Class
Book xi_
Copyright^
COPYRIGHT DEPOEffi
Mechanical Drawing
A Treatise on Technical Drawing as Ex-
pressed through the Medium of
the Graphic Language
BY
OTHO M. GRAVES
Assistant Professor of Graphics, Lafayette College
Author of Orthographic Projection
EASTON, PA.
THE CHEMICAL PUBLISHING CO.
1912
Copyright, 1912, by Otho M. Graves.
GCLA327<^3
PREFACE.
A course in mechanical drawing should be so designed as to
awaken the creative faculty of design latent in every student and
to so train his mechanical execution that he may correctly express
his thoughts through the medium of the graphic language. The
power to form a mental image of any proposed design and to
represent the object on paper by the necessary views or, con-
versely, to mentally visualize an object by an examination of
the views representing it, is essential to every successful engi-
neer. The training of this technical imagination of the student
should receive careful attention throughout any well planned
course in Mechanical Drawing. The student should be brought
to understand that Mechanical Drawing, so called, is in reality a
graphic language with its own alphabet, grammar, and idioms
which is to be used as a vehicle of graphic expression. The copy-
ing of a set of plates, complete in every detail, while affording
practice in the use of instruments and illustrating various stand-
ards of execution, is otherwise valueless. A knowledge of the
graphic language can no more be gained in this way, than one
could become familiar with any other foreign language by merely
copying page after page of printed text.
Xo language can be properly written until the grammar is
mastered, nor should working drawings be attempted until ortho-
graphic projection, the grammar of the graphic language, has
been carefully studied. In the treatment of orthographic pro-
jection it would seem obvious that concrete objects, such as solids
of various forms, should be first considered before dealing with
the more abstruse points and lines. The truth of this state-
ment has been unquestionably proven by the experience of
many teachers.
In the appendix at the rear of this book is a suggested course
in Mechanical Drawing including twenty-two plates The pur-
pose of the earlier plates is to familiarize the student with the
uses of the various instruments and to train his mechanical ex-
PREFACE IV
ecution. Yet even in these elementary plates an increasing
amount of original planning is left to the student subject to the
supervision of an instructor. As the plates progress a greater
demand is made upon the power of visualizing objects of three
dimensions. Those plates which demand a knowledge of ortho-
graphic projection are so arranged as to permit the instructor to
assign problems of differing data to students working at adjacent
tables.
One hour a week may well be spent in class room recitations
or lectures. If desired, free hand sketches of assigned models
may be made by the student as home work and presented at the
recitation period for examination and discussion.
The drawing plates of this text should be completed in a col-
lege year in which two two-hour periods per week — or an equiva-
lent amount of time- — are devoted to drawing. The theory may
be cared for in one one-hour recitation per week throughout the
year. The Lettering plates outlined in Chapter III should be
completed in twenty one-hour periods.
Grateful appreciation is due to Mr. M. Berry Doub, Instructor
in Graphics, Lafayette College, for valuable aid in connection
with the preparation of this text, and to Messrs. Kielman '14,
Reside '14, and Ellis '15. students in Lafayette College, for their
assistance in preparing the illustrations.
The following firms have been most courteous in supplying
desired cuts for illustrations: F. Weber and Co., Philadelphia;
Keuffel & Esser, New York; Dietzgen & Co., Chicago; Kolesch
and Co., New York; and The Technical Supply Co., of Scranton.
Pa.
Easton, Pa., O. M. G.
September, 19 12.
CONTENTS.
Page
Chapter I. — Instruments and their Use 1-24
List of Equipment, 1; Instruments, 2; Large Compass,
3; Large Divider, 6; Bow Pen and Bow Pencil, 7; Bow
Divider, 9; Ruling Pen, 9; Drawing Board, 11; T Square,
\2\ Scales, 14; Triangles, 17; Irregular Curves, 20;
Protractor, 22; Pencils, 22; Ink, 23; Paper, 23; Erasers.
24; Miscellaneous, 25.
Chapter II. — General Instructions 26-33
To Make a Stretch, 26; Penciling, 26; Character of
Lines, 26; Inking, 28; Symbolic Cross Hatching, 28;
Tinting, 31; Erasing, 32; Abbreviations, 33.
Chapter III. — Lettering 35-41
Purpose, 35; Style, 35; Suggested Course in Lettering,
37; Composition, 41; Lettering for Architectural De-
signs and Maps, 41.
Chapter IV. —Conic Sections 4 2_ 49
Cone, 42; Cutting Planes, 42; The Circle, 44; The
Ellipse, 44; The Parabola, 46; The Hyperbola, 47.
Chapter V. — Orthographic Projection 50-68
Orthographic Projection, 50; Projection on One Plane.
50; Projection on Three Planes, 52; Fundamental
Principles, 54; Sequence of Views, 54; To Obtain the
Top, Front and Right Side View of a Hollow Cylinder.
56; To Obtain the Usual Three Views of a Hollow
Cylinder, 57; To Obtain the Usual Three Views of a
Cone, 57; To Obtain the Top, Front and Left Side
Views of the Frustrum of a Cone, 57; To Obtain the
Top, Front and Right Side Views of a Hexagonal
Prism, 58; To Obtain the Usual Three Views of a
Hexagonal Prism, 59; Revolution, 60; Successive
Revolutions, 62; Oblique Plane of Projection, 67; Sec-
tional Views, 68.
Chapter VI. — Working Drawings 79-92
Clearness, 79; Assembly and Detail Drawings, 80; The
Number of views Required, 81; Notes, 81; Dimension-
ing, 81; Title, 84; Checking, 85; Sketching, 86; Shade
Lines, 88; Line Shading, 89; Structural Drawing, 92.
VI CONTENTS
Chapter VII. — Bolts and Screw Threads 95-102
The Helix, 95; Various Forms of Screw Threads, 96;
Conventional Representation, 97; Bolt Heads and Nuts,
98; Set Screws, 101; A Stud Bolt, 102; Machine Screws,
102; Foundation Bolts.
Chapter VIII. — Tracings and Prints 103-105
Tracings, 103; Prints, 104; Sun Frames, 105; Electric
Printing Machines.
Appendix.— Suggested Course in Mechanical Drawing. 11 3-1 16
Time Devoted to Course, 113; Roll Call, 113; Stamping
Plates, 113; Posting of x\ccepted Plates, 113; Plates Re-
turned for Correction, 114; Rejected Plates, 114; Time
of Posting and Returning Plates, 114; Conduct in Draft-
ing Room, 114; Work Done Outside of Class Hours,
115; Bulletin Boards, 115; Size of Drawing Plates, 115;
Instructions Regarding Each Plate, 116 ; Finding
Plates, 116.
Plates 1 17-13S
Plate No. 1, 117; Plate No. 2, 119; Plate No. 3, 120;
Plate No. 4, 120; Plate No. 5, 122; Plate No. 6, 124;
Plate No. 7, 124; Plates No. 8 and 9, 126; Plates No. 10
and n, 126; Plates No. 12 and 13, 127; PlateNo. 14, 127;
Plate No. 15, 127; Plate No. 16, 128; Plate No. 17, 130;
Plate No. 18, 132; Plate No. 19, 134; Plate No. 20, 136;
Plate No. 21, 13S; Plate No. 22, 138.
CHAPTER I.
Instruments and their Use.
I. List of Equipment. — Each man must be provided with the
following list of equipment, all articles of which are essential.
This outfit is sufficiently complete for the beginner, but as the
student gains in experience he will feel the need of useful tools
not mentioned in this list. Such further tools or instruments
should be procured as experience indicates and finances permit.
Any manufacturer is glad to send his catalog upon request, from
which much valuable information may be obtained both as to
the care and construction of the instruments already purchased
and suggestions as to other instruments and devices valuable to
the draftsman.
i. Set of drawing instruments of any standard make. The
set should contain the following instruments :
Hairspring Compass, S 1 /*", with pen and pencil attach-
ments and lengthening bar.
Hairspring Divider, 5".
Bow Pen, ^/ A " .
Bow Divider, 3^".
Ruling Pen, 5^2", with cleaning device.
Ruling Pen, 4^2", with cleaning device.
2. Drawing Board, 20" x 28".
3. T square, 30", with transparent edge.
4. Triangular boxwood scale. Architect's, or three flat scales.
5. Triangular boxwood scale, Engineer's, or three flat scales.
6. 30°-6o° celluloid triangle, 10".
7. 45 celluloid triangle, 8".
8. Irregular curve, celluloid.
9. One bottle black, waterproof, India ink.
10. Emery pencil pointer, or file.
II. Ruby pencil eraser.
12. Ink eraser.
13. Sponge rubber, or cube of Artgum.
14. One dozen small thumb tacks.
2 MECHANICAL DRAWING
15. Pen holder, three pens Gillott No. 303, and three pens
Gillott No. 404.
16. Two 6H pencils, and one 3H.
17. Medium sized sponge.
18. Small glass bowl.
19. One sheet of Whatman's cold pressed paper, 19" x 27" .
20. One 3 oz. bottle of white paste.
Assuming the cost of the instruments given in item 1 to be
$10.00 (which should be regarded as a minimum), the cost of
the foregoing equipment is about $18.00.
The purpose and use of the various supplies enumerated in
Article 1 will now be discussed.
2. Instruments. — No more serious mistake could be made than
to imagine that a cheap set of instruments is good enough with
which to learn to draw, and that a better set may be purchased
after proficiency has been attained. The cheaper grades of
instruments begin to show signs of wear in a relatively short
time. The compasses gradually lose their alignment, the nibs of
the pens wear unevenly, pivots become loose and screw threads
worn. Instruments in this condition are a source of annoyance
and error, and with them even the most experienced draftsman
would find it difficult to do creditable work. On the other hand
the life of good instruments is practically unlimited if they are
used with thoughtful care, and are a constant pleasure to the
draftsman. It is then, advisable for those men who intend to
make any branch of engineering their life work to purchase as
fine instruments as possible. If the state of one's finances pro-
hibits the purchase of a complete set of the finest grade of instru-
ments, it might be well to purchase individually as many instru-
ments as possible at the time, and add to the collection as
circumstances permit. Eventually such a buyer would be the
possessor of a set of instruments of which he might well be
proud. A soft leather case designed to contain any collection of
instruments will be made to order by any manufacturer of draft-
ing supplies. Until such a case is desired, the instruments may
be kept in a piece of chamois folded so that no instrument is
in contact with another.
INSTRUMENTS AND THEIR USE 3
Those men who are pursuing mechanical drawing only tem-
porarily may reasonably purchase a less expensive set of instru-
ments. In general, however, a set of instruments as enumerated
in item i. Art. i, which costs less than $10.00 is expensive at any
price.
Nearly all of the well known brands of instruments sold in
this country are manufactured abroad, notably in Germany and
Switzerland. The foremost American made instruments are
those manufactured by Theodore Alteneder & Sons of Philadel-
phia. These instruments have borne an enviable reputation for
more than half a century, and many draftsmen consider them to
be without an equal.
The Riefler instruments are favorably known abroad and are
used extensively in the United States. These instruments are of
unquestioned merit and excellence, and are sold by F. Weber &,
Co. of Philadelphia. The "Sphinx" instruments, manufactured
exclusively for the same firm, are acceptable in every way.
The "Paragon" and "Key Brand" instruments manufactured
and sold by Keuffel & Esser of New York are worthy of the
highest praise. This firm has been eminently successful in the
effort to place the manufacture and sale of drafting supplies in
general on an honest and reliable foundation.
Eugene Dietzgen & Co. manufacture and sell the "Gem Union"
instruments. These instruments have a large sale and are of
excellent design and workmanship.
The "T. S. Co." instruments, manufactured for and sold by
the Technical Supply Co. of Scranton, are favorably known.
The "Richter" instruments, manufactured in Germany and sold
by various agents in this country, are worthy of the highest
praise.
The "Kern" instruments are a leading Swiss brand.
Many other instruments are sold in this country and no criti-
cism of them is intended, but in the opinion of the author the
ones here named are the best and most reliable.
3. Large Compass. — The principal material used in the con-
struction of this instrument is German silver in rolled sheet form.
4 MECHANICAL, DRAWING
The nibs of the pen attachment are made of properly tempered
steel in order to afford the requisite spring.
Possibly the most important part of the compass is the head
which forms the joint between the two legs. Unfortunately the
amateur is unable to ascertain from inspection whether or not
1
m
Sift
Fig. i. — Tongue joint.
Fig. 2. — Pivot joint.
the head is properly constructed, though a poorly constructed
head is sure to make itself annoyingly obtrusive when in use.
The surest guide in purchasing is the reputation of the manu-
facturer and the reliability of the dealer. The tongue joint of
former years has now given way to the more desirable pivot
Fig. 3. — Test for alignment.
joint. In the pivot joint each leg terminates in a disc, the two
discs being held together in a fork by means of two pivot screws.
The fork is provided with a handle for convenience in handling.
All joints and parts should move in the same plane. The test
INSTRUMENTS AND THEIR USE 5
for this feature is made by bending the legs outward from the
head and inward at the knuckle joints, when the points should
meet exactly. Every good instrument should stand this test.
The large compass is used for either inking or penciling by
means of the two attachments. Circles of about n" in diameter
may be drawn with the $ l / 2 " compass. If a larger diameter is
desired the lengthening bar must be inserted.
In order to avoid making large holes in the paper, use that end
of the needle point which has a shoulder. The needle point
should be set a little longer than the pen attachment, and kept,
permanently in this position. When using the pencil attachment
adjust the lead to suit the needle point. The lead should be
sharpened to a chisel edge about 3 / 64 " long. The direction of
the edge of the lead should be tangent to the circle drawn ; other-
wise a line broader than the edge of the lead would result.
To set the compass to any desired radius, place two points
on the drawing paper whose distance apart is equal to the given
radius. Set the needle point of the compass on one point and,
spread the other leg until it is approximately over the second
point. The exact setting is now made by turning the adjusting
screw which controls the hairspring.
The compass should be rotated clockwise, with only enough
downward pressure to keep the needle point in place. Do not
rotate the compass backward, nor continue the rotation after
the circle has been completed. When drawing circles of a large
radius, the knuckle joints should be bent so as to bring the two
legs perpendicular to the plane of the paper.
If the circle to be drawn is so large as to require the use of
the lengthening bar, the leg containing the needle point is steadied
with the left hand while the pen or pencil point is rotated with-
the right hand.
For circles having a radius longer than can be attained by
the 53/2" compass and lengthening bar, the beam compass is used.
The needle point and the pen (or pencil) point are placed on two
separate pieces of metal which are clamped onto a bar of hard
wood. These bars may be obtained any length from 24" to 60" \
6 MECHANICAL DRAWING
so that a circle may be drawn having a diameter of very nearly
120". A steel bar is frequently used instead of wood. A beam
compass of this type is shown in Fig. 4.
Fig. 4. — Beam compass.
4. Large Divider. — This instrument is similar in general design
and construction to the compass except that it has no removable
parts. It has a two-fold use, first, to transfer dimensions from
one part of a drawing to another, and second, to divide a line
into any desired number of equal parts when the divisions cannot
be readily obtained from the scale.
To transfer a dimension from one part of a drawing to
another, set one leg on an end of the dimension to be transferred
and spread the legs until the other divider point is approximately
over the other end of the dimension. The exact position of the
second divider leg may be obtained by means of the set screw'
controlling the hairspring attachment. The distance between the
points of the divider legs being equal to the given dimension, this
distance can be laid off on any desired line. Of course the same
Fig. 5. — Hairspring divider.
result could be obtained by scaling the length of the given dimen-
sion, and laying off the same distance by scale on any other
desired line. The second method is, however, somewhat more
INSTRUMENTS AND THEIR USE
7
laborious with the possibility of an error through misreading the
scale.
To divide a line into a certain number of equal parts, let it
be desired to divide a line which is about j" long into five equal
parts. Judging solely by the eye, set the divider points a little
more than one inch apart and step this distance along the line.
Suppose that at the last step one leg extends a small amount
beyond the end of the line. Keep the other leg fixed, and by
means of the hairspring draw the legs together an amount equal
to one-fifth the excess. The line should now be re-stepped and
the process continued until the desired result is exactly attained.
In stepping off divisions with the dividers, the instrument should
be rotated in opposite directions at every other step, as though
describing a series of semi-circles alternately on opposite sides
of the given line.
Great care should be taken to avoid pricking holes which are
needlessly heavy and unsightly. The final points of division
should be extremely small, yet easily visible. If it is desired to
save these points for future reference, a light free-hand circle
should be drawn around each.
5. Bow Pen and Bow Pencil. — The bow instruments, including
Fig. 6. — Bow pen.
pen. pencil, and divider, are made entirely of steel. The legs
should have a firm outward spring, and are connected by a
Fig. 7. — Bow pencil.
threaded bar. The distance between the legs is regulated by a
thumbnut placed on the threaded bar. The thumbnut may be
MECHANICAL DRAWING
placed on the outside of one leg, the legs being held apart, solely
by their intrinsic spring. Or the thumbnut may be placed
between the two legs, the connecting bar having a right hand
thread at one end and a left hand thread at the other end, and
engaging the legs in swiveling sockets. The advantage of this
type is that the legs are held rigidly in position without depend-
ing on the spring. Since the two threads engage simultaneously
the motion is double that of a single thread, and the legs can be
set with only one-half the number of turns of the thumbnut,
which is an added advantage.
Due to the more rigid construction of the bow instruments,
circles of small radii can be more accurately drawn than would
be possible with the large compass. Moreover the radius is
fixed beyond chance of a change due to an inadvertent pressure
on the legs. This feature is particularly desirable when drawing
a number of circles of the same radii.
