. If
+there is no slipping, the speeds of the rims of the pulleys will be the
+same as that of the belt, and will therefore be equal. Now the speed of
+the rim of A is evidently = D_{1} × 3.1416 × N_{1}; while the speed of
+the rim of B is = D_{2} × 3.1416 × N_{2}. Hence D_{1} × 3.1416 × N_{1} =
+D_{2} × 3.1416 × N_{2}, and therefore
+
+    N_{1}   D_{2}
+    ----- = -----.
+    N_{2}   D_{1}
+
+_Pulleys for Flat Bands._--In cross section the rim of a pulley for
+carrying a flat band is generally curved as shown in figs. 31 and 32,
+but very often the cross section is straight. The curved cross section
+of the rim tends to keep the band from coming off as long as the pulley
+is rotating. Sometimes the rim of the pulley is provided with flanges
+which keep the band from falling off.
+
+Pulleys are generally made entirely of cast iron, but a great many
+pulleys are now made in which the centre or nave only is of cast iron,
+the arms being of wrought iron cast into the nave, while the rim is of
+wrought sheet iron.
+
+The arms of pulleys when made of wrought iron are invariably straight,
+but when made of cast iron they are very often curved. In fig. 31, which
+shows an arrangement of two cast-iron pulleys, the arms are straight;
+while in fig. 32, which shows another cast-iron pulley, the arms are
+curved. Through unequal cooling, and therefore unequal contraction of a
+cast-iron, pulley in the mould, the arms are generally in a state of
+tension or compression; and if the arms are straight they are very
+unyielding, so that the result of this initial stress is often the
+breaking of an arm, or of the rim where it joins an arm. With the curved
+arm, however, its shape permits it to yield, and thus cause a diminution
+of the stress due to unequal contraction.
+
+The cross section of the arms of cast-iron pulleys is generally
+elliptical.
+
+[Illustration: Fig. 31.]
+
+    EXERCISE 31: _Fast and Loose Pulleys_.--Fig. 31 shows an
+    arrangement of fast and loose pulleys. A is the fast pulley,
+    secured to the shaft C by a sunk key; B is the loose pulley, which
+    turns freely upon the shaft. The loose pulley is prevented from
+    coming off by a collar D, which is secured to the shaft by a
+    tapered pin as shown. The nave or boss of the loose pulley is here
+    fitted with a brass liner, which may be renewed when it becomes
+    too much worn. Draw the elevations shown, completing the left-hand
+    one. Scale 6 inches to a foot.
+
+    By the above arrangement of pulleys a machine may be stopped or
+    set in motion at pleasure. When the driving band is on the loose
+    pulley the machine is at rest, and when it is on the fast pulley
+    the machine is in motion. The driving band is shifted from the one
+    pulley to the other by pressing on that side of the band which is
+    advancing towards the pulleys.
+
+[Illustration: FIG. 32.]
+
+    EXERCISE 32: _Cast-iron Pulley with Curved Arms and Cone
+    Keys_.--Draw a complete side elevation and a complete cross
+    section of the pulley represented in fig. 32 to a scale of 3
+    inches to a foot. In drawing the side elevation of the arms first
+    draw the centre lines as shown; next draw three circles for each
+    arm, one at each end and one in the middle; the centres of these
+    circles being on the centre line of the arm, and their diameters
+    equal to the widths of the arm at the ends and at the middle
+    respectively. Arcs of circles are then drawn to touch these three
+    circles. The centres and radii of these arcs may be found by
+    trial. The cone keys for securing the pulley to the shaft were
+    described on p. 23.
+
+_Pulleys for Ropes_.--Ropes made of hemp are now extensively used for
+transmitting power. These ropes vary in diameter from 1 inch to 2
+inches, and are run at a speed of about 4,500 feet per minute. The
+pulleys for these ropes are made of cast iron, and have their rims
+grooved as shown in fig. 33, which is a cross section of the rim of a
+pulley carrying three ropes. The angle of the V is usually 45°, and the
+rope rests on the sides of the groove, and not on the bottom, so that
+it is wedged in, and has therefore a good hold of the pulley. The
+diameter of the pulley should not be less than 30 times the diameter of
+the rope. Two pulleys connected by ropes should not be less than thirty
+feet apart from centre to centre, but this distance may be as much as
+100 feet.
+
+[Illustration: FIG. 33.]
+
+    EXERCISE 33: _Section of Rim of Rope Pulley._--Draw, half size,
+    the section of the rim of a rope pulley shown in fig. 33.
+
+
+
+
+IX. TOOTHED WHEELS.
+
+
+_Pitch Surfaces of Spur Wheels._--Let two smooth rollers be placed in
+contact with their axes parallel, and let one of them rotate about its
+axis; then if there is no slipping the other roller will rotate in the
+opposite direction with the same surface velocity; and if D_{1}, D_{2}
+be the diameters of the rollers, and N_{1}, N_{2} their speeds in
+revolutions per minute, it follows as in belt gearing that--
+
+    N_{1}   D_{2}
+    ----- = -----.
+    N_{2}   D_{1}
+
+If there be considerable resistance to the motion of the follower
+slipping may take place, and it may stop. To prevent this the rollers
+may be provided with teeth; then they become _spur wheels_; and if the
+teeth be so shaped that the ratio of the speeds of the toothed rollers
+at any instant is the same as that of the smooth rollers, the surfaces
+of the latter are called the _pitch surfaces_ of the former.
+
+_Pitch Circle._--A section of the pitch surface of a toothed wheel by a
+plane perpendicular to its axis is a circle, and is called a _pitch
+circle_. We may also say that the pitch circle is the edge of the pitch
+surface. The pitch circle is generally traced on the side of a toothed
+wheel, and is rather nearer the points of the teeth than the roots.
+
+_Pitch of Teeth._--The distance from the centre of one tooth to the
+centre of the next, or from the front of one to the front of the next,
+_measured at the pitch circle_, is called the _pitch of the teeth_. If D
+be the diameter of the pitch circle of a wheel, _n_ the number of teeth,
+and _p_ the pitch of the teeth, then D × 3.1416 = _n_ × _p_.
+
+[Illustration: FIG. 34.]
+
+By the diameter of a wheel is meant the diameter of its pitch circle.
+
+_Form and Proportions of Teeth._--The ordinary form of wheel teeth is
+shown in fig. 34. The curves of the teeth should be cycloidal curves,
+although they are generally drawn in as arcs of circles. It does not
+fall within the scope of this work to discuss the correct forms of wheel
+teeth. The student will find the theory of the teeth of wheels clearly
+and fully explained in Goodeve's 'Elements of Mechanism,' and in Unwin's
+'Machine Design.'
+
+The following proportions for the teeth of ordinary toothed wheels may
+be taken as representing average practice:--
+
+  Pitch of teeth             = _p_   = arc _a b c_ (fig. 34).
+  Thickness of tooth         = _b c_ = .48_p_.
+  Width of space             = _a b_ = .52_p_.
+  Total height of tooth              = _h_ = .7_p_.
+  Height of tooth above pitch line   = _k_ = .3_p_.
+  Depth of tooth below pitch line    = _l_ = .4_p_.
+  Width of tooth                     = 2_p_ to 3_p_.
+
+    EXERCISE 34: _Spur Wheel._--Fig. 35 shows the elevation and
+    sectional plan of a portion of a cast-iron spur wheel. The diameter
+    of the pitch circle is 23-7/8 inches, and the pitch of the teeth is
+    1-1/2 inches, so that there will be 50 teeth in the wheel. The
+    wheel has six arms. Draw a complete elevation of the wheel and a
+    half sectional plan, also a half-plan without any section. Draw
+    also a cross section of one arm. Scale 4 inches to a foot.
+
+[Illustration: FIG. 35.]
+
+_Mortise Wheels._--When two wheels gearing together run at a high speed
+the teeth of one are made of wood. These teeth, or cogs, as they are
+generally called, have tenons formed on them, which fit into mortises in
+the rim of the wheel. This wheel with the wooden teeth is called a
+_mortise wheel_. An example of a mortise wheel is shown in fig. 36.
+
+[Illustration: FIG. 36.]
+
+_Bevil Wheels._--In bevil wheels the pitch surfaces are parts of cones.
+Bevil wheels are used to connect shafts which are inclined to one
+another, whereas spur wheels are used to connect parallel shafts. In
+fig. 36 is shown a pair of bevil wheels in gear, one of them being a
+mortise wheel. At (_a_) is a separate drawing, to a smaller scale, of
+the pitch cones. The pitch cones are shown on the drawing of the
+complete wheels by dotted lines.
+
+The diameters of bevil wheels are the diameters of the bases of their
+pitch cones.
+
+    EXERCISE 35: _Pair of Bevil Wheels._--Draw the sectional elevation
+    of the bevil wheels shown in gear in fig. 36. Commence by drawing
+    the centre lines of the shafts, which in this example are at right
+    angles to one another; then draw the pitch cones shown by dotted
+    lines. Next put in the teeth which come into the plane of the
+    section, then complete the sections of the wheels. The pinion or
+    smaller wheel has 25 teeth, and the wheel has 50 teeth, which makes
+    the pitch a little over 3 inches. Each tooth of the mortise wheel
+    is secured as shown by an iron pin 5/16 inch diameter. Scale 3
+    inches to a foot.
+
+
+
+
+X. CRANKS AND CRANKED SHAFTS.
+
+
+The most important application of the crank is in the steam-engine,
+where the reciprocating rectilineal motion of the piston is converted
+into the rotary motion of the crank-shaft by means of the crank and
+connecting rod.
+
+At one time steam-engine cranks were largely made of cast iron, now they
+are always made of wrought iron or steel. The crank is either forged in
+one piece with the shaft, or it is made separately and then keyed to it.
+
+_Overhung Crank._--Fig. 37 shows a wrought-iron overhung crank. A is the
+crank-shaft, B the crank arm, provided at one end with a boss C, which
+is bored out to fit the shaft; at the other end of the crank arm is a
+boss D, which is bored out to receive the crank-pin E, which works in
+one end of the connecting rod. The crank is secured to the shaft by the
+sunk key F. It is also good practice to _shrink_ the crank on to the
+shaft. The process of shrinking consists of boring out the crank a
+little smaller than the shaft, and then heating it, which causes it to
+expand sufficiently to go on to the shaft. As the crank cools, it
+shrinks and grips the shaft firmly. The crank may also be shrunk on to
+the crank-pin, the latter being then riveted over as shown in fig. 37.
+
+[Illustration: FIG. 37.]
+
+A good plan to adopt in preference to the shrinking process is to force
+the parts together by hydraulic pressure. This method is adopted for
+placing locomotive wheels on their axles, and for putting in crank-pins.
+As to the amount of pressure to be used, the practice is to allow a
+force of 10 tons for every inch of diameter of the pin, axle, or shaft.
+
+Instead of being riveted in, the crank pin may be prolonged and screwed,
+and fitted with a nut. Another plan is to put a cotter through the crank
+and the crank-pin.
+
+The distance from the centre of the crank-shaft to the centre of the
+crank-pin is called the radius of the crank. The _throw_ of the crank is
+twice the radius. In a direct-acting engine the throw of the crank is
+equal to the stroke of the piston.
+
+    EXERCISE 36: _Wrought-iron Overhung Crank._--Draw the two
+    elevations shown in fig. 37, also a plan. Scale 1-1/2 inches
+    to a foot.
+
+    _Proportions of Overhung Cranks._
+
+      D   = diameter of shaft.
+      _d_ =    "       crank-pin.
+      Length of large boss = .9 D.
+      Diameter      "      = 1.8 D.
+      Length of small boss = 1.1 _d_.
+      Diameter      "      = 1.8 _d_.
+      Width of crank arm at centre of shaft     = 1.3 D.
+           "           "              crank-pin = 1.5 _d_.
+      The thickness of the crank arm may be roughly taken as = .7 D.
+
+    EXERCISE 37.--Design a wrought-iron crank for an engine having a
+    stroke of 4 feet. The crank-shaft is 9 inches in diameter, and
+    the crank-pin is 4-3/4 inches in diameter and 6-1/2 inches long.
+
+[Illustration: FIG. 38.]
+
+_Locomotive Cranked Axle._--As an example of a cranked shaft we take the
+cranked axle for a locomotive with inside cylinders shown in fig. 38;
+here the crank and shaft or axle are forged in one piece. A is the wheel
+seat, B the journal, C the crank-pin, and D and E the crank arms. Only
+one half of the axle is shown in fig. 38, but the other half is exactly
+the same. The cranks on the two halves are, however, at right angles to
+one another. The ends of the crank arms are turned in the lathe, the
+crank-pin ends being turned at the same time as the axle, and the other
+ends at the same time as the crank-pin. This consideration determines
+the centres for the arcs shown in the end view.
+
+    EXERCISE 38.--Draw to a scale of 2 inches to a foot the side and
+    end elevations of the locomotive cranked axle partly shown in
+    fig. 38. The distance between the centre lines of the cylinders
+    is 2 feet.
+
+[Illustration: FIG. 39.]
+
+_Built-up Cranks._--The form of cranked shaft shown in fig. 38 is
+largely used for marine engines, but for the very powerful engines now
+fitted in large ships this design of shaft is very unreliable, the
+built-up crank shown in fig. 39 being preferred, although it is much
+heavier than the other. It will be seen from the figure that the shaft,
+crank arms, and crank-pin are made separately. The arms are shrunk on to
+the pin and the shaft, and secured to the latter by sunk keys. These
+heavy shafts and cranks are generally made of steel.
+
+    EXERCISE 39.--Keeping to the dimensions marked in fig. 39, draw
+    the views there shown of a built-up crank-shaft for a marine
+    engine. Scale 3/4 inch to a foot.
+
+
+
+
+XI. ECCENTRICS.
+
+
+The _eccentric_ is a particular form of crank, being a crank in which
+the crank-pin is large enough to embrace the crank-shaft. In the
+eccentric what corresponds to the crank-pin is called the sheave or
+pulley. The advantage which an eccentric possesses over a crank is that
+the shaft does not require to be divided at the point where the
+eccentric is put on. The crank, however, has this advantage over the
+eccentric, namely, that it can be used for converting circular into
+reciprocating motion, or _vice versâ_, while the eccentric can only be
+used for converting circular into reciprocating motion. This is owing to
+the great leverage at which the friction of the eccentric acts.
+
+The chief application of the eccentric is in the steam-engine, where it
+is used for working the valve gear.
+
+To permit of the sheave being placed on the shaft without going over the
+end (which could not be done at all in the case of a cranked axle, and
+would be a troublesome operation in most cases) it is generally made in
+two pieces, as shown in fig. 40, which represents one of the eccentrics
+of a locomotive. The two parts of the sheave are connected by two cotter
+bolts. The part which embraces the sheave is called the eccentric strap,
+and corresponds to, and is, in fact, a connecting rod end: the rod
+proceeding from this is called the eccentric rod.
+
+The distance from the centre of the sheave to the centre of the shaft is
+called the _radius_ or _eccentricity_ of the eccentric. The _throw_ is
+twice the eccentricity.
+
+The sheave is generally made of cast iron. The strap may be of brass,
+cast iron, or wrought iron; when the strap is made of wrought iron it is
+commonly lined with brass.
+
+[Illustration: FIG. 40.]
+
+    EXERCISE 40: _Locomotive Eccentric._--In fig. 40 D E is the
+    sheave, F H the strap, and K the eccentric rod. The sheave and
+    strap are made of cast iron, and the eccentric rod is made of
+    wrought iron. (_a_) is a vertical cross section through the
+    oil-box of the strap; (_b_) is a plan of the end of the eccentric
+    rod and part of the strap. All the nuts are locked by means of
+    cotters. Draw first the elevation, partly in section as shown.
+    Next draw two end elevations, one looking each way. Afterwards
+    draw a horizontal section through the centre, and also a plan.
+    Scale 4 inches to a foot.
+
+
+
+
+XII. CONNECTING RODS.
+
+
+The most familiar example of the use of a connecting rod is in the
+steam-engine, where it is used to connect the rotating crank with the
+reciprocating piston. The rod itself is made of wrought iron or steel,
+and is generally circular or rectangular in section. The ends of the rod
+are fitted with steps, which are held together in a variety of ways.
+
+_Strap End._--A form of connecting rod end, which is not so common as it
+used to be, is shown in fig. 41. At (_a_) is shown a longitudinal
+section with all the parts put together, while at (_b_), (_c_), _(d)_
+and (_e_) the details are shown separately. A B is the end of the rod
+which butts against the brass bush C D, which is in two pieces. A
+_strap_ E passes round the bush and on to the end of the rod as shown.
+The arms of the strap have rectangular holes in them, which are not
+quite opposite a similar hole in the rod when the parts are put
+together. If a wedge or _cotter_ F be driven into these three holes they
+will tend to come into line, and the parts of the bush will be pressed
+together. To prevent the cotter opening out the strap, and to increase
+the sliding surface, a _gib_ H is introduced. The gib is provided with
+horns at its ends to keep it in its place. Sometimes two gibs are used,
+one on each side of the cotter; this makes the sliding surface on both
+sides of the cotter the same. The cotter is secured by a set screw K.
+The unsectioned portion of fig. (_a_) to the right of the gib, or to the
+left of the cotter, is called the _clearance_ or _draught._
+
+[Illustration: FIG. 41.]
+
+    EXERCISE 41: _Connecting Rod End._--Make the following views of
+    the connecting rod end illustrated by fig. 41. First, a vertical
+    section, the same as shown at (_a_). Second, a horizontal section.
+    Third, side elevation. Fourth, a plan. Or the first and third
+    views may be combined in a half vertical section and half
+    elevation; and the second and fourth views may be combined in
+    a half horizontal section and half plan.
+
+    All the dimensions are to be taken from the detail drawings (_b_),
+    (_c_), (_d_), and (_e_), _but the details need not be drawn
+    separately_. The brass bush is shown at (_d_) by half elevation,
+    half vertical section, half plan, and half horizontal section.
+    The draught or clearance is 7-16ths of an inch.
+
+_Box End._--At (_a_), fig. 42, is shown what is known as a box end for a
+connecting rod. The part which corresponds to the loose strap in the
+last example is here forged in one piece with the connecting rod. In
+this form the brass bush is provided with a flange all round on one
+side, but on the opposite side the flange is omitted except at one end;
+this is to allow of the bush being placed within the end of the rod. The
+construction of the bush will be understood by reference to the sketch
+shown at (_b_). The bush is in two parts, which are pressed tightly
+together by means of a cotter. This cotter is prevented from slackening
+back by two set screws. Each set screw is cut off square at the point,
+and presses on the flat bottom of a very shallow groove cut on the side
+of the cotter.
+
+The top, bottom, and ends of this box end are turned in the lathe at the
+same time as the rod itself; this accounts for the curved sections of
+these parts.
+
+It is clear from the construction of a box end that it is only suitable
+for an overhung crank.
+
+    EXERCISE 42: _Locomotive Connecting Rod._--In fig. 42 is shown a
+    connecting rod for an outside cylinder locomotive. (_a_) is the
+    crank-pin end, and (_c_) the cross-head end. The end (_a_) has just
+    been described under the head 'box end.' We may just add that in
+    this particular example the brass bush is lined with white metal as
+    shown, and that the construction of the oil-box is the same as that
+    on the coupling rod end shown in fig. 44. The end (_c_) is forked,
+    and through the prongs of the fork passes the cross-head pin, of
+    which a separate dimensioned drawing is shown at (_d_). Observe
+    that the tapered parts A and B of this pin are parts of the same
+    cone. The rotation of the pin is prevented by a small key as shown.
+    The cross-head pin need not be drawn separately, and the isometric
+    projection of the bush at (_b_) may be omitted, but all the other
+    views shown are to be drawn to a scale of 6 inches to a foot.
+
+_Marine Connecting Rod._--The form of connecting rod shown in fig. 43 is
+that used in marine engines, but it is also used extensively in land
+engines. A B is the crank-pin end, and C the cross-head end. The end A B
+is forged in one piece, and after it is turned, planed, and bored it is
+slotted across, so as to cut off the cap A. The parts A and B are held
+together by two bolts as shown. This end of the rod is fitted with brass
+steps, which are lined with white metal. The cross-head end is forked,
+and through the prongs of the fork passes a pin D, which also passes
+through the cross-head, which is forged on to the piston rod or attached
+to it in some other way.
+
+[Illustration: FIG. 42.]
+
+[Illustration: FIG. 43.]
+
+    EXERCISE 43: _Marine Connecting Rod._--Draw all the views shown in
+    fig. 43 of one form of marine connecting rod. For detail drawings
+    of the locking arrangement for the nuts see fig. 19, page 21. Scale
+    4 inches to a foot.
+
+_Coupling Rods._--A rod used to transmit the motion of one crank to
+another is called a _coupling rod_. A familiar example of the use of
+coupling rods will be found in the locomotive. Coupling rods are made of
+wrought iron or steel, and are generally of rectangular section. The
+ends are now generally made solid and lined with solid brass bushes,
+_without any adjustment for wear_. This form of coupling rod end is
+found to answer very well in locomotive practice where the workmanship
+and arrangements for lubrication are excellent. When the brass bush
+becomes worn it is replaced by a new one.
+
+Fig. 44 shows an example of a locomotive coupling rod end for an outside
+cylinder engine. In this case it is desirable to have the crank-pin
+bearings for the coupling rods as short as possible, for a connecting
+rod and coupling rod in this kind of engine work side by side on the
+same crank-pin, which, being overhung, should be as short as convenient
+for the sake of strength. The requisite bearing surface is obtained by
+having a pin of large diameter. The brass bush is prevented from
+rotating by means of the square key shown. The oil-box is cut out of the
+solid, and has a wrought-iron cover slightly dovetailed at the edges.
+This cover fits into a check round the top inner edge of the box, which
+is originally parallel, but is made to close on the dovetailed edges of
+the cover by riveting. A hole in the centre of this cover, which gives
+access to the oil-box, is fitted with a screwed brass plug. The brass
+plug has a screwed hole in the centre, through which oil may be
+introduced to the box. Dust is kept out of the oil-box by screwing into
+the hole in the brass plug a common cork. The oil is carried slowly but
+regularly from the oil-box over to the bearing by a piece of cotton
+wick.
+
+[Illustration: FIG. 44.]
+
+    EXERCISE 44: _Coupling Rod End._--Draw first the side elevation and
+    plan, each partly in section as shown in fig. 44. Then instead of
+    the view to the left, which is an end elevation partly in section,
+    draw a complete end elevation looking to the right, and also a
+    complete vertical cross section through the centre of the bearing.
+    Scale 6 inches to a foot.
+
+
+
+
+XIII. CROSS-HEADS.
+
+
+An example of a steam-engine cross-head is shown in fig. 45. A is the
+end of the piston rod which has forged upon it the cross-head B. The
+cross-head pin shown at (_d_), fig. 42, and to which the connecting rod
+is attached, works in the bearing C. Projecting pieces D, forged on the
+top and bottom of the cross-head, carry the slide blocks E which work on
+the slide bars, and thus guide the motion of the piston rod.
+
+[Illustration: FIG. 45.]
+
+    EXERCISE 45: _Locomotive Cross-head._--In fig. 45 are shown side
+    and end elevations, partly in section, of the cross-head and slide
+    blocks for an outside cylinder locomotive. Draw these views half
+    size, showing also on the end elevation the cross-head pin and a
+    vertical section of the connecting rod end from fig. 42. The bush
+    in the cross-head which forms the bearing for the cross-head pin is
+    of wrought iron, case-hardened, and is prevented from rotating by
+    the key shown. The cross-head is of wrought iron, and the slide
+    blocks are of cast iron, and are fitted with white metal strips as
+    shown. A short brass tube leads oil from the upper slide block into
+    a hole in the cross-head as shown, which carries it to a slot in
+    the bush which distributes it over the cross-head pin.
+
+
+
+
+XIV. PISTONS.
+
+
+A _piston_ is generally a cylindrical piece which slides backwards and
+forwards inside a hollow cylinder. The piston may be moved by the action
+of fluid pressure upon it as in a steam-engine, or it may be used to
+give motion to a fluid as in a pump.
+
+A piston is usually attached to a rod, called a _piston rod_, which
+passes through the end of the cylinder inside which the piston works,
+and which serves to transmit the motion of the piston to some piece
+outside the cylinder, or _vice versâ_.
+
+[Illustration: FIG. 46.]
+
+A _plunger_ is a piston made in one piece with its piston rod, the
+piston and the rod being of the same diameter.
+
+A piston which is provided with one or more valves which allow the
+fluid to pass through it from one side to the other is called a
+_bucket_.
+
+_Simple Piston._--The simplest form of piston is a plain cylinder
+fitting accurately another, inside which it moves. Such a piston works
+with very little friction, but as there is no adjustment for wear, such
+a piston is not suitable for a high fluid pressure if it has to work
+constantly. This simple form of piston is used in the steam-engine
+indicator, and also in pumps.
+
+Fig. 46 shows the piston of the circulation pump of a marine engine.
+A is the cast-iron casing or barrel of the pump; B is a brass liner
+fitting tightly into the former at its ends, and secured by eight
+screwed Muntz metal pins C, four at each end; D is the piston, which is
+made of brass, and is attached to a Muntz metal piston rod E. The liner
+is bored out smooth and true from end to end, and the piston is turned
+so as to be a sliding fit to the liner. The wear in this form of piston
+is diminished by making the rubbing surface large.
+
+    EXERCISE 46: _Piston for Circulating Pump._--Draw the vertical
+    sectional elevation of the piston, &c., shown in fig. 46, also a
+    half plan and half horizontal section through the centre. Scale 4
+    inches to a foot.
+
+_Pump Bucket._--The next form of piston which we illustrate is shown in
+fig. 47. This represents the air-pump bucket of a marine engine. The
+bucket is made of brass, and is provided with six india-rubber disc
+valves. The rod is in this case made of Muntz metal. Air-pump rods for
+marine engines are very often made of wrought iron cased with brass. It
+will be observed that there is a wide groove around the bucket, which is
+filled with hempen rope or gasket. This gasket forms an elastic packing
+which prevents leakage. This is an old-fashioned form of packing, and is
+now only used for pump buckets.
+
+[Illustration: FIG. 47.]
+
+    EXERCISE 47: _Air-pump Bucket._--Draw the sectional elevation of
+    the air-pump bucket shown in fig. 47. Also draw a half plan looking
+    downwards and a half plan looking upwards. Scale 4 inches to a
+    foot.
+
+_Ramsbottom's Packing._--The form of packing used in the air-pump
+bucket, fig. 47, is not suitable for steam pistons. For the latter the
+packing is now always metallic. The simplest form of metallic packing is
+that known as Ramsbottom's. This form is very largely used for
+locomotive pistons, and for small pistons in many kinds of engines
+besides. A locomotive piston for an 18-inch cylinder with Ramsbottom's
+packing is shown in fig. 48. The particular piston there illustrated is
+made of brass, and is secured to a wrought-iron piston rod by a brass
+nut. Two circumferential grooves of rectangular section are turned out
+of the piston, and into these fit two corresponding rings, which may be
+of brass, cast iron, or steel. In this example the rings are of cast
+iron. These rings are first turned a little larger in diameter than the
+bore of the cylinder (in this example 1/2 inch), and then sprung over
+the piston into the groves prepared for them. Their own elasticity
+causes the rings to press outwards on the cylinder. At the point where a
+ring is split a leakage of steam will take place, but with quick-running
+pistons this leakage is unimportant. The points where the rings are cut
+should be placed diametrically opposite, so as to diminish the leakage
+of steam.
+
+[Illustration: FIG. 48.]
+
+    EXERCISE 48: _Locomotive Piston._--A part elevation and part
+    section of a locomotive piston, for a cylinder having a bore 18
+    inches in diameter, is shown in fig. 48. Draw this, and also a view
+    looking on the nut in the direction of the axis of the piston rod.
+    Scale 6 inches to a foot.
+
+    _Note._--The reason why the part of the piston rod within the
+    piston has such a quick taper is that the piston has to be taken
+    off the rod while it is in the cylinder. The cross-head being
+    forged on the end of the piston rod prevents the piston and piston
+    rod being withdrawn together.
+
+_Large Pistons._--Pistons of large diameter are generally provided with
+two cast-iron packing rings placed within the same groove. These rings
+are pressed outwards against the cylinder, and also against the sides of
+the groove by one or more springs. One form of this packing
+(Lancaster's) is shown in fig. 49. Here one spring only is used, and it
+is first made a straight spiral spring, and then bent round and its ends
+united. The action of the spring will be clearly understood from the
+illustration. For the purpose of admitting the packing rings the piston
+is divided into two parts, one the piston proper, and the other the
+_junk ring_. In fig. 49, A is the junk ring, which is secured to the
+piston by means of bolts as shown.
+
+[Illustration: FIG. 49.]
+
+    EXERCISE 49: _Marine Engine Piston._--The piston illustrated by
+    fig. 49 is for the high-pressure cylinder of a marine engine. The
+    piston, junk ring, and packing rings are of cast iron. The piston
+    rod and nut are of wrought iron, so also are the junk ring bolts.
+    The nuts for the latter are of brass. The spiral spring is made
+    from steel wire 3/8 inch diameter. An enlarged section of one of
+    the packing rings is shown at (_a_). A front elevation of the
+    locking arrangement for the piston rod nut is shown at (_b_). A
+    sectional plan of one of the nuts for the junk ring bolts is shown
+    at (_c_).
+
+    First draw the vertical section of this piston, next draw a plan,
+    one-third of which is to show the piston complete, one-third to
+    show the junk ring removed, and the remaining third to be a
+    horizontal section through between the packing rings. The details
+    (_a_) and (_c_) need not be drawn separately. Scale 3 inches to a
+    foot.
+
+_Proportions of Marine Engine Pistons._--Mr. Seaton, in his 'Manual of
+Marine Engineering,' gives the following rules for designing marine
+engine pistons:--
+
+  D   = diameter of piston in inches.
+  _p_ = effective pressure in lbs. per square inch.
+  _x_ = D/50 × [sqrt (_p_)] + 1.
+
+  Thickness of front of piston near boss        0.2  × _x_.
+       "         "         "        rim         0.17 × _x_.
+       "       back of piston                   0.18 × _x_.
+       "       boss around rod                  0.3  × _x_.
+       "       flange inside packing ring       0.23 × _x_.
+       "          "   at edge                   0.25 × _x_.
+       "       junk ring at edge                0.23 × _x_.
+       "           "     inside packing ring.   0.21 × _x_.
+       "           "     at bolt-holes          0.35 × _x_.
+       "       metal around piston edge         0.25 × _x_.
+  Breadth of packing ring                       0.63 × _x_.
+  Depth of piston at centre                     1.4  × _x_.
+  Lap of junk ring on piston                    0.45 × _x_.
+  Space between piston body and packing ring    0.3  × _x_.
+  Diameter of junk-ring bolts                   0.1  × _x_ + .25 inch.
+  Pitch of junk-ring bolts                      10 diameters.
+  Number of webs in piston                      (D + 20)/12.
+  Thickness        "                            0.18 × _x_.
+
+    EXERCISE 50: _Design for Marine Engine Piston._--Calculate by
+    Seaton's rules the dimensions for a marine engine piston 40 inches
+    in diameter, and subjected to an effective pressure of 36 lbs. per
+    square inch. Then make the necessary working drawings for this
+    piston to a scale of, say, 3 inches to a foot.
+
+    _Note._--Take the dimensions got by calculation to the nearest
+    1-16th of an inch.
+
+
+
+
+XV. STUFFING-BOXES.
+
+
+[Illustration: FIG. 50.]
+
+In fig. 50 is shown a gland and stuffing-box for the piston rod of a
+vertical engine. A B is the piston rod, C D a portion of the cylinder
+cover, and E F the _stuffing-box_. Fitting into the bottom of the
+stuffing-box is a brass bush H. The space K around the rod A B is filled
+with _packing_, of which there is a variety of kinds, the simplest
+being greased hempen rope. The packing is compressed by screwing down
+the cast-iron gland L M, which is lined with a brass bush N. In this
+case the gland is screwed down by means of three stud-bolts P, which are
+screwed into a flange cast on the stuffing-box. Surrounding the rod on
+the top of the gland there is a recess R for holding the lubricant.
+
+[Illustration: FIG. 51.]
+
+[Illustration: FIG. 52.]
+
+The object of the gland and stuffing-box is to allow the piston rod to
+move backwards and forwards freely without any leakage of steam.
+
+Fig. 51 shows a gland and stuffing-box for a horizontal rod. The
+essential difference between this example and the last is in the mode of
+lubrication. The gland flange has cast within it an oil-box which is
+covered by a lid; this lid is kept shut or open by the action of a small
+spring as shown. A piece of cotton wick (not shown in the figure) has
+one end trailing in the oil in the oil-box, while the other is carried
+over and passed down the hole A B. The wick acts as a siphon, and drops
+the oil gradually on to the rod. In this example only two bolts are used
+for screwing in the gland; and the flanges of the gland and stuffing-box
+are not circular, but oval-shaped.
+
+In the case of small rods the gland is made entirely of brass, and no
+liner is then necessary. Fig. 52 shows a form of gland and stuffing-box
+sometimes used for small rods. The stuffing-box is screwed externally,
+and carries a nut A B which moves the gland.
+
+    EXERCISE 51: _Gland and Stuffing-box for a Vertical Rod._--Draw the
+    views shown in fig. 50 to the dimensions given. Scale 6 inches to a
+    foot.
+
+    EXERCISE 52: _Gland and Stuffing-box for a Horizontal Rod._--Fig.
+    51 shows a plan, half in section, and an elevation half of which is
+    a section through the gland flange. Draw these to a scale of 6
+    inches to a foot, using the dimensions marked in the figure.
+
+    EXERCISE 53: _Screwed Gland and Stuffing-box._--Draw, full size,
+    the views shown in fig. 52 to the given dimensions.
+
+A more elaborate form of gland and stuffing-box is shown in fig. 53.
+This is for a large marine engine with inverted cylinders, such as is
+used on board large ocean steamers. The stuffing-box is cast separate
+from the cylinder cover to which it is afterwards bolted. The lubricant
+is first introduced to the oil-boxes marked A, from which it passes to
+the recess B, where it comes in contact with the piston rod. To prevent
+the lubricant from being wasted by running down the rod, the main gland
+is provided with a shallow gland and stuffing-box which is filled with
+soft cotton packing, which soaks up the lubricant.
+
+The main gland is screwed up by means of six bolts, and to prevent the
+gland from locking itself in the stuffing-box, it is necessary that the
+nuts should be turned together. This is done in a simple and ingenious
+manner. One-half of each nut is provided with teeth, and these gear with
+a toothed wheel which has a rim only; this rim is held up by a ring C.
+When one nut is turned, all the rest follow in the same direction.
+
+[Illustration: FIG. 53.]
+
+    EXERCISE 54: _Gland and Stuffing-box for Piston Rod of Large
+    Inverted Cylinder Engine._--The lower view in fig. 53 is a half
+    plan looking upwards, and a half section of the gland looking
+    downwards. The upper view is a vertical section. Complete all these
+    views and add an elevation. Scale 3 inches to a foot.
+
+    _Note._--The large nuts, the wheel, the supporting ring, and small
+    gland are made of brass.
+
+_Dimensions of Stuffing-boxes and Glands._
+
+  _d_     = diameter of rod.          _t__{1} = thickness of
+  _d__{1} = diameter of box (inside).             stuffing-box flange.
+  _l_     = length of stuffing-box    _t__{2} = thickness of gland
+              bush.                               flange.
+  _l__{1} = length of packing space.  _t__{3} = thickness of bushes in
+  _l__{2} = length of gland.                      box and gland.
+  _t_     = thickness of metal in     _d__{2} = diameter of gland bolts.
+              stuffing-box.           _n_     = number of bolts.
+
+  +----------------------------------------------------------+
+  | _d_ | _d__{1} | _l_ | _l__{1} | _l__{2} | _t_  | _t__{1} |
+  +-----+---------+-----+---------+---------+------+---------+
+  |1    |  1-3/4  |  3/4|  2      |  1-1/2  |  7/16|   1/2   |
+  |1-1/2|  2-1/2  |1-1/4|  2-5/8  |  2      |  9/16|   11/16 |
+  |2    |  3-1/2  |1-3/4|  3-1/4  |  2-1/2  | 11/16|   7/8   |
+  |2-1/2|  4-1/8  |2-1/4|  3-7/8  |  2-7/8  | 13/16| 1-1/16  |
+  |3    |  4-3/4  |2-3/4|  4-1/2  |  3-1/4  | 15/16| 1-1/4   |
+  |3-1/2|  5-1/4  |  3  |  5-1/8  |  3-5/8  |1     | 1-3/8   |
+  |4    |  5-7/8  |3-1/4|  5-3/4  |  4      |1     | 1-3/8   |
+  |4-1/2|  6-3/8  |3-1/2|  6-3/8  |  4-3/8  |1-1/16| 1-9/16  |
+  |5    |  7      |3-3/4|  7      |  4-5/8  |1-1/16| 1-9/16  |
+  |6    |  8      |4-1/4|  8-1/4  |  5      |1-1/8 | 1-11/16 |
+  +----------------------------------------------------------+
+
+  +-------------------------------------------------+
+  | _d_ |     _t__{2}     | _t__{3} | _d__{2} | _n_ |
+  +-----+-----------------+---------+---------+-----+
+  |1    | _t__{2}=_t_     |   3/16  |   7/16  |  2  |
+  |1-1/2| when gland      |   1/4   |   5/8   |  2  |
+  |2    | flange is       |   5/16  |   3/4   |  2  |
+  |2-1/2| made of cast    |   5/16  |   7/8   |  2  |
+  |3    | iron and        |   3/8   | 1       |  2  |
+  |3-1/2| _t__{2}=_t__{1} |   3/8   | 1       |  2  |
+  |4    | when gland      |   7/16  | 1       |  2  |
+  |4-1/2| flange is       |   7/16  |   7/8   |  4  |
+  |5    | made of         |   7/16  | 1       |  4  |
+  |6    | brass.          |   1/2   | 1-1/4   |  4  |
+  +-------------------------------------------------+
+
+The proportions of glands and stuffing-boxes vary considerably but the
+above table represents average practice.
+
+    EXERCISE 55:--Make the necessary working drawings for a gland and
+    stuffing-box for a locomotive engine piston rod 2-1/2 inches in
+    diameter, to the dimensions given in the table.
+
+
+
+
+XVI. VALVES.
+
+
+Professor Unwin divides valves, according to their construction into
+three classes as follows:--(1) flap valves, which bond or turn upon a
+hinge; (2) lift valves, which rise perpendicularly to the seat; (3)
+sliding valves, which move parallel to the seat.
+
+Examples of flap valves are shown in figs. 54 and 55; two forms of lift
+valves are shown in figs. 56 and 57, and in figs. 58 and 59 are shown
+two forms of slide valve. The slide valve shown in fig. 58 moves in a
+straight line, while that shown in fig. 59 (called a cock) moves in
+circle.
+
+_India-rubber Valves._--In india-rubber valves there is a grating
+covered by a piece of india-rubber, which may be rectangular, but is
+generally circular, and which is held down along one edge if
+rectangular, or at the centre if circular. Water or other fluid can pass
+freely upwards through the grating, but when it attempts to return the
+elasticity of the india-rubber, and the pressure of the water upon it,
+cause it to lie close on the grating, and thus prevent the return of the
+water. The india-rubber is prevented from rising too high by a
+perforated guard. In fig. 54 is shown an example of an india-rubber disc
+valve. A is the grating, B the india-rubber, C the guard secured to the
+grating or seat by the stud D and nut E. The grating is held in position
+by bolts and nuts F. The grating and guard are generally of brass.
+
+India-rubber disc valves are also shown on the air-pump bucket, fig. 47.
+
+    EXERCISE 56: _India-rubber Disc Valve._--Fig. 54 shows a vertical
+    section and a plan of an india-rubber disc valve. In the plan
+    one-half of the guard and india-rubber are supposed to be removed
+    so as to show the grating or seat. Draw these views, and also an
+    elevation. A detail drawing of the central stud is shown in fig.
+    16, page 18. In fig. 54 the elevation of the guard is drawn as it
+    is usually drawn in practice, but if the student has a sufficient
+    knowledge of descriptive geometry he should draw the elevation
+    completely showing the perforations. Scale 6 inches to a foot.
+
+[Illustration: FIG. 54.]
+
+[Illustration: FIG. 55.]
+
+_Kinghorn's Metallic Valve._--The action of this valve is the same as
+that of an india-rubber valve, but a thin sheet of metal (phosphor
+bronze) takes the place of the india-rubber.
+
+This valve is now largely used in the pumps of marine engines, and is
+shown in fig. 55 as applied to an air-pump bucket. Three valves like the
+one shown are arranged round the bucket.
+
+    EXERCISE 57: _Kinghorn's Metallic Valve._--Fig. 55 shows an
+    elevation and plan of one form of this valve. In the plan one-half
+    of the guard and metal sheet are supposed to be removed, so as to
+    show the grating, which in this case is part of an air-pump bucket.
+    Draw the views shown, and also a vertical section of the guard
+    through the centres of the bolts. All the parts are of brass except
+    the valve proper, which is of phosphor bronze. Scale 6 inches to a
+    foot.
+
+_Conical Disc Valves._--A very common form of valve is that shown in
+figs. 56 and 57. This form of valve consists of a disc, the edge of
+which (called the face) is conical. The conical edge of this disc fits
+accurately on a corresponding seat. The angle which the valve face makes
+with its axis is generally 45°. If the disc is raised, either by the
+action of the fluid as in the india-rubber valve, or by other means, an
+opening is formed around the disc through which the fluid can pass. The
+valve is guided in rising and falling either by three feathers
+underneath it, as in fig. 56, or by a central spindle which moves freely
+through a hole in the centre of a bridge which stretches across the
+seat, as in fig. 57. The lift of the valve is limited by a stop above
+it, which forms part of the casing containing the valve. The lift should
+in no case exceed one-fourth of the diameter of the valve, and it is
+generally much less than this. The guiding feathers (fig. 56) are
+notched immediately under the disc for the purpose of making available
+the full circumferential opening of the valve for the passage of the
+fluid. These notches also prevent the feathers from interfering with the
+turning or scraping of the valve face.
+
+Conical disc valves and their seats are nearly always made of brass.
+
+    EXERCISE 58: _Conical Disc Valves._--Draw, half size, the plans and
+    elevations shown in figs. 56 and 57. In fig. 57 the valve is shown
+    open in the elevation, and in the plan it is removed altogether in
+    order to show the seat with its guide bridge.
+
+[Illustration: Plan of Valve. FIG. 56.]
+
+[Illustration: Plan of Seat. FIG. 57.]
+
+_Simple Slide Valve._--The form of valve shown in fig. 58, often called
+the _locomotive slide valve_, is very largely used in all classes of
+steam-engines for distributing the steam in the steam cylinders. The
+valve is shown separately at (_d_), (_e_), and (_f_), while at (_a_),
+(_b_), and (_c_) is shown its connection with the steam cylinder.
+
+It will be observed that the valve itself is in the shape of a box with
+one side open, the edges of the open side being flanged. When the valve
+is in its middle position, as shown at (_a_), two of these flanged edges
+completely cover two rectangular openings S_{1} and S_{2}, called _steam
+ports_, while the hollow part of the valve is opposite to a third port
+E, called the _exhaust port_. As shown at (_a_) the piston P would be
+moving upwards and the valve downwards. By the time the piston has
+reached the top of its stroke the valve will have moved so far down as
+to partly uncover the steam port S_{1}, and admit steam from the valve
+casing C through S_{1} and the passage P_{1} to the top of the piston.
+The pressure of this steam on the top of the piston will force the
+latter down. While the above action has been going on, the port S_{2}
+will have become uncovered, and the hollow part of the valve will be
+opposite both the steam port S_{2} and the exhaust port E, so that the
+steam from the under side of the piston, and which forced the piston up,
+can now escape by the passage P_{2}, the steam port S_{2}, and the
+exhaust port E to the exhaust outlet O, and thence into the atmosphere,
+if it is a non-condensing engine, or into the condenser if it is a
+condensing engine, or into another cylinder if it is a compound engine.
+After the piston has performed, a certain part of its downward stroke,
+the valve, which has been moving downwards, will commence to move
+upwards, and when it has reached a certain point it will cover the port
+S_{1}, and shut off the supply of steam to the top of the piston. It is
+generally arranged that the steam shall be cut off before the piston
+reaches the end of the stroke. When the piston reaches the bottom of its
+stroke the valve has moved far enough up to uncover the port S_{2} and
+admit steam to the bottom of the piston, and to uncover the port S_{1}
+and allow the steam to escape from the top of the piston through the
+passage P_{1}, the port S_{1}, the port E, and outlet O. In this way the
+piston is moved up and down in the cylinder.
+
+The valve is attached to a valve spindle S by nuts as shown, the hole in
+the valve through which the spindle passes being oval-shaped to permit
+of the valve adjusting itself so as to always press on its seat.
+
+When the valve is in its middle position it generally more than covers
+the steam ports. The amount which the valve projects over the steam port
+on the outside, the valve being in its middle position, is called the
+_outside lap_ of the valve, and the amount which it projects on the
+inside is called the _inside lap_. When the term lap is used without any
+qualification, outside lap is to be understood. In fig. 58 it will be
+seen that the valve has no inside lap, and that the outside lap is
+three-eighths of an inch. The inside lap is generally small compared
+with the outside lap.
+
+[Illustration: FIG. 58.]
+
+When the piston is at the beginning of its stroke the steam port is
+generally open by a small amount called the _lead_ of the valve.
+
+The reciprocating motion of the slide valve is nearly always derived
+from an eccentric fixed on the crank-shaft of the engine. Slide valves
+are generally made of brass, bronze, or cast iron.
+
+    EXERCISE 59: _Simple Slide Valve._--At (_d_), fig. 58, is shown a
+    sectional elevation of a simple slide valve for a steam-engine, the
+    section being taken through the centre line of the valve spindle,
+    while at (_e_) is shown a cross section and elevation, and at (_f_)
+    a plan of the same. Draw all these views full size, and also a
+    sectional elevation at A B. The valve is made of brass, and the
+    valve spindle and nuts of wrought iron.
+
+    EXERCISE 60: _Slide Valve Casing, &c., for Steam-engine._--Draw,
+    half size, the views shown at (_a_), (_b_), and (_c_), fig. 58;
+    also a sectional plan at L M. (_b_) is an elevation of the valve
+    casing with the cover and the valve removed. (_a_) is a sectional
+    elevation, the section being taken through the axes of the steam
+    cylinder and valve spindle. (_c_) is a sectional plan, the section
+    being a horizontal one through the centre of the exhaust port. The
+    inlet and outlet for the steam are clearly shown in the sectional
+    plan: in the sectional elevation their positions are shown by
+    dotted circles.
+
+    The stroke of the piston is in this case 12 inches, so that from
+    the dimensions given at (_a_) it must come within a quarter of an
+    inch of each end of the cylinder; this is called the _cylinder
+    clearance_.
+
+    The piston has three Ramsbottom rings, a quarter of an inch wide
+    and a quarter of an inch apart.
+
+    The steam cylinder and valve casing are made of cast iron.
+
+_Cocks._--A cock consists of a slightly conical plug which fits into a
+corresponding casing cast on a pipe. Through the plug is a hole which
+may be made by turning the plug to form a continuation of the hole in
+the pipe, and thus allow the fluid to pass, or it may be turned round so
+that the solid part of the plug lies across the hole in the pipe, and
+thus prevent the fluid from passing. As the student will be quite
+familiar with the common water cock or tap such as is used in
+dwelling-houses we need not illustrate it here.
+
+[Illustration: FIG. 59.]
+
+Fig. 59 shows a cock of considerable size, which may be used for water
+or steam under high pressure. The plug in this example is hollow, and is
+prevented from coming out by a cover which is secured to the casing by
+four stud bolts. An annular ridge of rectangular section projecting from
+the under side of the cover, and fitting into a corresponding recess on
+the top of the casing, serves to ensure that the cover and plug are
+concentric, and prevents leakage. Leakage at the neck of the plug is
+prevented by a gland and stuffing-box. The top end of the plug is made
+square to receive a handle for turning it. The size of a cock is taken
+from the bore of the pipe in which it is placed; thus fig. 59 shows a
+2-1/4-inch cock.
+
+    EXERCISE 61: 2-1/4-_inch Steam or Water Cock._--First draw the
+    views of this cock shown in fig. 59, then draw a half end elevation
+    and half cross section through the centre of the plug. Scale 6
+    inches to a foot.
+
+    Instead of drawing the parts of the pipe on the two sides of the
+    plug in the same straight line as in fig. 59, one may be shown
+    proceeding from the bottom of the casing, so that the fluid will
+    have to pass through the bottom of the plug and through one side.
+    This is a common arrangement.
+
+    All the parts of the valve and casing in this example are made of
+    brass.
+
+
+
+
+XVII. MATERIALS USED IN MACHINE CONSTRUCTION.
+
+
+_Cast Iron._--The essential constituents of cast iron are iron and
+carbon, the latter forming from 2 to 5 per cent. of the total weight.
+Cast iron, however, usually contains varying small amounts of silicon,
+sulphur, phosphorus, and manganese.
+
+In cast iron the carbon may exist partly in the free state and partly in
+chemical combination with the iron.
+
+In _white cast iron_ the whole of the carbon is in chemical combination
+with the iron, while in _grey cast iron_ the carbon is principally in
+the free state, that is, simply mixed mechanically with the iron. It is
+the free carbon which gives the grey iron its dark appearance. A mixture
+of the white and grey varieties of cast iron when melted produces
+_mottled cast iron_. The greater the amount of carbon chemically
+combined with the iron, the whiter, harder, and more brittle does it
+become.
+
+The white cast iron is stronger than the grey, but being more brittle it
+is not so suitable for resisting suddenly applied loads. White iron
+melts at a lower temperature than grey iron, but after melting it does
+not flow so well, or is not so liquid as the grey iron. White iron
+contracts while grey iron expands on solidifying. The grey iron,
+therefore, makes finer castings than the white. Castings after
+solidifying contract in cooling about 1/8 of an inch per foot. Castings
+possessing various degrees of strength and hardness are produced by
+melting mixtures of various proportions of white and grey cast irons.
+White cast iron has a higher specific gravity than grey cast iron.
+
+Cast iron gives little or no warning before breaking. The thickness of
+the metal throughout a casting in cast iron should be as uniform as
+possible, so that it may cool and therefore contract uniformly
+throughout; otherwise some parts may be in a state of initial strain
+after the casting has cooled, and will therefore be easier to fracture.
+Re-entrant angles should be avoided; such should be rounded out with
+fillets.
+
+The presence of phosphorus in cast iron makes it more fusible, and also
+more brittle. The presence of sulphur diminishes the strength
+considerably.
+
+The grey varieties of cast iron are called _foundry irons_ or _foundry
+pigs_, while the white varieties are called _forge irons_ or _forge
+pigs_, from the fact that they are used for conversion into wrought
+iron.
+
+Amongst iron manufacturers the different varieties of cast iron are
+designated by the numbers 1, 2, 3, &c., the lowest number being applied
+to the greyest variety.
+
+_Chilled Castings._--When grey cast iron is melted a portion of the free
+carbon combines chemically with the iron; this, however, separates out
+again if the iron is allowed to cool slowly; but if it is suddenly
+cooled a greater amount of the carbon remains in chemical combination,
+and a whiter and harder iron is produced. Advantage is taken of this in
+making _chilled castings_. In this process the whole or a part of the
+mould is lined with cast iron, which, being a comparatively good
+conductor of heat, chills a portion of the melted metal next to it,
+changing it into a hard white iron to a depth varying from 1/8 to 1/2 an
+inch. To protect the cast-iron lining of the mould from the molten metal
+it is painted with loam.
+
+_Malleable Cast Iron._--This is prepared by imbedding a casting in
+powdered red hematite (an oxide of iron), and keeping it at a bright red
+heat for a length of time varying from several hours to several days
+according to the size of the casting. By this process a portion of the
+carbon in the casting is removed, and the strength and toughness of the
+latter become more like the strength and toughness of wrought or
+malleable iron.
+
+_Wrought or Malleable Iron._--This is nearly pure iron, and is made from
+cast iron by the puddling process, which consists chiefly of raising the
+cast iron to a high temperature in a reverberatory furnace in the
+presence of air, which unites with the carbon and passes off as gas. In
+other words the carbon is burned out. The iron is removed from the
+puddling furnace in soft spongy masses called _blooms_, which are
+subjected to a process of squeezing or hammering called _shingling_.
+These shingled blooms still contain enough heat to enable them to be
+rolled into rough _puddled bars_. These puddled bars are of very
+inferior quality, having less than half the strength of good wrought
+iron. The puddled bars are cut into pieces which are piled together,
+reheated, and again rolled into bars, which are called _merchant bars_.
+This process of piling, reheating, and re-rolling may be repeated
+several times, depending on the quality of iron required. Up to a
+certain point the quality of the iron is improved by reheating and
+rolling or hammering, but beyond that a repetition of the process
+diminishes the strength of the iron.
+
+The process of piling and rolling gives wrought iron a fibrous
+structure. When subjected to vibrations for a long time, the structure
+becomes crystalline and the iron brittle. The crystalline structure
+induced in this way may be removed by the process of _annealing_, which
+consists in heating the iron in a furnace, and then allowing it to cool
+slowly.
+
+_Forging and Welding._--The process of pressing or hammering wrought
+iron when at a red or white heat into any desired shape is called
+_forging_. If at a white heat two pieces of wrought iron be brought
+together, their surfaces being clean, they may be pressed or hammered
+together, so as to form one piece. This is called _welding_, and is a
+very valuable property of wrought iron.
+
+_Steel._--This is a compound of iron with a small per-centage of carbon,
+and is made either by adding carbon to wrought iron, or by removing some
+of the carbon from cast iron.
+
+In the _cementation_ process, bars of wrought iron are imbedded in
+powdered charcoal in a fireclay trough, and kept at a high temperature
+in a furnace for several days. The iron combines with a portion of the
+carbon to form _blister steel_, so named because of the blisters which
+are found on the surface of the bars when they are removed from the
+furnace.
+
+The bars of blister steel are broken into pieces about 18 inches long,
+and tied together in bundles by strong steel wire. These bundles are
+raised to a welding heat in a furnace, and then hammered or rolled into
+bars of _shear steel_.
+
+To form _cast steel_ the bars of blister steel are broken into pieces
+and melted into crucibles.
+
+In the _Siemens-Martin_ process for making steel, cast and wrought iron
+are melted together on the hearth of a regenerative gas-furnace.
+
+_Bessemer steel_ is made by pouring melted cast iron into a vessel
+called a converter, through which a blast of air is then urged. By this
+means the carbon is burned out, and comparatively pure iron remains. To
+this is added a certain quantity of 'spiegeleisen,' which is a compound
+of iron, carbon, and manganese.
+
+_Hardening and Tempering of Steel._--Steel, if heated to redness and
+cooled suddenly, as by immersion in water, is hardened. The degree of
+hardness produced varies with the rate of cooling; the more rapidly the
+heated steel is cooled, the harder does it become. Hardened steel is
+softened by the process of _annealing_, which consists in heating the
+hardened steel to redness, and then allowing it to cool slowly. Hardened
+steel is _tempered_, or has its degree of hardness lowered, by being
+heated to a temperature considerably below that of a red heat, and then
+cooling suddenly. The higher the temperature the hardened steel is
+raised to, the lower does its 'temper' become.
+
+_Case-hardening._--This is the name given to the process by which the
+surfaces of articles made of wrought iron are converted into steel, and
+consists in heating the articles in contact with substances rich in
+carbon, such as bone-dust, horn shavings, or yellow prussiate of potash.
+This process is generally applied to the articles after they are
+completely finished by the machine tools or by hand. The coating of
+steel produced on the article by this process is hardened by cooling the
+article suddenly in water.
+
+_Copper._--This metal has a reddish brown colour, and when pure is very
+malleable and ductile, either when cold or hot, so that it may be rolled
+or hammered into thin plates, or drawn into wire. Slight traces of
+impurities cause brittleness, although from 2 to 4 per cent. of
+phosphorus increases its tenacity and fluidity. Copper is a good
+conductor of heat and of electricity. Copper is largely used for making
+alloys.
+
+_Alloys._--_Brass_ contains two parts by weight of copper to one of
+zinc. _Muntz metal_ consists of three parts of copper to two of zinc.
+Alloys consisting of copper and tin are called _bronze_ or _gun-metal_.
+Bronze is harder the greater the proportion of tin which it contains;
+five parts of copper to one of tin produce a very hard bronze, and ten
+of copper to one of tin is the composition of a soft bronze. _Phosphor
+bronze_ contains copper and tin with a little phosphorus; it has this
+advantage over ordinary bronze, that it may be remelted without
+deteriorating in quality. This alloy also has the advantage that it may
+be made to possess great strength accompanied with hardness, or less
+strength with a high degree of toughness.
+
+_Wood._--In the early days of machines wood was largely used in their
+construction, but it is now used to a very limited extent in that
+direction. _Beech_ and _hornbeam_ are used for the cogs of mortise
+wheels. _Yellow pine_ is much used by pattern-makers. _Box_, a heavy,
+hard, yellow-coloured wood, is used for the sheaves of pulley blocks,
+and sometimes for bearings in machines. _Lignum-vitæ_ is a very hard
+dark-coloured wood, and remarkable for its high specific gravity, being
+1-1/3 times the weight of the same volume of water. This wood is much
+used for bearings of machines which are under water.
+
+
+
+
+XVIII. MISCELLANEOUS EXERCISES.
+
+
+The illustrations in this chapter are in most cases not drawn to scale;
+they are also in some parts incomplete, and in others some of the lines
+are purposely drawn wrong. The student must keep to the dimensions
+marked on the drawings, and where no sizes are given he must use his own
+judgment in proportioning the parts. All errors must be corrected, and
+any details required, but not shown completely in the illustrations,
+must be filled in.
+
+    EXERCISE 62: _Single Riveted Butt Joint with Tee-iron Cover
+    Strap._--Two views, one a side elevation and the other a sectional
+    elevation, of a riveted joint are shown in fig. 60. Draw these
+    views, and also a plan projected from one of them. Show the rivets
+    completely in all the views. Scale 4 inches to a foot.
+
+[Illustration: FIG. 60.]
+
+[Illustration: FIG. 61.]
+
+    EXERCISE 63: _Girder Stay for Steam Boiler._--The flat crown of the
+    fire-box of locomotive and marine boilers is generally supported or
+    stayed by means of girder stays, an example of which is shown in
+    fig. 61. A B is the side elevation of a portion of one of these
+    girders. Each girder is supported at its ends by the plates forming
+    the vertical sides of the fire-box. The flat crown is bolted to the
+    girders as shown. Observe that the girders are in contact with the
+    crown only in the neighbourhood of the bolts. Consider carefully
+    this part of the design, and then answer the following questions:
+    (1) What objections are there to supporting the girders at the ends
+    only without the contact pieces at the bolts? (2) What objections
+    are there to having the girders in contact with the crown plate of
+    the fire-box throughout their whole length?
+
+    Draw the views shown in fig. 61, and from the right-hand one
+    project a plan. Scale 4 inches to a foot.
+
+[Illustration: FIG. 62.]
+
+    EXERCISE 64: _End of Bar Stay for Steam Boiler._--On page 12 one
+    form of stay for supporting the flat end of a steam boiler is
+    described. Another form of stay for the same purpose is shown in
+    fig. 62. A B is a portion of the end of a steam boiler. C D is one
+    end of a bar which extends from one end of the boiler to the
+    other. The ends of this bar are screwed, and when the bar is of
+    wrought iron the screwed parts are generally larger in diameter
+    than the rest of the bar. When made of steel the bar is generally
+    of uniform diameter throughout. In the case of wrought-iron bar
+    stays the enlarged ends are welded on to the smaller parts.
+    Welding is not so reliable with steel as with wrought iron. Write
+    out answers to the following questions: (1) What is the advantage
+    of having the screwed part of the bar larger in diameter than the
+    rest? (2) Why are steel bar stays not generally enlarged at their
+    screwed ends?
+
+    Draw the views shown in fig. 62, and project from one of them a
+    third view. Scale 4 inches to a foot.
+
+    EXERCISE 65: _Knuckle Joint._--Draw the plan and elevation of this
+    joint shown in fig. 63, and also draw an end elevation looking in
+    the direction of the arrow. The parts at A and B are octagonal in
+    cross section. Scale 4 inches to a foot.
+
+[Illustration: FIG. 63.]
+
+    EXERCISE 66: _Locomotive Coupling Rod Ends._--A form of knuckle
+    joint used on locomotive coupling rods is shown in fig. 64.
+
+    In this case two rods meet and work on the same pin, as shown at
+    (a) fig. 64. Draw, in addition to the views shown in fig. 64, a
+    plan and a vertical section through the axis of the pin. Scale 6
+    inches to a foot.
+
+    Would it be practicable to replace the two rods A B and B C by a
+    single rod working on the crank pins at A, B, and C? Give reasons
+    for your answer.
+
+[Illustration: FIG. 64.]
+
+    EXERCISE 67: _Bell Crank Lever._--Draw the plan and elevation of
+    the lever shown in fig. 65. Scale 6 inches to a foot.
+
+[Illustration: FIG. 65.]
+
+    EXERCISE 68: _Back Stay for Lathe._--Draw a plan and two elevations
+    of the stay shown in fig. 66. Make all necessary corrections and
+    show all the details in each view. Scale full size.
+
+[Illustration: FIG. 66.]
+
+[Illustration: FIG. 67.]
+
+    EXERCISE 69: _Conical Disc Valve and Casing._--Draw, half size, the
+    views shown in fig. 67 of the conical disc valve and casing, and
+    also add an elevation looking in the direction of the arrow.
+
+    EXERCISE 70: _Connecting Rod End._--The student should carefully
+    compare this connecting rod end (fig. 68) with those illustrated on
+    pages 50 and 52. The lower part of fig. 68 is a half plan and half
+    horizontal section, and the upper part is a half side elevation and
+    half vertical section. Draw these views and also an end elevation.
+    Scale 6 inches to a foot.
+
+[Illustration: FIG. 68.]
+
+[Illustration: FIG. 69.]
+
+[Illustration: FIG. 70.]
+
+[Illustration: FIG. 71.]
+
+[Illustration: FIG. 72.]
+
+[Illustration: FIG. 73.]
+
+[Illustration: FIG. 74.]
+
+    EXERCISE 71: _Engine Cross-head._--The cross-head shown in fig. 69
+    is for an inverted cylinder marine engine. A is the piston rod, and
+    B B are pins, forged in one piece with C, to which the forked end
+    of the connecting rod is attached. Draw the upper view with the
+    central part in section as shown. Make the right-hand half of the
+    lower view a plan without any section, and make the left-hand half
+    a horizontal section through the axis of the pins B B. Scale 4
+    inches to a foot.
