Machine Drawing - Oxford University Press

Associate Professor Department of Aerospace Engineering and Applied Mechanics

Indian Institute of Engineering Science and Technology, Shibpur

Machine Drawing

Basudeb Bhattacharyya

© Oxford University Press. All rights reserved.

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PrefaceA sentence should contain no unnecessary words, a paragraph no unnecessary sentences,

for the same reason that a drawing should have no unnecessary lines and a machine no unnecessary parts. William Strunk, Jr

Drawing is an art and artists aim at drawing objects the way they are visible to the naked eye or to beautify objects be-yond their original form. Engineering or machine drawing is somewhat different in the sense that it requires the engi-neer to not only sketch the object almost as a photographic image but also represent it in different views. These dif-ferent views are detailed exploded views of the object that are required to manufacture or engineer a product. Machine drawing in particular requires not just a steady hand but also a sense of perspective.

Machine drawing is a subject of utmost importance in the mechanical engineering curriculum because the manu-facturing of a machine depends completely on the design and drawing, including dimensional specifications, of the machine down to the last minute detail. For fabricating or manufacturing a machine or a component of a machine, the design is first prepared through analytical computations. Then the designed component is converted into pictorial representation on paper. It may be represented through two-dimensional or three-dimensional drawings, or both, depending on the requirement. For two dimensional rep-resentations, orthographic views are used and for picto-rial representations, conventionally isometric drawings are used. For the manufacturing process, the knowledge of pre-sentation of limits, tolerances, etc., on paper is a prerequi-site. All these, including the method of dimensioning, must follow the methods laid out in the various codes of practice published by the Bureau of Indian Standards (BIS). In fact, starting from the size and shape of drawing boards, draw-ing tools, to the representation methods of machine compo-nents, are all guided by Indian Standard codes of practice.

Traditionally this subject depended completely on manual drawings that were made using drafters. However, with the passage of time, computers have taken over, and machine parts are drawn using software applications for 2D and 3D design and drafting such as AutoCAD and SOLID EDGE. Design engineers now use these software for modelling

machine parts after the design is finalized. This is also why gradually the study of such software has become a part of the curriculum of machine drawing. Keeping this in mind this book, Machine Drawing, aims at providing readers a comprehensive understanding of the subject.

ABOUT THE BOOK

This book is primarily meant for undergraduate students of mechanical engineering for the course on machine draw-ing. It takes readers through a gradual process of master-ing the subject by first providing a detailed discourse on elementary generalized items covering drawing boards, sheets, instruments to conventional representation of vari-ous items in context with the recommendations of relevant latest BIS codes of practice. A list of relevant codes is also provided in the Appendix as a ready reckoner. In modern times, drawings prepared by hand using pencils or inking device are losing their importance especially in case of re-petitive and large scale use in industries as they cause num-ber of inconveniences. Computer-Aided Drafting (CAD) is the best suited alternative in such cases. Hence, relevant chapters are supplemented with drawing methods using AutoCAD.

KEY FEATURES

Comprehensive Coverage The book provides compre-hensive coverage of drawing instruments, sheets, lettering, and dimensioning, which enable students to understand different aspects of machine drawing. This is followed by a chapter on sectional views focusing on both obvious and specified section planes. A wide variety of fastening ar-rangements such as welding, riveting, cotter, and pin along with the different styles of attachment for shaft and pipe are discussed at length. Assembly and disassembly drawings are discussed in terms of different components of inter-nal combustion engine and steam power plant. Moreover,


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vi Preface

some machine tools and their components and some mis-cellaneous machines are discussed.Illustrations Figures are the soul of this book. The size of the book has been especially chosen to ensure that there is enough space to illustrate figures with clarity so that students get an explicit view of the drawings. Neat labels, proper dimensioning, and different views make the figures totally unambiguous and easy to analyse and understand. Full pages are dedicated to a number of complicated and intricate figures. As much as possible, it has been tried to place figures as close to the relevant text so that the stu-dents do not have to flip pages while reading.

AutoCAD and BIS codes Each relevant chapter has an AutoCAD supplement which provides drawing examples using AutoCAD. The book presents specifications of BIS codes of practice, up to the latest available edition, wher-ever required.