The lead of the bow pencil should be brought to a chisel edge
having a length of about 1 / n2 ", which is nearer a point than in
the case of the large compass.
The needle point should project slightly below the pen or
pencil point. The proper length is such that in drawing a circle
there is no tendency to lift the needle point from the paper, nor
the need to unduly force, it into the paper in order to keep the
moving point in contact with the paper.
The radius may be rapidly changed and the serviceable life
of the screw threads be appreciably prolonged, by pressing the
legs together with one hand, while turning the adjusting screw
with the fingers of the other hand.
Circles having a maximum diameter of 2 J A" an d a minimum
Fig. 8. — Drop pen.
diameter of about }i" can be drawn with a iVa" bow instrument.
The "drop pen" or "rivet pen" is a more convenient instrument
INSTRUMENTS AND THFJR USE O,
for drawing circles of very small radius than is the bow pen.
If many such circles are to be drawn, such as rivet and bolt
holes in structural and machine drawing, and transit stations in
topographical mapping, this instrument should be included in
the equipment of the draftsman.
6. Bow Divider. — The method of use of this instrument is the
same as for the large divider. It is particularly convenient if
many divisions are to be made, or if it is desired to keep a certain
spacing for some time. The setting cannot be changed without
Fig. 9. — Bow divider.
intentionally turning the adjusting screw, which precludes the
possibility of error due to an accidental pressure on the legs
while the instrument is not in use.
7. Ruling Pen. — The ruling pen consists of two nibs made of
properly tempered steel, fastened to a wood or aluminum handle.
The nibs should be fairly sharp, slightly rounded, and of equal
length and shape. The two nibs are held together by means of
a small screw, one nib having a strong outward spring which
keeps that nib flush against the head of the screw. The distance
between the nibs is controlled by the screw, thus rendering it
possible to draw any desired width (frequently called "weight")
of line.
The pen is filled by means of the quill attached to the stopper
of the ink bottle. Do not put too much ink in the pen at one
time. The ink should not extend upward from the points of
the nibs more than %.". The danger of overloading the pen is
that the ink is apt to be shaken from between the nibs, causing
blots. After filling the pen see that no ink remains on the out-
side of the nibs. In ruling a line hold the pen almost vertical,
but with a slight lean to the right. That nib which touches the
screw head should be on the far side from the ed^e of the T
io
MECHANICAL DRAWING
square or triangle. All lines should be drawn from left to right
with a free arm movement, making sure that both nibs are in
constant contact with the paper. If either nib fails to touch the
ffl
Fig. io. — Ruling pen with cleaning device,
paper, by reason of the pen leaning toward or away from the
draftsman, that edge of the line will be ragged.
India ink dries rapidly, leaving a slight deposit which if per-
mitted to remain between the nibs will cause an uneven flow of
ink and a consequent variation in the width of the line. Hence
the nibs should be frequently cleaned by drawing between them
a soft cloth kept for that purpose. Thoroughly clean the pen
Fig. ii. — Ruling pen with cleaning device,
before putting it away after the day's work. Most beginners
are apt to excuse poor work on the ground of a fault in the pen.
It is far more frequently the case that the pen is not kept suffi-
ciently clean to allow a uniform flow of the ink. Remember that
the ink cannot possibly flow if the nibs are screwed together
until they are in contact.
Fig. 12.— Detail pen.
In order to clean the dried ink from between the nibs of the
pen it is necessary to open the nibs to their full extent. Care
INSTRUMENTS AND THEIR USE
II
must then be taken to carefully reset the nibs to their original
spacing so that lines drawn before and after cleaning will show
no variation in width. This need has given rise to several forms
of "cleaning devices," by which the nibs are automatically re-
turned to their original positions. Two different forms of this
device are illustrated in Figs. 10 and 11.
A double pen is frequently useful for ruling two parallel lines.
Or a single very broad line can be obtained by filling the space
Fig. 13. — Double ruling pen.
between the two pairs of nibs with ink as well as the space be-
tween each pair of nibs.
A curve pen set into the handle with a swivel joint is useful
in drawing curves, contour lines in mapping, etc.
Fig. 14 — Curve pen with swivel joint.
The Payzant pen for free hand single stroke lettering is a
most useful device.
Fig. 15. — Payzant freehand lettering pen.
8. Drawing Board. — The drawing board should be made of
narrow strips of soft pine about one inch thick. The strips
should be held firmly together by hardwood ledges secured by
screws in oval slots to allow for contraction and expansion. A
series of grooves equal in depth to half the thickness of the
board should be sunk on the under side of the board to prevent
warping. A hardwood straight edge glued to each end of the
board is desirable though not essential. The under side of a
well made board is illustrated in Fig. 16.
12 MECHANICAL DRAWING
One of the short edges is made perfectly smooth and even
and is called the "working edge." This working edge is placed
to the left to receive the head of the T square. The evenness
of the working edge is best tested by applying a steel straight
Fig. 1 6. — Drawing board.
edge. Or it may be tested as follows : hold the head of the T 1
square firmly against the working edge and draw a pencil line
through the center of the paper. Using several points on this
line as centers, draw arcs of equal radii on each side of the line.
If the T square be moved along the working edge and can be
brought tangent to the arcs just drawn, the working edge is per-
fectly straight. This test assumes that the T square itself is
accurate.
It is sometimes convenient to rule lines parallel to the working
edge by placing the head of the T square against the edge of the
board nearest the body. This is permissible only when the two
edges are known to join at an angle of exactly 90 .
The upper and right hand edges are never used under any
circumstances.
9. T Square. — The T square consists of a long, light blade
rigidly attached at right angles to a head which is about double
the thickness of the blade. The most accurate and durable T
squares are made of steel, but the great majority in ordinary use
are made from woods such as cherry, maple, pear, or ash. The
two edges of the blade should consist of some transparent mate-
rial such as celluloid. The transparent edge renders it possible
to observe the work immediately adjacent to the line being
drawn, which is very helpful.
INSTRUMENTS AND THEIR USE 1 3
An adjustable T square is one which permits the angle between
Fig. 17. — T Squares with celluoid edges.
Fig. 18. — T Square with micrometer adjustable head.
Fig. 19. — T Square with micrometer adjusted protractor head.
the head and the blade to be regulated as desired. This type of
T square is convenient though not essential.
14 MECHANICAL DRAWING
In Fig. 20 is shown a T square holder which, when attached
to the end of the blade, holds the T square from slipping by
pressing against the drawing board. This device is particularly
useful on a long blade.
Fig. 20. — T Square holder.
To use the T square, press the head firmly against the working
edge of the board with the left hand. Slide the left hand along
the blade, to hold it firmly in position while drawing the line with
the right hand. Move the T square up and down the board by
means of the head. Use only the upper edge of the blade.
To test the blade for straightness : draw a line the full length
of the blade. Turn the T square, end for end, and if it can be
made to coincide with the line already drawn the ruling edge is
perfectly straight. The same ruling edge must be used, of
course, in each position of the T square.
10. Scales. — The two most common materials from which
scales are made are steel and boxwood. The main advantages
of the steel scale are its durability and the permanency of its
deep cut graduations. On the other hand the divisions are diffi-
cult to read and prove a constant strain on the eyes. For gen-
eral use the boxwood scale is to be preferred, the edges prefer-
ably being covered with some white material on which the gradu-
ations are stamped in black.
Scales are divided, as regards shape, into two main divisions,
flat and triangular. The triangular shape has the advantage of
containing on one scale all of the eleven sets of graduations in
common use. Its disadvantage is the danger of mistaking the
INSTRUMENTS AND THEIR USE
15
proper scale. A flat scale similar to the one shown in Fig. 23
and containing four sets of graduations is the most desirable
form. However, three such scales are needed to contain all of
the desired graduations.
In general the representation on paper of an object is neces-
sarily smaller than the actual size of the object represented.
The purpose of the scale is to facilitate this required reduction.
Suppose that it is desired to draw an object one-twelfth of its
actual size. Then for every twelve inches of the object, one
inch must be laid off on the drawing; the equivalent expression
of which is to say that one inch on the drawing is equal to twelve
Fig. 21. — Triangular boxwood scale, architects'.
Fig. 22. — Triangular boxwood scale, engineers'.
inches of the object. The scale to be used is, then, one inch
equals one foot. If on any straight edge points be set one inch
apart, the included spaces will represent one foot. If one space
be now divided into twelve parts, each division will represent
one inch ; each division may be sub-divided into four parts, each
sub-division representing one quarter inch. With a scale so
divided, distances may be laid off such that the resultant draw-
ing will be one-twelfth the actual size of the object. The evident
advantage of the scale is that it obviates the necessity of any
mental division on the part of the draftsman. In Fig. 23 the
distances i'-o" and io'-io l / 2 " are laid off to a 1" scale. The
distances 2'-o" and 20' -j" are laid off to a Yi" scale.
10
MECHANICAL DRAWING
The triangular architect's scale contains the following gradua-
tions which are the ones most frequently used:
(Full size)
(One quarter size)
(One eighth size)
(One twelfth size)
(One sixteenth size)
(One twenty-fourth size)
(One thirty-second size)
(One forty-eighth size)
(One sixty-fourth size)
(One ninety-sixth size)
(One one hundred twenty-eighth size)
A half size scale may be employed by mentally dividing all
actual dimensions by two, and then using the full size scale.
12"
= 1
-O
3"
= 1
-O
I/ 2 "
= 1
-O
1'
= 1
-O
Va"
= 1
-O
w
= 1
-O
w
= 1
-O
Va
— 1
-O
'A.'
=: I
-O
%'
=■1
-O
Vs."
= I
-O
Fig. 23. -The use of the scale in laying off dimensions.
The triangular engineer's scale is divided into ioths, 20ths,
30ths, 40ths, 50ths, and 6oths of an inch. The engineer's
scale is used for plotting all work the measurements for which
were taken in the decimal system. It is particularly valuable
to the civil engineer in the plotting of maps and surveys.
Transfer distances directly from the scale to the paper, mark-
ing the points with a finely pointed lead pencil. Do not set the
divider or compass legs against the scale graduations and attempt
INSTRUMENTS AND THEIR USE
17
to transfer distances by this means. The method is inaccurate
and has a disastrous effect on the graduations.
In laying off a number of equal distances carry the summation
of distances on the scale. Thus if it be required to lay off 24,
divisions of }i" each, set the zero of the scale at the starting
point and, holding the scale fixed, successively lay off y%" , y,
i}&", i/^", etc. The last point set should fall at the 9" mark,
which furnishes a valuable check on the work.
11. Triangles. — Triangles are made of wood, rubber, steel, and
celluloid. Though the steel triangles are more lastingly accurate
than those made from any other material, they are not popular
due to their weight and opaqueness. The celluloid triangles are
fairly accurate, light, easily handled, transparent, and for gen-
eral work are to be preferred to those of any other material.
Fig. 24. — Use of triangles — to obtain angles of 30 , 45 and 6o°.
It is advantageous to have several sizes of both the 30°-6o°
and 45 triangles, as it is not convenient to draw large figures
with small triangles or vice versa.
As the speed of the draftsman is largely dependent upon his
facility in the use of triangles in connection with the T square,
the beginner should at once familiarize himself with their various
uses, singly and in combination.
i8
MECHANICAL DRAWING
Lines drawn parallel to the blade of the T square are known;
as horizontal lines. Vertical lines are perpendicular to horizontal
lines.
By placing the triangles firmly against the T square blade,
vertical lines and lines making angles of 30 , 45 °, and 60 ° with
the horizontal (or vertical) may be drawn. Lines making angles
of 15 ° and 75 with either the horizontal or vertical may be
Fig. 25. — Use of triangles — to obtain angles of 15 and 75 .
drawn by combinations of the two triangles as shown in Fig. 25.
The student should draw through a point a series of radiating
lines 1 5 apart from o° to 360 by means of the T square and
triangle only.
If it be desired to draw a series of parallel lines which are
neither horizontal or vertical, place the triangles in conjunction
and slide one along the other which is held fixed by the left
hand.
To test the right angle of either triangle, hold the triangle
against the T square with the vertical edge at the right and draw
INSTRUMENTS AND THEIR USE
19
a fine vertical line. Reverse the triangle so that the vertical edge
is at the left. If the vertical edge now coincides with the line
already drawn the angle is 90°. If the edge and line do not
coincide they will form an angle one-half of which represents
the error in the 90 angle of the triangle. If the vertex of the
c
Fig. 26. — Use of triangles -to draw parallel and perpendicular lines.
angle is at the top, the angle of the triangle is greater than 90 ;
if the vertex is at the bottom the angle of the triangle is less
than 90 .
To test the 45 ° triangle, hold the triangle against the T
square and draw a line along the hypotenuse. Interchange the
positions of the two acute angles. If the hypotenuse now coin-
cides with the line already drawn, the angle of the triangle is
exactly 45 °. If they do not coincide the amount and direction
of the error is determined as in the preceding paragraph. This
test is based on the assumption that the 90 angle has already
been tested and found to be correct.
20
MECHANICAL DRAWING
To test the 6o° triangle ; by means of a protractor or geo-
metrical construction, draw a line making an angle of 6o° with
the blade of the T square. Place the short edge of the triangle
against the T square, and if the hypotenuse then coincides with
the line already drawn, the 6o° angle of the triangle is correct.
The 90 angle should have been previously tested. If the 6o°
and 90 angles are correct the remaining angle must be exactly
30°.
The side of a triangle which has been proven inaccurate by
any of the foregoing methods may be materially improved by a
judicious application of sand paper.
12. Irregular Curves are constructed of rubber, wood, and cel-
luloid, the latter material being preferable. It is frequently desir-
Fig. 27. — Irregular curves.
able to make pencil marks on the surface of the curve, hence
many draftsmen roughen the surface of the celluloid with sand
paper. The curves are made in a variety of shapes and sizes,
but for general use the curves of lone radii are most desirable.
INSTRUMENTS AND THEIR USE
21
A varied collection of irregular curves is a valuable part of a
draftsman's equipment.
In using an irregular curve do not ink the curved line to the
full extent of the distance that it apparently matches the irregu-
lar curve. The importance of this statement can hardly be
sufficiently emphasized. Let it be required to draw a curved
line through points a, b, c, d, e, f, g, h, i, j, k, etc. If the curve
can be fitted from a to / draw the line only as far as e. Now
fit the curve from d as far as possible, say to i, and draw the
line from e to h. Fit the curve from g as far as possible, say
to k, and draw the curve h to /. Proceed in this manner until
the curve is complete. By this method there are no visible and
unsightly joints in the curved line.
Fig. 28. — Protractor, particularly adapted to mapping.
In drawing a curved line which is symmetrical in respect to
a given axis, mark with a pencil on the surface of the irregular
curve the portions used in drawing one-half of the curve, and
then use the same portions in drawing the other half of the
curve. By this means the symmetry of the curve is preserved.
In order to make sure that the two symmetrical halves join one
another in a smooth curve, it is frequently advisable to stop each
22
MECHANICAL DRAWING
half just short of the axis and use a separate portion of the
irregular curve for the connection.
13. Protractor. — A protractor is a device by means of which
angles of any desired number of degrees may be laid off. It is
a necessity in nearly all forms of topographical mapping and is
frequently useful in machine drawing. A simple form of pro-
Fig. 29. — Protractor, particularly adapted to machine drawing.
tractor intended for general use and mapping is shown in Fig. 28.
The protractor shown in Fig. 29 is made of sheet steel with an
83^2" blade. The vernier reads to five minutes. This form is
particularly adapted to the requirements of machine drawing.
14. Pencils. — There are many good brands of pencils on the
market and an equal number of poor ones. Among the former
may be mentioned the excellent "Koh-i-Noor" pencils manufac-
tured by L. & C. Hardmuth and sold by all dealers. The
"Apollo" pencils manufactured by F. Weber & Co., the
"Hyperion" pencils of Eugene Dietzgen, Keuffel & Esser's
"Paragon" pencils, and the "Swan" pencils sold by the Technical
Supply Co. of Scranton are to be highly recommended.
The standard gradation of pencils according to the degree of
hardness of the lead is commonly accepted as. follows: 6B, 5B,
INSTRUMENTS AND THEIR USE 2$
4B, 3B, 2B, B, HB, F, H, 2H, 3H, 4H, 5H. and 6H. According
to this notation F and HB are considered medium, the leads
growing harder through the H's until 6H is reached and softer
through the Bs until 6B is reached. The degree of hardness
desired by the draftsman is considerably dependent upon the
class of work and the grade of paper employed. In general the
6H pencil is used for line drawing which is to be traced or inked,
and the 3H pencil for lettering.
The draftsman should possess two 6H pencils, one of which
should be brought to a chisel edge as follows : cut away the wood
for about i%", exposing about y%" of the lead. Flatten the lead
and bring to a knife edge by rubbing on an Emery pencil pointer
or file. The other 6H pencil is sharpened to a long conical point
for the laying off of dimensions.
Some draftsmen prefer to bring one end of the pencil to a
chisel point and the other end of the same pencil to a conical
point. It is claimed that this method saves time, since it is
quicker to turn the same pencil end for end in laying off a dimen-
sion, than to lay down one pencil and pick up another. On the
other side it may be said that the continued sharpening of a
pencil at both ends rapidly decreases its useful length. At best,
this is a matter of personal choice and that method should be
adopted which is best suited to one's own needs. It is impera-
tive, however, that a 6IT conical pointed lead be kept for no
other purpose than the laying off of dimensions.
15. Ink. — One of the best inks manufactured for drafting pur-
poses is Higgin's Water-proof India Ink. Other excellent inks
are made by F. \Yeber & Co., Keuffel & Esser and Eugene
Dietzgen. Inks are made in many colors, though the practice of
using colored inks on drawings is steadily decreasing. The use
of colored inks on some forms of mapping is frequently advan-
tageous.