+
+    EXERCISE 72: _Ratchet Lever._--The lever shown in fig. 70 is used
+    for turning the horizontal screw of a traversing screw jack. Draw
+    the two views shown, and from one of them project a plan. Scale
+    full size.
+
+    EXERCISE 73: _Steam Whistle._--Draw, full size, the elevation and
+    section of the steam whistle shown in fig. 71. Draw also horizontal
+    sections at A B, C D, and E F.
+
+[Illustration: FIG. 75.]
+
+    EXERCISE 74: _Screw Coupling for Railway Carriages._--Draw the
+    three views of the screw coupling shown in fig. 72. Scale 6 inches
+    to a foot.
+
+    If the link A is fixed, through what distance will the link B move
+    for two turns of the lever?
+
+[Illustration: FIG. 76.]
+
+    EXERCISE 75: _Loose Headstock for a 6-inch Lathe._--Two views of
+    this headstock are shown in fig. 73. On one of these views a few of
+    the chief dimensions are marked. The details, fully dimensioned,
+    are shown separately in figs. 74, 75, and 76.
+
+    Explain clearly how the centre is moved backwards and forwards, and
+    also how the spindle containing it is locked when it is not
+    required to move.
+
+    Draw, half-size, the views shown in fig. 73, and from the
+    left-hand view project a plan. Draw also the detail of the locking
+    arrangement shown in fig. 74.
+
+
+
+
+APPENDIX A.
+
+_SCIENCE AND ART DEPARTMENT, SOUTH KENSINGTON._
+
+
+SYLLABUS.
+
+SUBJECT II.--MACHINE CONSTRUCTION AND DRAWING.
+
+It is assumed that the student has already learnt to draw to scale, and
+that he can draw two or more views of the same object in simple or
+orthographic projection. To pass in machine construction and drawing, he
+must be able to apply this knowledge to the representation of machinery.
+He must be acquainted with the form and purpose of the simpler parts of
+which machines are built up and must have had some practice in drawing
+them. To test his knowledge, rough dimensioned sketches, more or less
+incomplete, of simple machine details will be given him, and he will be
+required to produce a complete drawing in pencil to a given scale. Two
+or more views of at least one subject will be required, and these must
+be so drawn as to be properly projected one from the other, _in order to
+show that the student appreciates that he is producing a representation
+of a solid piece of machinery, and not merely copying a sketch. No
+credit will be given unless some knowledge of projection is shown._ The
+centre lines of the drawings should be shown, and parts cut by planes of
+section should be indicated by diagonal shading. Bolts and other
+fastenings should be carefully shown where required. Any indication that
+a candidate has merely copied the sketches given, without understanding
+the part represented, will invalidate his examination.
+
+
+FIRST STAGE OR ELEMENTARY COURSE.
+
+In the elementary stage, a knowledge is required of the simple parts
+only of _machines in common use_. _Some_ of these are enumerated in the
+following list. The student should be practised in drawing them till he
+recognises their forms, and the object of the arrangement should be
+explained to him. He should also know the simple technical terms used in
+describing them.
+
+A few very simple questions relating to the arrangement, proportions,
+and strength of the simplest machine details will be set in the
+examination paper.
+
+In drawing the examples set to test a student's knowledge and skill in
+machine drawing, it must be remembered that only a limited time is
+available. It is only possible to set an example to be drawn in pencil,
+and the points which will receive attention are (1) accuracy of scale
+and projection; (2) power of reading a drawing, shown by the ability to
+transfer portions of the mechanism and dimensions from one view to
+another; (3) knowledge of machines, as shown by the ability to fill in
+small details, such as nuts, keys, etc., omitted in the sketches given.
+Bearing in mind the limited time available, the student should try to
+make his outline clear and decisive and complete. But the diagonal lines
+necessary for sectional parts may be done rapidly, though neatly, by
+freehand if necessary.
+
+_Riveted Joints._--Forms of rivets and arrangement of rivets in lap and
+butt joints with single and double riveting. Junction of plates by angle
+and T-irons.
+
+_Bolts, Studs, and Set Screws._--Forms of these fastenings. Forms and
+proportions of nuts and bolt-heads. Arrangement of flanges for bolting.
+
+_Pins, Keys, and Cotters._--Form of ordinary knuckle joint. Use of split
+pins. Connection of parts by a key. Connection of parts by a cotter. Gib
+and cotter.
+
+_Pipes and Cylinders._--Forms of ordinary pipes and cylinders and their
+flanges and covers.
+
+_Shafting._--Forms of shafts and axles and of journals and pivots. Use
+of collars and bosses. Half-lap coupling. Box coupling. Flange coupling.
+
+_Pedestals and Plummer Blocks._--Simplest forms of pedestals and hangers
+for shafts. Form and arrangement of brass steps. Arrangements for
+fixing pedestals and for neutralising the effects of wear.
+
+_Toothed Gearing._--Forms of ordinary spur and bevil wheels. Meaning of
+the terms pitch, breadth of face, thickness of tooth, pitch line, rim,
+nave, arm. Mode of drawing bevil wheels in section.
+
+_Belt Pulleys._--Forms of belt pulleys for flat and round belts. Stepped
+speed cones. Drawing of pulleys with curved arms.
+
+_Cranks and Levers._--Forms of ordinary cast-iron and wrought-iron
+cranks and levers. Modes of fixing crank pin. Modes of fixing crank
+shaft. Double cranks. Form of eccentrics.
+
+_Links._--Most simple forms of connecting rod ends, open or closed. Use
+of steps in connecting rods. Use of cotters to tighten the steps.
+
+_Pistons._--Simple forms of piston. Use of piston packing. Modes of
+attaching piston rod.
+
+_Stuffing-Boxes._--Simple form of stuffing-box and gland. Use of
+packing. Mode of tightening gland.
+
+_Valves._--Simple conical of puppet valve. Simple slide valve. Cock or
+conical sliding valve.
+
+
+
+
+APPENDIX B.
+
+_EXAMINATION PAPERS SET BY THE SCIENCE AND ART DEPARTMENT._
+
+
+SUBJECT II.--MACHINE CONSTRUCTION AND DRAWING.
+
+_Examiners_, PROF. T. A. HEARSON, M.Inst.C.E., and J. HARRISON, ESQ.,
+M.Inst.M.E.
+
+GENERAL INSTRUCTIONS.
+
+_If the rules are not attended to, the paper will be cancelled._
+
+You may take the Elementary, or the Advanced, or the Honours paper, but
+you must confine yourself to one of them.
+
+Put the number of the question before your answer.
+
+You are expected to prove your knowledge of machinery as well as your
+power of drawing neatly to scale. You are therefore to supply details
+omitted in the sketches, to fill in parts left incomplete, and to
+indicate, by diagonal lines, parts cut by planes of section.
+
+No credit will be given unless some knowledge of projection is shown, so
+that at least two views of one of the examples will be required properly
+projected one from the other. The centre lines should be clearly drawn.
+The figured dimensions need not be inserted.
+
+Your answers should be clearly and cleanly drawn in pencil. No extra
+marks will be allowed for inking in.
+
+All figures must be drawn on the single sheet of paper supplied, for no
+second sheet will be allowed.
+
+The value attached to each question is shown in brackets after the
+question. But a full and correct answer to an easy question will in all
+cases secure a larger number of marks than an incomplete or inexact
+answer to a more difficult one.
+
+Your name is not given to the Examiner, and you are forbidden to write
+to him about your answers.
+
+You are to confine your answers _strictly_ to the questions proposed.
+
+A single accent (') signifies _feet_; a double accent (") _inches_.
+
+_The examination in this subject lasts for four hours._
+
+       *       *       *       *       *
+
+First Stage or Elementary Examination. 1885.
+
+INSTRUCTIONS.
+
+Read the General Instructions above.
+
+Answer briefly any three, but not more than three, of the following
+questions, and draw two, but not more than two, of the examples.
+
+_Questions._
+
+ (_a._) Show two methods by which a cotter may be prevented from
+    slacking back.                                                  (6.)
+
+ (_b._) Sketch the brasses for a bearing, and show how they are
+    prevented from turning in the pedestal.                         (6.)
+
+ (_c._) Explain the object of the construction of the connecting rod
+    end shown in fig. 78. Describe how the adjustment must be made and
+    how it is locked.                                              (10.)
+
+ (_d._) Show the form of the Whitworth screw thread by drawing to
+    scale a part section of two or three threads taking a pitch of
+    1-1/2 inches. Figure the dimensions on the sketch. How many threads
+    to the inch are used on an inch bolt?                          (10.)
+
+ (_e._) Make a sketch showing how the adjustment is made in the
+    sliding parts of machine tools: as, for example, in the slide rest
+    of a lathe.                                                    (10.)
+
+ (_f._) Describe with sketches two methods by which the joints are
+    made in connecting lengths of cast-iron pipes.                  (6.)
+
+_Examples to be drawn._
+
+ 1. Jaw for four-screw dog chuck for 5" lathe. Draw the two views as
+    shown (fig. 77). Scale full size.
+
+    (Note.--The other three jaws of the chuck are not to be drawn.)
+                                                                   (35.)
+
+ 2. Connecting rod end. Draw the two views as shown, partly in
+    section (fig. 78). Draw full size.                             (35.)
+
+ 3. Hooke's coupling. Draw the three views shown (fig. 79), adding
+    any omitted lines where the views are incomplete. Draw to scale of
+    1/4 full size.                                                 (35.)
+
+[Illustration: FIGS. 77 AND 78.]
+
+[Illustration: FIG. 79.]
+
+       *       *       *       *       *
+
+First Stage or Elementary Examination. 1886.
+
+INSTRUCTIONS.
+
+Read the General Instructions (page 102).
+
+Answer briefly any three, but not more than three, of the following
+questions, and draw two, but not more than two, of the examples.
+
+_Questions._
+
+ (_a._) Give sketches showing how the cutting tool of a lathe or
+    other machine is secured in place.                              (6.)
+
+ (_b._) Make a sketch of a stud, describe how it is screwed into
+    place, and state some circumstances under which it is used in
+    preference to a bolt.                                           (6.)
+
+ (_c._) Give sketches showing one method of attaching the valve rod
+    to an ordinary slide valve.                                     (6.)
+
+ (_d._) Sketch a connecting rod end, with strap, gib, and cotter.
+    Explain the use of the gib.                                    (10.)
+
+ (_e._) Explain the use of the quadrant for change wheels for a
+    screw-cutting lathe shown in Example 1, fig. 80, by making a
+    sketch showing it in place on a lathe with wheels in gear.     (10.)
+
+ (_f._) Sketch one form of hanger suitable for supporting mill-shafting.
+                                                                   (10.)
+
+_Examples to be drawn._
+
+ 1. Quadrant for change wheels for screw-cutting lathe. Draw the two
+    views shown (fig. 80). Scale half-size.                        (35.)
+
+ 2. Crank-shaft. Draw the two views as shown, partly in section (fig
+    81). Scale 1/8 full size.                                      (35.)
+
+ 3. Ball bearing for tricycle. Draw the two views as shown, partly
+    in section (fig. 82). Draw full size.                          (35.)
+
+[Illustration: FIGS. 80 AND 81.]
+
+[Illustration: FIG. 82.]
+
+       *       *       *       *       *
+
+First Stage or Elementary Examination. 1887.
+
+INSTRUCTIONS.
+
+Read the General Instructions (page 102).
+
+Answer briefly any three, but not more than three, of the following
+questions, and draw two, but not more than two, of the examples.
+
+_Questions._
+
+ (_a._) Explain how the piston rings in Example 1, fig. 84, are made
+    so that the piston may work steam-tight in the cylinder. How are
+    these rings got into place?                                     (8.)
+
+ (_b._) Give two views of a double riveted lap joint for boiler-plates.
+                                                                    (8.)
+
+ (_c._) Show by sketches how a wheel is fixed on a shaft by means of
+    a sunk key. Explain how the key may be withdrawn when it cannot be
+    driven from the point end.                                      (8.)
+
+ (_d._) Give sketches showing the construction of a conical metal
+    lift or puppet valve and seating.                              (10.)
+
+ (_e._) With the aid of sketches explain how a piston rod is made to
+    work steam-tight through the end of the cylinder.              (10.)
+
+ (_f._) Explain how the slotting machine ram of Example 8, fig. 85,
+    may be made to move up and down when at work. How is the length of
+    the stroke altered, and what is the object of the slotway in the
+    upper part of the ram?                                         (10.)
+
+_Examples to be drawn._
+
+ 1. Piston for steam-engine. Draw and complete the two views shown
+    (fig. 84), the top half of the left-hand view to be in section.
+    Scale 1/2 size.                                                (30.)
+
+ 2. Plan and sectional elevation of a footstep bearing for an
+    upright shaft (fig. 83). Draw and complete these views. Scale
+    1/4 size.                                                      (35.)
+
+ 3. Ram of slotting machine. Draw and complete the two elevations
+    shown (fig. 85). The tool-holders must be drawn in their proper
+    positions in the ram, and not separate as in the diagram. Scale
+    1/4 size.                                                      (35.)
+
+[Illustration: FIGS. 83 AND 84.]
+
+[Illustration: FIG. 85.]
+
+       *       *       *       *       *
+
+First Stage or Elementary Examination. 1888.
+
+INSTRUCTIONS.
+
+Read the General Instructions on p. 102.
+
+Answer briefly any three, but not more than three, of the following
+questions, and draw two, but not more than two, of the examples.
+
+_Questions._
+
+ (_a._) Give sketches showing how the separate lengths of a line of
+    shafting may be connected together.                             (8.)
+
+ (_b._) What is the object of using chipping or facing strips in
+    fitting up machine parts? Give one or two examples.             (8.)
+
+ (_c._) Give sketches showing how you would grip and drive a round
+    iron bar for the purpose of turning it between the centres of a
+    lathe.                                                         (10.)
+
+ (_d._) Explain the action of the governor shown in Example 1
+    (fig. 86).                                                     (10.)
+
+ (_e._) Describe in detail how the mud-hole door in Example 2
+    (fig. 88) is removed for the purpose of cleaning the boiler and
+    how it is replaced and the joint made steam-tight.             (10.)
+
+ (_f._) Describe how the parts of the spur wheel in Example 3
+    (fig. 87) are put together, and explain why the wheel is made
+    in segments.                                                   (10.)
+
+_Examples to be drawn._
+
+ 1. Loaded governor for small gas engine. Draw and complete the two
+    views, partly in section as shown (fig. 86). Scale full size.  (35.)
+
+ 2. Mud-hole mouth-piece for Lancashire boiler. Draw and complete
+    the two views shown (fig. 88). Scale 3/8ths.                   (35.)
+
+ 3. Point for segments of large spur wheel. Draw and complete the
+    views shown (fig. 87). Scale 3/16ths.
+
+    _Note._--As the radius of the wheel is too large for your
+    instruments, the circumference at the joint may be set out
+    straight, as in a rack.                                        (35.)
+
+[Illustration: FIGS. 86 AND 87.]
+
+[Illustration: FIG. 88.]
+
+
+
+
+INDEX
+
+
+  Air-pump bucket, 58
+  Alloys, 80
+  Angle irons, 12
+  Annealing, 79, 80
+  Axles, 24
+
+
+  Back stay for lathe, 86
+  Bar stay, 83
+  Bearings for shafts, 30
+  Beech-wood, 81
+  Bell crank lever, 86
+  Bessemer steel, 79
+  Bevil wheels, 43
+  Blister steel, 79
+  Blooms, 78
+  Bolt-heads, proportions of, 18
+  Bolts, forms of, 17
+  Border lines, 4
+  Box couplings, 25
+  -- end, connecting rod, 51
+  Box-wood, 81
+  Brackets, 33
+  Brake shaft carrier, 30
+  Brass, 80
+  Brasses, 30
+  Bucket, 58
+  Built-up cranks, 46
+  Bush, 30, 49, 51, 54, 56, 63
+  Butt joints, 10, 11
+  -- strap, 10
+  Buttress screw thread, 15
+
+
+  Case-hardening, 80
+  Cast iron, 76
+  Cast iron flange coupling, 28, 29
+  -- steel, 79
+  Caulking, 8
+  Cementation process, 79
+  Centre lines, 2, 4
+  Chilled castings, 78
+  Circulating pump piston, 58
+  Clearance, cylinder, 74
+  -- of cotter, 49
+  Cocks, 74
+  Cogs, 41
+  -- wood for, 81
+  Collared stud, 18
+  Collars, 24
+  Colouring, 3
+  Colours for different materials, 3
+  Compasses, 1
+  Cone keys, 23, 38
+  Conical disc valve, 70, 71, 89
+  -- head, 7
+  Connecting rod, locomotive, 51
+  -- -- marine, 51
+  -- rods, 49, 89
+  Construction for rivet heads, 7
+  Contraction of castings, 77
+  Copper, 80
+  Cotters, 48, 49
+  Countersunk head, 7, 18
+  Coupling rod ends, 55, 84
+  -- rods, 54
+  -- screw, 96
+  Couplings, shaft, 25
+  Cover plate, 10
+  Cranked axle, 45
+  Cranks, 43
+  -- built-up, 46
+  Cross-head pin, 51
+  Cross-heads, 56, 89
+  Cross-key, 28
+  Cup-headed bolt, 17
+
+
+  Decimal equivalents, 6
+  Dimension lines, 5
+  Dimensions, 5
+  -- of box couplings, 26
+  -- cast-iron flange couplings, 29
+  -- keys, 24
+  -- stuffing-boxes and glands, 67
+  -- Whitworth screws, 15
+  Distance lines, 5
+  Dividers, 1
+  Draught of cotter, 49
+  Drawing board, 1
+  -- instruments, 1
+  -- paper, 2
+  -- pen, 1
+  -- pins, 2
+
+
+  Eccentrics, 47
+  Exhaust port, 71
+  Eye-bolt, 18
+
+
+  Fairbairn's coupling, 26
+  Fast and loose pulleys, 37
+  Feather key, 23
+  Flange couplings, 27
+  Flap valves, 68
+  Flat key, 22
+  Forge irons, 77
+  Forging, 79
+  Form of wheel teeth, 40
+  Forms of nuts, 16
+  -- rivet heads, 7
+  -- screw threads, 15
+  Foundry irons, 77
+
+
+  Gasket, 58
+  Gas threads, 15
+  Gib, 49
+  -- head, 23
+  Girder stay, 81
+  Gland, 64
+  Grey cast iron, 77
+  Gun-metal, 80
+  Gusset stay, 12
+
+
+  Half-lap coupling, 26
+  Hangers, 34
+  Hardening of steel, 80
+  Headstock lathe, 96
+  Hexagonal nut, 16
+  Hollow key, 22
+  Hook bolt, 18
+  Hornbeam, 81
+
+
+  India-rubber disc valves, 58, 68
+  Inking drawings, 2
+  Inside lap of valve, 72
+
+
+  Joggles, 33
+  Joint, knuckle, 84
+  Journals, 24
+  -- length of, 32
+  Junk ring, 61
+
+
+  Keys, 22
+  -- proportions of, 23
+  Kinghorn's metallic valve, 70
+  Knuckle joint, 84
+  -- screw thread, 15
+
+
+  Lancaster's piston packing, 61
+  Lap joints, 8, 9, 10, 12
+  -- of slide valve, 72
+  Lathe headstock, 96
+  Lead of valve, 74
+  Lever, bell crank, 86
+  -- ratchet, 96
+  Lignum-vitæ, 81
+  Locking arrangements for nuts, 21, 62
+  Lock nuts, 19
+  Locomotive connecting rod, 51
+  -- cranked axle, 45
+  -- cross-head, 56
+  Locomotive eccentric, 47
+  -- piston, 60
+  Lubricator, needle, 32
+
+
+  Malleable cast iron, 78
+  -- iron, 78
+  Marine connecting rod, 51
+  -- coupling, 28
+  -- crank-shaft, 46
+  -- piston, 61
+  Merchant bars, 78
+  Mortise wheels, 41
+  Mottled cast iron, 77
+  Muff couplings, 25
+  Muntz metal, 80
+
+
+  Needle lubricator, 32
+  Nuts, forms of, 16
+  -- lock, 19
+  -- proportions of, 18
+
+
+  Oil-box, 54, 65
+  Outside lap of slide valve, 72
+  Overhung crank, 43
+  -- cranks, proportions of, 45
+
+
+  Packing, 63
+  Pan head, 7
+  Pedestal, shaft, 30
+  Pencils, drawing, 1
+  Phosphor bronze, 80
+  Pillar bracket, 34
+  Pillow block, 30, 32
+  Pin, cross-head, 51, 54
+  -- split, 21
+  Piston rod, 57
+  Pistons, 57
+  Pitch circle, 40
+  -- of wheel teeth, 40
+  -- surfaces of wheels, 39, 43
+  Pivots, 24
+  Plummer block, 30
+  Plunger, 57
+  Printing, 4
+  Proportions of bolt-heads, 18
+  -- keys, 23
+  Proportions of lap joints, 9, 10
+  -- marine engine pistons, 62
+  -- nuts, 18
+  -- overhung cranks, 45
+  -- pillow blocks, 32
+  -- rivet heads, 7
+  -- wheel teeth, 40
+  Puddled bars, 78
+  Puddling process, 78
+  Pulley, eccentric, 47
+  Pulleys, 36
+  Pump bucket, 58
+
+
+  Ramsbottom's packing, 60
+  Ratchet lever, 96
+  Riveted joints, 8
+  Rivet heads, forms of, 7, 8
+  -- -- proportions of, 7
+  Riveting, 7
+  Rivets, 6
+  Rope pulley, 39
+  Round key, 23
+
+
+  Saddle key, 22
+  Scales, 5
+  Screw coupling, 96
+  Screwed gland and stuffing-box, 65
+  Screw threads, 14, 15
+  Screws, representation of, 16
+  Sellers =V= screw thread, 14
+  Set screw, 21, 49
+  -- squares, 1
+  Shaft couplings, 25
+  -- hanger, 34
+  Shafting, 24
+  Shear steel, 79
+  Sheave, eccentric, 47
+  Shingling, 78
+  Shrinking, process of, 44
+  Siemens-Martin steel, 79
+  Slide blocks, 56
+  -- valves, 68, 71
+  Sliding key, 23
+  Snap head, 7
+  Snug, 17
+  Spiegeleisen, 80
+  Spring bows, 1
+  Spur wheel, 41
+  Square nut, 16
+  -- screw thread, 14
+  Stay, back, for lathe, 86
+  -- bar, 83
+  -- girder, 81
+  -- gusset, 12
+  Steam ports, 71
+  -- whistle, 96
+  Steel, 79
+  Steps, 30
+  Strap, 49
+  -- eccentric, 47
+  -- end of connecting rod, 49
+  Stud bolts, 18
+  Studs, 18
+  Stuffing-boxes, 63
+  Sunk key, 22
+
+
+  Taper bolt, 18, 27
+  -- pin, 23
+  Tee-headed bolt, 18
+  Tee-iron cover strap, 81
+  Tee square, 1
+  Teeth of wheels, form and proportions of, 40
+  Teeth, pitch of, 40
+  Tempering of steel, 80
+  Throw of crank, 44
+  -- eccentric, 47
+  Toothed wheels, 39
+
+
+  Valve Kinghorn's metallic, 70
+  -- slide, 68, 71
+  Valves, 68
+  -- conical disc, 70
+  -- india-rubber, 58, 68
+  Velocity ratio in belt gearing, 36
+
+
+  Wall boxes, 34
+  Washers, 19
+  Welding, 79
+  Whistle, steam, 96
+  White cast iron, 77
+  Whitworth screws, dimensions of, 15
+  -- =V= screw thread, 14
+  Wood, 81
+  Working drawings, 4
+  Wrought iron, 78
+
+
+  Yellow pine, 81
+
+
+PRINTED BY
+
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+WORKSHOP APPLIANCES, including Descriptions of some of the Gauging and
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+and other Machine Tools used by Engineers. By C. P. B. SHELLEY, M.I.C.E.
+With 291 Woodcuts. Price 4_s._ 6_d._
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+STRUCTURAL and PHYSIOLOGICAL BOTANY. By Dr. OTTO WILHELM THOMÉ, Rector
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+QUALITATIVE ANALYSIS and LABORATORY PRACTICE. By T. E. THORPE, Ph.D.
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+ELEMENTS of MACHINE DESIGN; an Introduction to the Principles which
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+SOUND, LIGHT, and HEAT. By MARK R. WRIGHT (Hon. Inter. B.Sc. London).
+With 160 Illustrations. Crown 8vo. 2_s._ 6_d._
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+An INTRODUCTION to MACHINE DRAWING and DESIGN. By DAVID ALLAN LOW. With
+65 Illustrations. Crown 8vo. 2_s._
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+PRACTICAL CHEMISTRY: the Principles of Qualitative Analysis. By WILLIAM
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+ELEMENTARY INORGANIC CHEMISTRY. Alternative Course. By W. FURNEAUX,
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+ELEMENTARY BOTANY, THEORETICAL and PRACTICAL. By HENRY EDMONDS, B.Sc.
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+Construction at the Technical School of the People's Palace, Mile End.
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+      The Project Gutenberg eBook of An Introduction to Machine Drawing and Design, by David Allan Low.
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+<pre>
+
+The Project Gutenberg EBook of An Introduction to Machine Drawing and
+Design, by David Allan Low
+
+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: An Introduction to Machine Drawing and Design
+
+Author: David Allan Low
+
+Release Date: March 4, 2012 [EBook #39033]
+
+Language: English
+
+Character set encoding: ISO-8859-1
+
+*** START OF THIS PROJECT GUTENBERG EBOOK AN INTRODUCTION TO MACHINE ***
+
+
+
+
+Produced by Juliet Sutherland and the Online Distributed
+Proofreading Team at http://www.pgdp.net
+
+
+
+
+
+
+</pre>
+
+
+
+
+<h3>AN INTRODUCTION</h3>
+<h5>TO</h5>
+<h1>MACHINE DRAWING</h1>
+<h5>AND</h5>
+<h1>DESIGN</h1>
+
+<p>&nbsp;</p>
+<h5>BY</h5>
+
+<h3>DAVID ALLAN LOW</h3>
+
+<p class="center">(WHITWORTH SCHOLAR), M. INST. M.E.</p>
+
+<p class="center">HEAD MASTER OF THE PEOPLE'S PALACE TECHNICAL SCHOOLS, LONDON<br />
+AUTHOR OF 'A TEXT-BOOK ON PRACTICAL SOLID OR DESCRIPTIVE GEOMETRY'<br />
+'AN ELEMENTARY TEXT-BOOK OF APPLIED MECHANICS' ETC.</p>
+
+<div class="figcenter" style="width: 397px;">
+<img src="images/illus001.jpg" width="397" height="336" alt="" title="" />
+</div>
+
+<h4><i>FOURTH EDITION</i></h4>
+<p>&nbsp;</p>
+
+<h4>LONDON<br />
+<big>LONGMANS, GREEN, AND CO.</big><br />
+<small>AND NEW YORK: 15 EAST 16th STREET</small><br />
+1890</h4>
+
+
+<hr style="width: 15%;" />
+<p class="center">PRINTED BY<br />
+SPOTTISWOODE AND CO., NEW-STREET SQUARE<br />
+LONDON</p>
+
+
+<hr style="width: 100%;" />
+<p><span class='pagenum'><a name="Page_iii" id="Page_iii">[Pg iii]</a></span></p>
+<h2>PREFACE.</h2>
+
+
+<p>It is now generally recognised that the old-fashioned method
+of teaching machine drawing is very unsatisfactory. In
+teaching by this method an undimensioned scale drawing,
+often of a very elaborate description, is placed before the
+student, who is required to <i>copy</i> it. Very often the student
+succeeds in making a good copy of the drawing placed before
+him without learning very much about the object represented
+by it, and this state of matters is sometimes not much improved
+by the presence of the teacher, who is often simply an art
+master, knowing nothing about machine design. It is related
+of one school that a pupil, after making a copy of a particular
+drawing, had a discussion with his teacher as to whether the
+object represented was a sewing machine or an electrical
+machine. Evidently the publisher of the drawing example in
+this case did not adopt the precaution which a backward
+student used at an examination in machine design: he put on
+a full title above his drawing, for the information of his
+examiner.</p>
+
+<p>Now, if machine drawing is to be of practical use to any
+one, he must be able to understand the form and arrangement
+of the parts of a machine from an inspection of suitable drawings
+of them without seeing the parts themselves. Also he
+ought to be able to make suitable drawings of a machine or
+parts of a machine from the machine or the parts themselves.<span class='pagenum'><a name="Page_iv" id="Page_iv">[Pg iv]</a></span></p>
+
+<p>In producing this work the author has aimed at placing
+before young engineers and others, who wish to acquire the
+skill and knowledge necessary for making the simpler <i>working
+drawings</i> such as are produced in engineers' drawing offices, a
+number of good exercises in drawing, sufficient for one session's
+work, and at the same time a corresponding amount of information
+on the design of machine details generally.</p>
+
+<p>The exercises set are of various kinds. In the first and
+simplest certain views of some machine detail are given, generally
+drawn to a small scale, which the student is asked to reproduce
+<i>to dimensions marked on these views</i>, and he is expected
+to keep to these dimensions, and not to measure anything from
+the given illustrations. In the second kind of exercise the
+student is asked to reproduce certain views shown <i>to dimensions
+given in words or in tabular form</i>. In the third kind of
+exercise the student is required to make, in addition to certain
+views shown to given dimensions, others which he can only
+draw correctly if he thoroughly understands the design before
+him. In the fourth kind of exercise the student is asked to
+make the necessary working drawings for some part of a
+machine which has been previously described and illustrated,
+<i>the dimensions to be calculated by rules given in the text</i>.</p>
+
+<p>The illustrations for this work are all new, and have been
+specially prepared by the author from <i>working drawings</i>, and
+he believes that they will be found to represent the best
+modern practice.</p>
+
+<p>As exercises in drawing, those given in this book are not
+numbered exactly in their order of difficulty, but unless on the
+recommendation of a teacher, the student should take them up
+in the order given, omitting the following:&mdash;26, 27, 28, 35, 40,
+42, 43, 45, 49, 50, 54, 60, 61, as he comes to them, until he has
+been right through the book; afterwards he should work out
+those which he omitted on first going over the book.</p>
+<p><span class='pagenum'><a name="Page_v" id="Page_v">[Pg v]</a></span></p>
+<p>In addition to the exercises given in this work the student
+should practise making freehand sketches of machine details
+from actual machines or good models of them. Upon these
+sketches he should put the proper dimensions, got by direct
+measurement from the machine or model by himself. These
+sketches should be made in a note-book kept for the purpose,
+and no opportunity should be lost of inserting a sketch of any
+design which may be new to the student, always putting on
+the dimensions if possible. These sketches form excellent
+examples from which to make working drawings. The student
+should also note any rules which he may meet with for proportioning
+machines, taking care, however, in each case to state
+the source of such information for his future guidance and
+reference.</p>
+
+<p>As machine drawing is simply the application of the
+principles of descriptive geometry to the representation of
+machines, the student of the former subject, if he is not
+already acquainted with the latter, should commence to study
+it at once.</p>
+
+<p style='text-align: right'>D. A. L.</p>
+
+<p><span class="smcap">Glasgow</span>: <i>March</i> 1887.</p>
+
+
+
+<hr style="width: 15%;" />
+<h3><i>PREFACE TO THE THIRD EDITION.</i></h3>
+
+<p>To this edition another chapter has been added, containing a
+number of miscellaneous exercises, which it is hoped will add
+to the usefulness of the work as a text-book in science classes.
+The latest examination paper in machine drawing by the
+Science and Art Department has also been added to the
+Appendix.</p>
+
+<p style='text-align: right'>D. A. L.</p>
+
+<p><span class="smcap">London</span>: <i>August</i> 1888.</p>
+<p><span class='pagenum'><a name="Page_vi" id="Page_vi">[Pg vi]</a></span></p>
+
+
+<hr style="width: 100%;" />
+<p><span class='pagenum'><a name="Page_vii" id="Page_vii">[Pg vii]</a></span></p>
+<h2>CONTENTS.</h2>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='right'></td><td align='right'></td><td align='right'>PAGE</td></tr>
+<tr><td align='right'>I.</td><td align='left'>INTRODUCTION</td><td align='right'><a href="#Page_1">1</a></td></tr>
+<tr><td align='right'>II.</td><td align='left'>RIVETED JOINTS</td><td align='right'><a href="#Page_6">6</a></td></tr>
+<tr><td align='right'>III.</td><td align='left'>SCREWS, BOLTS, AND NUTS</td><td align='right'><a href="#Page_14">14</a></td></tr>
+<tr><td align='right'>IV.</td><td align='left'>KEYS</td><td align='right'><a href="#Page_22">22</a></td></tr>
+<tr><td align='right'>V.</td><td align='left'>SHAFTING</td><td align='right'><a href="#Page_24">24</a></td></tr>
+<tr><td align='right'>VI.</td><td align='left'>SHAFT COUPLINGS</td><td align='right'><a href="#Page_25">25</a></td></tr>
+<tr><td align='right'>VII.</td><td align='left'>BEARINGS FOR SHAFTS</td><td align='right'><a href="#Page_30">30</a></td></tr>
+<tr><td align='right'>VIII.</td><td align='left'>PULLEYS</td><td align='right'><a href="#Page_36">36</a></td></tr>
+<tr><td align='right'>IX.</td><td align='left'>TOOTHED WHEELS</td><td align='right'><a href="#Page_39">39</a></td></tr>
+<tr><td align='right'>X.</td><td align='left'>CRANKS AND CRANKED SHAFTS</td><td align='right'><a href="#Page_43">43</a></td></tr>
+<tr><td align='right'>XI.</td><td align='left'>ECCENTRICS</td><td align='right'><a href="#Page_47">47</a></td></tr>
+<tr><td align='right'>XII.</td><td align='left'>CONNECTING RODS</td><td align='right'><a href="#Page_49">49</a></td></tr>
+<tr><td align='right'>XIII.</td><td align='left'>CROSS-HEADS</td><td align='right'><a href="#Page_56">56</a></td></tr>
+<tr><td align='right'>XIV.</td><td align='left'>PISTONS</td><td align='right'><a href="#Page_57">57</a></td></tr>
+<tr><td align='right'>XV.</td><td align='left'>STUFFING-BOXES</td><td align='right'><a href="#Page_63">63</a></td></tr>
+<tr><td align='right'>XVI.</td><td align='left'>VALVES</td><td align='right'><a href="#Page_68">68</a></td></tr>
+<tr><td align='right'>XVII.</td><td align='left'>MATERIALS USED IN MACHINE CONSTRUCTION</td><td align='right'><a href="#Page_76">76</a></td></tr>
+<tr><td align='right'>XVIII.</td><td align='left'>MISCELLANEOUS EXERCISES</td><td align='right'><a href="#Page_81">81</a></td></tr>
+<tr><td align='right'></td></tr>
+<tr><td align='right'></td><td align='left'>APPENDIX A</td><td align='right'><a href="#Page_99">99</a></td></tr>
+<tr><td align='right'></td><td align='left'>APPENDIX B</td><td align='right'><a href="#Page_102">102</a></td></tr>
+<tr><td align='right'></td><td align='left'>INDEX</td><td align='right'><a href="#Page_113">113</a></td></tr>
+</table></div>
+<p><span class='pagenum'><a name="Page_viii" id="Page_viii">[Pg viii]</a></span></p>
+
+
+<hr style="width: 100%;" />
+<p><span class='pagenum'><a name="Page_1" id="Page_1">[Pg 1]</a></span></p>
+<h1>AN INTRODUCTION</h1>
+
+<h5>TO</h5>
+
+<h1>MACHINE DRAWING AND DESIGN.</h1>
+
+
+
+<hr style="width: 15%;" />
+<h2>I. &nbsp; INTRODUCTION.</h2>
+
+
+<p><i>Drawing Instruments.</i>&mdash;For working the exercises in this
+book the student should be provided with the following:&mdash;A
+well-seasoned yellow pine <i>drawing-board</i>, 24 inches long, 17
+inches wide, and <sup>3</sup>&frasl;<sub>8</sub> inch or <sup>1</sup>&frasl;<sub>2</sub> inch thick, provided with cross-bars
+on the back to give it strength and to prevent warping.
+A <b>T</b> <i>square</i>, with a blade 24 inches long attached permanently
+to the stock, <i>but not sunk into it</i>. One 45&deg; and one 60&deg; <i>set
+square</i>. The short edges of the former may be about 6 inches
+and the short edge of the latter about 5 inches long. A <i>pair
+of compasses</i> with pen and pencil attachments, and having legs
+from 5 inches to 6 inches long. A <i>pair of dividers</i>, with
+screw adjustment if possible. A <i>pair of small steel spring
+pencil bows</i> for drawing small circles, and a <i>pair of small steel
+spring pen bows</i> for inking in the same. A <i>drawing pen</i> for
+inking in straight lines. All compasses should have <i>round
+points</i>, and if possible <i>needle</i> points. A piece of india-rubber
+will also be required, besides two pencils, one marked H or HH
+and one marked HB or F; the latter to be used for lining in
+a drawing which is not to be inked in, or for freehand work.</p>
+
+<p>Pencils for mechanical drawing should be sharpened with
+a <i>chisel point</i>, and those for freehand work with a <i>round point</i>.<span class='pagenum'><a name="Page_2" id="Page_2">[Pg 2]</a></span>
+<i>Do not wet the pencil</i>, as the lines afterwards made with it are
+very difficult to rub out.</p>
+
+<p>Drawing-paper for working drawings may be secured to
+the board by <i>drawing-pins</i>, but the paper for finished drawings
+or drawings upon which there is to be a large amount of
+colouring should be <i>stretched</i> upon the board.</p>
+
+<p>The student should get the best instruments he can afford
+to buy, and he should rather have a few good instruments than
+a large box of inferior ones.</p>
+
+<p><i>Drawing-paper.</i>&mdash;The names and sizes of the sheets of
+drawing paper are given in the following table:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="1" cellspacing="0" summary="">
+<tr><td align='left'></td><td align='center'>Inches</td></tr>
+<tr><td align='left'>Demy</td><td align='left'>20 &times; 15</td></tr>
+<tr><td align='left'>Medium</td><td align='left'>22 &times; 17</td></tr>
+<tr><td align='left'>Royal</td><td align='left'>24 &times; 19</td></tr>
+<tr><td align='left'>Imperial</td><td align='left'>30 &times; 22</td></tr>
+<tr><td align='left'>Atlas</td><td align='left'>34 &times; 26</td></tr>
+<tr><td align='left'>Double Elephant &nbsp; &nbsp;</td><td align='left'>40 &times; 27</td></tr>
+<tr><td align='left'>Antiquarian</td><td align='left'>52 &times; 31</td></tr>
+</table></div>
+
+<p>The above sizes must not be taken as exact. In practice
+they will be found to vary in some cases as much as an inch.</p>
+
+<p>Cartridge-paper is made in sheets of various sizes, and also
+in rolls.</p>
+
+<p>Hand-made paper is the best, but it is expensive. Good
+cartridge-paper is quite suitable for ordinary drawings.</p>
+
+<p><i>Centre Lines.</i>&mdash;Drawings of most parts of machines will be
+found to be symmetrical about certain lines called <i>centre lines</i>.
+These lines should be drawn first with great care. On a pencil
+drawing centre lines should be thin continuous lines; in this
+book they are shown thus &mdash; - &mdash; - &mdash;.</p>
+
+<p>After drawing the centre line of any part the dimensions
+of that part must be marked off from the centre line, so as to
+insure that it really is the centre line of that part: thus in
+making a drawing of a rivet, such as is shown at (<i>a</i>) fig. 1,
+after drawing the centre line, half the diameter of the rivet
+would be marked off on each side of that line, in order to
+determine the lines for the sides of the rivet.</p>
+
+<p><i>Inking.</i>&mdash;For inking in drawings the best Indian ink
+should be used, and not common writing ink. Common ink<span class='pagenum'><a name="Page_3" id="Page_3">[Pg 3]</a></span>
+does not dry quick enough, and rapidly corrodes the drawing
+pens. The pen should be filled by means of a brush or a
+narrow strip of paper, and not by dipping the pen into the ink.</p>
+
+<p>In cases where there are straight lines and arcs of circles
+touching one another <i>ink in the arcs first</i>, then the straight
+lines; in this way it is easier to hide the joints.</p>
+
+<p><i>Colouring.</i>&mdash;Camel's-hair or sable brushes should be used;
+the latter are the best, but are much more expensive than the
+former. The colour should be rubbed down in a dish, and the
+tint should be light. The mistake which a beginner invariably
+makes is in having the colour of too dark a tint.</p>
+
+<p>First go over the part to be coloured with the brush and
+<i>clean</i> water for the purpose of damping it. Next dry with
+clean blotting-paper to take off any superfluous water. Then
+take another brush with the colour, and beginning at the top,
+work from left to right and downwards. If it is necessary to
+recolour any part let the first coating dry before beginning.</p>
+
+<p>Engineers have adopted certain colours to represent particular
+materials; these are given in the following table:&mdash;</p>
+
+<p class="tabcap"><i>Table showing Colours used to represent Different Materials.</i></p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='center'><span class="smcap">Material</span></td><td align='center'><span class="smcap">Colour</span></td></tr>
+<tr><td align='left'>Cast iron</td><td align='left'>Payne's grey or neutral tint.</td></tr>
+<tr><td align='left'>Wrought iron</td><td align='left'>Prussian blue.</td></tr>
+<tr><td align='left'>Steel</td><td align='left'>Purple (mixture of Prussian blue and crimson lake).</td></tr>
+<tr><td align='left'>Brass</td><td align='left'>Gamboge with a little sienna or a very little red added.</td></tr>
+<tr><td align='left'>Copper</td><td align='left'>A mixture of crimson lake and gamboge, the former colour predominating.</td></tr>
+<tr><td align='left'>Lead</td><td align='left'>Light Indian ink with a very little indigo added.</td></tr>
+<tr><td align='left'>Brickwork</td><td align='left'>Crimson lake and burnt sienna.</td></tr>
+<tr><td align='left'>Firebrick</td><td align='left'>Yellow and Vandyke brown.</td></tr>
+<tr><td align='left'>Greystones</td><td align='left'>Light sepia or pale Indian ink, with a little Prussian blue added.</td></tr>
+<tr><td align='left'>Brown freestone &nbsp; &nbsp;</td><td align='left'>Mixture of pale Indian ink, burnt sienna, and carmine.</td></tr>
+<tr><td align='left'>Soft woods</td><td align='left'>For ground work, pale tint of sienna.</td></tr>
+<tr><td align='left'>Hard woods</td><td align='left'>For ground work, pale tint of sienna with a little red added.</td></tr>
+<tr><td align='left'></td><td align='left'>For graining woods use darker tint with a greater proportion of red.</td></tr>
+</table></div>
+<p><span class='pagenum'><a name="Page_4" id="Page_4">[Pg 4]</a></span></p>
+
+<p><i>Printing.</i>&mdash;A good drawing should have its title printed,
+a plain style of letter being used for this purpose, such as the
+following:&mdash;</p>
+
+<div class="figcenter" style="width: 800px;">
+<img src="images/illus012a.png" width="800" height="388" alt="" title="" />
+</div>
+
+<p>The following letters look well <i>if they are well made</i>, but
+they are much more difficult to draw.</p>
+
+<div class="figcenter" style="width: 800px;">
+<img src="images/illus012b.png" width="800" height="188" alt="" title="" />
+</div>
+
+<p>For remarks on a drawing the following style is most suitable:&mdash;</p>
+
+<div class="figcenter" style="width: 800px;">
+<img src="images/illus012.png" width="800" height="68" alt="" title="" />
+</div>
+
+<p>All printing should be done by freehand.</p>
+
+<p><i>Border lines</i> are seldom put on engineering drawings.</p>
+
+<p><i>Working Drawings.</i>&mdash;A good working drawing should be
+prepared in the following manner. It must first be carefully
+outlined in pencil and then inked in. After this all parts cut
+by planes of section should be coloured, the colours used
+indicating the materials of which the parts are made. Parts
+which are round may also be lightly shaded with the brush
+and colours to suit the materials. The centre lines are now
+inked in with <i>red</i> or <i>blue ink</i>. The red ink may be prepared
+by rubbing down the cake of crimson lake, and the blue ink<span class='pagenum'><a name="Page_5" id="Page_5">[Pg 5]</a></span>
+in like manner from the cake of Prussian blue. Next come
+the <i>distance</i> or <i>dimension</i> lines, which should be put in with
+<i>blue</i> or <i>red ink</i>, depending on which colour was used for the
+centre lines. Dimension lines and centre lines are best put in
+of different colour. The arrow-heads at the ends of the
+dimension lines are now put in with <i>black ink</i>, and so are the
+figures for the dimensions. The arrow-heads and the figures
+should be made with a common writing pen. The dimensions
+should be put on neatly. Many a good drawing has its appearance
+spoiled through being slovenly dimensioned.</p>
+
+<p>We may here point out the importance of putting the
+dimensions on a working drawing. If the drawing is not
+dimensioned, the workman must get his sizes from the drawing
+by applying his rule or a suitable scale. Now this operation
+takes time, and is very liable to result in error. Time is
+therefore saved, and the chance of error reduced, by marking
+the sizes in figures.</p>
+
+<p>In practice it is not usual to send original drawings from
+the drawing office to the workshop, but copies only. The copies
+may be produced by various 'processes,' or they may be tracings
+drawn by hand. Many engineers do not ink in their
+original drawings, but leave them in pencil; especially is this
+the case if the drawings are not likely to be much used.</p>
+
+<p><i>Scales.</i>&mdash;The best scales are made of ivory, and are twelve
+inches long. Boxwood scales are much cheaper, although
+not so durable as those made of ivory. If the student does
+not care to go to the expense of ivory or boxwood scales, he
+can get paper ones very cheap, which will be quite sufficient
+for his purpose. The divisions of the scale should be marked
+down to its edge, so that measurements may be made by applying
+the scale directly to the drawing. For working such
+exercises as are in this book the student should be provided
+with the following scales:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="1" cellspacing="0" summary="">
+<tr><td align='center'></td><td align='center'>A scale of</td><td align='center'>1,</td><td align='center'>or</td><td align='center'>12</td><td align='center'>inches to a foot.</td></tr>
+<tr><td align='center'></td><td align='center'>&rdquo;</td><td align='center'><sup>1</sup>&frasl;<sub>2</sub></td><td align='center'>&rdquo;</td><td align='center'>6</td><td align='center'>&rdquo;</td></tr>
+<tr><td align='center'></td><td align='center'>&rdquo;</td><td align='center'><sup>1</sup>&frasl;<sub>3</sub></td><td align='center'>&rdquo;</td><td align='center'>4</td><td align='center'>&rdquo;</td></tr>
+<tr><td align='center'></td><td align='center'>&rdquo;</td><td align='center'><sup>1</sup>&frasl;<sub>4</sub></td><td align='center'>&rdquo;</td><td align='center'>3</td><td align='center'>&rdquo;</td></tr>
+<tr><td align='center'></td><td align='center'>&rdquo;</td><td align='center'><sup>1</sup>&frasl;<sub>6</sub></td><td align='center'>&rdquo;</td><td align='center'>2</td><td align='center'>&rdquo;</td></tr>
+</table></div>
+<p><span class='pagenum'><a name="Page_6" id="Page_6">[Pg 6]</a></span></p>
+
+<p>A scale of 1 is spoken of as 'full size,' and a scale of <sup>1</sup>&frasl;<sub>2</sub> as
+'half size.'</p>
+
+<p>Engineers in this country state dimensions of machines in
+feet, inches, and fractions of an inch, the latter being the <sup>1</sup>&frasl;<sub>2</sub>, <sup>1</sup>&frasl;<sub>4</sub>,
+<sup>1</sup>&frasl;<sub>8</sub>, <sup>1</sup>&frasl;<sub>16</sub>, &amp;c. In making calculations it is generally more convenient
+to use decimal fractions, and then substitute for the
+results the equivalent fractions in eighths, sixteenths, &amp;c.
+The following table will be found useful for this purpose:&mdash;</p>
+
+<p class="tabcap"><i>Decimal Equivalents of Fractions of an Inch.</i></p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="" rules="groups">
+<colgroup><col width="25%" /></colgroup>
+<colgroup><col width="25%" /></colgroup>
+<colgroup><col width="25%" /></colgroup>
+<colgroup><col width="25%" /></colgroup>
+<thead>
+<tr>
+<th class="bbox"><small>Fraction</small></th>
+<th class="bbox"><small>Decimal Equivalent</small></th>
+<th class="bbox"><small>Fraction</small></th>
+<th class="bbox"><small>Decimal Equivalent</small></th>
+</tr>
+</thead>
+<tbody>
+<tr><td align='left'> <sup>1</sup>&frasl;<sub>32</sub></td><td align='left'> &middot;03125</td><td align='left'> <sup>17</sup>&frasl;<sub>32</sub></td><td align='left'> &middot;53125</td></tr>
+<tr><td align='right'> <sup>1</sup>&frasl;<sub>16</sub></td><td align='left'> &middot;0625</td><td align='right'> <sup>9</sup>&frasl;<sub>16</sub></td><td align='left'> &middot;5625</td></tr>
+<tr><td align='left'> <sup>3</sup>&frasl;<sub>32</sub></td><td align='left'> &middot;09375</td><td align='left'> <sup>19</sup>&frasl;<sub>32</sub></td><td align='left'> &middot;59375</td></tr>
+<tr><td align='right'> <sup>1</sup>&frasl;<sub>8</sub></td><td align='left'> &middot;125</td><td align='right'> <sup>5</sup>&frasl;<sub>8</sub></td><td align='left'> &middot;625</td></tr>
+<tr><td align='left'> <sup>5</sup>&frasl;<sub>32</sub></td><td align='left'> &middot;15625</td><td align='left'> <sup>21</sup>&frasl;<sub>32</sub></td><td align='left'> &middot;65625</td></tr>
+<tr><td align='right'> <sup>3</sup>&frasl;<sub>16</sub></td><td align='left'> &middot;1875</td><td align='right'> <sup>11</sup>&frasl;<sub>16</sub></td><td align='left'> &middot;6875</td></tr>
+<tr><td align='left'> <sup>7</sup>&frasl;<sub>32</sub></td><td align='left'> &middot;21875</td><td align='left'> <sup>23</sup>&frasl;<sub>32</sub></td><td align='left'> &middot;71875</td></tr>
+<tr><td align='right'> <sup>1</sup>&frasl;<sub>4</sub></td><td align='left'> &middot;25</td><td align='right'> <sup>3</sup>&frasl;<sub>4</sub></td><td align='left'> &middot;75</td></tr>
+<tr><td align='left'> <sup>9</sup>&frasl;<sub>32</sub></td><td align='left'> &middot;28125</td><td align='left'> <sup>25</sup>&frasl;<sub>32</sub></td><td align='left'> &middot;78125</td></tr>
+<tr><td align='right'> <sup>5</sup>&frasl;<sub>16</sub></td><td align='left'> &middot;3125</td><td align='right'> <sup>13</sup>&frasl;<sub>16</sub></td><td align='left'> &middot;8125</td></tr>
+<tr><td align='left'> <sup>11</sup>&frasl;<sub>32</sub></td><td align='left'> &middot;34375</td><td align='left'> <sup>27</sup>&frasl;<sub>32</sub></td><td align='left'> &middot;84375</td></tr>
+<tr><td align='right'> <sup>3</sup>&frasl;<sub>8</sub></td><td align='left'> &middot;375</td><td align='right'> <sup>7</sup>&frasl;<sub>8</sub></td><td align='left'> &middot;875</td></tr>
+<tr><td align='left'> <sup>13</sup>&frasl;<sub>32</sub></td><td align='left'> &middot;40625</td><td align='left'> <sup>29</sup>&frasl;<sub>32</sub></td><td align='left'> &middot;90625</td></tr>
+<tr><td align='right'> <sup>7</sup>&frasl;<sub>16</sub></td><td align='left'> &middot;4375</td><td align='right'> <sup>15</sup>&frasl;<sub>16</sub></td><td align='left'> &middot;9375</td></tr>
+<tr><td align='left'> <sup>15</sup>&frasl;<sub>32</sub></td><td align='left'> &middot;46875</td><td align='left'> <sup>31</sup>&frasl;<sub>32</sub></td><td align='left'> &middot;96875</td></tr>
+<tr><td align='right'> <sup>1</sup>&frasl;<sub>2</sub></td><td align='left'> &middot;5</td><td align='right'> 1</td><td align='left'> 1&middot;0</td></tr>
+</tbody>
+</table></div>
+
+<p>Engineers use a single accent (&acute;) to denote <i>feet</i>, and a double
+accent (&acute;&acute;) to denote <i>inches</i>. Thus 2&acute; 9&acute;&acute; reads two feet nine
+inches.</p>
+
+
+
+<hr style="width: 15%;" />
+<h2>II. &nbsp; RIVETED JOINTS.</h2>
+
+
+<p>Two plates or pieces to be riveted together have holes
+punched or drilled in them in such a manner that one may be
+made to overlap the other so that the holes in the one may be
+opposite the holes in the other. The rivets, which are round
+bars of iron, or steel, or other metal, are heated to redness
+and inserted in the holes; the head already formed on the
+rivet, and called the tail, is then held up, and the point is hammered
+or pressed so as to form another head. This process of<span class='pagenum'><a name="Page_7" id="Page_7">[Pg 7]</a></span>
+forming the second head on the rivet is known as riveting,
+and may be done by hand-hammering or by a machine.</p>
+
+<p><i>Forms of Rivet Heads.</i>&mdash;In fig. 1 are shown four different
+forms of rivet heads: (<i>a</i>) is a <i>snap head</i>, (<i>b</i>) a <i>conical head</i>
+(<i>c</i>) a <i>pan head</i>, and (<i>d</i>) <i>a countersunk head</i>.</p>
+
+<p><i>Proportions of Rivet Heads.</i>&mdash;The diameter of the snap
+head is about 1&middot;7 times the diameter of the rivet, and its height
+about &middot;6 of the diameter of the rivet. The conical head has a
+diameter twice and a height three quarters of the rivet
+diameter. The greatest diameter of the pan head is about 1&middot;6,
+and its height &middot;7 of the rivet diameter. The greatest diameter
+of the countersunk head may be one and a half, and its depth
+a half of the diameter of the rivet.</p>
+
+<div class="figcenter" style="width: 800px;">
+<img src="images/illus015.jpg" width="800" height="353" alt="Fig. 1." title="Fig. 1." />
+<span class="caption">Fig. 1.</span>
+</div>
+
+<p>In fig. 1 at (<i>a</i>) and (<i>b</i>) are shown geometrical constructions
+devised by the author for drawing the snap and conical head
+for any size of rivet, the proportions being nearly the same as
+those given above.</p>
+
+<p><i>Geometrical Construction for Proportioning Snap Heads.</i>&mdash;With
+centre A, and radius equal to half diameter of rivet,
+describe a circle cutting the centre line of the rivet at B and C.
+With centre B and radius BC describe the arc CD. Make
+BE equal to AD. With centre E and radius ED describe the
+arc DFH.</p>
+
+<p><i>Construction for Conical Head.</i>&mdash;With centre K, and radius
+equal to diameter of rivet, describe the semicircle LMN, cutting
+the side of the rivet at M. With centre M and radius MN<span class='pagenum'><a name="Page_8" id="Page_8">[Pg 8]</a></span>
+describe the arc NP to cut the centre line of rivet at P. Join
+PL and PN.</p>
+
+<p>When a number of rivets of the same diameter have to be
+shown on the same drawing the above constructions need only
+be performed on one rivet. After the point E has been discovered
+the distance AE may be measured off on all the other
+rivets, and the arcs corresponding to DFH drawn with radii
+equal to ED. In like manner the height KP of the conical
+head may be marked off on all rivets of the same diameter
+with conical heads.</p>
+
+<p><i>Caulking.</i>&mdash;In order to make riveted joints steam- or water-tight
+the edges of the plates and the edges of the heads of the
+rivets are burred down by a blunt chisel or caulking tool as
+shown at Q and R.</p>
+
+<div class="figcenter" style="width: 800px;">
+<div class="figleft" style="width: 331px;">
+<img src="images/illus016a.jpg" width="331" height="640" alt="Fig. 2." title="Fig. 2." />
+<span class="caption">Fig. 2.</span>
+</div>
+<div class="figright" style="width: 396px;">
+<img src="images/illus016b.jpg" width="396" height="640" alt="Fig. 3." title="Fig. 3." />
+<span class="caption">Fig. 3.</span>
+</div>
+</div>
+<div style="clear: both;"></div>
+
+<div class="blockquot">
+<p><span class="smcap">Exercise</span> 1: <i>Forms of Rivets.</i>&mdash;Draw, full size, the rivets and
+rivet heads shown in fig. 1. The diameter of the rivet in each case
+to be 1<small><sup>1</sup>&frasl;<sub>8</sub></small> inches, and the thickness of the plates <sup>7</sup>&frasl;<sub>8</sub>
+inch.</p>
+
+<p><span class="smcap">Exercise</span> 2: <i>Single Riveted Lap Joint.</i>&mdash;Draw, full size, the<span class='pagenum'><a name="Page_9" id="Page_9">[Pg 9]</a></span>
+plan and sectional elevation of the <i>single riveted lap joint</i> shown
+in fig. 2.</p>
+</div>
+
+<p class="tabcap"><i>Table showing the Proportions of Single Riveted Lap Joints for various
+Thicknesses of Plates.</i> (<i>Plates and Rivets Wrought Iron.</i>)</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="" rules="cols">
+<thead>
+<tr><th class="bbox"><small>Thickness of plates</small></th>
+<th class="bbox"> <sup>1</sup>&frasl;<sub>4</sub></th>
+<th class="bbox"> <sup>5</sup>&frasl;<sub>16</sub></th>
+<th class="bbox"> <sup>3</sup>&frasl;<sub>8</sub></th>
+<th class="bbox"> <sup>7</sup>&frasl;<sub>16</sub></th>
+<th class="bbox"> <sup>1</sup>&frasl;<sub>2</sub></th>
+<th class="bbox"> <sup>9</sup>&frasl;<sub>16</sub></th>
+<th class="bbox"> <sup>5</sup>&frasl;<sub>8</sub></th>
+<th class="bbox"> <sup>11</sup>&frasl;<sub>16</sub></th>
+<th class="bbox"> <sup>3</sup>&frasl;<sub>4</sub></th>
+</tr>
+</thead>
+<tbody>
+<tr><td align='left'>Diameter of rivets</td>
+<td align='center'> <sup>9</sup>&frasl;<sub>16</sub></td>
+<td align='center'> <sup>5</sup>&frasl;<sub>8</sub></td>
+<td align='center'> <sup>11</sup>&frasl;<sub>16</sub></td>
+<td align='center'> <sup>3</sup>&frasl;<sub>4</sub></td>
+<td align='center'> <sup>13</sup>&frasl;<sub>16</sub></td>
+<td align='center'> <sup>7</sup>&frasl;<sub>8</sub></td>
+<td align='center'> <sup>15</sup>&frasl;<sub>16</sub></td>
+<td align='center'> 1</td>
+<td align='center'> 1<small><sup>1</sup>&frasl;<sub>16</sub></small></td></tr>
+<tr><td align='left'>Pitch of rivets</td>
+<td align='center'> 1<small><sup>5</sup>&frasl;<sub>8</sub></small></td>
+<td align='center'> 1&frac34;</td>
+<td align='center'> 1<small><sup>7</sup>&frasl;<sub>8</sub></small></td>
+<td align='center'> 2</td>
+<td align='center'> 2<small><sup>1</sup>&frasl;<sub>8</sub></small></td>
+<td align='center'> 2&frac14;</td>
+<td align='center'> 2<small><sup>5</sup>&frasl;<sub>16</sub></small></td>
+<td align='center'> 2<small><sup>3</sup>&frasl;<sub>8</sub></small></td>
+<td align='center'> 2&frac12;</td></tr>
+<tr><td align='left'>Width of lap</td>
+<td align='center'> 1&frac34;</td>
+<td align='center'> 2</td>
+<td align='center'> 2&frac14;</td>
+<td align='center'> 2&frac12;</td>
+<td align='center'> 2&frac34;</td>
+<td align='center'> 2<small><sup>7</sup>&frasl;<sub>8</sub></small></td>
+<td align='center'> 3</td>
+<td align='center'> 3<small><sup>1</sup>&frasl;<sub>8</sub></small></td>
+<td align='center'> 3&frac14;</td></tr>
+<tr><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td></tr>
+</tbody>
+</table></div>
+
+<p class="center">All the dimensions are in inches.</p>
+
+<div class="figcenter" style="width: 500px;">
+<img src="images/illus017.jpg" width="500" height="800" alt="Fig. 4." title="Fig. 4." />
+<span class="caption">Fig. 4.</span>
+</div>
+
+
+<div class="blockquot">
+<p><span class="smcap">Exercise</span> 3.&mdash;Draw, half size, a plan and section of a single
+riveted lap joint for plates <sup>3</sup>&frasl;<sub>4</sub>&acute;&acute; thick to the dimensions given in the
+above table.</p>
+
+<p><span class="smcap">Exercise</span> 4: <i>Double Riveted Lap Joint.</i>&mdash;Draw, full size, the
+two views of the <i>double riveted lap joint</i> shown in fig. 3.</p>
+</div>
+
+<p><span class='pagenum'><a name="Page_10" id="Page_10">[Pg 10]</a></span></p>
+
+<p class="tabcap"><i>Table showing the Proportions of Double Riveted Lap Joints for various
+Thicknesses of Plates.</i> (<i>Plates and Rivets Wrought Iron.</i>)</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="" rules="cols">
+<thead>
+<tr><th class="bbox"><small>Thickness of plates</small></th>
+<th class="bbox"> <sup>3</sup>&frasl;<sub>8</sub></th>
+<th class="bbox"> <sup>7</sup>&frasl;<sub>16</sub></th>
+<th class="bbox"> <sup>1</sup>&frasl;<sub>2</sub></th>
+<th class="bbox"> <sup>9</sup>&frasl;<sub>16</sub></th>
+<th class="bbox"> <sup>5</sup>&frasl;<sub>8</sub></th>
+<th class="bbox"> <sup>11</sup>&frasl;<sub>16</sub></th>
+<th class="bbox"> <sup>3</sup>&frasl;<sub>4</sub></th>
+<th class="bbox"> <sup>13</sup>&frasl;<sub>16</sub></th>
+<th class="bbox"> <sup>7</sup>&frasl;<sub>8</sub></th>
+<th class="bbox"> <sup>15</sup>&frasl;<sub>16</sub></th>
+<th class="bbox"> 1</th>
+</tr>
+</thead>
+<tbody>
+<tr><td align='left'>Diameter of rivets</td><td align='center'><sup>11</sup>&frasl;<sub>16</sub></td><td align='center'> <sup>3</sup>&frasl;<sub>4</sub></td><td align='center'><sup>13</sup>&frasl;<sub>16</sub></td><td align='center'> <sup>7</sup>&frasl;<sub>8</sub></td><td align='center'><sup>15</sup>&frasl;<sub>16</sub></td><td align='center'> 1</td><td align='center'>1<small><sup>1</sup>&frasl;<sub>16</sub></small></td><td align='center'> 1<small><sup>1</sup>&frasl;<sub>16</sub></small></td><td align='center'> 1<small><sup>1</sup>&frasl;<sub>8</sub></small></td><td align='center'> 1<small><sup>1</sup>&frasl;<sub>8</sub></small></td><td align='center'>1<small><sup>3</sup>&frasl;<sub>16</sub></small></td></tr>
+<tr><td align='left'>Pitch of rivets</td><td align='center'>2&frac12;</td><td align='center'>2<small><sup>5</sup>&frasl;<sub>8</sub></small></td><td align='center'>2&frac34;</td><td align='center'>2<small><sup>7</sup>&frasl;<sub>8</sub></small></td><td align='center'> 3</td><td align='center'> 3<small><sup>1</sup>&frasl;<sub>8</sub></small></td><td align='center'>3&frac14;</td><td align='center'> 3<small><sup>3</sup>&frasl;<sub>8</sub></small></td><td align='center'> 3&frac12;</td><td align='center'> 3<small><sup>5</sup>&frasl;<sub>8</sub></small></td><td align='center'> 3&frac34;</td></tr>
+<tr><td align='left'>Distance between rows of rivets</td><td align='center'>1<small><sup>1</sup>&frasl;<sub>8</sub></small></td><td align='center'>1&frac14;</td><td align='center'>1<small><sup>3</sup>&frasl;<sub>8</sub></small></td><td align='center'>1<small><sup>7</sup>&frasl;<sub>16</sub></small></td><td align='center'>1<small><sup>9</sup>&frasl;<sub>16</sub></small></td><td align='center'> 1&frac34;</td><td align='center'>1<small><sup>7</sup>&frasl;<sub>8</sub></small></td><td align='center'> 1<small><sup>7</sup>&frasl;<sub>8</sub></small></td><td align='center'>1<small><sup>15</sup>&frasl;<sub>16</sub></small></td><td align='center'>1<small><sup>15</sup>&frasl;<sub>16</sub></small></td><td align='center'> 2</td></tr>
+<tr><td align='left'>Width of lap</td><td align='center'>3&frac12;</td><td align='center'>3&frac34;</td><td align='center'> 4</td><td align='center'>4&frac14;</td><td align='center'>4&frac12;</td><td align='center'> 4&frac34;</td><td align='center'> 5</td><td align='center'> 5</td><td align='center'> 5&frac14;</td><td align='center'> 5&frac14;</td><td align='center'> 5&frac12;</td></tr>
+<tr><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td></tr>
+</tbody>
+</table></div>
+
+<div class="figcenter" style="width: 600px;">
+<img src="images/illus018.jpg" width="600" height="630" alt="Fig. 5." title="Fig. 5." />
+<span class="caption">Fig. 5.</span>
+</div>
+
+<div class="blockquot">
+<p><span class="smcap">Exercise</span> 5.&mdash;Draw, half size, a plan and section of a double
+riveted lap joint for plates <sup>7</sup>&frasl;<sub>8</sub> inch thick to the dimensions given in
+the above table.</p>
+
+<p><span class="smcap">Exercise</span> 6: <i>Single Riveted Butt Joints.</i>&mdash;In fig. 4 are shown
+<i>single riveted butt joints</i>. One of the sectional views shows a butt
+joint with one <i>cover plate</i> or <i>butt strap</i>; the other sectional view<span class='pagenum'><a name="Page_11" id="Page_11">[Pg 11]</a></span>
+shows the same joint with two cover plates; the third view is a
+plan of both arrangements. Draw all these views full size.</p>
+</div>
+
+<div class="figcenter" style="width: 600px;">
+<img src="images/illus019.jpg" width="600" height="703" alt="Fig. 6." title="Fig. 6." />
+<span class="caption">Fig. 6.</span>
+</div>
+
+<div class="blockquot">
+<p><span class="smcap">Exercise</span> 7.&mdash;Fig. 5 shows a plan and sectional elevation of the
+connection of three plates together, which are in the same plane,
+by means of single riveted butt joints and single cover plates. The
+butt straps where they overlap are forged so as to fit one another
+as shown, and thus form a close joint. Draw these views to the
+scale of 6 inches to a foot.</p>
+
+<p>The plates are <sup>1</sup>&frasl;<sub>2</sub> inch thick and the butt straps <sup>9</sup>&frasl;<sub>16</sub> inch thick.
