basic engineering drawing - the eye archive/rhodescook... · orthographicprojection:firstangle ......

BASIC

RS Rhodes& LBCook

ENGINEERINGDRAWING

R S RHODESM Weld J, Diploma in Advanced Studies in Education.Lecturer responsible for Engineering DrawingStafford College of Further Education.

L B COOKB A (Hons), MIED, Cert Ed.Lecturer in Engineering DrawingStafford College of Further Education.

Pitman Publishing

PITMAN PUBLISHING LIMITED39 Parker Street London WC2B 5PB

Associated CompaniesCopp Clark Ltd, TorontoFearon-Pitman Publishers Inc, Belmont, CaliforniaPitman Publishing New Zealand Ltd, WellingtonPitman Publishing Pty Ltd, Melbourne

© R S Rhodes & L B Cook 1975, 1978

First published in Great Britain 1975reprinted (with corrections and amendments) 1978

All rights reserved. No part of this publication may bereproduced, stored in a retrieval system, or transmitted,in any form or by any means, electronic, mechanical,photocopying, recording and/or otherwise without theprior written permission of the publishers. This bookmay not be lent, resold, hired out or otherwise disposedof by way of trade in any form of binding or cover otherthan that in which it is published, without the priorconsent of the publishers.

Camera copy prepared by Morgan-Westley /WPrinted in Great Britain by Unwin Brothers LtdThe Gresham Press, Old Woking, SurreyA member of the Staples Printing Group

ISBN: 273 318£7 X

) ACCESSION No.

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This book contains what we consider to be the "basics" ofEngineering Drawing. Orthographic Projection, Conventions,Sectioning, Pictorial Representation and Dimensioning havebeen covered in detail as we feel that a thorough under-standing of these topics forms a sound foundation upon whichto build. All technical information, examples, exercisesand solutions have been compiled in accordance with thelatest "metric" drawing office standards - B.S. 308:1972.

The book has not been written for any specific coursebut can be profitably used both by students being introducedto Engineering Drawing and also by those who have acquired alittle knowledge of the subject and wish to consolidate andincrease their understanding by working through carefullygraded exercises. It should prove useful for Craft, Tech-nician (T.E.C.), O.N.D., C.S.E. and G.C.E. students andalso for those H.N.D. and Degree students with littledrawing experience. The book is seen primarily as a studentself-educator though no doubt many teachers will find ituseful as a reference source and/or exercise "bank"

.

Topics have been presented in a similar manner whereverpossible. Generally the opening page introduces the topic,the next imparts the basic facts - visually rather thanverbally wherever possible. An illustrative example isprovided to aid understanding and this is followed by aseries of carefully graded exercises.

We are well aware of the dangers of presenting exer-cises which are known to contain errors. They have beenincluded because in our experience they are the commonmisconceptions among students of engineering drawing. Inall cases the correct method and answers are given, some-times immediately following the example, or in the solutionsat the end of the book.

It must be emphasized that this book not only trans-mits information it is also a work-book. Do not be afraidof drawing and writing on the pages! If maximum benefit isto be derived from the book then the old maxim, "I do and I

understand" must be the students' guide.We thank those people whose observations and suggestions

have helped us improve upon the first edition of the book.We also wish to thank the British Standards Institution forallowing, usf to use extracts from B.S. 308:1972.

Contents

ORTHOGRAPHIC PROJECTION 1

ORTHOGRAPHIC PROJECTION: FIRST ANGLE 2

Lines • 5

Missing detail • 11Missing views • 12Sketching orthographic views • 13

ORTHOGRAPHIC PROJECTION: THIRD ANGLE 14

Comparison of first and third angle projection • 15

SECTIONING 21

The rules of sectioning • 22Sectioning : exceptions • 23Staggered section planes • 24Exercises • 25

TERMINOLOGY 33

ABBREVIATIONS 36

CONVENTIONAL REPRESENTATION 38

Screw threads • 38Springs • 39Shaft details • 40Knurling • 41Bearings • 41Long components • 42Gears • 43

TESTS 45

Test for terminology • 45Test for abbreviations • 46Test for conventional representations • 47Test for abbreviations > terminology j andconventional representations • 48

PICTORIAL DRAWING 49

PICTORIAL DRAWING: ISOMETRIC 50

Inclined edges • 51Exercises • 52Construction of ellipses • 55Examples • 5 7

Exercises • 58Isometric freehand drawing • 59

PICTORIAL DRAWING: OBLIQUE 61

Methods of construction • 62Inclined edges • 63Methods of constructing oblique circles • 64Methods of constructing oblique ellipses • 65Examples • 66

DIMENSIONING 68

Arrangement of dimensions * 72

Dimensioning circles • 73Dimensioning radii • 74Dimensioning angles • 75Designation of plain holes • 76Location dimensions • 77Exercises • 78

LIMITS AND FITS FOR HOLES AND SHAFTS 84

Limit systems • 86Fit • 87Conventional method of illustrating terms • 89

ISO METRIC SCREW THREADS 91

Designation • 92Screw threads 3 nuts and bolts • 93Nuts and bolts exercises • 94

ASSEMBLY DRAWINGS 95

General assembly • 96Sectioned assembly • 98Exercises • 99

DEVELOPMENTS 105

PARALLEL LINE DEVELOPMENT 106

RADIAL LINE DEVELOPMENT 120

Pyramids • 120Right cones • 124

TRIANGULATION 130

SOLUTIONS 136

First angle orthographic projection • 137Third angle orthographic projection - 140Sectioning • 144Terminology 3 abbreviations 3 conventional representation • 148Isometric drawing • 149Oblique drawing • 153Dimensioning • 155Limits and fits • 161Sectioned assemblies • 162Developments: parallel line • 165Developments : radial line • 172Developments : triangulation • 180

Orthographic Projection

CommunicationThere are many different ways of communicating ideas, informa-tion, instructions, requests, etc. They can be transmitted bysigns or gestures, by word of mouth, in writing, or graphically.In an industrial context the graphical method is commonly used,communication being achieved by means of engineering drawings.

If oral and written communication only were used whendealing with technical matters, misunderstandings could arise,particularly in relation to shape and size. The lack of a univ-ersal spoken language makes communication and understanding evenmore difficult because of the necessity to translate both wordsand meaning from one language to another.

However, the universally accepted methods used in graphicalcommunication through engineering drawings eliminate many ofthese difficulties and make it possible for drawings prepared bya British designer to be correctly interpreted or "read" by, forexample, his German, French or Dutch counterpart.

Equally important, the components shown on the drawingscould be made by suitably skilled craftsmen of any nationalityprovided they can "read" an engineering drawing.

Conventionally prepared engineering drawings provide themain means of communication between the "ideas" men (the design-ers and draughtsmen) and the craftsmen (machinists, fitters,assemblers, etc.). For the communication to be effective, every-one concerned must interpret the drawings in the same way. Onlythen will the finished product be exactly as the designer envis-aged it.

To ensure uniformity of interpretation the British StandardsInstitution have prepared a booklet entitled BS 308:1972, Engin-eering Drawing Practice . Now in three parts, this publicationrecommends the methods which should be adopted for the prepara-tion of drawings used in the engineering industry.

The standards and conventions in most common use and hencethose required for a basic understanding of Engineering Drawingare illustrated and explained in this book.

Orthographic ProjectionIn the engineering industry communication between the drawingoffice and the workshop is achieved mainly by means of engineer-ing drawings. The principal method used to prepare these drawingsis known as Orthographic Projection.

Basically, Orthographic Projection is the representation of

a three-dimensional component on a flat surface (the drawingsheet) in two-dimensional form. At least two orthographic views,therefore, are required to indicate fully the shape and size of a

component. If the component is a complicated one then usuallymore than two views are shown to aid understanding.

In this country two methods of Orthographic Projection areused. One is known as First Angle Orthographic Projection (often

referred to as English Projection) , the other as Third AngleOrthographic Projection (American Projection) . Both methods ofrepresentation are illustrated and explained in this section.

Orthographic Projection: First AngleThe pictorial drawing opposite indicatesthe shape of the component with a singleview.

An orthographic drawing indicatesthe shape of a component by using a

number of views each looking at adifferent face of the component.

At least two views are necessaryto fully represent the component.Usually, however, three views areshown in order to clarify internaland external detail:

(1) A Front View

(2) A Plan View

(3) A Side View

Fig.l

Fig. 2 (1) The front view, or front elevation,represents what is seen when lookingat the front of the component in thedirection of arrow F.

Front View (F)

(2) The plan view represents what isseen when looking at the top of thecomponent in the direction of arrowP at 90° to arrow F.

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Fig. 3

Plan View (P)

(3) A side view, or side elevation, represents what is seen whenlooking at the side of the component in the direction of eitherarrow R or arrow L. These arrows are at 90 to both arrow F

and arrow P.

View looking indirection of

arrow R.

Ri ght-HandSide View

(R)Fig. 4 Fig.

5

View looking indirection of

arrow L.

Left-HandSide View

(L)

The separate views of the component are combined to form acomplete orthographic drawing as shown below.

The front and side views are drawn in line with each otherso that the side view may be "projected" from the front viewand vice versa.

The plan view is drawn in line with and below tne front view.In other words, the plan is projected from the front view.

R

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Note!

This symbol means

f'irst Angle Ortho-

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F i g . 6

Points to note when making a drawing using First Angle Ortho-graphic Projection:

(1) Corresponding heights in the front view and side view arethe same

.

For example, the height of the hole from tne base, H, isthe same in both front and side views.The thickness of the base, T, is the same in both frontand side views.

(2) Widths in the side view correspond to depths in the plan.For example, the total width, D, in the side view is thesame as the total depth, D, in the plan.The width, d, is the same in both plan and side views.

Projection of widths from side view to plan is made easierby using the 4 5° swing line as shown.

(3) The plan view is usually projected BELOW the front view.It can be above but this would be called an "inverted" plan.

(4) The R.H. side view is shown on the L.H. side of the front view.The L.H. side view is shown" on the R.H. side of the front view.

Note: Drawings should be read (or interpreted) by viewingfrom the R.H. side or bottom R.H. corner of the drawing.

The orthographic drawing of the bracket, Fig. 6, was constructed

step by step as follows:

STEP 1. The face to be used as the front view of the component was

chosen, in this case, looking in tne direction of arrow F (Fig-1) .

The selection of the front view is purely arbitrary.

STEP 2. The outline of tne

front view was drawn FAINTLY

in the position shown opp-

osite leaving room on the

drawing sheet for a plan

view and also both end views

to be added.

STEP 3. The outlines of the

plan view and side views

were projected FAINTLY from

the front view and

positioned as shown opposite

STEP 4. All remaining

external details were added

and centre lines inserted

as shown opposite.

STEP 5. All hidden detail, i.e. for hole and recess, was added and

the outline "heavied-in" to complete the drawing as shown in Fig. 6.

Lines

1 —2 —3 --

For general engineering drawings, the following typesof lines should be used.

Visible outlines

Dimension linesProjection linesConstruction linesHatching or section linesLeader lines for notes

Hidden detail

4

5

6

Centre lines;Pitch circles

(Cutting or viewing(planes

(Short break linesj Irregular boundary( lines

Typical applications of some of the recommended types of lineshave been shown in previous figures and are further illustratedbelow.

Hidden detail:shortthindashes

©Centrelines:longthinchain

©Outlinesthickcontinuous

Construc-tion lines:thincontinuous

I (theseare

erased oncompletionof drawing.)

£3-HIDDEN DETAIL

The line numbered 3 above is used to represent hidden detail, i.e.edges, holes, surfaces, etc., which are known to exist but cannotbe seen when viewed from outside the component

.

Note: A hidden detail line is a broken linenot a dotted line

The following drawings are further examples of components drawn

correctly in First Angle Orthographic Projection. Study each drawing

carefully until you understand how each view is obtained.

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Orthographic Projection: Third AngleYou may remember from information presentedearlier in the text that there are twomethods of orthographic projection used inthe preparation of engineering drawings.

You should, by now, be quite conversantwith one of them - First Angle OrthographicProjection. The other is known as ThirdAngle Orthographic Projection.

j

When representing a three-dimensionalcomponent in Third Angle OrthographicProjection, the basic views are exactlythe same as those shown when using FirstAngle Orthographic Projection. Thedifference between First Angle and ThirdAngle is in the positioning of the viewsrelative to each other.

In Third Angle Orthographic Projection the individual views areplaced on the drawing sheet in projection with each other as shown;

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PLAN VIEWlooking from P

Note!

This symbol means

Third Angle Ortho-

graphic Projection.

LEFT-HAND SIDE VIEWlooking from L

FRONT VIEWlooking from F

RIGHT-HAND SIDE VIEWlooking from R

Special pointsto note:

(1) The plan is always projected ABOVE the frontview

.