16. Paper. — Drawing paper is made in a variety of styles to
meet a variety of needs. In general, the white papers are in-
tended for finished or inked drawings, and the cream or buff
papers for pencilled or detail drawings. In the average drafting
24 MKCHANICAI, DRAWING
room by far the greater number of drawings are made in pencil
on the buff or cream detail paper. These drawings are then
traced and from the tracing blue prints are obtained ; this process
will be described later. Many drawings are made, however,
directly in ink on white paper. Maps, railroad layouts, or any
other drawings which may have to stand hard use, are made in
ink on a heavy white paper backed with tough linen. The sur-
face of such a drawing is sometimes protected by a coat of
white varnish.
A paper intended to receive ink should be white, of close firm
texture, and should neither repel nor unduly absorb liquids. A
good paper should stand at least four successive erasures of an
ink line.
Two papers which meet these requirements are Whatman's
and F. Weber & Co.'s "Fabriano." These papers are made in
standard commercial sized sheets, or in 10 to 50 yard rolls, with
three styles of finishing the surface, hot pressed (smooth), cold
pressed (medium), and rough (course grained). The cold
pressed paper is the most serviceable for general use. That side
of the paper from which the makers water mark can be read is
regarded as the "right" side.
17. Erasers.- — For the erasure of pencil lines use a Ruby eraser.
Fig. 29a. — Erasing shield.
Ink lines may best be erased by removing only the surface of the
line with an ink eraser, completing the erasure with a Ruby
eraser. Under no circumstances should any form of "scrateher"
or knife blade be used for erasing.
INSTRUMENTS AND THEIR USE 2$
An erasing stencil consisting of a thin piece of metal containing
holes of various shapes may be used to protect other lines adja-
cent to the one being erased.
A soft sponge eraser, or cube of Artgum, is serviceable in
giving the drawing a general cleaning without erasing any lines.
18. Miscellaneous. — Thumb tacks are useful for temporarily
holding the drawing in place or for holding reference notes or
sketches to the board.
If the paper is not to be stretched and the margins pasted
down, it should be held in place by one-ounce iron tacks. These
tacks can be pushed into the board until their heads are flush
with the paper. Such tacks offer no obstacle to the sliding back
and forth of T square and triangles as do the thumb tacks.
The pen holder should have a large grip (about y 2 " in diam-
eter) tapering off into a slender handle. The best material for
the grip is cork or soft unglazed wood. Gillott's No. 303 and
No. 404 are excellent pens for medium sized free hand lettering.
A pen wiper should be kept close at hand and frequently used.
Chamois or lintless linen are excellent materials for this purpose.
The sponge, glass bowl, and jar of paste are used in making
a stretch as described in Art. 19.
CHAPTER II.
General Instructions.
19. To Make a Stretch. — Lay the paper on the drawing board
and fold upward about y 2 " of each edge. Fill the small glass
bowl with water and by means of the sponge thoroughly wet the
exposed surface of the paper taking care not to dampen the
folded edges. Squeeze all water from the sponge and remove
all surplus water from the paper by absorbing it with the sponge.
Spread paste on the inner surfaces of the folded margins. Lift
the paper from the board and lay the side which has been wet
next to the board. Paste the margins to the board working from
the center outward and at the same time smoothing as many
wrinkles as possible from the paper. The paper should be
allowed to dry in a horizontal position, and when dry should
present a smooth surface free from wrinkles with edges firmly
fastened to the board.
20. Penciling. — The pencils should be sharpened as stated in
Art. 14, the 6H being used for the drawing of lines and the 3H
for lettering.
In making a line hold the pencil nearly vertical with a slight
inclination to the right. The chisel point should touch the paper
about 1 / 32 " away from the straight edge. All lines should be
cfrawn from left to right and away from the body, even
though to do this necessitates the turning of the drawing board
or moving around the drafting table, so that the free and even
movement of the arm may not be cramped. The lines should
be very fine which is accomplished only by maintaining a sharp
edge on the chisel point of the pencil.
The student should always remember that the three essential
characteristics of a good draftsman are speed, accuracy and
neatness. The last two go hand in hand and are of more impor-
tance than the first.
21. Character of Lines. — For ease in reading a drawing, various
kinds of lines are used, each kind expressing to the trained eye
a certain fixed meaning. Unfortunately there is no universally
GENERAL INSTRUCTIONS 2J
accepted standard, but the alphabet of lines shown in Fig. 30 is
commonly accepted by most draftsmen in this country.
' V/s/jb/e ouf/ine.
_ /^i/zs/bfe out/zne^crshesj-"
/one?, spaces -£ "/o/?y.
/7//77ens/o/7 //ne.
Center ///7e_, abs/?es ^"/onc?
c/ots §-' ' /ony, spaces A'Vor?^
. ■ //7c/ef/'/7/te bracr/r //s?e.
S/?ac/e //he., f-w/ce f/?e weight
of the ouf/zne.
Fig. 30. — Character of lines.
The dimensions given are to be judged solely by the eye. Prac-
tice so trains the judgment of the eye that these distances can
be obtained with surprising accuracy. Uniformity in the length
and spacing of the dots and dashes should be maintained, how-
ever long the line may be. The otherwise pleasing effect of a
drawing is easily marred by irregularity in dot and dash lines.
The same degree of care, in this regard, is not as essential in
pencil work which is to be inked or traced.
On inked drawings all the lines shown in Fig. 30 should be
drawn in black ink. A space is left near the center of dimension
lines for the insertion of figures. In structural drawing the
dimension line is continuous and the figures are placed just above
the line. The use of colored inks for dimension and center lines
is not desirable as it requires a greater expenditure of time on
the part of the draftsman, and good prints cannot be made from
tracings on which colored inks were used. Happily the modern
practice is to use only black ink on all drawings which are not
to be colored for display. An interesting inquiry into modern
drafting room practice, conducted by Prof. Reid of the Armour
Institute of Technology, shows that only 13 per cent, of one
hundred firms questioned use colored inks for dimension and
28 MECHANICAL DRAWING
center lines. The remaining 87 per cent, use the black line as
stated above.
22. Inking. — In general a drawing should be complete in pencil
before starting the inking. The speed of the inking will be
greatly increased if some definite system is followed such as the
one here outlined :
1. Ink all circles and circular arcs first, beginning with the
smallest.
2. Ink all horizontal dotted lines.
3. Ink all vertical dotted lines.
4. Ink all other dotted lines.
5. Ink all horizontal full lines.
6. Ink all vertical full lines.
7. Ink all other full lines.
8. Ink center and dimension lines.
9. All figures and notes.
10. All cross hatching.
11. Title and border.
In inking horizontal lines, ink those at the top of the drawing
first, and work downward; in inking vertical lines, ink those at
the left of the drawing first and work to the right.
The tendency of the student is to make all lines too light. The
finest line should be heavy enough to stand out clear and bold to
the eye. There should be no minute white spaces in the line
indicating that the nibs of the pen were set so close together as
to render impossible an even flow of ink. It is advisable to rule
on scrap paper a standard set of the lines to be used on the
drawing. These lines may then be referred to when resetting
the pen after cleaning. This is not so essential if the pen con-
tains a device which automatically returns the nibs to their origi-
nal position after cleaning.
23. Symbolic Cross Hatching. — It is frequently desirable to
represent an interior view of an object as though it had been
exposed to view by an imaginary cutting plane, that portion of
the object between the observer and the cutting plane being
regarded as removed. Such a view is called a section, and is
GENERAL INSTRUCTIONS
29
indicated on the drawing by covering the area in question with
parallel straight lines, usually making an angle of 45 ° with the
horizontal. These lines are called cross hatching.
^^^co^rr/? j|||||
Z/f/4^J
Fig. 31. — Symbolic cross hatching.
By varying the character and spacing of the lines composing
the cross hatching various materials may be indicated. There is
no universally accepted standard of symbolic cross hatching due,
30
MECHANICAL DRAWING
possibly, to the great number of materials used in engineering
construction. It is advisable, therefore, to plainly letter the
material in addition to the symbolic cross hatching, the function
of the latter being only to indicate that different materials are
used in the given design. The conventional symbols shown in
Fig. 31 are accepted and used by many draftsmen in this country.
TIN
7\
^
7Ps
Fig. 31a. — Representation of stone and brick masonry.
It is to be noted that different materials in the same section
are best contrasted by sloping the cross hatching in opposite
directions.
The spaces between the lines of the cross hatching are judged
solely by the eye, but care should be taken to maintain uniformity
of spacing. It is a helpful guide to glance back at the spacing
of the last four or five lines drawn. Various forms of "section
liners" are on the market which are merely devices for mechan-
ically regulating the spacing. Unless a great amount of cross
hatching is being done their purchase is not to be recommended.
A home-made device to accomplish the same purpose is shown
GENERAL INSTRUCTIONS
31
in Fig. 32. It is made of thin wood and is used by slipping the
block and holding the triangle, then holding the triangle and
slipping the block, etc. One piece of wood will evidently main-
tain the same spacing and cannot be changed, so that several
pieces should be kept on hand for various spacings.
Fig. 32. — Section line device.
The width of the spaces is largely dependent upon the area
to be cross hatched and no rule in this connection can be given.
The tendency of the student, however, is to place the lines too
close together.
24. Tinting. — On large drawings it is frequently more advan-
tageous to distinguish various materials by the use of different
colored washes, instead of by cross hatching. Tinting is also
largely used in map drawing to clearly indicate the various divi-
sions of the map. Architectural drawings are nearly always
tinted, thereby gaining greatly in beauty and realistic effect.
The paper should be of good quality and cold pressed.
The size of the brush should depend somewhat on the area
to be tinted, sharp turns and small corners demanding a finer
pointed brush than would a large unbroken area. In any case
the brush should naturally assume a good point when filled with
the wash or plain water.
The wash is prepared by lightly rubbing the moistened brush
on a cake of color and then stirring the brush in a small porce-
$2 MECHANICAL DRAWING
lain or china dish containing water. The wash had best be too
light in color rather than too dark. The tinted area may easily
be darkened by applying a second coat of the wash. But if the
original wash is too dark, it is an extremely difficult task to
lighten the tinted surface.
Before applying the wash the board should be inclined at an
angle of approximately 15 , so as to induce a gentle downward
flow of the liquid.
Fill the brush with the wash, and starting at the upper por-
tion of the drawing apply the wash from left to right in such a.
quantity as to form a narrow horizontal puddle of the wash.
Draw this surplus color downward, continuing to work from
left to right. When the bottom edge is reached, dry the brush
by pressing between the thumb and forefinger of the left hand,
and use the brush as a sponge to absorb the surplus wash. Any
part of the wash which has perchance been drawn outside the
bounding lines of the figure, should be permitted to thoroughly
dry before removing with a pencil eraser.
A graded tint may be secured by applying at the upper edge
of the area the darkest color desired and drawing the wash
downward by adding with the brush a gradually increasing quan-
tity of pure water.
Since sediment is apt to form in the bottom of the saucer con-
taining the wash, it is better to touch the brush to the upper
portion of the wash, not permitting it to touch the bottom of the
dish.
25. Erasing. — Pencil lines should be erased by means of a
Ruby or Emerald eraser. The small particles of rubber caused
by the erasing should be dusted off with a brush or cloth. The
palm of the hand, if clean and dry, may also be used for this
purpose.
Ink lines should not be erased until thoroughly dry. India ink
seldom penetrates the surface of good drawing papers. The
endeavor should be to remove the coating of ink without injur-
ing the surface of the paper. This is best accomplished by
disturbing and loosening the coating of ink with an ink eraser,
GENERAI, INSTRUCTIONS 33
and finishing the erasure with a pencil eraser. Any form of
knife edge or scratcher should be used with the greatest care.
The danger of such a tool is that the surface of the paper may
be so destroyed as to render it impossible to re-ink over the
erasure.
It is frequently desirable to give a drawing, a general cleaning.
This may be accomplished by lightly rubbing the drawing with
a sponge rubber or piece of Artgum. Pass over the inked lines
as lightly as possible as even the softest rubber tends to slightly
destroy the intense blackness of the ink which is so desirable.
Many draftsmen satisfactorily clean a drawing by rubbing
bread crumbs over its surface with the palm of the hand.
26. Abbreviations. — The following abbreviations are frequently
used in many drafting rooms :
Feet or Foot
Ft., ft., or '.
Inches or Inch
In., in., or ".
Degrees or Degree
o
Minutes or Minute
/
Seconds or Second
"
Angle
Z.
Center to Center
c to c.
Pitch
p.
Diameter
Dia. or D.
Radius
Rad. or R.
Circumference
Circum.
Hexagonal
Hex.
Square
Sq.
Threads
Thds.
Threads per Inch
Thds. per In
Revolutions per Minute
R. P. M.
Pounds
lbs or ±t
There is far less uniformity of practice as regards the sym-
bolic meaning of colors to represent various materials, than is
the case in cross hatching. The following washes are used by
some large concerns, but are by no means universal :
34
MECHANICAL, DRAWING
Cast Iron
Payne's Grey
Wrought Iron
Russian Blue
Steel
3 parts Russian Blue, i part
Crimson Lake.
Brass
Gamboge
Copper
4 parts Crimson Lake, I part
Burnt Sienna
Lead or Babbitt
Light India Ink
Glass
Light Prussian Blue with line
shading
Brick
Crimson Lake with section
lines
Manufacturers of drafting supplies have on the market vari-
ous colors labelled "Cast Iron," "Steel," "Wood," etc., which
closely approximate in color the material to be represented. Until
some standard is authoritatively recommended by the leading en-
gineering societies and generally adopted by draftsmen, all sec-
tions should be clearly lettered whether cross hatched or tinted.
CHAPTER III.
Lettering.
27. Purpose. — It is hardly possible to convey on a drawing
the required information by means of the graphic language of
lines alone. Such data as the figures representing lengths and
sizes, explanatory notes, statements as to kind of material, finish,
number of pieces desired, title, etc., must be lettered. If the
lettering is to be serviceable it must be neat and legible, and of
a style that permits rapid execution.
28. Style. — The style of lettering adopted for working draw-
ings should possess these three important characteristics, beauty,
legibility, and ease of execution. If any one of these features
be lacking the quality of the other two is necessarily depreciated.
Beauty to the trained, technical eye does not mean ornate
letters with fancy scrolls and appendages, but rather letters that
are appropriate to the work in hand and of modest, unassuming
appearance. The general tone of any drawing is greatly im-
proved by well executed lettering, and on the other hand poor,
or inappropriate, lettering spoils the appearance, however well
the line work be executed.
Legibility is dependent not only upon the type of the lettering,
but is even more affected by the spacing of letters and words
and whether lower case letters or capitals are used. Words are
read not by spelling out the composing letters, but by familiarity
with the forms of the words. The body of any written matter,
be it in long hand, typewritten, or printed, is in lower case letters,
and hence the eye of the reader has become accustomed to the
forms of words expressed in lower case letters. It is, then,
important that all notes on a drawing be stated in lower case
lettering, reserving the use of capitals for headings requiring
particular emphasis or titles. Unfortunately some men and some
systems advocate the use of capitals for all notes. Such prac-
tice is deplorable and is followed only by a small minority of
draftsmen.
2,6 MECHANICAL DRAWING
Ease of execution depends solely upon the type of lettering.
Economically any result which is disproportionate to the amount
of time and energy required in its accomplishment is undesirable.
No thinking person would tolerate an expenditure of four hours
in lettering a drawing the rest of whose execution required but
two hours. Ornate letters composed of tree limbs with clinging
vines, or isometric block letters casting shadows of questionable
accuracy, or even so-called mechanical letters laboriously made
with the ruling pen and bow compass at the expense of the
nervous system of the draftsman, are when used in ordinary
drafting, monstrosities which are happily passing into general
disrepute. Since the primary purpose of lettering a drawing is
to state additional information, no letters are appropriate which
detract attention from the drawing itself. The lettering and line
work should blend into one harmonious whole, and no form of
lettering which is unduly ornate will fulfill this requirement.
29. The Reinhardt Letter. — The system of lettering advocated
fofh /*/ jjy W*/r // tovm '5
«
X
"v
's
X
•s
•v
"s
•s
"s
X
X
X
^
*v
s
"s
X
X
X
X
X
X
X
s
"s
* S v
Is
■ v 3
*s
s
s
' v 1
X
"s
'V
•s
•s
X
X
X
^s
^
X
X
X
X
rs
^
X
X
rs
X
LETTERING
o&nsiclergiio.h though frmllfoffaw ind^Gou^so, JLr^
Ease hfr hfu ShoulqsHo want v i dent im pro vvnwnt ov&r Th&
PffimfmStrthata moderates// sKiltful 'fyana f $ w'ded
TraToyour Thought on the> WorK it] hancf
Fig. 36. — Lettering done by a student on entering course in lettering.
/ihe appearance of a drawing/ whose workmanship
/s otherwise exce/ient, may <6e compiefety ' spoiied Ay
poor fettering/. //? the pracficaf drafting room the
draftsman who fetters neatfy and rapidty is regarded
as more vaiuahfe than or?e w/?ose ietfering /j mediocre.
The engineering student shoufd master a er/6o/cr
Fig- 39- — Conic sections.
These four curves can be drawn by actually determining the
curve cut from the cone by any plane, or by plotting a series of
points according to the law known to govern the generation of
each curve. Only the latter method will be treated in this chap-
ter.
44
MECHANICAL DRAWING
35. The Circle. — A circle is generated by a point moving in a
plane and remaining at a constant distance from a fixed point
called the center. The compass is a mechanical device for the
drawing of circles and no further discussion of this curve is
needed.