+All other dimensions must be deduced from the table for single
+riveted lap joints.</p>
+
+<p><span class='pagenum'><a name="Page_12" id="Page_12">[Pg 12]</a></span></p>
+
+<p><span class="smcap">Exercise</span> 8.&mdash;The connection of three plates by single riveted
+lap joints is shown in fig. 6. To make the joint close one plate has
+a portion of its edge thinned out, and the plate above it is set up at
+this part so as to lie close to the former.</p>
+
+<p>Draw the three views shown in fig. 6 to the same scale as the
+last exercise.</p>
+
+<p>The plates are <sup>7</sup>&frasl;<sub>16</sub> inch thick. All other dimensions to be obtained
+from table for single riveted lap joints.</p>
+
+<p><span class="smcap">Exercise</span> 9: <i>Corner of Wrought-iron Tank.</i>&mdash;This exercise is
+to illustrate the connection of plates which are at right angles to
+one another by means of <i>angle irons</i>. Fig. 7 is a plan and elevation
+of the corner of a wrought-iron tank. The sides of the tank
+are riveted to a vertical angle iron, the cross section of which is
+clearly shown in the plan. Another angle iron of the same dimensions
+is used in the same way to connect the sides with the bottom.
+The sides do not come quite up to the corner of the vertical angle
+iron, excepting at the bottom where the horizontal angle iron comes
+in. At this point the vertical plates meet one another, and the
+edge formed is rounded over to fit the interior of the bend of the
+horizontal angle iron so as to make the joint tight. Draw half
+size.</p>
+
+<p>The dimensions are as follows: angle irons 2&frac12; inches &times; 2&frac12; inches
+&times; <sup>3</sup>&frasl;<sub>8</sub> inch; plates <sup>3</sup>&frasl;<sub>8</sub> inch thick;
+rivets <sup>11</sup>&frasl;<sub>16</sub> inch diameter and 2 inches
+pitch.</p>
+
+<p><span class="smcap">Exercise</span> 10: <i>Gusset Stay.</i>&mdash;In order that the flat ends of a
+steam boiler may not be bulged out by the pressure of the steam
+they are strengthened by means of stays. One form of boiler stay,
+called a 'gusset stay,' is shown in fig. 8. This stay consists of a
+strip of wrought-iron plate which passes in a diagonal direction
+from the flat end of the boiler to the cylindrical shell. One end of
+this plate is placed between and riveted to two angle irons
+which are riveted to the shell of the boiler. A similar arrangement
+connects the other end of the stay plate to the flat end of the
+boiler. In this example the stay or gusset plate is &frac34; of an inch
+thick; the angle irons are 4 inches broad and &frac12; inch thick. The
+rivets are 1 inch in diameter. The same figure also illustrates the
+most common method of connecting the ends of a boiler to the
+shell. The end plates are <i>flanged</i> or bent over at right angles and
+riveted to the shell as shown. The radius of the inside curve at
+the angle of the flange is 1&frac14; inches. Draw this example to a scale
+of 3 inches to 1 foot.</p>
+</div>
+
+<p><span class='pagenum'><a name="Page_13" id="Page_13">[Pg 13]</a></span></p>
+
+<div class="figcenter" style="width: 1024px;">
+<div class="figleft" style="width: 341px;">
+<img src="images/illus021a.jpg" width="341" height="640" alt="Fig. 7." title="Fig. 7." />
+<span class="caption">Fig. 7.</span>
+</div>
+<div class="figright" style="width: 630px;">
+<img src="images/illus021b.jpg" width="630" height="635" alt="Fig. 8." title="Fig. 8." />
+<span class="caption">Fig. 8.</span>
+</div>
+</div>
+
+
+
+
+<hr style="width: 15%;" />
+<p><span class='pagenum'><a name="Page_14" id="Page_14">[Pg 14]</a></span></p>
+<h2>III. &nbsp; SCREWS, BOLTS, AND NUTS.</h2>
+
+
+<p><i>Screw Threads.</i>&mdash;The various forms of screw threads used
+in machine construction are shown in fig. 9. The <i>Whitworth</i> <b>V</b>
+thread is shown at (<i>a</i>). This is the standard form of triangular
+thread used in this country. The angle between the sides of
+the <b>V</b> is 55&deg;, and one-sixth of the total depth is rounded off
+both at the top and bottom. At (<i>b</i>) is shown the <i>Sellers</i> <b>V</b>
+thread, which is the standard triangular thread used by engineers
+in America. In this form of thread the angle between the
+sides of the <b>V</b> is 60&deg;, and one-eighth of the total depth is cut
+square off at the top and bottom. The <i>Square</i> thread is shown
+at (<i>c</i>). This form is principally used for transmitting motion.</p>
+
+<div class="figcenter" style="width: 800px;">
+<img src="images/illus022.jpg" width="800" height="495" alt="Fig. 9." title="Fig. 9." />
+<span class="caption">Fig. 9.</span>
+</div>
+
+<p>Comparing the triangular and square threads, the former is
+the stronger of the two; but owing to the normal pressure on
+the <b>V</b> thread being inclined to the axis of the screw, that pressure
+must be greater than the pressure which is being transmitted
+by the screw; and therefore, seeing that the normal
+pressure on the square thread is parallel, and therefore equal
+to the pressure transmitted in the direction of the axis of the
+screw, the friction of the <b>V</b> thread must be greater than the
+<span class='pagenum'><a name="Page_15" id="Page_15">[Pg 15]</a></span>friction of the square thread. In the case of the triangular
+thread there is also a tendency of the pressure to burst the
+nut. The <i>Buttress</i> thread shown at (<i>e</i>) is designed to combine
+the advantages of the <b>V</b> and square threads, but it only has
+these advantages when the pressure is transmitted in one
+direction; if the direction of the pressure be reversed, the
+friction and bursting action on the nut are even greater than
+with the <b>V</b> thread, because of the greater inclination of the
+slant side of the buttress thread. The angles of the square
+thread are frequently rounded to a greater or less extent to
+render them less easily damaged. If this rounding is carried to
+excess we get the <i>Knuckle</i> thread shown at (<i>d</i>). The rounding
+of the angles increases both the strength and the friction.</p>
+
+
+<div class="blockquot">
+<p><span class="smcap">Exercise</span> 11: <i>Forms of Screw Threads.</i>&mdash;Draw to a scale of
+three times full size the sections of screw threads as shown in
+fig. 9. The pitch for the Whitworth, Sellers, and buttress threads
+to be <sup>3</sup>&frasl;<sub>8</sub> inch, and the pitch of the square and knuckle threads to be
+<sup>1</sup>&frasl;<sub>2</sub> inch.</p>
+</div>
+
+
+<p class="tabcap"><i>Dimensions of Whitworth Screws.</i></p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="" rules="cols">
+<thead>
+<tr>
+<th class="bbox"><small>Diameter<br />of screw</small></th>
+<th class="bbox"><small>Number of <br />threads per inch</small></th>
+<th class="bbox"><small>Diameter at<br />bottom of thread</small></th>
+<th class="bbox"><small>Diameter<br />of screw</small></th>
+<th class="bbox"><small>Number of <br />threads per inch</small></th>
+<th class="bbox"><small>Diameter at<br />bottom of thread</small></th>
+<th class="bbox"><small>Diameter<br />of screw</small></th>
+<th class="bbox"><small>Number of <br />threads per inch</small></th>
+<th class="bbox"><small>Diameter at<br />bottom of thread</small></th>
+</tr>
+</thead>
+<tbody>
+<tr><td align='right'> <sup>1</sup>&frasl;<sub>8</sub></td><td align='right'> 40</td><td align='right'> &middot;093</td>
+<td align='right'> 1&frac14;</td><td align='right'> 7</td><td align='right'> 1&middot;067</td>
+<td align='right'> 3&frac12;</td><td align='right'> 3&frac14;</td><td align='right'> 3&middot;106</td></tr>
+
+<tr><td align='left'> <sup>3</sup>&frasl;<sub>16</sub></td><td align='right'> 24</td><td align='right'> &middot;134</td>
+<td align='left'> 1<small><sup>3</sup>&frasl;<sub>8</sub></small></td><td align='right'> 6</td><td align='right'> 1&middot;162</td>
+<td align='left'> 3&frac34;</td><td align='right'> 3</td><td align='right'> 3&middot;323</td></tr>
+
+<tr><td align='right'> <sup>1</sup>&frasl;<sub>4</sub></td><td align='right'> 20</td><td align='right'> &middot;186</td>
+<td align='right'> 1&frac12;</td><td align='right'> 6</td><td align='right'> 1&middot;286</td>
+<td align='right'> 4</td><td align='right'> 3</td><td align='right'> 3&middot;573</td></tr>
+
+<tr><td align='left'> <sup>5</sup>&frasl;<sub>16</sub></td><td align='right'> 18</td><td align='right'> &middot;241</td>
+<td align='left'> 1<small><sup>5</sup>&frasl;<sub>8</sub></small></td><td align='right'> 5</td><td align='right'> 1&middot;369</td>
+<td align='left'> 4&frac14;</td><td align='right'> 2<small><sup>7</sup>&frasl;<sub>8</sub></small></td><td align='right'> 3&middot;805</td></tr>
+
+<tr><td align='right'> <sup>3</sup>&frasl;<sub>8</sub></td><td align='right'> 16</td><td align='right'> &middot;295</td>
+<td align='right'> 1&frac34;</td><td align='right'> 5</td><td align='right'> 1&middot;494</td>
+<td align='right'> 4&frac12;</td><td align='right'> 2<small><sup>7</sup>&frasl;<sub>8</sub></small></td><td align='right'> 4&middot;055</td></tr>
+
+<tr><td align='left'> <sup>7</sup>&frasl;<sub>16</sub></td><td align='right'> 14</td><td align='right'> &middot;346</td>
+<td align='left'> 1<small><sup>7</sup>&frasl;<sub>8</sub></small></td><td align='right'> 4&frac12;</td><td align='right'> 1&middot;590</td>
+<td align='left'> 4&frac34;</td><td align='right'> 2&frac34;</td><td align='right'> 4&middot;284</td></tr>
+
+<tr><td align='right'> <sup>1</sup>&frasl;<sub>2</sub></td><td align='right'> 12</td><td align='right'> &middot;393</td>
+<td align='right'> 2</td><td align='right'> 4&frac12;</td><td align='right'> 1&middot;715</td>
+<td align='right'> 5</td><td align='right'> 2&frac34;</td><td align='right'> 4&middot;534</td></tr>
+
+<tr><td align='left'> <sup>5</sup>&frasl;<sub>8</sub></td><td align='right'> 11</td><td align='right'> &middot;508</td>
+<td align='left'> 2&frac14;</td><td align='right'> 4</td><td align='right'> 1&middot;930</td>
+<td align='left'> 5&frac14;</td><td align='right'> 2<small><sup>5</sup>&frasl;<sub>8</sub></small></td><td align='right'> 4&middot;762</td></tr>
+
+<tr><td align='right'> <sup>3</sup>&frasl;<sub>4</sub></td><td align='right'> 10</td><td align='right'> &middot;622</td>
+<td align='right'> 2&frac12;</td><td align='right'> 4</td><td align='right'> 2&middot;180</td>
+<td align='right'> 5&frac12;</td><td align='right'> 2<small><sup>5</sup>&frasl;<sub>8</sub></small></td><td align='right'> 5&middot;012</td></tr>
+
+<tr><td align='left'> <sup>7</sup>&frasl;<sub>8</sub></td><td align='right'> 9</td><td align='right'> &middot;733</td>
+<td align='left'> 2&frac34;</td><td align='right'> 3&frac12;</td><td align='right'> 2&middot;384</td>
+<td align='left'> 5&frac34;</td><td align='right'> 2&frac12;</td><td align='right'> 5&middot;238</td></tr>
+
+<tr><td align='right'> 1</td><td align='right'> 8</td><td align='right'> &middot;840</td>
+<td align='right'> 3</td><td align='right'> 3&frac12;</td><td align='right'> 2&middot;634</td>
+<td align='right'> 6</td><td align='right'> 2&frac12;</td><td align='right'> 5&middot;488</td></tr>
+
+<tr><td align='left'> 1<small><sup>1</sup>&frasl;<sub>8</sub></small></td><td align='right'> 7</td><td align='right'> &middot;942</td>
+<td align='left'> 3&frac14;</td><td align='right'> 3&frac14;</td><td align='right'> 2&middot;856</td>
+<td></td><td></td><td></td></tr>
+
+<tr><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td></tr>
+</tbody>
+</table></div>
+
+<p class="tabcap"><i>Gas Threads</i><a name="FNanchor_1_1" id="FNanchor_1_1"></a><a href="#Footnote_1_1" class="fnanchor">[1]</a> (<i>Whitworth Standard</i>).</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="" rules="cols">
+<thead>
+<tr><th class="bbox"><small>Diameter of Screw</small></th>
+<th class="bbox"> <sup>1</sup>&frasl;<sub>8</sub></th>
+<th class="bbox"> <sup>1</sup>&frasl;<sub>4</sub></th>
+<th class="bbox"> <sup>3</sup>&frasl;<sub>8</sub></th>
+<th class="bbox"> <sup>1</sup>&frasl;<sub>2</sub></th>
+<th class="bbox"> <sup>5</sup>&frasl;<sub>8</sub></th>
+<th class="bbox"> <sup>3</sup>&frasl;<sub>4</sub></th>
+<th class="bbox"> 1</th>
+<th class="bbox"> 1&frac14;</th>
+<th class="bbox"> 1&frac12;</th>
+<th class="bbox"> 1&frac34;</th>
+<th class="bbox"> 2</th>
+</tr>
+</thead>
+<tbody>
+<tr><td align='center'>Number of threads per inch</td><td align='center'> 28</td><td align='center'> 19</td><td align='center'> 19</td><td align='center'> 14</td><td align='center'> 14</td><td align='center'> 14</td><td align='center'> 11</td><td align='center'> 11</td><td align='center'> 11</td><td align='center'> 11</td><td align='center'> 11</td></tr>
+<tr><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td></tr>
+</tbody>
+</table></div>
+
+<div class="footnote"><p><a name="Footnote_1_1" id="Footnote_1_1"></a><a href="#FNanchor_1_1"><span class="label">[1]</span></a> Used for wrought-iron and brass tubes.<span class='pagenum'><a name="Page_16" id="Page_16">[Pg 16]</a></span></p></div>
+
+<p><i>Representation of Screws.</i>&mdash;The correct method of representing
+screw threads involves considerable trouble, and is
+seldom adopted by engineers for working drawings. For an
+explanation of the method see the author's Text-book on
+Practical Solid Geometry, Part II., problem 134. A method
+very often adopted on working drawings is shown in fig. 15;
+here the thin lines represent the points, and the thick lines
+the roots of the threads. At fig. 16 is shown a more complete
+method. The simplest method is illustrated by figs. 10, 11,
+13, and 14.</p>
+
+<p>Here dotted lines are drawn parallel to the axis of the
+screw as far as it extends, and at a distance from one another
+equal to the diameter of the screw at the bottom of the
+thread.</p>
+
+<div class="figcenter" style="width: 800px;">
+<img src="images/illus024.jpg" width="800" height="510" alt="Figs. 10, 11." title="Figs. 10, 11." />
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="" width="80%">
+<tr><td align='left'><span class="caption">Fig. 10.</span></td><td align='right'><span class="caption">Fig. 11.</span></td></tr>
+</table></div>
+</div>
+
+<p><i>Forms of Nuts.</i>&mdash;The most common form of nut is the
+hexagonal shown in figs. 10, 13, 14, 15, and 16; next to this
+comes the square nut shown in fig. 11. The method of drawing
+these nuts will be understood by reference to the figures; the
+small circles indicate the centres, and the inclined lines passing
+through them the radii of the curves which represent the
+chamfered or bevelled edge of the nut. In all the figures but<span class='pagenum'><a name="Page_17" id="Page_17">[Pg 17]</a></span>
+the first the chamfer is just sufficient to touch the middle
+points of the sides, and in these cases the drawing of the nut is
+simpler.</p>
+
+<div class="figcenter" style="width: 640px;">
+<img src="images/illus025a.jpg" width="640" height="407" alt="Fig. 12." title="Fig. 12." />
+<span class="caption">Fig. 12.</span>
+</div>
+
+<div class="figcenter" style="width: 800px;">
+<img src="images/illus025b.jpg" width="800" height="388" alt="Figs. 13, 14." title="Figs. 13, 14." />
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="" width="80%">
+<tr><td align='left'><span class="caption">Fig. 13.</span></td><td align='right'><span class="caption">Fig. 14.</span></td></tr>
+</table></div>
+</div>
+
+<p><i>Forms of Bolts.</i>&mdash;At (<i>a</i>), fig. 12, is shown a bolt with a
+square head and a square neck. If this form of bolt is passed
+through a square hole the square neck prevents the bolt from
+turning when the nut is being screwed up. Instead of a
+square neck a snug may be used for the same purpose, as shown
+on the cup-headed bolt at (<i>b</i>). The snug fits into a short
+groove cut in the side of the hole through which the bolt<span class='pagenum'><a name="Page_18" id="Page_18">[Pg 18]</a></span>
+passes. At (<i>a</i>) the diagonal lines are used to distinguish the
+flat side of the neck from the round part of the bolt above
+it. At (<i>c</i>) is shown a tee-headed bolt, and at (<i>d</i>) an eye-bolt.
+Fig. 13 represents a hook bolt. A bolt with a countersunk head
+is shown in fig. 11. If the countersunk head be lengthened so
+as to take up the whole of the unscrewed part of the bolt, we
+get the taper bolt shown in fig. 14, which is often used in the
+couplings of the screw shafts of steamships. The taper bolt
+has the advantage of having no projecting head, and it may
+also be made a tight fit in the hole with less trouble than a
+parallel bolt. Bolts may also have hexagonal heads.</p>
+
+<div class="figcenter" style="width: 800px;">
+<div class="figleft" style="width: 390px;">
+<img src="images/illus026a.png" width="390" height="415" alt="Fig. 15." title="Fig. 15." />
+<span class="caption">Fig. 15.</span>
+</div>
+<div class="figright" style="width: 336px;">
+<img src="images/illus026b.png" width="336" height="414" alt="Fig. 16." title="Fig. 16." />
+<span class="caption">Fig. 16.</span>
+</div>
+</div>
+<div style="clear: both;"></div>
+
+<p><i>Studs</i>, or <i>stud bolts</i>, are shown in figs. 15 and 16; that in
+fig. 15 is a <i>plain stud</i>, while that in fig. 16 has an intermediate
+collar forged upon it, and is therefore called a <i>collared stud</i>.</p>
+
+<p><i>Proportions of Nuts and Bolt-heads.</i>&mdash;In the hexagonal nut
+the diameter D across the flats is 1&frac12;<i>d</i> + <sup>1</sup>&frasl;<sub>8</sub>, where <i>d</i> is the
+diameter of the bolt. The same rule gives the width of a
+square nut across the flats. A rule very commonly used in
+making drawings of hexagonal nuts is to make the diameter
+D, across the angles equal to 2<i>d</i>. H, the height of the nut,
+is equal to the diameter of the bolt. In square and hexagonal
+headed bolts the height of the head varies from <i>d</i> to <sup>2</sup>&frasl;<sub>3</sub><i>d</i>;
+the other dimensions are the same as for the corresponding
+nuts.<span class='pagenum'><a name="Page_19" id="Page_19">[Pg 19]</a></span></p>
+
+<p><i>Washers</i> are flat, circular, wrought-iron plates, having holes
+in their centres of the same diameter as the bolts on which
+they are used. The object of the washer is to give a smooth
+bearing surface for the nut to turn upon, and it is used when
+the surfaces of the pieces to be connected are rough, or when
+the bolt passes through a hole larger than itself, as shown in
+fig. 10. The diameter of the washer is a little more than the
+diameter of the nut across the angles, and its thickness about
+<sup>1</sup>&frasl;<sub>8</sub> of the diameter of the bolt.</p>
+
+
+<div class="blockquot">
+<p><span class="smcap">Exercise</span> 12.&mdash;Draw, full size, the views shown in fig. 10 of an
+hexagonal nut and washer for a bolt 1&frac14; inches in diameter. The bolt
+passes through a hole 1&frac34; &times; 1&frac14;. All the dimensions are to be calculated
+from the rules which have just been given.</p>
+
+<p><span class="smcap">Exercise</span> 13.&mdash;Draw, full size, the plan and elevation of the
+square nut and bolt with countersunk head shown in fig. 11, to the
+dimensions given.</p>
+
+<p><span class="smcap">Exercise</span> 14.&mdash;Draw, full size, the elevation of the hook bolt
+with hexagonal nut shown in fig. 13 to the dimensions given, and
+show also a plan.</p>
+
+<p><span class="smcap">Exercise</span> 15.&mdash;Draw, to a scale of 4 inches to a foot, the conical
+bolt for a marine shaft coupling shown in fig. 14. All the parts are
+of wrought iron.</p>
+
+<p><span class="smcap">Exercise</span> 16.&mdash;Fig. 15 is a section of the mouth of a small steam-engine
+cylinder, showing how the cover is attached; draw this full
+size.</p>
+
+<p><span class="smcap">Exercise</span> 17.&mdash;Fig. 16 shows the central portion of the india-rubber
+disc valve which is described on page 68. A is the central
+boss of the grating, into which is screwed the stud B, upon which is
+forged the collar C. The upper part of the stud is screwed, and
+carries the guard D and an hexagonal nut E. F is the india-rubber.
+The grating and guard are of brass. The stud and nut are of
+wrought iron. Draw full size the view shown.</p>
+</div>
+
+
+<p><i>Lock Nuts.</i>&mdash;In order that a nut may turn freely upon a
+bolt, there is always a very small clearance space between the
+threads of the nut and those of the bolt. This clearance is shown
+exaggerated at (<i>a</i>), fig. 17, where A is a portion of a bolt within
+a nut B. Suppose that the bolt is stretched by a force W.
+When the nut B is screwed up, the upper surfaces of the
+projecting threads of the nut will press on the under surfaces<span class='pagenum'><a name="Page_20" id="Page_20">[Pg 20]</a></span>
+of the threads of the bolt with a force P equal and opposite to
+W, as shown at (<i>b</i>), fig. 17. When in this condition the nut
+has no tendency to slacken back, because of the friction due to
+the pressure on the nut. Now suppose that the tension W
+on the bolt is momentarily diminished, then the friction which
+opposes the turning of the nut may be so much diminished
+that a vibration may cause it to slacken back through a small
+angle. If this is repeated a great many times the nut may
+slacken back so far as to become useless.</p>
+
+<div class="figcenter" style="width: 800px;">
+<img src="images/illus028.png" width="800" height="317" alt="Figs. 17, 18." title="Figs. 17, 18." />
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="" width="70%">
+<tr><td align='left'><span class="caption">Fig. 17.</span></td><td align='right'><span class="caption">Fig. 18.</span></td></tr>
+</table></div>
+</div>
+
+<div class="figright" style="width: 412px;">
+<img src="images/illus029.png" width="412" height="640" alt="Fig. 19." title="Fig. 19." />
+<span class="caption">Fig. 19.</span>
+</div>
+
+<p>A very common arrangement for locking a nut is shown at
+(<i>a</i>), fig. 18. C is an ordinary nut, and B one having half the
+thickness of C. B is first screwed up tight so as to act on the
+bolt, as shown at (<i>b</i>), fig. 17. C is then screwed on top of B.
+When C is almost as tight as it can be made, it is held by one
+spanner, while B is turned back through a small angle with
+another. The action of the nuts upon the bolt and upon one
+another is now as shown at (<i>b</i>), fig. 18. It will be seen that
+the nuts are wedged tight on to the bolt, and that this action
+is independent of the tension W in the bolt. The nuts will,
+therefore, remain tight after the tension in the bolt is removed.</p>
+
+<p>It is evident that if the nuts are screwed up in the manner
+explained, the outer nut C will carry the whole load on the
+bolt; hence C should be the thicker of the two nuts. In
+practice, the thin nut, called the lock nut, is often placed on
+the outside, for the reason that ordinary spanners are too
+thick to act on the thin nut when placed under the other.<span class='pagenum'><a name="Page_21" id="Page_21">[Pg 21]</a></span></p>
+
+<p>Another very common arrangement for locking a nut is
+shown in fig. 19. A is the bolt and B the nut, the lower part
+of which is turned circular. A groove C is also turned on the
+nut at this part. The circular part of the nut fits into a
+circular recess in one of the parts connected by the bolt.
+Through this part passes a set screw D, the point of which can
+be made to press on the nut at the bottom of the groove C. D
+is turned back when the nut B is being moved, and when B
+is tightened up, the set
+screw is screwed up so as
+to press hard on the bottom
+of the groove C. The
+nut B is thus prevented
+from slackening back. The
+screw thread is turned off
+the set screw at the point
+where it enters the groove
+on the nut.</p>
+
+<p>The use of the groove
+for receiving the point of
+the set screw is this: The
+point of the set screw indents
+the nut and raises a
+bur which would interfere
+with the free turning of
+the nut in the recess if
+the bur was not at the
+bottom of a groove. Additional
+security is obtained
+by drilling a hole
+through the point of the bolt, and fitting it with a split pin E.</p>
+
+<p>Locking arrangements for nuts are exceedingly numerous,
+and many of them are very ingenious, but want of space prevents
+us describing them. We may point out, however, that
+many very good locking arrangements have the defect of only
+locking the nut at certain points of a revolution, say at every
+30&deg;. It will be noticed that the two arrangements which we
+have described are not open to this objection.<span class='pagenum'><a name="Page_22" id="Page_22">[Pg 22]</a></span></p>
+
+<div class="blockquot">
+<p><span class="smcap">Exercise</span> 18.&mdash;Draw, full size, a plan, front elevation, and side
+elevation of the arrangement of nuts shown in fig. 18, for a bolt <sup>7</sup>&frasl;<sub>8</sub>
+inch diameter.</p>
+
+<p><span class="smcap">Exercise</span> 19.&mdash;Draw the plan and elevation of the nut and locking
+arrangement shown in fig. 19. Make also an elevation looking
+in the direction of the arrow. Scale 6 inches to a foot.</p>
+</div>
+
+
+
+<hr style="width: 15%;" />
+<h2>IV. &nbsp; KEYS.</h2>
+
+
+<p><i>Keys</i> are wedges, generally rectangular in section, but sometimes
+circular; they are made of wrought iron or steel, and
+are used for securing wheels, pulleys, cranks, &amp;c., to shafts.</p>
+
+<div class="figcenter" style="width: 640px;">
+<img src="images/illus030.jpg" width="640" height="398" alt="Fig. 20." title="Fig. 20." />
+<span class="caption">Fig. 20.</span>
+</div>
+
+<p>Various sections of keys are shown in fig. 20. At (<i>a</i>) is the
+<i>hollow</i> or <i>saddle key</i>. With this form of key it is not necessary
+to cut the shaft in any way, but its holding power is small, and
+it is therefore only used for light work. At (<i>b</i>) is the <i>key on a
+flat</i>, sometimes called a <i>flat key</i>. The holding power of this
+key is much greater than that of the saddle key. At (<i>c</i>) is
+the <i>sunk key</i>, a very secure and very common form.</p>
+
+<p>The part of the shaft upon which a key rests is called the
+<i>key bed</i> or <i>key way</i>, and the recess in the boss of the wheel or
+pulley into which the key fits is called the <i>key way</i>; both are
+also called <i>key seats</i>. With saddle, flat, and sunk keys the key
+bed is parallel to the axis of the shaft; but the key way is<span class='pagenum'><a name="Page_23" id="Page_23">[Pg 23]</a></span>
+deeper at one end than the other to accommodate the taper of
+the key. The sides of the key are parallel.</p>
+
+<p>The <i>round key</i> or taper pin shown at (<i>d</i>) is in general only
+used for wheels or cranks which have been previously shrunk
+on to their shafts or forced on by great pressure. After the
+wheel or crank has been shrunk on, a hole is drilled, half into
+the shaft and half into the wheel or crank, to receive the
+pin.</p>
+
+<p>When the point of a key is inaccessible the other end is
+provided with a <i>gib head</i> as shown at (<i>e</i>), to enable the key to
+be withdrawn.</p>
+
+<p>A <i>sliding</i> or <i>feather key</i> secures a piece to a shaft so far as
+to prevent the one from rotating without the other, but allows
+of relative motion in the direction of the axis of the shaft.
+This form of key has no taper, and it is secured to the piece
+carried by the shaft, but is made a <i>sliding fit</i> in the key way of
+the shaft. In one form of feather key the part within the
+piece carried by the shaft is dovetailed as shown at (<i>f</i>). In
+another form the key has a round projecting pin forged upon
+it, which enters a corresponding hole as shown at (<i>g</i>). The
+feather key may also be secured to the piece carried by the
+shaft by means of one or more screws as shown at (<i>h</i>). The
+key way in the shaft is made long enough to permit of the
+necessary sliding motion.</p>
+
+<p><i>Cone Keys.</i>&mdash;These are sometimes fitted to pulleys, and are
+shown in fig. 32, page 38. In this case the eye of the pulley
+is tapered and is larger than the shaft. The space between
+the shaft and the boss of the pulley is filled with three <i>saddle</i> or
+<i>cone keys</i>. These keys are made of cast iron and are all cast
+together, and before being divided the casting is bored to fit
+the shaft and turned to fit the eye of the pulley. By this
+arrangement of keys the same pulley may be fixed on shafts of
+different diameters by using keys of different thicknesses; also
+the pulley may be bored out large enough to pass over any
+boss which may be forged on the shaft.</p>
+
+<p><i>Proportions of Keys.</i>&mdash;The following rules are taken from
+Unwin's 'Machine Design,' pp. 142-43.<span class='pagenum'><a name="Page_24" id="Page_24">[Pg 24]</a></span></p>
+
+
+<div class='center'>
+<table border="0" cellpadding="2" cellspacing="0" summary="">
+<tr><td align='left'>Diameter of eye of wheel, or boss of shaft</td><td align='left'>= <i>d</i>.</td></tr>
+<tr><td align='left'>Width of key</td><td align='left'>= <sup>3</sup>&frasl;<sub>4</sub><i>d</i> + <sup>1</sup>&frasl;<sub>8</sub>.</td></tr>
+<tr><td align='left'>Mean thickness of sunk key</td><td align='left'>= <sup>1</sup>&frasl;<sub>8</sub><i>d</i> + <sup>1</sup>&frasl;<sub>8</sub>.</td></tr>
+<tr><td align='left'> &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &rdquo; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; key on flat</td><td align='left'>= <sup>1</sup>&frasl;<sub>16</sub><i>d</i> + <sup>1</sup>&frasl;<sub>16</sub>.</td></tr>
+</table></div>
+
+<p>The following table gives dimensions agreeing with average
+practice.</p>
+
+<p class="tabcap"><i>Dimensions of Keys.</i></p>
+
+
+<div class='center'>
+<table border="0" cellpadding="2" cellspacing="0" summary="">
+<tr><td align='left'>D</td><td align='left'>=</td><td align='left'>diameter of shaft.</td></tr>
+<tr><td align='left'>B</td><td align='left'>=</td><td align='left'>breadth of key.</td></tr>
+<tr><td align='left'>T</td><td align='left'>=</td><td align='left'>thickness of sunk key.</td></tr>
+<tr><td align='left'>T<sub>1</sub></td><td align='left'>=</td><td align='left'>thickness of flat key, also = thickness of saddle key. Taper of key <sup>1</sup>&frasl;<sub>8</sub> inch per foot of length, <i>i.e.</i> 1 in 96.</td></tr>
+</table></div>
+
+<p>&nbsp;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="" rules="cols" width="90%">
+<thead>
+<tr><th class="bbox"><small>D</small></th>
+<th class="bbox"> &frac34;</th>
+<th class="bbox"> 1</th>
+<th class="bbox"> 1&frac14;</th>
+<th class="bbox"> 1&frac12;</th>
+<th class="bbox"> 1&frac34;</th>
+<th class="bbox"> 2</th>
+<th class="bbox"> 2&frac14;</th>
+<th class="bbox"> 2&frac12;</th>
+<th class="bbox"> 2&frac34;</th>
+<th class="bbox"> 3</th>
+<th class="bbox"> 3&frac12;</th>
+</tr>
+</thead>
+<tbody>
+<tr><td align='left'> B</td><td align='center'> <sup>5</sup>&frasl;<sub>16</sub></td><td align='center'> <sup>3</sup>&frasl;<sub>8</sub></td><td align='center'> <sup>7</sup>&frasl;<sub>16</sub></td><td align='center'> <sup>1</sup>&frasl;<sub>2</sub></td><td align='center'> <sup>9</sup>&frasl;<sub>16</sub></td><td align='center'> <sup>5</sup>&frasl;<sub>8</sub></td><td align='center'> <sup>11</sup>&frasl;<sub>16</sub></td><td align='center'> <sup>11</sup>&frasl;<sub>16</sub></td><td align='center'> <sup>3</sup>&frasl;<sub>4</sub></td><td align='center'> <sup>7</sup>&frasl;<sub>8</sub></td><td align='center'> 1</td></tr>
+<tr><td align='left'> T</td><td align='center'> <sup>1</sup>&frasl;<sub>4</sub></td><td align='center'> <sup>1</sup>&frasl;<sub>4</sub></td><td align='center'> <sup>1</sup>&frasl;<sub>4</sub></td><td align='center'> <sup>5</sup>&frasl;<sub>16</sub></td><td align='center'> <sup>5</sup>&frasl;<sub>16</sub></td><td align='center'> <sup>5</sup>&frasl;<sub>16</sub></td><td align='center'> <sup>3</sup>&frasl;<sub>8</sub></td><td align='center'> <sup>3</sup>&frasl;<sub>8</sub></td><td align='center'> <sup>3</sup>&frasl;<sub>8</sub></td><td align='center'> <sup>7</sup>&frasl;<sub>16</sub></td><td align='center'> <sup>1</sup>&frasl;<sub>2</sub></td></tr>
+<tr><td align='left'>T<sub>1</sub></td><td align='center'> <sup>3</sup>&frasl;<sub>16</sub></td><td align='center'> <sup>3</sup>&frasl;<sub>16</sub></td><td align='center'> <sup>3</sup>&frasl;<sub>16</sub></td><td align='center'> <sup>3</sup>&frasl;<sub>16</sub></td><td align='center'> <sup>1</sup>&frasl;<sub>4</sub></td><td align='center'> <sup>1</sup>&frasl;<sub>4</sub></td><td align='center'> <sup>1</sup>&frasl;<sub>4</sub></td><td align='center'> <sup>5</sup>&frasl;<sub>16</sub></td><td align='center'> <sup>5</sup>&frasl;<sub>16</sub></td><td align='center'> <sup>5</sup>&frasl;<sub>16</sub></td><td align='center'> <sup>3</sup>&frasl;<sub>8</sub></td></tr>
+<tr><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td></tr>
+</tbody>
+</table></div>
+
+<p>&nbsp;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="" rules="cols" width="90%">
+<thead>
+<tr><th class="bbox"><small>D</small></th>
+<th class="bbox"> 4</th>
+<th class="bbox"> 4&frac12;</th>
+<th class="bbox"> 5</th>
+<th class="bbox"> 5&frac12;</th>
+<th class="bbox"> 6</th>
+<th class="bbox"> 7</th>
+<th class="bbox"> 8</th>
+<th class="bbox"> 9</th>
+<th class="bbox"> 10</th>
+<th class="bbox"> 11</th>
+<th class="bbox"> 12</th>
+</tr>
+</thead>
+<tbody>
+<tr><td align='left'> B</td><td align='center'> 1<small><sup>1</sup>&frasl;<sub>8</sub></small></td><td align='center'> 1<small><sup>1</sup>&frasl;<sub>4</sub></small></td><td align='center'> 1<small><sup>3</sup>&frasl;<sub>8</sub></small></td><td align='center'> 1<small><sup>1</sup>&frasl;<sub>2</sub></small></td><td align='center'> 1<small><sup>5</sup>&frasl;<sub>8</sub></small></td><td align='center'> 1<small><sup>7</sup>&frasl;<sub>8</sub></small></td><td align='center'>2<small><sup>1</sup>&frasl;<sub>8</sub></small></td><td align='center'>2<small><sup>3</sup>&frasl;<sub>8</sub></small></td><td align='center'> 2<small><sup>5</sup>&frasl;<sub>8</sub></small></td><td align='center'> 2<small><sup>7</sup>&frasl;<sub>8</sub></small></td><td align='center'> 3<small><sup>1</sup>&frasl;<sub>8</sub></small></td></tr>
+<tr><td align='left'> T</td><td align='center'> <sup>1</sup>&frasl;<sub>2</sub></td><td align='center'> <sup>9</sup>&frasl;<sub>16</sub></td><td align='center'> <sup>5</sup>&frasl;<sub>8</sub></td><td align='center'> <sup>11</sup>&frasl;<sub>16</sub></td><td align='center'> <sup>3</sup>&frasl;<sub>4</sub></td><td align='center'> <sup>13</sup>&frasl;<sub>16</sub></td><td align='center'><sup>15</sup>&frasl;<sub>16</sub></td><td align='center'> 1</td><td align='center'>1<small><sup>1</sup>&frasl;<sub>16</sub></small></td><td align='center'>1<small><sup>3</sup>&frasl;<sub>16</sub></small></td><td align='center'> 1<small><sup>1</sup>&frasl;<sub>4</sub></small></td></tr>
+<tr><td align='left'>T<sub>1</sub></td><td align='center'> <sup>7</sup>&frasl;<sub>16</sub></td><td align='center'> <sup>1</sup>&frasl;<sub>2</sub></td><td align='center'> <sup>1</sup>&frasl;<sub>2</sub></td><td align='center'> <sup>9</sup>&frasl;<sub>16</sub></td><td align='center'> <sup>5</sup>&frasl;<sub>8</sub></td><td align='center'> <sup>11</sup>&frasl;<sub>16</sub></td><td align='center'> <sup>3</sup>&frasl;<sub>4</sub></td><td align='center'> <sup>7</sup>&frasl;<sub>8</sub></td><td align='center'> <sup>15</sup>&frasl;<sub>16</sub></td><td align='center'>1<small><sup>1</sup>&frasl;<sub>16</sub></small></td><td align='center'> 1<small><sup>1</sup>&frasl;<sub>8</sub></small></td></tr>
+<tr><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td></tr>
+</tbody>
+</table></div>
+
+
+
+<hr style="width: 15%;" />
+<h2>V. &nbsp; SHAFTING.</h2>
+
+
+<p>Shafting is nearly always cylindrical and made of wrought
+iron or steel. Cast iron is rarely used for shafting.</p>
+
+<p><i>Axles</i> are shafts which are subjected to bending without
+twisting.</p>
+
+<p>The parts of a shaft or axle which rest upon the bearings
+or supports are called <i>journals</i>, <i>pivots</i>, or <i>collars</i>.</p>
+
+<p>In journals the supporting pressure is at right angles to the
+axis of the shaft, while in pivots and collars the pressure is
+parallel to that axis.</p>
+
+<p>Shafts may be solid or hollow. Hollow shafts are stronger
+than solid shafts for the same weight of material. Thus a
+hollow shaft having an external diameter of 10&frac14; inches and an
+internal diameter of 7 inches would have about the same weight<span class='pagenum'><a name="Page_25" id="Page_25">[Pg 25]</a></span>
+as a solid shaft of the same material 7&frac12; inches in diameter, but
+the former would have about double the strength of the latter.
+Hollow shafts are also stiffer and yield less to bending action
+than solid shafts, which in some cases, as in propeller shafts,
+is an objection.</p>
+
+
+
+<hr style="width: 15%;" />
+<h2>VI. &nbsp; SHAFT COUPLINGS.</h2>
+
+
+<p>For convenience of making and handling, shafts used for
+transmitting power are generally made in lengths not exceeding
+30 feet. These lengths are connected by couplings, of which
+we give several examples.</p>
+
+<div class="figcenter" style="width: 706px;">
+<img src="images/illus033.jpg" width="706" height="600" alt="Figs. 21, 22." title="Figs. 21, 22." />
+<span class="caption">Figs. 21 and 22.</span>
+</div>
+
+<p><i>Solid</i>, <i>Box</i>, or <i>Muff Couplings.</i>&mdash;One form of box coupling is
+shown in fig. 21. Here the ends of the shafts to be connected
+butt against one another, meeting at the centre of the box,
+which is made of cast iron. The shafts are made to rotate as<span class='pagenum'><a name="Page_26" id="Page_26">[Pg 26]</a></span>
+one by being secured to the box by two wrought-iron or steel
+keys, both driven from the same end of the box. A clearance
+space is left between the head of the forward key and the
+point of the hind one, to facilitate the driving of them out, as
+then only one key needs to be started at a time. Sometimes
+a single key the whole length of the box is used, in which case
+it is necessary that the key ways in the shafts be of exactly
+the same depth.</p>
+
+<p>The half-lap coupling, introduced by Sir William Fairbairn,
+is shown in fig. 22. In this form of box coupling the ends of
+the shafts overlap within the box. It is evident that one shaft
+cannot rotate without the other as long as the box remains over
+the lap. To keep the box in its place it is fitted with a saddle
+key.</p>
+
+<p>It will be noticed that the lap joint is sloped in such a
+way as to prevent the two lengths of shaft from being
+pulled asunder by forces acting in the direction of their length.</p>
+
+<p>Half-lap couplings are not used for shafts above 5 inches
+in diameter.</p>
+
+<p>It may here be pointed out that the half-lap coupling is
+expensive to make, and is now not much used.</p>
+
+<p>As shafts are weakened by cutting key ways in them, very
+often the ends which carry couplings are enlarged in diameter,
+as shown in fig. 21, by an amount equal to the thickness of the
+key. An objection to this enlargement is that wheels and
+pulleys require either that their bosses be bored out large
+enough to pass over it, or that they be split into halves, which
+are bolted together after being placed on the shaft.</p>
+
+
+<p class="tabcap"><i>Dimensions of Box Couplings.</i></p>
+
+
+<div class='center'>
+<table border="0" cellpadding="2" cellspacing="2" summary="">
+<tr><td align='left'>D</td><td align='left'>=</td><td align='left'>diameter of shaft.</td></tr>
+<tr><td align='left'>T</td><td align='left'>=</td><td align='left'>thickness of metal in box.</td></tr>
+<tr><td align='left'>L</td><td align='left'>=</td><td align='left'>length of box for butt coupling.</td></tr>
+<tr><td align='left'>L<sub>1</sub></td><td align='left'>=</td><td align='left'>length of box for lap coupling.</td></tr>
+<tr><td align='left'><i>l</i></td><td align='left'>=</td><td align='left'>length of lap.</td></tr>
+<tr><td align='left'>D<sub>1</sub></td><td align='left'>=</td><td align='left'>diameter of shaft at lap.</td></tr>
+</table></div>
+
+<p><span class='pagenum'><a name="Page_27" id="Page_27">[Pg 27]</a></span></p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="" rules="cols" width="90%">
+<thead>
+<tr><th class="bbox"><small>D</small></th>
+<th class="bbox"> 1&frac12;</th>
+<th class="bbox"> 2</th>
+<th class="bbox"> 2&frac12;</th>
+<th class="bbox"> 3</th>
+<th class="bbox"> 3&frac12;</th>
+<th class="bbox"> 4</th>
+<th class="bbox"> 4&frac12;</th>
+<th class="bbox"> 5</th>
+<th class="bbox"> 5&frac12;</th>
+<th class="bbox"> 6</th>
+</tr>
+</thead>
+<tbody>
+<tr><td align='left'>T</td><td align='center'> 1<small><sup>1</sup>&frasl;<sub>8</sub></small></td><td align='center'>1<small><sup>5</sup>&frasl;<sub>16</sub></small></td><td align='center'> 1&frac12;</td><td align='center'> 1&frac34;</td><td align='center'>1<small><sup>15</sup>&frasl;<sub>16</sub></small></td><td align='center'> 2<small><sup>1</sup>&frasl;<sub>8</sub></small></td><td align='center'> 2<small><sup>5</sup>&frasl;<sub>16</sub></small></td><td align='center'> 2&frac12;</td><td align='center'> 2&frac34;</td><td align='center'>2<small><sup>15</sup>&frasl;<sub>16</sub></small></td></tr>
+<tr><td align='left'>L</td><td align='center'> 5&frac34;</td><td align='center'> 7</td><td align='center'> 8&frac14;</td><td align='center'> 9&frac12;</td><td align='center'> 10&frac34;</td><td align='center'> 12</td><td align='center'> 13&frac14;</td><td align='center'>14&frac12;</td><td align='center'>15&frac34;</td><td align='center'> 17</td></tr>
+<tr><td align='left'>L<sub>1</sub></td><td align='center'> 4<small><sup>1</sup>&frasl;<sub>8</sub></small></td><td align='center'> 5&frac14;</td><td align='center'> 6<small><sup>3</sup>&frasl;<sub>8</sub></small></td><td align='center'> 7&frac12;</td><td align='center'> 8<small><sup>5</sup>&frasl;<sub>8</sub></small></td><td align='center'> 9&frac34;</td><td align='center'> 10<small><sup>7</sup>&frasl;<sub>8</sub></small></td><td align='center'> 12</td><td align='center'> &mdash;</td><td align='center'> &mdash;</td></tr>
+<tr><td align='left'><i>l</i></td><td align='center'> 7<small><sup>1</sup>&frasl;<sub>16</sub></small></td><td align='center'> 1<small><sup>7</sup>&frasl;<sub>8</sub></small></td><td align='center'> 2<small><sup>5</sup>&frasl;<sub>16</sub></small></td><td align='center'> 2&frac34;</td><td align='center'> 3<small><sup>3</sup>&frasl;<sub>16</sub></small></td><td align='center'> 3<small><sup>5</sup>&frasl;<sub>8</sub></small></td><td align='center'> 4<small><sup>1</sup>&frasl;<sub>16</sub></small></td><td align='center'> 4&frac12;</td><td align='center'> &mdash;</td><td align='center'> &mdash;</td></tr>
+<tr><td align='left'>D<sub>2</sub></td><td align='center'> 2<small><sup>5</sup>&frasl;<sub>16</sub></small></td><td align='center'> 3</td><td align='center'>3<small><sup>11</sup>&frasl;<sub>16</sub></small></td><td align='center'> 4<small><sup>3</sup>&frasl;<sub>8</sub></small></td><td align='center'> 5<small><sup>1</sup>&frasl;<sub>16</sub></small></td><td align='center'> 5&frac34;</td><td align='center'> 6<small><sup>7</sup>&frasl;<sub>16</sub></small></td><td align='center'> 7<small><sup>1</sup>&frasl;<sub>8</sub></small></td><td align='center'> &mdash;</td><td align='center'> &mdash;</td></tr>
+<tr><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td></tr>
+</tbody>
+</table></div>
+
+<p class="center">Slope of lap 1 in 12.</p>
+
+<div class="figright" style="width: 600px;">
+<img src="images/illus035.jpg" width="480" height="502" alt="Fig. 23." title="Fig. 23." /><br />
+<span class="caption">Fig. 23.</span>
+</div>
+
+
+<div class="blockquot">
+<p><span class="smcap">Exercise</span> 20: <i>Solid Butt Coupling.</i>&mdash;From the above table of
+dimensions make a longitudinal and a transverse section of a solid
+butt coupling for a shaft 2&frac12; inches in diameter. Scale 6 inches to
+a foot.</p>
+
+<p><span class="smcap">Exercise</span> 21: <i>Fairbairn's Half-Lap Coupling.</i>&mdash;Make the
+same views as in the last exercise of a half-lap coupling for a 3-inch
+shaft to the dimensions in the above table. Scale 6 inches to
+a foot.</p>
+</div>
+
+
+<p><i>Flange Couplings.</i>&mdash;The form of coupling used for the
+shafts of marine engines is shown in fig. 23. The ends of the
+different lengths of shaft
+have flanges forged on
+them, which are turned
+along with the shaft. These
+flanges butt against one
+another, and are connected
+by bolts. These bolts may
+be parallel or tapered;
+generally they are tapered.
+A parallel bolt must have
+a head, but a tapered bolt
+will act without one. In
+fig. 23 the bolts are tapered,
+and also provided with
+heads. In fig. 14, page 17,
+is shown a tapered bolt without a head. The variation of
+diameter in tapered bolts is <sup>3</sup>&frasl;<sub>8</sub> of an inch per foot of length.</p>
+
+<p>Sometimes a projection is formed on the centre of one
+flange which fits into a corresponding recess in the centre of
+the other, for the purpose of ensuring the shafts being in line.<span class='pagenum'><a name="Page_28" id="Page_28">[Pg 28]</a></span></p>
+
+<p>Occasionally a cross-key is fitted in between the flanges,
+being sunk half into each, for the purpose of diminishing the
+shearing action on the bolts.</p>
+
+
+<div class="blockquot">
+<p><span class="smcap">Exercise</span> 22: <i>Marine Coupling.</i>&mdash;Draw the elevation and
+section of the coupling shown in fig. 23; also an elevation looking
+in the direction of the arrow. Scale 3 inches to a foot.</p>
+</div>
+
+
+<p>The following table gives the dimensions of a few marine
+couplings taken from actual practice.</p>
+<div style="clear: both;"></div>
+
+
+<p class="tabcap"><i>Examples of Marine Couplings.</i></p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="" rules="cols" width="90%">
+<thead>
+<tr><th class="bbox"><small>Diameter of shaft</small></th>
+<th class="bbox"> 2<small><sup>3</sup>&frasl;<sub>8</sub></small></th>
+<th class="bbox"> 9&frac34;</th>
+<th class="bbox"> 12<small><sup>7</sup>&frasl;<sub>8</sub></small></th>
+<th class="bbox"> 16&frac12;</th>
+<th class="bbox"> 22&frac12;</th>
+<th class="bbox"> 23</th>
+</tr>
+</thead>
+<tbody>
+<tr><td align='left'>Diameter of flange</td><td align='center'> 6</td><td align='center'> 19</td><td align='center'> 24</td><td align='center'> 32</td><td align='center'> 35</td><td align='center'> 38</td></tr>
+<tr><td align='left'>Thickness of flange</td><td align='center'> 1</td><td align='center'> 2&frac34;</td><td align='center'> 3<small><sup>1</sup>&frasl;<sub>8</sub></small></td><td align='center'> 4&frac14;</td><td align='center'> 6</td><td align='center'> 5</td></tr>
+<tr><td align='left'>Diameter of bolts</td><td align='center'> &frac34;</td><td align='center'> 2&frac34;</td><td align='center'> 2<small><sup>11</sup>&frasl;<sub>16</sub></small></td><td align='center'> 3&frac12;</td><td align='center'> 4&frac14;</td><td align='center'> 4&frac14;</td></tr>
+<tr><td align='left'>Number of bolts</td><td align='center'> 3</td><td align='center'> 6</td><td align='center'> 6</td><td align='center'> 8</td><td align='center'> 9</td><td align='center'> 8</td></tr>
+<tr><td align='left'>Diameter of bolt circle</td><td align='center'> 4<small><sup>1</sup>&frasl;<sub>8</sub></small></td><td align='center'> 14<small><sup>1</sup>&frasl;<sub>8</sub></small></td><td align='center'>18<small><sup>13</sup>&frasl;<sub>16</sub></small></td><td align='center'> 25</td><td align='center'> 28&frac34;</td><td align='center'>30<small><sup>3</sup>&frasl;<sub>8</sub></small></td></tr>
+<tr><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td></tr>
+</tbody>
+</table></div>
+
+<p class="center">All the above dimensions are in inches.</p>
+
+
+<div class="blockquot">
+<p><span class="smcap">Exercise</span> 23.&mdash;Select one of the couplings from the above table,
+and make the necessary working drawings for it to a suitable
+scale.</p>
+</div>
+
+
+<p>The cast-iron flange coupling is shown in fig. 24. In this
+kind of coupling a cast-iron centre or boss provided with a
+flange is secured to the end of each shaft by a sunk key driven
+from the face of the flange. These flanges are then connected
+by bolts and nuts as in the marine coupling.</p>
+
+<p>To ensure the shafts being in line the end of one projects
+into the flange of the other.</p>
+
+<p>In order that the face of each flange may be exactly perpendicular
+to the axis of the shaft they should be 'faced' in
+the lathe, after being keyed on to the shaft.</p>
+
+<p>If the coupling is in an exposed position, where the nuts
+and bolt-heads would be liable to catch the clothes of workmen
+or an idle driving band which might come in the way, the
+flanges should be made thicker, and be provided with recesses
+for the nuts and bolt-heads.<span class='pagenum'><a name="Page_29" id="Page_29">[Pg 29]</a></span></p>
+
+<div class="figcenter" style="width: 800px;">
+<img src="images/illus037.jpg" width="800" height="582" alt="Fig. 24." title="Fig. 24." />
+<span class="caption">Fig. 24.</span>
+</div>
+
+
+<p class="tabcap"><i>Dimensions of Cast-iron Flange Couplings.</i></p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="" rules="cols" width="90%">
+<thead>
+<tr>
+<th class="bbox"><small>Diameter<br />of shaft<br />D</small></th>
+<th class="bbox"><small>Diameter<br />of flange<br />F</small></th>
+<th class="bbox"><small>Thickness<br />of flange<br />T</small></th>
+<th class="bbox"><small>Diameter<br />of boss<br />B</small></th>
+<th class="bbox"><small>Depth at<br />boss<br />L</small></th>
+<th class="bbox"><small>Number<br />of<br />bolts</small></th>
+<th class="bbox"><small>Diameter<br />of bolts<br /><i>d</i></small></th>
+<th class="bbox"><small>Diameter of<br />bolt circle<br />C</small></th>
+</tr>
+</thead>
+<tbody>
+<tr><td align='center'> 1&frac12;</td><td align='center'> 7&frac14;</td><td align='center'> <sup>7</sup>&frasl;<sub>8</sub> </td><td align='center'> 3&frac12;</td><td align='center'> 2<small><sup>5</sup>&frasl;<sub>8</sub></small></td><td align='center'> 3</td><td align='center'><sup>5</sup>&frasl;<sub>8</sub></td><td align='center'> 5&frac12;</td></tr>
+<tr><td align='center'> 2</td><td align='center'> 8<small><sup>7</sup>&frasl;<sub>8</sub></small></td><td align='center'> 1<small><sup>1</sup>&frasl;<sub>16</sub></small></td><td align='center'> 4<small><sup>3</sup>&frasl;<sub>8</sub></small></td><td align='center'> 3<small><sup>3</sup>&frasl;<sub>16</sub></small></td><td align='center'> 4</td><td align='center'> <sup>3</sup>&frasl;<sub>4</sub></td><td align='center'> 6&frac34;</td></tr>
+<tr><td align='center'> 2&frac12;</td><td align='center'> 10<small><sup>5</sup>&frasl;<sub>8</sub></small></td><td align='center'> 1&frac14;</td><td align='center'> 5<small><sup>5</sup>&frasl;<sub>16</sub></small></td><td align='center'> 3&frac34;</td><td align='center'> 4</td><td align='center'><sup>7</sup>&frasl;<sub>8</sub></td><td align='center'> 8<small><sup>1</sup>&frasl;<sub>8</sub></small></td></tr>
+<tr><td align='center'> 3</td><td align='center'> 12<small><sup>3</sup>&frasl;<sub>8</sub></small></td><td align='center'> 1<small><sup>7</sup>&frasl;<sub>16</sub></small></td><td align='center'> 6&frac14;</td><td align='center'> 4<small><sup>5</sup>&frasl;<sub>16</sub></small></td><td align='center'> 4</td><td align='center'> 1</td><td align='center'> 9&frac12;</td></tr>
+<tr><td align='center'> 3&frac12;</td><td align='center'> 13<small><sup>1</sup>&frasl;<sub>8</sub></small></td><td align='center'> 1<small><sup>5</sup>&frasl;<sub>8</sub></small></td><td align='center'> 7<small><sup>1</sup>&frasl;<sub>8</sub></small></td><td align='center'> 4<small><sup>7</sup>&frasl;<sub>8</sub></small></td><td align='center'> 4</td><td align='center'> 1</td><td align='center'>10<small><sup>5</sup>&frasl;<sub>16</sub></small></td></tr>
+<tr><td align='center'> 4</td><td align='center'> 14</td><td align='center'> 1&frac34;</td><td align='center'> 8</td><td align='center'> 5<small><sup>7</sup>&frasl;<sub>16</sub></small></td><td align='center'> 6</td><td align='center'> 1</td><td align='center'>11&frac14;</td></tr>
+<tr><td align='center'> 4&frac12;</td><td align='center'> 15<small><sup>5</sup>&frasl;<sub>8</sub></small></td><td align='center'> 2</td><td align='center'> 8<small><sup>7</sup>&frasl;<sub>8</sub></small></td><td align='center'> 6</td><td align='center'> 6</td><td align='center'>1<small><sup>1</sup>&frasl;<sub>8</sub></small></td><td align='center'>12&frac12;</td></tr>
+<tr><td align='center'> 5</td><td align='center'> 17<small><sup>3</sup>&frasl;<sub>8</sub></small></td><td align='center'> 2<small><sup>1</sup>&frasl;<sub>8</sub></small></td><td align='center'> 9<small><sup>13</sup>&frasl;<sub>16</sub></small></td><td align='center'> 6<small><sup>5</sup>&frasl;<sub>8</sub></small></td><td align='center'> 6</td><td align='center'> 1&frac14;</td><td align='center'>13<small><sup>13</sup>&frasl;<sub>16</sub></small></td></tr>
+<tr><td align='center'> 5&frac12;</td><td align='center'> 18&frac14;</td><td align='center'> 2<small><sup>5</sup>&frasl;<sub>16</sub></small></td><td align='center'>10&frac34;</td><td align='center'> 7&frac14;</td><td align='center'> 6</td><td align='center'>1&frac14;</td><td align='center'>14&frac34;</td></tr>
+<tr><td align='center'> 6</td><td align='center'> 19<small><sup>7</sup>&frasl;<sub>8</sub></small></td><td align='center'> 2&frac12;</td><td align='center'>11<small><sup>5</sup>&frasl;<sub>8</sub></small></td><td align='center'> 7&frac34;</td><td align='center'> 6</td><td align='center'> 1<small><sup>3</sup>&frasl;<sub>8</sub></small></td><td align='center'> 16</td></tr>
+<tr><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td></tr>
+</tbody>
+</table></div>
+
+<p>The projection of the shaft <i>p</i> varies from <sup>1</sup>&frasl;<sub>4</sub> inch in the small
+shafts to <sup>1</sup>&frasl;<sub>2</sub> inch in the large ones.</p>
+
+
+<div class="blockquot">
+<p><span class="smcap">Exercise</span> 24: <i>Cast-iron Flange Coupling.</i>&mdash;Draw
+the views shown in fig. 24 of a cast-iron flange coupling, for a shaft 4&frac12; inches
+in diameter, to the dimensions given in the above table. Scale 4
+inches to a foot.</p>
+</div>
+
+
+
+
+<hr style="width: 15%;" />
+<p><span class='pagenum'><a name="Page_30" id="Page_30">[Pg 30]</a></span></p>
+<h2>VII. &nbsp; BEARINGS  FOR  SHAFTS.</h2>
+
+
+<div class="figleft" style="width: 640px;">
+<img src="images/illus038.jpg" width="484" height="480" alt="Fig. 25." title="Fig. 25." /><br />
+<span class="caption">Fig. 25.</span>
+</div>
+
+<p>An example of a very simple form of bearing is shown in
+fig. 25, which represents a brake shaft carrier of a locomotive
+tender. The bearing in this example is made of cast iron and
+in one piece. Through the oval-shaped flange two bolts pass
+for attaching the bearing to the wrought-iron framing of the
+tender. With this form of bearing there is no adjustment for
+wear, so that when it becomes worn it must be renewed.</p>
+
+<div class="blockquot"><p><span class="smcap">Exercise</span> 25: <i>Brake Shaft Carrier.</i>&mdash;Draw the elevation and
+sectional plan of the bearing shown in fig. 25. Draw also a vertical
+section through the axis. The latter view to be projected from
+the first elevation. Scale 6 inches to a foot.</p></div>
+
+
+<p><i>Pillow Block</i>, <i>Plummer Block</i>, or <i>Pedestal</i>.&mdash;The ordinary
+form of plummer block is represented in fig. 26. A is the
+block proper, B the
+sole through which
+pass the holding-down
+bolts. C is the cap.