(2) The right-hand side view is shown on theRIGHT-hand side of the front view.

(3) The left-hand side view is shown on theLEFT-hand side of the front view.

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drawings

opposite

show

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a

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Angle

thographic

Projection

OR

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which

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19

The components below are drawn pictorially. For each componentsketch an orthographic drawing, in good proportion, using ThirdAngle Orthographic Projection. Sketch a front view in thedirection of F, a plan view and a right-hand side view showingall hidden detail. Use the 5 mm squared grid on page 6 7 withtracing paper to aid sketching if you wish. Solution on p. 142.

1 2S N/

I**- s\

f <%s 1<Z\

_^*—

-

K\ ,;—

f

/(\\ *

/ // */ / 1f

—r / /r

1/

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/— f" J' / \ J i/'

. ,/ //

^m / \>»-. *.*/ /

—1~F- ^

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r „,l

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s>l

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sIti k

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s_. \ \\

J ]

- I \ \s^ ^/ / r *\pH \Sw >/ ^ KJ

-_M-<f

S— s

s

-

\\ \ \\ r— \F \

F

5. A partly sectioned assembly drawing in shown on page 48.Sketch, in good proportion, using 5 mm squared paper or thegrid on page 67, an EXTERNAL front view, side view and planview of the complete assembly using Third Angle OrthographicProjection. Solns. p. 141 and p. 142

20

SectioningDrawings of the outside of simple components are oftensufficient to convey all the information necessary to makethe component. More complicated components, however, mayrequire sectional views to clarify internal details.

A sectional view is obtainedwhen one imagines thecomponent to be cut througha chosen section plane - oftenon a centre line.

If the vee-block is cuton section plane C-C asshown above, the result-ing sectional viewprojected from the planreplaces the usual frontview of the outside ofthe block.

-E3End view Sectional Front View

looking on cutting plane C-C

Sectional views are drawn only when it is necessary to explainthe construction of a complex object or assembly. Some of tneexamples used in the next few pages have been chosen to illus-trate the rules of sectioning although in practice, as in thecase of the vee-block drawn above, a sectional view may nothave been necessary

The draughtsman has to decide how a component or assemblyshould be sectioned in order to provide the fullest possibleinformation. The recommendations of BS 308 enable him to dothis in a way tnat is understood by all engineers.

21

The rules of sectioning

1. A sectioned object is shownby lines drawn preferablyat 45'

the outline.Thin lines touch

Size of sectionedpart determines linespacing - preferablynot less than 4 mm.

2. If two adjacent parts

are sectioned, the

section lines are

drawn in opposite

directions

.

'/tiWky///,>§^

Lines are staggered

where the parts are

in contact.

3 . Where more than two

parts of an assembly

are to be sectioned,

the lines cannot all

be opposite.

Section lines are

closer together on

the third area —usually the smallest

The sectional view ofa symmetrical objectis obtained when thesection plane cutsthrough the obviouscentre line.Hatching may be omittedif the meaning is clearwithout it.

5. If an object is NOT

symmetrical the section

plane chosen should be

clearly stated, ^-j

7

V///X

cz

A

Secti onal Vi ew

Section A-A

22

Sectioning: exceptionsThere are a number of features and parts which are NOT normally-sectioned even though they may lie in the section plane. Agood way to accept these exceptions to the general rule is toimagine how complicated the drawing would look if they weresectioned. They are sectioned, however, when they lie ACROSSthe section plane. See section D-D. *

Sectioned shaftis more difficultto visualize thanit is whennot sectioned.

Shaft lyingi n thesecti on plane

Secti onalEnd View

BS 308 states that the following are NOT sectioned even if theylie in a given section plane:

ShaftsCotters

Keys Rivets RibsBolts Gear Wheels Nuts

PinsWebs

DowelsWashers

Some of these are illustrated in BS 308 by this diagram:

DShaft( Spindle) \

Section D-DCas ting only

Washer

23

Staggered section planes

ExamplesSection X-X

Section A-ARe-al igned

Each part of the sectionplane is swung to thevertical before projectingto the sectional End View.

By using this conventionthe draughtsman avoids usingtoo many auxiliary views.

A staggered section planeshould only be used whenthere is a resulting gainin clarity.

T

-*-r

IM1.

<t3>n,

!

+

B

Section B-BStaggered or offset

TB

Applications of thisconvention tospecific cases aregiven below.

Spoke

Solid

Section C-CRe vol ved

Section D-DRevol ved

Section E-ERevol ved

24

Errors in sectioning occur in each of the drawings below.Trace or re-draw a correct sectional view in each case.State the method of projection used where applicable.

Solns. p. 144

25

~.

A IExample

H

qj

-4.

ei • i

7

i

8

V

i

V

H

7

'A h

PT

-d

A

N

v,

~d

7"

A

WYZA

IMEZ

7

K G

From the lettered drawings choose the correctsectional view for each numbered drawing.Sketch the view in the space provided. Solns. p. 144s26

(XX)

\y

td

}r\

7

cffi

1 ..1

-LLL

rv

a 8

10

BK

M

f\

N

Q

From the lettered drawings choose the correctsectional view for each numbered drawing.Sketch the view in the space provided. Solns. p. 144

-e*

27

Sectioningexercises

j 'j

Tc

B-ii

6

Solns. p. 145

1. Complete the sectional front view looking on plane C-C,2. Complete the sectional end view looking on plane B-B.

F— End View

F^-

Section E-E

(Both holes

right through)

1. Draw an end view looking in the direction of arrows F-F.2. Complete the sectional front view looking on plane D-D.3. Complete the sectional end view looking on plane E-E.

28

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Sectioning exercises

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30

Sectioning exercises

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32

Information on Engineering DrawingsCommunication between the drawing office and the workshop is mainlyachieved via the engineering drawing - orthographic and/or pictorial.In order to reduce drafting time a number of standard parts ' aredrawn in a simplified form and many items of written information areabbreviated. In BS 308 Part 1:1972 recommendations have been made for

Conventional representation of commonly used parts & materials andAbbreviations of terms frequently used on drawings.

Before this engineers' "shorthand" can be used correctly it isnecessary to understand the terms used to describe features ofengineering components. This terminology is common to both drawingoffice and workshop and is often used when discussing the variousmanufacturing and machining processes used in engineering.

Terminology

Bush(bearing)

VeeBlock

HOUSING A component into which

a "male" mating part fits, sits

or is "housed".

BUSH A removable sleeve or liner.

Known alternatively as a simple

bearing. Fig. shows a flanged bush.

RecessedSurface

Base or Foot

CurvedSlot

Boss

BASE (or FOOT) That part upon

which the component rests

.

RECESSED SURFACE Ensures better

seating of the base. Minimises

machining of the base.

BOSS A cylindrical projection on

the surface of a component -

usually a casting or a forging.

CURVED SLOT An elongated hole

whose centre line lies on an arc.

Usually used on components whose

position has to be adjusted.

33

Terminology

Rib

Fillet:

FILLET A rounded portion, or

radius, suppressing a sharp

internal corner.

RIB A reinforcement positioned

to stiffen surfaces usually at

right angles to each other

KEY A small block or wedge

inserted between a shaft and

mating part (a hub) to prevent

circumferential movement.

KEYWAY A parallel sided groove

or slot cut in a bore or on a

shaft to 'house' a mating key.

TeeGroove(slot)

Flat

TEE SLOT Machined to "house"mating fixing bolts and preventthem turning

FLAT A surface

machined

parallel to

the shaft axis.

Usually used to

locate and/or lock a mating

component.

HEXAGONHEADBOLT

4=4=^1

HEXAGONHEADSCREW

TAPER DOWELPIN PIN

Notethreadlengths

yj

STUD

f4=* n

COTTERor SPLIT

PIN

®

A cylindricalA pin pin used toused locate matingfor parts,fastening

(3D

Used forfastening

34

TerminologyMany different types of holes may be seen on engineering drawings.

The more common ones, associated with drilling, reaming and/or

tapping, are shown below in Fig.l. The name and where appropriate

the application of each is indicated.

Figures 2 and 3 indicate the different terms which may be seen on

drawings that are associated particularly with lathe work.

1

1

2 3 4 5

//

1

17/

1

y//i

1

/// i

1

//7 7///

s\

V W i

/

w>Fig.l

1. A drilled hole or, if greater accuracy is required, a reamed hole,2. A 'blind' tapped hole i.e., a threaded hole which passes only part

way through the plate.3. A countersunk hole. Provides a mating seat for a countersunk

headed screw or rivet.4. A oounterbore . Provides a 'housing' for the heads of capscrews

,

bolts, etc.5. A spotfaae . A much shallower circular recess. Provides a

machined seat for nuts, bolt heads, washers, etc.

StraightKnurling Shoulder Undercut

(or groove)

Chamfer KeywayF i g . 2

Taper Domed or SphericalEnd

StandardCentre

This is a machining symbol. (It indicatesthat a surface is to be machined, without

defining either the surface texturegrade or process to be used)

.

Radius Collar orFlange

Splines Fig. 3

35

AbbreviationsMany terms and expressions in engineering need to be written ondrawings so frequently as to justify the use of abbreviations whichhelp to reduce drafting time and costs. Many of these abbreviationshave been standardized as can be seen in BS 308: 1972: section 11.

A selection of the more commonly used ones are stated and clarifiedin the following tables.

ABBREVIATION MEANING SKETCH/NOTES

A/C

A/F

HEX HD

Across corners

Across flats

Hexagon headHEX HO

ASSY Assembly See page 96

"W~ 25 CRS *4sCRS Centres—

H

£ or CL Centre line +CHAM Chamfered CHAM ^CH HD Cheese head I U I CH HD

^ ^ SCREW]SCSK Countersunk CSK

SCREW ^5 -CSK

C'BORE Counterbore C'BORE

CYL Cylinder or cylindrical

DIA

t

R

Diameter (in a note)

Diameter(preceding a dimension)

Radius (preceding adimension, capital only)

DRG Drawing

FIG. Figure

LH Left hand

LG Long

MATL Material

NO. Number

36

ABBREVIATION

L

PATT NO.

PCD

,/D

0/ D

RH

RD HD

SCR

SPEC

S'FACE

SO

STD

U CUT

M/CD

mm

NTS

RPM

SWG

TPI

MEANING

Pattern number

Pitch circle diameter

Inside diameter

SKETCH/NOTES

Outside diameter

Right hand

Round head

Screwed

Specification

Spotface

Square (in a note)

4 HOLES& 3 e<?u/-

s PACED ON16 PCD

/^r*\ RD HDL * SCREW

S ' FACE

Square(preceding a dimension)

Standard

Undercut

Machined

Millimetre

Not to scale

Revolutions per minute

Standard wire gauge

Threads per inch

See page 4 forconventionalrepresentation

SI symbol: rev/min

* Abbreviations commonly used in practice but not listed in

BS 308: Part 1: 1972

Notes(1) Abbreviations are the same in the singular and plural.(2) Capital letters are shown above, lower case letters may

be used where appropriate. For other abbreviations upperor lower case letters should be used as specified byother relevant British Standards.

(3) Full stops are not used except when the abbreviation makesa word which may be confusing, e.g. NO. for 'number'.

37

Conventional Representationof Common Features: Screw threadsThere are many components commonly used in engineering which are com-plicated to draw in full. In order to save drawing time, these partsare shown in a simplified, conventional form. Some of the morefrequently drawn features are shown in this section.

Subject - STUD

i;t

Convention

The screw thread is represented bytwo parallel lines. The distance be-tween these lines is approximatelyequal to the depth of thread.

Note The inside line is THIN andthe circle is broken \

4 b».

External Screw Thread(Stud, bolt, set-screw, etc.) Front view Side view

TAPPED

"BLIND HOLE"

The shape of the hole formed bythe tapping size drill is drawnin heavy lines.

Note Section linescross thethread

The outsideline is THINand the circleis broken

V^«

/H

Internal Screw Thread Front view Side view

STUD INSIDETAPPED HOLE

The external thread is super-imposed over the internal thread.

Note Section lines are not drawnacross the external thread.

Screw Threads(Assembly) Front view Side view

38

Conventional representation: SpringsA spring is designated by stating the diameter of the wire, thecoil diameter (inside or outside), the form of the spring ends,the total number of coils and its free length - See BS 1726.

In the case of the compression spring, the pitch of the coilsmay be deduced from its free length and number of coils.

Subject Convention

t_I 9 ?I *I I i * i I I

COMPRESSION SPRING

Note

The construction onthe right shows howthe convention maybe drawn from thespring details.Extreme accuracy isnot essential; forexample, a radiusgauge may be usedfor the small radii.

