• Author / Uploaded
• Saurabh Kumar Yadav

• Categories
• Dibujo técnico
• Dibujo
• Diseño asistido por computadora
• Ingeniería
• Tecnología

Citation preview

'

1

A

A

'M.

1

J

o

AND DESIGN Jensen/Helsel ^i

Third Edition

J>

»

'M:r-:i4-i

)'

VH^^H r.^-:#

r*:;

:«!»

IPL1CII

J7IMM nirffr

««,

no

IPlMCB

Kiel/ in-ai

nBB

r

l*WC'-i KM H*il!

Digitized by the Internet Archive in

2011

http://www.archive.org/details/engineeringdrawiOOjens

Engineering

Drawing and Design

THIRD EDITION

CECIL JENSEN Former Technical Director R. S. McLaughlin Collegiate and Vocational Institute Oshawa, Ontario. Canada

JAY D. HELSEL Professor Department of Industrial Arts and Technology California University of Pennsylvania California. Pennsylvania

GREGG DIVISION McGRAW-HILL BOOK COMPANY

New York Guatemala

New

Delhi

Panama

Atlanta

Dallas

Hamburg Paris

St.

Lisbon San Juan

Louis

San Francisco Madrid

London Sao Paulo

Singapore

Auckland Bogota Montreal Mexico Tokyo Toronto Sydney

Sponsoring Editor: D. Eugene Gilmore Editing Supervisor: Alfred Bernardi Design and Art Supervisor: Patricia Lowy Production Supervisor: Frank Bellantoni

Cover Photographs: Computervision and Evans

& Sutherland

Library of Congress Cataloging in Publication Data

Jensen. Cecil Howard, (date) Engineering drawing and design. Includes bibliographical references and index. Mechanical drawing. 2. Engineering design. 1. II. Title. I. Helsel. Jay D. 83-19896 604.2 T353.J47 1985 ISBN 0-07-032533-2

Engineering Drawing and Design. Third Edition

Copyright

©

1985. 1979, 1968

by McGraw-Hill.

Inc. All

United States of America. Except as permitted under the United States Copyright Act of 1976. no part of this publication may

rights reserved. Printed in the

be reproduced or distributed in any form or by any

means, or stored

in

a data base or retrieval system,

without the prior written permission of the publisher. 5 6 7 8 9

VHVH

ISBN Q-D7-D32533-Z

8 9

10

9 8

CONTENTS

PART FOUR

Preface

POWER TRANSMISSIONS

PART ONE BASIC

DRAWING DESIGN

1

Chapter 1 Chapter 2

The Language of Industry Drafting Skills and Drawing

Chapter Chapter Chapter Chapter Chapter

Theory of Shape Description Applied Geometry Basic Dimensioning Working Drawings Sections and Conventions

Office Practices 3

4 5

6 7

PART TWO FASTENERS, MATERIALS, 8

9 10 1 1

12

7

44 72 82 127 140

AND

FORMING PROCESSES Chapter Chapter Chapter Chapter Chapter

2

164

Threaded Fasteners Miscellaneous Types of Fasteners Forming Processes Welding Drawings Manufacturing Materials

Chapter Chapter Chapter Chapter

13

Auxiliary Views

14

Pictorial

15

Functional Drafting

16

Drawing

Drawings for

Numerical Control

Belts, Chains,

and Gears

329

Couplings, Clutches, Brakes, and

Speed Reducers Chapter 19 Chapter 20 Chapter 21

366 375 398 419

Bearings, Lubricants, and Seals Cams, Linkages, and Actuators Fluid Power

PART FIVE SPECIAL FIELDS Chapter Chapter Chapter Chapter Chapter Chapter

22 23 24 25 26 27

OF DRAFTING

Development and Intersections Pipe Drawings Structural Drafting

and Electronics Drawings and Fixtures Die Design Electrical

Jigs

436 ,

437 460 473 499 522 538

165

188

209 225 246

PART THREE INTERMEDIATE DRAWING DESIGN

Chapter 17 Chapter 18

328

268 269 278 306 319

PART SIX ADVANCED DRAFTING DESIGN Chapter Chapter Chapter Chapter Chapter Chapter

28 29 30

Applied Mechanics Strength of Materials Engineering Tolerancing

31

Descriptive Geometry

32 33

Computer-Aided Design and Drafting Design Concepts

554 555 569 600 654 672 694

Appendix

704

Index

777

iii

«

A«£HBIWI

1

PREFACE

Engineering Drawing and Design, Third Edition, is prepared for a two-semester course in engineering drawing. The contents are consistent with the trends and practices currently used in the preparation of engineering drawings. Technical drafting, like all technical areas, is constantly changing. The computer has revolutionized the way in which drawings are prepared. For this reason, three new topics have been introduced in the third edition of Engineering Drawing and Design computer-aided draft-

—

ing

(CAD), computer-aided manufacturing (CAM), and

and electronics drafting. In this new edition, the authors have made every effort to translate the most current technical information available into the most usable electrical

form from the standpoint of both teacher and student. The latest developments and current practices in all areas of graphic communication, computer-aided drafting (CAD), electronics drafting, functional drafting, materials repre-

shop processes, numerical control, true positiongeometric tolerancing. and metrication have been

sentation, ing,

incorporated into this text in a

manner

that synthesizes,

and converts complex drafting standards and procedures into understandable instructional units. Extensive author research and visits to drafting rooms throughout the country have resulted in a combination of current drafting practices and practical pedagogical techniques that produces the most efficient learning system yet designed for simplifies,

the instruction of engineering

drawing.