+Between the block
+and the cap is the
+brass bush, which is in
+halves, called <i>brasses</i>
+or <i>steps</i>. The bed for
+the steps in this example
+is cylindrical,
+and is prepared by the
+easy process of boring.
+The steps are not
+supported throughout
+their whole length,
+but at their ends only where fitting strips are provided as
+shown. As the wear on a step is generally greatest at the
+bottom, it is made thicker there than at the sides, except
+where the fitting strips come in. To prevent the steps turning
+within the block they are generally furnished with lugs, which
+enter corresponding recesses in the block and cover.<span class='pagenum'><a name="Page_31" id="Page_31">[Pg 31]</a></span></p>
+
+<div class="figcenter" style="width: 900px;">
+<img src="images/illus039.png" width="900" height="540" alt="Fig. 26." title="Fig. 26." />
+<span class="caption">Fig. 26.</span>
+</div>
+
+<p><span class='pagenum'><a name="Page_32" id="Page_32">[Pg 32]</a></span></p>
+
+<p>In the block illustrated the journal is lubricated by a <i>needle
+lubricator</i>; this consists of an inverted glass bottle fitted with
+a wood stopper, through a hole in which passes a piece of wire,
+which has one end in the oil within the bottle, and the other
+resting on the journal of the shaft. The wire or needle does
+not fill the hole in the stopper, but if the needle is kept from
+vibrating the oil does not escape owing to capillary attraction.
+When, however, the shaft rotates, the needle begins to vibrate,
+and the oil runs down slowly on to the journal; oil is therefore
+only used when the shaft is running.</p>
+
+
+<div class="blockquot"><p><span class="smcap">Exercise</span> 26: <i>Pillow Block for a Four-inch Shaft.</i>&mdash;Draw
+the views shown of this block in fig. 26. Make also separate drawings,
+full size, of one of the steps. Scale 6 inches to a foot.</p></div>
+
+
+<p><i>Proportions of Pillow Blocks.</i>&mdash;The following rules may
+be used for proportioning pillow blocks for shafts up to 8 inches
+diameter. It should be remembered that the proportions used
+by different makers vary considerably, but the following rules
+represent average practice.</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="2" cellspacing="0" summary="">
+<tr><td align='left'>Diameter of journal</td><td align='left'>= <i>d</i>.</td></tr>
+<tr><td align='left'>Length of journal</td><td align='left'>= <i>l</i>.</td></tr>
+<tr><td align='left'>Height to centre</td><td align='left'>= 1&middot;05<i>d</i> + &middot;5.</td></tr>
+<tr><td align='left'>Length of base</td><td align='left'>= 3&middot;6<i>d</i> + 5.</td></tr>
+<tr><td align='left'>Width of base</td><td align='left'>= &middot;8<i>l</i>.</td></tr>
+<tr><td align='left'> &nbsp; &nbsp; &nbsp; &rdquo; &nbsp; &nbsp; &nbsp; block</td><td align='left'>= &middot;7<i>l</i>.</td></tr>
+<tr><td align='left'>Thickness of base</td><td align='left'>= &middot;3<i>d</i> + &middot;3.</td></tr>
+<tr><td align='left'> &nbsp; &nbsp;  &nbsp; &nbsp; &nbsp; &rdquo;  &nbsp; &nbsp; &nbsp; &nbsp; cap</td><td align='left'>= &middot;3<i>d</i> + &middot;4.</td></tr>
+<tr><td align='left'>Diameter of bolts</td><td align='left'>= &middot;25<i>d</i> + &middot;25.</td></tr>
+<tr><td align='left'>Distance between centres of cap bolts</td><td align='left'>= 1&middot;6<i>d</i> + 1&middot;5.</td></tr>
+<tr><td align='left'> &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;&nbsp; &rdquo; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &rdquo; &nbsp;  &nbsp; &nbsp; &nbsp; &nbsp; base bolts</td><td align='left'>= 2&middot;7<i>d</i> + 4&middot;2.</td></tr>
+<tr><td align='left'>Thickness of step at bottom</td><td align='left'>= <i>t</i> = &middot;09<i>d</i> + &middot;15.</td></tr>
+<tr><td align='left'> &nbsp; &nbsp; &nbsp; &nbsp; &rdquo; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &rdquo; &nbsp;  &nbsp; &nbsp; &nbsp; sides</td><td align='left'>= &frac34;<i>t</i>.</td></tr>
+</table></div>
+
+
+<p>The length of the journal varies very much in different
+cases, and depends upon the speed of the shaft, the load which
+it carries, the workmanship of the journal and bearing, and the
+method of lubrication. For ordinary shafting one rule is to
+make <i>l</i> = <i>d</i> + 1. Some makers use the rule <i>l</i> = 1&middot;5<i>d</i>; others
+make <i>l</i> = 2<i>d</i>.<span class='pagenum'><a name="Page_33" id="Page_33">[Pg 33]</a></span></p>
+
+<div class="figcenter" style="width: 768px;">
+<img src="images/illus041.png" width="768" height="925" alt="Fig. 27." title="Fig. 27." />
+<span class="caption">Fig. 27.</span>
+</div>
+
+
+<div class="figleft" style="width: 300px;">
+<img src="images/illus042.png" width="154" height="448" alt="Fig. 28." title="Fig. 28." /><br />
+<span class="caption">Fig. 28.</span>
+</div>
+
+<div class="blockquot"><p><span class="smcap">Exercise</span> 27: <i>Design for Pillow Block.</i>&mdash;Make the necessary
+working drawings for a pillow block for a shaft 5 inches in diameter,
+and having a journal 7 inches long.</p></div>
+
+<p><i>Brackets.</i>&mdash;When a pillow block has to be fixed to a wall
+or column a bracket such as that shown in figs. 27 and 28 may
+be used. The pillow block rests between the <i>joggles</i> A A,
+and is bolted down to the bracket and secured in addition
+with keys at the ends of the base of the block, in the same<span class='pagenum'><a name="Page_34" id="Page_34">[Pg 34]</a></span>
+manner as is shown, for the attachment of the bracket to the
+column.</p>
+
+
+<div class="blockquot"><p><span class="smcap">Exercise</span> 28: <i>Pillar Bracket.</i>&mdash;Fig. 27 shows a side elevation
+and part horizontal section, and fig. 28 shows an end elevation of a
+pillar bracket for carrying a pillow block for a 3-inch shaft. Draw
+these views <i>properly projected from one another</i>, showing the
+pillow block, which is to be proportioned
+by the rules given on page
+32. Draw also a plan of the whole.
+Scale 4 inches to a foot.</p></div>
+
+
+<p><i>Hangers.</i>&mdash;When a shaft is suspended
+from a ceiling it is carried
+by hangers, one form of which is
+shown in fig. 29, and which will be
+readily understood. The cap of
+the bearing, it will be noticed, is
+secured by means of a bolt, and
+also by a square key.</p>
+
+
+<div class="blockquot"><p><span class="smcap">Exercise</span> 29: <i>Shaft Hanger.</i>&mdash;Draw
+the two elevations shown in
+fig. 29, and also a sectional plan. The
+section to be taken at a point 5 inches
+above the centre of the shaft. Scale
+6 inches to a foot.</p></div>
+
+
+<p><i>Wall Boxes.</i>&mdash;In passing from
+one part of a building to another
+a shaft may have to pass through
+a wall. In that case a neat appearance
+is given to the opening
+and a suitable support obtained
+for a pillow block by building into
+the wall a <i>wall box</i>, one form of
+which is shown in fig. 30.</p>
+
+
+<div class="blockquot"><p><span class="smcap">Exercise</span> 30: <i>Wall Box.</i>&mdash;Draw the views of the wall box
+shown in fig. 30, and also a sectional plan; the plane of section to
+pass through the box a little above the joggles for the pillow block.
+Scale 3 inches to a foot.</p></div>
+
+
+<p><span class='pagenum'><a name="Page_35" id="Page_35">[Pg 35]</a></span></p>
+
+<div class="figcenter" style="width: 758px;">
+<img src="images/illus043a.png" width="758" height="600" alt="Fig. 29." title="Fig. 29." />
+<span class="caption">Fig. 29.</span>
+</div>
+
+<div class="figcenter" style="width: 800px;">
+<img src="images/illus043b.png" width="800" height="475" alt="Fig. 30." title="Fig. 30." />
+<span class="caption">Fig. 30.</span>
+</div>
+
+
+
+<hr style="width: 15%;" />
+<p><span class='pagenum'><a name="Page_36" id="Page_36">[Pg 36]</a></span></p>
+<h2>VIII. &nbsp;  PULLEYS.</h2>
+
+
+<p><i>Velocity Ratio in Belt Gearing.</i>&mdash;Let two pulleys A and B
+be connected by a belt, and let their diameters be D<sub>1</sub> and D<sub>2</sub>;
+and let their speeds, in revolutions per minute, be N<sub>1</sub> and N<sub>2</sub>
+respectively. If there is no slipping, the speeds of the rims of
+the pulleys will be the same as that of the belt, and will therefore
+be equal. Now the speed of the rim of A is evidently
+= D<sub>1</sub> &times; 3&middot;1416 &times; N<sub>1</sub>; while the speed of the rim of B is =
+D<sub>2</sub> &times; 3&middot;1416 &times; N<sub>2</sub>. Hence D<sub>1</sub> &times; 3&middot;1416 &times; N<sub>1</sub> = D<sub>2</sub> &times; 3&middot;1416 &times; N<sub>2</sub>,
+and therefore</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='center'> N<sub>1</sub> <br /> &mdash;&mdash; <br /> N<sub>2</sub> </td><td align='center'> = </td><td align='center'> D<sub>2</sub> <br /> &mdash;&mdash;. <br /> D<sub>1</sub></td></tr>
+</table></div>
+
+<p><i>Pulleys for Flat Bands.</i>&mdash;In cross section the rim of a
+pulley for carrying a flat band is generally curved as shown
+in figs. 31 and 32, but very often the cross section is straight.
+The curved cross section of the rim tends to keep the band
+from coming off as long as the pulley is rotating. Sometimes
+the rim of the pulley is provided with flanges which keep the
+band from falling off.</p>
+
+<p>Pulleys are generally made entirely of cast iron, but a great
+many pulleys are now made in which the centre or nave only
+is of cast iron, the arms being of wrought iron cast into the
+nave, while the rim is of wrought sheet iron.</p>
+
+<p>The arms of pulleys when made of wrought iron are
+invariably straight, but when made of cast iron they are very
+often curved. In fig. 31, which shows an arrangement of two
+cast-iron pulleys, the arms are straight; while in fig. 32, which
+shows another cast-iron pulley, the arms are curved. Through
+unequal cooling, and therefore unequal contraction of a cast-iron,
+pulley in the mould, the arms are generally in a state of
+tension or compression; and if the arms are straight they are
+very unyielding, so that the result of this initial stress is often
+the breaking of an arm, or of the rim where it joins an arm.
+With the curved arm, however, its shape permits it to yield,
+and thus cause a diminution of the stress due to unequal contraction.<span class='pagenum'><a name="Page_37" id="Page_37">[Pg 37]</a></span></p>
+
+<p>The cross section of the arms of cast-iron pulleys is generally
+elliptical.</p>
+
+<div class="figcenter" style="width: 718px;">
+<img src="images/illus045.png" width="718" height="600" alt="Fig. 31." title="Fig. 31." />
+<span class="caption">Fig. 31.</span>
+</div>
+
+<div class="blockquot"><p><span class="smcap">Exercise 31:</span> <i>Fast and Loose Pulleys</i>.&mdash;Fig. 31 shows an
+arrangement of fast and loose pulleys. A is the fast pulley, secured
+to the shaft C by a sunk key; B is the loose pulley, which turns
+freely upon the shaft. The loose pulley is prevented from coming off
+by a collar D, which is secured to the shaft by a tapered pin as
+shown. The nave or boss of the loose pulley is here fitted with a
+brass liner, which may be renewed when it becomes too much worn.
+Draw the elevations shown, completing the left-hand one. Scale 6
+inches to a foot.</p>
+
+<p>By the above arrangement of pulleys a machine may be stopped
+or set in motion at pleasure. When the driving band is on the
+loose pulley the machine is at rest, and when it is on the fast
+pulley the machine is in motion. The driving band is shifted from
+the one pulley to the other by pressing on that side of the band
+which is advancing towards the pulleys.</p>
+</div>
+<p><span class='pagenum'><a name="Page_38" id="Page_38">[Pg 38]</a></span></p>
+
+<div class="figcenter" style="width: 756px;">
+<img src="images/illus046.png" width="756" height="600" alt="Fig. 32." title="Fig. 32." />
+<span class="caption">Fig. 32.</span>
+</div>
+
+<div class="blockquot"><p><span class="smcap">Exercise 32</span>: <i>Cast-iron Pulley with Curved Arms and Cone
+Keys</i>.&mdash;Draw a complete side elevation and a complete cross section
+of the pulley represented in fig. 32 to a scale of 3 inches to a foot.
+In drawing the side elevation of the arms first draw the centre lines
+as shown; next draw three circles for each arm, one at each end
+and one in the middle; the centres of these circles being on the
+centre line of the arm, and their diameters equal to the widths of the
+arm at the ends and at the middle respectively. Arcs of circles are
+then drawn to touch these three circles. The centres and radii of
+these arcs may be found by trial. The cone keys for securing the
+pulley to the shaft were described on p. 23.</p></div>
+
+<p><i>Pulleys for Ropes</i>.&mdash;Ropes made of hemp are now extensively
+used for transmitting power. These ropes vary in
+diameter from 1 inch to 2 inches, and are run at a speed of
+about 4,500 feet per minute. The pulleys for these ropes are
+made of cast iron, and have their rims grooved as shown in
+fig. 33, which is a cross section of the rim of a pulley carrying
+three ropes. The angle of the V is usually 45&deg;, and the rope<span class='pagenum'><a name="Page_39" id="Page_39">[Pg 39]</a></span>
+rests on the sides of the groove, and not on the bottom, so that
+it is wedged in, and has therefore a good hold of the pulley.
+The diameter of the pulley should not be less than 30 times
+the diameter of the rope. Two pulleys connected by ropes
+should not be less than thirty feet apart from centre to centre,
+but this distance may be as much as 100 feet.</p>
+
+<div class="figcenter" style="width: 640px;">
+<img src="images/illus047.jpg" width="640" height="418" alt="Fig. 33." title="Fig. 33." />
+<span class="caption">Fig. 33.</span>
+</div>
+
+<div class="blockquot"><p><span class="smcap">Exercise 33</span>: <i>Section of Rim of Rope Pulley.</i>&mdash;Draw, half
+size, the section of the rim of a rope pulley shown in fig. 33.</p></div>
+
+
+
+<hr style="width: 15%;" />
+<h2>IX. &nbsp;  TOOTHED WHEELS.</h2>
+
+
+<p><i>Pitch Surfaces of Spur Wheels.</i>&mdash;Let two smooth rollers be
+placed in contact with their axes parallel, and let one of them
+rotate about its axis; then if there is no slipping the other
+roller will rotate in the opposite direction with the same
+surface velocity; and if D<sub>1</sub>, D<sub>2</sub> be the diameters of the rollers,
+and N<sub>1</sub>, N<sub>2</sub> their speeds in revolutions per minute, it follows as
+in belt gearing that&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='center'> N<sub>1</sub> <br /> &mdash;&mdash; <br /> N<sub>2</sub> </td><td align='center'> = </td><td align='center'> D<sub>2</sub> <br /> &mdash;&mdash;. <br /> D<sub>1</sub></td></tr>
+</table></div>
+
+<p>If there be considerable resistance to the motion of the
+follower slipping may take place, and it may stop. To prevent
+this the rollers may be provided with teeth; then they become
+<i>spur wheels</i>; and if the teeth be so shaped that the ratio of
+the speeds of the toothed rollers at any instant is the same as<span class='pagenum'><a name="Page_40" id="Page_40">[Pg 40]</a></span>
+that of the smooth rollers, the surfaces of the latter are called
+the <i>pitch surfaces</i> of the former.</p>
+
+<p><i>Pitch Circle.</i>&mdash;A section of the pitch surface of a toothed
+wheel by a plane perpendicular to its axis is a circle, and is
+called a <i>pitch circle</i>. We may also say that the pitch circle is
+the edge of the pitch surface. The pitch circle is generally
+traced on the side of a toothed wheel, and is rather nearer the
+points of the teeth than the roots.</p>
+
+<p><i>Pitch of Teeth.</i>&mdash;The distance from the centre of one tooth
+to the centre of the next, or from the front of one to the front
+of the next, <i>measured at the pitch circle</i>, is called the <i>pitch of
+the teeth</i>. If D be the diameter of the pitch circle of a wheel,
+<i>n</i> the number of teeth, and <i>p</i> the pitch of the teeth, then
+D &times; 3&middot;1416 = <i>n</i> &times; <i>p</i>.</p>
+
+<div class="figcenter" style="width: 640px;">
+<img src="images/illus048.jpg" width="640" height="253" alt="Fig. 34." title="Fig. 34." />
+<span class="caption">Fig. 34.</span>
+</div>
+
+<p>By the diameter of a wheel is meant the diameter of its
+pitch circle.</p>
+
+<p><i>Form and Proportions of Teeth.</i>&mdash;The ordinary form of
+wheel teeth is shown in fig. 34. The curves of the teeth should
+be cycloidal curves, although they are generally drawn in as
+arcs of circles. It does not fall within the scope of this work
+to discuss the correct forms of wheel teeth. The student will
+find the theory of the teeth of wheels clearly and fully explained
+in Goodeve's 'Elements of Mechanism,' and in Unwin's
+'Machine Design.'</p>
+
+<p>The following proportions for the teeth of ordinary toothed
+wheels may be taken as representing average practice:&mdash;</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Pitch of teeth</td><td align='left'>= <i>p</i> = arc <i>a b c</i> (fig. 34).</td></tr>
+<tr><td align='left'>Thickness of tooth</td><td align='left'>= <i>b c</i> = &middot;48<i>p</i>.</td></tr>
+<tr><td align='left'>Width of space</td><td align='left'>= <i>a b</i> = &middot;52<i>p</i>.</td></tr>
+<tr><td align='left'><span class='pagenum'><a name="Page_41" id="Page_41">[Pg 41]</a></span>Total height of tooth</td><td align='left'>= <i>h</i> = &middot;7<i>p</i>.</td></tr>
+<tr><td align='left'>Height of tooth above pitch line</td><td align='left'>= <i>k</i> = &middot;3<i>p</i>.</td></tr>
+<tr><td align='left'>Depth of tooth below pitch line</td><td align='left'>= <i>l</i> = &middot;4<i>p</i>.</td></tr>
+<tr><td align='left'>Width of tooth</td><td align='left'>= 2<i>p</i> to 3<i>p</i>.</td></tr>
+</table></div>
+
+<div class="blockquot"><p><span class="smcap">Exercise</span> 34: <i>Spur Wheel.</i>&mdash;Fig. 35 shows the elevation and
+sectional plan of a portion of a cast-iron spur wheel. The diameter
+of the pitch circle is 23<small><sup>7</sup>&frasl;<sub>8</sub></small> inches, and the pitch of the teeth is 1&frac12;
+inches, so that there will be 50 teeth in the wheel. The wheel has
+six arms. Draw a complete elevation of the wheel and a half sectional
+plan, also a half-plan without any section. Draw also a
+cross section of one arm. Scale 4 inches to a foot.</p></div>
+
+<div class="figcenter" style="width: 600px;">
+<img src="images/illus049.png" width="600" height="600" alt="Fig. 35." title="Fig. 35." />
+<span class="caption">Fig. 35.</span>
+</div>
+
+<p><i>Mortise Wheels.</i>&mdash;When two wheels gearing together run
+at a high speed the teeth of one are made of wood. These
+teeth, or cogs, as they are generally called, have tenons formed
+on them, which fit into mortises in the rim of the wheel. This
+wheel with the wooden teeth is called a <i>mortise wheel</i>. An
+example of a mortise wheel is shown in fig. 36.<span class='pagenum'><a name="Page_42" id="Page_42">[Pg 42]</a></span></p>
+
+<div class="figcenter" style="width: 1024px;">
+<img src="images/illus050.png" width="1024" height="645" alt="Fig. 36." title="Fig. 36." />
+<span class="caption">Fig. 36.</span>
+</div>
+<p><span class='pagenum'><a name="Page_43" id="Page_43">[Pg 43]</a></span></p>
+
+<p><i>Bevil Wheels.</i>&mdash;In bevil wheels the pitch surfaces are parts
+of cones. Bevil wheels are used to connect shafts which are
+inclined to one another, whereas spur wheels are used to connect
+parallel shafts. In fig. 36 is shown a pair of bevil wheels in
+gear, one of them being a mortise wheel. At (<i>a</i>) is a separate
+drawing, to a smaller scale, of the pitch cones. The pitch
+cones are shown on the drawing of the complete wheels by
+dotted lines.</p>
+
+<p>The diameters of bevil wheels are the diameters of the bases
+of their pitch cones.</p>
+
+<div class="blockquot"><p><span class="smcap">Exercise</span> 35: <i>Pair of Bevil Wheels.</i>&mdash;Draw the sectional elevation
+of the bevil wheels shown in gear in fig. 36. Commence by
+drawing the centre lines of the shafts, which in this example are at
+right angles to one another; then draw the pitch cones shown by
+dotted lines. Next put in the teeth which come into the plane of
+the section, then complete the sections of the wheels. The pinion
+or smaller wheel has 25 teeth, and the wheel has 50 teeth, which
+makes the pitch a little over 3 inches. Each tooth of the mortise
+wheel is secured as shown by an iron pin <sup>5</sup>&frasl;<sub>16</sub> inch diameter. Scale
+3 inches to a foot.</p></div>
+
+
+
+<hr style="width: 15%;" />
+<h2>X. &nbsp; CRANKS AND CRANKED SHAFTS.</h2>
+
+
+<p>The most important application of the crank is in the
+steam-engine, where the reciprocating rectilineal motion of
+the piston is converted into the rotary motion of the crank-shaft
+by means of the crank and connecting rod.</p>
+
+<p>At one time steam-engine cranks were largely made of
+cast iron, now they are always made of wrought iron or steel.
+The crank is either forged in one piece with the shaft, or it is
+made separately and then keyed to it.</p>
+
+<p><i>Overhung Crank.</i>&mdash;Fig. 37 shows a wrought-iron overhung
+crank. A is the crank-shaft, B the crank arm, provided at
+one end with a boss C, which is bored out to fit the shaft; at
+the other end of the crank arm is a boss D, which is bored out
+to receive the crank-pin E, which works in one end of the
+connecting rod. The crank is secured to the shaft by the<span class='pagenum'><a name="Page_44" id="Page_44">[Pg 44]</a></span>
+sunk key F. It is also good practice to <i>shrink</i> the crank on
+to the shaft. The process of shrinking consists of boring out
+the crank a little smaller than the shaft, and then heating it,
+which causes it to expand sufficiently to go on to the shaft.
+As the crank cools, it shrinks and grips the shaft firmly. The
+crank may also be shrunk on to the crank-pin, the latter being
+then riveted over as shown in fig. 37.</p>
+
+<div class="figcenter" style="width: 781px;">
+<img src="images/illus052.png" width="781" height="600" alt="Fig. 37." title="Fig. 37." />
+<span class="caption">Fig. 37.</span>
+</div>
+
+<p>A good plan to adopt in preference to the shrinking process
+is to force the parts together by hydraulic pressure. This
+method is adopted for placing locomotive wheels on their axles,
+and for putting in crank-pins. As to the amount of pressure
+to be used, the practice is to allow a force of 10 tons for every
+inch of diameter of the pin, axle, or shaft.</p>
+
+<p>Instead of being riveted in, the crank pin may be prolonged
+and screwed, and fitted with a nut. Another plan is to put a
+cotter through the crank and the crank-pin.</p>
+
+<p>The distance from the centre of the crank-shaft to the
+centre of the crank-pin is called the radius of the crank. The
+<i>throw</i> of the crank is twice the radius. In a direct-acting<span class='pagenum'><a name="Page_45" id="Page_45">[Pg 45]</a></span>
+engine the throw of the crank is equal to the stroke of the
+piston.</p>
+
+<div class="blockquot"><p><span class="smcap">Exercise</span> 36: <i>Wrought-iron Overhung Crank.</i>&mdash;Draw the
+two elevations shown in fig. 37, also a plan. Scale 1&frac12; inches to a
+foot.</p>
+
+<p class="tabcap"><i>Proportions of Overhung Cranks.</i></p>
+
+<div class='center'>
+<table border="0" cellpadding="2" cellspacing="0" summary="">
+<tr><td align='left' colspan='2'>D = diameter of shaft.</td></tr>
+<tr><td align='left' colspan='2'><i>d</i> = &nbsp; &nbsp; &nbsp;  &nbsp;   &rdquo; &nbsp; &nbsp; &nbsp; &nbsp;      crank-pin.</td></tr>
+<tr><td align='left'>Length of large boss</td><td align='left'>= &middot;9 D.</td></tr>
+<tr><td align='left'>Diameter &nbsp; &nbsp; &rdquo;</td><td align='left'>= 1&middot;8 D.</td></tr>
+<tr><td align='left'>Length of small boss</td><td align='left'>= 1&middot;1 <i>d</i>.</td></tr>
+<tr><td align='left'>Diameter &nbsp; &nbsp; &rdquo;</td><td align='left'>= 1&middot;8 <i>d</i>.</td></tr>
+<tr><td align='left' colspan='2'>Width of crank arm at centre of shaft</td><td align='left'>= 1&middot;3 D.</td></tr>
+<tr><td align='left' colspan='2'>&nbsp; &nbsp; &nbsp; &nbsp;  &nbsp;  &rdquo; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;  &nbsp;   &rdquo;  &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;  &nbsp;  crank-pin</td><td align='left'>= 1&middot;5 <i>d</i>.</td></tr>
+</table></div>
+
+<p class="center">The thickness of the crank arm may be roughly taken as = &middot;7 D.</p>
+
+<p><span class="smcap">Exercise</span> 37.&mdash;Design a wrought-iron crank for an engine
+having a stroke of 4 feet. The crank-shaft is 9 inches in diameter,
+and the crank-pin is 4&frac34; inches in diameter and 6&frac12; inches long.</p></div>
+
+<div class="figcenter" style="width: 800px;">
+<img src="images/illus053.png" width="800" height="350" alt="Fig. 38." title="Fig. 38." />
+<span class="caption">Fig. 38.</span>
+</div>
+
+<p><i>Locomotive Cranked Axle.</i>&mdash;As an example of a cranked
+shaft we take the cranked axle for a locomotive with inside
+cylinders shown in fig. 38; here the crank and shaft or axle
+are forged in one piece. A is the wheel seat, B the journal, C
+the crank-pin, and D and E the crank arms. Only one half of
+the axle is shown in fig. 38, but the other half is exactly the
+same. The cranks on the two halves are, however, at right
+angles to one another. The ends of the crank arms are turned
+in the lathe, the crank-pin ends being turned at the same time<span class='pagenum'><a name="Page_46" id="Page_46">[Pg 46]</a></span>
+as the axle, and the other ends at the same time as the crank-pin.
+This consideration determines the centres for the arcs
+shown in the end view.</p>
+
+<div class="blockquot"><p><span class="smcap">Exercise</span> 38.&mdash;Draw to a scale of 2 inches to a foot the side
+and end elevations of the locomotive cranked axle partly shown in
+fig. 38. The distance between the centre lines of the cylinders is
+2 feet.</p></div>
+
+<div class="figcenter" style="width: 800px;">
+<img src="images/illus054.png" width="800" height="476" alt="Fig. 39." title="Fig. 39." />
+<span class="caption">Fig. 39.</span>
+</div>
+
+<p><i>Built-up Cranks.</i>&mdash;The form of cranked shaft shown in
+fig. 38 is largely used for marine engines, but for the very powerful
+engines now fitted in large ships this design of shaft is
+very unreliable, the built-up crank shown in fig. 39 being
+preferred, although it is much heavier than the other. It will
+be seen from the figure that the shaft, crank arms, and crank-pin
+are made separately. The arms are shrunk on to the pin
+and the shaft, and secured to the latter by sunk keys. These
+heavy shafts and cranks are generally made of steel.</p>
+
+<div class="blockquot"><p><span class="smcap">Exercise</span> 39.&mdash;Keeping to the dimensions marked in fig. 39,
+draw the views there shown of a built-up crank-shaft for a marine
+engine. Scale <sup>3</sup>&frasl;<sub>4</sub> inch to a foot.</p></div>
+
+
+
+<hr style="width: 15%;" />
+<p><span class='pagenum'><a name="Page_47" id="Page_47">[Pg 47]</a></span></p>
+<h2>XI. &nbsp; ECCENTRICS.</h2>
+
+
+<p>The <i>eccentric</i> is a particular form of crank, being a crank in
+which the crank-pin is large enough to embrace the crank-shaft.
+In the eccentric what corresponds to the crank-pin is called
+the sheave or pulley. The advantage which an eccentric
+possesses over a crank is that the shaft does not require to be
+divided at the point where the eccentric is put on. The crank,
+however, has this advantage over the eccentric, namely, that it
+can be used for converting circular into reciprocating motion,
+or <i>vice vers&acirc;</i>, while the eccentric can only be used for converting
+circular into reciprocating motion. This is owing to
+the great leverage at which the friction of the eccentric
+acts.</p>
+
+<p>The chief application of the eccentric is in the steam-engine,
+where it is used for working the valve gear.</p>
+
+<p>To permit of the sheave being placed on the shaft without
+going over the end (which could not be done at all in the case of
+a cranked axle, and would be a troublesome operation in most
+cases) it is generally made in two pieces, as shown in fig. 40,
+which represents one of the eccentrics of a locomotive. The
+two parts of the sheave are connected by two cotter bolts. The
+part which embraces the sheave is called the eccentric strap,
+and corresponds to, and is, in fact, a connecting rod end: the
+rod proceeding from this is called the eccentric rod.</p>
+
+<p>The distance from the centre of the sheave to the centre of
+the shaft is called the <i>radius</i> or <i>eccentricity</i> of the eccentric.
+The <i>throw</i> is twice the eccentricity.</p>
+
+<p>The sheave is generally made of cast iron. The strap may
+be of brass, cast iron, or wrought iron; when the strap is made
+of wrought iron it is commonly lined with brass.</p>
+
+
+<div class="blockquot"><p><span class="smcap">Exercise</span> 40: <i>Locomotive Eccentric.</i>&mdash;In fig. 40 D E is the
+sheave, F H the strap, and K the eccentric rod. The sheave and
+strap are made of cast iron, and the eccentric rod is made of wrought
+iron. (<i>a</i>) is a vertical cross section through the oil-box of the
+strap; (<i>b</i>) is a plan of the end of the eccentric rod and part of the<span class='pagenum'><a name="Page_48" id="Page_48">[Pg 48]</a></span>
+strap. All the nuts are locked by means of cotters. Draw first
+the elevation, partly in section as shown. Next draw two end
+elevations, one looking each way. Afterwards draw a horizontal
+section through the centre, and also a plan. Scale 4 inches to a
+foot.</p></div>
+
+<div class="figcenter" style="width: 751px;">
+<img src="images/illus056.png" width="751" height="1024" alt="Fig. 40." title="Fig. 40." />
+<span class="caption">Fig. 40.</span>
+</div>
+
+
+
+
+<hr style="width: 15%;" />
+<p><span class='pagenum'><a name="Page_49" id="Page_49">[Pg 49]</a></span></p>
+<h2>XII. &nbsp; CONNECTING RODS.</h2>
+
+
+<p>The most familiar example of the use of a connecting rod
+is in the steam-engine, where it is used to connect the rotating
+crank with the reciprocating piston. The rod itself is made of
+wrought iron or steel, and is generally circular or rectangular in
+section. The ends of the rod are fitted with steps, which are
+held together in a variety of ways.</p>
+
+<p><i>Strap End.</i>&mdash;A form of connecting rod end, which is not
+so common as it used to be, is shown in fig. 41. At (<i>a</i>) is
+shown a longitudinal section with all the parts put together,
+while at (<i>b</i>), (<i>c</i>), <i>(d)</i> and (<i>e</i>) the details are shown separately.
+A B is the end of the rod which butts against the brass bush
+C D, which is in two pieces. A <i>strap</i> E passes round the bush
+and on to the end of the rod as shown. The arms of the strap
+have rectangular holes in them, which are not quite opposite
+a similar hole in the rod when the parts are put together. If
+a wedge or <i>cotter</i> F be driven into these three holes they will
+tend to come into line, and the parts of the bush will be pressed
+together. To prevent the cotter opening out the strap, and to
+increase the sliding surface, a <i>gib</i> H is introduced. The gib is
+provided with horns at its ends to keep it in its place. Sometimes
+two gibs are used, one on each side of the cotter; this
+makes the sliding surface on both sides of the cotter the same.
+The cotter is secured by a set screw K. The unsectioned
+portion of fig. (<i>a</i>) to the right of the gib, or to the left of the
+cotter, is called the <i>clearance</i> or <i>draught.</i></p>
+
+
+<div class="blockquot"><p><span class="smcap">Exercise</span> 41: <i>Connecting Rod End.</i>&mdash;Make the following views
+of the connecting rod end illustrated by fig. 41. First, a vertical
+section, the same as shown at (<i>a</i>). Second, a horizontal section.
+Third, side elevation. Fourth, a plan. Or the first and third views
+may be combined in a half vertical section and half elevation; and
+the second and fourth views may be combined in a half horizontal
+section and half plan.</p>
+
+<p>All the dimensions are to be taken from the detail drawings (<i>b</i>),
+(<i>c</i>), (<i>d</i>), and (<i>e</i>), <i>but the details need not be drawn separately</i>. The
+brass bush is shown at (<i>d</i>) by half elevation, half vertical section,
+<span class='pagenum'><a name="Page_50" id="Page_50">[Pg 50]</a></span>half plan, and half horizontal section. The draught or clearance is
+7-16ths of an inch.</p>
+</div>
+
+<div class="figcenter" style="width: 637px;">
+<img src="images/illus058.png" width="637" height="1024" alt="Fig. 41." title="Fig. 41." />
+<span class="caption">Fig. 41.</span>
+</div>
+
+<p><span class='pagenum'><a name="Page_51" id="Page_51">[Pg 51]</a></span></p>
+
+<p><i>Box End.</i>&mdash;At (<i>a</i>), fig. 42, is shown what is known as a box
+end for a connecting rod. The part which corresponds to the
+loose strap in the last example is here forged in one piece with
+the connecting rod. In this form the brass bush is provided
+with a flange all round on one side, but on the opposite side
+the flange is omitted except at one end; this is to allow of the
+bush being placed within the end of the rod. The construction
+of the bush will be understood by reference to the sketch shown
+at (<i>b</i>). The bush is in two parts, which are pressed tightly together
+by means of a cotter. This cotter is prevented from
+slackening back by two set screws. Each set screw is cut off
+square at the point, and presses on the flat bottom of a very
+shallow groove cut on the side of the cotter.</p>
+
+<p>The top, bottom, and ends of this box end are turned in
+the lathe at the same time as the rod itself; this accounts for
+the curved sections of these parts.</p>
+
+<p>It is clear from the construction of a box end that it is
+only suitable for an overhung crank.</p>
+
+<div class="blockquot"><p><span class="smcap">Exercise 42:</span> <i>Locomotive Connecting Rod.</i>&mdash;In fig. 42 is shown
+a connecting rod for an outside cylinder locomotive. (<i>a</i>) is the
+crank-pin end, and (<i>c</i>) the cross-head end. The end (<i>a</i>) has just
+been described under the head 'box end.' We may just add that
+in this particular example the brass bush is lined with white metal
+as shown, and that the construction of the oil-box is the same as
+that on the coupling rod end shown in fig. 44. The end (<i>c</i>) is
+forked, and through the prongs of the fork passes the cross-head pin,
+of which a separate dimensioned drawing is shown at (<i>d</i>). Observe
+that the tapered parts A and B of this pin are parts of the same
+cone. The rotation of the pin is prevented by a small key as shown.
+The cross-head pin need not be drawn separately, and the isometric
+projection of the bush at (<i>b</i>) may be omitted, but all the other
+views shown are to be drawn to a scale of 6 inches to a foot.</p></div>
+
+<p><span class='pagenum'><a name="Page_52" id="Page_52">[Pg 52]</a></span></p>
+
+<div class="figcenter" style="width: 1024px;">
+<img src="images/illus060.png" width="1024" height="641" alt="Fig. 42." title="Fig. 42." />
+<span class="caption">Fig. 42.</span>
+</div>
+
+<p><span class='pagenum'><a name="Page_53" id="Page_53">[Pg 53]</a></span></p>
+
+<div class="figcenter" style="width: 1024px;">
+<img src="images/illus061.png" width="1024" height="601" alt="Fig. 43." title="Fig. 43." />
+<span class="caption">Fig. 43.</span>
+</div>
+
+<p><span class='pagenum'><a name="Page_54" id="Page_54">[Pg 54]</a></span></p>
+
+<p><i>Marine Connecting Rod.</i>&mdash;The form of connecting rod
+shown in fig. 43 is that used in marine engines, but it is also
+used extensively in land engines. A B is the crank-pin end,
+and C the cross-head end. The end A B is forged in one piece,
+and after it is turned, planed, and bored it is slotted across, so
+as to cut off the cap A. The parts A and B are held together
+by two bolts as shown. This end of the rod is fitted with
+brass steps, which are lined with white metal. The cross-head
+end is forked, and through the prongs of the fork passes a pin
+D, which also passes through the cross-head, which is forged on
+to the piston rod or attached to it in some other way.</p>
+
+<div class="blockquot"><p><span class="smcap">Exercise 43:</span> <i>Marine Connecting Rod.</i>&mdash;Draw all the views
+shown in fig. 43 of one form of marine connecting rod. For detail
+drawings of the locking arrangement for the nuts see fig. 19, page
+21. Scale 4 inches to a foot.</p></div>
+
+<p><i>Coupling Rods.</i>&mdash;A rod used to transmit the motion of one
+crank to another is called a <i>coupling rod</i>. A familiar example
+of the use of coupling rods will be found in the locomotive.
+Coupling rods are made of wrought iron or steel, and are
+generally of rectangular section. The ends are now generally
+made solid and lined with solid brass bushes, <i>without any
+adjustment for wear</i>. This form of coupling rod end is found
+to answer very well in locomotive practice where the workmanship
+and arrangements for lubrication are excellent.
+When the brass bush becomes worn it is replaced by a new
+one.</p>
+
+<p>Fig. 44 shows an example of a locomotive coupling rod end
+for an outside cylinder engine. In this case it is desirable to
+have the crank-pin bearings for the coupling rods as short as
+possible, for a connecting rod and coupling rod in this kind of
+engine work side by side on the same crank-pin, which, being
+overhung, should be as short as convenient for the sake of
+strength. The requisite bearing surface is obtained by having
+a pin of large diameter. The brass bush is prevented from
+rotating by means of the square key shown. The oil-box is
+cut out of the solid, and has a wrought-iron cover slightly
+dovetailed at the edges. This cover fits into a check round
+the top inner edge of the box, which is originally parallel, but
+is made to close on the dovetailed edges of the cover by riveting.
+A hole in the centre of this cover, which gives access to
+the oil-box, is fitted with a screwed brass plug. The brass<span class='pagenum'><a name="Page_55" id="Page_55">[Pg 55]</a></span>
+plug has a screwed hole in the centre, through which oil may
+be introduced to the box. Dust is kept out of the oil-box by
+screwing into the hole in the brass plug a common cork. The
+oil is carried slowly but regularly from the oil-box over to the
+bearing by a piece of cotton wick.</p>
+
+<div class="figcenter" style="width: 600px;">
+<img src="images/illus063.png" width="600" height="660" alt="Fig. 44." title="Fig. 44." />
+<span class="caption">Fig. 44.</span>
+</div>
+
+<div class="blockquot"><p><span class="smcap">Exercise 44:</span> <i>Coupling Rod End.</i>&mdash;Draw first the side elevation
+and plan, each partly in section as shown in fig. 44. Then instead
+of the view to the left, which is an end elevation partly in
+section, draw a complete end elevation looking to the right, and also
+a complete vertical cross section through the centre of the bearing.
+Scale 6 inches to a foot.</p></div>
+
+
+
+<hr style="width: 15%;" />
+<p><span class='pagenum'><a name="Page_56" id="Page_56">[Pg 56]</a></span></p>
+<h2>XIII. &nbsp; CROSS-HEADS.</h2>
+
+
+<p>An example of a steam-engine cross-head is shown in
+fig. 45. A is the end of the piston rod which has forged upon it
+the cross-head B. The cross-head pin shown at (<i>d</i>), fig. 42, and
+to which the connecting rod is attached, works in the bearing
+C. Projecting pieces D, forged on the top and bottom of the
+cross-head, carry the slide blocks E which work on the slide
+bars, and thus guide the motion of the piston rod.</p>
+
+<div class="figcenter" style="width: 800px;">
+<img src="images/illus064.png" width="800" height="530" alt="Fig. 45." title="Fig. 45." />
+<span class="caption">Fig. 45.</span>
+</div>
+
+
+<div class="blockquot"><p><span class="smcap">Exercise 45:</span> <i>Locomotive Cross-head.</i>&mdash;In fig. 45 are shown
+side and end elevations, partly in section, of the cross-head and
+slide blocks for an outside cylinder locomotive. Draw these views
+half size, showing also on the end elevation the cross-head pin and a
+vertical section of the connecting rod end from fig. 42. The bush
+in the cross-head which forms the bearing for the cross-head pin is
+of wrought iron, case-hardened, and is prevented from rotating by the
+key shown. The cross-head is of wrought iron, and the slide blocks
+are of cast iron, and are fitted with white metal strips as shown. A
+short brass tube leads oil from the upper slide block into a hole in
+the cross-head as shown, which carries it to a slot in the bush
+which distributes it over the cross-head pin.</p></div>
+
+
+
+<hr style="width: 15%;" />
+<p><span class='pagenum'><a name="Page_57" id="Page_57">[Pg 57]</a></span></p>
+<h2>XIV. &nbsp; PISTONS.</h2>
+
+
+<p>A <i>piston</i> is generally a cylindrical piece which slides backwards
+and forwards inside a hollow cylinder. The piston may
+be moved by the action of fluid pressure upon it as in a
+steam-engine, or it may be used to give motion to a fluid as in
+a pump.</p>
+
+<p>A piston is usually attached to a rod, called a <i>piston rod</i>,
+which passes through the end of the cylinder inside which the
+piston works, and which serves to transmit the motion of the
+piston to some piece outside the cylinder, or <i>vice vers&acirc;</i>.</p>
+
+<div class="figcenter" style="width: 629px;">
+<img src="images/illus065.png" width="629" height="600" alt="Fig. 46." title="Fig. 46." />
+<span class="caption">Fig. 46.</span>
+</div>
+
+<p>A <i>plunger</i> is a piston made in one piece with its piston rod,
+the piston and the rod being of the same diameter.</p>
+
+<p>A piston which is provided with one or more valves which<span class='pagenum'><a name="Page_58" id="Page_58">[Pg 58]</a></span>
+allow the fluid to pass through it from one side to the other is
+called a <i>bucket</i>.</p>
+
+<p><i>Simple Piston.</i>&mdash;The simplest form of piston is a plain
+cylinder fitting accurately another, inside which it moves.
+Such a piston works with very little friction, but as there is
+no adjustment for wear, such a piston is not suitable for a high
+fluid pressure if it has to work constantly. This simple form of
+piston is used in the steam-engine indicator, and also in
+pumps.</p>
+
+<p>Fig. 46 shows the piston of the circulation pump of a marine
+engine. A is the cast-iron casing or barrel of the pump; B is
+a brass liner fitting tightly into the former at its ends, and
+secured by eight screwed Muntz metal pins C, four at each end;
+D is the piston, which is made of brass, and is attached to
+a Muntz metal piston rod E. The liner is bored out smooth
+and true from end to end, and the piston is turned so as to be
+a sliding fit to the liner. The wear in this form of piston is
+diminished by making the rubbing surface large.</p>
+
+<div class="blockquot"><p><span class="smcap">Exercise 46:</span> <i>Piston for Circulating Pump.</i>&mdash;Draw the
+vertical sectional elevation of the piston, &amp;c., shown in fig. 46, also
+a half plan and half horizontal section through the centre. Scale 4
+inches to a foot.</p></div>
+
+<p><i>Pump Bucket.</i>&mdash;The next form of piston which we illustrate
+is shown in fig. 47. This represents the air-pump bucket of a
+marine engine. The bucket is made of brass, and is provided
+with six india-rubber disc valves. The rod is in this case
+made of Muntz metal. Air-pump rods for marine engines are
+very often made of wrought iron cased with brass. It will be
+observed that there is a wide groove around the bucket, which
+is filled with hempen rope or gasket. This gasket forms an
+elastic packing which prevents leakage. This is an old-fashioned
+form of packing, and is now only used for pump
+buckets.</p>
+
+<div class="blockquot"><p><span class="smcap">Exercise 47:</span> <i>Air-pump Bucket.</i>&mdash;Draw the sectional elevation
+of the air-pump bucket shown in fig. 47. Also draw a half plan
+looking downwards and a half plan looking upwards. Scale 4 inches
+to a foot.</p></div><p><span class='pagenum'><a name="Page_59" id="Page_59">[Pg 59]</a></span></p>
+
+<div class="figcenter" style="width: 1024px;">
+<img src="images/illus067.png" width="1024" height="523" alt="Fig. 47." title="Fig. 47." />
+<span class="caption">Fig. 47.</span>
+</div>
+<p><span class='pagenum'><a name="Page_60" id="Page_60">[Pg 60]</a></span></p>
+
+<div class="figleft" style="width: 292px;">
+<img src="images/illus068.png" width="292" height="640" alt="Fig. 48." title="Fig. 48." />
+<span class="caption">Fig. 48.</span>
+</div>
+
+<p><i>Ramsbottom's Packing.</i>&mdash;The form of packing used in the
+air-pump bucket, fig. 47, is not suitable for steam pistons.
+For the latter the packing is now always metallic. The
+simplest form of metallic packing is that known as Ramsbottom's.
+This form is very largely used for locomotive pistons,
+and for small pistons in many kinds of engines besides. A
+locomotive piston for an 18-inch cylinder with Ramsbottom's
+packing is shown in fig. 48. The
+particular piston there illustrated
+is made of brass, and is secured
+to a wrought-iron piston rod by
+a brass nut. Two circumferential
+grooves of rectangular section are
+turned out of the piston, and into
+these fit two corresponding rings,
+which may be of brass, cast iron,
+or steel. In this example the
+rings are of cast iron. These rings
+are first turned a little larger
+in diameter than the bore of the
+cylinder (in this example <sup>1</sup>&frasl;<sub>2</sub> inch),
+and then sprung over the piston
+into the groves prepared for them.
+Their own elasticity causes the
+rings to press outwards on the
+cylinder. At the point where a
+ring is split a leakage of steam
+will take place, but with quick-running
+pistons this leakage is unimportant.
+The points where the
+rings are cut should be placed diametrically opposite, so as to
+diminish the leakage of steam.</p>
+
+<div class="blockquot"><p><span class="smcap">Exercise 48:</span> <i>Locomotive Piston.</i>&mdash;A part elevation and part
+section of a locomotive piston, for a cylinder having a bore 18 inches
+in diameter, is shown in fig. 48. Draw this, and also a view looking
+on the nut in the direction of the axis of the piston rod. Scale 6
+inches to a foot.</p>
+
+<p><span class='pagenum'><a name="Page_61" id="Page_61">[Pg 61]</a></span></p>
+
+<p><i>Note.</i>&mdash;The reason why the part of the piston rod within the
+piston has such a quick taper is that the piston has to be taken off
+the rod while it is in the cylinder. The cross-head being forged on
+the end of the piston rod prevents the piston and piston rod being
+withdrawn together.</p></div>
+
+<p><i>Large Pistons.</i>&mdash;Pistons of large diameter are generally
+provided with two cast-iron packing rings placed within the
+same groove. These rings are pressed outwards against the
+cylinder, and also against the sides of the groove by one or
+more springs. One form of this packing (Lancaster's) is shown
+in fig. 49. Here one spring only is used, and it is first made
+a straight spiral spring, and then bent round and its ends united.
+The action of the spring will be clearly understood from the
+illustration. For the purpose of admitting the packing rings
+the piston is divided into two parts, one the piston proper,
+and the other the <i>junk ring</i>. In fig. 49, A is the junk ring,
+which is secured to the piston by means of bolts as shown.</p>
+
+
+<div class="blockquot"><p><span class="smcap">Exercise 49:</span> <i>Marine Engine Piston.</i>&mdash;The piston illustrated by
+fig. 49 is for the high-pressure cylinder of a marine engine. The
+piston, junk ring, and packing rings are of cast iron. The piston rod
+and nut are of wrought iron, so also are the junk ring bolts. The
+nuts for the latter are of brass. The spiral spring is made from
+steel wire <sup>3</sup>&frasl;<sub>8</sub> inch diameter. An enlarged section of one of the pack<span class='pagenum'><a name="Page_62" id="Page_62">[Pg 62]</a></span>ing
+rings is shown at (<i>a</i>). A front elevation of the locking arrangement
+for the piston rod nut is shown at (<i>b</i>). A sectional plan of
+one of the nuts for the junk ring bolts is shown at (<i>c</i>).</p>
+
+<p>First draw the vertical section of this piston, ne<i>x</i>t draw a plan,
+one-third of which is to show the piston complete, one-third to show
+the junk ring removed, and the remaining third to be a horizontal
+section through between the packing rings. The details (<i>a</i>) and (<i>c</i>)
+need not be drawn separately. Scale 3 inches to a foot.</p></div>
+
+<div class="figcenter" style="width: 800px;">
+<img src="images/illus069.png" width="800" height="516" alt="Fig. 49." title="Fig. 49." />
+<span class="caption">Fig. 49.</span>
+</div>
+
+
+<p><i>Proportions of Marine Engine Pistons.</i>&mdash;Mr. Seaton, in his
+'Manual of Marine Engineering,' gives the following rules for
+designing marine engine pistons:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='center'> D </td><td align='center'> = </td><td align='left' colspan='2'>diameter of piston in inches.</td></tr>
+<tr><td align='center'> <i>p</i> </td><td align='center'> = </td><td align='left' colspan='2'>effective pressure in lbs. per square inch.</td></tr>
+<tr><td align='center'> <i>x</i> </td><td align='center'> = </td><td align='left'> D <br /> &mdash; <br /> 50 </td><td align='left'> &times; &#8730;<span class="overline"><i>p</i> +</span> 1.</td></tr>
+</table></div>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Thickness of</td><td align='left'>front of piston near boss</td><td align='left'>0&middot;2 &nbsp; &times; <i>x</i>.</td></tr>
+<tr><td align='center'>&rdquo;</td><td align='left'> &nbsp; &nbsp;  &nbsp; &rdquo; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;  &nbsp; &rdquo; &nbsp; &nbsp; &nbsp; &nbsp; rim</td><td align='left'>0&middot;17 &times; <i>x</i>.</td></tr>
+<tr><td align='center'>&rdquo;</td><td align='left'>back of piston</td><td align='left'>0&middot;18 &times; <i>x</i>.</td></tr>
+<tr><td align='center'>&rdquo;</td><td align='left'>boss around rod</td><td align='left'>0&middot;3 &nbsp; &times; <i>x</i>.</td></tr>
+<tr><td align='center'>&rdquo;</td><td align='left'>flange inside packing ring</td><td align='left'>0&middot;23 &times; <i>x</i>.</td></tr>
+<tr><td align='center'>&rdquo;</td><td align='left'> &nbsp; &nbsp; &rdquo; &nbsp; &nbsp; at edge</td><td align='left'>0&middot;25 &times; <i>x</i>.</td></tr>
+<tr><td align='center'>&rdquo;</td><td align='left'>junk ring at edge</td><td align='left'>0&middot;23 &times; <i>x</i>.</td></tr>
+<tr><td align='center'>&rdquo;</td><td align='left'>&nbsp; &nbsp; &nbsp; &rdquo; &nbsp; &nbsp; &nbsp; inside packing ring.</td><td align='left'>0&middot;21 &times; <i>x</i>.</td></tr>
+<tr><td align='center'>&rdquo;</td><td align='left'> &nbsp; &nbsp; &nbsp; &rdquo; &nbsp; &nbsp; &nbsp; at bolt-holes</td><td align='left'>0&middot;35 &times; <i>x</i>.</td></tr>
+<tr><td align='center'>&rdquo;</td><td align='left'>metal around piston edge</td><td align='left'>0&middot;25 &times; <i>x</i>.</td></tr>
+<tr><td align='left' colspan='2'>Breadth of packing ring</td><td align='left'>0&middot;63 &times; <i>x</i>.</td></tr>
+<tr><td align='left' colspan='2'>Depth of piston at centre</td><td align='left'>1&middot;4 &nbsp; &times; <i>x</i>.</td></tr>
+<tr><td align='left' colspan='2'>Lap of junk ring on piston</td><td align='left'>0&middot;45 &times; <i>x</i>.</td></tr>
+<tr><td align='left' colspan='2'>Space between piston body and packing ring</td><td align='left'>0&middot;3 &nbsp; &times; <i>x</i>.</td></tr>
+<tr><td align='left' colspan='2'>Diameter of junk-ring bolts</td><td align='left'>0&middot;1 &nbsp; &times; <i>x</i> + &middot;25 inch.</td></tr>
+<tr><td align='left' colspan='2'>Pitch of junk-ring bolts</td><td align='left'>10 diameters.</td></tr>
+<tr><td align='left' colspan='2'>Number of webs in piston</td><td align='left'>D + 20<br /> &mdash;&mdash;&mdash;. <br /> &nbsp; &nbsp; 12</td></tr>
+<tr><td align='left'>Thickness</td><td align='left'>&rdquo;</td><td align='left'>0&middot;18 &times; <i>x</i>.</td></tr>
+</table></div>
+
+<div class="blockquot"><p><span class="smcap">Exercise 50:</span> <i>Design for Marine Engine Piston.</i>&mdash;Calculate
+by Seaton's rules the dimensions for a marine engine piston 40
+inches in diameter, and subjected to an effective pressure of 36 lbs.
+per square inch. Then make the necessary working drawings for
+this piston to a scale of, say, 3 inches to a foot.</p>
+
+<p><i>Note.</i>&mdash;Take the dimensions got by calculation to the nearest
+1-16th of an inch.</p></div>
+
+
+
+<hr style="width: 15%;" />
+<p><span class='pagenum'><a name="Page_63" id="Page_63">[Pg 63]</a></span></p>
+<h2>XV. &nbsp;  STUFFING-BOXES.</h2>
+
+
+<div class="figcenter" style="width: 590px;">
+<img src="images/illus071.png" width="590" height="1024" alt="Fig. 50." title="Fig. 50." />
+<span class="caption">Fig. 50.</span>
+</div>
+
+
+<p>In fig. 50 is shown a gland and stuffing-box for the piston
+rod of a vertical engine. A B is the piston rod, C D a portion
+of the cylinder cover, and E F the <i>stuffing-box</i>. Fitting into
+the bottom of the stuffing-box is a brass bush H. The space
+K around the rod A B is filled with <i>packing</i>, of which there is<span class='pagenum'><a name="Page_64" id="Page_64">[Pg 64]</a></span>
+a variety of kinds, the simplest being greased hempen rope.
+The packing is compressed by screwing down the cast-iron
+gland L M, which is lined with a brass bush N. In this case
+the gland is screwed down by means of three stud-bolts P,
+which are screwed into a flange cast on the stuffing-box.
+Surrounding the rod on the top of the gland there is a recess
+R for holding the lubricant.</p>
+
+<div class="figcenter" style="width: 768px;">
+<img src="images/illus072.png" width="768" height="881" alt="Figs. 51, 52." title="Figs. 51, 52." />
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="" width="80%">
+<tr><td align='left'><span class="caption">Fig. 51.</span></td><td align='right'><span class="caption">Fig. 52.</span></td></tr>
+</table></div>
+</div>
+
+<p>The object of the gland and stuffing-box is to allow the
+piston rod to move backwards and forwards freely without any
+leakage of steam.<span class='pagenum'><a name="Page_65" id="Page_65">[Pg 65]</a></span></p>
+
+<p>Fig. 51 shows a gland and stuffing-box for a horizontal rod.
+The essential difference between this example and the last is
+in the mode of lubrication. The gland flange has cast within
+it an oil-box which is covered by a lid; this lid is kept shut
+or open by the action of a small spring as shown. A piece of
+cotton wick (not shown in the figure) has one end trailing in the
+oil in the oil-box, while the other is carried over and passed
+down the hole A B. The wick acts as a siphon, and drops the
+oil gradually on to the rod. In this example only two bolts
+are used for screwing in the gland; and the flanges of the gland
+and stuffing-box are not circular, but oval-shaped.</p>
+
+<p>In the case of small rods the gland is made entirely of
+brass, and no liner is then necessary. Fig. 52 shows a form
+of gland and stuffing-box sometimes used for small rods. The
+stuffing-box is screwed externally, and carries a nut A B which
+moves the gland.</p>
+
+
+<div class="blockquot"><p><span class="smcap">Exercise 51:</span> <i>Gland and Stuffing-box for a Vertical Rod.</i>&mdash;Draw
+the views shown in fig. 50 to the dimensions given. Scale 6
+inches to a foot.</p>
+
+<p><span class="smcap">Exercise 52:</span> <i>Gland and Stuffing-box for a Horizontal Rod.</i>&mdash;Fig. 51
+shows a plan, half in section, and an elevation half of which
+is a section through the gland flange. Draw these to a scale of 6
+inches to a foot, using the dimensions marked in the figure.</p>
+
+<p><span class="smcap">Exercise 53:</span> <i>Screwed Gland and Stuffing-box.</i>&mdash;Draw, full
+size, the views shown in fig. 52 to the given dimensions.</p></div>
+
+<p>A more elaborate form of gland and stuffing-box is shown
+in fig. 53. This is for a large marine engine with inverted
+cylinders, such as is used on board large ocean steamers. The
+stuffing-box is cast separate from the cylinder cover to which
+it is afterwards bolted. The lubricant is first introduced to
+the oil-boxes marked A, from which it passes to the recess B,
+where it comes in contact with the piston rod. To prevent
+the lubricant from being wasted by running down the rod, the
+main gland is provided with a shallow gland and stuffing-box
+which is filled with soft cotton packing, which soaks up the
+lubricant.</p>
+
+<p><span class='pagenum'><a name="Page_66" id="Page_66">[Pg 66]</a></span></p>
+
+<div class="figcenter" style="width: 604px;">
+<img src="images/illus074.png" width="604" height="1024" alt="Fig. 53." title="Fig. 53." />
+<span class="caption">Fig. 53.</span>
+</div>
+
+<p>The main gland is screwed up by means of six bolts, and
+to prevent the gland from locking itself in the stuffing-box, it<span class='pagenum'><a name="Page_67" id="Page_67">[Pg 67]</a></span>
+is necessary that the nuts should be turned together. This is
+done in a simple and ingenious manner. One-half of each
+nut is provided with teeth, and these gear with a toothed
+wheel which has a rim only; this rim is held up by a ring C.
+When one nut is turned, all the rest follow in the same direction.</p>
+
+<div class="blockquot"><p><span class="smcap">Exercise 54:</span> <i>Gland and Stuffing-box for Piston Rod of Large
+Inverted Cylinder Engine.</i>&mdash;The lower view in fig. 53 is a half plan
+looking upwards, and a half section of the gland looking downwards.