Diameterof wire

This method is onlyused for quick dia-grammatic sketches

TENSION SPRING

Note

The construction onthe right shows onceagain how the pitchof the coils may beused to set out theconvention. Diagrammatic

representation

39

Conventional representation: Shaft DetailsIt is frequently necessary to fix a component to one end of a shaftor spindle so that a torque may be transmitted. Examples below are:

(1) Square on shaft(2) Serrated shaft(3) Splined shaft

Machine handles, valve wheel spindle.Typical example - steering wheel to column on car,Drive shaft on machine or vehicle when slidingalso has to take place, e.g. in a gear box.

Subject Convention

See page 96 forsquare on valvespindle.

SQUARE ON theend of a longSHAFT

^Side view

The enlarged sketchshows how the serrationsmay be constructed

SERRATED SHAFT

NoteThirty-six serrations areshown for convenience only

Vi ew onserrated end

NoteOnly a few teethneed be shown

Splines are usuallydrawn with parallelsides as emphasizedin the enlarged sketch

SPLINED SHAFT

NoteTwelve splines are shownfor convenience only

View onsplined end

Refer to section onterminology - page 35

40

Conventional representation: KnurlingKnurling is a common method of providing a roughened surface to aidtightening or slackening of a screw by hand. This is formed bypressing special rollers against the surface of the component whilstit revolves in a lathe. The commonly used diamond and straight knurlsare shown below.

Subject Convention

I

s*m*wm**&j

I'-'.:':"

i>>

DIAMOND KNURL ona machine screw head

JT'

*'',

i

t *\

ft

v /

STRAIGHT KNURL ona circuit terminal

Bearings

Notice how it ichless drawing isnecessary in orderto represent anyball or rollerbearing in aconventionalmanner

.

Cross-section of adouble rowself-aligningball bearing.

E332

fl

mSee assemblydrawing on page 103

BALL

41

Conventions I representat ion :

Long ComponentsThere are occasions when bars, shafts, spindles or tubes may betoo long to be drawn to a reasonable scale. In such cases theelevation may be interrupted as shown below.

Subject Convention

RECTANGULAR BAR

CIRCULAR SHAFT OR SPINDLE

«HOLLOW SHAFT OR TUBE

MULTIPLE HOLES

When a large number ofholes of equal diameterare equi-spaced arounda diameter or in line,only one hole need bedrawn in full with theremainder marked witha short centre-lineas shown in thedrawings on the right.

Remember that this circleis called the pitch circlediameter or PCD

Holes on a circular pitch

0- -0-

-p p—0~"~^ 0"

Holes on a linear pitch

42

Conventional representation: Gears (1)Before gears can be drawn a great deal of background knowledgeabout their nomenclature and construction must be acquired.The following drawings of gears are presented as conventions only.

Subject - GEARS Convent-ion

*'!.»»»!

Note

Side viewof gearwheel isinsection.

SPUR GEAR Single spur gear

Note

A pinion is so calledwhen it has a relativelysmall number of teethcompared with itsmating gear wheel.

Si devi ew

jL

XS

Pinion

In mesh with a. pinion

WORM AND WHEEL

Wheel

Wormandwheelinmesh.

Worm

43

Conventional representation: Gears (2)A good example of how a complex component may be drawn relativelysimply is the bevel gear. The assembly shown below is of a pair ofgears of equal size, the direction of motion being changed throughan angle of 90°. In this arrangement, the gears are often referredto as mitre wheels

.

The gears may be of differing sizes, of course, and the anglebetween the shafts may be other than 90°. In this latter case, theside view of the gear assembly would have to show one gear as anellipse

.

Sub j eat Convention

BEVEL WHEEL

Assemblyof a pairof bevelgears setat 90° toeach other.

Note BS 308: Part I: 1972 deals with a number of features whichrequire to be shown less frequently than those illustratedin this section. They are:

Thread inserts; repeated parts; semi-elliptic springs;conical springs; torsion springs and a rack and pinion.

Summary In all cases, conventional representation should only beused when it saves drawing time. Where it is not con-sidered adequate, a more detailed view should be shown.

44

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46

Test for conventional representations

Select, from the array, the names of the items for which thefollowing diagrams are conventional representations.Insert in the answer column the corresponding number and letter,

Conventional reps

Example

7

8

10

eaE EL

ET;K^-l;

£

Answer

4C

^ri1^

Solutions on page 148

ARRAY

WormWheel

Tensionspring

B

ShoulderKnurling

ExternalScrewThread

A Resistor

Square onShaft

7

8

MachineAll Over

RoundShaft

SplinedShaft

BevelGear

SpurGear

Worm

Form ofMachiningSymbol

SerratedShaft

Weld-symbol

InternalScrewThread

Break inRectangularShaft

Break inTubularShaft

Compressionspring

DiamondKnurling

Collar

Counterbore

Bearing

StraightKnurling

47

Pictorial Drawing

A component may be represented graphically in various ways.

An Orthographic Drawing, for example, requiring a minimum of

two views to fully communicate the size and shape of a com-

ponent, is used in engineering mainly to convey manufacturinginstructions from the designer to the craftsman. On the

other hand a well executed Pictorial Drawing, adequately

representing all but the most complicated components usingone view only, is used mainly as an aid to visualization of

the shape of a component rather than for communicating

detailed instructions for manufacture.

A pictorial drawing, generally, is a quickly produced,

approximately scaled representation of a component - a

"picture" rather than an accurately scaled line drawing.

There are many different types of pictorial representa-

tion. Two of the most commonly used ones are known as

Isometric Drawing and Oblique Drawing both of which are dis-

cussed in detail in this section.

Note! There is a method of isometric representation, more

precise than the one discussed here, known as Isometric

Projection. This method is much more time-consuming, and

therefore less commonly used, because all sizes for the

drawings have to be transferred from a specially constructed

isometric scale. It is the approximate method of represent-

ation, Isometric Drawing, which is used in this section.

49

Pictorial Drawing: Isometric

\^ —

»

|3 SC1 —P

in

— -

1

7 t—

s P

Note:All recedinglines aredrawnat 300.All linesare drawnfull-size,

Plan

SV/^Arrow L - Looking from LEFTArrow D - Looking DOWN. Isometric drawing

When making an isometric drawing from orthographic views of acomponent use an isometric grid at first, as shown above.Follow this simple procedure:

1. Choose the direction from which the component is to be viewedso that the resulting isometric drawing will show the mostdetail of the component. Compare the isometric drawings below.

Example A is drawn lookingfrom the left and down, andis a good representation ofthe component

.

Example C shows the samedetail but is drawn froma different direction.

All of the other drawingsfail to; show some of thedetails of the component.

Draw the outlineof a box into whichthe component willjust fit.

3. Use distances fromthe orthographic viewsto set out pointswithin this box, e.g. P.

Heavy-in thelines whenthe outlineis completed.

50

Isometric drawing: inclined edges-hdU square

I sometri c

When components have sloping surfaces, the edge distances inthe orthographic views are transferred to the isometric boxas shown by the dimension D in the above example.

-• —

i

^m- 2iiOlJARtS

1oin < /(Nl \ /

1E

1

11

A|

i

E E

I \ k/ \

>S,

IIy

v N T

4t \-kr

( 1 > .

The component shown above has surfaces sloping in two directionsresulting in inclined edges, for example, IE. In this case,pairs of distances from the orthographic views are used to plotpoints within the isometric box. Distances used in this, way forlocation purposes are called ORDINATES

.

Note:- The angles of inclination in the orthographic views arenever transferred to the isometric box. When I and Ehave been located, they are joined to produce thecorrect slope in the isometric drawing.

51

Isometr ic drawing exerc1

:ises, |

j

,

s

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ll

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1 2

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1

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j

1 — v5

1

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1 ' 6

Make an isometric drawing of each component on tracing paperplaced over the isometric grid on page 60. Sizes for the ^__-,^ x^isometric drawing are obtained by counting the relevant -£~~-\- 4rt/^number of squares in the orthographic views . * J v^xSolutions are given on p. 149.

52

1 2,

| U : i

l

1

J

1

i —V>V|

1"

' J

1|

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l 1i i 1

3 j_ |

4I 1

i

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-i

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i

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i

i nMake an isometric drawing of each component shown aboveusing isometric paper. If the isometric grid sizediffers from that of the squared grid, transfer EQUALnumbers of divisions from the orthoqraphic views to the _*iff^ -TO.1 sometric drawing Solut ic ns are give>n <an P ag e 14 9. ^ ^T

53

Make an isometric drawing of each component shown aboveusing tracing paper with the isometric grid or usingisometric paper. Solutions are given on page 150.Always start with a faintly drawn "isometric box" whichprovides three faces from which to set out ordinates.

54

Isometric drawing: construction of ellipses (1)

B-4s*r

I ^\H

J\V

s

y

A shape which is circular onan orthographic view is shownas an ellipse on an isometricdrawing.The following constructionsillustrate 3 different methodsof producing the ellipticalshape

.

Lines, called ordinates, aredrawn on the circle in theorthographic view as shown.Corresponding ordinates aredrawn on the isometric draw-ing with the same spacing S.The height H of each ordinateon the true circle is trans-ferred to the correspondingordinate on the isometricdrawing to form the outlineof the ellipse. These pointsare joined with a neatfreehand curve

.

The more ordinates, the moreaccurate the ellipse.As the circle and ellipse aresymmetrical, the ordinatesneed only be constructed ina quarter-circle.

2. Diagonals are drawn on theorthographic side view asshown on the left.

Horizontal and verticalordinates are drawn to touchthe points where the circlecrosses the diagonals.

The ordinates are transferredto the isometric box as shownand the resulting points ofintersection P are joinedwith a neat freehand curve.

As in method 1, only aquarter-circle need be drawnto obtain the four pointsrequired

.

This method is useful for quickfreehand sketching but is notas accurate as method 1.

55

Isometric drawing: construction of ellipses (2)

In this method, the ellipse isconstructed on the isometricbox with compasses and severalconstruction lines are neededto find the centres of arcs.

Centre lines and a diagonalare drawn across the face ofthe isometric box as shown.

FRUSTUM(a "beheaded"cone orpyramid)

Lines are drawn from thebottom corner of the box Bto the mid-points of theopposite sides.

The intersections C providethe centres for both minorarcs of the ellipse.

The corners of the box Bare the centres for themajor arcs of the ellipse.

If the centres have beenconstructed accurately,the arcs drawn withcompasses will blendperfectly.

The ellipses of the conicfrustum opposite havebeen drawn using method 3,i.e. with compasses.

Make further isometricdrawings of the frustumusing methods 1 and 2 toplot the ellipses

.

Compare the shapes andsizes of the ellipses ob-tained by the 3 methods

.

In general :

Method 1 gives the bestshaped ellipse and is veryuseful when there is onlypart of a circle to drawon the face of theisometric box.However, methods 2 and 3are more rapid than 1.

56

Isometric drawing examplesEXAMPLE 1

An isometric drawingof the Vee-block shownon page 21

The ellipseshave beenconstructedusing method 3,i.e. with compasses.

The Vee and thesloping facehave been con-structed byusing pairs ofordinates asshown onpage 51

The smallradius at theintersectionof surfaces Imay be drawn:

(a) using ordinatesor

(b) with a radiusgauge if thecurve is small.

EXAMPLE 2 The incompleteisometric drawing ofthe component belowis viewed from theright and

>v looking down

.

Use the procedure suggested on page 52 to complete theisometric drawing in the space provided or make a completeisometric drawing on isometric grid paper. For furtherexamples use the drawings provided for sectioning exerciseson pages 28-31 (solutions are not given)

.

57

1

Isometric drawing exercises

i

i

+)

-1-1

IN

1-

—^i

i

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Make an isometric drawing of each component shown above.Construct the ellipses by using one of the methods —

•

illustrated on pages 55 and 56. L^_~TIn each case view the components in the direction ^~~-J

indicated by the arrow and looking down.Solns. p. 151.

58

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59

ISOMETRIC GRID - to be used for isometric sketches.

The above grid is composed of lines drawn at an angle of 30° whichintersect with vertical lines . The equilateral triangles thusformed have lengths of side equal to 5 mm.Use the grid with tracing paper or detail paper.

60

Pictorial Drawing: Oblique

L y^

vL) N

_

1

'

Arrow LArrow D

Looking from LEFTLooking DOWN.

An oblique pictorial drawingpresents the component withone of its faces as a true shape.This true shape is drawn on tnefront face of the oblique boxas shown below.

The longest face is usually-drawn on the front of the obliquebox with receding lines betweenh and \ full size.

Compare tnese oblique drawings.Drawings 7, 8 and 9 representthe shape of the componentbetter than the others.