A new

Chapter 32, "Computer-Aided Design and Drafting," explains the basic concepts that a drafter or student drafter needs to know about CAD. It provides an excellent introduction to this topic.

Chapter 25, "Electrical and Electronics Drawings," introduces the student to the new state of the art the use of computer chips and logic diagrams. The authors are indebted to Robert Chadwick, Technical Director at the

—

McLaughlin C.V.I. Oshawa, Canada, for assisting in the selection of topics and projects for this chapter. Additional problems and the clustering of existing problems provides greater choice of material. Every chapter in ,

the text

is

divided into a

number of

single-concept units

each with its own objectives, instruction, examples, review, and assignments. This organization provides the student with a logical sequence of experiences which can be adjusted to individual needs and also provides for maximum efficiency in learning essential concepts. Development of each unit is from the simple to the complex and from the familiar to the unfamiliar. Checkpoints are included to provide maximum reinforcement at each level. Although the adoption of the metric system for drawings by smaller industries is not keeping pace with the large international companies, it is increasing in use. For that reason ANSI Y14.5M-1982 Dimensioning and Tolerancing, ANSI B4. 2-1978 Preferred Metric Limits and Fits, and ANSI Y14. 36-1978 Surface Texture Symbols have all been published in the metric units of size and measurement. In order to prepare our students for gainful employment upon graduation, it is recommended that both the International System of Units (SI) and the U.S. Customary System (USCS) units of measurement be included in all technical

drawing programs. Both SI and USCS units are used throughout the text and in all problems. Thus, the text may be used in a completely metric-oriented course, or in a course which utilizes both metric and customary systems. The teacher may also customize the course by selecting appropriate problems or materials to emphasize or deemphasize any degree of metrication. The dual dimensions shown in this book, especially in the assignment sections, are neither hard nor soft conversions. Instead, the sizes are those that would be most commonly used in the particular dimensioning units and so are only approximately equal. Dual dimensioning in this way avoids awkward amounts and allows instructor and student to be confident that a drawing using either set of dimensions will be no more difficult to work than one dimensioned exclusively in either dimensioning system. Two sets of A4- or B-size worksheets are available separately for the completion of the problems. The worksheets include the problem in metric form on one side and in customary form on the reverse side. They are preprinted with light lines to provide the student with a beginning to

each problem. Using these worksheets eliminates some of the initial work such as preparing borders, legends, data lines, and so forth. The worksheets also provide the student with the positioning of the drawing on each sheet, thus enabling the student to concentrate on the solution to the problem rather than on the mechanics of beginning the drawing. This focuses attention specifically on the concept under consideration and eliminates time wasted in nonessential aspects of the lesson. In earlier units, a certain

amount of the work

is completed for the student; in later however, fewer lines are provided. A complete solutions manual to most graphic problems found in the text is also available from the publisher. The authors would like to thank the many users of the previous edition of the textbook for their thoughtful and useful comments. In addition, the help of Hal Lindquist, Donald Voisinet, and John Nee is appreciated and gratefully acknowledged.

units,

Cecil Jensen Jay D. Helsel

Vi

PREFACE

ABOUT THE AUTHORS

CECIL JENSEN

is the author or coauthor of many sucbooks, including Engineering Drawing and Design, Fundamentals of Engineering Drawing, Drafting Fundamentals, Interpreting Engineering Drawings, Architectural Drawing and Design for Residential Construction, Home Planning and Design, and Interior Design. Some of these books are printed in three languages and are

cessful technical

used

in

many

countries.

He

has twenty-seven years of teaching experience in mechanical and architectural drafting and was a technical director for a large vocational school in Canada. Before entering the teaching profession, Mr. Jensen gained several years of design experience in the industry. He has also been responsible for the supervision of the teaching of technical courses for General Motors apprentices in

He

Oshawa, Canada.

member

of the Canadian Standards Committee (CSA) on Technical Drawings (which includes both mechanical and architectural drawing) and is chairman of the Committee on Dimensioning and Tolerancing. Mr. Jensen is Canada's representative on the American (ANSI) Standards for Dimensioning and Tolerancing and has recently represented Canada at two world (ISO) conferences in Oslo (Norway) and Paris on the standardization of technical drawings. He took an early retirement from the teaching profession in order to devote his full attention to writing. is

a

D. HELSEL is a professor of industrial arts and technology at California University of Pennsylvania. He completed his undergraduate work in industrial arts at California State College and was awarded a master's degree from Pennsylvania State University. He has done advanced graduate work at West Virginia and at the University of Pittsburgh, where he completed a doctoral degree in educational communications and technology. In addition. Dr. Helsel holds a certificate in airbrush techniques and technical illustration from the Pittsburgh Art Institute. He has worked in industry and has taught drafting, metalworking, woodworking, and a variety of laboratory and professional courses at both the secondary and college levels. During the past twenty years, he has also worked as a free-lance artist and illustrator. His work appears in many

JAY

technical publications.