+The upper view is a vertical section. Complete all these views and
+add an elevation. Scale 3 inches to a foot.</p>
+
+<p><i>Note.</i>&mdash;The large nuts, the wheel, the supporting ring, and small
+gland are made of brass.</p></div>
+
+<p class="tabcap"><i>Dimensions of Stuffing-boxes and Glands.</i></p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'><i>d</i></td><td align='left'>= diameter of rod.</td><td align='left'><i>t</i><sub>1</sub> = thickness of stuffing-box flange.</td></tr>
+<tr><td align='left'><i>d</i><sub>1</sub></td><td align='left'>= diameter of box (inside).</td><td align='left'><i>t</i><sub>2</sub> = thickness of gland flange.</td></tr>
+<tr><td align='left'><i>l</i></td><td align='left'>= length of stuffing-box bush.</td><td align='left'><i>t</i><sub>3</sub> = thickness of bushes in box and gland.</td></tr>
+<tr><td align='left'><i>l</i><sub>1</sub></td><td align='left'>= length of packing space.</td><td align='left'><i>d</i><sub>2</sub> = diameter of gland bolts.</td></tr>
+<tr><td align='left'><i>l</i><sub>2</sub></td><td align='left'>= length of gland.</td><td align='left'><i>n</i> = number of bolts.</td></tr>
+<tr><td align='left'><i>t</i></td><td align='left'>= thickness of metal in stuffing-box.</td></tr>
+</table></div>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="" rules="cols">
+<thead>
+<tr>
+<th class="bbox"><i>d</i></th>
+<th class="bbox"><i>d</i><sub>1</sub></th>
+<th class="bbox"><i>l</i></th>
+<th class="bbox"><i>l</i><sub>1</sub></th>
+<th class="bbox"><i>l</i><sub>2</sub></th>
+<th class="bbox"><i>t</i></th>
+<th class="bbox"><i>t</i><sub>1</sub></th>
+<th class="bbox"><i>t</i><sub>2</sub></th>
+<th class="bbox"><i>t</i><sub>3</sub></th>
+<th class="bbox"><i>d</i><sub>2</sub></th>
+<th class="bbox"><i>n</i></th>
+</tr>
+</thead>
+<tbody>
+<tr><td align='center'> 1</td><td align='center'> 1&frac34;</td><td align='center'> <sup>3</sup>&frasl;<sub>4</sub></td><td align='center'> 2</td><td align='center'> 1&frac12;</td><td align='center'> <sup>7</sup>&frasl;<sub>16</sub></td><td align='center'> <sup>1</sup>&frasl;<sub>2</sub></td><td align='center'><i>t</i><sub>2</sub>=<i>t</i></td><td align='center'> <sup>3</sup>&frasl;<sub>16</sub></td><td align='center'> <sup>7</sup>&frasl;<sub>16</sub></td><td align='center'> 2</td></tr>
+<tr><td align='center'>1&frac12;</td><td align='center'> 2&frac12;</td><td align='center'>1&frac14;</td><td align='center'> 2<small><sup>5</sup>&frasl;<sub>8</sub></small></td><td align='center'> 2</td><td align='center'> <sup>9</sup>&frasl;<sub>16</sub></td><td align='center'> <sup>11</sup>&frasl;<sub>16</sub></td><td align='center'>when gland</td><td align='center'> <sup>1</sup>&frasl;<sub>4</sub></td><td align='center'> <sup>5</sup>&frasl;<sub>8</sub></td><td align='center'> 2</td></tr>
+<tr><td align='center'> 2</td><td align='center'> 3&frac12;</td><td align='center'>1&frac34;</td><td align='center'> 3&frac14;</td><td align='center'> 2&frac12;</td><td align='center'><sup>11</sup>&frasl;<sub>16</sub></td><td align='center'> <sup>7</sup>&frasl;<sub>8</sub></td><td align='center'>flange is</td><td align='center'> <sup>5</sup>&frasl;<sub>16</sub></td><td align='center'> <sup>3</sup>&frasl;<sub>4</sub></td><td align='center'> 2</td></tr>
+<tr><td align='center'>2&frac12;</td><td align='center'> 4<small><sup>1</sup>&frasl;<sub>8</sub></small></td><td align='center'>2&frac14;</td><td align='center'> 3<small><sup>7</sup>&frasl;<sub>8</sub></small></td><td align='center'> 2<small><sup>7</sup>&frasl;<sub>8</sub></small></td><td align='center'><sup>13</sup>&frasl;<sub>16</sub></td><td align='center'> 1<small><sup>1</sup>&frasl;<sub>16</sub></small></td><td align='center'>made of</td><td align='center'> <sup>5</sup>&frasl;<sub>16</sub></td><td align='center'> <sup>7</sup>&frasl;<sub>8</sub></td><td align='center'> 2</td></tr>
+<tr><td align='center'> 3</td><td align='center'> 4&frac34;</td><td align='center'>2&frac34;</td><td align='center'> 4&frac12;</td><td align='center'> 3&frac14;</td><td align='center'><sup>15</sup>&frasl;<sub>16</sub></td><td align='center'> 1&frac14;</td><td align='center'>cast iron</td><td align='center'> <sup>3</sup>&frasl;<sub>8</sub></td><td align='center'> 1</td><td align='center'> 2</td></tr>
+<tr><td align='center'>3&frac12;</td><td align='center'> 5&frac14;</td><td align='center'> 3</td><td align='center'> 5<small><sup>1</sup>&frasl;<sub>8</sub></small></td><td align='center'> 3<small><sup>5</sup>&frasl;<sub>8</sub></small></td><td align='center'> 1</td><td align='center'> 1<small><sup>3</sup>&frasl;<sub>8</sub></small></td><td align='center'>and <i>t</i><sub>2</sub>=<i>t</i><sub>1</sub></td><td align='center'> <sup>3</sup>&frasl;<sub>8</sub></td><td align='center'> 1</td><td align='center'> 2</td></tr>
+<tr><td align='center'> 4</td><td align='center'> 5<small><sup>7</sup>&frasl;<sub>8</sub></small></td><td align='center'>3&frac14;</td><td align='center'> 5&frac34;</td><td align='center'> 4</td><td align='center'> 1</td><td align='center'> 1<small><sup>3</sup>&frasl;<sub>8</sub></small></td><td align='center'>when gland</td><td align='center'> <sup>7</sup>&frasl;<sub>16</sub></td><td align='center'> 1</td><td align='center'> 2</td></tr>
+<tr><td align='center'>4&frac12;</td><td align='center'> 6<small><sup>3</sup>&frasl;<sub>8</sub></small></td><td align='center'>3&frac12;</td><td align='center'> 6<small><sup>3</sup>&frasl;<sub>8</sub></small></td><td align='center'> 4<small><sup>3</sup>&frasl;<sub>8</sub></small></td><td align='center'>1<small><sup>1</sup>&frasl;<sub>16</sub></small></td><td align='center'> 1<small><sup>9</sup>&frasl;<sub>16</sub></small></td><td align='center'>flange is</td><td align='center'> <sup>7</sup>&frasl;<sub>16</sub></td><td align='center'> <sup>7</sup>&frasl;<sub>8</sub></td><td align='center'> 4</td></tr>
+<tr><td align='center'> 5</td><td align='center'> 7</td><td align='center'>3&frac34;</td><td align='center'> 7</td><td align='center'> 4<small><sup>5</sup>&frasl;<sub>8</sub></small></td><td align='center'>1<small><sup>1</sup>&frasl;<sub>16</sub></small></td><td align='center'> 1<small><sup>9</sup>&frasl;<sub>16</sub></small></td><td align='center'>made of</td><td align='center'> <sup>7</sup>&frasl;<sub>16</sub></td><td align='center'> 1</td><td align='center'> 4</td></tr>
+<tr><td align='center'> 6</td><td align='center'> 8</td><td align='center'>4&frac14;</td><td align='center'> 8&frac14;</td><td align='center'> 5</td><td align='center'>1<small><sup>1</sup>&frasl;<sub>8</sub></small></td><td align='center'>1<small><sup>11</sup>&frasl;<sub>16</sub></small></td><td align='center'>brass.</td><td align='center'> <sup>1</sup>&frasl;<sub>2</sub></td><td align='center'> 1&frac14;</td><td align='center'> 4</td></tr>
+<tr><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td><td class="bb"></td></tr>
+</tbody>
+</table></div>
+
+<p>The proportions of glands and stuffing-boxes vary considerably
+but the above table represents average practice.</p>
+
+<div class="blockquot"><p><span class="smcap">Exercise 55:</span>&mdash;Make the necessary working drawings for a
+gland and stuffing-box for a locomotive engine piston rod 2&frac12;
+inches in diameter, to the dimensions given in the table.</p></div>
+
+
+
+<hr style="width: 15%;" />
+<p><span class='pagenum'><a name="Page_68" id="Page_68">[Pg 68]</a></span></p>
+<h2>XVI. &nbsp;  VALVES.</h2>
+
+
+<p>Professor Unwin divides valves, according to their construction
+into three classes as follows:&mdash;(1) flap valves, which
+bond or turn upon a hinge; (2) lift valves, which rise perpendicularly
+to the seat; (3) sliding valves, which move parallel
+to the seat.</p>
+
+<p>Examples of flap valves are shown in figs. 54 and 55; two
+forms of lift valves are shown in figs. 56 and 57, and in figs.
+58 and 59 are shown two forms of slide valve. The slide valve
+shown in fig. 58 moves in a straight line, while that shown in
+fig. 59 (called a cock) moves in circle.</p>
+
+<p><i>India-rubber Valves.</i>&mdash;In india-rubber valves there is a
+grating covered by a piece of india-rubber, which may be rectangular,
+but is generally circular, and which is held down
+along one edge if rectangular, or at the centre if circular.
+Water or other fluid can pass freely upwards through the
+grating, but when it attempts to return the elasticity of the
+india-rubber, and the pressure of the water upon it, cause it to lie
+close on the grating, and thus prevent the return of the water.
+The india-rubber is prevented from rising too high by a perforated
+guard. In fig. 54 is shown an example of an india-rubber
+disc valve. A is the grating, B the india-rubber, C the
+guard secured to the grating or seat by the stud D and nut
+E. The grating is held in position by bolts and nuts F. The
+grating and guard are generally of brass.</p>
+
+<p>India-rubber disc valves are also shown on the air-pump
+bucket, fig. 47.</p>
+
+<div class="blockquot"><p><span class="smcap">Exercise</span> 56: <i>India-rubber Disc Valve.</i>&mdash;Fig. 54 shows a
+vertical section and a plan of an india-rubber disc valve. In the
+plan one-half of the guard and india-rubber are supposed to be removed
+so as to show the grating or seat. Draw these views, and
+also an elevation. A detail drawing of the central stud is shown in
+fig. 16, page 18. In fig. 54 the elevation of the guard is drawn as
+it is usually drawn in practice, but if the student has a sufficient
+knowledge of descriptive geometry he should draw the elevation
+completely showing the perforations. Scale 6 inches to a foot.</p></div>
+<p><span class='pagenum'><a name="Page_69" id="Page_69">[Pg 69]</a></span></p>
+
+<div class="figcenter" style="width: 1050px;">
+<div class="figleft" style="width: 465px;">
+<img src="images/illus077a.png" width="465" height="640" alt="Fig. 54." title="Fig. 54." />
+<span class="caption">Fig. 54.</span>
+</div>
+<div class="figright" style="width: 534px;">
+<img src="images/illus077b.png" width="534" height="638" alt="Fig. 55." title="Fig. 55." />
+<span class="caption">Fig. 55.</span>
+</div>
+</div>
+<div style="clear: both;"></div>
+
+<p><span class='pagenum'><a name="Page_70" id="Page_70">[Pg 70]</a></span></p>
+
+<p><i>Kinghorn's Metallic Valve.</i>&mdash;The action of this valve is the
+same as that of an india-rubber valve, but a thin sheet of
+metal (phosphor bronze) takes the place of the india-rubber.</p>
+
+<p>This valve is now largely used in the pumps of marine
+engines, and is shown in fig. 55 as applied to an air-pump
+bucket. Three valves like the one shown are arranged round
+the bucket.</p>
+
+<div class="blockquot"><p><span class="smcap">Exercise</span> 57: <i>Kinghorn's Metallic Valve.</i>&mdash;Fig. 55 shows an
+elevation and plan of one form of this valve. In the plan one-half
+of the guard and metal sheet are supposed to be removed, so as to
+show the grating, which in this case is part of an air-pump bucket.
+Draw the views shown, and also a vertical section of the guard
+through the centres of the bolts. All the parts are of brass except
+the valve proper, which is of phosphor bronze. Scale 6 inches to a
+foot.</p></div>
+
+<p><i>Conical Disc Valves.</i>&mdash;A very common form of valve is
+that shown in figs. 56 and 57. This form of valve consists of
+a disc, the edge of which (called the face) is conical. The
+conical edge of this disc fits accurately on a corresponding
+seat. The angle which the valve face makes with its axis is
+generally 45&deg;. If the disc is raised, either by the action of
+the fluid as in the india-rubber valve, or by other means, an
+opening is formed around the disc through which the fluid
+can pass. The valve is guided in rising and falling either by
+three feathers underneath it, as in fig. 56, or by a central
+spindle which moves freely through a hole in the centre of a
+bridge which stretches across the seat, as in fig. 57. The lift of
+the valve is limited by a stop above it, which forms part of the
+casing containing the valve. The lift should in no case exceed
+one-fourth of the diameter of the valve, and it is generally
+much less than this. The guiding feathers (fig. 56) are notched
+immediately under the disc for the purpose of making available
+the full circumferential opening of the valve for the passage
+of the fluid. These notches also prevent the feathers from
+interfering with the turning or scraping of the valve face.</p>
+
+<p>Conical disc valves and their seats are nearly always made
+of brass.<span class='pagenum'><a name="Page_71" id="Page_71">[Pg 71]</a></span></p>
+
+<div class="blockquot"><p><span class="smcap">Exercise</span> 58: <i>Conical Disc Valves.</i>&mdash;Draw, half size, the plans
+and elevations shown in figs. 56 and 57. In fig. 57 the valve is
+shown open in the elevation, and in the plan it is removed altogether
+in order to show the seat with its guide bridge.</p></div>
+
+<div class="figcenter" style="width: 1024px;">
+<div class="figleft" style="width: 404px;">
+<img src="images/illus079a.png" width="404" height="800" alt="Fig. 56." title="Fig. 56." />
+<span class="caption">Fig. 56.</span>
+</div>
+<div class="figright" style="width: 402px;">
+<img src="images/illus079b.png" width="402" height="800" alt="Fig. 57." title="Fig. 57." />
+<span class="caption">Fig. 57.</span>
+</div>
+</div>
+<div style="clear: both;"></div>
+
+<p><i>Simple Slide Valve.</i>&mdash;The form of valve shown in fig. 58,
+often called the <i>locomotive slide valve</i>, is very largely used in all
+classes of steam-engines for distributing the steam in the
+steam cylinders. The valve is shown separately at (<i>d</i>), (<i>e</i>),
+and (<i>f</i>), while at (<i>a</i>), (<i>b</i>), and (<i>c</i>) is shown its connection with
+the steam cylinder.</p>
+
+<p>It will be observed that the valve itself is in the shape of
+a box with one side open, the edges of the open side being
+flanged. When the valve is in its middle position, as shown
+at (<i>a</i>), two of these flanged edges completely cover two rectangular
+openings S<sub>1</sub> and S<sub>2</sub>, called <i>steam ports</i>, while the hollow
+part of the valve is opposite to a third port E, called the <i>exhaust
+port</i>. As shown at (<i>a</i>) the piston P would be moving<span class='pagenum'><a name="Page_72" id="Page_72">[Pg 72]</a></span>
+upwards and the valve downwards. By the time the piston
+has reached the top of its stroke the valve will have moved
+so far down as to partly uncover the steam port S<sub>1</sub>, and admit
+steam from the valve casing C through S<sub>1</sub> and the passage P<sub>1</sub>
+to the top of the piston. The pressure of this steam on the
+top of the piston will force the latter down. While the above
+action has been going on, the port S<sub>2</sub> will have become uncovered,
+and the hollow part of the valve will be opposite both
+the steam port S<sub>2</sub> and the exhaust port E, so that the steam
+from the under side of the piston, and which forced the piston
+up, can now escape by the passage P<sub>2</sub>, the steam port S<sub>2</sub>, and
+the exhaust port E to the exhaust outlet O, and thence into
+the atmosphere, if it is a non-condensing engine, or into the
+condenser if it is a condensing engine, or into another cylinder
+if it is a compound engine. After the piston has performed,
+a certain part of its downward stroke, the valve, which has
+been moving downwards, will commence to move upwards,
+and when it has reached a certain point it will cover the port
+S<sub>1</sub>, and shut off the supply of steam to the top of the piston.
+It is generally arranged that the steam shall be cut off before
+the piston reaches the end of the stroke. When the piston
+reaches the bottom of its stroke the valve has moved far
+enough up to uncover the port S<sub>2</sub> and admit steam to the
+bottom of the piston, and to uncover the port S<sub>1</sub> and allow
+the steam to escape from the top of the piston through the
+passage P<sub>1</sub>, the port S<sub>1</sub>, the port E, and outlet O. In this
+way the piston is moved up and down in the cylinder.</p>
+
+<p>The valve is attached to a valve spindle S by nuts as
+shown, the hole in the valve through which the spindle passes
+being oval-shaped to permit of the valve adjusting itself so as
+to always press on its seat.</p>
+
+<p>When the valve is in its middle position it generally more
+than covers the steam ports. The amount which the valve
+projects over the steam port on the outside, the valve being
+in its middle position, is called the <i>outside lap</i> of the valve,
+and the amount which it projects on the inside is called the
+<i>inside lap</i>. When the term lap is used without any qualification,
+outside lap is to be understood. In fig. 58 it will be<span class='pagenum'><a name="Page_73" id="Page_73">[Pg 73]</a></span>
+seen that the valve has no inside lap, and that the outside lap
+is three-eighths of an inch. The inside lap is generally small
+compared with the outside lap.</p>
+
+<div class="figcenter" style="width: 619px;">
+<img src="images/illus081.png" width="619" height="1024" alt="Fig. 58." title="Fig. 58." />
+<span class="caption">Fig. 58.</span>
+</div>
+
+<p><span class='pagenum'><a name="Page_74" id="Page_74">[Pg 74]</a></span></p>
+
+<p>When the piston is at the beginning of its stroke the steam
+port is generally open by a small amount called the <i>lead</i> of the
+valve.</p>
+
+<p>The reciprocating motion of the slide valve is nearly always
+derived from an eccentric fixed on the crank-shaft of the
+engine. Slide valves are generally made of brass, bronze, or
+cast iron.</p>
+
+<div class="blockquot"><p><span class="smcap">Exercise</span> 59: <i>Simple Slide Valve.</i>&mdash;At (<i>d</i>), fig. 58, is shown a
+sectional elevation of a simple slide valve for a steam-engine, the
+section being taken through the centre line of the valve spindle,
+while at (<i>e</i>) is shown a cross section and elevation, and at (<i>f</i>) a plan
+of the same. Draw all these views full size, and also a sectional
+elevation at A B. The valve is made of brass, and the valve spindle
+and nuts of wrought iron.</p>
+
+<p><span class="smcap">Exercise</span> 60: <i>Slide Valve Casing, &amp;c., for Steam-engine.</i>&mdash;Draw,
+half size, the views shown at (<i>a</i>), (<i>b</i>), and (<i>c</i>), fig. 58; also a
+sectional plan at L M. (<i>b</i>) is an elevation of the valve casing with the
+cover and the valve removed. (<i>a</i>) is a sectional elevation, the section
+being taken through the axes of the steam cylinder and valve spindle.
+(<i>c</i>) is a sectional plan, the section being a horizontal one through
+the centre of the exhaust port. The inlet and outlet for the steam
+are clearly shown in the sectional plan: in the sectional elevation
+their positions are shown by dotted circles.</p>
+
+<p>The stroke of the piston is in this case 12 inches, so that from
+the dimensions given at (<i>a</i>) it must come within a quarter of an
+inch of each end of the cylinder; this is called the <i>cylinder clearance</i>.</p>
+
+<p>The piston has three Ramsbottom rings, a quarter of an inch
+wide and a quarter of an inch apart.</p>
+
+<p>The steam cylinder and valve casing are made of cast iron.</p>
+</div>
+
+<p><i>Cocks.</i>&mdash;A cock consists of a slightly conical plug which
+fits into a corresponding casing cast on a pipe. Through the
+plug is a hole which may be made by turning the plug to form
+a continuation of the hole in the pipe, and thus allow the fluid
+to pass, or it may be turned round so that the solid part of
+the plug lies across the hole in the pipe, and thus prevent the<span class='pagenum'><a name="Page_75" id="Page_75">[Pg 75]</a></span>
+fluid from passing. As the student will be quite familiar
+with the common water cock or tap such as is used in dwelling-houses
+we need not illustrate it here.</p>
+
+<div class="figcenter" style="width: 560px;">
+<img src="images/illus083.png" width="560" height="1024" alt="Fig. 59." title="Fig. 59." />
+<span class="caption">Fig. 59.</span>
+</div>
+
+<p><span class='pagenum'><a name="Page_76" id="Page_76">[Pg 76]</a></span></p>
+
+<p>Fig. 59 shows a cock of considerable size, which may be
+used for water or steam under high pressure. The plug in
+this example is hollow, and is prevented from coming out by a
+cover which is secured to the casing by four stud bolts. An
+annular ridge of rectangular section projecting from the under
+side of the cover, and fitting into a corresponding recess on the
+top of the casing, serves to ensure that the cover and plug are
+concentric, and prevents leakage. Leakage at the neck of the
+plug is prevented by a gland and stuffing-box. The top end
+of the plug is made square to receive a handle for turning it.
+The size of a cock is taken from the bore of the pipe in which
+it is placed; thus fig. 59 shows a 2&frac14;-inch cock.</p>
+
+<div class="blockquot"><p><span class="smcap">Exercise</span> 61: 2&frac14;-<i>inch Steam or Water Cock.</i>&mdash;First draw the
+views of this cock shown in fig. 59, then draw a half end elevation
+and half cross section through the centre of the plug. Scale 6 inches
+to a foot.</p>
+
+<p>Instead of drawing the parts of the pipe on the two sides of the
+plug in the same straight line as in fig. 59, one may be shown proceeding
+from the bottom of the casing, so that the fluid will have to
+pass through the bottom of the plug and through one side. This is
+a common arrangement.</p>
+
+<p>All the parts of the valve and casing in this example are made
+of brass.</p></div>
+
+
+
+<hr style="width: 15%;" />
+<h2>XVII. &nbsp; MATERIALS USED IN MACHINE<br />
+CONSTRUCTION.</h2>
+
+
+<p><i>Cast Iron.</i>&mdash;The essential constituents of cast iron are iron
+and carbon, the latter forming from 2 to 5 per cent. of the
+total weight. Cast iron, however, usually contains varying
+small amounts of silicon, sulphur, phosphorus, and manganese.</p>
+
+<p>In cast iron the carbon may exist partly in the free state
+and partly in chemical combination with the iron.<span class='pagenum'><a name="Page_77" id="Page_77">[Pg 77]</a></span></p>
+
+<p>In <i>white cast iron</i> the whole of the carbon is in chemical
+combination with the iron, while in <i>grey cast iron</i> the carbon
+is principally in the free state, that is, simply mixed mechanically
+with the iron. It is the free carbon which gives the
+grey iron its dark appearance. A mixture of the white and
+grey varieties of cast iron when melted produces <i>mottled cast
+iron</i>. The greater the amount of carbon chemically combined
+with the iron, the whiter, harder, and more brittle does it
+become.</p>
+
+<p>The white cast iron is stronger than the grey, but being
+more brittle it is not so suitable for resisting suddenly applied
+loads. White iron melts at a lower temperature than grey
+iron, but after melting it does not flow so well, or is not so
+liquid as the grey iron. White iron contracts while grey iron
+expands on solidifying. The grey iron, therefore, makes finer
+castings than the white. Castings after solidifying contract in
+cooling about <sup>1</sup>&frasl;<sub>8</sub> of an inch per foot. Castings possessing
+various degrees of strength and hardness are produced by
+melting mixtures of various proportions of white and grey
+cast irons. White cast iron has a higher specific gravity than
+grey cast iron.</p>
+
+<p>Cast iron gives little or no warning before breaking. The
+thickness of the metal throughout a casting in cast iron
+should be as uniform as possible, so that it may cool and
+therefore contract uniformly throughout; otherwise some parts
+may be in a state of initial strain after the casting has cooled,
+and will therefore be easier to fracture. Re-entrant angles
+should be avoided; such should be rounded out with fillets.</p>
+
+<p>The presence of phosphorus in cast iron makes it more
+fusible, and also more brittle. The presence of sulphur
+diminishes the strength considerably.</p>
+
+<p>The grey varieties of cast iron are called <i>foundry irons</i> or
+<i>foundry pigs</i>, while the white varieties are called <i>forge irons</i>
+or <i>forge pigs</i>, from the fact that they are used for conversion
+into wrought iron.</p>
+
+<p>Amongst iron manufacturers the different varieties of cast
+iron are designated by the numbers 1, 2, 3, &amp;c., the lowest
+number being applied to the greyest variety.<span class='pagenum'><a name="Page_78" id="Page_78">[Pg 78]</a></span></p>
+
+<p><i>Chilled Castings.</i>&mdash;When grey cast iron is melted a portion
+of the free carbon combines chemically with the iron; this,
+however, separates out again if the iron is allowed to cool
+slowly; but if it is suddenly cooled a greater amount of the
+carbon remains in chemical combination, and a whiter and
+harder iron is produced. Advantage is taken of this in making
+<i>chilled castings</i>. In this process the whole or a part of the
+mould is lined with cast iron, which, being a comparatively
+good conductor of heat, chills a portion of the melted metal
+next to it, changing it into a hard white iron to a depth
+varying from <sup>1</sup>&frasl;<sub>8</sub> to <sup>1</sup>&frasl;<sub>2</sub> an inch. To protect the cast-iron lining
+of the mould from the molten metal it is painted with
+loam.</p>
+
+<p><i>Malleable Cast Iron.</i>&mdash;This is prepared by imbedding a
+casting in powdered red hematite (an oxide of iron), and
+keeping it at a bright red heat for a length of time varying
+from several hours to several days according to the size of the
+casting. By this process a portion of the carbon in the casting
+is removed, and the strength and toughness of the latter
+become more like the strength and toughness of wrought or
+malleable iron.</p>
+
+<p><i>Wrought or Malleable Iron.</i>&mdash;This is nearly pure iron, and
+is made from cast iron by the puddling process, which consists
+chiefly of raising the cast iron to a high temperature in a
+reverberatory furnace in the presence of air, which unites with
+the carbon and passes off as gas. In other words the carbon
+is burned out. The iron is removed from the puddling
+furnace in soft spongy masses called <i>blooms</i>, which are subjected
+to a process of squeezing or hammering called <i>shingling</i>.
+These shingled blooms still contain enough heat to enable
+them to be rolled into rough <i>puddled bars</i>. These puddled
+bars are of very inferior quality, having less than half the
+strength of good wrought iron. The puddled bars are cut into
+pieces which are piled together, reheated, and again rolled
+into bars, which are called <i>merchant bars</i>. This process of
+piling, reheating, and re-rolling may be repeated several times,
+depending on the quality of iron required. Up to a certain
+point the quality of the iron is improved by reheating and<span class='pagenum'><a name="Page_79" id="Page_79">[Pg 79]</a></span>
+rolling or hammering, but beyond that a repetition of the
+process diminishes the strength of the iron.</p>
+
+<p>The process of piling and rolling gives wrought iron a
+fibrous structure. When subjected to vibrations for a long
+time, the structure becomes crystalline and the iron brittle.
+The crystalline structure induced in this way may be removed
+by the process of <i>annealing</i>, which consists in heating the iron
+in a furnace, and then allowing it to cool slowly.</p>
+
+<p><i>Forging and Welding.</i>&mdash;The process of pressing or hammering
+wrought iron when at a red or white heat into any
+desired shape is called <i>forging</i>. If at a white heat two pieces
+of wrought iron be brought together, their surfaces being clean,
+they may be pressed or hammered together, so as to form one
+piece. This is called <i>welding</i>, and is a very valuable property
+of wrought iron.</p>
+
+<p><i>Steel.</i>&mdash;This is a compound of iron with a small per-centage
+of carbon, and is made either by adding carbon to wrought
+iron, or by removing some of the carbon from cast iron.</p>
+
+<p>In the <i>cementation</i> process, bars of wrought iron are imbedded
+in powdered charcoal in a fireclay trough, and kept
+at a high temperature in a furnace for several days. The
+iron combines with a portion of the carbon to form <i>blister
+steel</i>, so named because of the blisters which are found on
+the surface of the bars when they are removed from the
+furnace.</p>
+
+<p>The bars of blister steel are broken into pieces about 18
+inches long, and tied together in bundles by strong steel wire.
+These bundles are raised to a welding heat in a furnace, and
+then hammered or rolled into bars of <i>shear steel</i>.</p>
+
+<p>To form <i>cast steel</i> the bars of blister steel are broken into
+pieces and melted into crucibles.</p>
+
+<p>In the <i>Siemens-Martin</i> process for making steel, cast and
+wrought iron are melted together on the hearth of a regenerative
+gas-furnace.</p>
+
+<p><i>Bessemer steel</i> is made by pouring melted cast iron into a
+vessel called a converter, through which a blast of air is then
+urged. By this means the carbon is burned out, and comparatively
+pure iron remains. To this is added a certain quantity<span class='pagenum'><a name="Page_80" id="Page_80">[Pg 80]</a></span>
+of 'spiegeleisen,' which is a compound of iron, carbon, and
+manganese.</p>
+
+<p><i>Hardening and Tempering of Steel.</i>&mdash;Steel, if heated to
+redness and cooled suddenly, as by immersion in water, is
+hardened. The degree of hardness produced varies with the
+rate of cooling; the more rapidly the heated steel is cooled,
+the harder does it become. Hardened steel is softened by the
+process of <i>annealing</i>, which consists in heating the hardened
+steel to redness, and then allowing it to cool slowly. Hardened
+steel is <i>tempered</i>, or has its degree of hardness lowered, by
+being heated to a temperature considerably below that of a red
+heat, and then cooling suddenly. The higher the temperature
+the hardened steel is raised to, the lower does its 'temper'
+become.</p>
+
+<p><i>Case-hardening.</i>&mdash;This is the name given to the process
+by which the surfaces of articles made of wrought iron are
+converted into steel, and consists in heating the articles in
+contact with substances rich in carbon, such as bone-dust,
+horn shavings, or yellow prussiate of potash. This process
+is generally applied to the articles after they are completely
+finished by the machine tools or by hand. The coating of
+steel produced on the article by this process is hardened by
+cooling the article suddenly in water.</p>
+
+<p><i>Copper.</i>&mdash;This metal has a reddish brown colour, and when
+pure is very malleable and ductile, either when cold or hot, so
+that it may be rolled or hammered into thin plates, or drawn
+into wire. Slight traces of impurities cause brittleness,
+although from 2 to 4 per cent. of phosphorus increases its
+tenacity and fluidity. Copper is a good conductor of heat and
+of electricity. Copper is largely used for making alloys.</p>
+
+<p><i>Alloys.</i>&mdash;<i>Brass</i> contains two parts by weight of copper to
+one of zinc. <i>Muntz metal</i> consists of three parts of copper to
+two of zinc. Alloys consisting of copper and tin are called
+<i>bronze</i> or <i>gun-metal</i>. Bronze is harder the greater the proportion
+of tin which it contains; five parts of copper to one
+of tin produce a very hard bronze, and ten of copper to one
+of tin is the composition of a soft bronze. <i>Phosphor bronze</i>
+contains copper and tin with a little phosphorus; it has this<span class='pagenum'><a name="Page_81" id="Page_81">[Pg 81]</a></span>
+advantage over ordinary bronze, that it may be remelted without
+deteriorating in quality. This alloy also has the advantage
+that it may be made to possess great strength accompanied with
+hardness, or less strength with a high degree of toughness.</p>
+
+<p><i>Wood.</i>&mdash;In the early days of machines wood was largely
+used in their construction, but it is now used to a very limited
+extent in that direction. <i>Beech</i> and <i>hornbeam</i> are used for
+the cogs of mortise wheels. <i>Yellow pine</i> is much used by
+pattern-makers. <i>Box</i>, a heavy, hard, yellow-coloured wood,
+is used for the sheaves of pulley blocks, and sometimes for
+bearings in machines. <i>Lignum-vit&aelig;</i> is a very hard dark-coloured
+wood, and remarkable for its high specific gravity,
+being 1<small><sup>1</sup>&frasl;<sub>3</sub></small> times the weight of the same volume of water. This
+wood is much used for bearings of machines which are under
+water.</p>
+
+
+
+<hr style="width: 15%;" />
+<h2>XVIII. &nbsp; MISCELLANEOUS EXERCISES.</h2>
+
+
+<p>The illustrations in this chapter are in most cases not
+drawn to scale; they are also in some parts incomplete, and
+in others some of the lines are purposely drawn wrong. The
+student must keep to the dimensions marked on the drawings,
+and where no sizes are given he must use his own judgment
+in proportioning the parts. All errors must be corrected, and
+any details required, but not shown completely in the illustrations,
+must be filled in.</p>
+
+
+<div class="blockquot">
+<p><span class="smcap">Exercise 62:</span> <i>Single Riveted Butt Joint with Tee-iron Cover
+Strap.</i>&mdash;Two views, one a side elevation and the other a sectional
+elevation, of a riveted joint are shown in fig. 60. Draw these views,
+and also a plan projected from one of them. Show the rivets completely
+in all the views. Scale 4 inches to a foot.</p>
+</div>
+
+<p><span class='pagenum'><a name="Page_82" id="Page_82">[Pg 82]</a></span></p>
+
+<div class="figcenter" style="width: 640px;">
+<img src="images/illus090a.png" width="640" height="456" alt="Fig. 60." title="Fig. 60." />
+<span class="caption">Fig. 60.</span>
+</div>
+
+<div class="figcenter" style="width: 800px;">
+<img src="images/illus090b.png" width="800" height="440" alt="Fig. 61." title="Fig. 61." />
+<span class="caption">Fig. 61.</span>
+</div>
+
+
+<div class="blockquot">
+<p><span class="smcap">Exercise 63:</span> <i>Girder Stay for Steam Boiler.</i>&mdash;The flat crown
+of the fire-box of locomotive and marine boilers is generally supported
+or stayed by means of girder stays, an example of which is
+shown in fig. 61. A B is the side elevation of a portion of one of
+these girders. Each girder is supported at its ends by the plates
+forming the vertical sides of the fire-box. The flat crown is bolted
+to the girders as shown. Observe that the girders are in contact
+with the crown only in the neighbourhood of the bolts. Consider
+carefully this part of the design, and then answer the following
+<span class='pagenum'><a name="Page_83" id="Page_83">[Pg 83]</a></span>questions: (1) What objections are there to supporting the girders
+at the ends only without the contact pieces at the bolts? (2) What
+objections are there to having the girders in contact with the crown
+plate of the fire-box throughout their whole length?</p>
+
+<p>Draw the views shown in fig. 61, and from the right-hand one
+project a plan. Scale 4 inches to a foot.</p></div>
+
+<div class="figcenter" style="width: 800px;">
+<img src="images/illus091.png" width="800" height="422" alt="Fig. 62." title="Fig. 62." />
+<span class="caption">Fig. 62.</span>
+</div>
+
+
+<div class="blockquot">
+<p><span class="smcap">Exercise 64:</span> <i>End of Bar Stay for Steam Boiler.</i>&mdash;On page
+12 one form of stay for supporting the flat end of a steam boiler is
+described. Another form of stay for the same purpose is shown in
+fig. 62. A B is a portion of the end of a steam boiler. C D is one
+end of a bar which extends from one end of the boiler to the other.
+The ends of this bar are screwed, and when the bar is of wrought
+iron the screwed parts are generally larger in diameter than the
+rest of the bar. When made of steel the bar is generally of uniform
+diameter throughout. In the case of wrought-iron bar stays
+the enlarged ends are welded on to the smaller parts. Welding is
+not so reliable with steel as with wrought iron. Write out answers
+to the following questions: (1) What is the advantage of having
+the screwed part of the bar larger in diameter than the rest?
+(2) Why are steel bar stays not generally enlarged at their screwed
+ends?</p>
+
+<p><span class='pagenum'><a name="Page_84" id="Page_84">[Pg 84]</a></span></p>
+
+<p>Draw the views shown in fig. 62, and project from one of them
+a third view. Scale 4 inches to a foot.</p>
+
+<p><span class="smcap">Exercise 65:</span> <i>Knuckle Joint.</i>&mdash;Draw the plan and elevation of
+this joint shown in fig. 63, and also draw an end elevation looking
+in the direction of the arrow. The parts at A and B are octagonal
+in cross section. Scale 4 inches to a foot.</p></div>
+
+<div class="figcenter" style="width: 774px;">
+<img src="images/illus092.png" width="774" height="600" alt="Fig. 63." title="Fig. 63." />
+<span class="caption">Fig. 63.</span>
+</div>
+
+<div class="blockquot"><p><span class="smcap">Exercise 66:</span> <i>Locomotive Coupling Rod Ends.</i>&mdash;A form
+of knuckle joint used on locomotive coupling rods is shown in
+fig. 64.</p>
+
+<p>In this case two rods meet and work on the same pin, as shown
+at (a) fig. 64. Draw, in addition to the views shown in fig. 64, a
+plan and a vertical section through the axis of the pin. Scale
+6 inches to a foot.</p>
+
+<p>Would it be practicable to replace the two rods A B and B C by
+a single rod working on the crank pins at A, B, and C? Give
+reasons for your answer.</p>
+</div>
+
+<p><span class='pagenum'><a name="Page_85" id="Page_85">[Pg 85]</a></span></p>
+
+<div class="figcenter" style="width: 647px;">
+<img src="images/illus093.png" width="647" height="1024" alt="Fig. 64." title="Fig. 64." />
+<span class="caption">Fig. 64.</span>
+</div>
+<p><span class='pagenum'><a name="Page_86" id="Page_86">[Pg 86]</a></span></p>
+
+<div class="blockquot"><p><span class="smcap">Exercise 67:</span> <i>Bell Crank Lever.</i>&mdash;Draw the plan and elevation
+of the lever shown in fig. 65. Scale 6 inches to a foot.</p></div>
+
+<div class="figcenter" style="width: 673px;">
+<img src="images/illus094.png" width="673" height="1024" alt="Fig. 65." title="Fig. 65." />
+<span class="caption">Fig. 65.</span>
+</div>
+
+
+<div class="blockquot"><p><span class="smcap">Exercise 68:</span> <i>Back Stay for Lathe.</i>&mdash;Draw a plan and two
+elevations of the stay shown in fig. 66. Make all necessary corrections
+and show all the details in each view. Scale full size.</p></div><p><span class='pagenum'><a name="Page_87" id="Page_87">[Pg 87]</a></span></p>
+
+<div class="figcenter" style="width: 637px;">
+<img src="images/illus095.png" width="637" height="1024" alt="Fig. 66." title="Fig. 66." />
+<span class="caption">Fig. 66.</span>
+</div>
+<p><span class='pagenum'><a name="Page_88" id="Page_88">[Pg 88]</a></span></p>
+
+<div class="figcenter" style="width: 619px;">
+<img src="images/illus096.png" width="619" height="1024" alt="Fig. 67." title="Fig. 67." />
+<span class="caption">Fig. 67.</span>
+</div>
+<p><span class='pagenum'><a name="Page_89" id="Page_89">[Pg 89]</a></span></p>
+
+<div class="blockquot"><p><span class="smcap">Exercise 69:</span> <i>Conical Disc Valve and Casing.</i>&mdash;Draw, half
+size, the views shown in fig. 67 of the conical disc valve and casing,
+and also add an elevation looking in the direction of the arrow.</p>
+
+<p><span class="smcap">Exercise 70:</span> <i>Connecting Rod End.</i>&mdash;The student should carefully
+compare this connecting rod end (fig. 68) with those illustrated
+on pages 50 and 52. The lower part of fig. 68 is a half plan and
+half horizontal section, and the upper part is a half side elevation
+and half vertical section. Draw these views and also an end
+elevation. Scale 6 inches to a foot.</p></div>
+
+<div class="figcenter" style="width: 768px;">
+<img src="images/illus097.png" width="768" height="789" alt="Fig. 68." title="Fig. 68." />
+<span class="caption">Fig. 68.</span>
+</div>
+
+<p><span class='pagenum'><a name="Page_90" id="Page_90">[Pg 90]</a></span></p>
+
+<div class="figcenter" style="width: 608px;">
+<img src="images/illus098.png" width="608" height="1024" alt="Fig. 69." title="Fig. 69." />
+<span class="caption">Fig. 69.</span>
+</div>
+<p><span class='pagenum'><a name="Page_91" id="Page_91">[Pg 91]</a></span></p>
+
+<div class="figcenter" style="width: 604px;">
+<img src="images/illus099.png" width="604" height="1024" alt="Fig. 70." title="Fig. 70." />
+<span class="caption">Fig. 70.</span>
+</div>
+<p><span class='pagenum'><a name="Page_92" id="Page_92">[Pg 92]</a></span></p>
+
+<div class="figcenter" style="width: 606px;">
+<img src="images/illus100.png" width="606" height="1024" alt="Fig. 71." title="Fig. 71." />
+<span class="caption">Fig. 71.</span>
+</div>
+<p><span class='pagenum'><a name="Page_93" id="Page_93">[Pg 93]</a></span></p>
+
+<div class="figcenter" style="width: 1024px;">
+<img src="images/illus101.png" width="1024" height="617" alt="Fig. 72." title="Fig. 72." />
+<span class="caption">Fig. 72.</span>
+</div>
+
+<p><span class='pagenum'><a name="Page_94" id="Page_94">[Pg 94]</a></span></p>
+
+<div class="figcenter" style="width: 1024px;">
+<img src="images/illus102.png" width="1024" height="581" alt="Fig. 73." title="Fig. 73." />
+<span class="caption">Fig. 73.</span>
+</div>
+
+<p><span class='pagenum'><a name="Page_95" id="Page_95">[Pg 95]</a></span></p>
+
+<div class="figcenter" style="width: 748px;">
+<img src="images/illus103.png" width="748" height="1024" alt="Fig. 74." title="Fig. 74." />
+<span class="caption">Fig. 74.</span>
+</div>
+
+
+<div class="blockquot"><p><span class="smcap">Exercise 71:</span> <i>Engine Cross-head.</i>&mdash;The cross-head shown in
+fig. 69 is for an inverted cylinder marine engine. A is the piston
+rod, and B B are pins, forged in one piece with C, to which the
+forked end of the connecting rod is attached. Draw the upper
+view with the central part in section as shown. Make the right-hand
+half of the lower view a plan without any section, and make<span class='pagenum'><a name="Page_96" id="Page_96">[Pg 96]</a></span>
+the left-hand half a horizontal section through the axis of the pins
+B B. Scale 4 inches to a foot.</p>
+
+<p><span class="smcap">Exercise 72:</span> <i>Ratchet Lever.</i>&mdash;The lever shown in fig. 70 is
+used for turning the horizontal screw of a traversing screw jack.
+Draw the two views shown, and from one of them project a plan.
+Scale full size.</p>
+
+<p><span class="smcap">Exercise 73:</span> <i>Steam Whistle.</i>&mdash;Draw, full size, the elevation
+and section of the steam whistle shown in fig. 71. Draw also
+horizontal sections at A B, C D, and E F.</p></div>
+
+<div class="figcenter" style="width: 805px;">
+<img src="images/illus104.png" width="805" height="691" alt="Fig. 75." title="Fig. 75." />
+<span class="caption">Fig. 75.</span>
+</div>
+
+<div class="blockquot"><p><span class="smcap">Exercise 74:</span> <i>Screw Coupling for Railway Carriages.</i>&mdash;Draw
+the three views of the screw coupling shown in fig. 72. Scale 6
+inches to a foot.</p>
+
+<p>If the link A is fixed, through what distance will the link B
+move for two turns of the lever?</p>
+
+<p><span class="smcap">Exercise 75:</span> <i>Loose Headstock for a 6-inch Lathe.</i>&mdash;Two
+views of this headstock are shown in fig. 73. On one of these
+views a few of the chief dimensions are marked. The details, fully
+dimensioned, are shown separately in figs. 74, 75, and 76.</p></div><p><span class='pagenum'><a name="Page_97" id="Page_97">[Pg 97]</a></span></p>
+
+<div class="figcenter" style="width: 651px;">
+<img src="images/illus105.png" width="651" height="1024" alt="Fig. 76." title="Fig. 76." />
+<span class="caption">Fig. 76.</span>
+</div>
+
+<p><span class='pagenum'><a name="Page_98" id="Page_98">[Pg 98]</a></span></p>
+<div class="blockquot">
+<p>Explain clearly how the centre is moved backwards and forwards,
+and also how the spindle containing it is locked when it is
+not required to move.</p>
+
+<p>Draw, half-size, the views shown in fig. 73, and from the left-hand
+view project a plan. Draw also the detail of the locking
+arrangement shown in fig. 74.</p>
+</div>
+
+<hr style="width: 100%;" />
+<p><span class='pagenum'><a name="Page_99" id="Page_99">[Pg 99]</a></span></p>
+<h2>APPENDIX A.</h2>
+
+<hr style="width: 15%;" />
+<h3><i>SCIENCE AND  ART DEPARTMENT, SOUTH<br />
+KENSINGTON.</i></h3>
+
+<h3><span class="smcap">Syllabus.</span></h3>
+
+<h4>SUBJECT II.&mdash;MACHINE  CONSTRUCTION  AND<br />
+DRAWING.</h4>
+
+
+<p>It is assumed that the student has already learnt to draw to scale,
+and that he can draw two or more views of the same object in
+simple or orthographic projection. To pass in machine construction
+and drawing, he must be able to apply this knowledge to the representation
+of machinery. He must be acquainted with the form and
+purpose of the simpler parts of which machines are built up and
+must have had some practice in drawing them. To test his knowledge,
+rough dimensioned sketches, more or less incomplete, of
+simple machine details will be given him, and he will be required to
+produce a complete drawing in pencil to a given scale. Two or
+more views of at least one subject will be required, and these must
+be so drawn as to be properly projected one from the other, <i>in order
+to show that the student appreciates that he is producing a representation
+of a solid piece of machinery, and not merely copying a
+sketch. No credit will be given unless some knowledge of projection
+is shown.</i> The centre lines of the drawings should be shown,
+and parts cut by planes of section should be indicated by diagonal
+shading. Bolts and other fastenings should be carefully shown
+where required. Any indication that a candidate has merely
+copied the sketches given, without understanding the part represented,
+will invalidate his examination.</p>
+<p><span class='pagenum'><a name="Page_100" id="Page_100">[Pg 100]</a></span></p>
+
+<h4><span class="smcap">First Stage or Elementary Course.</span></h4>
+
+<p>In the elementary stage, a knowledge is required of the simple
+parts only of <i>machines in common use</i>. <i>Some</i> of these are
+enumerated in the following list. The student should be practised
+in drawing them till he recognises their forms, and the object of the
+arrangement should be explained to him. He should also know
+the simple technical terms used in describing them.</p>
+
+<p>A few very simple questions relating to the arrangement, proportions,
+and strength of the simplest machine details will be set
+in the examination paper.</p>
+
+<p>In drawing the examples set to test a student's knowledge and
+skill in machine drawing, it must be remembered that only a
+limited time is available. It is only possible to set an example to
+be drawn in pencil, and the points which will receive attention are
+(1) accuracy of scale and projection; (2) power of reading a drawing,
+shown by the ability to transfer portions of the mechanism
+and dimensions from one view to another; (3) knowledge of
+machines, as shown by the ability to fill in small details, such as
+nuts, keys, etc., omitted in the sketches given. Bearing in mind
+the limited time available, the student should try to make his
+outline clear and decisive and complete. But the diagonal lines
+necessary for sectional parts may be done rapidly, though neatly,
+by freehand if necessary.</p>
+
+<p><i>Riveted Joints.</i>&mdash;Forms of rivets and arrangement of rivets in
+lap and butt joints with single and double riveting. Junction of
+plates by angle and T-irons.</p>
+
+<p><i>Bolts, Studs, and Set Screws.</i>&mdash;Forms of these fastenings.
+Forms and proportions of nuts and bolt-heads. Arrangement of
+flanges for bolting.</p>
+
+<p><i>Pins, Keys, and Cotters.</i>&mdash;Form of ordinary knuckle joint. Use
+of split pins. Connection of parts by a key. Connection of parts by
+a cotter. Gib and cotter.</p>
+
+<p><i>Pipes and Cylinders.</i>&mdash;Forms of ordinary pipes and cylinders
+and their flanges and covers.</p>
+
+<p><i>Shafting.</i>&mdash;Forms of shafts and axles and of journals and
+pivots. Use of collars and bosses. Half-lap coupling. Box
+coupling. Flange coupling.</p>
+
+<p><i>Pedestals and Plummer Blocks.</i>&mdash;Simplest forms of pedestals
+and hangers for shafts. Form and arrangement of brass steps.<span class='pagenum'><a name="Page_101" id="Page_101">[Pg 101]</a></span>
+Arrangements for fixing pedestals and for neutralising the effects of
+wear.</p>
+
+<p><i>Toothed Gearing.</i>&mdash;Forms of ordinary spur and bevil wheels.
+Meaning of the terms pitch, breadth of face, thickness of tooth,
+pitch line, rim, nave, arm. Mode of drawing bevil wheels in
+section.</p>
+
+<p><i>Belt Pulleys.</i>&mdash;Forms of belt pulleys for flat and round belts.
+Stepped speed cones. Drawing of pulleys with curved arms.</p>
+
+<p><i>Cranks and Levers.</i>&mdash;Forms of ordinary cast-iron and wrought-iron
+cranks and levers. Modes of fixing crank pin. Modes of
+fixing crank shaft. Double cranks. Form of eccentrics.</p>
+
+<p><i>Links.</i>&mdash;Most simple forms of connecting rod ends, open or
+closed. Use of steps in connecting rods. Use of cotters to tighten
+the steps.</p>
+
+<p><i>Pistons.</i>&mdash;Simple forms of piston. Use of piston packing.
+Modes of attaching piston rod.</p>
+
+<p><i>Stuffing-Boxes.</i>&mdash;Simple form of stuffing-box and gland. Use of
+packing. Mode of tightening gland.</p>
+
+<p><i>Valves.</i>&mdash;Simple conical of puppet valve. Simple slide valve.
+Cock or conical sliding valve.</p>
+
+
+
+<hr style="width: 100%;" />
+<p><span class='pagenum'><a name="Page_102" id="Page_102">[Pg 102]</a></span></p>
+<h2>APPENDIX B.</h2>
+
+<hr style="width: 15%;" />
+<h3><i>EXAMINATION PAPERS SET BY THE SCIENCE<br />
+AND ART DEPARTMENT.</i></h3>
+
+
+<h4>SUBJECT II.&mdash;MACHINE CONSTRUCTION AND<br />
+DRAWING.</h4>
+
+<p class="center"><big><i>Examiners</i>, <span class="smcap">Prof. T. A. Hearson</span>, M.Inst.C.E., and<br />
+<span class="smcap">J. Harrison, Esq.</span>, M.Inst.M.E.</big></p>
+
+<p class="center"><span class="smcap">General Instructions.</span></p>
+
+<p class="center"><span class="u">If the rules are not attended to, the paper will be cancelled.</span></p>
+
+<p>You may take the Elementary, or the Advanced, or the
+Honours paper, but you must confine yourself to one of them.</p>
+
+<p>Put the number of the question before your answer.</p>
+
+<p>You are expected to prove your knowledge of machinery as
+well as your power of drawing neatly to scale. You are therefore
+to supply details omitted in the sketches, to fill in parts left
+incomplete, and to indicate, by diagonal lines, parts cut by planes of
+section.</p>
+
+<p>No credit will be given unless some knowledge of projection is
+shown, so that at least two views of one of the examples will be
+required properly projected one from the other. The centre lines
+should be clearly drawn. The figured dimensions need not be
+inserted.</p>
+
+<p>Your answers should be clearly and cleanly drawn in pencil.
+No extra marks will be allowed for inking in.<span class='pagenum'><a name="Page_103" id="Page_103">[Pg 103]</a></span></p>
+
+<p>All figures must be drawn on the single sheet of paper supplied,
+for no second sheet will be allowed.</p>
+
+<p>The value attached to each question is shown in brackets after
+the question. But a full and correct answer to an easy question will
+in all cases secure a larger number of marks than an incomplete or
+inexact answer to a more difficult one.</p>
+
+<p>Your name is not given to the Examiner, and you are forbidden
+to write to him about your answers.</p>
+
+<p>You are to confine your answers <i>strictly</i> to the questions
+proposed.</p>
+
+<p>A single accent (&acute;) signifies <i>feet</i>; a double accent (&acute;&acute;) <i>inches</i>.</p>
+
+<p><i>The examination in this subject lasts for four hours.</i></p>
+
+<hr style='width: 15%;' />
+
+<h4>First Stage or Elementary Examination. &nbsp; 1885.</h4>
+
+<p class="center"><span class="smcap">Instructions.</span></p>
+
+<p>Read the General Instructions above.</p>
+
+<p>Answer briefly any three, but not more than three, of the
+following questions, and draw two, but not more than two, of the
+examples.</p>
+
+<p class="tabcap"><i>Questions.</i></p>
+
+<div class="poem">
+<p class="negidt">(<i>a.</i>) Show two methods by which a cotter may be prevented
+from slacking back.  <span class="marks">(6.)</span></p>
+
+<p class="negidt">(<i>b.</i>) Sketch the brasses for a bearing, and show how they are
+prevented from turning in the pedestal.  <span class="marks">(6.)</span></p>
+
+<p class="negidt">(<i>c.</i>) Explain the object of the construction of the connecting rod
+end shown in fig. 78. Describe how the adjustment must
+be made and how it is locked.     <span class="marks">(10.)</span></p>
+
+<p class="negidt">(<i>d.</i>) Show the form of the Whitworth screw thread by drawing
+to scale a part section of two or three threads taking a
+pitch of 1&frac12; inches. Figure the dimensions on the sketch.
+How many threads to the inch are used on an inch bolt?     <span class="marks">(10.)</span></p>
+
+<p class="negidt">(<i>e.</i>) Make a sketch showing how the adjustment is made in
+the sliding parts of machine tools: as, for example, in the
+slide rest of a lathe.  <span class="marks">(10.)</span></p>
+
+<p class="negidt">(<i>f.</i>) Describe with sketches two methods by which the joints
+are made in connecting lengths of cast-iron pipes.  <span class="marks">(6.)</span></p>
+</div>
+<p><span class='pagenum'><a name="Page_104" id="Page_104">[Pg 104]</a></span></p>
+
+<div class="figcenter" style="width: 603px;">
+<img src="images/illus112.png" width="603" height="1024" alt="Figs. 77 and 78." title="Figs. 77 and 78." />
+<span class="caption">Figs. 77 and 78.</span>
+</div>
+
+<p><span class='pagenum'><a name="Page_105" id="Page_105">[Pg 105]</a></span></p>
+
+<p class="tabcap"><i>Examples to be drawn.</i></p>
+
+<div class="poem">
+<p class="negidt">1. Jaw for four-screw dog chuck for 5&acute;&acute; lathe. Draw the two
+views as shown (fig. 77). Scale full size.</p>
+
+<p class="negidt"> &nbsp; &nbsp; &nbsp; &nbsp; (Note.&mdash;The other three jaws of the chuck are not to be
+drawn.)  <span class="marks">(35.)</span></p>
+</div>
+
+<div class="figcenter" style="width: 638px;">
+<img src="images/illus113.png" width="638" height="600" alt="Fig. 79." title="Fig. 79." />
+<span class="caption">Fig. 79.</span>
+</div>
+
+<div class="poem">
+<p class="negidt">2. Connecting rod end. Draw the two views as shown, partly
+in section (fig. 78). Draw full size.  <span class="marks">(35.)</span></p>
+
+<p class="negidt">3. Hooke's coupling. Draw the three views shown (fig. 79),
+adding any omitted lines where the views are incomplete.
+Draw to scale of <sup>1</sup>&frasl;<sub>4</sub> full size.  <span class="marks">(35.)</span></p>
+</div>
+
+<hr style='width: 15%;' />
+<p><span class='pagenum'><a name="Page_106" id="Page_106">[Pg 106]</a></span></p>
+
+<div class="figcenter" style="width: 616px;">
+<img src="images/illus114.jpg" width="616" height="1024" alt="Figs. 80 and 81." title="Figs. 80 and 81." />
+<span class="caption">Figs. 80 and 81.</span>
+</div>
+
+
+<p><span class='pagenum'><a name="Page_107" id="Page_107">[Pg 107]</a></span></p>
+
+
+
+<h4>First Stage or Elementary Examination. &nbsp; 1886.</h4>
+
+<p class="center"><span class="smcap">Instructions.</span></p>
+
+<p>Read the General Instructions (page 102).</p>
+
+<p>Answer briefly any three, but not more than three, of the
+following questions, and draw two, but not more than two, of the
+examples.</p>
+
+<p class="tabcap"><i>Questions.</i></p>
+
+<div class="poem">
+<p class="negidt">(<i>a.</i>) Give sketches showing how the cutting tool of a lathe or
+other machine is secured in place.      <span class="marks">(6.)</span></p>
+
+<p class="negidt">(<i>b.</i>) Make a sketch of a stud, describe how it is screwed into
+place, and state some circumstances under which it is used
+in preference to a bolt.      <span class="marks">(6.)</span></p>
+
+<p class="negidt">(<i>c.</i>) Give sketches showing one method of attaching the valve
+rod to an ordinary slide valve.      <span class="marks">(6.)</span></p>
+
+<p class="negidt">(<i>d.</i>) Sketch a connecting rod end, with strap, gib, and cotter.
+Explain the use of the gib.      <span class="marks">(10.)</span></p>
+
+<p class="negidt">(<i>e.</i>) Explain the use of the quadrant for change wheels for a
+screw-cutting lathe shown in Example 1, fig. 80, by
+making a sketch showing it in place on a lathe with
+wheels in gear.      <span class="marks">(10.)</span></p>
+
+<p class="negidt">(<i>f.</i>) Sketch one form of hanger suitable for supporting mill-shafting.     <span class="marks">(10.)</span></p>
+</div>
+
+<div class="figcenter" style="width: 800px;">
+<img src="images/illus115.jpg" width="800" height="349" alt="Fig. 82." title="Fig. 82." />
+<span class="caption">Fig. 82.</span>
+</div>
+
+
+<p class="tabcap"><i>Examples to be drawn.</i></p>
+
+<div class="poem">
+<p class="negidt">1. Quadrant for change wheels for screw-cutting lathe. Draw
+the two views shown (fig. 80). Scale half-size.      <span class="marks">(35.)</span></p>
+<p><span class='pagenum'><a name="Page_108" id="Page_108">[Pg 108]</a></span></p>
+
+<p class="negidt">2. Crank-shaft. Draw the two views as shown, partly in section
+(fig 81). Scale <sup>1</sup>&frasl;<sub>8</sub> full size.      <span class="marks">(35.)</span></p>
+
+<p class="negidt">3. Ball bearing for tricycle. Draw the two views as shown,
+partly in section (fig. 82). Draw full size.      <span class="marks">(35.)</span></p>
+</div>
+
+<hr style='width: 15%;' />
+
+<h4>First Stage or Elementary Examination.  &nbsp; 1887.</h4>
+
+<p class="center"><span class="smcap">Instructions.</span></p>
+
+<p>Read the General Instructions (page 102).</p>
+
+<p>Answer briefly any three, but not more than three, of the
+following questions, and draw two, but not more than two, of the
+examples.</p>
+
+<p class="tabcap"><i>Questions.</i></p>
+
+<div class="poem">
+<p class="negidt">(<i>a.</i>) Explain how the piston rings in Example 1, fig. 84, are
+made so that the piston may work steam-tight in the
+cylinder. How are these rings got into place?      <span class="marks">(8.)</span></p>
+
+<p class="negidt">(<i>b.</i>) Give two views of a double riveted lap joint for boiler-plates.   <span class="marks">(8.)</span></p>
+
+<p class="negidt">(<i>c.</i>) Show by sketches how a wheel is fixed on a shaft by means
+of a sunk key. Explain how the key may be withdrawn
+when it cannot be driven from the point end.      <span class="marks">(8.)</span></p>
+
+<p class="negidt">(<i>d.</i>) Give sketches showing the construction of a conical metal
+lift or puppet valve and seating.      <span class="marks">(10.)</span></p>
+
+<p class="negidt">(<i>e.</i>) With the aid of sketches explain how a piston rod is made
+to work steam-tight through the end of the cylinder.      <span class="marks">(10.)</span></p>
+
+<p class="negidt">(<i>f.</i>) Explain how the slotting machine ram of Example 8, fig.
+85, may be made to move up and down when at work.
+How is the length of the stroke altered, and what is the
+object of the slotway in the upper part of the ram?      <span class="marks">(10.)</span></p>
+</div>
+
+<p class="tabcap"><i>Examples to be drawn.</i></p>
+
+<div class="poem">
+<p class="negidt">1. Piston for steam-engine. Draw and complete the two views
+shown (fig. 84), the top half of the left-hand view to be in
+section. Scale <sup>1</sup>&frasl;<sub>2</sub> size.      <span class="marks">(30.)</span></p>
+</div>
+<p><span class='pagenum'><a name="Page_109" id="Page_109">[Pg 109]</a></span></p>
+
+<div class="figcenter" style="width: 627px;">
+<img src="images/illus117.jpg" width="627" height="1024" alt="Figs. 83 and 84." title="Figs. 83 and 84." />
+<span class="caption">Figs. 83 and 84.</span>
+</div>
+
+<p><span class='pagenum'><a name="Page_110" id="Page_110">[Pg 110]</a></span></p>
+
+<div class="poem">
+<p class="negidt">2. Plan and sectional elevation of a footstep bearing for an
+upright shaft (fig. 83). Draw and complete these views.