Rich Pedagogy There are a number of solved examples in each chapter with step-by-step solutions. A detailed point-wise recapitulation at the end of each chapter revisits all the important points discussed in the chapter making for a fine guide for revision before the exams. This is followed by numerous multiple-choice questions, review questions, and numerical problems that promise to provide students ample practice to make them perfect in the subject. Answers to the multiple choice questions have also been provided at the end of the chapters.

CONTENTS AND COVERAGE

The book is divided into 6 chapters. A brief of each of the chapters is mentioned below:

Chapter 1 deals with different items in context with the provisions laid out in the various codes of practice pub-lished by the Bureau of Indian Standards.

Chapter 2 discusses how to draw different sectioned views of objects. The standard conventions of hatching pattern for different section planes are discussed following BIS conventions.

Chapter 3 presents different fastening arrangements that include welded, riveted, and threaded joints along with variety of threads, bolt–nut assembly, and their drawing methods.

Chapter 4 discusses shaft and pipe joining arrangements and shaft attachments. Different types of valves and belt–pulley assembly are detailed here. This chapter also in-cludes of a variety of bearing, gears, and worm wheel.

Chapter 5 discusses part and assembly drawings in rela-tion to parts of internal combustion engine (ICE) and steam power plant. Major components of ICE and steam power plant are suitably presented here either in orthographic or isometric or both systems.

Chapter 6 provides detailed drawings of some common machine tools and some miscellaneous equipment such as crane hook, surface roughness measuring stand, screw jack, knife switch, centrifugal pump, relief valve, belt drive, worm reduction gear box, and bevel gear junction box.

ACKNOWLEDGEMENTSIt is a great pleasure and honour for me to be associated with Oxford University Press. I express my sincere grati-tude and thanks to the entire editorial team and production department of Oxford University Press for publishing my book in time while maintaining a high degree of precision and accuracy. I thank the senior teachers of my department for their encouragement. I also express gratitude towards my family members for their unfathomable inspirations. A very special mention goes to Mr Subir Pal of M/s Books and Equipment Distributors, Howrah.

I am thankful to Prof. D.V. Srikanth (St. Martin’s Engineering College, Secunderabad) for his valuable feedback and con-tribution in enhancing the content.

Every effort has been made to produce an error-free text; however, I would be grateful if readers can point out any unintended error or discrepancy. Readers can write to me with their suggestions and feedback on [email protected].

Basudeb Bhattacharyya


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1. Introductory Concepts and BIS Conventions 1Introduction 1Classification of Drawing 1Code of Practice 1Drawing Instruments 2 Drawing Board 2 T-Square 2 Set-Square 3 Protractor 3 Drafting Machine 3 Ruling Machine 4 French Curves 4 Scale 5 Pencil and Eraser 5 Compass and Dividers 6Size and Layout of Drawing Sheets 6 Dimension 6 Title Block 7 Borders and Frame 7 Centring Marks 7 Grid Reference System 8 Trimming Marks 8Folding of Drawing Sheets 9Description of Different Types of Lines 10 Lines Used in Construction Drawing 11 Lines Used in Mechanical Drawing 11Patterns of Lettering 13Patterns of Section and Other Conventions 15General System of Dimensioning 16 Functional Dimension 16 Nonfunctional Dimension 16 Basic Rules of Placement of Dimensions 16 Elements of Dimensioning 16 System of Dimensioning 17 Arrangement of Dimensions 18 Special Indications in Dimensioning 19Conventional Representation of Threads and

Threaded Parts 20 Representation of Single Entity 20

Representation of Assembled Parts 21 Designation and Dimensioning of Threaded

Parts 21Conventional Representation of Springs 22 Helical Compression Springs 22 Helical Extension Springs 23 Torsion Springs 23 Disc Springs 23 Spiral Springs 23 Leaf Springs 23Conventional Representation of Gears 24 Contours 24 Pitch 24 Root Surface 24 Teeth 24

2. Sectional Views 27Introduction 27Convention for Placement of Section Planes 27Types of Section Planes 28 Obvious Section Plane 28 Specified Section Plane 28Convention for Placement of Sectioned Views 30Section of Interpenetrated Solids 31AutoCAD Supplement 43

3. Different Fastening Arrangements 49Introduction 49Welded Joint 49 Types of Welding Processes 49 Types of Welds 50 Symbols of Welds 54 Edge Preparation for Welding 56Riveted Joint 56 Types of Rivets 57 Types of Riveted Joints 58 Parameters Associated with Riveted Joints 59 Application in Structures with Conventional Sections 65 Application in Shells 67 Caulking and Fullering 69