Dr. Helsel is coauthor of Engineering Drawing and Design, Fundamentals of Engineering Drawing, Programmed Blueprint Reading, and Mechanical Drawing. He is also the author of a series of Mechanical Drawing Film Loops.

vii

DRAFTING UPDATE (PRESENT DRAWING PRACTICES) ANSI PUBLICATION Y14.5M-1982

(EXCEPT WHERE NOTED, REFER

SYMBOL

FEATURE

TO CLAUSE THICK THIN

LINES (THREE LINE WIDTHS NOW REPLACED BY TWO LINE WIDTHS.)

NO.)

Y14.2M-1979

LETTERING (TWO APPROVED STYLES. HEIGHT OF LETTERING DEPENDENT ON DRAWING SIZE.

Y14.2M-1979

MILLIMETER DIMENSIONING PRACTICES

CLAUSE

METRIC LIMITS AND FITS

B4. 2-1978

DIAMETER SYMBOL (NOW PRECEDES THE DIAMETER VALUE. THE SYMBOL REPLACES THE ABBREVIATION DIA) RADIUS SYMBOL (NOW PRECEDES THE RADIUS VALUE)

REFERENCE DIMENSION SURFACE TEXTURE SYMBOL

(8.6)

y v v

1.6.1

CLAUSE

1.8.1

CLAUSE

1.8.2

CLAUSE

1.7.6

Y14. 36-1978

SPECIFYING REPETITIVE FEATURES

CLAUSE

1.9.5

COUNTERBORE OR SPOTFACE

CLAUSE

3.3.10

v

CLAUSE

3.3.11

J

CLAUSE

3.3.12

^- 0.2

CLAUSE

2.13

CLAUSE

2.14

CLAUSE

1.8.8

CLAUSE

3.4.2.3

CLAUSE

1.8.3

CLAUSE

1.7.9

CLAUSE

3.4.2

CLAUSE

3.3.3

COUNTERSINK DEPTH

CONICAL TAPER

— L^

FLAT TAPER

SYMMETRICAL OUTLINES

0.I5:

n

^ o

ALL AROUND DIMENSIONING CHORDS, ANGLES,

— 50—

60°-

AND ARCS NOT TO SCALE DIMENSION

FEATURE CONTROL FRAME (FORMERLY CALLED FEATURE CONTROL SYMBOL. ORDER OF SEQUENCE CHANGED)

20-

$-

O0.I

DATUM TARGET SYMBOL

AND

GEOMETRIC CHARACTERISTIC SYMBOLS

PARALLELISM

SYMMETRY CIRCULAR RUNOUT

TOTAL RUNOUT

4.5.1

CLAUSE

6.4.1

no

CLAUSE

6.4.2

//

CLAUSE

6.6.3

O

CLAUSE

5.12

/

CLAUSE

6.7.2.1

A/

CLAUSE

6.7.2.2

STRAIGHTNESS

FLATNESS

A

PARTI

Basic

Drawing

Design

CHAPTER

1

The Language of Industry

UNIT

1-1

The Language of Industry Since earliest times people have used drawings to communicate and record ideas so that they would not be forgotten. The earliest forms of writing, such as the Egyptian hieroglyphics, were picture forms. The word graphic means dealing with the expression of ideas by lines or marks impressed on a surface. A drawing is a graphic representation of a real is a graphic uses pictures to communicate thoughts and ideas. Because these pictures are understood by people of different nations, drafting is referred to as a "universal language." Drawing has developed along two distinct lines, with each form having a different purpose. On the one hand, artistic drawing is concerned mainly with the expression of real or imagined ideas of a cultural nature. Technical drawing, on the other hand, is concerned with the expression of technical ideas or ideas of a practical nature, and it is the method used in all branches of technical industry. Even highly developed word languages are inadequate for describing the size, shape, and relationship of physical objects. For every manufac-

tured object there are drawings that describe its physical shape completely and accurately, communicating engineering concepts to manufacturing. For this reason, drafting is referred to as the "language of industry." Drafters translate the ideas, rough sketches, specifications, and calculations of engineers, architects, and designers into working plans which are used in making a product. See Figs. 1-1-1 through 1-1-7. Drafters may calculate the strength, reliability, and cost of materials. In their drawings and specifications, they describe exactly what materials workers are to use on a

To prepare

DRAWING DESIGN

may

specialize in a

me-

chanical, electrical, electronic, aero-

nautical, structural, or architectural drafting.