Note:- TL= TRUE LENGTH

45'\!_TL

S=£K3

H5

TL'/2TU f (D«fNL_TL

HK

30°

TL

r^ TL

©

61

Oblique drawing: methods of constructionThere are many variations in angle, length of receding lines,and directions from which a component may be viewed in orderto produce an oblique drawing, as can be seen by the exampleson the previous page. Different oblique drawings of the samecomponent may each provide the detail required.

In general: 1. The receding lines may be drawn at any angleto the horizontal but an angle of 30°, 45°or 60° is preferred as lines can be drawnwith set-squares.

2

.

Receding lines may be any proportion of theirtrue length. A good pictorial representationis obtained if lengths from \ to \ x actuallength is used.

\^ Note: All vertical and horizontal lines are drawn true length.

V

r__

11-

i

^i

ri ,

4 SCI

' I

/oTL

This oblique drawing is ofthe component viewed fromthe left (arrow L) andlooking down (arrow D)

.

Receding lines are drawnat 45° and \ true lengthusing tee and set-squares

.

When making freehand oblique sketches it is convenient to use5 mm squared paper and to draw the receding lines at 45° and

7 x true length. As the diagonal of a square is 1*4 x sideof the square, then each diagonal can be used to representtwo squares on the orthographic views as shown below.

N XLConstruct the shape with faintlines. Complete by lining inthe outline heavily.

An alternative view

62

Oblique drawing: inclined edges

D 6 SQ £>Q

j

l

D

j' 'I

/ \'

/ \/ \

1

1

L

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representedby

3 diagonals

When components have sloping surfaces, the edge distances inthe orthographic views are transferred to the oblique box asshown by the dimension D in the above example.

1

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The component shown above has surfaces sloping in two directionsresulting in inclined edges, for example IE. Pairs of ordinatesfrom the orthographic views are used to plot points within theoblique box, for example point E.

Note: The angles of inclination in the orthographic views arenever transferred to the oblique box. When I and Ehave been located they are joined to produce the correctslope in the oblique drawing.

63

Nlethods of

1III!

1 1 1 :

constructing "oblique circles"

! 1

i

l l

j^T1 1

1

|f 1

I

A shape which is circular in an

z \\

i

\

orrnograpnic view may be snownas a circle on the obliquedrawing if the component isviewed as shown in example 1.L_

^ //

v ^ The end of the cylinder is a1 true circle which may be drawn

with compasses.

The linfis nf t.hp "nhl irmp lir>v"

have been drawn to show thesize of a box into which thecylinder will just fit.

If the circular face is receding,e.g. at 45°, it will appearelliptical and will have to beplotted. Examples 2, 3 and 4

show ways of constructingTL ,-, -r, ellipses.

T yf When making an oblique drawing_ «« v 45 view the component, if possible,

in a direction which will allowcircular and part-circular facesto be drawn with compasses.

"X\*

1

Tl

1

,

A S 1—

1

The oblique ellipses on the leftare plotted by using a methodsimilar to that used forplotting an isometric ellipse.

The ordinates, however, haveto be proportionately spacedalong the receding lines.

'* =-—=qs,

/ Ci \l. ^

L .

V / l

^ - ^.^y

\lxSk

i

In the case of the freehand\ "

oblique drawing shown in—jr-i example 2, the spacing S is

J" *

1

"^.

^0*7 x s i.e. trie length of

1 N l\1 diagonal represents 2

squares on the orthographicview

.

V ^^ J

\ s^ \v 1

i

s

— sJ \ As in the construction for

>u an isometric ellipse, the

/..t. T L \ X>ordinates need only be

45 >L,ri_

constructed in aquarter-circle

.

2

64

Methods of constructing "oblique ellipses'

The method for constructing anoblique ellipse shown oppositeis only used when the recedinglines are drawn at0*7 x true length,mainly for quickly drawnfreehand sketches.

The larger scale drawing belowshows how the length CD isobtained. The length ^CD canbe judged by eye.

Note: Theactual lengthof CD istransferredto the obliquebox.

Represents8SQ/

TL

\/rJL

The ellipses of the conicfrustum in example 4 havebeen drawn freehand usingthe ordinate method.

The ordinates used for plottingthe points on the ellipse havebeen measured along horizontallines spaced proportionately.

Ordinates are true lengths.

Spacings are true length,

The ordinate method is alsouseful when there is onlypart of a circle to be drawnin the oblique box.

Exercises: Make obliquedrawings of the componentsshown on page 58. Solutionsare not given.

65

Oblique drawing examplesEXAMPLE 1 Two oblique drawings of the Vee-block shown ortho-graphically on page 21. Compare these with the isometricdrawing of the same component on page 57.

TL

Fig lb TL - TrueLength

Ordinates are spaced to suit the size of ellipse oeing plotted andthe accuracy required. More ordinates will make the drawing moreaccurate but it will take longer to draw. Note that ordinates setoff from receding lines are spaced at proportionate distances alongthese lines.

The length, width and height dimensionsof Fig. lb have been rounded off tomultiples of 5 mm so that the squaresof the 5 mm grid may be used to fulladvantage, particularly for lines

EXAMPLE 2 receding at 45° and 0-7 true length.

This viewshows themaximumuse ofcompasses

.

Fig. la has been drawnusing the actual dimensionsof the vee-block. Recedinglines at 45° and \ TL.

zz ~

N-._ i _L.- i^z^E"

l"\ . r

~t -^Sv> — -p-

^t X'V^^f4! — _ ,

—

-T

Complete theoblique viewon the right. -»-

This view in-volves the mostconstruction

.

For further exercises: Make oblique drawings of thecomponents shown on pages 52, 53 and 54, using tracing paper and the5 mm squared grid on page 67. Draw receding lines at 45° and 0*7 x TL,

Solutions are given on pages 153 and 154.

66

—

—

"

~

—

SQUARED GRID - to be used for oblique pictorial drawing and ortho-graphic drawing and sketches.

The above grid is composed of lines drawn to form squares which havelengths of side equal to 5 mm.Use the grid with tracing paper or detail paper.

67

Dimensioning

Any drawing from which a component is to be made must conveyinformation from the designer to the craftsmen in three ways.It must

Describe the shape of the component by using orthographicand, sometimes > pictorial views

Give sizes by dimensioning

Provide information about the workshop processes involved

Draughtsmen and designers should understand not only methodsof projection, but also dimensioning methods and processes requiredfor the manufacture of an engineering component, so that correctinstructions may be issued to the craftsman. Most of the problemsof dimensioning may be solved by the application of a few simplerules. Some may be simply stated, e.g. 1, 2 and 3 below whilst otherscan be more easily explained by reference to diagrams (next page)

.

(1) Dimensions should be placed on drawings so that they may beeasily "read". They must be clearly printed and placed outsidethe outline of the most appropriate view wherever possible.

(2) The drawing must include the minimum number of dimensions necessaryto manufacture the component and a dimension should not be statedmore than once unless it aids communication.

(3) It should not be necessary for dimensions to be deduced by thecraftsman.

The way a draughtsman dimensions a component or assembly is influencedalso by the need to consider the "type" of dimension he will use.

These may be classed broadly as

(i) SIZE DIMENSIONS - used to describe heights, widths, thicknesses,diameters, radii, etc., and, where appropriate, the shapes of

the component.

(ii) LOCATION DIMENSIONS - necessary to locate the various featuresof a component relative to each other, to a reference surface or

to a centre line, etc.

(iii) MATING DIMENSIONS - applied to parts that fit together. This

implies a certain degree of accuracy, and in the case of shaftswhich fit into holes, the application of limits and fits willmost likely be necessary. For details of limits and fits referto pages 84-90.

All the examples in this section are intended to explain the rules ofdimensioning which are set out as recommendations in BS 308: Part 2:1972,

It must be stressed, however, that the dimensioning of any componentdepends on the draughtsman's interpretation of the recommendations.A component may be dimensioned in a number of different ways yet stillbe dimensioned correctly.

68

Dimensioning

A number of the basic rules of dimensioning can be explained byreference to _ the above drawing of a thin plate.The sides marked A and B are known as DATUM faces. They are usedas reference edges from which dimensions are drawn. Datums mayor may not be machined. Even if they are not machined it is goodpractice to choose reference edges in order to simplify thelayout of dimensions.

Points to note:

(1) DIMENSION LINES - thin full lines placed outside the componentwherever possible and spaced well away from the outlines. Thelonger dimension lines are placed outside shorter ones.PROJECTION LINES - thin full lines which extend from the viewto provide a boundary for the dimension line. Drawn at 90° tothe outline.

(3) ARROWHEADS - drawn with sharp strokes which must touch theextension lines.A LEADER LINE is a thin full line which is drawn from a notea dimension or, in this case, a "balloon" and terminates in anarrowhead or a dot.Relatively small gap.Relatively short tail.Crossing extension lines - usually a break to ensure clarity.Dimension placed above the dimension line. This is preferredto the alternative method of placing the dimension in a gap inthe line. Avoid using both methods on the same drawing ifpossible.Dimension placed so that it may be read from the bottom or

(10) Dimension placed so that it may be read from the right handside of the drawing sheet.

Study this information before turning to the next page.

(2)

(4)

(5)

(6)

(7)

(8)

(9)

69

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71

Arrangement of dimensionsDimensions should be placed so that they may be read from eitherthe bottom or right-hand side of a drawing, for example:

25

o

The arrangements at 1 and 2 are themost usual but there are occasionswhen it may be necessary to use thearrangement at 3

.

Avoid placing dimensionlines in the shaded area- zones of about 30°

.

Various methods of dimensioning narrow spaces or widths are shownbelow. Note the placing of the arrows outside the extension lines.

3

T? J ? )

/

%A m

//n ^nThe figures shown below aredimensioned incorrectly.

2-8 — V^O)^v

1

-.20

,

\

2

\

)

\..

25 \

/ / / \A\ >

4'V / H

7

Exercise : Dimension the figurescorrectly. (Solns. p. 155)

c

Kto

-M

\t^

%o-J 5:

D

y

v s s s n

7

-if

TTT-n J

72

Dimensioning circles

On an engineering drawing a circle may be one of the following;

A thindi sc

A hole in a

thin plateThe side viewof a cyl inder

~e-The side view of a

cylindrical hole

The way a circle is dimensioned is influenced by the factors shownabove and also by the size of the circle and the space availablewithin the circle.

Points to note: (i) The dimension always refers to the diameter andNOT the radius

(ii) A circle is never dimensioned on a centre line,(iii) The conventional symbol for diameter is <j>

Methods used for dimensioning relatively small circles

and larger circles

For diameters of cylinders

7

o<r>

oCM

is7 Z3

*-4 IS

<±^

10In 3 and 4

the leaderline mustbe drawn inin linewith thecentre ofthe circle

When the dimension linehas to be drawn as inexample 6 it is prefer-able to place thedimension as shown sothat it may be easilyread from the bottomof the sheet.

Side view Front view

In this example itis preferable todimension the sideview even thoughthe cylindricalshape is not apparent.Dimensions in thisview, however, mustalways be precededby the symbol

<J>

73

Dimensioning radii

On an engineering drawing a radius usually describes the shape orcontour of a component in a particular view and may beeither

An external radius An internal radius or A spherical radius

A radius should be dimensioned by a dimension line which passesthrough, or is in line with, the centre of the arc.The dimension line should have one arrowhead which should beplaced at the point of contact with the arc.The abbreviation R should always precede the dimension.

The above statements may be interpreted as follows:

For small radii —\

For spherical radii

reR 5

yR 5

ZJFor larger radii

R 5spH£B&

R20

-R 10

The circles shown below are incorrectly dimensioned,

Exercise

:

Dimension thecircles on theright correctlyusing theinformation givenon the previouspage (Solns. p. 155)

74

Dimensioning anglesAngles should be expressed in: (1) degrees e.g. 90°

or (2) degrees and minutes e.g. 27° 30'0° 15'

The placing of the angular dimension depends on:

the position of the angle in relation to the bottom and/or theright-hand side of the drawing sheet and the size of the angle.

Angles may be dimensioned using one of the methods shown in theseexamples

qoo

Alter-native /

Alter-native

Arc struckfrom apexof angle

L /

DIMENSIONING CHAMFERS

45° chamfers should be specified by one of the methods shown below:

251e2x45

2x45

Chamfers at angles other than 45° shouldbe shown as a dimension and not as a note, e.gChamfers should not be specified bya note and a leader line.

The radii below are dimensioned incorrectly.

lORad cfpsExercise:- Dimension the radii below correctly using the information

given on the previous page. (Solutions on page 155)

-26

22V

75

Designation of plain holesIt is often necessary to specify not only the diameter of a holebut also, the way the hole is produced. Processes for forming holesinclude drilling, boring, reaming and coring (holes made whencasting). The drawing below shows how these may be designated.