+Scale <sup>1</sup>&frasl;<sub>4</sub> size.      <span class="marks">(35.)</span></p>
+</div>
+
+<div class="figcenter" style="width: 800px;">
+<img src="images/illus118.jpg" width="800" height="505" alt="Fig. 85." title="Fig. 85." />
+<span class="caption">Fig. 85.</span>
+</div>
+
+<div class="poem">
+<p class="negidt">3. Ram of slotting machine. Draw and complete the two
+elevations shown (fig.  85). The tool-holders  must be
+drawn in their proper positions in the ram, and not
+separate as in the diagram. Scale <sup>1</sup>&frasl;<sub>4</sub> size.      <span class="marks">(35.)</span></p>
+</div>
+
+<hr style="width: 15%;" />
+<h4>First Stage or Elementary Examination. &nbsp; 1888.</h4>
+
+<p class="center"><span class="smcap">Instructions.</span></p>
+
+<p>Read the General Instructions on p. 102.</p>
+
+<p>Answer briefly any three, but not more than three, of the
+following questions, and draw two, but not more than two, of the
+examples.</p>
+
+<p class="tabcap"><i>Questions.</i></p>
+
+<div class="poem">
+<p class="negidt">(<i>a.</i>) Give sketches showing how the separate lengths of a line
+of shafting may be connected together.      <span class="marks">(8.)</span></p>
+
+<p class="negidt">(<i>b.</i>) What is the object of using chipping or facing strips in fitting
+up machine parts? Give one or two examples.      <span class="marks">(8.)</span></p>
+<p><span class='pagenum'><a name="Page_111" id="Page_111">[Pg 111]</a></span></p>
+
+<p class="negidt">(<i>c.</i>) Give sketches showing how you would grip and drive a
+round iron bar for the purpose of turning it between the
+centres of a lathe.      <span class="marks">(10.)</span></p>
+</div>
+
+
+<div class="figcenter" style="width: 677px;">
+<img src="images/illus119.jpg" width="677" height="1024" alt="Figs. 86 and 87." title="Figs. 86 and 87." />
+<span class="caption">Figs. 86 and 87.</span>
+</div>
+<p><span class='pagenum'><a name="Page_112" id="Page_112">[Pg 112]</a></span></p>
+
+<div class="poem">
+<p class="negidt">(<i>d.</i>) Explain the action of the governor shown in Example 1
+(fig. 86).      <span class="marks">(10.)</span></p>
+
+<p class="negidt">(<i>e.</i>) Describe in detail how the mud-hole door in Example 2
+(fig. 88) is removed for the purpose of cleaning the boiler
+and how it is replaced and the joint made steam-tight.      <span class="marks">(10.)</span></p>
+
+<p class="negidt">(<i>f.</i>) Describe how the parts of the spur wheel in Example 3
+(fig. 87) are put together, and explain why the wheel is
+made in segments.      <span class="marks">(10.)</span></p>
+</div>
+
+
+<div class="figcenter" style="width: 800px;">
+<img src="images/illus120.jpg" width="800" height="509" alt="Fig. 88." title="Fig. 88." />
+<span class="caption">Fig. 88.</span>
+</div>
+
+
+
+<p class="tabcap"><i>Examples to be drawn.</i></p>
+
+<div class="poem">
+<p class="negidt">1. Loaded governor for small gas engine. Draw and complete
+the two views, partly in section as shown (fig. 86). Scale
+full size.      <span class="marks">(35.)</span></p>
+
+<p class="negidt">2. Mud-hole mouth-piece for Lancashire boiler. Draw and
+complete the two views shown (fig. 88). Scale <sup>3</sup>&frasl;<sub>8</sub>ths.      <span class="marks">(35.)</span></p>
+
+<p class="negidt">3. Point for segments of large spur wheel. Draw and complete
+the views shown (fig. 87). Scale <sup>3</sup>&frasl;<sub>16</sub>ths.</p>
+
+<p class="negidt"> &nbsp; &nbsp; &nbsp; &nbsp; <i>Note.</i>&mdash;As the radius of the wheel is too large for your
+instruments, the circumference at the joint may be set out
+straight, as in a rack.      <span class="marks">(35.)</span></p>
+</div>
+
+
+<hr style="width: 100%;" />
+<p><span class='pagenum'><a name="Page_113" id="Page_113">[Pg 113]</a></span></p>
+<h2>INDEX</h2>
+
+<div class="blockquot">
+<p class="noidt">
+Air-pump bucket, <a href="#Page_58">58</a><br />
+Alloys, <a href="#Page_80">80</a><br />
+Angle irons, <a href="#Page_12">12</a><br />
+Annealing, <a href="#Page_79">79</a>, <a href="#Page_80">80</a><br />
+Axles, <a href="#Page_24">24</a><br />
+<br />
+Back stay for lathe, <a href="#Page_86">86</a><br />
+Bar stay, <a href="#Page_83">83</a><br />
+Bearings for shafts, <a href="#Page_30">30</a><br />
+Beech-wood, <a href="#Page_81">81</a><br />
+Bell crank lever, <a href="#Page_86">86</a><br />
+Bessemer steel, <a href="#Page_79">79</a><br />
+Bevil wheels, <a href="#Page_43">43</a><br />
+Blister steel, <a href="#Page_79">79</a><br />
+Blooms, <a href="#Page_78">78</a><br />
+Bolt-heads, proportions of, <a href="#Page_18">18</a><br />
+Bolts, forms of, <a href="#Page_17">17</a><br />
+Border lines, <a href="#Page_4">4</a><br />
+Box couplings, <a href="#Page_25">25</a><br />
+&mdash; end, connecting rod, <a href="#Page_51">51</a><br />
+Box-wood, <a href="#Page_81">81</a><br />
+Brackets, <a href="#Page_33">33</a><br />
+Brake shaft carrier, <a href="#Page_30">30</a><br />
+Brass, <a href="#Page_80">80</a><br />
+Brasses, <a href="#Page_30">30</a><br />
+Bucket, <a href="#Page_58">58</a><br />
+Built-up cranks, <a href="#Page_46">46</a><br />
+Bush, <a href="#Page_30">30</a>, <a href="#Page_49">49</a>, <a href="#Page_51">51</a>, <a href="#Page_54">54</a>, <a href="#Page_56">56</a>, <a href="#Page_63">63</a><br />
+Butt joints, <a href="#Page_10">10</a>, <a href="#Page_11">11</a><br />
+&mdash; strap, <a href="#Page_10">10</a><br />
+Buttress screw thread, <a href="#Page_15">15</a><br />
+<br />
+Case-hardening, <a href="#Page_80">80</a><br />
+Cast iron, <a href="#Page_76">76</a><br />
+Cast iron flange coupling, <a href="#Page_28">28</a>, <a href="#Page_29">29</a><br />
+&mdash; steel, <a href="#Page_79">79</a><br />
+Caulking, <a href="#Page_8">8</a><br />
+Cementation process, <a href="#Page_79">79</a><br />
+Centre lines, <a href="#Page_2">2</a>, <a href="#Page_4">4</a><br />
+Chilled castings, <a href="#Page_78">78</a><br />
+Circulating pump piston, <a href="#Page_58">58</a><br />
+Clearance, cylinder, <a href="#Page_74">74</a><br />
+&mdash; of cotter, <a href="#Page_49">49</a><br />
+Cocks, <a href="#Page_74">74</a><br />
+Cogs, <a href="#Page_41">41</a><br />
+&mdash; wood for, <a href="#Page_81">81</a><br />
+Collared stud, <a href="#Page_18">18</a><br />
+Collars, <a href="#Page_24">24</a><br />
+Colouring, <a href="#Page_3">3</a><br />
+Colours for different materials, <a href="#Page_3">3</a><br />
+Compasses, <a href="#Page_1">1</a><br />
+Cone keys, <a href="#Page_23">23</a>, <a href="#Page_38">38</a><br />
+Conical disc valve, <a href="#Page_70">70</a>, <a href="#Page_71">71</a>, <a href="#Page_89">89</a><br />
+&mdash; head, <a href="#Page_7">7</a><br />
+Connecting rod, locomotive, <a href="#Page_51">51</a><br />
+&mdash; &mdash; marine, <a href="#Page_51">51</a><br />
+&mdash; rods, <a href="#Page_49">49</a>, <a href="#Page_89">89</a><br />
+Construction for rivet heads, <a href="#Page_7">7</a><br />
+Contraction of castings, <a href="#Page_77">77</a><br />
+Copper, <a href="#Page_80">80</a><br />
+Cotters, <a href="#Page_48">48</a>, <a href="#Page_49">49</a><br />
+Countersunk head, <a href="#Page_7">7</a>, <a href="#Page_18">18</a><br />
+Coupling rod ends, <a href="#Page_55">55</a>, <a href="#Page_84">84</a><br />
+&mdash; rods, <a href="#Page_54">54</a><br />
+&mdash; screw, <a href="#Page_96">96</a><br />
+Couplings, shaft, <a href="#Page_25">25</a><br />
+Cover plate, <a href="#Page_10">10</a><br />
+Cranked axle, <a href="#Page_45">45</a><br />
+Cranks, <a href="#Page_43">43</a><br />
+&mdash; built-up, <a href="#Page_46">46</a><br />
+<span class='pagenum'><a name="Page_114" id="Page_114">[Pg 114]</a></span>
+Cross-head pin, <a href="#Page_51">51</a><br />
+Cross-heads, <a href="#Page_56">56</a>, <a href="#Page_89">89</a><br />
+Cross-key, <a href="#Page_28">28</a><br />
+Cup-headed bolt, <a href="#Page_17">17</a><br />
+<br />
+Decimal equivalents, <a href="#Page_6">6</a><br />
+Dimension lines, <a href="#Page_5">5</a><br />
+Dimensions, <a href="#Page_5">5</a><br />
+&mdash; of box couplings, <a href="#Page_26">26</a><br />
+&mdash; cast-iron flange couplings, <a href="#Page_29">29</a><br />
+&mdash; keys, <a href="#Page_24">24</a><br />
+&mdash; stuffing-boxes and glands, <a href="#Page_67">67</a><br />
+&mdash; Whitworth screws, <a href="#Page_15">15</a><br />
+Distance lines, <a href="#Page_5">5</a><br />
+Dividers, <a href="#Page_1">1</a><br />
+Draught of cotter, <a href="#Page_49">49</a><br />
+Drawing board, <a href="#Page_1">1</a><br />
+&mdash; instruments, <a href="#Page_1">1</a><br />
+&mdash; paper, <a href="#Page_2">2</a><br />
+&mdash; pen, <a href="#Page_1">1</a><br />
+&mdash; pins, <a href="#Page_2">2</a><br />
+<br />
+Eccentrics, <a href="#Page_47">47</a><br />
+Exhaust port, <a href="#Page_71">71</a><br />
+Eye-bolt, <a href="#Page_18">18</a><br />
+<br />
+Fairbairn's coupling, <a href="#Page_26">26</a><br />
+Fast and loose pulleys, <a href="#Page_37">37</a><br />
+Feather key, <a href="#Page_23">23</a><br />
+Flange couplings, <a href="#Page_27">27</a><br />
+Flap valves, <a href="#Page_68">68</a><br />
+Flat key, <a href="#Page_22">22</a><br />
+Forge irons, <a href="#Page_77">77</a><br />
+Forging, <a href="#Page_79">79</a><br />
+Form of wheel teeth, <a href="#Page_40">40</a><br />
+Forms of nuts, <a href="#Page_16">16</a><br />
+&mdash; rivet heads, <a href="#Page_7">7</a><br />
+&mdash; screw threads, <a href="#Page_15">15</a><br />
+Foundry irons, <a href="#Page_77">77</a><br />
+<br />
+Gasket, <a href="#Page_58">58</a><br />
+Gas threads, <a href="#Page_15">15</a><br />
+Gib, <a href="#Page_49">49</a><br />
+&mdash; head, <a href="#Page_23">23</a><br />
+Girder stay, <a href="#Page_81">81</a><br />
+Gland, <a href="#Page_64">64</a><br />
+Grey cast iron, <a href="#Page_77">77</a><br />
+Gun-metal, <a href="#Page_80">80</a><br />
+Gusset stay, <a href="#Page_12">12</a><br />
+<br />
+Half-lap coupling, <a href="#Page_26">26</a><br />
+Hangers, <a href="#Page_34">34</a><br />
+Hardening of steel, <a href="#Page_80">80</a><br />
+Headstock lathe, <a href="#Page_96">96</a><br />
+Hexagonal nut, <a href="#Page_16">16</a><br />
+Hollow key, <a href="#Page_22">22</a><br />
+Hook bolt, <a href="#Page_18">18</a><br />
+Hornbeam, <a href="#Page_81">81</a><br />
+<br />
+India-rubber disc valves, <a href="#Page_58">58</a>, <a href="#Page_68">68</a><br />
+Inking drawings, <a href="#Page_2">2</a><br />
+Inside lap of valve, <a href="#Page_72">72</a><br />
+<br />
+Joggles, <a href="#Page_33">33</a><br />
+Joint, knuckle, <a href="#Page_84">84</a><br />
+Journals, <a href="#Page_24">24</a><br />
+&mdash; length of, <a href="#Page_32">32</a><br />
+Junk ring, <a href="#Page_61">61</a><br />
+<br />
+Keys, <a href="#Page_22">22</a><br />
+&mdash; proportions of, <a href="#Page_23">23</a><br />
+Kinghorn's metallic valve, <a href="#Page_70">70</a><br />
+Knuckle joint, <a href="#Page_84">84</a><br />
+&mdash; screw thread, <a href="#Page_15">15</a><br />
+<br />
+Lancaster's piston packing, <a href="#Page_61">61</a><br />
+Lap joints, <a href="#Page_8">8</a>, <a href="#Page_9">9</a>, <a href="#Page_10">10</a>, <a href="#Page_12">12</a><br />
+&mdash; of slide valve, <a href="#Page_72">72</a><br />
+Lathe headstock, <a href="#Page_96">96</a><br />
+Lead of valve, <a href="#Page_74">74</a><br />
+Lever, bell crank, <a href="#Page_86">86</a><br />
+&mdash; ratchet, <a href="#Page_96">96</a><br />
+Lignum-vit&aelig;, <a href="#Page_81">81</a><br />
+Locking arrangements for nuts, <a href="#Page_21">21</a>, <a href="#Page_62">62</a><br />
+Lock nuts, <a href="#Page_19">19</a><br />
+Locomotive connecting rod, <a href="#Page_51">51</a><br />
+&mdash; cranked axle, <a href="#Page_45">45</a><br />
+&mdash; cross-head, <a href="#Page_56">56</a><br />
+<span class='pagenum'><a name="Page_115" id="Page_115">[Pg 115]</a></span>
+Locomotive eccentric, <a href="#Page_47">47</a><br />
+&mdash; piston, <a href="#Page_60">60</a><br />
+Lubricator, needle, <a href="#Page_32">32</a><br />
+<br />
+Malleable cast iron, <a href="#Page_78">78</a><br />
+&mdash; iron, <a href="#Page_78">78</a><br />
+Marine connecting rod, <a href="#Page_51">51</a><br />
+&mdash; coupling, <a href="#Page_28">28</a><br />
+&mdash; crank-shaft, <a href="#Page_46">46</a><br />
+&mdash; piston, <a href="#Page_61">61</a><br />
+Merchant bars, <a href="#Page_78">78</a><br />
+Mortise wheels, <a href="#Page_41">41</a><br />
+Mottled cast iron, <a href="#Page_77">77</a><br />
+Muff couplings, <a href="#Page_25">25</a><br />
+Muntz metal, <a href="#Page_80">80</a><br />
+<br />
+Needle lubricator, <a href="#Page_32">32</a><br />
+Nuts, forms of, <a href="#Page_16">16</a><br />
+&mdash; lock, <a href="#Page_19">19</a><br />
+&mdash; proportions of, <a href="#Page_18">18</a><br />
+<br />
+Oil-box, <a href="#Page_54">54</a>, <a href="#Page_65">65</a><br />
+Outside lap of slide valve, <a href="#Page_72">72</a><br />
+Overhung crank, <a href="#Page_43">43</a><br />
+&mdash; cranks, proportions of, <a href="#Page_45">45</a><br />
+<br />
+Packing, <a href="#Page_63">63</a><br />
+Pan head, <a href="#Page_7">7</a><br />
+Pedestal, shaft, <a href="#Page_30">30</a><br />
+Pencils, drawing, <a href="#Page_1">1</a><br />
+Phosphor bronze, <a href="#Page_80">80</a><br />
+Pillar bracket, <a href="#Page_34">34</a><br />
+Pillow block, <a href="#Page_30">30</a>, <a href="#Page_32">32</a><br />
+Pin, cross-head, <a href="#Page_51">51</a>, <a href="#Page_54">54</a><br />
+&mdash; split, <a href="#Page_21">21</a><br />
+Piston rod, <a href="#Page_57">57</a><br />
+Pistons, <a href="#Page_57">57</a><br />
+Pitch circle, <a href="#Page_40">40</a><br />
+&mdash; of wheel teeth, <a href="#Page_40">40</a><br />
+&mdash; surfaces of wheels, <a href="#Page_39">39</a>, <a href="#Page_43">43</a><br />
+Pivots, <a href="#Page_24">24</a><br />
+Plummer block, <a href="#Page_30">30</a><br />
+Plunger, <a href="#Page_57">57</a><br />
+Printing, <a href="#Page_4">4</a><br />
+Proportions of bolt-heads, <a href="#Page_18">18</a><br />
+&mdash; keys, <a href="#Page_23">23</a><br />
+Proportions of lap joints, <a href="#Page_9">9</a>, <a href="#Page_10">10</a><br />
+&mdash; marine engine pistons, <a href="#Page_62">62</a><br />
+&mdash; nuts, <a href="#Page_18">18</a><br />
+&mdash; overhung cranks, <a href="#Page_45">45</a><br />
+&mdash; pillow blocks, <a href="#Page_32">32</a><br />
+&mdash; rivet heads, <a href="#Page_7">7</a><br />
+&mdash; wheel teeth, <a href="#Page_40">40</a><br />
+Puddled bars, <a href="#Page_78">78</a><br />
+Puddling process, <a href="#Page_78">78</a><br />
+Pulley, eccentric, <a href="#Page_47">47</a><br />
+Pulleys, <a href="#Page_36">36</a><br />
+Pump bucket, <a href="#Page_58">58</a><br />
+<br />
+Ramsbottom's packing, <a href="#Page_60">60</a><br />
+Ratchet lever, <a href="#Page_96">96</a><br />
+Riveted joints, <a href="#Page_8">8</a><br />
+Rivet heads, forms of, <a href="#Page_7">7</a>, <a href="#Page_8">8</a><br />
+&mdash; &mdash; proportions of, <a href="#Page_7">7</a><br />
+Riveting, <a href="#Page_7">7</a><br />
+Rivets, <a href="#Page_6">6</a><br />
+Rope pulley, <a href="#Page_39">39</a><br />
+Round key, <a href="#Page_23">23</a><br />
+<br />
+Saddle key, <a href="#Page_22">22</a><br />
+Scales, <a href="#Page_5">5</a><br />
+Screw coupling, <a href="#Page_96">96</a><br />
+Screwed gland and stuffing-box, <a href="#Page_65">65</a><br />
+Screw threads, <a href="#Page_14">14</a>, <a href="#Page_15">15</a><br />
+Screws, representation of, <a href="#Page_16">16</a><br />
+Sellers <b>V</b> screw thread, <a href="#Page_14">14</a><br />
+Set screw, <a href="#Page_21">21</a>, <a href="#Page_49">49</a><br />
+&mdash; squares, <a href="#Page_1">1</a><br />
+Shaft couplings, <a href="#Page_25">25</a><br />
+&mdash; hanger, <a href="#Page_34">34</a><br />
+Shafting, <a href="#Page_24">24</a><br />
+Shear steel, <a href="#Page_79">79</a><br />
+Sheave, eccentric, <a href="#Page_47">47</a><br />
+Shingling, <a href="#Page_78">78</a><br />
+Shrinking, process of, <a href="#Page_44">44</a><br />
+Siemens-Martin steel, <a href="#Page_79">79</a><br />
+Slide blocks, <a href="#Page_56">56</a><br />
+&mdash; valves, <a href="#Page_68">68</a>, <a href="#Page_71">71</a><br />
+Sliding key, <a href="#Page_23">23</a><br />
+Snap head, <a href="#Page_7">7</a><br />
+Snug, <a href="#Page_17">17</a><br />
+Spiegeleisen, <a href="#Page_80">80</a><br />
+Spring bows, <a href="#Page_1">1</a><br />
+<span class='pagenum'><a name="Page_116" id="Page_116">[Pg 116]</a></span>
+Spur wheel, <a href="#Page_41">41</a><br />
+Square nut, <a href="#Page_16">16</a><br />
+&mdash; screw thread, <a href="#Page_14">14</a><br />
+Stay, back, for lathe, <a href="#Page_86">86</a><br />
+&mdash; bar, <a href="#Page_83">83</a><br />
+&mdash; girder, <a href="#Page_81">81</a><br />
+&mdash; gusset, <a href="#Page_12">12</a><br />
+Steam ports, <a href="#Page_71">71</a><br />
+&mdash; whistle, <a href="#Page_96">96</a><br />
+Steel, <a href="#Page_79">79</a><br />
+Steps, <a href="#Page_30">30</a><br />
+Strap, <a href="#Page_49">49</a><br />
+&mdash; eccentric, <a href="#Page_47">47</a><br />
+&mdash; end of connecting rod, <a href="#Page_49">49</a><br />
+Stud bolts, <a href="#Page_18">18</a><br />
+Studs, <a href="#Page_18">18</a><br />
+Stuffing-boxes, <a href="#Page_63">63</a><br />
+Sunk key, <a href="#Page_22">22</a><br />
+<br />
+Taper bolt, <a href="#Page_18">18</a>, <a href="#Page_27">27</a><br />
+&mdash; pin, <a href="#Page_23">23</a><br />
+Tee-headed bolt, <a href="#Page_18">18</a><br />
+Tee-iron cover strap, <a href="#Page_81">81</a><br />
+Tee square, <a href="#Page_1">1</a><br />
+Teeth of wheels, form and proportions of, <a href="#Page_40">40</a><br />
+Teeth, pitch of, <a href="#Page_40">40</a><br />
+Tempering of steel, <a href="#Page_80">80</a><br />
+Throw of crank, <a href="#Page_44">44</a><br />
+&mdash; eccentric, <a href="#Page_47">47</a><br />
+Toothed wheels, <a href="#Page_39">39</a><br />
+<br />
+Valve Kinghorn's metallic, <a href="#Page_70">70</a><br />
+&mdash; slide, <a href="#Page_68">68</a>, <a href="#Page_71">71</a><br />
+Valves, <a href="#Page_68">68</a><br />
+&mdash; conical disc, <a href="#Page_70">70</a><br />
+&mdash; india-rubber, <a href="#Page_58">58</a>, <a href="#Page_68">68</a><br />
+Velocity ratio in belt gearing, <a href="#Page_36">36</a><br />
+<br />
+Wall boxes, <a href="#Page_34">34</a><br />
+Washers, <a href="#Page_19">19</a><br />
+Welding, <a href="#Page_79">79</a><br />
+Whistle, steam, <a href="#Page_96">96</a><br />
+White cast iron, <a href="#Page_77">77</a><br />
+Whitworth screws, dimensions of, <a href="#Page_15">15</a><br />
+&mdash; <b>V</b> screw thread, <a href="#Page_14">14</a><br />
+Wood, <a href="#Page_81">81</a><br />
+Working drawings, <a href="#Page_4">4</a><br />
+Wrought iron, <a href="#Page_78">78</a><br />
+<br />
+Yellow pine, <a href="#Page_81">81</a><br />
+</p>
+</div>
+
+
+<h5>PRINTED BY<br />
+
+SPOTTISWOODE AND CO., NEW-STREET SQUARE<br />
+
+LONDON</h5>
+
+
+
+<hr style="width: 100%;" />
+<h2>TEXT-BOOKS OF SCIENCE</h2>
+
+<div class="poem">
+<p class="negidt"><span class="ft20">PHOTOGRAPHY.</span> By Captain <span class="smcap">W. De Wiveleslie Abney</span>,
+C.B. F.R.S. late Instructor in Chemistry and Photography at the School of
+Military Engineering, Chatham. With 105 Woodcuts. Price 3<i>s.</i> 6<i>d.</i></p>
+
+<p class="negidt"><span class="ft20">The STRENGTH of MATERIALS and STRUCTURES;</span>
+the Strength of Materials as depending on their quality and as
+ascertained by Testing Apparatus; the Strength of Structures as depending
+on their form and arrangement, and on the materials of which they are composed.
+By Sir <span class="smcap">J. Anderson</span>, C.E. &amp;c. With 66 Woodcuts. Price 3<i>s.</i> 6<i>d.</i></p>
+
+<p class="negidt"><span class="ft20">INTRODUCTION to the STUDY of ORGANIC
+CHEMISTRY;</span> the CHEMISTRY of CARBON and its COMPOUNDS.
+By <span class="smcap">Henry E. Armstrong</span> Ph.D. F.R.S. With 8 Woodcuts. Price 3<i>s.</i> 6<i>d.</i></p>
+
+<p class="negidt"><span class="ft20">ELEMENTS of ASTRONOMY.</span> By Sir R. S. <span class="smcap">Ball</span>, LL.D.
+F.R.S. Andrews Professor of Astronomy in the Univ. of Dublin, Royal
+Astronomer of Ireland. With 136 Woodcuts. Price 6<i>s.</i></p>
+
+<p class="negidt"><span class="ft20">RAILWAY APPLIANCES.</span> A Description of Details of
+Railway Construction subsequent to the completion of Earthworks and
+Structures, including a short Notice of Railway Rolling Stock. By <span class="smcap">John
+Wolfe Barry</span>, M.I.C.E. With 207 Woodcuts. Price 3<i>s.</i> 6<i>d.</i></p>
+
+<p class="negidt"><span class="ft20">SYSTEMATIC MINERALOGY.</span> By <span class="smcap">Hilary Bauerman</span>,
+F.G.S. Associate of the Royal School of Mines. With 373 Woodcuts.
+Price 6<i>s.</i></p>
+
+<p class="negidt"><span class="ft20">DESCRIPTIVE MINERALOGY.</span> By <span class="smcap">Hilary Bauerman</span>,
+F.G.S. &amp;c. With 236 Woodcuts. Price 6<i>s.</i></p>
+
+<p class="negidt"><span class="ft20">METALS, their PROPERTIES and TREATMENT.</span>
+By <span class="smcap">C. L. Bloxam</span> and <span class="smcap">A. K. Huntington</span>, Professors in King's College,
+London. With 130 Woodcuts. Price 5<i>s.</i></p>
+
+<p class="negidt"><span class="ft20">PRACTICAL PHYSICS.</span> By <span class="smcap">R. T. Glazebrook</span>, M.A.
+F.R.S. and W. N. SHAW, M.A. With 80 Woodcuts. Price 6<i>s.</i></p>
+
+<p class="negidt"><span class="ft20">PHYSICAL OPTICS.</span> By <span class="smcap">R. T. Glazebrook</span>, M.A.
+F.R.S. Fellow and Lecturer of Trin. Coll. Demonstrator of Physics at the
+Cavendish Laboratory, Cambridge. With 183 Woodcuts. Price 6<i>s.</i></p>
+
+<p class="negidt"><span class="ft20">The ART of ELECTRO-METALLURGY,</span> including all
+known Processes of Electro-Deposition. By <span class="smcap">G. Gore</span>, LL.D. F.R.S.
+With 56 Woodcuts. Price 6<i>s.</i></p>
+
+<p class="negidt"><span class="ft20">ALGEBRA and TRIGONOMETRY.</span> By <span class="smcap">William
+Nathaniel Griffin</span>, B.D. Price 3<i>s.</i> 6<i>d.</i> NOTES ON, with SOLUTIONS
+of the more difficult QUESTIONS. Price 3<i>s.</i> 6<i>d.</i></p>
+
+<p class="negidt"><span class="ft20">The STEAM ENGINE.</span> By <span class="smcap">George C. V. Holmes</span>,
+Whitworth Scholar; Secretary of the Institution of Naval Architects, With
+212 Woodcuts. Price 6<i>s.</i></p>
+
+<p class="negidt"><span class="ft20">ELECTRICITY and MAGNETISM.</span> By <span class="smcap">Fleeming
+Jenkin</span>, F.R.SS. L. &amp; E. late Professor of Engineering in the University of
+Edinburgh. With 177 Woodcuts. Price 3<i>s.</i> 6<i>d.</i></p>
+
+<p class="negidt"><span class="ft20">THEORY of HEAT.</span> By <span class="smcap">J. Clerk Maxwell</span>, M.A. LL.D.
+Edin. F.R.SS. L. &amp; E. With 41 Woodcuts. Price 3<i>s.</i> 6<i>d.</i></p>
+
+<p class="negidt"><span class="ft20">TECHNICAL ARITHMETIC and MENSURATION.</span>
+By <span class="smcap">Charles W. Merrifield</span>, F.R.S. Price 3<i>s.</i> 6<i>d.</i> <span class="smcap">Key</span>, by
+the Rev. <span class="smcap">John Hunter</span>, M.A. Price 3<i>s.</i> 6<i>d.</i></p>
+
+<p class="negidt"><span class="ft20">INTRODUCTION to the STUDY of INORGANIC
+CHEMISTRY.</span> By <span class="smcap">William Allen Miller</span>, M.D. LL.D. F.R.S. With
+72 Woodcuts. Price 3<i>s.</i> 6<i>d.</i></p>
+
+<p class="negidt"><span class="ft20">TELEGRAPHY.</span> By <span class="smcap">W. H. Preece</span>, F.R.S. M.I.C.E, and
+<span class="smcap">J. Sivewright</span>, M.A. C.M.G. With 160 Woodcuts. Price 5<i>s.</i></p>
+
+<p class="negidt"><span class="ft20">The STUDY of ROCKS,</span> an ELEMENTARY Text-Book
+of PETROLOGY. By <span class="smcap">Frank Rutley</span>, F.G.S. of Her Majesty's
+Geological Survey. With 6 Plates and 88 Woodcuts. Price 4<i>s.</i> 6<i>d.</i></p>
+
+<p class="negidt"><span class="ft20">WORKSHOP APPLIANCES,</span> including Descriptions of
+some of the Gauging and Measuring Instruments&mdash;Hand-Cutting Tools,
+Lathes, Drilling, Planing, and other Machine Tools used by Engineers.
+By <span class="smcap">C. P. B. Shelley</span>, M.I.C.E. With 291 Woodcuts. Price 4<i>s.</i> 6<i>d.</i></p>
+
+<p class="negidt"><span class="ft20">STRUCTURAL and PHYSIOLOGICAL BOTANY.</span>
+By Dr. <span class="smcap">Otto Wilhelm Thom&eacute;</span>, Rector of the High School, Cologne, and
+<span class="smcap">A. W. Bennett</span>, M.A. B.Sc. F.L.S. With 600 Woodcuts and a
+Coloured Map. Price 6<i>s.</i></p>
+
+<p class="negidt"><span class="ft20">QUANTITATIVE CHEMICAL ANALYSIS.</span>  By <span class="smcap">T.
+E. Thorpe</span>, F.R.S. Ph.D. Professor of Chemistry in the Andersonian
+University, Glasgow. With 88 Woodcuts. Price 4<i>s.</i> 6<i>d.</i></p>
+
+<p class="negidt"><span class="ft20">QUALITATIVE ANALYSIS and LABORATORY
+PRACTICE.</span> By <span class="smcap">T.
+E. Thorpe</span>, Ph.D. F.R.S. Professor of Chemistry
+in the Andersonian University, Glasgow, and M. M. PATTISON MUIR,
+M.A. and F.R.S.E. With Plate of Spectra and 57 Woodcuts. Price 3<i>s.</i> 6<i>d.</i></p>
+
+<p class="negidt"><span class="ft20">INTRODUCTION to the STUDY of CHEMICAL
+PHILOSOPHY;</span> the PRINCIPLES of THEORETICAL and SYSTEMATICAL
+CHEMISTRY. By <span class="smcap">William A. Tilden</span>, D.Sc. London,
+F.R.S. With 5 Woodcuts. With or without Answers to Problems, 4<i>s.</i> 6<i>d.</i></p>
+
+<p class="negidt"><span class="ft20">ELEMENTS of MACHINE DESIGN;</span> an Introduction
+to the Principles which determine the Arrangement and Proportion of the
+Parts of Machines, and a Collection of Rules for Machine Design. By
+<span class="smcap">W. Cawthorne Unwin</span>, B.Sc. M.I.C.E. With 325 Woodcuts. Price 6s.</p>
+
+<p class="negidt"><span class="ft20">PLANE and SOLID GEOMETRY.</span> By <span class="smcap">H. W. Watson</span>,
+M.A. formerly Fellow of Trinity College, Cambridge. Price 3<i>s.</i> 6<i>d.</i></p>
+</div>
+
+<hr style="width: 15%;" />
+<h4>London: LONGMANS, GREEN, &amp; CO.</h4>
+
+
+
+<hr style="width: 100%;" />
+<h2>SCIENTIFIC CLASS-BOOKS.</h2>
+
+<div class="poem">
+<p class="negidt"><span class="ft20">GANOT'S NATURAL PHILOSOPHY for GENERAL
+READERS and YOUNG PERSONS:</span> a Course of Physics
+divested of Mathematical Formul&aelig;, expressed in the language
+of daily life. Translated and edited, from Ganot's <i>Cours
+&Eacute;l&eacute;mentaire de Physique</i>, by <span class="smcap">E. Atkinson</span>, Ph.D. F.C.S.
+Sixth Edition, with 34 pages of new matter, 2 Plates, 518
+Woodcuts, and an Appendix of Questions. Crown 8vo. 7<i>s.</i> 6<i>d.</i></p>
+
+<p class="negidt"><span class="ft20">GANOT'S ELEMENTARY TREATISE on PHYSICS,</span>
+Experimental and Applied, for the use of Colleges and Schools.
+Translated and edited, from Ganot's <i>&Eacute;l&eacute;ments de Physique</i>, by
+<span class="smcap">E. Atkinson</span>, Ph.D. F.C.S. Twelfth Edition, revised and enlarged;
+with 5 Coloured Plates and 923 Woodcuts. Cr. 8vo. 15<i>s.</i></p>
+
+<p class="negidt"><span class="ft20">LESSONS in ELEMENTARY MECHANICS.</span> Designed
+for the use of Schools, and of Candidates for the London Matriculation,
+and other Examinations; with 52 Examples, nearly
+500 Exercises and Examination Questions with Answers, and
+124 Woodcuts. By Sir <span class="smcap">Philip Magnus</span>, B.Sc. B.A. Thirteenth
+Edition. Fcp. 8vo. 3<i>s.</i> 6<i>d.</i></p>
+
+<p class="negidt"><span class="ft20">PRINCIPLES of MECHANICS.</span> By <span class="smcap">T. M. Goodeve</span>, M.A.
+Professor of Mechanics at the Royal School of Mines. New
+Edition. With 253 Woodcuts. Crown 8vo. 6<i>s.</i></p>
+
+<p class="negidt"><span class="ft20">The ELEMENTS of MECHANISM.</span> By <span class="smcap">T. M. Goodeve</span>,
+M.A. Professor of Mechanics at the Royal School of Mines.
+New Edition. With 342 Woodcuts. Crown 8vo. 6<i>s.</i></p>
+
+<p class="negidt"><span class="ft20">PRACTICAL MECHANICS:</span> an Elementary Introduction
+to their Study. With 855 Exercises with Answers and 184
+Diagrams. By the Rev. <span class="smcap">J. F. Twisden</span>. Crown 8vo. 10<i>s.</i> 6<i>d.</i></p>
+
+<p class="negidt"><span class="ft20">THEORETICAL MECHANICS.</span> By the Rev. <span class="smcap">J. F. Twisden</span>.
+With 172 Examples, numerous Exercises, and 154 Diagrams.
+Crown 8vo. 8<i>s.</i> 6<i>d.</i></p>
+
+<p class="negidt"><span class="ft20">LESSONS in ELEMENTARY MECHANICS.</span> By
+<span class="smcap">W. H. Grieve</span>, Demonstrator in Mechanics to the London
+School Board. Fully Illustrated. Stage III. Fcp. 8vo. 1<i>s.</i> 6<i>d.</i>
+Stage II. 1<i>s.</i> 6<i>d.</i> Stage I. 1<i>s.</i> 6<i>d.</i></p>
+
+<p class="negidt"><span class="ft20">EXPERIMENTAL CHEMISTRY</span> for Junior Students. By
+<span class="smcap">J. Emerson Reynolds</span>, M.D. F.R.S. Professor of Chemistry,
+University Dublin. Fcp. 8vo. with numerous Woodcuts.</p>
+
+<p class="center">
+<span class="smcap">Part I. Introductory.</span> 1<i>s.</i> 6<i>d.</i> <span class="smcap">Part II. Non-Metals</span>. 2<i>s.</i> 6<i>d.</i><br />
+<span class="smcap">Part III. Metals and Allied Bodies.</span> 3<i>s.</i> 6<i>d.</i><br />
+<span class="smcap">Part IV. Carbon Compounds.</span> 4<i>s.</i><br />
+</p>
+</div>
+
+<hr style="width: 15%;" />
+<h4>London: LONGMANS, GREEN, &amp; CO.</h4>
+
+
+<hr style="width: 100%;" />
+<h2>LONGMANS' ELEMENTARY SCIENCE MANUALS.</h2>
+
+<p class="center"><i>Written specially to meet the requirements of the Elementary Stage<br />
+of Science Subjects as laid down in the Syllabus of the Directory<br />
+of the Science and Art Department, South Kensington.</i></p>
+
+<div class="poem">
+<p class="negidt"><span class="ft20">SOUND, LIGHT, and HEAT.</span> By <span class="smcap">Mark R. Wright</span>
+(Hon. Inter. B.Sc. London). With 160 Illustrations. Crown 8vo. 2<i>s.</i> 6<i>d.</i></p>
+
+<p class="negidt"><span class="ft20">An INTRODUCTION to MACHINE DRAWING and
+DESIGN.</span> By <span class="smcap">David Allan Low</span>. With 65 Illustrations. Crown 8vo. 2<i>s.</i></p>
+
+<p class="negidt"><span class="ft20">TEXT-BOOK on PRACTICAL SOLID or DESCRIPTIVE
+GEOMETRY.</span> By <span class="smcap">David Allan Low</span>.  Part. I. 2<i>s.</i> Part II. 3<i>s.</i></p>
+
+<p class="negidt"><span class="ft20">ELEMENTARY PHYSIOGRAPHY.</span> By <span class="smcap">J. Thornton</span>,
+M.A. With 10 Maps and 150 Illustrations. Crown 8vo. 2<i>s.</i> 6<i>d.</i></p>
+
+<p class="negidt"><span class="ft20">A MANUAL of MECHANICS:</span> an Elementary Text-Book
+for Students of Applied Mechanics. With 138 Illustrations and Diagrams,
+and 188 Examples taken from the Science Department Examination Papers,
+with Answers. By <span class="smcap">T. M. Goodeve</span>, M.A. Fcp. 8vo. 2<i>s.</i> 6<i>d.</i></p>
+
+<p class="negidt"><span class="ft20">INORGANIC CHEMISTRY,</span> <span class="smcap">Theoretical</span> and <span class="smcap">Practical</span>.
+With an Introduction to the Principles of Chemical Analysis. By <span class="smcap">William
+Jago</span>. With 49 Woodcuts and Questions and Exercises. Fcp. 8vo. 2<i>s.</i> 6<i>d.</i></p>
+
+<p class="negidt"><span class="ft20">An INTRODUCTION to PRACTICAL INORGANIC
+CHEMISTRY.</span> By <span class="smcap">William
+Jago</span>, F.C.S. F.I.C. Crown 8vo. 1<i>s.</i> 6<i>d.</i></p>
+
+<p class="negidt"><span class="ft20">PRACTICAL CHEMISTRY:</span> the Principles of Qualitative
+Analysis. By <span class="smcap">William A. Tilden</span>, D.Sc. Fcp. 8vo. 1<i>s.</i> 6<i>d.</i></p>
+
+<p class="negidt"><span class="ft20">ELEMENTARY INORGANIC CHEMISTRY.</span> Alternative
+Course. By <span class="smcap">W. Furneaux</span>, F.R.G.S. 2<i>s.</i> 6<i>d.</i></p>
+
+<p class="negidt"><span class="ft20">ELEMENTARY BOTANY,</span> <span class="smcap">Theoretical</span> and <span class="smcap">Practical</span>.
+By <span class="smcap">Henry Edmonds</span>, B.Sc. London. With 319 Woodcuts. Cr. 8vo 2<i>s.</i> 6<i>d.</i></p>
+
+<p class="negidt"><span class="ft20">An ELEMENTARY COURSE of MATHEMATICS.</span>
+Specially adapted to the requirements of the Science and Art Department.
+Crown 8vo. 2<i>s.</i> 6<i>d.</i></p>
+
+<p class="negidt"><span class="ft20">BUILDING CONSTRUCTION.</span> By <span class="smcap">Edward J. Burrell</span>,
+Teacher of Building Construction at the Technical School of the People's
+Palace, Mile End. With 308 Illustrations, &amp;c. Crown 8vo. 2<i>s.</i> 6<i>d.</i></p>
+
+<p class="negidt"><span class="ft20">THEORETICAL MECHANICS.</span> BY <span class="smcap">J. Edward Taylor</span>,
+M.A. Lond, With 175 Illustrations and Examples and Answers. Cr. 8vo. 2<i>s.</i> 6<i>d.</i></p>
+
+<p class="negidt"><span class="ft20">ANIMAL PHYSIOLOGY.</span> By <span class="smcap">William S. Furneaux</span>,
+Special Science Teacher, London School Board. With 218 Illustrations.
+Crown 8vo. 2<i>s.</i> 6<i>d.</i></p>
+
+<p class="negidt"><span class="ft20">MAGNETISM and ELECTRICITY.</span> By <span class="smcap">A.W. Poyser</span>,
+M.A. With 235 Illustrations. Crown 8vo. 2<i>s.</i> 6<i>d.</i></p>
+
+<p class="negidt"><span class="ft20">STEAM.</span> By <span class="smcap">William Ripper</span>, Member of the Institution of
+Mechanical Engineers. With 142 Illustrations. Crown 8vo. 2<i>s.</i> 6<i>d.</i></p>
+
+<p class="negidt"><span class="ft20">PHYSICS:</span> Alternative Course. By <span class="smcap">Mark R. Wright</span>. With
+242 Illustrations. Crown 8vo. 2<i>s.</i> 6<i>d.</i></p>
+</div>
+
+<hr style="width: 15%;" />
+<h4>London: LONGMANS, GREEN, &amp; CO.</h4>
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<div class="notebox">
+<p class="noidt"><b>Transcriber's Note:</b> Obvious misprints in spelling and punctuation have been silently
+corrected.</p>
+</div>
+
+
+
+
+
+
+
+
+<pre>
+
+
+
+
+
+End of the Project Gutenberg EBook of An Introduction to Machine Drawing and
+Design, by David Allan Low
+
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+</body>
+</html>
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+The Project Gutenberg EBook of An Introduction to Machine Drawing and
+Design, by David Allan Low
+
+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: An Introduction to Machine Drawing and Design
+
+Author: David Allan Low
+
+Release Date: March 4, 2012 [EBook #39033]
+
+Language: English
+
+Character set encoding: ASCII
+
+*** START OF THIS PROJECT GUTENBERG EBOOK AN INTRODUCTION TO MACHINE ***
+
+
+
+
+Produced by Juliet Sutherland and the Online Distributed
+Proofreading Team at http://www.pgdp.net
+
+
+
+
+
+
+
+
+  AN INTRODUCTION
+  TO
+  MACHINE DRAWING
+  AND
+  DESIGN
+
+  BY
+
+  DAVID ALLAN LOW
+
+  (WHITWORTH SCHOLAR), M. INST. M.E.
+
+  HEAD MASTER OF THE PEOPLE'S PALACE TECHNICAL SCHOOLS, LONDON
+  AUTHOR OF 'A TEXT-BOOK ON PRACTICAL SOLID OR DESCRIPTIVE GEOMETRY'
+  'AN ELEMENTARY TEXT-BOOK OF APPLIED MECHANICS' ETC.
+
+  [Illustration]
+
+  _FOURTH EDITION_
+
+  LONDON
+  LONGMANS, GREEN, AND CO.
+  AND NEW YORK: 15 EAST 16th STREET
+  1890
+
+
+
+  PRINTED BY
+  SPOTTISWOODE AND CO., NEW-STREET SQUARE
+  LONDON
+
+
+
+
+PREFACE.
+
+
+It is now generally recognised that the old-fashioned method of teaching
+machine drawing is very unsatisfactory. In teaching by this method an
+undimensioned scale drawing, often of a very elaborate description, is
+placed before the student, who is required to _copy_ it. Very often the
+student succeeds in making a good copy of the drawing placed before him
+without learning very much about the object represented by it, and this
+state of matters is sometimes not much improved by the presence of the
+teacher, who is often simply an art master, knowing nothing about
+machine design. It is related of one school that a pupil, after making a
+copy of a particular drawing, had a discussion with his teacher as to
+whether the object represented was a sewing machine or an electrical
+machine. Evidently the publisher of the drawing example in this case did
+not adopt the precaution which a backward student used at an examination
+in machine design: he put on a full title above his drawing, for the
+information of his examiner.
+
+Now, if machine drawing is to be of practical use to any one, he must be
+able to understand the form and arrangement of the parts of a machine
+from an inspection of suitable drawings of them without seeing the parts
+themselves. Also he ought to be able to make suitable drawings of a
+machine or parts of a machine from the machine or the parts themselves.
+
+In producing this work the author has aimed at placing before young
+engineers and others, who wish to acquire the skill and knowledge
+necessary for making the simpler _working drawings_ such as are produced
+in engineers' drawing offices, a number of good exercises in drawing,
+sufficient for one session's work, and at the same time a corresponding
+amount of information on the design of machine details generally.
+
+The exercises set are of various kinds. In the first and simplest
+certain views of some machine detail are given, generally drawn to a
+small scale, which the student is asked to reproduce _to dimensions
+marked on these views_, and he is expected to keep to these dimensions,
+and not to measure anything from the given illustrations. In the second
+kind of exercise the student is asked to reproduce certain views shown
+_to dimensions given in words or in tabular form_. In the third kind of
+exercise the student is required to make, in addition to certain views
+shown to given dimensions, others which he can only draw correctly if he
+thoroughly understands the design before him. In the fourth kind of
+exercise the student is asked to make the necessary working drawings for
+some part of a machine which has been previously described and
+illustrated, _the dimensions to be calculated by rules given in the
+text_.
+
+The illustrations for this work are all new, and have been specially
+prepared by the author from _working drawings_, and he believes that
+they will be found to represent the best modern practice.
+
+As exercises in drawing, those given in this book are not numbered
+exactly in their order of difficulty, but unless on the recommendation
+of a teacher, the student should take them up in the order given,
+omitting the following:--26, 27, 28, 35, 40, 42, 43, 45, 49, 50, 54, 60,
+61, as he comes to them, until he has been right through the book;
+afterwards he should work out those which he omitted on first going over
+the book.
+
+In addition to the exercises given in this work the student should
+practise making freehand sketches of machine details from actual
+machines or good models of them. Upon these sketches he should put the
+proper dimensions, got by direct measurement from the machine or model
+by himself. These sketches should be made in a note-book kept for the
+purpose, and no opportunity should be lost of inserting a sketch of any
+design which may be new to the student, always putting on the dimensions
+if possible. These sketches form excellent examples from which to make
+working drawings. The student should also note any rules which he may
+meet with for proportioning machines, taking care, however, in each case
+to state the source of such information for his future guidance and
+reference.
+
+As machine drawing is simply the application of the principles of
+descriptive geometry to the representation of machines, the student of
+the former subject, if he is not already acquainted with the latter,
+should commence to study it at once.
+
+                                                              D. A. L.
+  GLASGOW: _March_ 1887.
+
+
+_PREFACE TO THE THIRD EDITION._
+
+To this edition another chapter has been added, containing a number of
+miscellaneous exercises, which it is hoped will add to the usefulness of
+the work as a text-book in science classes. The latest examination paper
+in machine drawing by the Science and Art Department has also been added
+to the Appendix.
+
+                                                              D. A. L.
+  LONDON: _August_ 1888.
+
+
+
+
+CONTENTS.
+
+
+                                                    PAGE
+      I.  INTRODUCTION                                 1
+     II.  RIVETED JOINTS                               6
+    III.  SCREWS, BOLTS, AND NUTS                     14
+     IV.  KEYS                                        22
+      V.  SHAFTING                                    24
+     VI.  SHAFT COUPLINGS                             25
+    VII.  BEARINGS FOR SHAFTS                         30
+   VIII.  PULLEYS                                     36
+     IX.  TOOTHED WHEELS                              39
+      X.  CRANKS AND CRANKED SHAFTS                   43
+     XI.  ECCENTRICS                                  47
+    XII.  CONNECTING RODS                             49
+   XIII.  CROSS-HEADS                                 56
+    XIV.  PISTONS                                     57
+     XV.  STUFFING-BOXES                              63
+    XVI.  VALVES                                      68
+   XVII.  MATERIALS USED IN MACHINE CONSTRUCTION      76
+  XVIII.  MISCELLANEOUS EXERCISES                     81
+
+          APPENDIX A                                  99
+          APPENDIX B                                 102
+          INDEX                                      113
+
+
+
+
+AN INTRODUCTION
+
+TO
+
+MACHINE DRAWING AND DESIGN.
+
+
+
+
+I. INTRODUCTION.
+
+
+_Drawing Instruments._--For working the exercises in this book the
+student should be provided with the following:--A well-seasoned yellow
+pine _drawing-board_, 24 inches long, 17 inches wide, and 3/8 inch or
+1/2 inch thick, provided with cross-bars on the back to give it strength
+and to prevent warping. A =T= _square_, with a blade 24 inches long
+attached permanently to the stock, _but not sunk into it_. One 45 deg. and
+one 60 deg. _set square_. The short edges of the former may be about 6
+inches and the short edge of the latter about 5 inches long. A _pair of
+compasses_ with pen and pencil attachments, and having legs from 5
+inches to 6 inches long. A _pair of dividers_, with screw adjustment if
+possible. A _pair of small steel spring pencil bows_ for drawing small
+circles, and a _pair of small steel spring pen bows_ for inking in the
+same. A _drawing pen_ for inking in straight lines. All compasses should
+have _round points_, and if possible _needle_ points. A piece of
+india-rubber will also be required, besides two pencils, one marked H or
+HH and one marked HB or F; the latter to be used for lining in a drawing
+which is not to be inked in, or for freehand work.
+
+Pencils for mechanical drawing should be sharpened with a _chisel
+point_, and those for freehand work with a _round point_. _Do not wet
+the pencil_, as the lines afterwards made with it are very difficult to
+rub out.
+
+Drawing-paper for working drawings may be secured to the board by
+_drawing-pins_, but the paper for finished drawings or drawings upon
+which there is to be a large amount of colouring should be _stretched_
+upon the board.
+
+The student should get the best instruments he can afford to buy, and he
+should rather have a few good instruments than a large box of inferior
+ones.
+
+_Drawing-paper._--The names and sizes of the sheets of drawing paper are
+given in the following table:--
+
+                     Inches
+  Demy              20 x 15
+  Medium            22 x 17
+  Royal             24 x 19
+  Imperial          30 x 22
+  Atlas             34 x 26
+  Double Elephant   40 x 27
+  Antiquarian       52 x 31
+
+The above sizes must not be taken as exact. In practice they will be
+found to vary in some cases as much as an inch.
+
+Cartridge-paper is made in sheets of various sizes, and also in rolls.
+
+Hand-made paper is the best, but it is expensive. Good cartridge-paper
+is quite suitable for ordinary drawings.
+
+_Centre Lines._--Drawings of most parts of machines will be found to
+be symmetrical about certain lines called _centre lines_. These lines
+should be drawn first with great care. On a pencil drawing centre
+lines should be thin continuous lines; in this book they are shown
+thus -- - -- - --.
+
+After drawing the centre line of any part the dimensions of that part
+must be marked off from the centre line, so as to insure that it really
+is the centre line of that part: thus in making a drawing of a rivet,
+such as is shown at (_a_) fig. 1, after drawing the centre line, half
+the diameter of the rivet would be marked off on each side of that line,
+in order to determine the lines for the sides of the rivet.
+
+_Inking._--For inking in drawings the best Indian ink should be used,
+and not common writing ink. Common ink does not dry quick enough, and
+rapidly corrodes the drawing pens. The pen should be filled by means of
+a brush or a narrow strip of paper, and not by dipping the pen into the
+ink.
+
+In cases where there are straight lines and arcs of circles touching one
+another _ink in the arcs first_, then the straight lines; in this way it
+is easier to hide the joints.
+
+_Colouring._--Camel's-hair or sable brushes should be used; the latter
+are the best, but are much more expensive than the former. The colour
+should be rubbed down in a dish, and the tint should be light. The
+mistake which a beginner invariably makes is in having the colour of too
+dark a tint.
+
+First go over the part to be coloured with the brush and _clean_ water
+for the purpose of damping it. Next dry with clean blotting-paper to
+take off any superfluous water. Then take another brush with the colour,
+and beginning at the top, work from left to right and downwards. If it
+is necessary to recolour any part let the first coating dry before
+beginning.
+
+Engineers have adopted certain colours to represent particular
+materials; these are given in the following table:--
+
+_Table showing Colours used to represent Different Materials._
+
+  MATERIAL          COLOUR
+
+  Cast iron         Payne's grey or neutral tint.
+  Wrought iron      Prussian blue.
+  Steel             Purple (mixture of Prussian blue and crimson lake).
+  Brass             Gamboge with a little sienna or a very little red
+                         added.
+  Copper            A mixture of crimson lake and gamboge, the former
+                         colour predominating.
+  Lead              Light Indian ink with a very little indigo added.
+  Brickwork         Crimson lake and burnt sienna.
+  Firebrick         Yellow and Vandyke brown.
+  Greystones        Light sepia or pale Indian ink, with a little
+                         Prussian blue added.
+  Brown freestone   Mixture of pale Indian ink, burnt sienna, and
+                         carmine.
+  Soft woods        For ground work, pale tint of sienna.
+  Hard woods        For ground work, pale tint of sienna with a little
+                         red added.
+                    For graining woods use darker tint with a greater
+                         proportion of red.
+
+_Printing._--A good drawing should have its title printed, a plain style
+of letter being used for this purpose, such as the following:--
+
+  [Illustration: ABCDEFGHIJKLMNOPQRST
+                        UVWXYZ
+                      1234567890]
+
+  [Illustration: ABCDEFGHIJKLMNOPQR
+                      STUVWXYZ
+                     1234567890]
+
+The following letters look well _if they are well made_, but they are
+much more difficult to draw.
+
+  [Illustration: ABCDEFGHIJKLMNOP
+                    QRSTUVWXYZ
+                    1234567890]
+
+For remarks on a drawing the following style is most suitable:--
+
+  [Illustration: abcdefghijklmnopqrstuvwxyz]
+
+All printing should be done by freehand.
+
+_Border lines_ are seldom put on engineering drawings.
+
+_Working Drawings._--A good working drawing should be prepared in the
+following manner. It must first be carefully outlined in pencil and then
+inked in. After this all parts cut by planes of section should be
+coloured, the colours used indicating the materials of which the parts
+are made. Parts which are round may also be lightly shaded with the
+brush and colours to suit the materials. The centre lines are now inked
+in with _red_ or _blue ink_. The red ink may be prepared by rubbing down
+the cake of crimson lake, and the blue ink in like manner from the cake
+of Prussian blue. Next come the _distance_ or _dimension_ lines, which
+should be put in with _blue_ or _red ink_, depending on which colour was
+used for the centre lines. Dimension lines and centre lines are best put
+in of different colour. The arrow-heads at the ends of the dimension
+lines are now put in with _black ink_, and so are the figures for the
+dimensions. The arrow-heads and the figures should be made with a common
+writing pen. The dimensions should be put on neatly. Many a good drawing
+has its appearance spoiled through being slovenly dimensioned.
+
+We may here point out the importance of putting the dimensions on a
+working drawing. If the drawing is not dimensioned, the workman must get
+his sizes from the drawing by applying his rule or a suitable scale. Now
+this operation takes time, and is very liable to result in error. Time
+is therefore saved, and the chance of error reduced, by marking the
+sizes in figures.
+
+In practice it is not usual to send original drawings from the drawing
+office to the workshop, but copies only. The copies may be produced by
+various 'processes,' or they may be tracings drawn by hand. Many
+engineers do not ink in their original drawings, but leave them in
+pencil; especially is this the case if the drawings are not likely to be
+much used.
+
+_Scales._--The best scales are made of ivory, and are twelve inches
+long. Boxwood scales are much cheaper, although not so durable as those
+made of ivory. If the student does not care to go to the expense of
+ivory or boxwood scales, he can get paper ones very cheap, which will be
+quite sufficient for his purpose. The divisions of the scale should be
+marked down to its edge, so that measurements may be made by applying
+the scale directly to the drawing. For working such exercises as are in
+this book the student should be provided with the following scales:--
+
+  A scale of  1, or 12 inches to a foot.
+     "       1/2  "  6         "
+     "       1/3  "  4         "
+     "       1/4  "  3         "
+     "       1/6  "  2         "
+
+A scale of 1 is spoken of as 'full size,' and a scale of 1/2 as 'half
+size.'
+
+Engineers in this country state dimensions of machines in feet, inches,
+and fractions of an inch, the latter being the 1/2, 1/4, 1/8, 1/16, &c.
+In making calculations it is generally more convenient to use decimal
+fractions, and then substitute for the results the equivalent fractions
+in eighths, sixteenths, &c. The following table will be found useful for
+this purpose:--
+
+_Decimal Equivalents of Fractions of an Inch._
+
+  +----------+--------------------+
+  | Fraction | Decimal Equivalent |
+  +----------+--------------------+
+  |  1/32    |      .03125        |
+  |  1/16    |      .0625         |
+  |  3/32    |      .09375        |
+  |  1/8     |      .125          |
+  |  5/32    |      .15625        |
+  |  3/16    |      .1875         |
+  |  7/32    |      .21875        |
+  |  1/4     |      .25           |
+  |  9/32    |      .28125        |
+  |  5/16    |      .3125         |
+  | 11/32    |      .34375        |
+  |  3/8     |      .375          |
+  | 13/32    |      .40625        |
+  |  7/16    |      .4375         |
+  | 15/32    |      .46875        |
+  |  1/2     |      .5            |
+  | 17/32    |      .53125        |
+  |  9/16    |      .5625         |
+  | 19/32    |      .59375        |
+  |  5/8     |      .625          |
+  | 21/32    |      .65625        |
+  | 11/16    |      .6875         |
+  | 23/32    |      .71875        |
+  |  3/4     |      .75           |
+  | 25/32    |      .78125        |
+  | 13/16    |      .8125         |
+  | 27/32    |      .84375        |
+  |  7/8     |      .875          |
+  | 29/32    |      .90625        |
+  | 15/16    |      .9375         |
+  | 31/32    |      .96875        |
+  |   1      |     1.0            |
+  +----------+--------------------+
+
+Engineers use a single accent (') to denote _feet_, and a double
+accent (") to denote _inches_. Thus 2' 9" reads two feet nine inches.
+
+
+
+
+II. RIVETED JOINTS.
+
+
+Two plates or pieces to be riveted together have holes punched or
+drilled in them in such a manner that one may be made to overlap the
+other so that the holes in the one may be opposite the holes in the
+other. The rivets, which are round bars of iron, or steel, or other
+metal, are heated to redness and inserted in the holes; the head already
+formed on the rivet, and called the tail, is then held up, and the point
+is hammered or pressed so as to form another head. This process of
+forming the second head on the rivet is known as riveting, and may be
+done by hand-hammering or by a machine.
+
+_Forms of Rivet Heads._--In fig. 1 are shown four different forms of
+rivet heads: (_a_) is a _snap head_, (_b_) a _conical head_ (_c_) a
+_pan head_, and (_d_) _a countersunk head_.
+
+_Proportions of Rivet Heads._--The diameter of the snap head is about
+1.7 times the diameter of the rivet, and its height about .6 of the
+diameter of the rivet. The conical head has a diameter twice and a
+height three quarters of the rivet diameter. The greatest diameter of
+the pan head is about 1.6, and its height .7 of the rivet diameter. The
+greatest diameter of the countersunk head may be one and a half, and its
+depth a half of the diameter of the rivet.
+
+[Illustration: FIG. 1.]
+
+In fig. 1 at (_a_) and (_b_) are shown geometrical constructions devised
+by the author for drawing the snap and conical head for any size of
+rivet, the proportions being nearly the same as those given above.
+
+_Geometrical Construction for Proportioning Snap Heads._--With centre A,
+and radius equal to half diameter of rivet, describe a circle cutting
+the centre line of the rivet at B and C. With centre B and radius BC
+describe the arc CD. Make BE equal to AD. With centre E and radius ED
+describe the arc DFH.
+
+_Construction for Conical Head._--With centre K, and radius equal to
+diameter of rivet, describe the semicircle LMN, cutting the side of the
+rivet at M. With centre M and radius MN describe the arc NP to cut the
+centre line of rivet at P. Join PL and PN.
+
+When a number of rivets of the same diameter have to be shown on the
+same drawing the above constructions need only be performed on one
+rivet. After the point E has been discovered the distance AE may be
+measured off on all the other rivets, and the arcs corresponding to
+DFH drawn with radii equal to ED. In like manner the height KP of the
+conical head may be marked off on all rivets of the same diameter with
+conical heads.
+
+_Caulking._--In order to make riveted joints steam- or water-tight the
+edges of the plates and the edges of the heads of the rivets are burred
+down by a blunt chisel or caulking tool as shown at Q and R.
+
+[Illustration: FIG. 2.]
+
+[Illustration: FIG. 3.]
+
+    EXERCISE 1: _Forms of Rivets._--Draw, full size, the rivets and
+    rivet heads shown in fig. 1. The diameter of the rivet in each
+    case to be 1-1/8 inches, and the thickness of the plates 7/8 inch.
+
+    EXERCISE 2: _Single Riveted Lap Joint._--Draw, full size, the
+    plan and sectional elevation of the _single riveted lap joint_
+    shown in fig. 2.
+
+_Table showing the Proportions of Single Riveted Lap Joints for various
+Thicknesses of Plates._ (_Plates and Rivets Wrought Iron._)
+
+  +--------------+-------------+----------+--------------+
+  | Thickness of | Diameter of | Pitch of | Width of lap |
+  |    plates    |    rivets   |  rivets  |              |
+  +--------------+-------------+----------+--------------+
+  |      1/4     |     9/16    |  1-5/8   |    1-3/4     |
+  |      5/16    |     5/8     |  1-3/4   |    2         |
+  |      3/8     |    11/16    |  1-7/8   |    2-1/4     |
+  |      7/16    |     3/4     |  2       |    2-1/2     |
+  |      1/2     |    13/16    |  2-1/8   |    2-3/4     |
+  |      9/16    |     7/8     |  2-1/4   |    2-7/8     |
+  |      5/8     |    15/16    |  2-5/16  |    3         |
+  |     11/16    |   1         |  2-3/8   |    3-1/8     |
+  |      3/4     |   1-1/16    |  2-1/2   |    3-1/4     |
+  +------------------------------------------------------+
+
+  All the dimensions are in inches.
+
+[Illustration: FIG. 4.]
+
+    EXERCISE 3.--Draw, half size, a plan and section of a single
+    riveted lap joint for plates 3/4" thick to the dimensions given in
+    the above table.
+
+    EXERCISE 4: _Double Riveted Lap Joint._--Draw, full size, the two
+    views of the _double riveted lap joint_ shown in fig. 3.
+
+_Table showing the Proportions of Double Riveted Lap Joints for various
+Thicknesses of Plates._ (_Plates and Rivets Wrought Iron._)
+
+  +-----------+-------------+----------+------------------+----------+
+  | Thickness | Diameter of | Pitch of | Distance between | Width of |
+  | of plates |    rivets   |  rivets  |  rows of rivets  |    lap   |
+  +-----------+-------------+----------+------------------+----------+
+  |   3/8     |    11/16    |  2-1/2   |    1-1/8         |  3-1/2   |
+  |   7/16    |     3/4     |  2-5/8   |    1-1/4         |  3-3/4   |
+  |   1/2     |    13/16    |  2-3/4   |    1-3/8         |  4       |
+  |   9/16    |     7/8     |  2-7/8   |    1-7/16        |  4-1/4   |
+  |   5/8     |    15/16    |  3       |    1-9/16        |  4-1/2   |
+  |  11/16    |   1         |  3-1/8   |    1-3/4         |  4-3/4   |
+  |   3/4     |   1-1/16    |  3-1/4   |    1-7/8         |  5       |
+  |  13/16    |   1-1/16    |  3-3/8   |    1-7/8         |  5       |
+  |   7/8     |   1-1/8     |  3-1/2   |    1-15/16       |  5-1/4   |
+  |  15/16    |   1-1/8     |  3-5/8   |    1-15/16       |  5-1/4   |
+  | 1         |   1-3/16    |  3-3/4   |    2             |  5-1/2   |
+  +-----------+-------------+----------+------------------+----------+
+
+[Illustration: FIG. 5.]