DRAWING STANDARDS Throughout the long history of drafting, many drawing conventions, terms, abbreviations, and practices have come into common use. It is

They also may use engineering handbooks,

nication, the

ings, drafters use instruments

BASIC

Drafters also

particular field of work, such as

essential that different drafters use the

particular job.

language, because

2

specifications.

drawsuch as compasses, dividers, protractors, templates, and triangles, as well as drafting machines that combine the func-

thing. Drafting, therefore, it

examine drawings for errors in computing or recording dimensions and

their

tions of several devices. tables, calculators,

and computers to

assist in solving technical

problems.

Drafters are often classified according to their type of

work or

their level

of responsibility. Senior drafters (designers) take the preliminary infor-

mation provided by engineers and architects to prepare design "layouts"

(drawings to

be

made

to scale of the object

built). Detailers (junior drafters)

make drawings of each part shown on the layout, giving dimensions, mateand any other information necesmake the detailed drawing clear and complete. Checkers carefully

rial,

sary to

same practices a reliable

if

drafting

is

to serve as

means of communicating

technical theories and ideas. In the interest of efficient

commu-

American National Standards Institute (ANSI) has adopted a set of drafting standards which are rec-

ommended

drawing practice in all and are used and explained throughout this text. These standards apply primarily to end product drawings, which usually consist of detail or part drawings and assembly or subassembly drawings, and are not intended to fully cover other supplementary drawings such as checklists, parts lists, schematic diagrams, electrical wiring diagrams, flowcharts, installation drawings, process drawings, architectural drafting, and picfor

fields of engineering

torial

drawing.

Fig. 1-1-1

Drafting

— today and tomorrow. (Auto-Trol Corporation.) THE LANGUAGE OF INDUSTRY

3

25973

-Q 23059-^£

0^23143

Fig. 1-1-2

Pictorial

drawings.

|Skil

^©-2320-

Corp.) Fig. 1-1-4

Fig. 1-1-3

4

BASIC

Structural drawings. (American Institute of Steel Construction.)

DRAWING DESIGN

Pipe drawings. fJenkins

Fig. 1-1-5

Bros., Ltd.]

Machine drawings.

substantially to the improved quality of photographically reproduced engineering drawings.

CHANGING

TIMES'

have brought great changes room. Its physical appearance, furnishings, even its drafters and engineers have moved quickly from their battered domain of old into the Space Age. These changes were brought about largely by the recognition of many factors that affect the performances of working people. Because designing and drafting are specialized technical fields today that require a high level of precision, personnel efficiency in these areas has been closely linked to the working atmosphere. A constant reappraisal of this atmosphere should be a prime responsibility of all chief engineers and chief drafters. With an eye to improving working conditions, thereby increasing efficiency and bettering performance, Fifty years

to the drafting

PLAN AREA:

1350 sq

ft

(EXCLUDING CARPORT AND OUTSIDE STORAGE)

Fig. 1-1-6

Architectural drawings. OUTPUT OFFSET NULL

-12V

they should reevaluate periodically the tables, boards, seating arrangements,

machines and tools, lighting, reference materials, and file units assigned to their department. Drafting room technology has progressed at the same rapid pace as the economy of our country. Many changes have taken place in the modern drafting room as compared to a typical drafting room scene before the turn of the century, shown in Fig. 1-1-8. Not only are there far more tools, but they are of much higher quality. From automated drafting machines to computer-aided drafting systems and from combination reference tables with adjustable drawing boards to drawing media that contain all the desired qualities for reproduction. Noteworthy progress has been made and continues to be made as our expanding technology takes giant steps forward in this modern age. drafting

Fig. 1-1-7

Electrical

drawings.

The information and illustrations shown have been revised to reflect current industrial practices in the preparation and handling of engineering

documents. The increased use of reduced-size copies of engineering drawings made from microfilm and the

reading of microfilm require the proper preparation of the original engineering document. All future drawings should be prepared for eventual photographic reduction or reproduction. The obser-

PLACES OF EMPLOYMENT 2 There are over 400 000 people working in drafting positions in the United States. Approximately 4 percent are

vance of the drafting practices

women. About 9 out of 10 drafters are employed in private industry. Man-

described in this text will contribute

ufacturing industries that

employ

large

THE LANGUAGE OF INDUSTRY

5

Qualifications for success as a

may include the ability both to visualize objects in three dimensions

drafter

and to do freehand drawing. Although artistic ability is not generally required, it may be helpful in some specialized fields.

Drafting work also requires good eyesight (corrected or uncorrected), eye-hand coordination, and manual dexterity.

EMPLOYMENT OUTLOOK Employment opportunities

for draft-

ers are expected to be favorable in the future. Prospects will be best for those

The drafting

Fig. 1-1-8

office at

the turn of the century. (Bettman Archive,

numbers are those making machinery, equipment, transportation equipment, and fabricated metal prodelectrical

ucts.

Nonmanufacturing industries

employing large numbers are engineering and architectural consulting firms, construction companies, and public utilities.

Over 25 000 drafters work for the government; the majority work for the armed services. Drafters employed by state

and local governments work highway and public works

chiefly for

departments. Several thousand draft-

employed by colleges and universities and by nonprofit organi-

ers are

zations.