36. The Ellipse. — An ellipse is generated by a point moving in
a plane so that the sum of its distances from two fixed points,
called foci, remains constant.
To Construct an Ellipse. First Method.
Given: The major and minor axes. In Fig. 40 let AA X and
BB X be the major and minor axes, respectively. The foci may
be determined as follows : With B as a center and a radius
Fig. 40. — Construction of ellipse, first method.
equal to CAj (one-half the major axis) describes arcs cutting
the major axis in the points F and F x which are the desired foci.
The sum of the distances from any point on the ellipse to F and
F T must equal the constant distance represented by the major
axis AA a . The point B Tone end of the minor axis) is a point
on the ellipse since by construction
FB + F X B = 2A X C = AA X .
Assume any point on AA, lying between F and F l5 such as P.
With F as a center and a radius equal to A X P describe an arc.
CONIC sections 45
With F, as a center and a radius equal to AP, describe a second
arc cutting the first arc in the points M and M x . These two
points are on the ellipse since
MF + MF T — AP -f AjP = AA X .
In like manner other positions of P may be assumed and further
points of the ellipse obtained.
If it is clearly perceived that the sum of the distances from
the foci to one extremity of the minor axis must be equal to the
major axis (i. e., FB -j- F X B — AA X ) no difficulty should exist
in plotting an ellipse from any of the following combinations of
known data: (i) the major and minor axes, (2) the major axis
and one or both foci, (3) the minor axis and one or both foci.
At a given point on the ellipse to construct a tangent: Let R
be the given point. Draw RF and RF., ; TR bisecting the angle
thus formed is the required tangent.
At a given point outside the ellipse to construct a tangsnt:
Let X be the given point. With F x as a center and AA X as a
radius describe an arc. With X as a center and XF as a radius
describe a second arc cutting the first arc in the points H and K.
Draw FjK and F X H cutting the ellipse in the points Z and Y
which are points of tangency. The required tangents are XZ
and XY.
To Construct an Ellipse. Second Method.
Given: The major and minor axes. In Fig. 41 let AA X and
BB X be the major and minor axes respectively. With AA X and
BB, as diameters describe two concentric circles and through
the center draw any number of radial lines. At the points where
the radial lines intersect the smaller circle draw horizontal lines.
At the points where the radial lines intersect the larger circle
draw vertical lines. The horizontal and vertical lines intersect
at points of the required ellipse.
To construct a tangent at any point on the ellipse such as R;
draw a tangent to the outer circle at R r This tangent produced
meets the major axis at T. The required tangent to the ellipse
is T R.
4 6
MECHANICAL DRAWING
37. The Parabola. — A parabola is generated by a point mov-
ing in a plane so that its distance from a fixed point is constant-
ly equal to its distance from a given straight line. The given
Fig. 41. — Construction of ellipse, second method.
point is the focus and the straight line is the directrix. The axis
is a straight line drawn through the focus and perpendicular to
the directrix. The vertex is the point of intersection between
the curve and the axis, and lies midway between the focus and
the directrix.
To Construct a Parabola. First Method, Fig. 42.
Given: The focus and directrix. In Fig. 42, F is the focus,
DD X the directrix, AA t the axis, and V, midway between F
and A, is the vertex. At any point on the axis, as P, erect the
perpendicular MPM n . With F as a center and AP as a radius
describe an arc cutting the perpendicular through P at the points
M and M x which are two points on the required curve. The
law governing the motion of the generating point is fulfilled
since
MF --= AP = DM
Other points, such as N and N\ may be obtained in like manner.
CONIC SECTIONS
47
At a given point on the parabola to construct a tangent: Let
N be the given point. Draw NF and NC ; TN bisecting the
angle thus formed is the required tangent.
DJ234S678 9/\
Fig. 42. — Construction of parabola,
first method.
Fig. 43. — Construction of para-
bola, second method.
At a given point outside the hyperbola to construct a tangent:
Let X be the given point. With X as a center and XF as a
radius, describe an arc intersecting DD 1 at G and K. Through
G and K draw lines parallel to the axis, AA X , intersecting the
curve in the points of tangency H and L. The required tan-
gents are XH and HL.
To Construct a Parabola. Second Method, Fig. 43.
Given: The abscissa VC and the double ordinate AB.
Draw DA and EB equal and parallel to VC, and draw DE
parallel to AB. Divide DA and AC into the same number of
equal parts. From the divisions on DA draw lines to V and
through the divisions on AC draw lines parallel to VC. The
lines drawn from corresponding points of division intersect in
points on the parabola.
38. The Hyperbola. — An hyperbola is generated by a point
moving in the same place so that the difference of its distances
from two fixed points remains constant.
4 8
MECHANICAL DRAWING
To construct an hyperbola: In Fig. 44 let Wj represent the
constant difference, and let the two foci F and F x be the two
fixed points so placed that FV = F^j.
w
*&-£*
Fig. 44. — Construction of hyperbola.
Draw BBj, the perpendicular bisector of VV^. With F as
a center and any radius greater than FV X , as FP, describe an
arc. With F x as a center and a radius equal to FP — Wj de-
scribe a second arc cutting the first arc in the points N and N x .
These points will lie on the hyperbola since
FP = (FP— WJ = W x
which satisfies the law governing the motion of the generating
point. In a similar manner other points may be obtained.
If F x is used as a center for the larger radii and F as a center
for the smaller, the other branch of the hyperbola will be ob-
tained.
At a given point on the hyperbola to construct a tangent: Let
R be the given point. Draw RF and RF t ; TR bisecting the
angle thus formed is the required tangent.
CONTC SECTIONS 49
At a given point outside the hyperbola to construct a tangent:
Let X be the given point. With F x as a center and VV\ as a
radius describe an arc. With X as a center and XF as a radius
describe the arc FGK cutting the first arc in the points G and
K. Draw FK and F X G cutting the hyperbola in the points of
tangency Y and Z. The required tangents are XY and XZ.
If C, the point of intersection of the two axes be taken as the
point through which the tangents to the hyperbola are to be
drawn, the points of tangency will lie at infinity and the tangent
lines will be asymptotes.
CHAPTER V.
Orthographic Projection.
39. Orthographic Projection is the art of representing an ob-
ject on one or more planes so as to graphically show the lengths
and shapes of its lines and surfaces. All working drawings in-
tended to convey exact technical information from the designer
to the reader are made in accordance with the principles of or-
thographic projection. Technical drawing is a graphic language
of universal usage, its alphabet and vocabulary being the char-
acter of lines, conventions, and symbols previously discussed,
and orthographic projection its grammar.
40. Projection on One Plane. — An object is projected onto any
desired plane by drawing through the various points of the ob-
Fig. 45. — Projection of an object onto a single plane of projection.
ject lines perpendicular to the given plane; the points in which
these lines pierce the plane are the projections of the correspond-
ing points of the object. The projecting lines are called projec-
tors and the plane onto which the object is projected is the plane
of projection. Thus in Fig. 45 the object has been projected onto
ORTHOGRAPHIC PROJECTION
51
tht plane as shown. The resultant projection represents the ob-
ject as it would appear if viewed from in front, the point of sight
being an infinite distance away. This view alone describes only
the front face of the object and gives no information as to the
Fig. 46. — Cast iron fork projected onto three planes of projection.
shape of the top and sides. In order, therefore, to completely
represent any object it must, in general, be projected onto three
different planes, thus showing three views. The planes are gen-
erally placed so as to be mutually perpendicular (as the top,
52 MECHANICAL DRAWING
front and side of a box), the resultant projections showing the
object as though viewed successively from the top, front and
side.
41. Projection on Three Planes. — In Fig. 46 is shown a cast iron
fork surrounded by three planes which may be regarded as trans-
parent. The top plane lettered H is called the horizontal plane
of projection, the plane in front lettered V is called the vertical
plane of projection, and the plane at the side lettered P is called
the profile plane of projection. By letting fall from the object
lines perpendicular respectively to each of these planes, three
views of the fork are obtained. The projection on the H plane
represents the fork as it would appear were the observer look-
ing down upon it; the projection on V represents the fork as
though viewed from in front; and the projection on P represents
the fork as though viewed from the side. These three views
graphically describe all lines and surfaces of the fork, and
taken in conjunction give the three dimensions, length, breadth
and thickness.
The line of intersection between the H and V planes is known
as the ground line and is lettered GL. The line of intersection
between the P and V planes is lettered XY.
It is obviously impossible for the draftsman to actually draw
on three mutually perpendicular planes. He is limited to the one
plane as represented by his drawing paper. Some method, then,
must be used for bringing the three planes containing the three
views into one plane. This is accomplished as shown in Fig. 47
by raising the H plane about GL as an axis until it is coincident
with V, and revolving the P plane to the right about LY as an
axis until it also is coincident with V. The three views are now
found on one plane, the top view above the front view and the
side view at the right of the front view. In practice the drafts-
man, though employing mentally the process here given, does not
draw the three planes but shows only the three views as given
in Fig. 48. In Fig. 48 it should be noted that LX and LX 12 are
revolved positions of the same line, LX 3 .
Fig. 47. — The three planes of projection opened to form one plane.
"l — r
1 1
j i_
> —
\ 1 '■ ' ■ '
o o :
— 1 — 1 — 1 — 1 —
"A O V--
Fig. 48. — Top, front and side views of a cast iron fork.
54 MECHANICAL DRAWING
A dotted line is used to signify the invisibility of the line rep-
resented. A line may be invisible in one view and visible in an-
other.
42. Fundamental Principles. — From the foregoing discussion
and figures the following important principles are evident :
i. If a line is perpendicular to a plane its projection on that
plane is a point.
2. If a line is parallel to a plane its projection on that plane
will be parallel to the line.
3. If a surface is perpendicular to a plane its projection on
that plane is a line.
4. If a surface is parallel to a plane its projection on that
plane will show the true size and shape of the surface.
5. The top and front views of any point lie in the same verti-
cal line.
6. The front and side views of any point lie in the same hori-
zontal line.
7. The side view of any point is as far from XY as is the
top view from GL.
43. Sequence of Views. — In general it is advisable to first con-
struct that view most of whose lines are shown in true length.
Let it be desired to show three views of the square based wedge
illustrated in Fig. 49. It is evident that all lines of the base as
well as the edge AB are parallel to H and hence the top view
will be first constructed. At any convenient distance above GL
draw a square, equal in size to the base of the wedge, and in the
center draw a line equal to the length of the edge AB. The top
view is now completed by connecting the ends of the edge with
the corners of the square.
The front view is a triangle whose base is equal in length to
a side of the square, and whose altitude is equal to the height
of the wedge. All points of the front view must lie vertically
ORTHOGRAPHIC PROJECTION
55
under the corresponding points of the top view (Art. 42. Rule
5)-
To obtain the side view draw XY at any convenient distance
to the rig-lit of the front view. Draw horizontal lines from the
Fig. 49. — Three views of a wedge, pictorially showing method of
obtaining side view.
top view to XY, revolve to the right to meet GL, and let fall
perpendicular lines. These perpendiculars intersect horizontal
lines drawn from corresponding points of the front view in the
desired points of the side view.
56
MECHANICAL DRAWING
The student should never lose sight of the fact that the top,
front and side views have been made on mutually perpendicular
planes, and from these three views a mental conception of the
entire object is gained.
As an aid in properly locating the various points of an object,
the points of the top view are lettered a, b, c. etc., the corre-
sponding points of the front view a', b', c', etc., and the corre-
sponding points of the side view a 1 ', b p , c p , etc. In actual draft-
ing practice the points of a drawing are not lettered nor are the
projecting lines shown. Also the center lines of the various
views are made to serve the purpose of the ground line (GL)
and the profile plane trace (XY). Until, however, the student
has thoroughly mastered the principles of orthographic projec-
tion, he will find it greatly to his advantage to letter all critical
points, draw all projecting lines, and to draw and letter GL
and XY.
A few illustrative problems will now be considered.
44. To Obtain the Top, Front and Right Side View of a Hollow
Cylinder. Fig. 50.
Fig. 50. — Hollow cylinder axis Fig. 51. — Hollow cylinder axis
perpendicular to H. perpendicular to P.
Given: The altitude and the outer and inner diameters of the
cylinder; the axis of the cylinder to be perpendicular to H.
ORTHOGRAPHIC PROJECTION 57
The top view consists of two concentric circles of the given di-
ameters.
For the front view construct a rectangle whose width is equal
to the diameter of the larger circle and the altitude equal to the
given altitude. Within this rectangle construct a second rectan-
gle of equal altitude but whose width is equal to the diameter of
the smaller circle. The limiting lines of the inner rectangle are
invisible and hence are dotted.
The right side view is identical with the front view ; or it may
be obtained by projecting the points of the top view onto XY,
revolving to meet GL, and letting fall perpendiculars to meet
horizontal lines drawn through the corresponding points of the
front view.
45. To Obtain the Usual Three Views of a Hollow Cylinder.
Fig. 51.
Given: As in the preceding problem except that the axis is
perpendicular to P.
Since the axis of the cylinder is perpendicular to P the center
lines of the rectangles forming the top and front views are paral-
lel to GL.
The construction of the three views is obvious.
46. To Obtain the Usual Three Views of a Cone. Fig. 52.
Given: The diameter of the base and the altitude; the axis
to be perpendicular to H; the apex pointing towards H.
The top view consists of a circle whose diameter is equal to
the given diameter of the base.
The front view is an isosceles triangle whose base is equal to
the given diameter and the altitude equal to the given altitude of
the cone.
The side view is identical with the front view, or it may be
constructed by the indicated revolution.
47. To Obtain the Top, Front and Left Side Views of the Frus-
trum of a Cone. Fig. 53.
Given: The altitude and the diameters of each of the bases;
the axis perpendicular to P ; the larger base nearer the profile
plane.
5
58
MECHANICAL, DRAWING
The top and front views are identical, each one consisting of
a trapezoid of the given altitude, the two ends being equal in
length to the given diameters of the bases.
Fig. 52. — Cone axis perpen- Fig. 53.— Frustrumof a cone, axis
dicular to H. perpendicular to P.
The left side view may be obtained by placing the profile plane
at the left and revolving the points of the top view counter-
clockwise as shown. The result of this revolution is two concen-
tric circles with diameters equal to the given diameters of the
bases. The smaller base is not visible from the left and hence
the inner circle is dotted.
48. To Obtain the Top, Front and Eight Side Views of a Hexago-
nal Prism. Fig. 54.
Given: The altitude, and the size of the base; the axis to be
perpendicular to H ; two faces parallel to V.
The top view consists of a regular polygon of given size, two
sides being parallel to GL.
The construction of the front and side views is obvious. Note
that in the front view the edges m'n' and kT are invisible but
coincide with the visible edges c'd and e'f respectively. A
similar case occurs in the side view.
In Fig. 55 is shown three views of the same hexagon except
that two faces are now perpendicular to V.
ORTHOGRAPHIC PROJECTION
59
Fig. 54. — Hexagonal prism two
faces parallel to V.
Fig- 55-— Hexagonal prism two
faces perpendicular to V.
49. To Obtain the Usual Three Views of a Hexagonal Prism.
Fig. 56.
Given: The altitude, and the size of the base; the axis to be
perpendicular to P ; no face to be either parallel or perpendicular
to H or V.
It is evidently more convenient to first construct the side view.
L
g .
n
k
-— <-
— ■ i-
"''•~^
1
f
e
m
'""-^ X
V, \ \
d
b
c
a
X '■ \ '"■
! 1
v» > ', ' . 1 1
ri
rri
_4-kk4iief
t
fc
a'
--*-
1
8
I!
d
\ A ! d\|P
i
c'
--4-
c^d/ j/
f
e
""
t
Fig. 56. — Hexagonal prism axis perpendicular to P.
To construct the side view; at any convenient distance be-
60 MECHANICAL DRAWING
tween GL and to the right of XY draw a regular hexagon no
side of which is either parallel or perpendicular to GL or XY.
To construct the top view; project the points of the side view
to GL, revolve counter-clockwise to XY, and draw ab, cd,
etc., equal in length to the given altitude. The lateral edges
CD and EF are invisible when viewed from above H (that is,
when looking down on the side view from above GL), hence
cd and ef are dotted. The top view is completed by drawing
ga and gb.
To construct the front view; project the points of the top
view downward to meet horizontal lines drawn from the cor-
responding points of the side view. The lateral degrees GH and
KL are invisible when viewed from in front of V (that is, when
looking at the side view from the left of XY), hence g'h' and
kT are dotted.
50. Revolution. — In the foregoing illustrations the objects
were situated in the simplest position relative to the planes of
projection, that is, with as many lines as possible parallel to H,
V and P. This is the natural way of placing an object and
would be the one chosen were the choice left to the convenience
of the draftsman. It is sometimes necessary, however, to rep-
resent an object with axis oblique to one or more of the planes
of projection.
Conceive three lines passed through the object and intersect-
ing at its center, one of the lines being perpendicular to H, the
second perpendicular to V, and the third perpendicular to P.
The object may be brought into obliquity with any desired plane
of projection by revolving the object about the proper one of the
foregoing three lines as follows :
First, the object may be revolved about the line perpendicular
to H, which has the effect of turning it on its base to the right or
left.
Second, it may be revolved about the line perpendicular to V,
causing the object to lean to the right or left.
Third, it may be revolved about the line perpendicular to P,
causing the object to tip forward or backward.
ORTHOGRAPHIC PROTECTION
6l
If an object be represented in its simplest position and is then
revolved in any one of the foregoing ways, two views will be
changed while the third view will remain identical with the cor-
responding view of the object in its original position. The un-
changed view will lie on that plane of projection to which the axis
of revolution is perpendicular and should be the first view con-
structed.