-cA HOLES EQUI- SPACED

<f>5 DRILL THROUGH

**• s

Section CC Front view

Note:- The 40 mmdiameter circle isreferred to as thePitch Circle DiameterPCD

Designation of "special" holes

COUNTERSINKS

^4 CSK AT 90°

TO 8

25 Ytifa-J I— 04

SCREW THREADS

M 12- 6H

mm«COUNTERBORES

J*6 C'BORE0IOx 5 DEEP

06 C'BORE 10x 5 DEEP

OR

SPOTFACES

OR

S'FACE(f> /2

Note:A coarse ISOthread isdesignated bydiameter andtolerance gradeonly.

MI2-6HTHROUGH

M I2-6H

I— 12 MIN

OR

MI2- feH

12 MIN LENGTHFULL THREAD

ORw>M 12 - GH

12 MIN LENGTHFULL THREAD

76

Location dimensionsExamples on previous pages have shown how components and featuresmay be dimensioned when size is the main consideration.Figures 1, 2 and 3 show how to dimension a component whenlocation is necessary. The features can be located from a machinedsurface or centre line. Such a surface or line is known as a DATUM.

-+oc

e

.m

25

r>B00 (^o

cc RJh

10^ «-15

1.Spigot located fromtwo referenceedges (R)

.

Both holes locatedfrom two referenceedges (R)

.

3.

Hole A located fromtwo reference edges(R) then hole Brelated to hole A.

Size anuse of

d location dimensions andthe machining symbol

20 REAMS

30 S

CD

o

L-r-t-r-1

34 S

44 L

0\2 DRILL

S

20 S'FACE

S SCALE

CD CO

4.The simple bearingbracket casting on theleft shows both sizeand location dimensions.

Reference surfaces aremarked wj.th a machiningsymbol:- s/

This is placed so thatit may be read from thebottom or from the rightof the sheet.

It is preferable toplace the symbol on theappropriate projectionline rather than asshown on the left.

No symbol is requiredwhere the machining isspecified i.e. in thecase of the drilledholes, the reamed holesand the spot-face.

The location dimensions are those shown with a letter L and sizedimensions by a letter S. Some of the size dimensions are less acc-urate than others e.g. the thickness of the rib is fixed during thecasting process whilst the 20 mm diameter hole is accurately reamed.The 20 mm diameter reamed hole is located by the dimension from themachined base to the centre line of the hole.

77

Dimensioning exercisesEach drawing below shows a component made from mild steel plate15 mm thick. Dimension both drawings so that accurate marking outand subsequent manufacture of the plates may be carried out.Use the machined surfaces as reference edges. The holes are tobe reamed. Sizes may be obtained by measuring the drawing.All dimensions in millimetres.

>

sL

Note: Each machining symbol in the following dimensioningexercises has been placed so that it appears "upright"when viewed from either the bottom right hand corner orright hand side of the drawing sheet."The symbol is placed on the machined surface itselfprovided that when it is so positioned it "falls" outsidethe outline of the component. Alternatively, it isplaced on a suitable projection line.

Solutions to the above exercises are given on page 156

78

ao•H4J

DrHOCO

0)

^n d)rH rH3 rH 0) • tn

(0 o •H X! o C(f)

o U P O Hi+-r •d nJ <Tl M

• ^^ O -P 4-1 3 .

o •H d> O M d) CO to

t tn XI 0) X! (0 a)

<DC -P tl cu > d) u•H Ifl (1) O O O O £ p

X £ X! u -P P P d)nJ P -H • T3 >l g

CD M 3 10 WOO) to X) •hO O ffd) •h x: o •H I-l

to d> P -p CO TJ rHto MO 0) 4-1 d) d) H

0)•HX C to t3 1 d) c£ OlH (d a -p • > •H

c -P O -H >h X) 3 O g tO Ci-l M o & £ d) •p H

'cc xi 'a nJ <D U W X! X!O 1 d> to xi to O -P O to-h 0) }-i en P d) CN c03 0) 3 0) trj XJ 4-1 d) . oC > -P o C d) 4-1 O X! tn •H

CO

cd> O 0) -H S-l O o C toBCUC ctj -P d) >itH CH O 4-1 d) U r-i fO S d)

-O ^ 3H rH 0) to d) tP & ca 6-H G rH O x! -H p fi M •H

E>t (d n) X! -P a> 0} CO 13 TJH4Jg QJ a d)rH 10 T3 (1) 13 rH (0 d) N d) rH

• ^— 3 (0 d) T3 Xi G O •h x: •H Xi rH

Q fo O X! < ^ (« x; tj ^ CO P <

I

79

Di mensioni ng exercisesFully dimension this drawing assuming that the component is to be /

machined all over. Take the datum as the face of the flange marked VSizes may be obtained by measuring the drawing.All dimensions in millimetres.Note: Holes - 4 mm drill equi-spaced

Chamfer - 2 mm at 45°

BUSH

#--E3-

Section CC Front view

Solutiononpage 158

Fully dimension this drawing assuming that the component is to be /

machined all over. Take the datum as the face of the flange marked vNote: (1) Use the horizontal centre line for locating the countersunk

holes in the front viewThe countersink is 90° and enlarges the drilled holes from5 mm diameter to 10 mm diameter.The internal chamfer - 3 mm x 60°

(2)

(3)

GLAND

Section CC

Solutiononpage 158

80

Dimensioning exercisesThe component below is to be made of brass. Fully dimension thedrawing to enable the bracket to be manufactured.Note:- (1) The only parts to be machined are the back face (which

should be used as the datum) and the tapped holes.(2) Locate the holes from the centre line in the front view.(3) Locate the holes and slot from point X in the side view,

"^"

*1

LOCATINGBRACKET

Side view Front viewSolutiononpage 159

Fully dimension the drawing so that the adjusting screw may be manu-factured. Take the shoulder marked v' as the datum face.Note:- The thread is M 6. The head is knurled (fine diamond).

The chamfers - 2 mm at 45°The radius at the end of the screw is 8 mm.

-£3#

Side view

ADJUSTINGSCREW

Machinedallover

Front view

Solutiononpage 159

81

Dimensioning exercise

Fully dimension the orthographic views shown above to enable thebracket to be manufactured. Details of sizes, locations, screwthreads, etc., may be taken from the pictorial view of the samecomponent shown on the opposite page. (All dimensions millimetres)Both the 8 mm base holes and the 35 mm bore must be located from themachined face R. The tapped hole must be located from the 3 5 mm bore,

Note: This drawing can be fully and clearly dimensioned using twoviews only. The drawing of a more complicated component wouldpossibly include a side view also to clarify both shape anddimensioning. The solution to this exercise is on page 160.

82

MI2-6H. 16 MiN LENGTH -

FULL THREAD. S'FACE 20

2 HOLES DRILL,

THROUGH 0'p

BOSS 16

HEIGHT 2

In this isometric view of the cast-ironbracket all the corner fillets(or radii) have been omittedin order to simplify thedrawing.

Cast ironBracketforVerticalSpindle.

83

Limits and Fits

In the early days of engineering, "mating" parts, e.g. a

shaft and the bearing in which it is housed, were manufac-tured individually and assembled only after laborious handfitting by craftsmen. This method of production demandedgreat skill, was slow, and thus an expensive operation.

To overcome this the first system of limits and fits

was introduced around the turn of the century. When thesystem was used correctly production costs were greatlyreduced because identical mass-produced components, even

those made in different places, could be readily inter-

changed without resorting to the time-consuming fitting

operation.

The use of a suitable system of limits and fits, the

latest of which (B.S. 4500) is outlined in the following

text, ensures that all identical components are made to a

specific size within narrow limits.

It must be stressed that when assigning limits to

the dimensions of a component it is necessary to consider

not only its function but also the skill of the operator

and the type and condition of the machines which are used

to manufacture the component.

Limits should be applied to the dimensions of a com-

ponent only if the resulting degree of accuracy is essential

for the efficient functioning of the component. It is un-

economical to limit the accuracy of a dimension to ± 0.005 mm

when ± 1 mm would prove satisfactory.

84

Limits and Fits for Holes and Shafts

7

A

Hole

Shaft(normalrepreseri't a t i o n

)

V7,

A

Hole

Tolerance zones(exaggerated

)

Shaftwithtolerancezones

A TOLERANCE on a holeor a shaft is apermissible degreeor error.It depends on:

(1) Machining or cuttingoperation used.

(2) Quality of work.

(3) Type of fit betweenhole and shaft.

Effect of manufacturing process on degree of accuracy obtainable

Process(typical)

Numerical value of tolerance forsample sizes

BS 1916 inch BS 4500 metric0.001 in 0.001 mm

S- (U

-— £o z»

1 Slip blocks, reference gauges

2 High quality gauges

3 Good qual i ty gauges

4 Gauges and precision fits

5 Ball bearings, fine grinding

6 Grinding, fine honing

7 High quality turning, broaching

8 Centre lathe turning and reaming

9 Horiz. and vert, boring

10 Milling, planing, extrusion

11 Drilling, rough turn-ing, boring

12 Light press work, tube drawing

13 Press work, tube rolling

14 Die casting or moulding

15 Stamping (approx)

16 Sand casting, flame cutting

0.119to

0.237

1 .969to

3.150

4.725to

7.087

0.06 0„08 0.16

0.08 0.12 0.2

0.12 0.2 0.32

0.15 0.3 0.5

0.2 0.5 0.7

0.3 0.7 1 .0

0.5 1 .2 1.6

0.7 1 .8 2.5

1 .2 3.0 4.0

1 .8 4.5 6.0

3.0 7.0 10.0

5.0 12.0 16.0

7.0 18.0 25.0

12.0 30.0 40.0

18.0 45.0 60.0

30.0 70.0 100.0

3 mmto

6 mm

50 mmto

80 mm

120 mmto

180 mm

1 .0 2 3.5

1 .5 3 5

2.5 5 8

4 8 12

5 13 18

8 19 25

12 30 40

18 46 63

30 74 100

48 120 160

75 190 250

120 300 400

180 460 630

300 750 1000

480 1200 1600

750 1900 2500

For more detailed lists referto BS 1916 and BS 4500

Tolerance i ncreases wi th size of component

The tolerance number is directly related to the manufacturingprocess and hence to the quality of work in terms of the degreeof dimensional accuracy required. The permissible degree of errorincreases (a) as the process becomes less precise and

{b) as the size of component increases.Tolerance number should not be confused with the numbers whichrelate to surface roughness.

Refer to British Standards for further information.Use BS 1916 for inch sizesand BS 4 500 for metric sizes.

85

Limit systems

vHole sizeconstant

Shaft sizevaries toprovide therequired fit

Shaft sizeconstant

Hole sizevaries toprovide therequired fit

Clearance Interference

HOLE BASIS

Clearance Interference

SHAFT BASIS

BS 1916 and BS 4500 use the hole basis but there are occasionswhen it is necessary to design a fit on a shaft basis.

Basic size and disposition of tolerance

Whenever possible, holes are designed and machined to sizesobtained with standard tools and/or to preferred sizes inmillimetres (see BS 4318)

.

The basic size of a hole is the dimension used if no toleranceswere applied. Another name used is "nominal size".

Tolerances can be applied to holes and shafts in various ways.o

'///, ofooo

CM

V///

Uni 1 ateraldisposition

Basic size = 24.000Tolerance = 0.030

+ 0-0 30

Write 24.000 °

or 24.0302 4 . 000

Toleranceplaced toONE side ofbasic size

Bi

1

ateraldisposition

Basic size = 24.000Tolerance = 0.030

+ 0-0 1 5

Write 2 4.000-0 - 015

or 24.01523.985

Tol erancesplit aboveand belowbasi c size

BS 1916 and BS 4500 generally use the unilateral method ofapplying limits to a size.

The tolerances can be represented as shapes on a graph. TheOX axis is the top side of the basic size, in this case, the hole,

+

0.

InchesSHAFT

HOLE 1

15HAFToo

r*

CI earance

IHOLE

<2 NCD U>

Interference

Mi 1

1

imetresISHAFT

HOLE

5HAFT

CI earance

©*ooM

1 HOLE1

U

< —CO u>

Interference

86

piT-the relationship between hole (or internal feature) and shaft(or external feature)

ALLOWANCE - the prescribed (algebraic) difference between the lowlimit of size for the hole (or internal feature) andthe high limit of size for the "mating" shaft (orexternal feature), i.e.

allowance*^_y (positive)T

maximum metal condition

lllllllftfllglllltf v vv * %

SHAFT

e.g.a simplebearing

(exaggerated)

The shaft is"loose" running or"easy" running or"slide".