TRAINING, QUALIFICATIONS,

ADVANCEMENT

Inc

Studying shop practices and learning

some shop

are helpful, since draftingjobs require knowledge of manufacturing or construction methods. Many technical schools offer courses in structural design, strength of materials, and physical metallurgy. skills also

many higher-level

Young people having only

high

school drafting training usually start out as tracers, or detailers. Those having some formal post-high school technical training can often qualify as junior drafters. As drafters gain skill and experience, they may advance to higher-level positions as checkers, detailers. senior drafters, designers, or supervisors of other drafters. See Fig. 1-1-9. Drafters who take courses in

engineering and mathematics are sometimes able to transfer to engineering positions.

Young people

interested in

becoming

drafters can acquire the necessary training from a number of sources,

including technical institutes, junior and community colleges, extension divisions of universities, vocational and technical high schools, and corre-

spondence schools. Others may

The prospective whether obtained

STANDARDS DEPT COORDINATOR

SPECIFICATIONS

WRITER

References 1. Charles Bruning Co. 2. Occupational Outlook Handbook.

DESIGN TEAMS

ILLUSTRATIONS

DESIGNER

COORDINATOR

/ CHECKER

\

SENIOR

DRAFTER

in

mechanical drawing and drafting.

BASIC

drafters.

drafter's training,

high school or post-high school drafting programs, should include courses in mathematics and physical sciences, as well as in

6

ment and computers are eliminating some routine tasks done by drafters. This development will probably reduce the need for some less skilled

DRAFTING OFFICE SUPERVISOR

qualify for drafting positions through

on-the-job training programs combined with part-time schooling or through 3- or 4-year apprenticeship programs.

having post-high school drafting training as many industries now regard the 2-year post-high school program as a prerequisite for their drafters. Wellqualified high school graduates who have had only high school drafting, however, also will be in demand. Employment of drafters is expected to rise rapidly as a result of the increasingly complex design problems of modern products and processes. In addition, as engineering and scientific occupations continue to grow, more drafters will be needed as support personnel. On the other hand, photoreproduction of drawings and expanding use of electronic drafting equip-

DRAWING DESIGN

DETA Fig. 1-1-9

'

CD

Positions within the drafting office.

JUNIOR

DRA FTER

ILLUSTRATOR

CHAPTER

2

J

is the starting point engineering work. Its product, the engineering drawing, is the main method of communication between all people concerned with the design and manufacture of parts. Therefore the

for

drafting office

all

must provide accommodations and equipment for the drafters, from designer and checker to drafting office

detailer or tracer; for the personnel

who make file

copies of the drawings and

the originals

staff

the

who

Office Practices

is all

that

is

nec-

Equipment for manual drafting is varied and is steadily being improved. Where a high volume of finished or repetitive work is not necessary, this equipment does the job adequately and inexpensively, and most designers are accustomed to working with it. A growing number of companies have turned to automated drafting. The reason is not simply to speed the drafting process. Automated drafting essary.

The Drafting Office

;

and for the secretarial

assist in the preparation of

drawings (Fig.

2-1-1).

Most engineering departments still on manual drafting needs. In the

rely

Skills

and Drawing

majority of cases, this

UNIT 2-1

The

Drafting

can serve as a

full

partner in the design

process, enabling the designer to do jobs that are simply not possible or feasible with manual equipment.

Computer-aided-drafting, normally CAD. and drawings for numerical control are covered in detail in Chaps. 32 and 16, respectively. referred to as

UNIT

2-2

Manual Drafting Equipment ana Supplies Over the years, the designer's chair and drafting table have evolved into a drafting station which provides a com-

work area. Yet of the equipment and supplies employed years ago are still in use today, although they have been vastly fortable, integrated

much

improved.

DRAFTING FURNITURE Special tables and desks are manufactured for use in single-station or multistation design offices. Typical are desks with attached drafting boards (Fig. 2-2-1). The boards may be used by the occupant of the desk to which it is attached, in which case it may swing

out of the way when not in use, or may be reversed for use by the person in the adjoining station. In addition to such special work stations, a variety of individual desks, chairs, tracing tables, filing cabinets,

and special storage devices for drawings are available (Fig. 2-2-2).

The simplest manually adjustable tables typically consist of a hinged sur-

Fig. 2-1-1

Drafting Office. |Vemco Corp.;

face riding on a vertical rod secured by a setscrew. The setscrew is loosened,

Drafting Machines In the well-equipped engineering department, where the designer is expected to do accurate drafting, the T square has been replaced largely by the drafting machine. This device, which combines the functions of T square, triangles, scale, and protractor, is estimated to save up to 50 per-

cent of the user's time. All positioning is done with one hand, while the other

hand

is

free to draw.

Drafting machines may be attached to any drafting board or table. Two types are currently available. In the track type, a vertical beam carrying the drafting instruments rides along a horizontal beam fastened to the top of the table. In the arm, or elbow type

two arms pivot from the top of the machine and are relative to (Fig. 2-2-5),

Fig. 2-2-1 Drafting tables are available Addressograph Multigraph Corp.)

work

Fig. 2-2-2

Drafting

the top

set at the desired angle,

is

the setscrew

is

in

a variety of sizes and

stations. (Teledyne Post.)

styles. (Bruning Division,

each other.