In Fig. 57 are shown three views of a wedge in its simplest po-
sition . The arrow points are placed on the projecting lines to in-
dicate the direction in which they were drawn.
In Fig. 58 the wedge has been revolved from its original posi-
tion through an angle of 45 ° to the right about an axis perpen-
X
Y
Fig. 57- Fig- 58.
Wedge revolved about an axis perpendicular to H.
dicular to H. The top view is identical with the top view of Fig.
57, except that the sides make an angle 45 ° with GL. During
this revolution all points of the wedge remain the same distance
from H. Hence the front view of Fig. 58 is constructed by let-
ting fall perpendicular lines from points of the top view to meet
horizontal lines drawn from corresponding points of the front
view of Fig. 57. The side view is constructed in the usual
manner.
In Fig. 60 the wedge has been revolved .from its original posi-
tion through an angle of 45 to the right about an axis perpen-
62
MECHANICAL DRAWING
dicular to V. The front view is identical with the front view of
Fig. 59 except that it leans to the right at an angle of 45 °. Dur-
ing this revolution all points of the wedge remain the same dis-
Fig. 59. Fig. 60.
Wedge revolved about an axis perpendicular to V.
tance from V. Hence the top view is constructed by erecting
perpendicular lines, from the points of the front view, to meet
horizontal lines drawn from corresponding points of the top
view of Fig. 59. The side view is constructed in the usual
manner.
In Fig. 62 the wedge has been revolved from its original posi-
tion backward through an angle of 30 about an axis perpendicu-
lar to P. The side view is identical with the side view of Fig.
61 except that it tips backward. During this revolution all points
of the wedge remain at the same distance from P. Hence the
top view is constructed as follows : From points on the side
view erect perpendiculars to GL, revolve to XY, and draw hori-
zontal lines to meet vertical lines let fall from corresponding
points on the top view of Fig. 61. The front view is obtained by
drawing horizontal lines from points on the side view to meet
vertical lines let fall from corresponding points of the top view.
Careful attention is needed to ascertain those lines which are
invisible and hence dotted.
51. Successive Revolutions. — In the problems of Art. 50 the
initial position of the wedge was the same before each revolu-
ORTHOGRAPHIC PROJECTION
63
tion. It is sometimes necessary for the draftsman to revolve an
object about a certain axis, and from that position to again re-
volve it about a second axis, and possibly to again revolve it
about a third axis. In this manner the object can be placed in
any conceivable position relative to the planes of projection. No
d
^"-^S^-^
b
^^^
^"-^-^
c
Fig. 6r.
Fig. 62.
Wedge revolved about an axis perpendicular to P.
principles are used in successive revolutions other than those de-
veloped in the preceding articles.
In Fig. 63 is shown the original position of a pyramid and its
successive revolutions about axes perpendicular to H, V and P
respectively. In revolving about the axis perpendicular to V
6 4
MECHANICAL DRAWING
13
ORTHOGRAPHIC PROJECTION
65
the front view is identical with the front view immediately pre-
ceding, the other two views being constructed in the usual man-
ner.
Fig. 64. — Circle revolved successively about axes perpendicular to V and//.
In revolving about the axis perpendicular to P the side view
is identical with the side view immediately preceding. The
auxiliary line G x Lj is used as an aid in reproducing this view.
Fig. 65. — Cone revolved successively about axes perpendicular to Kand H.
In Fig. 64 the original position of the circle is parallel to H
and perpendicular to V, the top and front views only being
66
MECHANTCAI, DRAWING
Fig. 67.
Auxiliary plane of projection.
ORTHOGRAPHIC PROJECTION
67
shown. The circle is then revolved about an axis perpendicular
to V. The front view remains a straight line but is inclined to
GL, at any desired angle. The top view is constructed in the
usual manner. The circle is now further revolved about an axis
perpendicular to H. The top view is identical with the preced-
ing top view except that the axis makes any desired angle with
GL. The front view is constructed as usual.
In Fig. 65 is shown a cone which has been successively revolved
about an axis perpendicular to V and about an axis perpendicu-
lar to H. The original position of the cone was taken so as to
make the base parallel to H, the apex pointing downward from
H.
52. Oblique Plane of Projection. — An object is sometimes en-
countered which can not be placed so that all of its faces are
parallel to the three planes of projection. One face, at least,
may be oblique and this face may be best shown by projecting it
onto an auxiliary parallel plane. The projection on this paral-
lel plane will show the true shape and size of the face. A case
of this kind is illustrated in Fig. 66, the orthographic projection
being shown in Fig. 67.
It is frequently sufficient to project only the oblique face onto
Top V/ew
L eft Side View
Fig. 68. — Auxiliary end view of pipe elbow,
the auxiliary plane and to disregard, in that view, all other lines
of the object. Thus in Fig. 68 only the oblique flange is projected
6S
MECHANICAL DRAWING
onto the parallel plane whose line of intersection with H is AB.
The auxiliary plane is then revolved about AB as an axis until
coincident with H.
53. Sectional Views. — The internal construction can sometimes
be shown to best advantage, by passing an imaginary cutting
plane through the object and theoretically removing that part
of the object which lies between the observer and the cutting
plane. In Fig. 69 is shown a top view and a vertical section of
Fig. 69. — Top view and cross section of a cylinder cover.
a cast iron cylinder and cover. Note that the cutting plane passes
through two bolts but that these bolts are not cross hatched. It
is an idiom of the graphic language that bolts, arms of pulleys,
webs, keys, shafts, and gear teeth are never cross hatched. More-
over in Fig. 55 only two bolts are shown in section, whereas it is
obvious that five could be seen in the sectional view. The loca-
tion of these bolts, however, is clearly shown in the plan and
their position in the sectional view would appear peculiar and
confusing. Practical utility warrants the statement that the
ORTHOGRAPHIC PROJECTION
6 9
sectional view should show only that data which conveys useful
information and discard all else even though pure theory would
require it to be shown.
The cross section of a pulley is shown in Fig. 70. The arm is
Section on AB
Section onAB
Not thus § 77? us
Fig. 70. — Front view and cross sections of a pulley.
not cross hatched but the shape is shown by a separate section
revolved into the plane of the paper.
The draftsman may legitimately make use of the fact that an
Fig. 71. — Top view and half section of a Hill coupling,
object is symmetrical about a certain axis, by showing one-half
?o
MECHANICAL DRAWING
the view full and the other half in section. Fig. ji illustrates
this practice.
It is sometimes convenient to represent only a small part of a
surface as removed in order to show in section the construction
Fig. 72. — Globe valve showing broken section,
lying beneath. Such a view is called a broken section and is il-
lustrated in Fig. 72.
ORTHOGRAPHIC PROJECTION JL
PROBLEMS.
Geometric Solids.
Each of the following problems may be placed in a space
5" x.5". The layout of a plate which is adaptable to spaces of
this size is shown in the appendix.
The expression "three views" is understood to mean the top,
front and side views.
ia, ib, ic. Draw three views of a hollow cylinder. Fig. 73, with
(a) axis perpendicular to V; (b) axis perpendicular to H; (c)
axis perpendicular to P.
2a, 2b, 2c. Draw three views of a cone. Fig. j$, (a) axis per-
pendicular to V, apex towards V; (b) axis perpendicular to H,
apex away from H; (c) axis perpendicular to P, apex towards
P.
3a, 3b, 3c. Draw three views of a square based pyramid. Fig.
73, (a) axis perpendicular to V, apex away from V; (b) axis
perpendicular to H, apex towards H; (c) axis perpendicular to
P, apex away from P.
4a, 4b, 4c. Draw three views of a hexagonal pyramid, Fig. y^,
(a) axis perpendicular to V, apex towards V; (b) axis perpen-
dicular to H, apex away from H, no side of the base parallel or
perpendicular to V; (c) axis perpendicular to P, apex towards
P, two sides of the base perpendicular to V.
5a, 5b, 5c. Draw three views of a triangular pyramid. Fig. y^,
(a) axis perpendicular to V, apex away from V, no side of the
base parallel to H; (b) axis perpendicular to H, apex towards
H, one side of the base parallel to V; (c) axis perpendicular to
P, apex towards P.
6a, 6b, 6c. Draw three views of a hexagonal prism, Fig. y^>,
(a), (b) and (c) as in problem 4.
7a, 7b, 7c. Draw three views of a wedge. Fig. y^, ( a ) short
edge nearest H, long side of base parallel to V; (b) base parallel
to V, short edge farthest from V, short side of base parallel to H.
8a, 8b, 8c. Draw three views of a triangular prism, Fig. y^,
(a) axis perpendicular to V; (b) axis perpendicular to H; (c)
axis perpendicular to P.
72
MECHANICAI, DRAWING
Fig. 73. — Geometric objects.
coa/£, rtrusr/euM.
orthographic projection 73
9. Draw three views of a flight of steps, Fig. 73. Scale 1" =
i'-o".
10a, 10b, ioc. Draw three views of a frustrum of a square
based pyramid, Fig. y^, (a) axis perpendicular to V, small base
nearest V; (b) axis perpendicular to H, large base nearest H;
(c) axis perpendicular to P, large base nearest P.
11a, 11b, lie. Draw three views of a cross, Fig. 73, (a) face
marked "A" nearest V; (b) "A" nearest H; (c) "A" nearest P.
12a, 12b, 12c. Draw three views of a frustrum of a cone, Fig.
73, (a), (b) and (c) as in problem 10.
Machine Details.
13. Draw top and front views of a monkey wrench. Fig. 74.
Scale
14. Draw front view and longitudinal section of a bearing,
Fig. 74. Scale
15. Draw three views of a bracket, Fig. 74. Scale
16. Draw three views of a support. Fig. 74. Scale.
17. Draw an end view and longitudinal section of a flange
connection, Fig. 75. Half size.
18. Draw three views of a pivot. Fig. 75. Half size.
19. Draw three views of a bearing, Fig. 75. Scale 3" = i'-o".
20. Draw three views of a pedal. Fig. 75. Scale i^i" = i'-o".
21. Draw the top, front, and auxiliary plane view of a lever,
Fig. 76. Scale 3"= i'-o". (Break the rod in order to shorten
length.)
22. Draw three views of a rod support, Fig. 76. Scale 3" =
i'-o".
2^. Draw three views of a packing gland, Fig. 76. Half size.
24. Draw three views of a lever support, Fig. 76. Full size.
Kevolution.
An entire plate had best be devoted to each of the following
problems. If a plate of the size shown in the appendix is used,
each group of three views will be placed in a rectangle 5" x 7^2".
25. Draw three views of a wedge, Fig. 73, axis perpendicular
to H, short edge nearest H, and long side of base parallel to V,
6
74
MECHANICAL DRAWING
Cast /ron
Fig. 74.— Machine details.
ORTHOGRAPHIC PROJECTION /5
and revolve it (a) through an angle of 15 to the right about an
axis perpendicular to H; (b) through an angle of 45 to the left
about an axis perpendicular to V; (c) forward through an angle
of 45 about an axis perpendicular to P.
26. Draw three views of a hexagonal prism. Fig. 73, axis per-
pendicular to H, two sides of the base parallel to V, and revolve it
(a) 30 to the right about an axis perpendicular to V; (b) 30 to
the right about an axis perpendicular to H; (c) 30 forward
about an axis perpendicular to P.
27. Draw three views of a hexagonal pyramid, Fig. y^, accord-
ing to the instructions given in problem 26.
28. Draw three views of the frustrum of a pyramid. Fig. y^,
axis perpendicular to H, large base nearest H, two sides of base
parallel to V, and revolve it (a) 30 to the left about an axis per-
pendicular to H; (b) 1-5 ° to the left about an axis perpendicular
to V; (c) 45 forward about an axis perpendicular to P.
29. Draw three views of a triangular prism, Fig. 73, long side
parallel to H and V, and revolve it (a) 30 to the right about an
axis perpendicular to H; (b) 6o° to the left about an axis per-
pendicular to V; (c) 45 backward about an axis perpendicular
to P.
30. Draw three views of a square pyramid, Fig. y^, axis per-
pendicular to H, two sides of the base parallel to V, and revolve
it (a) 15 to the right about an axis perpendicular to H; (b) 45
to the left about an axis perpendicular to V; (c) 6o° forward
about an axis perpendicular to P.
Successive Revolution.
31. Draw three views of a hollow cylinder. Fig. 73, axis per-
pendicular to P, and revolve it (a) 30 to the right about an
axis perpendicular to H; (b) from the position obtained in (a)
revolve 45 ° to the left about an axis perpendicular to V; (c)
from the position obtained in (b) revolve 30 backward about
an axis perpendicular to P.
32. Draw three views of a cone, Fig. 73, axis perpendicular
to H, apex nearest H, and revolve it (a) 45 to the right about
an axis perpendicular to V; (b) from (a) revolve 6o° to the left
76
MECHANICAL DRAWING
Stee
Fig. 75.— Machine details.
ORTHOGRAPHIC PROJECTION
77
Forgecf Sfe e/
FACK/NG GLAND.
Stee/
LEVER SUPPORT.
$ fee/
Fig. 76. — Machine details.
78 MECHANICAL DRAWING
about an axis perpendicular to H; (c) from (b) revolve 30
forward about an axis perpendicular to P.
33. The same as problem 25 except that the revolutions are to
be continuous. \
34. The same as problem 26 except that the revolutions are to
be continuous.
35. The same as problem 27 except that the revolutions are to
be continuous.
36. The same as problem 28 except that the revolutions are to
be continuous.
37. The same as problem 29 except that the revolutions are to
be continuous.
38. The same as problem 30 except that the revolutions are to
be continuous.
Auxiliary Views.
39. Draw the top and front views of the given object in its
simplest position. Obtain an auxiliary view projected onto a
plane parallel to an inclined face.
a. Wedge.
b. Triangular prism.
c. Square pyramid.
d. Hexagonal pyramid.
e. Frustrum of a square pyramid.
The foregoing objects are dimensioned in Fig. 73.
CHAPTER VI.
Working Drawings.
54. Clearness. — It has been previously stated that practically
all working drawings are made in accordance with the principles
of orthographic projection. The purpose of such a drawing is
to give clearly all the information needed to construct the object
represented. A drawing which does not fulfill this purpose is a
failure, however artistic it may be in appearance and accurate
in execution. Failure to clearly express the design is, in general,
due to one of two main causes; either the information is not
complete, due to an omitted view, dimension line, or note, or the
information may be confused by an excess of data such as too
many views, several separate notes pertaining to the same matter
with possible confliction, needlessly repeated dimensions, or con-
fusing lines due to a rigid adherence to the laws of projection.
Lack of sufficient data is due partly to carelessness on the part
of the draftsman and partly to his failure to theoretically place
himself in the position of the one who is to use the drawing in
order to ascertain if all needed information has been given.
Excess of data, the second cause for failure in clear expression,
is due partly to the mistaken belief that no idioms exist in
graphic language, and partly to an inherent verbosity of ex-
pression whether the language be English or graphic. To a
great extent this matter is solely one of common sense and the
following rules are offered merely as a general guide :
i. Show only as many views as are necessary to completely
portray the object.
2. Do not repeat dimensions on one view which are clearly
shown on another.
3. Do not treat the same subject matter in several scattered
notes.
4. Written notes, figured dimensions, and the graphic line work
must all be so clearly expressed as to render vagueness or
ambiguity impossible.
5. If, in any particular case, a law of projection conflicts with
80 MECHANICAL DRAWING
clearness, sacrifice the letter of the law and stick to clearness
which is, in reality, the spirit of all laws of projection.
The draftsman who is thoroughly aware of the fact that the
fundamental test of any drawing is its readableness cannot go
far astray.
The rules just suggested, as well as other means to secure
simple and clear expression, will be discussed in subsequent
articles of this chapter.
55. Assembly and Detail Drawings. — Working drawings are
divided into two main divisions, assembly drawings and detail
drawings.
The purpose of the detail drawing is to portray each part of
the machine or structure separately. The details may all be
placed on one drawing with the name of the piece under each
detail ; or, if there are many details, one drawing may consist
solely of castings, another of forgings and still another of bolts
and screws. Due to the probable great variance in size of the
different pieces, it is frequently desirable to use several scales on
the same detail drawing. In such a case the scale should be
placed under each piece drawn. If all the pieces on one drawing
are to be made from the same material, the name of the material
is placed in the title. If various materials are represented on the
same sheet, the material should be stated under each piece, and the
title should read "Material as indicated." A "Bill of Material"
is generally placed on each drawing, which is a tabulation of
the name, material, and number required, of each piece. One
column is usually left for remarks. Some firms prefer to omit
the Bill of Material from the drawing and place it on a separate
sheet which accompanies the drawing.
An assembly drawing is a representation of the machine or
structure as a whole with its various pieces in their proper places.
On such a drawing is shown only the over-all dimensions and the
distances from center to center of the various pieces in order
that the drawing may be of service in erecting the machine or
structure.
If the object represented is sufficiently simple the assembly
and detail drawings may be combined. In such a drawing each
WORKING DRAWINGS Ol
piece is completely represented and dimensioned and yet shown
in its proper place in relation to the other pieces.
56. The number of views required to completely represent an
object will vary from two to possibly five or six. In general, the
top, front and side views are required, though many simple
objects may be clearly shown in two views. Frequently the top
view and a cross section give an ample description, or the top
view and front view. When only two views are shown the side
view is seldom one of the two. A more complicated object may
require the top, front, right and left side views, a view on an
auxiliary plane, as well as several cross sections. The only guide
in this matter is to remember that the machine or structure must
be clearly and completely represented in as few views as possible.