CLEARANCE FITShaft is ALWAYSsmaller than hole.

e.g. for <j>2 inch (BS1916:53)

Hole sizes 2.00182.0000

"Mating" shaft sizes 1.99881.99702.00001.9988

BEARING

Verbal descriptionsof the fit may varywidely. Numericaldifferences are moreimportant.

Smallest holeLargest shaftALLOWANCE + 0.0012

for $24 mm (BS4500:69)

Hole sizes

"Mating" shaft sizes

Smallest holeLargest shaftALLOWANCE

24.03324.00023.98023.9592 4 . 00023.9800.020

Note I Allowance is ALWAYS positive ( + ) for a clearance fit.

/allowance*/ (negative)

e.g. a gearwheel on ashaft(exaggerated)

INTERFERENCE FITShaft is ALWAYSlarger than hole.

/

5252

2

GEAR

The shaft is forcedinto the hole.

The fit can bedescribed in suchterms as

:

"light press" or"press" or"heavy press" or"shrink"

Numerical differencesare more important.

e.g. for $2 inch (BS1916:53)

Hole sizes"Mating" shaft


(as above)sizes 2.0032

2.00202 . 00002.0032

- 0.0032

for $24 mm (BS4500:69)

Hole sizes"Mating" shaft sizes


(as above)24.04824.0352 4.00024.0480.048

As shaft sizes are subtracted from hole sizes, the allowance willalways be negative (-) for an interference fit.* The use of the word "allowance" has been omitted from BS4500. Ithas been used here solely to explain the difference between clearancefit and interference fit. It is still used, of course, in BS1916:53.

87

Both BS 1916 and BS 4500 recommend limits and fits for a wide rangeof engineering processes and activities - even horology J For mostgeneral purposes a carefully selected range of hole and shaft sizesare given in each standard.

-Holes are lettered by capitals, A, B,C, etc., the limits allocatedto the H-hole being recommended. The H-hole always has the basicsize of the hole as one size. The letter is followed by thetolerance grade number e.g. H8 . Shafts are lettered by lower caseletters, a,b,c, etc., and a range of fits is provided by those given

the charts below.inBS 1916 01.182-1 .575 in

Tolerance grade number

BS 4500 <j)30-40 mm

+ 160+ 10

+ 75.

+ 50

+ 25.

- 25-

- 50

- 75-

-100

-125-

-150

-1 75-

-20-280

"•%£**•

Hll

$ 30 40 mm

H9

DH8 H7 o-

D U

I- 0.02S mm

n

d

10

If the tolerances on hole and shaft overlap it is possible in therandom selection of components to obtain either clearance orinterference. These are called TRANSITION fits e.g. H7 with k6,and are described as "push", "easy keying", "tight keying" or"drive". A fit between an H8 hole and an f7 shaft is writtenH8-f7 and reference to the chart above will show that this mustalways be a CLEARANCE fit. Further reference to BS 1916, parts2 and 3 will show the types of fit recommended for particulartypes of work.Extract from BS 1916-Limit values. Extract from BS 4500-Limit values

HoleH7

3.001 in

Shafts

componentbetween

e8 f7 h6 J6 s6+

+ 0.5i n

0.12i n

0.24- 0.8- 1.5

- 0.4- 0.9 - 0.3

+ 0.2- 0.1

+ 1 .0+ 0.7

+ 0.6 0.24 0.40- 1.0- 1 .9

- 0.5-1.1 - 0.4

+ 0.3- 0.1

+ 1 .4+ 1 .0

+ 0.70.40 0.71

- 1 .2- 2.2

- 0.6- 1 .3 - 0.4

+ 0.3- 0.1

+ 1 .6+ 1 .2

+ 0.8 0.71 1 .19- 1.6- 2.8

- 0.8- 1 .6 - 0.5

+ 0.3- 0.2

+ 1.9+ 1.4

+ 1 .01.19 1 .97

- 2.0- 3.6

- 1 .0- 2.0 - 0.2

+ 0.4- 0.2

+ 2.4+ 1 .8

+ 1 .2 1 .97 2.56 - 2.5

- 4.3

- 1 .2

- 2.4 - 0.7

+ 0.4

- 0.3

+ 2.7+ 2.0

2.56 3.15+ 2.9+ 2.2

HoleH7

3.001 mm

ShaftsSize o t

componentbetween

96 k6+

n6+

s6+

ESEI

+ 15mm6

mm10

- 5

- 14

+ 10+ 1

+ 19+ 10

+ 32+ 23

esei

ESEI

+ 1810 18

- 6- 17

+ 12+ 1

+ 23+ 12

+ 39+ 28

esei

ESEI

+ 2118 30

- 7

- 20+ 15+ 2

+ 28+ 15

+ 48+ 35

esei

ESEI

+ 2530 40

- 9

- 25+ 18+ 2

+ 33+ 17

+ 59+ 43

esei

40 50

ES

EI

+ 3050 65

- 10

- 29

+ 21

+ 2

+ 39

+ 20

+ 72+ 53

+ 78+ 59

esei

esei

65 80

88

Conventional method of illustrating terms

BS 1916 - H hole

Q

X<S

1LE J SHAFT

<a

x<2i

BS 4500

BASIC SIZE

DEVIATION

For H hole.Zero line coincides with basic sizeline, hence lower deviation = 0,as shown above.

The size to which hole and shaft are referred.

The algebraic difference between a size and thecorresponding basic size.

UPPER DEVIATION The difference between the maximum limit of sizeand the basic size._ . , , ES for hole The letters standDesignated: c , c . ~ .. _ , .^ es for shaft for the French term

ecart superieur.

LOWER DEVIATION The- difference between the lower limit of sizeand the basic size._ . , EI for holeDesignated

r

ei for shaft ecart inferieur,

ZERO LINE

FUNDAMENTALDEVIATION

The line to which the deviations are referred.The line of zero deviation.The line which represents the basic size.

For each pair of deviations, the fundamentaldeviation is the one nearer to the zero line.This defines the position of the tolerance zonein relation to the zero line.

Graphical representation of fits - H holes

Clearance Interference Transi tion

HOLE HK ZERO o

SHAFT^SECT '

HOLE± HOLE I t

ES ES

SHAFTKSSSSSa'

es LINE TiT es TTes

nes es

EI XERO

BSSCT3.

vm t

ET EI

^im^i.

eL LINE EI » et SHAFT TeL et

t

el

89

Ho le

CL>

>oUp

to

and

including

ShaftExerci ses

Fit

^ H7-g6

H 7

0.001mm96

0.001mm v///,-r^SxV/////>/>/?/

ZERO/ 1

ES+

EI es ei V///A holeH 7 YLirife

oJ

15 6 10 5 14V///A shaft n h 1

—

'

i ,_ . ///////////.\_r

i^^^

18 10 18 6 17 CI earan-ce

r^^21 18 30 7 20

Hoi e Shaft

Basicsize

ES EIMax.si ze

Mi n

.

sizeBasicsize es ei

Max .

si zeMi n .

si ze25 30 50 9 25

10 0-015 10-015 10-000 10 0-0051)0»4 9-995 9-986

30 50 80 >0 29

HoleH 7

0.001mm

Complete the table for any other two hole and shaft sizes.

H7-s6

ES+

15

18

21

25

30

EI

CD

>o

10

18

30

50

-a co

ca -i-

-ao 3+-> r—

OQ- CZD -i-

Shafts 6

0.001mm

10

18

30

es+

32

39

48

50 59

80 78 50

ei+

23

28

35

43

Fit

S6&ZZ2 SHAFT

H7^houE

Interference

Hole

Basi c

sizeES EI

Max .

sizeMi n

.

size

Shaft

Basicsize es ei

Max .

sizeMi n .

size

HoleH 7

0.001mm

Complete the table for any three hole and shaft sizes,

H7-k6

ES+

15

18

21

25

30

EI

~0 CDc c(O -r-

J- -ocu O =3

> +J 1—o o

10

18

30

Q- £=

10

18

30

50

50

80

Shaftk 6

0.001mm

es+

10

12

15

18

21

ei+ H7^

Fit

k6 SHAFT

I HOLE

,^5^

f5

Z. Y7>?>f///1

V////S

Transition

f/SM/S/^

s:

Hole

Basicsize ES EI

Max.size

Mi n .

size

Shaft

Basicsize es ei

Max .

sizeMi n .

size

Complete the table for any three hole and shaft sizes. Solns . p. 161.

90

ISO Metric Screw Threads (BS3643)One of the most common items which needs to be clearly described onan engineering drawing is the screw thread which may be used for:

(1) Transmitting power, e.g. square thread in a vice or a lathe.(2) Adjusting parts relative to each other (usually a Vee-thread)

.

(3) Fastening parts together, e.g. a nut and bolt (a Vee-thread).

The following section deals mainly with the ISO metric thread whichis recognized internationally and, over the next few years, will beused in preference to the many varied types of threads which exist inindustry today. In order to specify an ISO metric thread on a drawingit is necessary to understand the basic terminology of screw threadsand how the fit between internal and external threads is derived.

The fit is basedon the "effective"diameter, i.e. thediameter at whichthe pitch ismeasured.

NUT(INTERNAL)

BOLT (EXTERNAL)

Threadangl eW Pitch

Note: Thehelix andthread formare drawnsimplified.

BOLTSecti onshowi ngthread formor "profile"

Class of fit

,

s_

<D+->

s_ CD

o Ec fO•1— •1—

2: -a'

CD

>+->

CJ

CD

crest

Right-hand thread

CD

Although the thread profile is a Vee in section, the nuts are classedas "holes" and the bolts as "shafts" and tolerances are appliedaccording to BS 4500 (Limits and Fits) . They may be representedgraphically like any hole and shaft combination.

NUTS Close fitInternal thread

+zero line 5H

4h* 0)

> U0)

-uCD

Fi

External threadBOLTS

-p

fd «wffl 0)1

Medium fit Free fit

6H 7H

K 8g

1— minimumclearance

Fit designated as -*- 5H/4h 6H/6g 7H/8g

Coarse and fine pitches are available but it is expected that thecoarse pitch screw threads will suffice for most applications andthat the medium fit will be the most commonly used. This may besummarized as follows:

Class of fit

medium

Bolts & screws

6g

Nuts

6H

91

ISO Metric screw thread designation

In production engineering it is necessary to provide informationabout the size of thread and the tolerance allocated to it. On a

drawing, the thread would be "dimensioned" or designated by-

stating the information as shown in the following examples:

M 10 x 1.5 - 6H [NUT - capital H for hole or internal thread.]

M 10 x 1.5 - 6g [BOLT - small g for shaft or external thread.]

Thread tolerance grade number y—MI0~6H

-Pitch in millimetres

•Nominal size in millimetres

Symbol for ISO metric.

The ISO metric coarse is the thread most commonly used and adesignation for this would omit the pitch, e.g. M 10-6H as shown.

Isometric threadsPreferred sizes

Nominaldi ameter

mm

Pitchcoarse

mm

1 .6 0.35

2 0.4

2.5 0.45

3 0.5

4 0.7

5 0.8

6 1

8 1 .25

10 1 .5

12 1.75

16 2

20 2.5

24 3

Note

In thetable onthe right,the inchand numbersizesrelateonlyapprox-imatelyto theISO metricsizes inthe centrecolumn,e.g.5 .

S ln

actuallyequals

15. 875 mm

13 ISO metric threads comp (jred with74 Imperial inch and number sizes

UNC UNF ISO metric BA BSW BSF

No. No. DIA mm No.

D] A D [A

1-6 10

1 1

2 9

2 2

8

3 32-5

4 4 7 1

5 5 3"5

6 6 6 5

8

10

8

10

45

4

3

T2"

3c 2 T6

12 12 1

11

75

I

5

T*3"8"

e\

T53"5

7i

7

TE 1

92

TE 1

92

i 2T6 c T5 K

5"5

i 65"8

3

"ZF

7"5

3

J1"5

2

1 2 4 1

92

Screw threads, nuts and bolts (ISO metric series)

A rapid, easy-to-remember method of drawing screw threads, nutsand bolts is essential if templates are not available. The drawingshould look right and slight discrepancies in size are not impor-tant. The most used ISO metric bolts (up to <}>24 mm) are:

Major diameter mm

Minor diameter

Minor diameter(approx.

)

Example ofapplication

M6 M8 M10 M12 M14 M16 M20 M22 M24

6-00 8-00 10-00 12 «00 14-00 16-00 20-00 22-00 24-00

4-77 6-47 8-16 9-85 11-55 13-55 16-93 18-93 20-32

4-8 6-5 8-2 9-8 11-6 13-6 17-0 19-0 20-4

M 16 StudCD CD

CO

Nut and bolt head sizes across the flats (spanner sizes) in mm.