[Bruning.]

and

retightened.

DRAFTING EQUIPMENT See Fig. 2-2-3 for a variety of drafting equipment.

Drawing Boards The drawing sheet

is

attached directly

to the surface of a drafting table or a

portable drawing board (Fig. 2-2-4). Drafting boards are used in schools and for home use and generally have a smaller work surface than what is found on drafting tables. They are designed to stay flat and have straight guiding edges.

8

BASIC

DRAWING DESIGN

Fig. 2-2-3

Drafting equipment. (Staedtler-Mars.)

*

i I (A)

Drafting table with parallel |Addressograph Multigraph Corp.)

Fig. 2-2-6

Fig. 2-2-4

Drawing boards.

slide.

WOOD OR

PLASTIC HEAD WITH PLASTIC EDGE BLADE

(Teledyne Post.)

(C)

ADJUSTABLE HEAD WITH PLASTIC EDGE BLADE

Fig. 2-2-7

styles Fig. 2-2-5

Arm

type drafting machine.

(Keuffel

Track-type drafting machines are especially suitable for long-line

work

Parallel Slide parallel slide

is

used

in

drawing

horizontal lines and for supporting angles,

when

vertical

T Squares The T square

and sloping

tri-

lines

are being drawn. (See Fig. 2-2-6.) It is fastened on each end to cords, which pass over pulleys. This arrangement permits movement up and down the

(Fig. 2-2-7)

The head of the T square is placed on the left side of a drawing board for use by right-handed people and on the right side of the drawing board for use by left-handed people.

performs the

as the parallel slide.

T

squares are made of various materials, the more popular being plastic-edged wood blades with heads made from wood or plastic. To check the accuracy of a T square draw a sharp line along the drawing edge of the T square on a sheet of paper. Turn the T square upside down and using the same drawing edge

board while maintaining the parallel

check the line for error. If the drawing edge and the pencil line do not match,

slide in a horizontal position.

the

T

square

T squares are available in various (AM Bruning

materials.

International.)

same function

and large drawings.

The

and Esser Co.)

and

is

not accurate.

Triangles Triangles are used together with the parallel straightedge or T square when you are drawing vertical and sloping lines (Fig. 2-2-8).

commonly used

The

triangles

most

are the 30/60° and the

45° triangles. Singly or in combination,

these triangles can be used to form angles in multiples of 15°. For other

DRAFTING SKILLS AND DRAWING OFFICE PRACTICES

9

D

c

angles, the protractor (Fig. 2-2-9)

is

used. All angles can be drawn with the adjustable triangle (Fig. 2-2-10); this

common

instrument replaces the two '

triangles

^

*

(A)

D

and the protractor.

THE 45 TRIANGLE

/

C Fig. 2-2-10

Adjustable triangle. (Charles

Bruning Co.; i

Scales

Shown

K

WM J

common

make measurements on

their

draw-

used only for measuring and are not to be used as a straightedge when drawing lines. It is important that drafters draw accuings. Scales are

rately to scale. The scale to which the drawing is made must be given in the title block or strip.

c

~fe

3H

in Fig. 2-2-11 are the

shapes of scales used by drafters to

\

REGULAR

X

RELIEVED FACET

TRIANGULAR SCALES DOUBLE BEVEL (C)

THE TRIANGLES

IN

OPPOSITE

BEVEL

FLAT BEVEL

COMBINATION

FLAT SCALES Fig. 2-2-8

The

triangles.

End view shapes

Fig. 2-2-11

of scales.

When objects are drawn at their actual size, the drawing is called full scale or scale 1:1. Many objects, however, such as buildings, ships, or airplanes, are too large to be drawn full

must be drawn to a reduced scale. An example would be the drawing of a house to a scale of

scale, so they

Va in.

Fig. 2-2-9

10

BASIC

A protractor

is

DRAWING DESIGN

used to lay out, or measure, angles.

=

1

ft.

Frequently, objects such as small watch parts are drawn larger than their actual size so that their shape can be seen clearly. Such a drawing has been drawn to an enlarged scale. The minute hand of a wristwatch. for example, could be drawn to a scale of 5:1.

1

Many mechanical parts are drawn to half scale. 1:2,

and quarter

or nearest metric scale, 1:5. Notice that the scale is expressed as an equation. The left side of the equation rep-

-02

1.04-

2468 Itl 2468

scale, 1:4,

mm

/ 50

TTTT

"

'

'

1:1

resents a unit of the size drawn; on the right side, a unit of the actual drawing

equals five units of measurement of the

1:1

SCALE

(1

mm

DIVISIONS)

DECIMAL INCH SCALE (FULL

SIZE)

actual object.

made with a

Scales are

variety of

combined scales marked on their surfaces. This combination of scales spares the drafter the necessity of calculating the sizes to be

working to a scale other than

is

'

SIZE

full size.