+
+    EXERCISE 5.--Draw, half size, a plan and section of a double
+    riveted lap joint for plates 7/8 inch thick to the dimensions
+    given in the above table.
+
+    EXERCISE 6: _Single Riveted Butt Joints._--In fig. 4 are shown
+    _single riveted butt joints_. One of the sectional views shows a
+    butt joint with one _cover plate_ or _butt strap_; the other
+    sectional view shows the same joint with two cover plates; the
+    third view is a plan of both arrangements. Draw all these views
+    full size.
+
+    EXERCISE 7.--Fig. 5 shows a plan and sectional elevation of the
+    connection of three plates together, which are in the same plane,
+    by means of single riveted butt joints and single cover plates.
+    The butt straps where they overlap are forged so as to fit one
+    another as shown, and thus form a close joint. Draw these views to
+    the scale of 6 inches to a foot.
+
+    The plates are 1/2 inch thick and the butt straps 9/16 inch thick.
+    All other dimensions must be deduced from the table for single
+    riveted lap joints.
+
+    EXERCISE 8.--The connection of three plates by single riveted lap
+    joints is shown in fig. 6. To make the joint close one plate has a
+    portion of its edge thinned out, and the plate above it is set up
+    at this part so as to lie close to the former.
+
+    Draw the three views shown in fig. 6 to the same scale as the last
+    exercise.
+
+    The plates are 7/16 inch thick. All other dimensions to be
+    obtained from table for single riveted lap joints.
+
+    EXERCISE 9: _Corner of Wrought-iron Tank._--This exercise is to
+    illustrate the connection of plates which are at right angles to
+    one another by means of _angle irons_. Fig. 7 is a plan and
+    elevation of the corner of a wrought-iron tank. The sides of the
+    tank are riveted to a vertical angle iron, the cross section of
+    which is clearly shown in the plan. Another angle iron of the same
+    dimensions is used in the same way to connect the sides with the
+    bottom. The sides do not come quite up to the corner of the
+    vertical angle iron, excepting at the bottom where the horizontal
+    angle iron comes in. At this point the vertical plates meet one
+    another, and the edge formed is rounded over to fit the interior
+    of the bend of the horizontal angle iron so as to make the joint
+    tight. Draw half size.
+
+    The dimensions are as follows: angle irons 2-1/2 inches x 2-1/2
+    inches x 3/8 inch; plates 3/8 inch thick; rivets 11/16 inch
+    diameter and 2 inches pitch.
+
+    EXERCISE 10: _Gusset Stay._--In order that the flat ends of a
+    steam boiler may not be bulged out by the pressure of the steam
+    they are strengthened by means of stays. One form of boiler stay,
+    called a 'gusset stay,' is shown in fig. 8. This stay consists of
+    a strip of wrought-iron plate which passes in a diagonal direction
+    from the flat end of the boiler to the cylindrical shell. One end
+    of this plate is placed between and riveted to two angle irons
+    which are riveted to the shell of the boiler. A similar
+    arrangement connects the other end of the stay plate to the flat
+    end of the boiler. In this example the stay or gusset plate is 3/4
+    of an inch thick; the angle irons are 4 inches broad and 1/2 inch
+    thick. The rivets are 1 inch in diameter. The same figure also
+    illustrates the most common method of connecting the ends of a
+    boiler to the shell. The end plates are _flanged_ or bent over at
+    right angles and riveted to the shell as shown. The radius of the
+    inside curve at the angle of the flange is 1-1/4 inches. Draw this
+    example to a scale of 3 inches to 1 foot.
+
+[Illustration: FIG. 6.]
+
+[Illustration: FIG. 7.]
+
+[Illustration: FIG. 8.]
+
+
+
+
+III. SCREWS, BOLTS, AND NUTS.
+
+
+_Screw Threads._--The various forms of screw threads used in machine
+construction are shown in fig. 9. The _Whitworth_ =V= thread is shown at
+(_a_). This is the standard form of triangular thread used in this
+country. The angle between the sides of the =V= is 55 deg., and one-sixth of
+the total depth is rounded off both at the top and bottom. At (_b_) is
+shown the _Sellers_ =V= thread, which is the standard triangular thread
+used by engineers in America. In this form of thread the angle between
+the sides of the =V= is 60 deg., and one-eighth of the total depth is cut
+square off at the top and bottom. The _Square_ thread is shown at (_c_).
+This form is principally used for transmitting motion.
+
+[Illustration: FIG. 9.]
+
+Comparing the triangular and square threads, the former is the stronger
+of the two; but owing to the normal pressure on the =V= thread being
+inclined to the axis of the screw, that pressure must be greater than
+the pressure which is being transmitted by the screw; and therefore,
+seeing that the normal pressure on the square thread is parallel, and
+therefore equal to the pressure transmitted in the direction of the axis
+of the screw, the friction of the =V= thread must be greater than the
+friction of the square thread. In the case of the triangular thread
+there is also a tendency of the pressure to burst the nut. The
+_Buttress_ thread shown at (_e_) is designed to combine the advantages
+of the =V= and square threads, but it only has these advantages when the
+pressure is transmitted in one direction; if the direction of the
+pressure be reversed, the friction and bursting action on the nut are
+even greater than with the =V= thread, because of the greater
+inclination of the slant side of the buttress thread. The angles of the
+square thread are frequently rounded to a greater or less extent to
+render them less easily damaged. If this rounding is carried to excess
+we get the _Knuckle_ thread shown at (_d_). The rounding of the angles
+increases both the strength and the friction.
+
+    EXERCISE 11: _Forms of Screw Threads._--Draw to a scale of three
+    times full size the sections of screw threads as shown in fig. 9.
+    The pitch for the Whitworth, Sellers, and buttress threads to be
+    3/8 inch, and the pitch of the square and knuckle threads to be 1/2
+    inch.
+
+_Dimensions of Whitworth Screws._
+
+  +-----------------------------------+
+  | Diameter |   Number   | Diameter  |
+  | of screw | of threads | at bottom |
+  |          |  per inch  | of thread |
+  +----------+------------+-----------+
+  |  1/8     |    40      |   .093    |
+  |  3/16    |    24      |   .134    |
+  |  1/4     |    20      |   .186    |
+  |  5/16    |    18      |   .241    |
+  |  3/8     |    16      |   .295    |
+  |  7/16    |    14      |   .346    |
+  |  1/2     |    12      |   .393    |
+  |  5/8     |    11      |   .508    |
+  |  3/4     |    10      |   .622    |
+  |  7/8     |     9      |   .733    |
+  |   1      |     8      |   .840    |
+  |  1-1/8   |     7      |   .942    |
+  |  1-1/4   |     7      |  1.067    |
+  |  1-3/8   |     6      |  1.162    |
+  |  1-1/2   |     6      |  1.286    |
+  |  1-5/8   |     5      |  1.369    |
+  |  1-3/4   |     5      |  1.494    |
+  |  1-7/8   |   4-1/2    |  1.590    |
+  |   2      |   4-1/2    |  1.715    |
+  |  2-1/4   |     4      |  1.930    |
+  |  2-1/2   |     4      |  2.180    |
+  |  2-3/4   |   3-1/2    |  2.384    |
+  |   3      |   3-1/2    |  2.634    |
+  |  3-1/4   |   3-1/4    |  2.856    |
+  |  3-1/2   |   3-1/4    |  3.106    |
+  |  3-3/4   |     3      |  3.323    |
+  |   4      |     3      |  3.573    |
+  |  4-1/4   |   2-7/8    |  3.805    |
+  |  4-1/2   |   2-7/8    |  4.055    |
+  |  4-3/4   |   2-3/4    |  4.284    |
+  |   5      |   2-3/4    |  4.534    |
+  |  5-1/4   |   2-5/8    |  4.762    |
+  |  5-1/2   |   2-5/8    |  5.012    |
+  |  5-3/4   |   2-1/2    |  5.238    |
+  |   6      |   2-1/2    |  5.488    |
+  +-----------------------------------+
+
+_Gas Threads_[1] (_Whitworth Standard_).
+
+[1] Used for wrought-iron and brass tubes.
+
+  +-------------------------------------------------------------+
+  | Diameter of Screw | 1/8 | 1/4 | 3/8 | 1/2 | 5/8 | 3/4 |  1  |
+  +-------------------+-----+-----+-----+-----+-----+-----+------
+  | Number of threads |     |     |     |     |     |     |     |
+  |     per inch      | 28  | 19  | 19  |  14 |  14 |  14 | 11  |
+  +-------------------------------------------------------------+
+
+  +-------------------------------------------------+
+  | Diameter of Screw | 1-1/4 | 1-1/2 | 1-3/4 |  2  |
+  +-------------------+-------+-------+-------+-----+
+  | Number of threads |       |       |       |     |
+  |     per inch      |  11   |  11   |  11   |  11 |
+  +-------------------------------------------------+
+
+_Representation of Screws._--The correct method of representing screw
+threads involves considerable trouble, and is seldom adopted by
+engineers for working drawings. For an explanation of the method see the
+author's Text-book on Practical Solid Geometry, Part II., problem 134. A
+method very often adopted on working drawings is shown in fig. 15; here
+the thin lines represent the points, and the thick lines the roots of
+the threads. At fig. 16 is shown a more complete method. The simplest
+method is illustrated by figs. 10, 11, 13, and 14.
+
+Here dotted lines are drawn parallel to the axis of the screw as far as
+it extends, and at a distance from one another equal to the diameter of
+the screw at the bottom of the thread.
+
+[Illustration: FIG. 10.]
+
+[Illustration: FIG. 11.]
+
+_Forms of Nuts._--The most common form of nut is the hexagonal shown in
+figs. 10, 13, 14, 15, and 16; next to this comes the square nut shown in
+fig. 11. The method of drawing these nuts will be understood by
+reference to the figures; the small circles indicate the centres, and
+the inclined lines passing through them the radii of the curves which
+represent the chamfered or bevelled edge of the nut. In all the figures
+but the first the chamfer is just sufficient to touch the middle points
+of the sides, and in these cases the drawing of the nut is simpler.
+
+[Illustration: FIG. 12.]
+
+[Illustration: FIG. 13.]
+
+[Illustration: FIG. 14.]
+
+_Forms of Bolts._--At (_a_), fig. 12, is shown a bolt with a square head
+and a square neck. If this form of bolt is passed through a square hole
+the square neck prevents the bolt from turning when the nut is being
+screwed up. Instead of a square neck a snug may be used for the same
+purpose, as shown on the cup-headed bolt at (_b_). The snug fits into a
+short groove cut in the side of the hole through which the bolt passes.
+At (_a_) the diagonal lines are used to distinguish the flat side of the
+neck from the round part of the bolt above it. At (_c_) is shown a
+tee-headed bolt, and at (_d_) an eye-bolt. Fig. 13 represents a hook
+bolt. A bolt with a countersunk head is shown in fig. 11. If the
+countersunk head be lengthened so as to take up the whole of the
+unscrewed part of the bolt, we get the taper bolt shown in fig. 14,
+which is often used in the couplings of the screw shafts of steamships.
+The taper bolt has the advantage of having no projecting head, and it
+may also be made a tight fit in the hole with less trouble than a
+parallel bolt. Bolts may also have hexagonal heads.
+
+[Illustration: FIG. 15]
+
+[Illustration: FIG. 16]
+
+_Studs_, or _stud bolts_, are shown in figs. 15 and 16; that in fig. 15
+is a _plain stud_, while that in fig. 16 has an intermediate collar
+forged upon it, and is therefore called a _collared stud_.
+
+_Proportions of Nuts and Bolt-heads._--In the hexagonal nut the diameter
+D across the flats is 1-1/2_d_ + 1/8, where _d_ is the diameter of the
+bolt. The same rule gives the width of a square nut across the flats. A
+rule very commonly used in making drawings of hexagonal nuts is to make
+the diameter D, across the angles equal to 2_d_. H, the height of the
+nut, is equal to the diameter of the bolt. In square and hexagonal
+headed bolts the height of the head varies from _d_ to 2/3_d_; the other
+dimensions are the same as for the corresponding nuts.
+
+_Washers_ are flat, circular, wrought-iron plates, having holes in their
+centres of the same diameter as the bolts on which they are used. The
+object of the washer is to give a smooth bearing surface for the nut to
+turn upon, and it is used when the surfaces of the pieces to be
+connected are rough, or when the bolt passes through a hole larger than
+itself, as shown in fig. 10. The diameter of the washer is a little more
+than the diameter of the nut across the angles, and its thickness about
+1/8 of the diameter of the bolt.
+
+    EXERCISE 12.--Draw, full size, the views shown in fig. 10 of an
+    hexagonal nut and washer for a bolt 1-1/4 inches in diameter. The
+    bolt passes through a hole 1-3/4 x 1-1/4. All the dimensions are
+    to be calculated from the rules which have just been given.
+
+    EXERCISE 13.--Draw, full size, the plan and elevation of the
+    square nut and bolt with countersunk head shown in fig. 11, to the
+    dimensions given.
+
+    EXERCISE 14.--Draw, full size, the elevation of the hook bolt with
+    hexagonal nut shown in fig. 13 to the dimensions given, and show
+    also a plan.
+
+    EXERCISE 15.--Draw, to a scale of 4 inches to a foot, the conical
+    bolt for a marine shaft coupling shown in fig. 14. All the parts
+    are of wrought iron.
+
+    EXERCISE 16.--Fig. 15 is a section of the mouth of a small
+    steam-engine cylinder, showing how the cover is attached; draw
+    this full size.
+
+    EXERCISE 17.--Fig. 16 shows the central portion of the
+    india-rubber disc valve which is described on page 68. A is the
+    central boss of the grating, into which is screwed the stud B,
+    upon which is forged the collar C. The upper part of the stud is
+    screwed, and carries the guard D and an hexagonal nut E. F is the
+    india-rubber. The grating and guard are of brass. The stud and nut
+    are of wrought iron. Draw full size the view shown.
+
+_Lock Nuts._--In order that a nut may turn freely upon a bolt, there is
+always a very small clearance space between the threads of the nut and
+those of the bolt. This clearance is shown exaggerated at (_a_), fig.
+17, where A is a portion of a bolt within a nut B. Suppose that the bolt
+is stretched by a force W. When the nut B is screwed up, the upper
+surfaces of the projecting threads of the nut will press on the under
+surfaces of the threads of the bolt with a force P equal and opposite
+to W, as shown at (_b_), fig. 17. When in this condition the nut has no
+tendency to slacken back, because of the friction due to the pressure on
+the nut. Now suppose that the tension W on the bolt is momentarily
+diminished, then the friction which opposes the turning of the nut may
+be so much diminished that a vibration may cause it to slacken back
+through a small angle. If this is repeated a great many times the nut
+may slacken back so far as to become useless.
+
+[Illustration: FIG. 17.]
+
+[Illustration: FIG. 18.]
+
+A very common arrangement for locking a nut is shown at (_a_), fig. 18.
+C is an ordinary nut, and B one having half the thickness of C. B is
+first screwed up tight so as to act on the bolt, as shown at (_b_), fig.
+17. C is then screwed on top of B. When C is almost as tight as it can
+be made, it is held by one spanner, while B is turned back through a
+small angle with another. The action of the nuts upon the bolt and upon
+one another is now as shown at (_b_), fig. 18. It will be seen that the
+nuts are wedged tight on to the bolt, and that this action is
+independent of the tension W in the bolt. The nuts will, therefore,
+remain tight after the tension in the bolt is removed.
+
+It is evident that if the nuts are screwed up in the manner explained,
+the outer nut C will carry the whole load on the bolt; hence C should be
+the thicker of the two nuts. In practice, the thin nut, called the lock
+nut, is often placed on the outside, for the reason that ordinary
+spanners are too thick to act on the thin nut when placed under the
+other.
+
+Another very common arrangement for locking a nut is shown in fig. 19. A
+is the bolt and B the nut, the lower part of which is turned circular. A
+groove C is also turned on the nut at this part. The circular part of
+the nut fits into a circular recess in one of the parts connected by the
+bolt. Through this part passes a set screw D, the point of which can be
+made to press on the nut at the bottom of the groove C. D is turned back
+when the nut B is being moved, and when B is tightened up, the set screw
+is screwed up so as to press hard on the bottom of the groove C. The nut
+B is thus prevented from slackening back. The screw thread is turned off
+the set screw at the point where it enters the groove on the nut.
+
+[Illustration: FIG. 19]
+
+The use of the groove for receiving the point of the set screw is this:
+The point of the set screw indents the nut and raises a bur which would
+interfere with the free turning of the nut in the recess if the bur was
+not at the bottom of a groove. Additional security is obtained by
+drilling a hole through the point of the bolt, and fitting it with a
+split pin E.
+
+Locking arrangements for nuts are exceedingly numerous, and many of them
+are very ingenious, but want of space prevents us describing them. We
+may point out, however, that many very good locking arrangements have
+the defect of only locking the nut at certain points of a revolution,
+say at every 30 deg.. It will be noticed that the two arrangements which we
+have described are not open to this objection.
+
+    EXERCISE 18.--Draw, full size, a plan, front elevation, and side
+    elevation of the arrangement of nuts shown in fig. 18, for a bolt
+    7/8 inch diameter.
+
+    EXERCISE 19.--Draw the plan and elevation of the nut and locking
+    arrangement shown in fig. 19. Make also an elevation looking in
+    the direction of the arrow. Scale 6 inches to a foot.
+
+
+
+
+IV. KEYS.
+
+
+_Keys_ are wedges, generally rectangular in section, but sometimes
+circular; they are made of wrought iron or steel, and are used for
+securing wheels, pulleys, cranks, &c., to shafts.
+
+[Illustration: Fig. 20.]
+
+Various sections of keys are shown in fig. 20. At (_a_) is the _hollow_
+or _saddle key_. With this form of key it is not necessary to cut the
+shaft in any way, but its holding power is small, and it is therefore
+only used for light work. At (_b_) is the _key on a flat_, sometimes
+called a _flat key_. The holding power of this key is much greater than
+that of the saddle key. At (_c_) is the _sunk key_, a very secure and
+very common form.
+
+The part of the shaft upon which a key rests is called the _key bed_ or
+_key way_, and the recess in the boss of the wheel or pulley into which
+the key fits is called the _key way_; both are also called _key seats_.
+With saddle, flat, and sunk keys the key bed is parallel to the axis of
+the shaft; but the key way is deeper at one end than the other to
+accommodate the taper of the key. The sides of the key are parallel.
+
+The _round key_ or taper pin shown at (_d_) is in general only used for
+wheels or cranks which have been previously shrunk on to their shafts or
+forced on by great pressure. After the wheel or crank has been shrunk
+on, a hole is drilled, half into the shaft and half into the wheel or
+crank, to receive the pin.
+
+When the point of a key is inaccessible the other end is provided with a
+_gib head_ as shown at (_e_), to enable the key to be withdrawn.
+
+A _sliding_ or _feather key_ secures a piece to a shaft so far as to
+prevent the one from rotating without the other, but allows of relative
+motion in the direction of the axis of the shaft. This form of key has
+no taper, and it is secured to the piece carried by the shaft, but is
+made a _sliding fit_ in the key way of the shaft. In one form of feather
+key the part within the piece carried by the shaft is dovetailed as
+shown at (_f_). In another form the key has a round projecting pin
+forged upon it, which enters a corresponding hole as shown at (_g_). The
+feather key may also be secured to the piece carried by the shaft by
+means of one or more screws as shown at (_h_). The key way in the shaft
+is made long enough to permit of the necessary sliding motion.
+
+_Cone Keys._--These are sometimes fitted to pulleys, and are shown in
+fig. 32, page 38. In this case the eye of the pulley is tapered and is
+larger than the shaft. The space between the shaft and the boss of the
+pulley is filled with three _saddle_ or _cone keys_. These keys are made
+of cast iron and are all cast together, and before being divided the
+casting is bored to fit the shaft and turned to fit the eye of the
+pulley. By this arrangement of keys the same pulley may be fixed on
+shafts of different diameters by using keys of different thicknesses;
+also the pulley may be bored out large enough to pass over any boss
+which may be forged on the shaft.
+
+_Proportions of Keys._--The following rules are taken from Unwin's
+'Machine Design,' pp. 142-43.
+
+  Diameter of eye of wheel, or boss of shaft = _d_.
+  Width of key                               = 3/4_d_ + 1/8.
+  Mean thickness of sunk key                 = 1/8_d_ + 1/8.
+         "          key on flat              = 1/16_d_ + 1/16.
+
+The following table gives dimensions agreeing with average practice.
+
+_Dimensions of Keys._
+
+  D   = diameter of shaft.
+  B   = breadth of key.
+  T   = thickness of sunk key.
+  T_{1} = thickness of flat key, also = thickness of saddle key. Taper
+  of key 1/8 inch per foot of length, _i.e._ 1 in 96.
+
+  +---------------------------------------------------------------+
+  |  D  | 3/4 |  1  | 1-1/4 | 1-1/2 | 1-3/4 |  2  | 2-1/4 | 2-1/2 |
+  +-----+-----+-----+-------+-------+-------+-----+-------+-------+
+  |  B  | 5/16| 3/8 | 7/16  |  1/2  | 9/16  | 5/8 | 11/16 | 11/16 |
+  |  T  | 1/4 | 1/4 |  1/4  | 5/16  | 5/16  | 5/16|  3/8  |  3/8  |
+  |T_{1}| 3/16| 3/16|  3/16 | 3/16  |  1/4  | 1/4 |  1/4  | 5/16  |
+  +---------------------------------------------------------------+
+
+  +-------------------------------------------------------------------+
+  |  D  | 2-3/4 |  3  | 3-1/2 |   4   | 4-1/2 |   5   | 5-1/2 |   6   |
+  +-----+-------+-----+-------+-------+-------+-------+-------+-------+
+  |  B  |  3/4  | 7/8 |   1   | 1-1/8 | 1-1/4 | 1-3/8 | 1-1/2 | 1-5/8 |
+  |  T  |  3/8  | 7/16|  1/2  |  1/2  | 9/16  |  5/8  | 11/16 |  3/4  |
+  |T_{1}|  5/16 | 5/16|  3/8  | 7/16  |  1/2  |  1/2  |  9/16 |  5/8  |
+  +-------------------------------------------------------------------+
+
+  +-------------------------------------------------------+
+  |  D  |   7   |   8   |   9   |   10   |   11   |   12  |
+  +-----+-------+-------+-------+--------+--------+-------+
+  |  B  | 1-7/8 | 2-1/8 | 2-3/8 | 2-5/8  | 2-7/8  | 3-1/8 |
+  |  T  | 13/16 | 15/16 |   1   | 1-1/16 | 1-3/16 | 1-1/4 |
+  |T_{1}| 11/16 |  3/4  |  7/8  | 15/16  | 1-1/16 | 1-1/8 |
+  +-------------------------------------------------------+
+
+
+
+
+V. SHAFTING.
+
+
+Shafting is nearly always cylindrical and made of wrought iron or steel.
+Cast iron is rarely used for shafting.
+
+_Axles_ are shafts which are subjected to bending without twisting.
+
+The parts of a shaft or axle which rest upon the bearings or supports
+are called _journals_, _pivots_, or _collars_.
+
+In journals the supporting pressure is at right angles to the axis of
+the shaft, while in pivots and collars the pressure is parallel to that
+axis.
+
+Shafts may be solid or hollow. Hollow shafts are stronger than solid
+shafts for the same weight of material. Thus a hollow shaft having an
+external diameter of 10-1/4 inches and an internal diameter of 7 inches
+would have about the same weight as a solid shaft of the same material
+7-1/2 inches in diameter, but the former would have about double the
+strength of the latter. Hollow shafts are also stiffer and yield less to
+bending action than solid shafts, which in some cases, as in propeller
+shafts, is an objection.
+
+
+
+
+VI. SHAFT COUPLINGS.
+
+
+For convenience of making and handling, shafts used for transmitting
+power are generally made in lengths not exceeding 30 feet. These lengths
+are connected by couplings, of which we give several examples.
+
+[Illustration: FIGS. 21 and 22.]
+
+_Solid_, _Box_, or _Muff Couplings._--One form of box coupling is shown
+in fig. 21. Here the ends of the shafts to be connected butt against one
+another, meeting at the centre of the box, which is made of cast iron.
+The shafts are made to rotate as one by being secured to the box by two
+wrought-iron or steel keys, both driven from the same end of the box. A
+clearance space is left between the head of the forward key and the
+point of the hind one, to facilitate the driving of them out, as then
+only one key needs to be started at a time. Sometimes a single key the
+whole length of the box is used, in which case it is necessary that the
+key ways in the shafts be of exactly the same depth.
+
+The half-lap coupling, introduced by Sir William Fairbairn, is shown in
+fig. 22. In this form of box coupling the ends of the shafts overlap
+within the box. It is evident that one shaft cannot rotate without the
+other as long as the box remains over the lap. To keep the box in its
+place it is fitted with a saddle key.
+
+It will be noticed that the lap joint is sloped in such a way as to
+prevent the two lengths of shaft from being pulled asunder by forces
+acting in the direction of their length.
+
+Half-lap couplings are not used for shafts above 5 inches in diameter.
+
+It may here be pointed out that the half-lap coupling is expensive to
+make, and is now not much used.
+
+As shafts are weakened by cutting key ways in them, very often the ends
+which carry couplings are enlarged in diameter, as shown in fig. 21, by
+an amount equal to the thickness of the key. An objection to this
+enlargement is that wheels and pulleys require either that their bosses
+be bored out large enough to pass over it, or that they be split into
+halves, which are bolted together after being placed on the shaft.
+
+_Dimensions of Box Couplings._
+
+  D     = diameter of shaft.
+  T     = thickness of metal in box.
+  L     = length of box for butt coupling.
+  L_{1} = length of box for lap coupling.
+  _l_   = length of lap.
+  D_{1} = diameter of shaft at lap.
+
+  +---------------------------------------------------------------+
+  |   D   | 1-1/2  |    2   |  2-1/2  |   3   |   3-1/2  |   4    |
+  +-------+--------+--------+---------+-------+----------+--------+
+  | T     | 1-1/8  | 1-5/16 | 1-1/2   | 1-3/4 |  1-15/16 |  2-1/8 |
+  | L     | 5-3/4  | 7      | 8-1/4   | 9-1/2 | 10-3/4   | 12     |
+  | L_{1} | 4-1/8  | 5-1/4  | 6-3/8   | 7-1/2 |  8-5/8   |  9-3/4 |
+  | _l_   | 1-7/16 | 1-7/8  | 2-5/16  | 2-3/4 |  3-3/16  |  3-5/8 |
+  | D_{2} | 2-5/16 | 3      | 3-11/16 | 4-3/8 |  5-1/16  |  5-3/4 |
+  +---------------------------------------------------------------+
+
+  +----------------------------------------------+
+  |   D   |  4-1/2  |   5    |  5-1/2 |     6    |
+  +-------+---------+--------+--------+----------+
+  | T     |  2-5/16 |  2-1/2 |  2-3/4 |  2-15/16 |
+  | L     | 13-1/4  | 14-1/2 | 15-3/4 | 17       |
+  | L_{1} | 10-7/8  | 12     |  --    |   --     |
+  | _l_   |  4-1/16 |  4-1/2 |  --    |   --     |
+  | D_{2} |  6-7/16 |  7-1/8 |  --    |   --     |
+  +----------------------------------------------+
+
+  Slope of lap 1 in 12.
+
+    EXERCISE 20: _Solid Butt Coupling._--From the above table of
+    dimensions make a longitudinal and a transverse section of a solid
+    butt coupling for a shaft 2-1/2 inches in diameter. Scale 6 inches
+    to a foot.
+
+    EXERCISE 21: _Fairbairn's Half-Lap Coupling._--Make the same views
+    as in the last exercise of a half-lap coupling for a 3-inch shaft
+    to the dimensions in the above table. Scale 6 inches to a foot.
+
+_Flange Couplings._--The form of coupling used for the shafts of marine
+engines is shown in fig. 23. The ends of the different lengths of shaft
+have flanges forged on them, which are turned along with the shaft.
+These flanges butt against one another, and are connected by bolts.
+These bolts may be parallel or tapered; generally they are tapered. A
+parallel bolt must have a head, but a tapered bolt will act without one.
+In fig. 23 the bolts are tapered, and also provided with heads. In fig.
+14, page 17, is shown a tapered bolt without a head. The variation of
+diameter in tapered bolts is 3/8 of an inch per foot of length.
+
+[Illustration: FIG. 23.]
+
+Sometimes a projection is formed on the centre of one flange which fits
+into a corresponding recess in the centre of the other, for the purpose
+of ensuring the shafts being in line.
+
+Occasionally a cross-key is fitted in between the flanges, being sunk
+half into each, for the purpose of diminishing the shearing action on
+the bolts.
+
+    EXERCISE 22: _Marine Coupling._--Draw the elevation and section of
+    the coupling shown in fig. 23; also an elevation looking in the
+    direction of the arrow. Scale 3 inches to a foot.
+
+The following table gives the dimensions of a few marine couplings taken
+from actual practice.
+
+_Examples of Marine Couplings._
+
+  +--------------------------------------------------------------------+
+  | Diameter of shaft  |2-3/8 | 9-3/4 | 12-7/8 |16-1/2 | 22-1/2 |  23  |
+  +--------------------+------+-------+--------+-------+--------+------+
+  |Diameter of flange  |  6   |  19   |   24   |  32   |   35   |  38  |
+  |Thickness of flange |  1   | 2-3/4 |  3-1/8 | 4-1/4 |    6   |   5  |
+  |Diameter of bolts   | 3/4  | 2-3/4 | 2-11/16| 3-1/2 |  4-1/4 | 4-1/4|
+  |Number of bolts     |  3   |   6   |    6   |   8   |    9   |   8  |
+  |Diameter of bolt    |      |       |        |       |        |      |
+  |  circle            |4-1/8 | 14-1/8|18-13/16|  25   | 28-3/4 |30-3/8|
+  +--------------------------------------------------------------------+
+
+  All the above dimensions are in inches.
+
+    EXERCISE 23.--Select one of the couplings from the above table, and
+    make the necessary working drawings for it to a suitable scale.
+
+The cast-iron flange coupling is shown in fig. 24. In this kind of
+coupling a cast-iron centre or boss provided with a flange is secured to
+the end of each shaft by a sunk key driven from the face of the flange.
+These flanges are then connected by bolts and nuts as in the marine
+coupling.
+
+To ensure the shafts being in line the end of one projects into the
+flange of the other.
+
+In order that the face of each flange may be exactly perpendicular to
+the axis of the shaft they should be 'faced' in the lathe, after being
+keyed on to the shaft.
+
+If the coupling is in an exposed position, where the nuts and bolt-heads
+would be liable to catch the clothes of workmen or an idle driving band
+which might come in the way, the flanges should be made thicker, and be
+provided with recesses for the nuts and bolt-heads.
+
+[Illustration: FIG. 24.]
+
+_Dimensions of Cast-iron Flange Couplings._
+
+  +--------------------------------------------------------------------+
+  |        |Diameter|         |        |Depth |      |Diameter|Diameter|
+  |Diameter|  of    |Thickness|Diameter|  at  |Number|   of   | of bolt|
+  |of shaft| flange |of flange| of boss| boss |  of  | bolts  | circle |
+  |   D    |    F   |    T    |   B    |   L  | bolts|   d    |    C   |
+  +--------|--------|---------|--------|------|------|--------|--------+
+  | 1-1/2  |  7-1/4 |    7/8  | 3-1/2  |2-5/8 |   3  |5/8     | 5-1/2  |
+  | 2      |  8-7/8 |  1-1/16 | 4-3/8  |3-3/16|   4  |     3/4| 6-3/4  |
+  | 2-1/2  | 10-5/8 |  1-1/4  | 5-5/16 |3-3/4 |   4  |7/8     | 8-1/8  |
+  | 3      | 12-3/8 |  1-7/16 | 6-1/4  |4-5/16|   4  |      1 | 9-1/2  |
+  | 3-1/2  | 13-1/8 |  1-5/8  | 7-1/8  |4-7/8 |   4  | 1      |10-5/16 |
+  | 4      | 14     |  1-3/4  | 8      |5-7/16|   6  |      1 |11-1/4  |
+  | 4-1/2  | 15-5/8 |  2      | 8-7/8  |6     |   6  |1-1/8   |12-1/2  |
+  | 5      | 17-3/8 |  2-1/8  | 9-13/16|6-5/8 |   6  |   1-1/4|13-13/16|
+  | 5-1/2  | 18-1/4 |  2-5/16 |10-3/4  |7-1/4 |   6  |1-1/4   |14-3/4  |
+  | 6      | 19-7/8 |  2-1/2  |11-5/8  |7-3/4 |   6  |   1-3/8|   16   |
+  +--------------------------------------------------------------------+
+
+The projection of the shaft _p_ varies from 1/4 inch in the small shafts
+to 1/2 inch in the large ones.
+
+    EXERCISE 24: _Cast-iron Flange Coupling._--Draw the views shown in
+    fig. 24 of a cast-iron flange coupling, for a shaft 4-1/2 inches in
+    diameter, to the dimensions given in the above table. Scale 4 inches
+    to a foot.
+
+
+
+
+VII. BEARINGS  FOR  SHAFTS.
+
+
+An example of a very simple form of bearing is shown in fig. 25, which
+represents a brake shaft carrier of a locomotive tender. The bearing in
+this example is made of cast iron and in one piece. Through the
+oval-shaped flange two bolts pass for attaching the bearing to the
+wrought-iron framing of the tender. With this form of bearing there is
+no adjustment for wear, so that when it becomes worn it must be renewed.
+
+[Illustration: FIG. 25.]
+
+    EXERCISE 25: _Brake Shaft Carrier._--Draw the elevation and
+    sectional plan of the bearing shown in fig. 25. Draw also a
+    vertical section through the axis. The latter view to be projected
+    from the first elevation. Scale 6 inches to a foot.
+
+_Pillow Block_, _Plummer Block_, or _Pedestal_.--The ordinary form of
+plummer block is represented in fig. 26. A is the block proper, B the
+sole through which pass the holding-down bolts. C is the cap. Between
+the block and the cap is the brass bush, which is in halves, called
+_brasses_ or _steps_. The bed for the steps in this example is
+cylindrical, and is prepared by the easy process of boring. The steps
+are not supported throughout their whole length, but at their ends only
+where fitting strips are provided as shown. As the wear on a step is
+generally greatest at the bottom, it is made thicker there than at the
+sides, except where the fitting strips come in. To prevent the steps
+turning within the block they are generally furnished with lugs, which
+enter corresponding recesses in the block and cover.
+
+[Illustration: FIG. 26]
+
+In the block illustrated the journal is lubricated by a _needle
+lubricator_; this consists of an inverted glass bottle fitted with a
+wood stopper, through a hole in which passes a piece of wire, which has
+one end in the oil within the bottle, and the other resting on the
+journal of the shaft. The wire or needle does not fill the hole in the
+stopper, but if the needle is kept from vibrating the oil does not
+escape owing to capillary attraction. When, however, the shaft rotates,
+the needle begins to vibrate, and the oil runs down slowly on to the
+journal; oil is therefore only used when the shaft is running.
+
+    EXERCISE 26: _Pillow Block for a Four-inch Shaft._--Draw the views
+    shown of this block in fig. 26. Make also separate drawings, full
+    size, of one of the steps. Scale 6 inches to a foot.
+
+_Proportions of Pillow Blocks._--The following rules may be used for
+proportioning pillow blocks for shafts up to 8 inches diameter. It
+should be remembered that the proportions used by different makers vary
+considerably, but the following rules represent average practice.
+
+  Diameter of journal                     = _d_.
+  Length of journal                       = _l_.
+  Height to centre                        = 1.05_d_ + .5.
+  Length of base                          = 3.6_d_ + 5.
+  Width of base                           = .8_l_.
+      "    block                          = .7_l_.
+  Thickness of base                       = .3_d_ + .3.
+      "        cap                        = .3_d_ + .4.
+  Diameter of bolts                       = .25_d_ + .25.
+  Distance between centres of cap bolts   = 1.6_d_ + 1.5.
+      "         "             base bolts  = 2.7_d_ + 4.2.
+  Thickness of step at bottom             = _t_ = .09_d_ + .15.
+      "         "      sides              = 3/4 _t_.
+
+The length of the journal varies very much in different cases, and
+depends upon the speed of the shaft, the load which it carries, the
+workmanship of the journal and bearing, and the method of lubrication.
+For ordinary shafting one rule is to make _l_ = _d_ + 1. Some makers use
+the rule _l_ = 1.5_d_; others make _l_ = 2_d_.
+
+    EXERCISE 27: _Design for Pillow Block._--Make the necessary
+    working drawings for a pillow block for a shaft 5 inches in
+    diameter, and having a journal 7 inches long.
+
+[Illustration: FIG. 27.]
+
+_Brackets._--When a pillow block has to be fixed to a wall or column a
+bracket such as that shown in figs. 27 and 28 may be used. The pillow
+block rests between the _joggles_ A A, and is bolted down to the bracket
+and secured in addition with keys at the ends of the base of the block,
+in the same manner as is shown, for the attachment of the bracket to
+the column.
+
+    EXERCISE 28: _Pillar Bracket._--Fig. 27 shows a side elevation and
+    part horizontal section, and fig. 28 shows an end elevation of a
+    pillar bracket for carrying a pillow block for a 3-inch shaft.
+    Draw these views _properly projected from one another_, showing
+    the pillow block, which is to be proportioned by the rules given
+    on page 32. Draw also a plan of the whole. Scale 4 inches to a
+    foot.
+
+[Illustration: FIG. 28.]
+
+_Hangers._--When a shaft is suspended from a ceiling it is carried by
+hangers, one form of which is shown in fig. 29, and which will be
+readily understood. The cap of the bearing, it will be noticed, is
+secured by means of a bolt, and also by a square key.
+
+    EXERCISE 29: _Shaft Hanger._--Draw the two elevations shown in
+    fig. 29, and also a sectional plan. The section to be taken at a
+    point 5 inches above the centre of the shaft. Scale 6 inches to a
+    foot.
+
+_Wall Boxes._--In passing from one part of a building to another a shaft
+may have to pass through a wall. In that case a neat appearance is given
+to the opening and a suitable support obtained for a pillow block by
+building into the wall a _wall box_, one form of which is shown in fig.
+30.
+
+    EXERCISE 30: _Wall Box._--Draw the views of the wall box shown in
+    fig. 30, and also a sectional plan; the plane of section to pass
+    through the box a little above the joggles for the pillow block.
+    Scale 3 inches to a foot.
+
+[Illustration: FIG. 29.]
+
+[Illustration: FIG. 30.]
+
+
+
+
+VIII. PULLEYS.
+
+
+_Velocity Ratio in Belt Gearing._--Let two pulleys A and B be connected
+by a belt, and let their diameters be D_{1} and D_{2}; and let their
+speeds, in revolutions per minute, be N_{1} and N_{2} respectively. If
+there is no slipping, the speeds of the rims of the pulleys will be the
+same as that of the belt, and will therefore be equal. Now the speed of
+the rim of A is evidently = D_{1} x 3.1416 x N_{1}; while the speed of
+the rim of B is = D_{2} x 3.1416 x N_{2}. Hence D_{1} x 3.1416 x N_{1} =
+D_{2} x 3.1416 x N_{2}, and therefore
+
+    N_{1}   D_{2}
+    ----- = -----.
+    N_{2}   D_{1}
+
+_Pulleys for Flat Bands._--In cross section the rim of a pulley for
+carrying a flat band is generally curved as shown in figs. 31 and 32,
+but very often the cross section is straight. The curved cross section
+of the rim tends to keep the band from coming off as long as the pulley
+is rotating. Sometimes the rim of the pulley is provided with flanges
+which keep the band from falling off.
+
+Pulleys are generally made entirely of cast iron, but a great many
+pulleys are now made in which the centre or nave only is of cast iron,
+the arms being of wrought iron cast into the nave, while the rim is of
+wrought sheet iron.
+
+The arms of pulleys when made of wrought iron are invariably straight,
+but when made of cast iron they are very often curved. In fig. 31, which
+shows an arrangement of two cast-iron pulleys, the arms are straight;
+while in fig. 32, which shows another cast-iron pulley, the arms are
+curved. Through unequal cooling, and therefore unequal contraction of a
+cast-iron, pulley in the mould, the arms are generally in a state of
+tension or compression; and if the arms are straight they are very
+unyielding, so that the result of this initial stress is often the
+breaking of an arm, or of the rim where it joins an arm. With the curved
+arm, however, its shape permits it to yield, and thus cause a diminution
+of the stress due to unequal contraction.
+
+The cross section of the arms of cast-iron pulleys is generally
+elliptical.
+
+[Illustration: Fig. 31.]
+
+    EXERCISE 31: _Fast and Loose Pulleys_.--Fig. 31 shows an
+    arrangement of fast and loose pulleys. A is the fast pulley,
+    secured to the shaft C by a sunk key; B is the loose pulley, which
+    turns freely upon the shaft. The loose pulley is prevented from
+    coming off by a collar D, which is secured to the shaft by a
+    tapered pin as shown. The nave or boss of the loose pulley is here
+    fitted with a brass liner, which may be renewed when it becomes
+    too much worn. Draw the elevations shown, completing the left-hand
+    one. Scale 6 inches to a foot.
+
+    By the above arrangement of pulleys a machine may be stopped or
+    set in motion at pleasure. When the driving band is on the loose
+    pulley the machine is at rest, and when it is on the fast pulley
+    the machine is in motion. The driving band is shifted from the one
+    pulley to the other by pressing on that side of the band which is
+    advancing towards the pulleys.
+
+[Illustration: FIG. 32.]
+
+    EXERCISE 32: _Cast-iron Pulley with Curved Arms and Cone
+    Keys_.--Draw a complete side elevation and a complete cross
+    section of the pulley represented in fig. 32 to a scale of 3
+    inches to a foot. In drawing the side elevation of the arms first
+    draw the centre lines as shown; next draw three circles for each
+    arm, one at each end and one in the middle; the centres of these
+    circles being on the centre line of the arm, and their diameters
+    equal to the widths of the arm at the ends and at the middle
+    respectively. Arcs of circles are then drawn to touch these three
+    circles. The centres and radii of these arcs may be found by
+    trial. The cone keys for securing the pulley to the shaft were
+    described on p. 23.
+
+_Pulleys for Ropes_.--Ropes made of hemp are now extensively used for
+transmitting power. These ropes vary in diameter from 1 inch to 2
+inches, and are run at a speed of about 4,500 feet per minute. The
+pulleys for these ropes are made of cast iron, and have their rims
+grooved as shown in fig. 33, which is a cross section of the rim of a
+pulley carrying three ropes. The angle of the V is usually 45 deg., and the
+rope rests on the sides of the groove, and not on the bottom, so that
+it is wedged in, and has therefore a good hold of the pulley. The
+diameter of the pulley should not be less than 30 times the diameter of
+the rope. Two pulleys connected by ropes should not be less than thirty
+feet apart from centre to centre, but this distance may be as much as
+100 feet.
+
+[Illustration: FIG. 33.]
+
+    EXERCISE 33: _Section of Rim of Rope Pulley._--Draw, half size,
+    the section of the rim of a rope pulley shown in fig. 33.
+
+
+
+
+IX. TOOTHED WHEELS.
+
+
+_Pitch Surfaces of Spur Wheels._--Let two smooth rollers be placed in
+contact with their axes parallel, and let one of them rotate about its
+axis; then if there is no slipping the other roller will rotate in the
+opposite direction with the same surface velocity; and if D_{1}, D_{2}
+be the diameters of the rollers, and N_{1}, N_{2} their speeds in
+revolutions per minute, it follows as in belt gearing that--
+
+    N_{1}   D_{2}
+    ----- = -----.
+    N_{2}   D_{1}
+
+If there be considerable resistance to the motion of the follower
+slipping may take place, and it may stop. To prevent this the rollers
+may be provided with teeth; then they become _spur wheels_; and if the
+teeth be so shaped that the ratio of the speeds of the toothed rollers
+at any instant is the same as that of the smooth rollers, the surfaces
+of the latter are called the _pitch surfaces_ of the former.
+
+_Pitch Circle._--A section of the pitch surface of a toothed wheel by a
+plane perpendicular to its axis is a circle, and is called a _pitch
+circle_. We may also say that the pitch circle is the edge of the pitch
+surface. The pitch circle is generally traced on the side of a toothed
+wheel, and is rather nearer the points of the teeth than the roots.
+
+_Pitch of Teeth._--The distance from the centre of one tooth to the
+centre of the next, or from the front of one to the front of the next,
+_measured at the pitch circle_, is called the _pitch of the teeth_. If D
+be the diameter of the pitch circle of a wheel, _n_ the number of teeth,
+and _p_ the pitch of the teeth, then D x 3.1416 = _n_ x _p_.
+
+[Illustration: FIG. 34.]
+
+By the diameter of a wheel is meant the diameter of its pitch circle.
+
+_Form and Proportions of Teeth._--The ordinary form of wheel teeth is
+shown in fig. 34. The curves of the teeth should be cycloidal curves,
+although they are generally drawn in as arcs of circles. It does not
+fall within the scope of this work to discuss the correct forms of wheel
+teeth. The student will find the theory of the teeth of wheels clearly
+and fully explained in Goodeve's 'Elements of Mechanism,' and in Unwin's
+'Machine Design.'
+
+The following proportions for the teeth of ordinary toothed wheels may
+be taken as representing average practice:--
+
+  Pitch of teeth             = _p_   = arc _a b c_ (fig. 34).
+  Thickness of tooth         = _b c_ = .48_p_.
+  Width of space             = _a b_ = .52_p_.
+  Total height of tooth              = _h_ = .7_p_.
+  Height of tooth above pitch line   = _k_ = .3_p_.
+  Depth of tooth below pitch line    = _l_ = .4_p_.
+  Width of tooth                     = 2_p_ to 3_p_.
+
+    EXERCISE 34: _Spur Wheel._--Fig. 35 shows the elevation and
+    sectional plan of a portion of a cast-iron spur wheel. The diameter
+    of the pitch circle is 23-7/8 inches, and the pitch of the teeth is
+    1-1/2 inches, so that there will be 50 teeth in the wheel. The
+    wheel has six arms. Draw a complete elevation of the wheel and a
+    half sectional plan, also a half-plan without any section. Draw
+    also a cross section of one arm. Scale 4 inches to a foot.
+
+[Illustration: FIG. 35.]
+
+_Mortise Wheels._--When two wheels gearing together run at a high speed
+the teeth of one are made of wood. These teeth, or cogs, as they are
+generally called, have tenons formed on them, which fit into mortises in
+the rim of the wheel. This wheel with the wooden teeth is called a
+_mortise wheel_. An example of a mortise wheel is shown in fig. 36.
+
+[Illustration: FIG. 36.]
+
+_Bevil Wheels._--In bevil wheels the pitch surfaces are parts of cones.
+Bevil wheels are used to connect shafts which are inclined to one
+another, whereas spur wheels are used to connect parallel shafts. In
+fig. 36 is shown a pair of bevil wheels in gear, one of them being a
+mortise wheel. At (_a_) is a separate drawing, to a smaller scale, of
+the pitch cones. The pitch cones are shown on the drawing of the
+complete wheels by dotted lines.
+
+The diameters of bevil wheels are the diameters of the bases of their
+pitch cones.
+
+    EXERCISE 35: _Pair of Bevil Wheels._--Draw the sectional elevation
+    of the bevil wheels shown in gear in fig. 36. Commence by drawing
+    the centre lines of the shafts, which in this example are at right
+    angles to one another; then draw the pitch cones shown by dotted
+    lines. Next put in the teeth which come into the plane of the
+    section, then complete the sections of the wheels. The pinion or
+    smaller wheel has 25 teeth, and the wheel has 50 teeth, which makes
+    the pitch a little over 3 inches. Each tooth of the mortise wheel
+    is secured as shown by an iron pin 5/16 inch diameter. Scale 3
+    inches to a foot.
+
+
+
+
+X. CRANKS AND CRANKED SHAFTS.
+
+
+The most important application of the crank is in the steam-engine,
+where the reciprocating rectilineal motion of the piston is converted
+into the rotary motion of the crank-shaft by means of the crank and
+connecting rod.
+
+At one time steam-engine cranks were largely made of cast iron, now they
+are always made of wrought iron or steel. The crank is either forged in
+one piece with the shaft, or it is made separately and then keyed to it.
+
+_Overhung Crank._--Fig. 37 shows a wrought-iron overhung crank. A is the
+crank-shaft, B the crank arm, provided at one end with a boss C, which
+is bored out to fit the shaft; at the other end of the crank arm is a
+boss D, which is bored out to receive the crank-pin E, which works in
+one end of the connecting rod. The crank is secured to the shaft by the
+sunk key F. It is also good practice to _shrink_ the crank on to the
+shaft. The process of shrinking consists of boring out the crank a
+little smaller than the shaft, and then heating it, which causes it to
+expand sufficiently to go on to the shaft. As the crank cools, it
+shrinks and grips the shaft firmly. The crank may also be shrunk on to
+the crank-pin, the latter being then riveted over as shown in fig. 37.
+
+[Illustration: FIG. 37.]
+
+A good plan to adopt in preference to the shrinking process is to force
+the parts together by hydraulic pressure. This method is adopted for
+placing locomotive wheels on their axles, and for putting in crank-pins.
+As to the amount of pressure to be used, the practice is to allow a
+force of 10 tons for every inch of diameter of the pin, axle, or shaft.
+
+Instead of being riveted in, the crank pin may be prolonged and screwed,
+and fitted with a nut. Another plan is to put a cotter through the crank
+and the crank-pin.
+
+The distance from the centre of the crank-shaft to the centre of the
+crank-pin is called the radius of the crank. The _throw_ of the crank is
+twice the radius. In a direct-acting engine the throw of the crank is
+equal to the stroke of the piston.
+
+    EXERCISE 36: _Wrought-iron Overhung Crank._--Draw the two
+    elevations shown in fig. 37, also a plan. Scale 1-1/2 inches
+    to a foot.
+
+    _Proportions of Overhung Cranks._
+
+      D   = diameter of shaft.
+      _d_ =    "       crank-pin.
+      Length of large boss = .9 D.
+      Diameter      "      = 1.8 D.
+      Length of small boss = 1.1 _d_.
+      Diameter      "      = 1.8 _d_.
+      Width of crank arm at centre of shaft     = 1.3 D.
+           "           "              crank-pin = 1.5 _d_.
+      The thickness of the crank arm may be roughly taken as = .7 D.
+
+    EXERCISE 37.--Design a wrought-iron crank for an engine having a
+    stroke of 4 feet. The crank-shaft is 9 inches in diameter, and
+    the crank-pin is 4-3/4 inches in diameter and 6-1/2 inches long.
+
+[Illustration: FIG. 38.]
+
+_Locomotive Cranked Axle._--As an example of a cranked shaft we take the
+cranked axle for a locomotive with inside cylinders shown in fig. 38;
+here the crank and shaft or axle are forged in one piece. A is the wheel
+seat, B the journal, C the crank-pin, and D and E the crank arms. Only
+one half of the axle is shown in fig. 38, but the other half is exactly
+the same. The cranks on the two halves are, however, at right angles to
+one another. The ends of the crank arms are turned in the lathe, the
+crank-pin ends being turned at the same time as the axle, and the other
+ends at the same time as the crank-pin. This consideration determines
+the centres for the arcs shown in the end view.
+
+    EXERCISE 38.--Draw to a scale of 2 inches to a foot the side and
+    end elevations of the locomotive cranked axle partly shown in
+    fig. 38. The distance between the centre lines of the cylinders
+    is 2 feet.
+
+[Illustration: FIG. 39.]
+
+_Built-up Cranks._--The form of cranked shaft shown in fig. 38 is
+largely used for marine engines, but for the very powerful engines now
+fitted in large ships this design of shaft is very unreliable, the
+built-up crank shown in fig. 39 being preferred, although it is much
+heavier than the other. It will be seen from the figure that the shaft,
+crank arms, and crank-pin are made separately. The arms are shrunk on to
+the pin and the shaft, and secured to the latter by sunk keys. These
+heavy shafts and cranks are generally made of steel.
+
+    EXERCISE 39.--Keeping to the dimensions marked in fig. 39, draw
+    the views there shown of a built-up crank-shaft for a marine
+    engine. Scale 3/4 inch to a foot.
+
+
+
+
+XI. ECCENTRICS.
+
+
+The _eccentric_ is a particular form of crank, being a crank in which
+the crank-pin is large enough to embrace the crank-shaft. In the
+eccentric what corresponds to the crank-pin is called the sheave or
+pulley. The advantage which an eccentric possesses over a crank is that
+the shaft does not require to be divided at the point where the
+eccentric is put on. The crank, however, has this advantage over the
+eccentric, namely, that it can be used for converting circular into
+reciprocating motion, or _vice versa_, while the eccentric can only be
+used for converting circular into reciprocating motion. This is owing to
+the great leverage at which the friction of the eccentric acts.
+
+The chief application of the eccentric is in the steam-engine, where it
+is used for working the valve gear.
+
+To permit of the sheave being placed on the shaft without going over the
+end (which could not be done at all in the case of a cranked axle, and
+would be a troublesome operation in most cases) it is generally made in
+two pieces, as shown in fig. 40, which represents one of the eccentrics
+of a locomotive. The two parts of the sheave are connected by two cotter
+bolts. The part which embraces the sheave is called the eccentric strap,
+and corresponds to, and is, in fact, a connecting rod end: the rod
+proceeding from this is called the eccentric rod.
+
+The distance from the centre of the sheave to the centre of the shaft is
+called the _radius_ or _eccentricity_ of the eccentric. The _throw_ is
+twice the eccentricity.
+
+The sheave is generally made of cast iron. The strap may be of brass,
+cast iron, or wrought iron; when the strap is made of wrought iron it is
+commonly lined with brass.
+
+[Illustration: FIG. 40.]
+
+    EXERCISE 40: _Locomotive Eccentric._--In fig. 40 D E is the
+    sheave, F H the strap, and K the eccentric rod. The sheave and
+    strap are made of cast iron, and the eccentric rod is made of
+    wrought iron. (_a_) is a vertical cross section through the
+    oil-box of the strap; (_b_) is a plan of the end of the eccentric
+    rod and part of the strap. All the nuts are locked by means of
+    cotters. Draw first the elevation, partly in section as shown.
+    Next draw two end elevations, one looking each way. Afterwards
+    draw a horizontal section through the centre, and also a plan.
+    Scale 4 inches to a foot.
+
+
+
+
+XII. CONNECTING RODS.
+
+
+The most familiar example of the use of a connecting rod is in the
+steam-engine, where it is used to connect the rotating crank with the
+reciprocating piston. The rod itself is made of wrought iron or steel,
+and is generally circular or rectangular in section. The ends of the rod
+are fitted with steps, which are held together in a variety of ways.
+
+_Strap End._--A form of connecting rod end, which is not so common as it
+used to be, is shown in fig. 41. At (_a_) is shown a longitudinal
+section with all the parts put together, while at (_b_), (_c_), _(d)_
+and (_e_) the details are shown separately. A B is the end of the rod
+which butts against the brass bush C D, which is in two pieces. A
+_strap_ E passes round the bush and on to the end of the rod as shown.
+The arms of the strap have rectangular holes in them, which are not
+quite opposite a similar hole in the rod when the parts are put
+together. If a wedge or _cotter_ F be driven into these three holes they
+will tend to come into line, and the parts of the bush will be pressed
+together. To prevent the cotter opening out the strap, and to increase
+the sliding surface, a _gib_ H is introduced. The gib is provided with
+horns at its ends to keep it in its place. Sometimes two gibs are used,
+one on each side of the cotter; this makes the sliding surface on both
+sides of the cotter the same. The cotter is secured by a set screw K.
+The unsectioned portion of fig. (_a_) to the right of the gib, or to the
+left of the cotter, is called the _clearance_ or _draught._
+
+[Illustration: FIG. 41.]
+
+    EXERCISE 41: _Connecting Rod End._--Make the following views of
+    the connecting rod end illustrated by fig. 41. First, a vertical
+    section, the same as shown at (_a_). Second, a horizontal section.
+    Third, side elevation. Fourth, a plan. Or the first and third
+    views may be combined in a half vertical section and half
+    elevation; and the second and fourth views may be combined in
+    a half horizontal section and half plan.
+
+    All the dimensions are to be taken from the detail drawings (_b_),
+    (_c_), (_d_), and (_e_), _but the details need not be drawn
+    separately_. The brass bush is shown at (_d_) by half elevation,
+    half vertical section, half plan, and half horizontal section.
+    The draught or clearance is 7-16ths of an inch.
+
+_Box End._--At (_a_), fig. 42, is shown what is known as a box end for a
+connecting rod. The part which corresponds to the loose strap in the
+last example is here forged in one piece with the connecting rod. In
+this form the brass bush is provided with a flange all round on one
+side, but on the opposite side the flange is omitted except at one end;
+this is to allow of the bush being placed within the end of the rod. The
+construction of the bush will be understood by reference to the sketch
+shown at (_b_). The bush is in two parts, which are pressed tightly
+together by means of a cotter. This cotter is prevented from slackening
+back by two set screws. Each set screw is cut off square at the point,
+and presses on the flat bottom of a very shallow groove cut on the side
+of the cotter.
+
+The top, bottom, and ends of this box end are turned in the lathe at the
+same time as the rod itself; this accounts for the curved sections of
+these parts.
+
+It is clear from the construction of a box end that it is only suitable
+for an overhung crank.
+
+    EXERCISE 42: _Locomotive Connecting Rod._--In fig. 42 is shown a
+    connecting rod for an outside cylinder locomotive. (_a_) is the
+    crank-pin end, and (_c_) the cross-head end. The end (_a_) has just
+    been described under the head 'box end.' We may just add that in
+    this particular example the brass bush is lined with white metal as
+    shown, and that the construction of the oil-box is the same as that
+    on the coupling rod end shown in fig. 44. The end (_c_) is forked,
+    and through the prongs of the fork passes the cross-head pin, of
+    which a separate dimensioned drawing is shown at (_d_). Observe
+    that the tapered parts A and B of this pin are parts of the same
+    cone. The rotation of the pin is prevented by a small key as shown.
+    The cross-head pin need not be drawn separately, and the isometric
+    projection of the bush at (_b_) may be omitted, but all the other
+    views shown are to be drawn to a scale of 6 inches to a foot.
+
+_Marine Connecting Rod._--The form of connecting rod shown in fig. 43 is
+that used in marine engines, but it is also used extensively in land
+engines. A B is the crank-pin end, and C the cross-head end. The end A B
+is forged in one piece, and after it is turned, planed, and bored it is
+slotted across, so as to cut off the cap A. The parts A and B are held
+together by two bolts as shown. This end of the rod is fitted with brass
+steps, which are lined with white metal. The cross-head end is forked,
+and through the prongs of the fork passes a pin D, which also passes
+through the cross-head, which is forged on to the piston rod or attached
+to it in some other way.
+
+[Illustration: FIG. 42.]
+
+[Illustration: FIG. 43.]
+
+    EXERCISE 43: _Marine Connecting Rod._--Draw all the views shown in
+    fig. 43 of one form of marine connecting rod. For detail drawings
+    of the locking arrangement for the nuts see fig. 19, page 21. Scale
+    4 inches to a foot.
+
+_Coupling Rods._--A rod used to transmit the motion of one crank to
+another is called a _coupling rod_. A familiar example of the use of
+coupling rods will be found in the locomotive. Coupling rods are made of
+wrought iron or steel, and are generally of rectangular section. The
+ends are now generally made solid and lined with solid brass bushes,
+_without any adjustment for wear_. This form of coupling rod end is
+found to answer very well in locomotive practice where the workmanship
+and arrangements for lubrication are excellent. When the brass bush
+becomes worn it is replaced by a new one.
+
+Fig. 44 shows an example of a locomotive coupling rod end for an outside
+cylinder engine. In this case it is desirable to have the crank-pin
+bearings for the coupling rods as short as possible, for a connecting
+rod and coupling rod in this kind of engine work side by side on the
+same crank-pin, which, being overhung, should be as short as convenient
+for the sake of strength. The requisite bearing surface is obtained by
+having a pin of large diameter. The brass bush is prevented from
+rotating by means of the square key shown. The oil-box is cut out of the
+solid, and has a wrought-iron cover slightly dovetailed at the edges.
+This cover fits into a check round the top inner edge of the box, which
+is originally parallel, but is made to close on the dovetailed edges of
+the cover by riveting. A hole in the centre of this cover, which gives
+access to the oil-box, is fitted with a screwed brass plug. The brass
+plug has a screwed hole in the centre, through which oil may be
+introduced to the box. Dust is kept out of the oil-box by screwing into
+the hole in the brass plug a common cork. The oil is carried slowly but
+regularly from the oil-box over to the bearing by a piece of cotton
+wick.
+
+[Illustration: FIG. 44.]
+
+    EXERCISE 44: _Coupling Rod End._--Draw first the side elevation and
+    plan, each partly in section as shown in fig. 44. Then instead of
+    the view to the left, which is an end elevation partly in section,
+    draw a complete end elevation looking to the right, and also a
+    complete vertical cross section through the centre of the bearing.
+    Scale 6 inches to a foot.
+
+
+
+
+XIII. CROSS-HEADS.
+
+
+An example of a steam-engine cross-head is shown in fig. 45. A is the
+end of the piston rod which has forged upon it the cross-head B. The
+cross-head pin shown at (_d_), fig. 42, and to which the connecting rod
+is attached, works in the bearing C. Projecting pieces D, forged on the
+top and bottom of the cross-head, carry the slide blocks E which work on
+the slide bars, and thus guide the motion of the piston rod.
+
+[Illustration: FIG. 45.]
+
+    EXERCISE 45: _Locomotive Cross-head._--In fig. 45 are shown side
+    and end elevations, partly in section, of the cross-head and slide
+    blocks for an outside cylinder locomotive. Draw these views half
+    size, showing also on the end elevation the cross-head pin and a
+    vertical section of the connecting rod end from fig. 42. The bush
+    in the cross-head which forms the bearing for the cross-head pin is
+    of wrought iron, case-hardened, and is prevented from rotating by
+    the key shown. The cross-head is of wrought iron, and the slide
+    blocks are of cast iron, and are fitted with white metal strips as
+    shown. A short brass tube leads oil from the upper slide block into
+    a hole in the cross-head as shown, which carries it to a slot in
+    the bush which distributes it over the cross-head pin.