It has been previously shown that the logical arrangement of
views requires that the front view be under the top view, and the
side view at the left or right of the front view. This arrange-
ment should be adhered to rigidly. In this connection it is of
interest to note that the English practice is to regard the object
as being above the horizontal plane and in front of the vertical
plane. The planes are brought into coincidence by revolving the
profile plane backward to coincide with the vertical plane, and
lowering the horizontal plane until coincident with the verti-
cal plan, the front view thus being shown above the top view
and the side view at the right of the front view. This system
has but little to recommend it and was discarded in the United
States some twenty years ago. It is still used in England, though
at various times attempts have been made to change to the system
used in this country.
57. Notes. — The language of graphics should be supplemented
by the English language whenever additional clearness can be
gained by so doing. Sometimes 'a well worded note will save the
making of a view. The note should be lettered in lower case
letters and should be so clearly expressed that a vague or ambigu-
ous interpretation is impossible.
58. Dimensioning. — The neat, accurate, and legible dimension-
ing of a drawing is as important a part of the drawing as the
82 MECHANICAL DRAWING
actual graphic representation of the various views. In dimen-
sioning a working drawing the draftsman must assume the point
of view of the artisan who is to construct the object represented
and give those dimensions which will best aid in the construction.
The well equipped draftsman should have a working knowledge
of the general methods used in pattern-making, casting, forging,
and machine shop practice, in order that his designs may be con-;
structed economically.
The following rules for dimensioning represent the accepted
practice of most modern drafting rooms :
i. Dimension lines should be fine, continuous, black lines with
an open space near the center for the insertion of the figures.
2. Draw all dimension lines before inserting the figures.
3. Figures should always read from the bottom or right side
of the drawing.
4. Arrow points should be neatly made and should touch the
lines between which the dimension is given.
5. Dimension only between center lines and finished surfaces.
6. Do not give a dimension between dotted lines if it can be
avoided.
7. The total sum of a series of dimensions (called an "over-all"
dimension) should always be given.
8. Do not require the user of a drawing to add or subtract in
order to obtain a desired distance.
9. Do not repeat a dimension on one view which is clearly
shown on another. Divide the dimensions between the various
views by selecting the dimensions best suited to each view.
10. Dimension lines should not be crowded close to other lines
of the drawings, but should be placed clearly and conspicuously.
11. In general place the dimension lines outside the view.
Occasionally clearness may be gained by violating this rule.
12. Do not place dimension figures on a center line or on a line
of the drawing.
13. Give diameters of circles and radii of arcs, and abbreviate
diameter to Dia. or D. and radius to Rad. or R.
14. Locate holes by giving dimensions to their center lines.
WORKING DRAWINGS
83
15. Dimensions of less than two feet should be given in inches,
as 17", 23", and two feet and over in feet and inches, as 2'-o",
3'~7"-
CORRECT D/ME/VStON/NG.
/vor mus.
/A/CORRECT 0/MENSION/NG.
I 1 1 1
II 1
II II
*—
7J.
■ 1 1 1
11 . 1 1
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*-■*£•
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/£./%./£■ / &>&-'&
/6 > 'S2
THUS,
A/or mi/4", aYa" x 3" and 5" x 3^"
respectively. The lettering of the title should be free hand, ver-
tical preferred, and of such a size as will artistically fill the space
reserved. Nearly every engineering firm has its own standard
title containing such information as is most suitable for the
requirements of that particular firm. Many firms print the
standard form for the title onto the tracing cloth, others use a
WORKING DRAWINGS
85
rubber stamp, while still others leave the construction of the title
entirely to the draftsman. Various titles have been designed for
various needs so that it is impossible to give a form sufficiently
general to cover all requirements. The following data is, how-
ever, included on most title forms :
1. Name of the firm.
Name of machine or structure.
Scale.
Drawn by , traced by , checked by •
2.
3-
4-
5-
6.
Approved by
Date; usually that of completing tracing.
7. Number; for filing purposes.
In small detail drawings the material and finish are sometimes
included in the title. A characteristic free hand title is illus-
trated in Fig. 74.
60. Checking. — Before leaving the drafting room, a drawing
should be carefully examined by someone other than the drafts-
UN /TED T/i/?£AP CO.
EA/G/NEEff/NG DEPARTMENT
WALL BftAC/ffr.
Material, Gatst/ron.
Prawn by, £-.l.t.
7raced Jby, S.i'/f
Sc&/e-/~/ L
Unfinished
Checked by, d&E.
Approved 6y. 7&&.
/872. Ocr.Ji.i9/ J
Fig. 78.— Typical title.
man who executed it. In large drafting rooms "checkers" are
employed whose sole duty is the examination of drawings. In
smaller drafting rooms the draftsmen check each others work.
The checker, by signing his name to the drawing becomes respon-
sible for the accuracy and correctness of the work. The fact
86 MECHANICAL DRAWING
that a drawing is to be examined by a professional checker does
not relieve the draftsman from the necessity of carefully and
thoroughly examining his own work before turning it over to
the checker. A drawing should be examined systematically
according to some standard outline such as the one here sug-
gested :
1. Before checking any details read the drawing as a whole to
see if the general meaning is clear.
2. See if a sufficient number of views are given to clearly rep-
resent each piece, and that there are no unnecessary or confus-
ing views.
3. See that the material, finish, and scale for each piece are
properly stated.
5. Carefully examine all dimensions to ascertain, that all neces-
sary dimensions are clearly shown; that there are no superfluous
ones ; that scaled distances agree with the given dimensions ; that
no arrow points are omitted ; and that all dimensions are placed
to the best advantage.
6. Check all computations, and see that there is a sufficient
amount of clearance wherever clearance is required.
7. See that, wherever possible, standard sizes of bolts, screws,
pipes, shafting, etc., have been specified.
8. See that notes are briefly and clearly expressed.
The student before handing in a plate should apply the fore-
going examination and in addition should farther check his work
to see, ( r ) that wherever an erasure has been made all lines
affected have been re-inked; (2) that all visible lines are full and
all invisible lines are dotted; and (3) that his name, date, number,
and plate number are on the drawing. When the student finally
hands in his plate at the office it is the equivalent of saying in
words, "This plate has been executed with all the care and con-
scientious work of which I am capable. It is a true measure of
my present ability as a draftsman."
61. Sketching. — The ability to rapidly execute a neat, readable
sketch is essential to the engineer or draftsman. Those men
whose time is valuable frequently express the general idea of a
WORKING DRAWINGS 87
design by means of a free hand sketch, leaving the execution of
the working drawing to a draftsman. A good engineer can
express his ideas as fluently, and even more clearly, by sketching
than by talking. The draftsman is frequently required to make
sketches of existing machinery which may be at some distance
from the drafting room, and from these sketches to make the
working drawings. It is this phase of sketching which will be
discussed in this article.
In sketching from an object these tools are necessary; paper
(preferably cross section paper), a 3H pencil, a two-foot folding
rule, and a pair of calipers. The sketch should be made entirely
free hand, but its neatness and accuracy are limited only by the
ability of the draftsman. The making of a sketch should be
divided into three distinct parts as indicated by the following
paragraphs.
Views. — First decide on those views which will best illustrate
the object. Sketch the views decided upon, judging relative
lengths solely by the eye but as accurately as ability permits.
Remember that too many views are better than not enough, since
on the ultimate working drawing unnecessary data can easily be
discarded.
Dimension Lines. — After having made the requisite views place
dimension lines on the sketch but do not fill in the dimension
figures. A more systematic and thorough dimensioning of the
sketch is insured in this way, than by diverting the attention to
actually measure distances and fill in the figures. The danger at
this point of the work is that not a sufficient number of dimension
lines will be used. Regard the various views critically and see
that a dimension line is placed wherever it will be needed in the
making of the final drawing. Draw all center lines and extension
lines while placing the dimension lines. It will be noted that up
to this point of the work handling of the object, which is apt to
be greasy, oily, or dusty, is unnecessary, thus insuring a neater,
cleaner, sketch than would be the case were the object handled
frequently and needlessly.
Dimension Figures. — -By means of the two-foot rule and cali-
88 MECHANICAL DRAWING
pers obtain the dimensions from the object and record them in
the proper dimension lines previously placed.
It should be remembered that the sketching may be done at
some distance from the drafting room, and that omitted data will
cause trips to and from the drafting which should be regarded
as an ignominious loss of time. Therefore the completed sketch
should be subjected to a rigid examination, checking its various
views and dimensions along the lines explained for working
drawings in article 60. A well executed sketch should be sus-
ceptible of translation into a complete working drawing by a
draftsman other than the sketcher.
62. Shade Lines. — The shade line is a heavy weight line used to
indicate which surfaces are raised and which are depressed.
Shade lines undoubtedly lend a touch of realism to the flatness of
orthographic projection, and their use is to be commended when-
ever the gain in clearness is sufficient to compensate for the addi-
tional time required in execution. Some drafting rooms prohibit
absolutely the use of shade lines, while a smaller number require
shade lines to be used on all drawings. Neither of these extreme
systems is to be recommended. It is not a matter to be settled
by a fixed and unalterable rule, but should be given a more
flexible treatment. The two adverse factors, gain in clearness
and loss of time, must be balanced one against the other in guid-
ing the judgment as to a wise use of shade lines.
The light is regarded as coming from the upper left corner
of the drawing in parallel rays, making an angle of 45 ° with the
horizontal. A shade line is used to separate a surface which
receives the light from one which does not. By sliding the 45 °
triangle along the T square and regarding the hypotenuse as a
light ray, the surfaces receiving the light may be easily distin-
guished from those which do not. In general, the lower and
right hand edges of all raised surfaces should be shade lines,
while on depressed surfaces the shade lines are placed on the
upper and left edges. The line of intersection between visible
surfaces is not shaded, nor should dotted lines be shaded. A
circle representing a hole is shaded as follows: Draw a 45 ° line
through the center extending upward to the left. Set the com-
WORKING DRAWINGS
89
passes to the radius of the circle and place the needle point on
the line just drawn and at a distance from the center of the circle
equal to the desired maximum thickness of the shade line.
Describe a semicircle which becomes tangent to the original circle
on each side. A circle representing a raised surface is shaded in
a similar manner except that the center for the semicircle is taken
downward to the right.
Fig. 79 is an illustration of the use of shade lines.
n
n
(O)
n
Fig. 79- — Shade lines.
63. Line Shading. — On display drawings or drawings intended
for non-technical readers, it is highly desirable to represent more
artistically and naturally the nature and relation of surfaces than
is possible by the mere outline even though reinforced by shade
lines. To gain a realistic effect surfaces in shade are distin-
guished from those in light by line shading. In general a sur-
face is shaded by a series of parallel lines which decrease in
weight as the lighter portion of the surface is approached. The
gradual increase in width of the spaces between the line further
increases the effect of the surface becoming lighter. Concave and
convex surfaces are readily shown in this way.
7
90
MECHANICAL DRAWING
The direction of the light is regarded to be such that the pro-
jections of the light rays make an angle of 45 ° with the horizon-
tal. In Fig. 80 is shown the top and front views of a cylinder.
If a plane of light rays be passed tangent to the cylinder the line
of tangency is the darkest element. The brightest element will
be the one from which the light is reflected directly to the eye of
the observer. Since the angle of reflection of a light ray must
equal the angle of incidence it becomes obvious by an inspection
of Fig. 80 that the brightest element is found 22^° to the left
of the center line.
\ I
Fig. 80.— Position of light and dark elements of a cylindrical surface.
The cast iron pipe shown in Fig. 81 is shaded according to the
method just discussed. Note that, beginning at the lowest side
of the convex portion, the lines grow gradually heavier and closer
together until the darkest element is reached, and then become
gradually lighter in weight and further apart until the lightest
element is attained. From the lightest element to the top of the
cylinder the lines maintain the same weight but the width of
spacing gradually decreases. In the concave portion of the pipe
WORKING DRAWINGS
91
Fig. 81. — Line shading.
92
MECHANICAL DRAWING
the lightest element is below the center line and the darkest
element above. The methods used in shading the other objects
of Fig. 81 are obvious. It is perhaps worth while to observe
that, due to the closeness of the lines, it is almost impossible for
the engraver to satisfactorily reproduce line shading. Hence the
artistic effect which can be gained by line shading is not fairly
represented in these illustrations.
The shading should progress from the bounding lines of the
object inward toward the center, as it is easier to gradually
increase the spacing than to decrease it. Center lines are not
drawn in this class of work.
Line shading is required by the United States Government on
all drawings submitted to the Patent Office.
64. Structural Drawing. — That portion of graphic language
pertaining to the representation of all forms of steel construction,
such as bridges, the skeleton framework for large buildings, etc..
is called structural drawing. The steel used in the construction
is rolled in various standard shapes and fastened together per-
^ffH\ ,
A7V7
Fig. 82. — Rolled steel shapes.
manently with rivets. The purpose of this article is to point out
certain idioms of expression used in structural drawing as well
as to illustrate the principal shapes and forms of riveting used in
steel construction.
The six most important shapes made in rolled steel are the
I-beam, Channel, Z-bar, Angle, Tee, and Plate as illustrated in
Fig. 82. In addition to these may be mentioned bars of various
cross sections such as round, flat, and oval. These shapes are
rolled in numerous standard sizes and are catalogued in the hand-
books of the various steel companies.
WORKING DRAWINGS
93
The foregoing shapes are fastened together by rivets driven
either by hand or machine, the latter being exclusively used
•Shojo /? /VgAg
P/a/n
C?/7//Ofpea(
Near r~ar £?ofh
S/de S/'de. S/des
./^/trrfened -£ '/?/c?h^
CounfersunK
Near r~~ar &of/7
S/de S/de. Sides
,. /-y&fre/y&d.
Near r^ar
Side S/de
o n
nir
{Wu^m^4M^MM
C7
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Fig. 83. — Standard representation of rivets.
wherever much riveting is to be done. All possible riveting is
done at the shop, but a certain, remainder must be driven in the
field. One duty of the structural draftsman is to indicate which
rivets are to be driven in the shop and which in the field. It must
94 MECHANICAL DRAWING
also be shown whether the rivet heads are full, flattened, or
countersunk. Fortunately there is a universally accepted stand-
ard for the representation of rivet heads. The symbols shown
in Fig. 83 are so commonly known as to require no explanation
when used on a drawing. Rivets vary in diameter from ^" to 1".
The method of showing a section in structural drawing differs
from that to which the machine draftsman is accustomed. In
Fig. 83 is shown an end section of the two angles and plate.
Note that instead of cross hatching the cut material it is made
solid black. The two angles are, of course, in actual contact with
the plate, yet a hair line of white, or "streak of daylight" as it is
sometimes called, is left between the pieces. This violates the
letter of the law yet is justified by the increased clearness, for
were the hair line of white omitted the section would become an
unintelligible mass of black ink.
Dimension figures are placed just above the dimension lines,
and dimensions over one foot are given in feet and inches, thus
differing from machine drawing in both particulars.
The word "pitch" is used to indicate the distance from center
to center of rivets which are equally spaced. Thus, if "3" pitch"
be written just above a dimension line extending from one rivet
to another, it is to be understood that all rivets included between
the two extreme ones are 3" apart center to center.
The size of an angle is stated thus, 5" x 3^" x 5 / 16 " angle,
the first two dimensions being the over-all lengths of the legs
and the third representing the thickness of the material. The
longer length is stated first.
In giving the size of a Z-bar, Channel, or I-beam, the over-all
length of one leg, the distance back to back of the legs, the over-
all length of the other leg, and the thickness of the material are
stated in the order named, thus: 3^2" x 6" x 3^" x 3 / 16 " Z-bar,
3/ 2 "xio"x3/ 2 "x/ 2 " Channel, or 4" x 3" x 4" x %" I-beam.
The size of a Tee is stated thus, 4" x 4" x y 2 " Tee.
The length, width and thickness of a plate is given thus,
i2'-o"x8"x/ 2 " plate.
A Bill of Material must always accompany a structural draw-
ing, either on the drawing, or separately.
CHAPTER VII.
Bolts and Screw Threads.
65. Since bolts and screws are the commonest forms of fasten-
ings for machines, it behooves the draftsman to have a working
knowledge of their formation. Fortunately the important dimen-
sions are fixed by the United States Government and are regarded
as standard. The purpose of this chapter is to indicate the con-
ventional representation of bolt heads and nuts and screw threads.
66. The Helix is generated by a point moving around a given
straight line and at the same time in a direction parallel to the
m'
Fig. 84. — Construction of Helix, and application to square screw threads,
straight line, the two motions being uniform. The curve of a
screw thread is the helix.
9 6
MECHANICAL, DRAWING
To construct a helix : In Fig. 84 let the circle adgj be the
horizontal projection of the circular path of the generating point
and let the line m'n' — mn be the given straight line. Divide
the circle and the straight line into any number of equal parts,
in this case twelve. Consider the initial position of the generating
point to be at a. As the point moves from a to b on the circle it
must ascend 1 / 12 of the length of the line m'n' ; similarly when
the generating point has reached d on the circle it must have
ascended y± of the length of m'n'. Therefore from a, b, c, etc.,
erect perpendicular lines to meet horizontal lines drawn from the
corresponding points of division on m'n'. The corresponding
vertical and horizontal lines meet in points on the desired helix.
The pitch is the distance the generating point moves along the
line while making one complete revolution around it.
67. Various Forms of Screw Threads are in use which may be
roughly divided into two classes, V threads and square threads.
In general the V threads are used solely as fastenings and the
square thread used to transmit power. In Fig. 85 are shown
SHARP 1/
| c Pitch ,|
SQUARE
& U. S. STANDARD
P/tah.
21
WH/TWORTH
\,Pitch \
acme: AtL/rrRfss
Fig. 85. — Standard screw threads,
cross sections of various types of threads. The United States
Standard thread is the one most commonly employed in this
country, while the Whitworth thread is the English Standard.