DECIMAL INCH SCALE (HALF

Metric Scales The linear unit of measurement for mechanical drawings

iii|iiii|iiM|iMiimi|iii

'HALF

drawn when

the millimeter.

SCALE (2mm DIVISIONS)

1:2

Scale multipliers and divisors of 2 and 5 are recommended, which give the

shown in Fig. 2-2-12. The numbers shown indicate

7

/

the dif-

ference in size between the drawing and the actual part. For example, the ratio 10:1 shown on the drawing means

drawing

times the actual size of the part, whereas a ratio of 1:5 on the drawing means the object is 5 times as large as it is shown on the drawing. The units of measurement for architectural

«.

The same

MM I'M Ml 1

1

1

1

1

1

1

1

1

1

1

!

1

N IP

1

________^___^_

.

FRACTIONAL INCH SCALE (FULL

mm

SIZE)

1:5

1:5

SCALE (5mm DIVISIONS)

XT""'

drawings are the meter and

millimeter.

1B lb

*JU5

10

is

4

8

scales

that the

SIZE)

1

'!

11

11 '!

'!

11 '!

scale multipliers

and divisors as used for mechanical drawings are used for architectural drawings.

FRACTIONAL INCH SCALE (HALF 1

U.S.

SIZE)

•-50

800

Customary Scales There are three types of which show various values that

Inch Scales

scales

are equal to

inch

1

mm 1:50

(in.) (Fig. 2-2-13).

10

They are the decimal inch scale, the fractional inch scale, and the scale

1:50

SCALE (50mm DIVISIONS)

which has divisions of 10. 20. 30. 40, 50, 60, and 80 parts to the inch. The last scale is

known

gineer's scale.

maps and

It

is

charts.

as the civil en-

used for making

The

divisions or

parts of an inch can be used to repre-

sent feet, yards, rods, or miles. This scale is also useful in mechanical drawing

when

the drafter

is

dealing with

decimal dimensions. On fractional inch scales, multipliers or divisors of 2, 4, 8, and 16 are used, offering such scales as full size, half size, quarter size, etc.

CIVIL ENGINEER SCALE

ENLARGED I

000 500 200 I

SIZE AS I

:

I

DIVISIONS)

2 5

10

00 50 20

20 50 00 200 500 000

30

I

10 5 2 Fig. 2-2-12

(10

REDUCED

I

Metric scales.

CIVIL ENGINEER SCALE (30 DIVISIONS) Fig. 2-2-13

Inch scales.

DRAFTING SKILLS AND DRAWING OFFICE PRACTICES

1

Fool Scales These scales are used mostly in architectural work. See Fig. 2-2-14.

They

from the inch scales

differ

each major division represents a an inch, and the end units are subdivided into inches or parts of an

in that

foot, not

The more common

inch.

= =

in. in.

1

=

=

'/s

cles

ft.

1

ft,

1

in.

inch and foot scales are

1

in Fig.

•

turning a large knurled nut. •

2-2-15.

TITI'ITI'I'l'I'l'I'

I'I

'I'l'I'I 'I'l'

1

Drop bow compass, mostly used for drawing small circles. The center

rod contains the needle point and remains stationary while the pencil or pen leg revolves around it. • Beam compass, a bar with an adjustable needle and pencil-and-pen attachment for drawing large arcs or

r-3"

/

head compass, standard in most drafting sets. Bow compass, which operates on the jackscrew or ratchet principle by

• Friction

ft,

shown

is used for drawing cirand arcs. Several basic types and

sizes are available (Fig. 2-2-16).

and 3 The most commonly used

ft, Va in. 1

scales are

Compasses The compass

'!''

circles.

• Circuit scribing instrument, a

modi-

bow compass, used

to cut

fied

l"= I'-O" SCALE

drop

terminal pads and prepare printedon scribe coat film.

circuit layouts

r- 0"

The bow compass is adjusted by whose knurled head is

turning a screw

located either in the center or to one

/,4

I'l'l'l'l

II

I

|

I

I

I

I

2

I

I

I

«

I

4

side. The bow compass can be used and adjusted with one hand as shown in Fig. 2-2-17. The proper technique is:

I

I

1.

Adjust the compass to the correct radius.

|/4"= |'-0" Fig. 2-2-14

Foot

2.

SCALE

scales.

Hold the compass between the thumb and finger.

DIMENSIONED IN DECIMALLY FRACTIONALLY FEET AND INCHES DIMENSIONED DIMENSIONED EQUIVALENT DRAWINGS DRAWINGS SCALE RATIO :

1

6 IN.=

1

FT

1:2

:

1

3 IN.=

1

FT

1:4

1

2:

1

li|N.=

1

FT

1:8

:

1

1

:

1

IN.=

1

FT

1:12

1

:

2

1

:2

flN.=

1

FT

1

:

1

:5

1

:

4

i|N.=

1

FT

1

:

1

:

10

1

:8

|lN.=

1

FT

1

:

1

:

20

1

:

\\H.=

1

FT

1

:

i|lN.=

1

FT

1

:

•§IN.=

1

FT

1

i^lN.=

1

FT

1:192

10:

1

8

5

:

1

4

2

:

1

ETC.