+
+
+
+
+XIV. PISTONS.
+
+
+A _piston_ is generally a cylindrical piece which slides backwards and
+forwards inside a hollow cylinder. The piston may be moved by the action
+of fluid pressure upon it as in a steam-engine, or it may be used to
+give motion to a fluid as in a pump.
+
+A piston is usually attached to a rod, called a _piston rod_, which
+passes through the end of the cylinder inside which the piston works,
+and which serves to transmit the motion of the piston to some piece
+outside the cylinder, or _vice versa_.
+
+[Illustration: FIG. 46.]
+
+A _plunger_ is a piston made in one piece with its piston rod, the
+piston and the rod being of the same diameter.
+
+A piston which is provided with one or more valves which allow the
+fluid to pass through it from one side to the other is called a
+_bucket_.
+
+_Simple Piston._--The simplest form of piston is a plain cylinder
+fitting accurately another, inside which it moves. Such a piston works
+with very little friction, but as there is no adjustment for wear, such
+a piston is not suitable for a high fluid pressure if it has to work
+constantly. This simple form of piston is used in the steam-engine
+indicator, and also in pumps.
+
+Fig. 46 shows the piston of the circulation pump of a marine engine.
+A is the cast-iron casing or barrel of the pump; B is a brass liner
+fitting tightly into the former at its ends, and secured by eight
+screwed Muntz metal pins C, four at each end; D is the piston, which is
+made of brass, and is attached to a Muntz metal piston rod E. The liner
+is bored out smooth and true from end to end, and the piston is turned
+so as to be a sliding fit to the liner. The wear in this form of piston
+is diminished by making the rubbing surface large.
+
+    EXERCISE 46: _Piston for Circulating Pump._--Draw the vertical
+    sectional elevation of the piston, &c., shown in fig. 46, also a
+    half plan and half horizontal section through the centre. Scale 4
+    inches to a foot.
+
+_Pump Bucket._--The next form of piston which we illustrate is shown in
+fig. 47. This represents the air-pump bucket of a marine engine. The
+bucket is made of brass, and is provided with six india-rubber disc
+valves. The rod is in this case made of Muntz metal. Air-pump rods for
+marine engines are very often made of wrought iron cased with brass. It
+will be observed that there is a wide groove around the bucket, which is
+filled with hempen rope or gasket. This gasket forms an elastic packing
+which prevents leakage. This is an old-fashioned form of packing, and is
+now only used for pump buckets.
+
+[Illustration: FIG. 47.]
+
+    EXERCISE 47: _Air-pump Bucket._--Draw the sectional elevation of
+    the air-pump bucket shown in fig. 47. Also draw a half plan looking
+    downwards and a half plan looking upwards. Scale 4 inches to a
+    foot.
+
+_Ramsbottom's Packing._--The form of packing used in the air-pump
+bucket, fig. 47, is not suitable for steam pistons. For the latter the
+packing is now always metallic. The simplest form of metallic packing is
+that known as Ramsbottom's. This form is very largely used for
+locomotive pistons, and for small pistons in many kinds of engines
+besides. A locomotive piston for an 18-inch cylinder with Ramsbottom's
+packing is shown in fig. 48. The particular piston there illustrated is
+made of brass, and is secured to a wrought-iron piston rod by a brass
+nut. Two circumferential grooves of rectangular section are turned out
+of the piston, and into these fit two corresponding rings, which may be
+of brass, cast iron, or steel. In this example the rings are of cast
+iron. These rings are first turned a little larger in diameter than the
+bore of the cylinder (in this example 1/2 inch), and then sprung over
+the piston into the groves prepared for them. Their own elasticity
+causes the rings to press outwards on the cylinder. At the point where a
+ring is split a leakage of steam will take place, but with quick-running
+pistons this leakage is unimportant. The points where the rings are cut
+should be placed diametrically opposite, so as to diminish the leakage
+of steam.
+
+[Illustration: FIG. 48.]
+
+    EXERCISE 48: _Locomotive Piston._--A part elevation and part
+    section of a locomotive piston, for a cylinder having a bore 18
+    inches in diameter, is shown in fig. 48. Draw this, and also a view
+    looking on the nut in the direction of the axis of the piston rod.
+    Scale 6 inches to a foot.
+
+    _Note._--The reason why the part of the piston rod within the
+    piston has such a quick taper is that the piston has to be taken
+    off the rod while it is in the cylinder. The cross-head being
+    forged on the end of the piston rod prevents the piston and piston
+    rod being withdrawn together.
+
+_Large Pistons._--Pistons of large diameter are generally provided with
+two cast-iron packing rings placed within the same groove. These rings
+are pressed outwards against the cylinder, and also against the sides of
+the groove by one or more springs. One form of this packing
+(Lancaster's) is shown in fig. 49. Here one spring only is used, and it
+is first made a straight spiral spring, and then bent round and its ends
+united. The action of the spring will be clearly understood from the
+illustration. For the purpose of admitting the packing rings the piston
+is divided into two parts, one the piston proper, and the other the
+_junk ring_. In fig. 49, A is the junk ring, which is secured to the
+piston by means of bolts as shown.
+
+[Illustration: FIG. 49.]
+
+    EXERCISE 49: _Marine Engine Piston._--The piston illustrated by
+    fig. 49 is for the high-pressure cylinder of a marine engine. The
+    piston, junk ring, and packing rings are of cast iron. The piston
+    rod and nut are of wrought iron, so also are the junk ring bolts.
+    The nuts for the latter are of brass. The spiral spring is made
+    from steel wire 3/8 inch diameter. An enlarged section of one of
+    the packing rings is shown at (_a_). A front elevation of the
+    locking arrangement for the piston rod nut is shown at (_b_). A
+    sectional plan of one of the nuts for the junk ring bolts is shown
+    at (_c_).
+
+    First draw the vertical section of this piston, next draw a plan,
+    one-third of which is to show the piston complete, one-third to
+    show the junk ring removed, and the remaining third to be a
+    horizontal section through between the packing rings. The details
+    (_a_) and (_c_) need not be drawn separately. Scale 3 inches to a
+    foot.
+
+_Proportions of Marine Engine Pistons._--Mr. Seaton, in his 'Manual of
+Marine Engineering,' gives the following rules for designing marine
+engine pistons:--
+
+  D   = diameter of piston in inches.
+  _p_ = effective pressure in lbs. per square inch.
+  _x_ = D/50 x [sqrt (_p_)] + 1.
+
+  Thickness of front of piston near boss        0.2  x _x_.
+       "         "         "        rim         0.17 x _x_.
+       "       back of piston                   0.18 x _x_.
+       "       boss around rod                  0.3  x _x_.
+       "       flange inside packing ring       0.23 x _x_.
+       "          "   at edge                   0.25 x _x_.
+       "       junk ring at edge                0.23 x _x_.
+       "           "     inside packing ring.   0.21 x _x_.
+       "           "     at bolt-holes          0.35 x _x_.
+       "       metal around piston edge         0.25 x _x_.
+  Breadth of packing ring                       0.63 x _x_.
+  Depth of piston at centre                     1.4  x _x_.
+  Lap of junk ring on piston                    0.45 x _x_.
+  Space between piston body and packing ring    0.3  x _x_.
+  Diameter of junk-ring bolts                   0.1  x _x_ + .25 inch.
+  Pitch of junk-ring bolts                      10 diameters.
+  Number of webs in piston                      (D + 20)/12.
+  Thickness        "                            0.18 x _x_.
+
+    EXERCISE 50: _Design for Marine Engine Piston._--Calculate by
+    Seaton's rules the dimensions for a marine engine piston 40 inches
+    in diameter, and subjected to an effective pressure of 36 lbs. per
+    square inch. Then make the necessary working drawings for this
+    piston to a scale of, say, 3 inches to a foot.
+
+    _Note._--Take the dimensions got by calculation to the nearest
+    1-16th of an inch.
+
+
+
+
+XV. STUFFING-BOXES.
+
+
+[Illustration: FIG. 50.]
+
+In fig. 50 is shown a gland and stuffing-box for the piston rod of a
+vertical engine. A B is the piston rod, C D a portion of the cylinder
+cover, and E F the _stuffing-box_. Fitting into the bottom of the
+stuffing-box is a brass bush H. The space K around the rod A B is filled
+with _packing_, of which there is a variety of kinds, the simplest
+being greased hempen rope. The packing is compressed by screwing down
+the cast-iron gland L M, which is lined with a brass bush N. In this
+case the gland is screwed down by means of three stud-bolts P, which are
+screwed into a flange cast on the stuffing-box. Surrounding the rod on
+the top of the gland there is a recess R for holding the lubricant.
+
+[Illustration: FIG. 51.]
+
+[Illustration: FIG. 52.]
+
+The object of the gland and stuffing-box is to allow the piston rod to
+move backwards and forwards freely without any leakage of steam.
+
+Fig. 51 shows a gland and stuffing-box for a horizontal rod. The
+essential difference between this example and the last is in the mode of
+lubrication. The gland flange has cast within it an oil-box which is
+covered by a lid; this lid is kept shut or open by the action of a small
+spring as shown. A piece of cotton wick (not shown in the figure) has
+one end trailing in the oil in the oil-box, while the other is carried
+over and passed down the hole A B. The wick acts as a siphon, and drops
+the oil gradually on to the rod. In this example only two bolts are used
+for screwing in the gland; and the flanges of the gland and stuffing-box
+are not circular, but oval-shaped.
+
+In the case of small rods the gland is made entirely of brass, and no
+liner is then necessary. Fig. 52 shows a form of gland and stuffing-box
+sometimes used for small rods. The stuffing-box is screwed externally,
+and carries a nut A B which moves the gland.
+
+    EXERCISE 51: _Gland and Stuffing-box for a Vertical Rod._--Draw the
+    views shown in fig. 50 to the dimensions given. Scale 6 inches to a
+    foot.
+
+    EXERCISE 52: _Gland and Stuffing-box for a Horizontal Rod._--Fig.
+    51 shows a plan, half in section, and an elevation half of which is
+    a section through the gland flange. Draw these to a scale of 6
+    inches to a foot, using the dimensions marked in the figure.
+
+    EXERCISE 53: _Screwed Gland and Stuffing-box._--Draw, full size,
+    the views shown in fig. 52 to the given dimensions.
+
+A more elaborate form of gland and stuffing-box is shown in fig. 53.
+This is for a large marine engine with inverted cylinders, such as is
+used on board large ocean steamers. The stuffing-box is cast separate
+from the cylinder cover to which it is afterwards bolted. The lubricant
+is first introduced to the oil-boxes marked A, from which it passes to
+the recess B, where it comes in contact with the piston rod. To prevent
+the lubricant from being wasted by running down the rod, the main gland
+is provided with a shallow gland and stuffing-box which is filled with
+soft cotton packing, which soaks up the lubricant.
+
+The main gland is screwed up by means of six bolts, and to prevent the
+gland from locking itself in the stuffing-box, it is necessary that the
+nuts should be turned together. This is done in a simple and ingenious
+manner. One-half of each nut is provided with teeth, and these gear with
+a toothed wheel which has a rim only; this rim is held up by a ring C.
+When one nut is turned, all the rest follow in the same direction.
+
+[Illustration: FIG. 53.]
+
+    EXERCISE 54: _Gland and Stuffing-box for Piston Rod of Large
+    Inverted Cylinder Engine._--The lower view in fig. 53 is a half
+    plan looking upwards, and a half section of the gland looking
+    downwards. The upper view is a vertical section. Complete all these
+    views and add an elevation. Scale 3 inches to a foot.
+
+    _Note._--The large nuts, the wheel, the supporting ring, and small
+    gland are made of brass.
+
+_Dimensions of Stuffing-boxes and Glands._
+
+  _d_     = diameter of rod.          _t__{1} = thickness of
+  _d__{1} = diameter of box (inside).             stuffing-box flange.
+  _l_     = length of stuffing-box    _t__{2} = thickness of gland
+              bush.                               flange.
+  _l__{1} = length of packing space.  _t__{3} = thickness of bushes in
+  _l__{2} = length of gland.                      box and gland.
+  _t_     = thickness of metal in     _d__{2} = diameter of gland bolts.
+              stuffing-box.           _n_     = number of bolts.
+
+  +----------------------------------------------------------+
+  | _d_ | _d__{1} | _l_ | _l__{1} | _l__{2} | _t_  | _t__{1} |
+  +-----+---------+-----+---------+---------+------+---------+
+  |1    |  1-3/4  |  3/4|  2      |  1-1/2  |  7/16|   1/2   |
+  |1-1/2|  2-1/2  |1-1/4|  2-5/8  |  2      |  9/16|   11/16 |
+  |2    |  3-1/2  |1-3/4|  3-1/4  |  2-1/2  | 11/16|   7/8   |
+  |2-1/2|  4-1/8  |2-1/4|  3-7/8  |  2-7/8  | 13/16| 1-1/16  |
+  |3    |  4-3/4  |2-3/4|  4-1/2  |  3-1/4  | 15/16| 1-1/4   |
+  |3-1/2|  5-1/4  |  3  |  5-1/8  |  3-5/8  |1     | 1-3/8   |
+  |4    |  5-7/8  |3-1/4|  5-3/4  |  4      |1     | 1-3/8   |
+  |4-1/2|  6-3/8  |3-1/2|  6-3/8  |  4-3/8  |1-1/16| 1-9/16  |
+  |5    |  7      |3-3/4|  7      |  4-5/8  |1-1/16| 1-9/16  |
+  |6    |  8      |4-1/4|  8-1/4  |  5      |1-1/8 | 1-11/16 |
+  +----------------------------------------------------------+
+
+  +-------------------------------------------------+
+  | _d_ |     _t__{2}     | _t__{3} | _d__{2} | _n_ |
+  +-----+-----------------+---------+---------+-----+
+  |1    | _t__{2}=_t_     |   3/16  |   7/16  |  2  |
+  |1-1/2| when gland      |   1/4   |   5/8   |  2  |
+  |2    | flange is       |   5/16  |   3/4   |  2  |
+  |2-1/2| made of cast    |   5/16  |   7/8   |  2  |
+  |3    | iron and        |   3/8   | 1       |  2  |
+  |3-1/2| _t__{2}=_t__{1} |   3/8   | 1       |  2  |
+  |4    | when gland      |   7/16  | 1       |  2  |
+  |4-1/2| flange is       |   7/16  |   7/8   |  4  |
+  |5    | made of         |   7/16  | 1       |  4  |
+  |6    | brass.          |   1/2   | 1-1/4   |  4  |
+  +-------------------------------------------------+
+
+The proportions of glands and stuffing-boxes vary considerably but the
+above table represents average practice.
+
+    EXERCISE 55:--Make the necessary working drawings for a gland and
+    stuffing-box for a locomotive engine piston rod 2-1/2 inches in
+    diameter, to the dimensions given in the table.
+
+
+
+
+XVI. VALVES.
+
+
+Professor Unwin divides valves, according to their construction into
+three classes as follows:--(1) flap valves, which bond or turn upon a
+hinge; (2) lift valves, which rise perpendicularly to the seat; (3)
+sliding valves, which move parallel to the seat.
+
+Examples of flap valves are shown in figs. 54 and 55; two forms of lift
+valves are shown in figs. 56 and 57, and in figs. 58 and 59 are shown
+two forms of slide valve. The slide valve shown in fig. 58 moves in a
+straight line, while that shown in fig. 59 (called a cock) moves in
+circle.
+
+_India-rubber Valves._--In india-rubber valves there is a grating
+covered by a piece of india-rubber, which may be rectangular, but is
+generally circular, and which is held down along one edge if
+rectangular, or at the centre if circular. Water or other fluid can pass
+freely upwards through the grating, but when it attempts to return the
+elasticity of the india-rubber, and the pressure of the water upon it,
+cause it to lie close on the grating, and thus prevent the return of the
+water. The india-rubber is prevented from rising too high by a
+perforated guard. In fig. 54 is shown an example of an india-rubber disc
+valve. A is the grating, B the india-rubber, C the guard secured to the
+grating or seat by the stud D and nut E. The grating is held in position
+by bolts and nuts F. The grating and guard are generally of brass.
+
+India-rubber disc valves are also shown on the air-pump bucket, fig. 47.
+
+    EXERCISE 56: _India-rubber Disc Valve._--Fig. 54 shows a vertical
+    section and a plan of an india-rubber disc valve. In the plan
+    one-half of the guard and india-rubber are supposed to be removed
+    so as to show the grating or seat. Draw these views, and also an
+    elevation. A detail drawing of the central stud is shown in fig.
+    16, page 18. In fig. 54 the elevation of the guard is drawn as it
+    is usually drawn in practice, but if the student has a sufficient
+    knowledge of descriptive geometry he should draw the elevation
+    completely showing the perforations. Scale 6 inches to a foot.
+
+[Illustration: FIG. 54.]
+
+[Illustration: FIG. 55.]
+
+_Kinghorn's Metallic Valve._--The action of this valve is the same as
+that of an india-rubber valve, but a thin sheet of metal (phosphor
+bronze) takes the place of the india-rubber.
+
+This valve is now largely used in the pumps of marine engines, and is
+shown in fig. 55 as applied to an air-pump bucket. Three valves like the
+one shown are arranged round the bucket.
+
+    EXERCISE 57: _Kinghorn's Metallic Valve._--Fig. 55 shows an
+    elevation and plan of one form of this valve. In the plan one-half
+    of the guard and metal sheet are supposed to be removed, so as to
+    show the grating, which in this case is part of an air-pump bucket.
+    Draw the views shown, and also a vertical section of the guard
+    through the centres of the bolts. All the parts are of brass except
+    the valve proper, which is of phosphor bronze. Scale 6 inches to a
+    foot.
+
+_Conical Disc Valves._--A very common form of valve is that shown in
+figs. 56 and 57. This form of valve consists of a disc, the edge of
+which (called the face) is conical. The conical edge of this disc fits
+accurately on a corresponding seat. The angle which the valve face makes
+with its axis is generally 45 deg.. If the disc is raised, either by the
+action of the fluid as in the india-rubber valve, or by other means, an
+opening is formed around the disc through which the fluid can pass. The
+valve is guided in rising and falling either by three feathers
+underneath it, as in fig. 56, or by a central spindle which moves freely
+through a hole in the centre of a bridge which stretches across the
+seat, as in fig. 57. The lift of the valve is limited by a stop above
+it, which forms part of the casing containing the valve. The lift should
+in no case exceed one-fourth of the diameter of the valve, and it is
+generally much less than this. The guiding feathers (fig. 56) are
+notched immediately under the disc for the purpose of making available
+the full circumferential opening of the valve for the passage of the
+fluid. These notches also prevent the feathers from interfering with the
+turning or scraping of the valve face.
+
+Conical disc valves and their seats are nearly always made of brass.
+
+    EXERCISE 58: _Conical Disc Valves._--Draw, half size, the plans and
+    elevations shown in figs. 56 and 57. In fig. 57 the valve is shown
+    open in the elevation, and in the plan it is removed altogether in
+    order to show the seat with its guide bridge.
+
+[Illustration: Plan of Valve. FIG. 56.]
+
+[Illustration: Plan of Seat. FIG. 57.]
+
+_Simple Slide Valve._--The form of valve shown in fig. 58, often called
+the _locomotive slide valve_, is very largely used in all classes of
+steam-engines for distributing the steam in the steam cylinders. The
+valve is shown separately at (_d_), (_e_), and (_f_), while at (_a_),
+(_b_), and (_c_) is shown its connection with the steam cylinder.
+
+It will be observed that the valve itself is in the shape of a box with
+one side open, the edges of the open side being flanged. When the valve
+is in its middle position, as shown at (_a_), two of these flanged edges
+completely cover two rectangular openings S_{1} and S_{2}, called _steam
+ports_, while the hollow part of the valve is opposite to a third port
+E, called the _exhaust port_. As shown at (_a_) the piston P would be
+moving upwards and the valve downwards. By the time the piston has
+reached the top of its stroke the valve will have moved so far down as
+to partly uncover the steam port S_{1}, and admit steam from the valve
+casing C through S_{1} and the passage P_{1} to the top of the piston.
+The pressure of this steam on the top of the piston will force the
+latter down. While the above action has been going on, the port S_{2}
+will have become uncovered, and the hollow part of the valve will be
+opposite both the steam port S_{2} and the exhaust port E, so that the
+steam from the under side of the piston, and which forced the piston up,
+can now escape by the passage P_{2}, the steam port S_{2}, and the
+exhaust port E to the exhaust outlet O, and thence into the atmosphere,
+if it is a non-condensing engine, or into the condenser if it is a
+condensing engine, or into another cylinder if it is a compound engine.
+After the piston has performed, a certain part of its downward stroke,
+the valve, which has been moving downwards, will commence to move
+upwards, and when it has reached a certain point it will cover the port
+S_{1}, and shut off the supply of steam to the top of the piston. It is
+generally arranged that the steam shall be cut off before the piston
+reaches the end of the stroke. When the piston reaches the bottom of its
+stroke the valve has moved far enough up to uncover the port S_{2} and
+admit steam to the bottom of the piston, and to uncover the port S_{1}
+and allow the steam to escape from the top of the piston through the
+passage P_{1}, the port S_{1}, the port E, and outlet O. In this way the
+piston is moved up and down in the cylinder.
+
+The valve is attached to a valve spindle S by nuts as shown, the hole in
+the valve through which the spindle passes being oval-shaped to permit
+of the valve adjusting itself so as to always press on its seat.
+
+When the valve is in its middle position it generally more than covers
+the steam ports. The amount which the valve projects over the steam port
+on the outside, the valve being in its middle position, is called the
+_outside lap_ of the valve, and the amount which it projects on the
+inside is called the _inside lap_. When the term lap is used without any
+qualification, outside lap is to be understood. In fig. 58 it will be
+seen that the valve has no inside lap, and that the outside lap is
+three-eighths of an inch. The inside lap is generally small compared
+with the outside lap.
+
+[Illustration: FIG. 58.]
+
+When the piston is at the beginning of its stroke the steam port is
+generally open by a small amount called the _lead_ of the valve.
+
+The reciprocating motion of the slide valve is nearly always derived
+from an eccentric fixed on the crank-shaft of the engine. Slide valves
+are generally made of brass, bronze, or cast iron.
+
+    EXERCISE 59: _Simple Slide Valve._--At (_d_), fig. 58, is shown a
+    sectional elevation of a simple slide valve for a steam-engine, the
+    section being taken through the centre line of the valve spindle,
+    while at (_e_) is shown a cross section and elevation, and at (_f_)
+    a plan of the same. Draw all these views full size, and also a
+    sectional elevation at A B. The valve is made of brass, and the
+    valve spindle and nuts of wrought iron.
+
+    EXERCISE 60: _Slide Valve Casing, &c., for Steam-engine._--Draw,
+    half size, the views shown at (_a_), (_b_), and (_c_), fig. 58;
+    also a sectional plan at L M. (_b_) is an elevation of the valve
+    casing with the cover and the valve removed. (_a_) is a sectional
+    elevation, the section being taken through the axes of the steam
+    cylinder and valve spindle. (_c_) is a sectional plan, the section
+    being a horizontal one through the centre of the exhaust port. The
+    inlet and outlet for the steam are clearly shown in the sectional
+    plan: in the sectional elevation their positions are shown by
+    dotted circles.
+
+    The stroke of the piston is in this case 12 inches, so that from
+    the dimensions given at (_a_) it must come within a quarter of an
+    inch of each end of the cylinder; this is called the _cylinder
+    clearance_.
+
+    The piston has three Ramsbottom rings, a quarter of an inch wide
+    and a quarter of an inch apart.
+
+    The steam cylinder and valve casing are made of cast iron.
+
+_Cocks._--A cock consists of a slightly conical plug which fits into a
+corresponding casing cast on a pipe. Through the plug is a hole which
+may be made by turning the plug to form a continuation of the hole in
+the pipe, and thus allow the fluid to pass, or it may be turned round so
+that the solid part of the plug lies across the hole in the pipe, and
+thus prevent the fluid from passing. As the student will be quite
+familiar with the common water cock or tap such as is used in
+dwelling-houses we need not illustrate it here.
+
+[Illustration: FIG. 59.]
+
+Fig. 59 shows a cock of considerable size, which may be used for water
+or steam under high pressure. The plug in this example is hollow, and is
+prevented from coming out by a cover which is secured to the casing by
+four stud bolts. An annular ridge of rectangular section projecting from
+the under side of the cover, and fitting into a corresponding recess on
+the top of the casing, serves to ensure that the cover and plug are
+concentric, and prevents leakage. Leakage at the neck of the plug is
+prevented by a gland and stuffing-box. The top end of the plug is made
+square to receive a handle for turning it. The size of a cock is taken
+from the bore of the pipe in which it is placed; thus fig. 59 shows a
+2-1/4-inch cock.
+
+    EXERCISE 61: 2-1/4-_inch Steam or Water Cock._--First draw the
+    views of this cock shown in fig. 59, then draw a half end elevation
+    and half cross section through the centre of the plug. Scale 6
+    inches to a foot.
+
+    Instead of drawing the parts of the pipe on the two sides of the
+    plug in the same straight line as in fig. 59, one may be shown
+    proceeding from the bottom of the casing, so that the fluid will
+    have to pass through the bottom of the plug and through one side.
+    This is a common arrangement.
+
+    All the parts of the valve and casing in this example are made of
+    brass.
+
+
+
+
+XVII. MATERIALS USED IN MACHINE CONSTRUCTION.
+
+
+_Cast Iron._--The essential constituents of cast iron are iron and
+carbon, the latter forming from 2 to 5 per cent. of the total weight.
+Cast iron, however, usually contains varying small amounts of silicon,
+sulphur, phosphorus, and manganese.
+
+In cast iron the carbon may exist partly in the free state and partly in
+chemical combination with the iron.
+
+In _white cast iron_ the whole of the carbon is in chemical combination
+with the iron, while in _grey cast iron_ the carbon is principally in
+the free state, that is, simply mixed mechanically with the iron. It is
+the free carbon which gives the grey iron its dark appearance. A mixture
+of the white and grey varieties of cast iron when melted produces
+_mottled cast iron_. The greater the amount of carbon chemically
+combined with the iron, the whiter, harder, and more brittle does it
+become.
+
+The white cast iron is stronger than the grey, but being more brittle it
+is not so suitable for resisting suddenly applied loads. White iron
+melts at a lower temperature than grey iron, but after melting it does
+not flow so well, or is not so liquid as the grey iron. White iron
+contracts while grey iron expands on solidifying. The grey iron,
+therefore, makes finer castings than the white. Castings after
+solidifying contract in cooling about 1/8 of an inch per foot. Castings
+possessing various degrees of strength and hardness are produced by
+melting mixtures of various proportions of white and grey cast irons.
+White cast iron has a higher specific gravity than grey cast iron.
+
+Cast iron gives little or no warning before breaking. The thickness of
+the metal throughout a casting in cast iron should be as uniform as
+possible, so that it may cool and therefore contract uniformly
+throughout; otherwise some parts may be in a state of initial strain
+after the casting has cooled, and will therefore be easier to fracture.
+Re-entrant angles should be avoided; such should be rounded out with
+fillets.
+
+The presence of phosphorus in cast iron makes it more fusible, and also
+more brittle. The presence of sulphur diminishes the strength
+considerably.
+
+The grey varieties of cast iron are called _foundry irons_ or _foundry
+pigs_, while the white varieties are called _forge irons_ or _forge
+pigs_, from the fact that they are used for conversion into wrought
+iron.
+
+Amongst iron manufacturers the different varieties of cast iron are
+designated by the numbers 1, 2, 3, &c., the lowest number being applied
+to the greyest variety.
+
+_Chilled Castings._--When grey cast iron is melted a portion of the free
+carbon combines chemically with the iron; this, however, separates out
+again if the iron is allowed to cool slowly; but if it is suddenly
+cooled a greater amount of the carbon remains in chemical combination,
+and a whiter and harder iron is produced. Advantage is taken of this in
+making _chilled castings_. In this process the whole or a part of the
+mould is lined with cast iron, which, being a comparatively good
+conductor of heat, chills a portion of the melted metal next to it,
+changing it into a hard white iron to a depth varying from 1/8 to 1/2 an
+inch. To protect the cast-iron lining of the mould from the molten metal
+it is painted with loam.
+
+_Malleable Cast Iron._--This is prepared by imbedding a casting in
+powdered red hematite (an oxide of iron), and keeping it at a bright red
+heat for a length of time varying from several hours to several days
+according to the size of the casting. By this process a portion of the
+carbon in the casting is removed, and the strength and toughness of the
+latter become more like the strength and toughness of wrought or
+malleable iron.
+
+_Wrought or Malleable Iron._--This is nearly pure iron, and is made from
+cast iron by the puddling process, which consists chiefly of raising the
+cast iron to a high temperature in a reverberatory furnace in the
+presence of air, which unites with the carbon and passes off as gas. In
+other words the carbon is burned out. The iron is removed from the
+puddling furnace in soft spongy masses called _blooms_, which are
+subjected to a process of squeezing or hammering called _shingling_.
+These shingled blooms still contain enough heat to enable them to be
+rolled into rough _puddled bars_. These puddled bars are of very
+inferior quality, having less than half the strength of good wrought
+iron. The puddled bars are cut into pieces which are piled together,
+reheated, and again rolled into bars, which are called _merchant bars_.
+This process of piling, reheating, and re-rolling may be repeated
+several times, depending on the quality of iron required. Up to a
+certain point the quality of the iron is improved by reheating and
+rolling or hammering, but beyond that a repetition of the process
+diminishes the strength of the iron.
+
+The process of piling and rolling gives wrought iron a fibrous
+structure. When subjected to vibrations for a long time, the structure
+becomes crystalline and the iron brittle. The crystalline structure
+induced in this way may be removed by the process of _annealing_, which
+consists in heating the iron in a furnace, and then allowing it to cool
+slowly.
+
+_Forging and Welding._--The process of pressing or hammering wrought
+iron when at a red or white heat into any desired shape is called
+_forging_. If at a white heat two pieces of wrought iron be brought
+together, their surfaces being clean, they may be pressed or hammered
+together, so as to form one piece. This is called _welding_, and is a
+very valuable property of wrought iron.
+
+_Steel._--This is a compound of iron with a small per-centage of carbon,
+and is made either by adding carbon to wrought iron, or by removing some
+of the carbon from cast iron.
+
+In the _cementation_ process, bars of wrought iron are imbedded in
+powdered charcoal in a fireclay trough, and kept at a high temperature
+in a furnace for several days. The iron combines with a portion of the
+carbon to form _blister steel_, so named because of the blisters which
+are found on the surface of the bars when they are removed from the
+furnace.
+
+The bars of blister steel are broken into pieces about 18 inches long,
+and tied together in bundles by strong steel wire. These bundles are
+raised to a welding heat in a furnace, and then hammered or rolled into
+bars of _shear steel_.
+
+To form _cast steel_ the bars of blister steel are broken into pieces
+and melted into crucibles.
+
+In the _Siemens-Martin_ process for making steel, cast and wrought iron
+are melted together on the hearth of a regenerative gas-furnace.
+
+_Bessemer steel_ is made by pouring melted cast iron into a vessel
+called a converter, through which a blast of air is then urged. By this
+means the carbon is burned out, and comparatively pure iron remains. To
+this is added a certain quantity of 'spiegeleisen,' which is a compound
+of iron, carbon, and manganese.
+
+_Hardening and Tempering of Steel._--Steel, if heated to redness and
+cooled suddenly, as by immersion in water, is hardened. The degree of
+hardness produced varies with the rate of cooling; the more rapidly the
+heated steel is cooled, the harder does it become. Hardened steel is
+softened by the process of _annealing_, which consists in heating the
+hardened steel to redness, and then allowing it to cool slowly. Hardened
+steel is _tempered_, or has its degree of hardness lowered, by being
+heated to a temperature considerably below that of a red heat, and then
+cooling suddenly. The higher the temperature the hardened steel is
+raised to, the lower does its 'temper' become.
+
+_Case-hardening._--This is the name given to the process by which the
+surfaces of articles made of wrought iron are converted into steel, and
+consists in heating the articles in contact with substances rich in
+carbon, such as bone-dust, horn shavings, or yellow prussiate of potash.
+This process is generally applied to the articles after they are
+completely finished by the machine tools or by hand. The coating of
+steel produced on the article by this process is hardened by cooling the
+article suddenly in water.
+
+_Copper._--This metal has a reddish brown colour, and when pure is very
+malleable and ductile, either when cold or hot, so that it may be rolled
+or hammered into thin plates, or drawn into wire. Slight traces of
+impurities cause brittleness, although from 2 to 4 per cent. of
+phosphorus increases its tenacity and fluidity. Copper is a good
+conductor of heat and of electricity. Copper is largely used for making
+alloys.
+
+_Alloys._--_Brass_ contains two parts by weight of copper to one of
+zinc. _Muntz metal_ consists of three parts of copper to two of zinc.
+Alloys consisting of copper and tin are called _bronze_ or _gun-metal_.
+Bronze is harder the greater the proportion of tin which it contains;
+five parts of copper to one of tin produce a very hard bronze, and ten
+of copper to one of tin is the composition of a soft bronze. _Phosphor
+bronze_ contains copper and tin with a little phosphorus; it has this
+advantage over ordinary bronze, that it may be remelted without
+deteriorating in quality. This alloy also has the advantage that it may
+be made to possess great strength accompanied with hardness, or less
+strength with a high degree of toughness.
+
+_Wood._--In the early days of machines wood was largely used in their
+construction, but it is now used to a very limited extent in that
+direction. _Beech_ and _hornbeam_ are used for the cogs of mortise
+wheels. _Yellow pine_ is much used by pattern-makers. _Box_, a heavy,
+hard, yellow-coloured wood, is used for the sheaves of pulley blocks,
+and sometimes for bearings in machines. _Lignum-vitae_ is a very hard
+dark-coloured wood, and remarkable for its high specific gravity, being
+1-1/3 times the weight of the same volume of water. This wood is much
+used for bearings of machines which are under water.
+
+
+
+
+XVIII. MISCELLANEOUS EXERCISES.
+
+
+The illustrations in this chapter are in most cases not drawn to scale;
+they are also in some parts incomplete, and in others some of the lines
+are purposely drawn wrong. The student must keep to the dimensions
+marked on the drawings, and where no sizes are given he must use his own
+judgment in proportioning the parts. All errors must be corrected, and
+any details required, but not shown completely in the illustrations,
+must be filled in.
+
+    EXERCISE 62: _Single Riveted Butt Joint with Tee-iron Cover
+    Strap._--Two views, one a side elevation and the other a sectional
+    elevation, of a riveted joint are shown in fig. 60. Draw these
+    views, and also a plan projected from one of them. Show the rivets
+    completely in all the views. Scale 4 inches to a foot.
+
+[Illustration: FIG. 60.]
+
+[Illustration: FIG. 61.]
+
+    EXERCISE 63: _Girder Stay for Steam Boiler._--The flat crown of the
+    fire-box of locomotive and marine boilers is generally supported or
+    stayed by means of girder stays, an example of which is shown in
+    fig. 61. A B is the side elevation of a portion of one of these
+    girders. Each girder is supported at its ends by the plates forming
+    the vertical sides of the fire-box. The flat crown is bolted to the
+    girders as shown. Observe that the girders are in contact with the
+    crown only in the neighbourhood of the bolts. Consider carefully
+    this part of the design, and then answer the following questions:
+    (1) What objections are there to supporting the girders at the ends
+    only without the contact pieces at the bolts? (2) What objections
+    are there to having the girders in contact with the crown plate of
+    the fire-box throughout their whole length?
+
+    Draw the views shown in fig. 61, and from the right-hand one
+    project a plan. Scale 4 inches to a foot.
+
+[Illustration: FIG. 62.]
+
+    EXERCISE 64: _End of Bar Stay for Steam Boiler._--On page 12 one
+    form of stay for supporting the flat end of a steam boiler is
+    described. Another form of stay for the same purpose is shown in
+    fig. 62. A B is a portion of the end of a steam boiler. C D is one
+    end of a bar which extends from one end of the boiler to the
+    other. The ends of this bar are screwed, and when the bar is of
+    wrought iron the screwed parts are generally larger in diameter
+    than the rest of the bar. When made of steel the bar is generally
+    of uniform diameter throughout. In the case of wrought-iron bar
+    stays the enlarged ends are welded on to the smaller parts.
+    Welding is not so reliable with steel as with wrought iron. Write
+    out answers to the following questions: (1) What is the advantage
+    of having the screwed part of the bar larger in diameter than the
+    rest? (2) Why are steel bar stays not generally enlarged at their
+    screwed ends?
+
+    Draw the views shown in fig. 62, and project from one of them a
+    third view. Scale 4 inches to a foot.
+
+    EXERCISE 65: _Knuckle Joint._--Draw the plan and elevation of this
+    joint shown in fig. 63, and also draw an end elevation looking in
+    the direction of the arrow. The parts at A and B are octagonal in
+    cross section. Scale 4 inches to a foot.
+
+[Illustration: FIG. 63.]
+
+    EXERCISE 66: _Locomotive Coupling Rod Ends._--A form of knuckle
+    joint used on locomotive coupling rods is shown in fig. 64.
+
+    In this case two rods meet and work on the same pin, as shown at
+    (a) fig. 64. Draw, in addition to the views shown in fig. 64, a
+    plan and a vertical section through the axis of the pin. Scale 6
+    inches to a foot.
+
+    Would it be practicable to replace the two rods A B and B C by a
+    single rod working on the crank pins at A, B, and C? Give reasons
+    for your answer.
+
+[Illustration: FIG. 64.]
+
+    EXERCISE 67: _Bell Crank Lever._--Draw the plan and elevation of
+    the lever shown in fig. 65. Scale 6 inches to a foot.
+
+[Illustration: FIG. 65.]
+
+    EXERCISE 68: _Back Stay for Lathe._--Draw a plan and two elevations
+    of the stay shown in fig. 66. Make all necessary corrections and
+    show all the details in each view. Scale full size.
+
+[Illustration: FIG. 66.]
+
+[Illustration: FIG. 67.]
+
+    EXERCISE 69: _Conical Disc Valve and Casing._--Draw, half size, the
+    views shown in fig. 67 of the conical disc valve and casing, and
+    also add an elevation looking in the direction of the arrow.
+
+    EXERCISE 70: _Connecting Rod End._--The student should carefully
+    compare this connecting rod end (fig. 68) with those illustrated on
+    pages 50 and 52. The lower part of fig. 68 is a half plan and half
+    horizontal section, and the upper part is a half side elevation and
+    half vertical section. Draw these views and also an end elevation.
+    Scale 6 inches to a foot.
+
+[Illustration: FIG. 68.]
+
+[Illustration: FIG. 69.]
+
+[Illustration: FIG. 70.]
+
+[Illustration: FIG. 71.]
+
+[Illustration: FIG. 72.]
+
+[Illustration: FIG. 73.]
+
+[Illustration: FIG. 74.]
+
+    EXERCISE 71: _Engine Cross-head._--The cross-head shown in fig. 69
+    is for an inverted cylinder marine engine. A is the piston rod, and
+    B B are pins, forged in one piece with C, to which the forked end
+    of the connecting rod is attached. Draw the upper view with the
+    central part in section as shown. Make the right-hand half of the
+    lower view a plan without any section, and make the left-hand half
+    a horizontal section through the axis of the pins B B. Scale 4
+    inches to a foot.
+
+    EXERCISE 72: _Ratchet Lever._--The lever shown in fig. 70 is used
+    for turning the horizontal screw of a traversing screw jack. Draw
+    the two views shown, and from one of them project a plan. Scale
+    full size.
+
+    EXERCISE 73: _Steam Whistle._--Draw, full size, the elevation and
+    section of the steam whistle shown in fig. 71. Draw also horizontal
+    sections at A B, C D, and E F.
+
+[Illustration: FIG. 75.]
+
+    EXERCISE 74: _Screw Coupling for Railway Carriages._--Draw the
+    three views of the screw coupling shown in fig. 72. Scale 6 inches
+    to a foot.
+
+    If the link A is fixed, through what distance will the link B move
+    for two turns of the lever?
+
+[Illustration: FIG. 76.]
+
+    EXERCISE 75: _Loose Headstock for a 6-inch Lathe._--Two views of
+    this headstock are shown in fig. 73. On one of these views a few of
+    the chief dimensions are marked. The details, fully dimensioned,
+    are shown separately in figs. 74, 75, and 76.
+
+    Explain clearly how the centre is moved backwards and forwards, and
+    also how the spindle containing it is locked when it is not
+    required to move.
+
+    Draw, half-size, the views shown in fig. 73, and from the
+    left-hand view project a plan. Draw also the detail of the locking
+    arrangement shown in fig. 74.
+
+
+
+
+APPENDIX A.
+
+_SCIENCE AND ART DEPARTMENT, SOUTH KENSINGTON._
+
+
+SYLLABUS.
+
+SUBJECT II.--MACHINE CONSTRUCTION AND DRAWING.
+
+It is assumed that the student has already learnt to draw to scale, and
+that he can draw two or more views of the same object in simple or
+orthographic projection. To pass in machine construction and drawing, he
+must be able to apply this knowledge to the representation of machinery.
+He must be acquainted with the form and purpose of the simpler parts of
+which machines are built up and must have had some practice in drawing
+them. To test his knowledge, rough dimensioned sketches, more or less
+incomplete, of simple machine details will be given him, and he will be
+required to produce a complete drawing in pencil to a given scale. Two
+or more views of at least one subject will be required, and these must
+be so drawn as to be properly projected one from the other, _in order to
+show that the student appreciates that he is producing a representation
+of a solid piece of machinery, and not merely copying a sketch. No
+credit will be given unless some knowledge of projection is shown._ The
+centre lines of the drawings should be shown, and parts cut by planes of
+section should be indicated by diagonal shading. Bolts and other
+fastenings should be carefully shown where required. Any indication that
+a candidate has merely copied the sketches given, without understanding
+the part represented, will invalidate his examination.
+
+
+FIRST STAGE OR ELEMENTARY COURSE.
+
+In the elementary stage, a knowledge is required of the simple parts
+only of _machines in common use_. _Some_ of these are enumerated in the
+following list. The student should be practised in drawing them till he
+recognises their forms, and the object of the arrangement should be
+explained to him. He should also know the simple technical terms used in
+describing them.
+
+A few very simple questions relating to the arrangement, proportions,
+and strength of the simplest machine details will be set in the
+examination paper.
+
+In drawing the examples set to test a student's knowledge and skill in
+machine drawing, it must be remembered that only a limited time is
+available. It is only possible to set an example to be drawn in pencil,
+and the points which will receive attention are (1) accuracy of scale
+and projection; (2) power of reading a drawing, shown by the ability to
+transfer portions of the mechanism and dimensions from one view to
+another; (3) knowledge of machines, as shown by the ability to fill in
+small details, such as nuts, keys, etc., omitted in the sketches given.
+Bearing in mind the limited time available, the student should try to
+make his outline clear and decisive and complete. But the diagonal lines
+necessary for sectional parts may be done rapidly, though neatly, by
+freehand if necessary.
+
+_Riveted Joints._--Forms of rivets and arrangement of rivets in lap and
+butt joints with single and double riveting. Junction of plates by angle
+and T-irons.
+
+_Bolts, Studs, and Set Screws._--Forms of these fastenings. Forms and
+proportions of nuts and bolt-heads. Arrangement of flanges for bolting.
+
+_Pins, Keys, and Cotters._--Form of ordinary knuckle joint. Use of split
+pins. Connection of parts by a key. Connection of parts by a cotter. Gib
+and cotter.
+
+_Pipes and Cylinders._--Forms of ordinary pipes and cylinders and their
+flanges and covers.
+
+_Shafting._--Forms of shafts and axles and of journals and pivots. Use
+of collars and bosses. Half-lap coupling. Box coupling. Flange coupling.
+
+_Pedestals and Plummer Blocks._--Simplest forms of pedestals and hangers
+for shafts. Form and arrangement of brass steps. Arrangements for
+fixing pedestals and for neutralising the effects of wear.
+
+_Toothed Gearing._--Forms of ordinary spur and bevil wheels. Meaning of
+the terms pitch, breadth of face, thickness of tooth, pitch line, rim,
+nave, arm. Mode of drawing bevil wheels in section.
+
+_Belt Pulleys._--Forms of belt pulleys for flat and round belts. Stepped
+speed cones. Drawing of pulleys with curved arms.
+
+_Cranks and Levers._--Forms of ordinary cast-iron and wrought-iron
+cranks and levers. Modes of fixing crank pin. Modes of fixing crank
+shaft. Double cranks. Form of eccentrics.
+
+_Links._--Most simple forms of connecting rod ends, open or closed. Use
+of steps in connecting rods. Use of cotters to tighten the steps.
+
+_Pistons._--Simple forms of piston. Use of piston packing. Modes of
+attaching piston rod.
+
+_Stuffing-Boxes._--Simple form of stuffing-box and gland. Use of
+packing. Mode of tightening gland.
+
+_Valves._--Simple conical of puppet valve. Simple slide valve. Cock or
+conical sliding valve.
+
+
+
+
+APPENDIX B.
+
+_EXAMINATION PAPERS SET BY THE SCIENCE AND ART DEPARTMENT._
+
+
+SUBJECT II.--MACHINE CONSTRUCTION AND DRAWING.
+
+_Examiners_, PROF. T. A. HEARSON, M.Inst.C.E., and J. HARRISON, ESQ.,
+M.Inst.M.E.
+
+GENERAL INSTRUCTIONS.
+
+_If the rules are not attended to, the paper will be cancelled._
+
+You may take the Elementary, or the Advanced, or the Honours paper, but
+you must confine yourself to one of them.
+
+Put the number of the question before your answer.
+
+You are expected to prove your knowledge of machinery as well as your
+power of drawing neatly to scale. You are therefore to supply details
+omitted in the sketches, to fill in parts left incomplete, and to
+indicate, by diagonal lines, parts cut by planes of section.
+
+No credit will be given unless some knowledge of projection is shown, so
+that at least two views of one of the examples will be required properly
+projected one from the other. The centre lines should be clearly drawn.
+The figured dimensions need not be inserted.
+
+Your answers should be clearly and cleanly drawn in pencil. No extra
+marks will be allowed for inking in.
+
+All figures must be drawn on the single sheet of paper supplied, for no
+second sheet will be allowed.
+
+The value attached to each question is shown in brackets after the
+question. But a full and correct answer to an easy question will in all
+cases secure a larger number of marks than an incomplete or inexact
+answer to a more difficult one.
+
+Your name is not given to the Examiner, and you are forbidden to write
+to him about your answers.
+
+You are to confine your answers _strictly_ to the questions proposed.
+
+A single accent (') signifies _feet_; a double accent (") _inches_.
+
+_The examination in this subject lasts for four hours._
+
+       *       *       *       *       *
+
+First Stage or Elementary Examination. 1885.
+
+INSTRUCTIONS.
+
+Read the General Instructions above.
+
+Answer briefly any three, but not more than three, of the following
+questions, and draw two, but not more than two, of the examples.
+
+_Questions._
+
+ (_a._) Show two methods by which a cotter may be prevented from
+    slacking back.                                                  (6.)
+
+ (_b._) Sketch the brasses for a bearing, and show how they are
+    prevented from turning in the pedestal.                         (6.)
+
+ (_c._) Explain the object of the construction of the connecting rod
+    end shown in fig. 78. Describe how the adjustment must be made and
+    how it is locked.                                              (10.)
+
+ (_d._) Show the form of the Whitworth screw thread by drawing to
+    scale a part section of two or three threads taking a pitch of
+    1-1/2 inches. Figure the dimensions on the sketch. How many threads
+    to the inch are used on an inch bolt?                          (10.)
+
+ (_e._) Make a sketch showing how the adjustment is made in the
+    sliding parts of machine tools: as, for example, in the slide rest
+    of a lathe.                                                    (10.)
+
+ (_f._) Describe with sketches two methods by which the joints are
+    made in connecting lengths of cast-iron pipes.                  (6.)
+
+_Examples to be drawn._
+
+ 1. Jaw for four-screw dog chuck for 5" lathe. Draw the two views as
+    shown (fig. 77). Scale full size.
+
+    (Note.--The other three jaws of the chuck are not to be drawn.)
+                                                                   (35.)
+
+ 2. Connecting rod end. Draw the two views as shown, partly in
+    section (fig. 78). Draw full size.                             (35.)
+
+ 3. Hooke's coupling. Draw the three views shown (fig. 79), adding
+    any omitted lines where the views are incomplete. Draw to scale of
+    1/4 full size.                                                 (35.)
+
+[Illustration: FIGS. 77 AND 78.]
+
+[Illustration: FIG. 79.]
+
+       *       *       *       *       *
+
+First Stage or Elementary Examination. 1886.
+
+INSTRUCTIONS.
+
+Read the General Instructions (page 102).
+
+Answer briefly any three, but not more than three, of the following
+questions, and draw two, but not more than two, of the examples.
+
+_Questions._
+
+ (_a._) Give sketches showing how the cutting tool of a lathe or
+    other machine is secured in place.                              (6.)
+
+ (_b._) Make a sketch of a stud, describe how it is screwed into
+    place, and state some circumstances under which it is used in
+    preference to a bolt.                                           (6.)
+
+ (_c._) Give sketches showing one method of attaching the valve rod
+    to an ordinary slide valve.                                     (6.)
+
+ (_d._) Sketch a connecting rod end, with strap, gib, and cotter.
+    Explain the use of the gib.                                    (10.)
+
+ (_e._) Explain the use of the quadrant for change wheels for a
+    screw-cutting lathe shown in Example 1, fig. 80, by making a
+    sketch showing it in place on a lathe with wheels in gear.     (10.)
+
+ (_f._) Sketch one form of hanger suitable for supporting mill-shafting.
+                                                                   (10.)
+
+_Examples to be drawn._
+
+ 1. Quadrant for change wheels for screw-cutting lathe. Draw the two
+    views shown (fig. 80). Scale half-size.                        (35.)
+
+ 2. Crank-shaft. Draw the two views as shown, partly in section (fig
+    81). Scale 1/8 full size.                                      (35.)
+
+ 3. Ball bearing for tricycle. Draw the two views as shown, partly
+    in section (fig. 82). Draw full size.                          (35.)
+
+[Illustration: FIGS. 80 AND 81.]
+
+[Illustration: FIG. 82.]
+
+       *       *       *       *       *
+
+First Stage or Elementary Examination. 1887.
+
+INSTRUCTIONS.
+
+Read the General Instructions (page 102).
+
+Answer briefly any three, but not more than three, of the following
+questions, and draw two, but not more than two, of the examples.
+
+_Questions._
+
+ (_a._) Explain how the piston rings in Example 1, fig. 84, are made
+    so that the piston may work steam-tight in the cylinder. How are
+    these rings got into place?                                     (8.)
+
+ (_b._) Give two views of a double riveted lap joint for boiler-plates.
+                                                                    (8.)
+
+ (_c._) Show by sketches how a wheel is fixed on a shaft by means of
+    a sunk key. Explain how the key may be withdrawn when it cannot be
+    driven from the point end.                                      (8.)
+
+ (_d._) Give sketches showing the construction of a conical metal
+    lift or puppet valve and seating.                              (10.)
+
+ (_e._) With the aid of sketches explain how a piston rod is made to
+    work steam-tight through the end of the cylinder.              (10.)
+
+ (_f._) Explain how the slotting machine ram of Example 8, fig. 85,
+    may be made to move up and down when at work. How is the length of
+    the stroke altered, and what is the object of the slotway in the
+    upper part of the ram?                                         (10.)
+
+_Examples to be drawn._
+
+ 1. Piston for steam-engine. Draw and complete the two views shown
+    (fig. 84), the top half of the left-hand view to be in section.
+    Scale 1/2 size.                                                (30.)
+
+ 2. Plan and sectional elevation of a footstep bearing for an
+    upright shaft (fig. 83). Draw and complete these views. Scale
+    1/4 size.                                                      (35.)
+
+ 3. Ram of slotting machine. Draw and complete the two elevations
+    shown (fig. 85). The tool-holders must be drawn in their proper
+    positions in the ram, and not separate as in the diagram. Scale
+    1/4 size.                                                      (35.)
+
+[Illustration: FIGS. 83 AND 84.]
+
+[Illustration: FIG. 85.]
+
+       *       *       *       *       *
+
+First Stage or Elementary Examination. 1888.
+
+INSTRUCTIONS.
+
+Read the General Instructions on p. 102.
+
+Answer briefly any three, but not more than three, of the following
+questions, and draw two, but not more than two, of the examples.
+
+_Questions._
+
+ (_a._) Give sketches showing how the separate lengths of a line of
+    shafting may be connected together.                             (8.)
+
+ (_b._) What is the object of using chipping or facing strips in
+    fitting up machine parts? Give one or two examples.             (8.)
+
+ (_c._) Give sketches showing how you would grip and drive a round
+    iron bar for the purpose of turning it between the centres of a
+    lathe.                                                         (10.)
+
+ (_d._) Explain the action of the governor shown in Example 1
+    (fig. 86).                                                     (10.)
+
+ (_e._) Describe in detail how the mud-hole door in Example 2
+    (fig. 88) is removed for the purpose of cleaning the boiler and
+    how it is replaced and the joint made steam-tight.             (10.)
+
+ (_f._) Describe how the parts of the spur wheel in Example 3
+    (fig. 87) are put together, and explain why the wheel is made
+    in segments.                                                   (10.)
+
+_Examples to be drawn._
+
+ 1. Loaded governor for small gas engine. Draw and complete the two
+    views, partly in section as shown (fig. 86). Scale full size.  (35.)
+
+ 2. Mud-hole mouth-piece for Lancashire boiler. Draw and complete
+    the two views shown (fig. 88). Scale 3/8ths.                   (35.)
+
+ 3. Point for segments of large spur wheel. Draw and complete the
+    views shown (fig. 87). Scale 3/16ths.
+
+    _Note._--As the radius of the wheel is too large for your
+    instruments, the circumference at the joint may be set out
+    straight, as in a rack.                                        (35.)
+
+[Illustration: FIGS. 86 AND 87.]
+
+[Illustration: FIG. 88.]
+
+
+
+
+INDEX
+
+
+  Air-pump bucket, 58
+  Alloys, 80
+  Angle irons, 12
+  Annealing, 79, 80
+  Axles, 24
+
+
+  Back stay for lathe, 86
+  Bar stay, 83
+  Bearings for shafts, 30
+  Beech-wood, 81
+  Bell crank lever, 86
+  Bessemer steel, 79
+  Bevil wheels, 43
+  Blister steel, 79
+  Blooms, 78
+  Bolt-heads, proportions of, 18
+  Bolts, forms of, 17
+  Border lines, 4
+  Box couplings, 25
+  -- end, connecting rod, 51
+  Box-wood, 81
+  Brackets, 33
+  Brake shaft carrier, 30
+  Brass, 80
+  Brasses, 30
+  Bucket, 58
+  Built-up cranks, 46
+  Bush, 30, 49, 51, 54, 56, 63
+  Butt joints, 10, 11
+  -- strap, 10
+  Buttress screw thread, 15
+
+
+  Case-hardening, 80
+  Cast iron, 76
+  Cast iron flange coupling, 28, 29
+  -- steel, 79
+  Caulking, 8
+  Cementation process, 79
+  Centre lines, 2, 4
+  Chilled castings, 78
+  Circulating pump piston, 58
+  Clearance, cylinder, 74
+  -- of cotter, 49
+  Cocks, 74
+  Cogs, 41
+  -- wood for, 81
+  Collared stud, 18
+  Collars, 24
+  Colouring, 3
+  Colours for different materials, 3
+  Compasses, 1
+  Cone keys, 23, 38
+  Conical disc valve, 70, 71, 89
+  -- head, 7
+  Connecting rod, locomotive, 51
+  -- -- marine, 51
+  -- rods, 49, 89
+  Construction for rivet heads, 7
+  Contraction of castings, 77
+  Copper, 80
+  Cotters, 48, 49
+  Countersunk head, 7, 18
+  Coupling rod ends, 55, 84
+  -- rods, 54
+  -- screw, 96
+  Couplings, shaft, 25
+  Cover plate, 10
+  Cranked axle, 45
+  Cranks, 43
+  -- built-up, 46
+  Cross-head pin, 51
+  Cross-heads, 56, 89
+  Cross-key, 28
+  Cup-headed bolt, 17
+
+
+  Decimal equivalents, 6
+  Dimension lines, 5
+  Dimensions, 5
+  -- of box couplings, 26
+  -- cast-iron flange couplings, 29
+  -- keys, 24
+  -- stuffing-boxes and glands, 67
+  -- Whitworth screws, 15
+  Distance lines, 5
+  Dividers, 1
+  Draught of cotter, 49
+  Drawing board, 1
+  -- instruments, 1
+  -- paper, 2
+  -- pen, 1
+  -- pins, 2
+
+
+  Eccentrics, 47
+  Exhaust port, 71
+  Eye-bolt, 18
+
+
+  Fairbairn's coupling, 26
+  Fast and loose pulleys, 37
+  Feather key, 23
+  Flange couplings, 27
+  Flap valves, 68
+  Flat key, 22
+  Forge irons, 77
+  Forging, 79
+  Form of wheel teeth, 40
+  Forms of nuts, 16
+  -- rivet heads, 7
+  -- screw threads, 15
+  Foundry irons, 77
+
+
+  Gasket, 58
+  Gas threads, 15
+  Gib, 49
+  -- head, 23
+  Girder stay, 81
+  Gland, 64
+  Grey cast iron, 77
+  Gun-metal, 80
+  Gusset stay, 12
+
+
+  Half-lap coupling, 26
+  Hangers, 34
+  Hardening of steel, 80
+  Headstock lathe, 96
+  Hexagonal nut, 16
+  Hollow key, 22
+  Hook bolt, 18
+  Hornbeam, 81
+
+
+  India-rubber disc valves, 58, 68
+  Inking drawings, 2
+  Inside lap of valve, 72
+
+
+  Joggles, 33
+  Joint, knuckle, 84
+  Journals, 24
+  -- length of, 32
+  Junk ring, 61
+
+
+  Keys, 22
+  -- proportions of, 23
+  Kinghorn's metallic valve, 70
+  Knuckle joint, 84
+  -- screw thread, 15
+
+
+  Lancaster's piston packing, 61
+  Lap joints, 8, 9, 10, 12
+  -- of slide valve, 72
+  Lathe headstock, 96
+  Lead of valve, 74
+  Lever, bell crank, 86
+  -- ratchet, 96
+  Lignum-vitae, 81
+  Locking arrangements for nuts, 21, 62
+  Lock nuts, 19
+  Locomotive connecting rod, 51
+  -- cranked axle, 45
+  -- cross-head, 56
+  Locomotive eccentric, 47
+  -- piston, 60
+  Lubricator, needle, 32
+
+
+  Malleable cast iron, 78
+  -- iron, 78
+  Marine connecting rod, 51
+  -- coupling, 28
+  -- crank-shaft, 46
+  -- piston, 61
+  Merchant bars, 78
+  Mortise wheels, 41
+  Mottled cast iron, 77
+  Muff couplings, 25
+  Muntz metal, 80
+
+
+  Needle lubricator, 32
+  Nuts, forms of, 16
+  -- lock, 19
+  -- proportions of, 18
+
+
+  Oil-box, 54, 65
+  Outside lap of slide valve, 72
+  Overhung crank, 43
+  -- cranks, proportions of, 45
+
+
+  Packing, 63
+  Pan head, 7
+  Pedestal, shaft, 30
+  Pencils, drawing, 1
+  Phosphor bronze, 80
+  Pillar bracket, 34
+  Pillow block, 30, 32
+  Pin, cross-head, 51, 54
+  -- split, 21
+  Piston rod, 57
+  Pistons, 57
+  Pitch circle, 40
+  -- of wheel teeth, 40
+  -- surfaces of wheels, 39, 43
+  Pivots, 24
+  Plummer block, 30
+  Plunger, 57
+  Printing, 4
+  Proportions of bolt-heads, 18
+  -- keys, 23
+  Proportions of lap joints, 9, 10
+  -- marine engine pistons, 62
+  -- nuts, 18
+  -- overhung cranks, 45
+  -- pillow blocks, 32
+  -- rivet heads, 7
+  -- wheel teeth, 40
+  Puddled bars, 78
+  Puddling process, 78
+  Pulley, eccentric, 47
+  Pulleys, 36
+  Pump bucket, 58
+
+
+  Ramsbottom's packing, 60
+  Ratchet lever, 96
+  Riveted joints, 8
+  Rivet heads, forms of, 7, 8
+  -- -- proportions of, 7
+  Riveting, 7
+  Rivets, 6
+  Rope pulley, 39
+  Round key, 23
+
+
+  Saddle key, 22
+  Scales, 5
+  Screw coupling, 96
+  Screwed gland and stuffing-box, 65
+  Screw threads, 14, 15
+  Screws, representation of, 16
+  Sellers =V= screw thread, 14
+  Set screw, 21, 49
+  -- squares, 1
+  Shaft couplings, 25
+  -- hanger, 34
+  Shafting, 24
+  Shear steel, 79
+  Sheave, eccentric, 47
+  Shingling, 78
+  Shrinking, process of, 44
+  Siemens-Martin steel, 79
+  Slide blocks, 56
+  -- valves, 68, 71
+  Sliding key, 23
+  Snap head, 7
+  Snug, 17
+  Spiegeleisen, 80
+  Spring bows, 1
+  Spur wheel, 41
+  Square nut, 16
+  -- screw thread, 14
+  Stay, back, for lathe, 86
+  -- bar, 83
+  -- girder, 81
+  -- gusset, 12
+  Steam ports, 71
+  -- whistle, 96
+  Steel, 79
+  Steps, 30
+  Strap, 49
+  -- eccentric, 47
+  -- end of connecting rod, 49
+  Stud bolts, 18
+  Studs, 18
+  Stuffing-boxes, 63
+  Sunk key, 22
+
+
+  Taper bolt, 18, 27
+  -- pin, 23
+  Tee-headed bolt, 18
+  Tee-iron cover strap, 81
+  Tee square, 1
+  Teeth of wheels, form and proportions of, 40
+  Teeth, pitch of, 40
+  Tempering of steel, 80
+  Throw of crank, 44
+  -- eccentric, 47
+  Toothed wheels, 39
+
+
+  Valve Kinghorn's metallic, 70
+  -- slide, 68, 71
+  Valves, 68
+  -- conical disc, 70
+  -- india-rubber, 58, 68
+  Velocity ratio in belt gearing, 36
+
+
+  Wall boxes, 34
+  Washers, 19
+  Welding, 79
+  Whistle, steam, 96
+  White cast iron, 77
+  Whitworth screws, dimensions of, 15
+  -- =V= screw thread, 14
+  Wood, 81
+  Working drawings, 4
+  Wrought iron, 78
+
+
+  Yellow pine, 81
+
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+London, F.R.S. With 5 Woodcuts. With or without Answers to Problems,
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