The standard proportions adopted in this country are as
follows :
Let P = pitch, D = outside diameter and N = number of
threads per inch ; then
P= =lf = 0.241
D t 0.625 — O.175.
BOLTS AND SCRFW THREADS
97
It will be observed, then, that the determination of either P, N
or D immediately fixes the values of the other two. Thus, if the
pitch desired is %", N must equal 8 and the value of D may be
deduced from the formula or by reference to one of the common
tables of screw thread proportions.
A double screw thread consists of two threads, side by side,
wound around the cylindrical core.
SINGLE V
S/NGLEV
SINGLE V
DOUBLE (/ DOUBLE V SINGLE SQ. DOUBLE SQ.
Fig. 86. — Conventional representations of screw threads.
Threads may be either right hand or left hand; the former
advance away from the body when turned clockwise and the
reverse is true for the latter. A left hand thread should be
plainly marked on the drawing with the abbreviation L. H.
68. Conventional Representation. — It would be an absurd waste
of time to show all screw threads as helixes. In Fig. 86 are
shown several conventions for the representation of threads. The
most, frequently used conventions for single Y threads are those
given at B and C. The spacing of the lines is clone solely by the
9 8
MECHANICAL DRAWING
eye and the root lines are made heavier for effect. It is not
necessary to actually draw the correct number of threads per
inch. If the thread is standard mark it so and give the outside
diameter. The threads shown in Fig. 86 are all right hand; left
hand threads would slant in the opposite direction.
Some of the threads in Fig. 86 are shown partly in section
merely to illustrate the construction. Note that the inner threads
are not parallel to the outside threads- — shown at A and D — but
in the conventional representation shown at B and C all thread
lines are made parallel for ease in drawing.
Two tapped holes are shown in Fig. 87, one in section and the
other in elevation. Note that both of these holes are to receive
Fig. 87. — Tapped holes, in elevation and section.
right hand threads, hence the thread lines in the sectional view
must slant in the opposite direction.
69. Bolt Heads and Nuts are generally square or hexagonal,
and may be either chamfered or rounded. The chamfered nuts
and heads are used on general work where nicety of finish is not
desired, while the rounded forms are used on finished machinery
where beauty as well as utility is a factor.
Three dimensions, pertaining to heads and nuts, have been
fixed by the Government as standard : ( 1 ) the short diameter
r.
^Across forne,rs\
T
1
/iex. nut and head.
RouncS.
Trial-
Trial
/iex nut anal
hecrc/. Chamf.
/=--
< r— *h
Across Corners
^i,JQ3
Cha/rtf.
X-
lOO
MECHANICAL DRAWING
or distance across flats, (2) the thickness of the nut, (3) the
thickness of the head. In Fig. 88 are shown various forms of
hexagonal and square nuts and heads, whose construction is
obvious from an examination of the figures. It is not necessary
to draw a plan of a head or nut merely to ascertain the value of
F, the distance across corners, since this distance can be obtained
by the geometrical operation shown in both figures. It is, of
course, evident that in elevation the two side faces of a hexagonal
nut or head are each one-half as wide as the front face.
A nut or head should generally be drawn across corners, thus
showing graphically the amount of clearance needed. Some
drafting rooms even make it a fixed rule to require all nuts and
heads to be drawn across corners in all views.
A standard nut or head is not dimensioned on a drawing but
is marked "U. S. Standard" stating whether it is hexagonal or
square and whether chamfered or rounded.
A lock nut is shown in Fig. 89. This nut is used on quick mov-
AOCK A/UT
&TUD BOLT
SETSCffE-WS
O,, CD
rin
CONE
w^O
\\\^\\<^
ROUND\^^ l-psa SUNK
Fig. 89. — Lock nut, stud bolt, and set screws.
ing parts where a single nut could be easily loosened. Frequently
both nuts are made equal in thickness, in which case the thick-
ness of each is made equal to V^ D, all the other dimensions being
standard.
BOLTS AND SCREW THREADS
IOI
70. Set Screws. — The purpose of a set screw is to prevent the
motion of one piece by pressing against another. In Fig. 89 are
shown several forms of heads and ends.
r=u=^
ROUND
¥
¥
OVAL FLAT
Fig. 90. — Machine screws.
r/USTF/?
The character of the ends is dependent upon the amount of
resistance necessary. The resistance developed by the end of a
f?AG BOLT
££W/S &oir
Fig. 91. — Foundation bolts,
set screw which protrudes into another piece is of course greater
102 MECHANICAL DRAWING
than an end which depends upon friction alone, but with the
disadvantage of requiring a cut in the piece touched.
71. A Stud Bolt is a screw, one end of which is to receive a
nut and the other end to fit a tapped hole. In Fig. 89, note that
in order to avoid confusion the threads of the tapped hole are
not shown.
72. Machine Screws are used for fastenings. The four types
of head in common usage are shown in Fig. 90. The dimensions
for these screws may be obtained from any of the various
machinists' hand-books.
73. Foundation Bolts are used for fastening heavy machinery
to the foundation. There are various forms, two of which are
shown in Fig. 91. The Rag bolt is inserted into a conical shaped
hole which is then filled with molten lead, thus permanently
fastening the bolt in place. In the case of the Lewis bolt the
holding key can be withdrawn and the bolt removed.
CHAPTER VIII.
Tracings and Prints.
74. In general, the original pencil drawing does not leave the
office but is kept on file for reference. The drawing is traced
onto tracing cloth and from the tracing prints are made which
are distributed as desired. The purpose of this chapter is to
describe the details of this process.
75. Tracings. — Tracing cloth is a fine grained fabric treated
with a preparation consisting principally of starch in order to
render it transparent and fit to receive ink lines. One side is
highly polished and glazed and the reverse side is dull. Either
side may be used, but most draftsmen prefer the dull side since
it takes the ink more readily and permits of pencilled detailing
as well. On the other hand it is harder to erase an ink line
from the dull side. If the smooth side is used it should be dusted
with powdered chalk and then wiped clean. The red selvage edge
should be removed ana the tracing tacked tightly and smoothly
over the drawing. This is best accomplished by first tacking
diagonally opposite corners and then tacking the sides.
The pencil lines of the drawing are easily visible through the
tracing cloth and the ink lines of the tracing are drawn imme-
diately over the pencil lines of the drawing. The lines are inked
in the same general order as given in Art. 22. It should, however,
be borne in mind that tracing cloth contracts or expands accord-
ing to the state of the atmosphere, and hence had best be inked
in sections so that no unfinished section will be left from one
day to another. The invariable tendency of the novice is to
make the ink lines too light. In order to insure good printing,
the lines of a tracing should be heavier than would be required
on a drawing.
Dampness ruins tracing cloth and for this reason hands and
bare arms should be kept off the cloth.
In general lettered notes or titles or cross hatching should not
be traced, but should be placed on the tracing as though it were
original work. A scrap paper copy can be made of the lettering
I04 MECHANICAL DRAWING
and a sheet of white paper slipped under the tracing and over
the lettering of the drawing. Then proceed with the lettering
of the tracing without reference to the drawing. Traced letter-
ing seldom looks well, especially if traced by one who did not
letter the original drawing.
Tracings may be cleaned by lightly rubbing with a cloth satu-
rated with benzine or gasoline.
Pen wipers may be obtained by soaking scrap pieces of tracing
cloth in water until the starch is thoroughly removed.
Tracing cloth is sold in 30" to 54" widths and in rolls from 10
to 24 yards long.
The tracing should never leave the office, the purpose of the
tracing being to furnish prints as will be described in the next
article.
76. Prints. — The most common form of print is the so-called
blue print. Blue prints are made by laying the tracing face
up on a sheet of specially prepared sensitized paper, clamping the
two tightly together and exposing to the sunlight or strong arti-
ficial light. The light affects all of the sensitized paper except
those parts covered by the ink lines of the tracing. The length
of the exposure is dependent upon the degree of sensitiveness of
the blue print paper and the strength of the light. The sensitized
paper is then thoroughly washed in water and as a result white
lines on a blue background are obtained. Such a print is called
a blue print.
By using specially prepared papers the following kinds of
prints can be obtained, Vandyke Negatives (white lines on a
brown background), Blue Line Prints (blue lines on a white
background), and Black Line Prints (black lines on a white
background).
It is of interest to know that good prints can be made from
typewritten matter provided a sheet of carbon paper was placed
behind the page (carbon side next the paper) while doing the
typewriting.
In the next article will be described several types of machines
used in making prints.
TRACINGS AND PRINTS
I05
77. Sun Frames. — In Fig. 92 is shown a sun frame mounted on
a truck to run on rails outside a window so that it may be fully
exposed to the sunlight. The tracing is laid face down against
the glass in the frame, the sensitized paper is then placed against
the tracing and covered by a piece of felt in order to uniformly
distribute the pressure, and the whole clamped into position by
the back of the frame. The truck is then run into the sunlight
and the frame revolved about a horizontal axis until the glass
surface is exposed to the light. Prints may be made on a cloudy
day by giving a longer exposure. The length of exposure
depends not only upon the sensitiveness of the paper but on the
strength of the light, and for any given combination is best ascer-
Fig. 92. — Sun frame.
tained by trial. Good prints cannot be made by this method on
rainy days, and wherever much printing is done the sun method
has been entirely supplanted by some form of electric printing
machine as described in the next article.
78. Electric Printing Machines may be divided into two classes,
those in which the paper and the tracing remain stationary
during the time of the exposure and which may therefore be
called the stationary type of blue printing machine. In the
second type of machine the sensitized paper and the tracing
are moved before a light in such a manner that successive prints
are made on the sensitized paper. This machine is a continuous
printing machine.
A Stationary Printing Machine of the vertical type is shown in
Fig. 93. It consists essentially of a glass cylinder which is sup-
io6
MECHANICAL DRAWING
ported on end in a suitable frame. An arc light is arranged so
that it may be moved up and down through the center of the
cylinder, the speed of the movement being controlled by a pendu-
lum or other device. To operate this machine the tracing or
tracings, from which the print is to be made, is placed next to
Fig- 93- — Buckeye Vertical Electric Printing Machine. — Sold by Technical
Supply Co., Scranton, Pa.
the glass cylinder and the sensitized paper is held against the
tracing by a curtain which is held tight by weights suitably
arranged. The light having been raised, is then turned on and
allowed to pass downward through the cylinder, the length of
the speed regulating device having been so adjusted that one
pass of the light will give the required length of exposure.
TRACINGS AND PRINTS
IC7
These machines are built in various sizes, any one of which
will make a number of small prints or one large one at a time,
one pass of the light making the exposure in either case. An
exposure on this machine takes from one and one-half to three
minutes, depending upon the sensitiveness of the paper and the
condition of the tracing.
The Continuous Printing Machines are most successful when the
surface on which the exposure is made is placed horizontally.
Fig. 94. — Diagrammatic view of Everett-McAdams Continuous
Printing Machine.
They may be lighted by one or more arc lights or Cooper-Hewitt
lights. The method of making the exposure differs somewhat,
however, in different makes of the continuous printing machine.
Fig. 94 is a diagrammatic end view of one of these machines.
There is a glass cylinder which revolves around two Cooper-
Hewitt lights placed near its center. The sensitized paper is
passed around the cylinder to which it is held by the endless
ioS
MECHANICAL, DRAWING
belts. The tracings from which prints are to be made, are fed
between the sensitized paper and the glass cylinder. It is obvious
that the speed of this machine must be such that one revolution
of the cylinder takes the time required to make an exposure.
A continuous printing machine that differs quite radically from
the one just described is shown diagrammatically in Fig. 96.
,Fig. 95.— Bverett-McAdams Continuous Printing Machine. — Sold by
Technical Supply Co., Scranton, Pa.
This machine uses two, three, or four Cooper-Hewitt lights
shown at a. The glass plates over which the tracings and paper
are passed while making the exposure are portions of a cylinder
having a long radius. These glass plates are placed close to the
lamps so that the full intensity of the light is concentrated on
the printing surface. The tracings and sensitized paper are held
against the glass plates by tension belts, d, each of which is
driven independently of the other. It is therefore possible to
TRACINGS AND PRINTS
109
make prints with two different kinds of sensitized paper at the
same time even though the time of exposure may not be the same
or, in case an extra long exposure is required, the print be passed
first above the lights and then below them. This machine will
Fig. 96. — Diagrammatic view of Continuous Printing Machine.
print at the rate of from 1% to 12 feet per minute depending on
the sensitiveness of the paper and the clearness of the tracing.
A print washing attachment may be combined with a continu-
ous printing machine but, owing to the fact that it is difficult to
wash a print thoroughly as fast as it can be exposed, this
arrangement does not promise very good results.
APPENDIX.
SUGGESTED COURSE IN MECHANICAL
DRAWING.
First Year Course in Drawing
and Lettering.
79. Time Devoted to Course. — The course in drawing extends
throughout the Freshman year. During the first, second and
third terms there are two two-hour drawing exercises per week,
and during the second and third terms there are two one-hour
recitations per week. Twenty-two plates are completed in this
course. The course in lettering covers the first term, in which
there are two one-hour exercises per week. Fifteen plates are
made during the course.
80. Roll Call. — A roll will be called immediately at the opening
of each exercise, and a student arriving after this roll has been
called will be marked tardy. Two such tardinesses, unless
excused for special reasons by the instructor in charge, will be
regarded as one absence, and reported as such. A second roll
call will be taken five minutes before the close of each exercise,
and any student who is not working at his own table at this time,
will be regarded as having been absent the entire period.
No preparations for leaving the drafting room should be made
until after the conclusion of the final roll call.
81. Stamping Plates. —As soon as the border lines of a plate
are laid out in pencil, the student should ink his name, number,
and plate number in their proper places. Before doing any fur-
ther work on the plate see that an instructor stamps the plate
with a form which states ''Started , Finished In-
structor " and places the date after the word "Started."
When the plate is completed do not remove same from the board
until an instructor has placed the date of completion after "Fin-
ished" and signed his initials after "Instructor."
82. Posting of Accepted Plates. — On the bulletin board will be
found- a form stating the names of the men taking each course
and the number of plates in each course. Under each plate
number is a date, which indicates the last day on which that par-
ticular plate will be accepted with full credit. A plate handed
in less than two weeks after that date will be given half credit and
] 14 MECHANICAL DRAWING
any plate more than two weeks overdue will be given a grade of
zero in making up the final grade for the course. In this connec-
tion due allowance will be made for permitted absences.
A plate handed in during one exercise will be examined before
the next exercise and if satisfactory an X will be placed opposite
the name of the student and under the proper plate number.
83. Plates Returned for Correction. — Any plate which is not
acceptable, but that can be made so, is returned to the student
for correction. Attached to the plate is a correction sheet on
which are noted the necessary corrections. These changes are to
be at once incorporated in the drawing, and both drawing and
correction sheet returned at once to the office. The immediate
correction of a plate should take precedence over any other work
upon which the student may be engaged.
84. Rejected Plates. — A plate will be rejected if the general
character of its work is not up to the standard required by this
department. The lower left hand corner of such a plate will be
cut off and a correction sheet attached on which are noted the
main reasons for the rejection of the plate. The rejected plate
must be redrawn immediately after the completion of the plate
upon which the student is then working, and the new plate handed
in with the correction sheet attached.
85. Time of Posting and Returning Plates. — At the next exer-
cise following the handing in of a plate, the student should deter-
mine from the list on the bulletin board whether or not the plate
has been accepted. If the plate is not posted as accepted, it should
be returned to the student, shortly after the opening of the exer-
cise, as rejected or needing correction. If the plate is not
accounted for in one of these ways, the matter should be called
to the attention of the instructor in charge.
86. Conduct in Drafting Room. — The general deportment of the
student in this drafting room will be governed by the same prac-
tical standards as effect the draftsman in professional drafting
rooms. Brief conversation relative to the work in hand and
carried on in a low tone of voice is permissible.
Necessary movement about the room such as for the purpose
FIRST YEAR COURSE IN DRAWING AND LETTERING 115
of turning in a plate, consulting an instructor, examination of
the model plates displayed on ♦the bulletin board, is permissible.
Loud or unnecessary conversation, excessive movement about
the room, or any manner of conduct which disturbs the others at
work will not be tolerated.
The good draftsman works quietly and steadily. The student
should do likewise.
Caps should be removed from the head before entering the
room and not replaced until again outside.
Equipment should be unpacked and packed with speed and
quietness.
87. Work Done Outside of Class Hours. — Under no condition is
the drawing board to be removed from the drafting room. The
student may work outside of the assigned class room hours, if he
so desires, but such work must be done in the drafting room.
Any work done on a plate outside of the drafting room, will be
regarded as sufficient cause for rejecting the plate without further
comment.
88. Bulletin Boards. — On the bulletin boards are displayed
plates whose excellence render them worthy models. Or it may
be that these plates indicate more clearly than do the plates in
the text-book certain details in construction. Notices pertaining
to the courses are frequently posted, for the knowledge of which
the student will be held responsible. It is, then, highly desirable
that the student should watch the bulletin boards carefully.
89. Size of Drawing Plates. — The over-all dimensions of the
drawing plates are 12" x 18". A border line is drawn 1" from
the top and bottom edges, 1^4" from the left hand edge and i*4"
from the right hand edge, making the inside dimensions 10" x 15".
From the lower right corner of the border draw a light pencil
line to the same corner of the cutting edge. Bisect this line, and
with this point as a center describe a circle having a radius of
7 / m ". The circle should be drawn in ink, the width of line being
somewhat heavier than a shade line. Draw in ink, but with a
narrow line, a concentric circle just inside the outer circle leav-
ing a hair space between the two circles. Draw lightly in pencil
u6
MECHANICAL DRAWING
the horizontal diameter of these circles and %." above this diam-
eter another pencilled horizontal line. Between these two guide
lines print in black numerals the number assigned the individual
student at the opening of the course. Just under the center of
the horizontal diameter print in letters 3 /hb" high the course of
study being pursued, using the following notation :
Civil Engineering C. E.