16

ETC.

Fig. 2-2-15

Commonly used

BASIC

foot

and

:

16

24

32 48 64

96

inch

Fig. 2-2-17

Fig. 2-2-16

scales.

12

1

DRAWING DESIGN

Compasses.

(Keuffel

&

Esser Co.)

Adjusting the radius for the

pencil compass.

bow

3.

STATIONARY ROD OR

PIN

With greater pressure on the with the needle located on the

leg in-

tersection of the center lines rotate the TUBE CARRIES PEN OR

compass

tion.

PENCIL AND REVOLVES AROUND ROD

in

a clockwise direc-

The compass should be

slightly tipped in the direction of

motion.

The drop-spring bow compass shown

SPRING

in Fig. 2-2-18 is

used for draw-

ing very small circles. ADJUSTING SCREW

Dividers Lines are divided and distances transferred (moved from one place to another) with dividers. The basic types of dividers are shown in Fig. 2-2-19. Dividers have a steel pin insert in each leg and come in a variety of sizes

DROP TUBE BODY AND REVOLVE TO

DRAW CIRCLE

and designs, similar to the compasses. A compass can be used as a divider by replacing

its

lead point with a steel pin.

Drawing Instrument Many

ing set,

The drop-spring bow compass is used for drawing very small where there are many to be drawn. (Keuffel & Esser Co.) Fig. 2-2-18

circles,

especially

Sets

drafters have a complete draw-

which usually includes several

compasses and dividers with extension attachments for making inked drawings (Fig. 2-2-20).

4P>*

,

FIRST

CENTER

BOW

FRICTION (A)

PROPORTIONAL

TYPES OF DIVIDERS IB)

Fig. 2-2-19

Dividers. (Keuffel

&

DIVIDERS ARE USED TO DIVIDE

AND TO TRANSFER DISTANCES

Esser Co.)

DRAFTING SKILLS AND DRAWING OFFICE PRACTICES

13

CENTER TACK

BOW DIVIDERS

PASS

Fig. 2-2-20

A

three-bow

Drafting Leads

set of

and

drawing instruments.

Pencils

Leads Because of the drawing media used and the type of reproduction

required, pencil manufacturers have marketed three types of lead for the preparation of engineering drawings. Graphite Lead This is the conventional type of lead which has been used for years. It is made from graphite, clay, and resin. It is available in a variety of grades or hardnesses 9H. 8H. 7H,

—

6H (hard); 5H and 4H (medium hard); 3H and 2H (medium): H and F and

(medium

soft);

and HB. B. 2B. 3B. 4B.

5B. and 6B (very soft), the latter not being recommended for drafting. The selection of the proper grade of lead is important. A hard lead might penetrate the drawing while a soft lead will smear. The next two types of drafting leads were developed as a result of the introduction of film as a drawing medium. A limited number of grades are available in these leads, and they do not correspond to the grades used

(Keuffel

&

Esser Co.)

but they are processed differently. They are designed for use on film only, erase well, do not readily smear, and

produce a good opaque line which is suitable for microform reproduction. The main drawback with this type of lead is that it does not hold a point well.

Drafting Pencils The leads are held either in the conventional woodbonded cases known as wooden pencils or in metal or plastic cases known as mechanical pencils. See Figs. 2-2-21

and 2-2-22. With the

latter, the

lead

ejected to the desired length of projection

from the clamping chuck and then

pointed

in

the

wood-bonded

same manner

as the

pencil. Recently, dis-

fast, convenient means of putting a clean drafter's point on mechanical or wood-cased pencils is not only desirable, but necessary. Mechanical

sharpeners (Fig. 2-2-23A) are made with special drafter's cutters that

remove the wood

as shown. The required point shape is then formed by hand sanding or by a special pointer.

When hand sanding (Fig. 2-2-23B) rub the lead back and forth on a sandpaper block or a fine file, while turning

GRADE MARK(A)

Lead This type of lead is designed for use on film only. It has good microform reproduction charac-

Lead Pointers

A

WOOD-BONDED CASE

for graphite lead.

Plastic

is

posable mechanical pencils became available. These operate just as any mechanical pencil, but they are discarded after the lead has been used.

STANDARD

SIZE

WOODEN

PENCILS

LEAD

3=-

teristics.

Lead As the name implies, this lead is made of plastic and graphite. There are two basic types: fired and extruded. They are similar in Plastic-Graphite

material content to plastic fired lead.

STANDARD LEAD HOLDER METAL OR PLASTIC CASE

^ai \-THIN LEAD (REQUIRES NO SHARPENING)

CONICAL Fig. 2-2-21

14

BASIC

WEDGE OR CHISEL Pencil point shapes.

DRAWING DESIGN

BEVEL

THIN LEAD HOLDER

(B) Fig. 2-2-22

Drafting pencils.

MECHANICAL PENCILS

5

«/^0P