Major diam. D.

Distance acrossthe flats

D x 1-5

(Dxl-5) + 1 mm""

Thickness of nut

Height of head

10

10

5-0

4-0

13

13

6-5

5-5

10

17

16

8-0

7-0

12

19

19

10-0

8-0

14

22

22

11-0

9-0

16

24

24

13-0

10-0

20

30

30

16-0

13-0

22

32

33

18-0

14-0

24

36

36

19-0

15-0

Approximate method: Thickness of nut = D x 0-8 e.g. M10Height of head = D x 0-7 e.g. M10

Example of application

M 16 Nut

Nuts are usually madefrom hexagonal stock barand a 30° chamfer ismachined on at least onesurface.In the plan view thisappears as a circle, thediameter of which isequal to the distanceacross the flats.The chamfer is drawnin the front view butnot in the side view.

,-No chamferhere

D* 0.8= 16x0.8

= 12.8

D = I6

93

Nuts and bolts exercisesThe drawing below is of an M 24 nut showing how the radii in thefront view and side view may be constructed. The major diameter ofthe bolt is the size D for calculating the distance across theflats and the thickness of the nut.

Major diameter D = 24 mmMinor diameter = 20-4 mm approx. (See p. 93).

D x 1.5 = 24 x 1-5 = 36 mm A/F

and R = 18 mm - this value of R is usedto .find the centres forradii (1), (2) and (3)

D x o-8 = 24 x o-8 = 19-2 mm

T = 19 '2 mm

Plan

Procedure

(1)

Side view

(2)

(3)

(4)

(5)

(6)

FrontviewDraw major and minor diameter circles in plan,

according to BS convention (See page 38)

.

Set out circle in plan with radius = 18 mm, i.e. distance A/F.Construct hexagon around this circle using 60° set-square.Set out thickness of nut = 19*2 mm and project the hexagon to thefront and side views.In the front view the centres for the radii marked (1) and (2) areobtained by setting out the radius R = 18 mm from and 0] as shown.In the side view the centres for the radii marked (3) are obtainedby setting out the radius R from 2 and 3 as shown.

Note:

Length of bolt = 60 mm

Front view

The length ofa bolt ismeasured fromunder thehead as shown

.

Exercise

M 20 Bolt with nut.

1. Verify that

(a) minor diameter =

(fc) distance across flats =

(c) thickness of nut =

(d) height of bolt head =

2. Complete the drawing.

17 -0 mm30*0 mm16*0 mm14 '0 mm

(approx.

)

94

Assembly DrawingsThe purpose of an assembly drawing is to. provide visual inform-ation about the way in which parts of a machine or structure fittogether. There are several types of assembly drawings and thedifferences in presentation depend on the uses for which they areintended. They are:

(1) LAYOUT ASSEMBLIES - in which the designer places together allthe various parts in order to establish overall sizes, dis-tances, etc., and, as a result, the feasibility of his design.

(2) OUTLINE ASSEMBLIES - these give general information about amachine or a group of components, for example, main sizes andcentre distances which would show how the unit would beinstalled. This type of assembly is often used in cataloguesgiving details of the range of units offered for sale.

(3) GENERAL ASSEMBLIES or ARRANGEMENT DRAWINGS - show clearly howcomponents fit together and, more important, how the assembledunit functions. Outside views, sectional and part-sectionalviews may be used but dimensions are rarely needed. The variousparts may be labelled by ballooning and a parts list would com-plete the drawing.

(4) SUB-ASSEMBLIES - are drawings which show only one unit of amulti-unit component. On more complicated or multiple partcomponents it may first be necessary to arrange parts intosub-assemblies which are then built up into the main assembly.

(5) SECTIONED ASSEMBLIES - a simple assembly may be drawn withoutthe need for sectional views and be clearly understood. Onmore complex assembly drawings, however, too many hidden detaillines tend to confuse and a sectional view of the assembledparts conveys the information more clearly.

Note An assembly drawing should not be overloaded with detail.The correct place to fully dimension and describe a" singlepart is on a detail drawing.

The drawings shown on the next page are typical of the use of ageneral assembly to give a general picture of a valve and a sub-assembly to show how the spindle unit is built up. A detaildrawing of one of the parts is added to emphasise that the physicalassembly of the valve depends on the manufacture of a large numberof individual items.

The exercises which follow are of relatively simple assemblieswhich could be drawn with reasonable clarity without the use ofsections but the resulting increase in clarity will show theadvantage to be gained by their use.

The solution to the example on page 98 indicates the way in whichthe exercises should be carried out.

95

General assembly (or General arrangement)

The above drawing is a general assembly of a screwdown valve

used to control the flow of water.

The purpose of this sectional view is to label the various parts

of the valve and to show how they fit together. A parts list

which matches the ballooned letters is necessary and this may be

either on the assembly drawing or on a separate document.

The general assembly is not dimensioned in detail although the

sizes of the inlet and outlet and a few overall sizes may be

shown as the drawing may be typical of a range of valves of

differing sizes.

96

_i

3+ _J

ni

*at

!

! i *i —i— t t^M24-6

3

SUB-ASSEMBLY DETAIL DRAWING

The above sub-assembly

drawing shows how several parts

are assembled together before

being fitted into the main body

of the valve. This type of

drawing is particularly useful

if information more detailed

than that shown on the general

assembly is required, for

example, by the person

assembling the valve or the

maintenance worker.

The detail drawing shown above

is of one of the numerous com-

ponents which make up the com-

plete valve and in this case is

a single-part drawing.

All the dimensions and processes

required to manufacture the part

must be shown on the drawing.

It is probable that the machin-

ist who makes this item will

take no part in assembling the

valve and will therefore use

only this detail drawing.

97

Sectioned assembly - Typical exercise

>

H*J

-

-

i :

i | | ("1

1 1

H Front view

End viewon bol

t

£3-

Exercise Build up a sectioned assembly drawing of the componentparts looking on cutting plane CC to obtain a sectionalfront view and cutting plane SS to obtain a sectionalend view, by tracing over and correctly positioningeach part

.

Solution Note that most of the outlines are unaltered.

Sectional Front View lookingon cutting plane CC

Sectional End Viewlooking on

cutting plane SS.

Note The bolt and rib are notsectioned in the front view, but are sectioned in the end view.

98

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99

Sectioned assembly exercisesHINGE FOR VICE

eI

1

!; I HI

Upper hinge

For both exercises

niT\

1

1

1

1

^Nri<k

ILower Hinge

2L

I ! !i

i

I

i

ca

i i

1 h :i i i

^ •»

-m

Hinge Pin -&Build up a sectioned assembly drawing of the componentparts looking on the cutting plane CC by tracing over

and positioning each part.

Ji

Solutiononpage 162

Pivot Arm

ANT I-VIBRATION MOUNTING

Steel Liner

Rubber Bush Rubber BushSide View Front View

^

^HingePin V-

)

--&--

mWeldedBaseforPivot Arm

-i—L.

Side View Front View

-E3-

Solutiononpage 163

100

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101

Sectioned assembly exerciseJOURNAL BEARING

Washer2 required

ED

Bearing Cap

1 f.1 1

1

1

1 1

1 1

1 1

i <H

1 1

! MI i

i i

i i

i \-

ii

i

• v. jl

t:

BearingHousing

Front view with R.H. half in section

Exercise Build up a sectioned assembly drawingof the component parts looking on thecutting plane CC by tracing over andcorrectly positioning each part.

Splitbearing

-e

Solutiononpage 163

102

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104

DevelopmentsMany objects in everyday use are made from thin materials such as

cardboard, plastic, aluminium, copper, brass and steel. Metals notmore than about 3 mm thick are referred to as SHEET METALS.

The objects made from these materials are developed from the flatsheet. A pattern is drawn on the sheet which is then cut to theoutline of the pattern. The material is bent, folded or rolled intothe required shape, these processes giving the object stiffness andstrength for a comparatively small weight of material.

A pattern which is used to mark out further patterns is called aTEMPLATE

.

There are four basic shapes in sheet metal development from whicha wide variety of work is fashioned, including hoppers, bins, chutes,vessels and ducts for ventilation and dust-extraction.

1. PRISM

CYLINDER

H E

2 . PYRAMIDL= Slant Height

on edge

4 . CONE

TTD

L=Slant Height

Simple shapes based on prisms, cylinders, pyramids and cones may bedeveloped by three commonly used methods of construction. They are

1. PARALLEL LINE DEVELOPMENT: for prisms and cylinders mainly.

2. RADIAL LINE DEVELOPMENT: for pyramids and cones.

3. TRIANGULATION: for transition pieces which are used to joindifferent shapes.

A pattern is usually folded so that the lines indicating its shapeappear on the inside of the component. In practice, allowances mayhave to be made for extra material required for joints, stiffenededges, bends and seams.

No such allowances have been made in the exercises in thefollowing pages so that basic principles can be emphasized.

105

"* -1_ ^

^r^

n

^V

(N Ll_

bull pueg

CO

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cCD

Eao

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u xSi (d= -p

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107

EXERCISES

Joint

True shape ofduct A

Start the shape ofthe hole at this point,

Solutionson p. 166

(1) Develop thepattern forbranch A.

(2) Develop thepattern forone half ofbranch B(SSS) tofind thetrue shapeof half ofthe hole.

Measure the orthographicviews to obtain dimensions.

All dimensions in millimetres

30° TEE-PIECE DIAMOND SECTION

PARALLEL LINE DEVELOPMENT

108

EXERCISE

True shape

of cross-section

of chute

looking in

direction X

Complete the pattern for

the | | -section chute in

the space provided.

Measure the orthographic

views to obtain dimensions.


Typi calchuteappl i cati on

Solutionon p. 166

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.

Note how theprojectionlines inter-sect to pro-vide pointson the curveof intersection.These corres-pond to pointsobtained bythe constructionused on page 112

2 Plan on T

Solutions on p. 168


(1) Complete the curve ofintersection at XX.

(2) Complete the patternfor one half of thecylinder B (SSS)showing the shapeof the hole in B.

90° TEE-PIECE FORMED WITH

CYLINDERS OF

UNEQUAL DIAMETERS.


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EXERCISES

Front view &

(1) Complete the end view looking on theinclined circle YY.

(2) Show that the curve of intersection isa straight line in the front view.

(3) Develop the pattern for the cylinder A.

Solutions on p. 16

9

30 TEE-PIECE FORMED WITH CYLINDERS

OF EQUAL DIAMETERS

All dimensions in millimetres. PARALLEL LINE DEVELOPMENT

116

EXERCISES

-GJ

Pattern B

(2) Complete the pattern for thecylinder marked B showingthe shape of the hole in B.

All dimensions in millimetres.

(1) Construct theellipse in theend view whichrepresentsthe inclinedcircle YY.

30 u TEE-PIECE

FORMED WITH

CYLINDERS

OF EQUAL

DIAMETERS

.

Solutionson p. 170


117

EXERCISE

True shape "

of cross-sectionof chute lookingin direction A.

Complete the pattern for

the \^J -section chute in the

space provided.

Solution on p. 170

All dimensions in millimetres. PARALLEL LINE DEVELOPMENT

118

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123

(b) Development ofright cones

Funcircumference = 2ttL

(360°)

There are two methodscommonly used for dev-eloping patterns ofconic shapes . Both areexplained below.

(1) The accurate method (Fig.l)

The true length of the slopingedge of the cone is L

.

Using as centre, an arc isdrawn of radius L

.

Before the circumference of thebase of the cone can be drawnalong this arc, angle 6 mustbe calculated as follows.

9 _ 360°ft

27Tr 2ttL

2-rrr 360°2-rrL

6 = j- x 360°

Fig.l

ise: Measure r and L (in milli-metres) from fig.l, calculateangle 6 , and check that thepattern is correctly drawn.

(2) The approximate method (Fig. 2)

An arc is drawn with ascentre and radius L as inmethod 1

.

The plan view is divided intoequal parts as shown. 12 partsare convenient, being easilyobtained using a 30° set-square.Distance d, which is the approx.length of the distance betweenpairs of points on the basecircle, is stepped off aroundthe arc 12 times to completethe development.The sketch below shows clearlythat a distance stepped off inthis way is the true length ofthe chord between the points andnot the true length of the arc.

Fig. 2

Exerc%se. Compare the pattern constructedby this method with the oneobtained using the accuratemethod by measuring theangles at 0.

124

DEVELOPMENT OF THE FRUSTUM OF A RIGHT CONE

Radial1 ines

Truelengthline 0-

(1) Develop the full surface areaby using either the approximatemethod or the accurate method.