Mechanical Engineering M. E.
Electrical Engineering E. E.
Mining Engineering E. M.
Chemistry C.
General Scientific G. S.
For an illustration of the foregoing data see Fig. 97.
Sorc/erL/ne-
A// p/afes fo Se
/cr/af out /'/? accord-
ance w/'th these d/men-
S/0/7S.
§
7
Fig. 97. — Layout of drawing plates.
90. Instructions Regarding Each Plate are given under the
proper plate numbers. These instructions should be read and
noted before starting the construction of each plate.
FIRST YEAR COURSE IN DRAWING AND LETTERING II7
91. Binding Plates. — At the conclusion of each course the
plates must be bound in bristol board covers, at a bindery
approved by this department. The cost for binding the drawing
plates is about thirty-five cents and for the lettering plates about
twenty-five cents. Before credit will be given the students in
either course the bound plates must be submitted to the instructor
in charge.
Plates.
PLATE 1.
Before starting work on this plate, study articles 7, 9, 20
and 21.
The purpose of this plate is to afford practice in the use of
the right line pen, and to illustrate the character of lines used
in mechanical drawing.
Construct six 3%" squares leaving a space of y^" between each
of the squares. The distance from the top border line to the top
edges of the upper squares should be the same as the distance
from the lower border line to the lowest edges of the under
squares. Similarly the margin to the left of the squares should
be equal to the margin at the right. It will be seen that the
result of the foregoing work is two horizontal rows of squares,
three J squares in each row.
Divide the left hand edge of the first square in each row into
thirty divisions of y&" each. By means of the T square carry
these points of division into each of the remaining squares. It
will be noted that up to this point the work has been in pencil,
whereas the following lines are ruled directly in ink without pre-
viously penciling them.
Through the points of divisions in each of the squares rule
horizontal lines of the following character; in the first square,
dimension lines ; in the second square, visible outline lines ; in
the third square invisible outline lines ; in the fourth square, cen-
ter lines ; in the fifth square, shade lines ; and in the sixth square
border lines which are one and one-half times as heavy as shade
lines. (The squares are numbered horizontally from left to
right.)
Ink the border lines of each square using the same weight line
as is included in each particular square.
Under each square in lower case letters y$" high state the
name of the lines included in that square.
PLATES 110
PLATE 2.
Before starting work on this plate study Article n.
The purpose of this plate is to afford practice in the use of tri-
angles and in the accurate drawing of radiating lines.
Set a point \Y%" from the left hand border line and 5" below
the top border line. With this point as a center describe two
concentric circles having diameters of 5" and Y^' , respectively.
Draw radial lines 15 apart terminating in these circles. Con-
nect the ends of the radial lines by straight lines, thus forming
a large and a small polygon of twenty-four sides. Divide the
left hand, horizontal radial line into eight equal parts. Through
these points of division construct eight more concentric poly-
gons. Carry the lines half way around in each direction from
the points of division, in order to reduce the closing error of the
polygons to a minimum. Ink the polygons before inking the
radial lines. Do not ink the circles as they were used for con-
struction only.
Construct a 5" square the right hand side of which is i 1 /^' from
the right hand border line, and which is equidistant from top and
bottom border lines. Divide the left and right sides into ten
equal parts. From the division points of one side draw lines
to the center point of the opposite side. Ink the radiating lines
before inking the sides of the square. One line should be al-
lowed to thoroughly dry before inking the next one to it. Use
great care to make the intersections at the centers clean-cut and
free from the blur of unnecessary ink.
J20 MECHANICAL DRAWING
PLATE 3.
Before starting work on this plate study Articles 3, 4 and 22.
The purpose of this plate is to afford practice in the joining
of straight lines to circular arcs, as well as to familiarize the
student with the use of both large and small dividers and com-
passes.
The layout and construction of this plate are indicated in the
illustration at the right.
Wherever a straight line joins a circular arc, the arc should
be first drawn and then the straight line drawn away from the
arc. A smooth connection is essential to the good appearance
of the work.
The centers of the circles inclosed in the equilateral triangle
are found by trial with the dividers. Before inking one of these
circles swing the pen of the compass around the path of the de-
sired circle and just above the plane of the paper so as to ascer-
tain if the circle will be exactly tangent at the proper points. If
necessary, slightly shift the center and make a slight change in
radius so as to obtain the desired result.
PLATE 4.
Before starting work on this plate study Article 23.
The purpose of this plate is to furnish practice in the drawing
of lines of varying weights, and to illustrate symbolic cross
hatching.
Construct two horizontal rows of 2"x2^" rectangles, four
rectangles in each row, the 2" side of the rectangles being paral-
lel to the long side of the plate. Allow a space of \ l /\" between
each rectangle and a space of ij4" between the two rows. The
two rows are to be centered on the plate as regards the border
lines.
In these rectangles represent the following materials, by sym-
bolic cross hatching, in the order here stated ; cast iron, wrought
iron, cast steel, wrought steel, copper, brass, lead, and rubber. In
each block state the name of the material represented using
lower case letters 3-32" high. Do not cross hatch over the let-
tering, but carry the lines as close to the letters as possible. All
122 MECHANICAL DRAWING
the section lines are to be drawn upward from left to right. Ink
the section lines before inking the outline of the blocks. Shade
the lower and right hand sides of each block.
The common fault of placing the lines of the cross hatching
too close together should be avoided.
The section representing rubber (also vulcanite or any insu-
lating material) is most easily made by ruling a series of heavy
parallel lines in pairs, and filling in with ink the spaces between
the adjacent pairs of lines.
PLATE 5.
The purpose of this plate is to afford an opportunity for gain-
ing experience in the use of the free hand pen to illustrate vari-
ous building materials. All lines on this plate are drawn free
hand with the exception of the lines representing water.
The same relative size of the various materials should be, in
general, the same as shown in the accompanying illustration.
The sand is composed of a great number of dots made with
a free hand pen held almost vertically. Do not work too long
at one spot as the ink of the individual blots will blur. Make a
reasonable number of dots at one place, then move further along
and return to the original place when the ink is dry. The dots
should be very close together at the top and gradually become
less towards the bottom.
The concrete is composed of fine dots representing sand and
cement through which are interspersed a number of small stones.
Note that the stones are indicated by a shade line around the
lower and right hand edges, no line being drawn for the upper
and left hand sides.
The uncoursed rubble is masonry composed of rough stones
which have been rudely dressed by knocking off angular cor-
ners. The stones are not laid in courses.
The coursed rubble is brought to a horizontal course line every
few feet. Care should be taken, in representing masonry of any
character, not to show too much mortar.
Earth and rock are represented by free hand parallel lines as
shown ; in the illustration these lines are too close together.
]24 MECHANICAL DRAWING
PLATE 6.
Before starting work on this plate study Articles 62 and 63.
The purpose of this plate is to afford practice in the use of
shade lines and line shading.
The accompanying illustration consists of free hand sketches
of various objects. These objects are to be accurately drawn
to scale, though not necessarily in the same positions as here
shown. Lay out all the pieces in pencil, before starting detail
work on any piece, and submit the arrangement to an instructor
for approval. After each piece is complete in pencil, apply the
line shading and then ink the outline.
Do not show the hole in the top view of the bearing block as it
would tend to destroy the effect of the shading.
State the name of each object but do not indicate the dimen-
sions or scale.
PLATE 7.
Before starting work on this place study Articles 12, 33, 34,
35, 36, 37 and 38.
The purpose of this plate is to familiarize the student with
the construction of the conic sections, as well as to afford prac-
tice in the use of the irregular curve.
The penciled layout of all the curves should be determined and
submitted to an instructor for approval, before plotting the points
of each curve.
Construct an ellipse according to the second method of Arti-
cle 36. Let the lengths of the major and minor axes be 4" and
3", respectively; use twenty-four radial lines spaced entirely by
means of the triangles. The weight of the radial lines when
inked should be the same as for dimension lines. The ellipse,
as well as all other curves on this plate, should be the same weight
as for a shade line. Draw a tangent to any point on the curve.
Construct an hyperbola, as explained in Article 38. Let
FF X — 2^4" and VV a = 2%.". Plot a sufficient number of
points to draw each branch of the curve with accuracy. Draw
tangents from a point outside the curve and at a point on the
126 MECHANICAL DRAWING
curve. Ink the construction lines used in obtaining one point
only, on each of the branches of the curve.
Construct a parabola according to the second method of Arti-
cle 37. Let the rectangle in which the parabola is enclosed be a
4" square. Plot a sufficient number of points to draw the curve
accurately.
Construct a parabola according to the first method of Article
37. Let F be distant £4" from the directrix. Let the last point
chosen on the axis be 3^2" from the directrix. Draw tangents
from a point outside the curve and also at a point on the curve.
In each of the foregoing constructions letter the axis, direc-
trix, foci, and vertex. State the name of each curve in capitals
H" high.
PLATES 8 and 9.
Orthographic Projection of Geometric Objects.
A thorough understanding of the chapter on orthographic pro-
jection is essential to the correct solutions of the problems on
these plates.
Divide each of these plates into six 5"x5" squares by light
pencil lines.
Plates 8 and 9 each consist of six problems assigned by the in-
structor from the following list of problems as stated on page — :
ia, ib, ic, 2a, 2b, 2c, 3a, 3b, 3c, 4a, 4b, 4c, 5a, 5b, 5c, 6a, 6b, 6c,
7a, 7b, 7c, 8a, 8b, 8c, 9, 10a, 10b, 10c, 11a, lib, 11c, 12a, 12b and
12c.
Completely solve each problem in pencil before starting the
inking. Ink the outlines of the various views, but do not ink the
ground line, profile plane trace, or the projecting lines. Erase
the pencil lines used to divide the plate into six equal parts.
PLATES 10 and 11.
Revolution of Geometric Objects.
A thorough knowledge of the chapter on orthographic projec-
tion is essential to the correct solutions of the problems on these
plates.
Divide each plate into four 5"x7^2" rectangles by light pencil
lines.
PLATES 127
Plates 11 and 12 each consist of one problem assigned by the
instructor from the following list of problems as stated on page
— : 25, 26, 27, 28, 29 and 30.
Complete each problem in pencil before starting the inking.
Ink only the outlines of the various views.
PLATES 12 and 13.
Successive Revolution of Geometric Objects.
A thorough knowledge of the chapter on orthographic pro-
jection is essential to the correct solutions of the problems on
these plates.
Divide each plate into four 5"x7^" rectangles by light pencil
lines.
Plates 12 and 13 each consist of one problem assigned by the
instructor from the following list of problems as stated on page
— : 3i, 32, 33, 34, 35, 3^, 37 and 38.
Complete each problem in pencil before starting the inking.
Ink only the outlines of the various views. .
PLATE 14.
Auxiliary Views.
A thorough knowledge of the chapter on orthographic pro-
jection is essential to the correct solutions of the problems on this
plate. '
Divide the plate into four 5"x7^" rectangles by light pencil
lines.
This plate consists of four problems assigned by the instruc-
tor from the following list of problems as stated on page — :
39a. 39b, 39c, 39d and 39c
Complete each problem in pencil before starting the inking.
Ink only the outlines of the various views.
PLATE 15.
Machine Details.
A thorough knowledge of the chapters on orthographic pro-
jection and working drawings is essential to the correct solutions
of the problems on this plate.
Divide the plate into six 5"x5" squares by light pencil lines.
128 MECHANICAL DRAWING
This plate consists of six problems assigned by the instructor
from the following list of problems as stated on page — : 13,
14, 15, 16, 17, 18, 19, 20, 21, 22, 23 and 24.
In drawing these objects do not use the ground line or profile
plane trace. If, in the opinion of the student, any view other
than those called for in these problems will better illustrate the
object in question, the student is at liberty to pencil the proposed
view and submit same to an instructor for approval or condem-
nation.
Complete each problem in pencil before starting the inking.
PLATE 16.
Before starting work on this plate study Articles 66, 67, 68
and 69.
This plate consists of the following drawings of bolt heads
and nuts, and screw threads :
Application of the helix to a single square thread of 1" pitch
and 3" diameter similar to the one shown in Fig. 84. The
thread is to be 3/^" long the lower part being shown in section.
The thread is to be shown upright at the extreme left of the
plate.
Rounded hexagonal head and nut, across corners.
Chamfered hexagonal head and nut, across flats.
Chamfered square head and nut, across corners.
Chamfered square head and nut across flats.
Two conventional representations — the style to be assigned by
the instructor — of a single V thread, diameter i^i", 6 threads
per inch.
One conventional representation of a double V thread, diame-
ter i}i".
One conventional representation of a double square thread,
pitch y 2 ".
Each thread is to be 3" long.
PLATES 129
The heads and nuts are to fit a bolt having a diameter of i}i",
I/4", or 1^4" as assigned by the instructor. In the case of a nut
show the bolt broken on each side of the nut; for the head the
bolt is shown on one side only.
The pencil layout of the various pieces, showing over all di-
mensions only, should be determined and submitted to an in-
structor for approval before detailing any view.
Draw threads directly in ink without previously pencilling
them.
State the names of the various pieces in lower case letters
TJ
3 / 16 " high ; also state the value of D, H, and — .
Dimension the heads and nuts in terms of D.
In the lower right hand corner of the plate state in capital let-
ters 3 / 16 " high, "Standard Nuts, Heads and Screw Threads."
130 MECHANICAL DRAWING
PLATE 17.
The accompanying illustration shows free hand sketches of
various washers and fastenings. From these sketches the stu-
dent is to make accurate working drawings.
In addition to the views shown in the illustration show a top
view of the Cup and Ogee Washers, Separator, Boat Spike, and
Drift Bolts.
Draw all pieces half size except the Dowel and Boat Spike
which are to be drawn full size.
Lay out the over all dimensions of each view and submit the
arrangement to an instructor for approval before detailing any
view.
Use shade lines on all views, and represent convex or concave
surfaces by line shading except in the case of screw threads.
In some of the sketches the word "round" is placed after a di-
mension representing the diameter of a circular piece. When
the top view is shown the word is omitted.
Some of the fastenings shown on this plate are used in the
construction of the timber trestle represented on the following
plate.
132 MECHANICAL DRAWING
PLATE 18.
In the accompanying illustration are shown the details of a
single deck bent for a squared timber trestle. From these de-
tails the student is to draw the complete bent to a scale of y 2 " —
1'— o".
The small drawing in the lower left hand corner shows the
general form of the completed bent, and is not to be placed on
the drawing made by the student.
Some of the fastenings enumerated in the note at the left are
not shown in the details, but should be shown by the student as
stated in the note. Some of the fastenings are shown in detail
on Plate 17.
Use shade lines.
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134 MECHANICAL DRAWING
PLATE 19.
The accompanying illustration is an uncompleted drawing of
a squared timber highway bridge. From the data given the stu-
dent is to make a complete drawing of this bridge to a scale of
i" = i'— o".
Both the side and end views of all timbers are to be grained.
The success of the graining is largely dependent upon the artis-
tic ability of the student. Any arrangement of lines which gives
a formal or mechanical appearance should be carefully avoided.
Examine Fig. 31, obtain personal instruction, and devote a few
minutes to practice before starting the graining. One result of
the graining should be to make adjoining timbers stand out
clearly.
After the drawing is completely inked and shade lined, apply
the following light washes of color :
To all wood, "Light Wood."
To all iron work, "Prussian Blue."
To all masonry, "Prussian Blue," somewhat lighter than for
iron.
To earth, one part of "Gamboge," two parts of "Light Wood,"
and a touch of India Ink.
To water, "Prussian Blue" dark at the surface and growing
gradually lighter towards the bottom.
The common fault of the amateur to make all the colors too
heavy should be avoided. Submit the washes to an instructor
before applying.
136
MECHANICAL DRAWING
PLATE 20.
Before starting work on this plate study Article 64.
This plate consists of three drawings as follows :
Two views of the Z Bar column shown in Fig. 98.
Z ANGLES 3 f'3i*.
RIVETS §D.
WEB PLATE 8*j
Fig. 98.— Z-Bar Column.
Two views of the Angle column whose cross section is shown
in the accompanying illustration.
Two views of the Girder whose front view is shown in the ac-
companying illustration.
The scale in each case is to be ij4" = i' — o".
Layout the over all dimensions of the various views and sub-
mit the arrangement to an instructor before detailing any view.
Locate the center lines of the rivets in pencil, but draw the
rivets directly in ink.
Do not use shade lines on this plate.
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PLATE 21.
Before starting work on this plate study Article 75.
This plate consists of a tracing made from one of the follow-
ing plates as assigned by instructor: 6, 15, 16, 17, 18, 19 and 20.
PLATE 22.
Plate 22 is the title plate. The lettering consists of block let-
ters similar to those shown on Plate VI of "Freehand Letter-
ing" — Reinhardt, or similar to a model plate posted for this pur-
pose by the instructor.
In capital letters 5/ 8 " high state "MECHANICAL DRAW-
ING." Underneath and distant 1" state in capital letters 7 / 16 "
high the name of the College. Below this line 7 / 1G " state in lower
case letters 3 / 16 " high the name of the department in which the
course was pursued, as "Department of Graphics ;" the D and
G in capitals 5 / 10 " high.
In the lower left hand corner of the plate in Reinhardt lower
case letters ]/%" high, state "Freshman Class 191- to 191-."
In the lower right hand corner state name, date and number
as usual.
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