(2)

(3)

(4)

Add radial lines as shown. Thesecorrespond to the radial linesdrawn on the surface of the cone.

From the points where the radiallines on the surface of the coneintersect the cutting plane SS

,

project horizontally to the truelength line e.g. 2 to 2

T , 3 to 3„ etc.

Swing these true lengths from Oto the corresponding radial lineson3T

the pattern, e.

to line 3 etc.to line 2

Frontview

Exercise: (5)

Note:

Plan

Complete the pattern by addingthe remaining points and joiningwith a heavy line.

All lengths on the pattern mustbe true lengths

.

The shortest edge is usuallyused as the joint line. In thiscase it is along line 0-1.

'As an aid to visualizing the shape of conicfrusta the construction of the front andplan views is illustrated and explained below.

Construction of plan view andside view of a conic frustum

Plan viewProject the points of inter-section of the radial linesand the cutting plane S-S fromthe front view to the corres-ponding radial lines in theplan as shown.

e.g. pointsg

to lines 6 and 8.

Side viewProject the points of inter-

* section of the radial linesand the cutting plane S-S fromthe front view to the corres-ponding radial lines in theside view as shown.

4e.g. points ,. to lines 4 and 10.

Exercises : Complete the planand side view.

Solns

.

RADIAL LINE DEVELOPMENT p. 175

125

EXERCISES

Completecone

\\ Sidevi ew

Solutionson p. 176.

(1) Complete the development of the pattern of the surfacearea of the frustum in the space provided.

(2) Complete the plan view.(3) Complete the side view. RADIAL LINE

DEVELOPMENT

126

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Solutions

In this section a solution is given for each of the exercises

presented in the text. Each solution is identified by the

page number on which the exercise appears. The solutions

are arranged in the order in which the exercises are set.

Where an exercise has specifically requested a sketch

or tracing the solution is sketched or traced freehand.

Where it is felt, however, that an accurate representation

makes it easier to understand the solutions they have been

drawn to scale using instruments. On some of the more com-

plicated solutions notes have been added in order to emphas-

ize important points.

The Isometric and Oblique solutions shown are those

thought to provide most detail. As explained in the text

there is not necessarily a unique solution for each of these

exercises.

Similarly the solution given for each of the dimension-

ing exercises may not be the only correct solution. The

alternatives must, however, not only meet the requirements

of the exercise but also obey the "rules" of dimensioning.

If cardboard or paper models are made of each of the

development solutions and folded into the three-dimensional

shape indicated in the corresponding exercise then these

solutions can be easily and convincingly verified. Notice

that all lines on the patterns are, as emphasized in the

text, "true length" lines.

136

Solutions: First AngleOrthographic Projection

Onpage7

Drg. Reason for incorrect interpretation

1Plan incorrectly positioned. It should be below F.

2 Plan incorrectly positioned. It should be projected below F.

3 Plan and side view incorrectly positioned. They shouldbe interchanged.

4 Side view out of position. It should be projected from F.

5 Plan incorrectly positioned. It should be projected below F.

6 Plan incorrectly drawn. The cut away should be at thefront of P.

7 Side view incorrectly drawn. The cut away should behidden detail.

8 Side view positioned incorrectly. It should be drawn onthe right hand side of F.

9 Plan drawn incorrectly. The cut away should be atthe rear of P.

On page 9 On page 8 Note These are sketched freehand.

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Drawing A B C D E F

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12 F

Side view indirection of R 5 16 2 12 13 15

137

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138

Solutions to exercises on pages 12 and 13 (sketched freehand)

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140

Solutions to exercises on page 19 Addition of missing views,

ThirdR . H . 5

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FirstFront

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Solution toexercise 1

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Solutions: Sectioning Exercises on page 25

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Solutions to sectioning

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Solutions to sectioning

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144

Solutions to sectioning exercises on page 28

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145


Third angle

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Third angle

Note: In exercise 1 there is no bolt in the threaded hole,so the section lines cross the thread.


Thi rd angle

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Third angle

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146


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148

Solutions: Pictorial Drawing isometric ex. P a ge 52

Solutions to exercises on page 53

149


Note In these, and the preceding exercises dealing with isometricprojection, each component has been viewed in the directionwhich shows the most detail.

150


Note Each view has been drawn looking the directions indicatedin the exercise. These were chosen so as to show the mostdetail in the pictorial view. All solutions have been drawnusing either an isometric grid or a framework of lines as in 2.

151


Note Each solution has been sketched freehand on an isometric grid.The resulting pictorial views are those which show the mostdetail of each component.

\l-"'l\U"' \i-" |\1.-"'|\U-

152

OBLIQUE Solutions to exercises on page 66 (drawings on page 52)

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Solutions to exercises on page 66 (drawings on page 53)

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153

Solutions to exercises on page 66 (drawings on page 54)

Note In these, and the preceding exercises dealing with obliqueprojection, each component has been viewed in the directionwhich shows the most detail.

154

Solutions:Dimensioning

Solutions toexercises on page 72

74

and 75

28

Note

The solutions given areideally spaced becausethere is adequate spacefor dimension linesand numbers

.

On an engineering drawing,other lines may reducethe amount of spaceavailable for dimensionsand care must be taken toensure that lines andnumbers are clear and donot clash with any otherdetail.This is particularly thecase with circles andradii when the dimensionis often taken outsidethe circle or the radius.

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see page 75

155

Solutions to

exercises on

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d 20 REAM

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MATL-I5mm MILD STEEL.

<f>30 REAM

R25

MATL - 15 mm MILD STEEL.

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Solutions to

exercises on

page 80

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3 HOLES EQUI-SPACCD

4 DRILL THROUCH

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158

Solutions to exercises

on page 81

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In this view, the heavyline of the root dia-meter is in front ofthe fine line circleof the thread.

FINEDIAMONDKNURL

MI0-6g

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Note: The brackets indicate that this isan AUXILIARY dimensiongiven for information only

159

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ALL DIMENSIONSMILLIMETRES.

Solution to exercise on page 82

In this exercise, an end view of the casting could have been used forindicating several of the above dimensions, but it is possible tofully dimension the component using two views only. There might wellbe other arrangements of the dimensions which would be quite satisfac-tory providing that the "rules" of dimensioning are observed and thata clear distinction is made between size and location dimensions.

160

Solutions: Limits and FitsSpecimen solutions to exercises on page 90

Note: All sizes are in millimetres.The decimal point is on the base line.

H7-g6

Hole Shaft

Basi c

Si zeES+

EI Max.Si ze

Min.Si ze

BasicSize

es ei Max

.

Si zeMin.Si ze

10 0.015 10.015 10.000 10 0.005 0.014 9.995 9.986

15 0.018 15.018 15.000 15 0.006 0.017 14.994 14.983

25 0.021 25.021 25.000 25 0.007 0.020 24.993 24.980

40 0.025 40.025 40.000 40 0.009 0.025 39.991 39.975

65 0.030 65.030 65.000 65 0.010 0.029 64.990 64.971

H7-s6

H7-k6

Hole Shaft

BasicSi ze

ES+

EI Max

.

Si zeMin.Si ze

BasicSi ze

es+

ei+

Max.Si ze

Min. .

Si ze

8 0.015 8.015 8.000 8 0.032 0.023 8.032 8.023

18 0.018 18.018 18.000 18 0.039 0.028 18.039 18.028

28 0.021 28.021 28.000 28 0.048 0.035 28.048 28.035

38 0.025 38.025 38.000 38 0.059 0.043 38.059 38.043

78 0.030 78.030 78.000 78 0.078 0.050 78.078 78.050

Hole Shaft

Basi c

Si zeES+

EI Max

.

Si zeMin.Si ze

BasicSi ze

es+

ei+

Max.Si ze

Mi n .

Si ze

7 0.015 7.015 7.000 7 0.010 0.001 7.010 7.001

11 0.018 11 .018 11 .000 11 0.012 0.001 11.012 11 .001

20 0.021 20.021 20.000 20 0.015 0.002 20.015 20.002

50 0.025 50.025 50.000 50 0.018 0.002 50.018 50.002

70 0.030 70.030 70.000 70 0.021 0.002 70.021 70.002

161

Solutions: Sectioned Assemblies

s^ffSS

Exercises on pages 99 and 100

On page 99

(1) Sectioned assembly looking on

cutting plane CC,

Note :

Although the screw lies in the

cutting plane it is not sectioned

when cut longitudinally

(i.e. along its length).

On page 99


cutting plane CC.

Note :

The pin, nut and washer are

not sectioned.

The spacer is not considered

to be the same as a washer

and is sectioned in this case.

On page 100


cutting plane CC.

Note :

The hinge pin lies across the

cutting plane and is sectioned

when cut transversely.

162

Solutions to Sectioned Assembly Exercises on pages 100, 101 and 102

On page 100

(4) Sectioned assembly

looking on cutting

plane CC.

Note ;

The thin steel liners

are sectioned by

single thick lines

On page 101

(5) Sectioned assembly

looking on cutting

plane CC.

Note :

As the Vee grooves are

at 4 5°, the section

lines may be drawn at

an angle other than

the normal 45°.

On page 102

(6) Sectioned

assembly

looking on

cutting

plane CC.

163

Solutions to Sectioned Assembly Exercises on pages 103 and 104

On page 103

(7) Sectioned Assembly looking on

cutting plane CC.

Note :

The grease nipple is similar to a nut

and need not be sectioned.

The ball race is shown in the

conventional manner. See page 41.

^

On page 104

(8) Sectioned Assembly

looking on cutting

pi ane CC

.

164

Solutions: Developments: Parallel Line

In the solutions of development exercises, the followingnotes will be useful:

(1) Types of line. Outlines

Bend lines

Construction lines

(2) All the prisms, cylinders, pyramids, cones and transitionpieces are hollow, thus no section lines are requiredon cut surfaces.

(3) The development of a sheet metal component can be shownto be correct by forming the required shape from thepattern. A tracing can be made of each solution andtransferred to thin card from which the pattern canbe cut. An allowance must be made for extra materialalong fixing edges. See the example on page 105.The card folds more easily if the bend lines are scoredon the inside surface of the pattern with a fine ballpoint pen. A quick drying latex type adhesive is idealfor joints.



Bend line

Pattern forbranch B

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166

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on

page

11

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linder

T

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Solutions to

exercises onpage 113

3 2 1 12

Pattern forone half ofcylinder B

showing theshape of thehole in B

.

Solutions toexercises on page 114

Pattern for branch A

1€8

Solutions toexercises onpage 1 1

5

Pattern A

Pattern BY Y

"Curve" ofi ntersecti on

Solutions toexercises onpage 116

r1^Ellipse YY

169

Solutions toexercises onpage 117

Ellipse YY

Pattern for B

showing shapeof hole

Pattern for the\J -section

chute

Note ;

Line isstraighthere *

Solution toexercise onpage 118

170

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174

Radial Line Development - Cones

Complete pattern forsurface area of frustumof a right cone

Completion of exercisesstarted on page 125

Note ;

A RIGHT CONE is one in whicha line drawn from the apex ofthe cone to the centre of thecircular base is always atright angles to the base.

Apex

Centre of base

An OBLIQUE CONE is one in whichthe line from apex to the centreof the circular base is inclinedat any angle other than" 90°to the base.

Note ;

Section lines are not drawn

on cut surfaces because

the cone is hollow

Plan

I/O

Patternfrustum

PlanSolutions toon page 126

exerci ses

176

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182

Basic Engineering Drawing is for any student about to begin the study of

engineering or technical drawing. It is actually used throughout the wholeeducational spectrum -from CSE to degree students. The pace of workingthrough the book is dictated by the ability of the student.

It is particularly suitable for craft and technician students and has found great

favour with first-year engineering degree students who have done little or noengineering drawing. For CSE and O-level students it provides a firm foundation

in the practicalities of engineering,

It is not oriented towards a particular syllabus but deals with the basic

requirements for the preparation and the interpretation of engineering

drawings, Information and exercises are presented on a one-sheet system,and attention is concentrated on particular topics by using a minimum of wordsand a maximum of pictorial explanation.

The approach to the subject is based largely on the interpretation of drawingsas a means of communication, The student is encouraged to interpret andproperly use the conventions of BS308:1972. Subjects covered are 1st and 3rd

angle projection, technology, abbreviations, conventional representation,

sectioning, isometric and oblique drawing, dimensioning, limits and fits, ISOmetric screw threads, assemblies, and parallel line, radial line, and triangulation

developments.

Each section deals with basic ideas and applications with the maximuminvolvement of the student. Many of the exercises are for completion in the

book itself, and solutions to exercises are given at the end. For these reasons,

the book is ideal for self-study.

iSBN 273 31887 X

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