Contents


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viii Contents

Threaded Fasteners 70 Types of Threaded Fasteners 70 Types of Threads 71 Parameters Associated with Threaded Fasteners 72 ISO Thread Profile 73 Other Thread Profiles 79 Types of Screws 81 Representation of Screws 82 Bolt and Nut Assembly 82 Hexagonal-headed Bolt and Hexagonal Nut 83 Square-headed Bolt and Square Nut 85 Locking Arrangement of Nuts 86 Representation of Nuts 89 Washers 89 Variety of Foundation Bolts 89AutoCAD Supplement 90 Creating a Block 90 Inserting a Block 92 Editing a Block 93

4. Shaft and Pipe Joiners and Shaft Attachments 97Introduction 97Keyed Joints 97 Types of Keyed Joints 98Cotter Joints 102Knuckle Joint 104Shaft Coupling 105 Rigid Shaft Coupling 105 Flexible shaft coupling 108Pipe Joints 112 Parameters Related to Pipe Threads 113 Forms of Pipe Threads 114 Dimensions of Pipe Threads 115 Types of Pipe Joints 115 Special Pipe Joints 118Pipe Fittings 119Valves 121Symbols used in Pipe Network 126Belt and Pulley 128 Belts and its Varieties 128 Pulleys 129Bearing 133 Fluid Bearing 134 Rolling Element Bearing 136 Plummer Block Bearing 139 Inclined Plummer Block Bearing 141 Marine Engine Shaft Bearing 142 Pedestal Bearing 143 Footstep Bearing 143 Swivel Bearing 145

Wall Bracket Bearing 147 Self Aligning Bearing 147 Hanger Bearing 149Gears 149 Gear Terminology 150 Proportion of Dimensions for Different Parameters 152 Profile of Gear Tooth 152 Drawing Profile of Gear Tooth 152 Spur Gear 154 Helical Gear 155 Bevel Gear 156 Worm and Worm Wheel 157 Rack and Pinion 159AutoCAD Supplement 159

5. Part and Assembly Drawing 165Introduction 165General Arrangement Drawing (GAD) 165Assembly Drawing 165Part Drawing 166Internal Combustion Engine (ICE) 166 Cylinder 167 Piston 170 Piston Ring 172 Piston Pin 175 Connecting Rod 176 Crankshaft 178 Cams and Followers 180 Valve Train 187 Venturi Carburettor 190 Fuel Pump 191 Fuel Injector 191 Spark Plug 193 Oil Pump 194 Water Circulating Pump 195Steam Power Plant 197 Feed Pump 197 Steam Injector 198 Feed Check Valve 198 Steam Stop Valve 199 Safety Valve 201 Blow-off Cock 206 General Arrangement of a Steam Engine 206 Cylinder 207 Piston and Piston Rod 207 Piston Rings 208 Stuffing Box 209 Crosshead 210 Connecting Rod 212 Crank 214 Eccentric 215


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Contents ix

D-slide Valve 217 Speed Governor 217

6. Machine Tools and Miscellaneous Drawings 223Introduction 223Lathe 223 Three-jaw Chuck 224 Four-jaw Chuck 224 Tool Post 226 Tool Holder 228 Tail Stock 231 Slide Rest 231 Revolving Centre 233Shaper 234 Tool Head 234 Clapper Box 236Hand Drill 236Vice 238 Bench Vice 238 Pipe Vice 238 Machine Vice 238 Swivel Vice 240

Jigs and Fixtures 240 Drilling Jig 240 Milling Jig 244 Tumble Jig 248 Jig for Valve Stem Hole 249 Indexing Fixture 249Miscellaneous Devices 251 Crane Hook 251 Surface Roughness Measuring Stand 251 Quick Change Drill Holder 252 Screw Jack 254 Knife Switch 255 Centrifugal Pump 255 Relief Valve 255 Three Way Stop Valve 255 Multiple Disc Friction Clutch 257 Belt Drive 257 Worm Reduction Gear Box 261 Bevel Gear Junction Box 264

Reference Codes of Practice 267Bibliography 269


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1.1 INTRODUCTION

Drawing is a form of visual expression. It is generally concerned with the mark-ing of lines and areas onto paper. The origin of drawing dates back to prehistoric times when rock and cave drawings and marks on sand and earth were used as the mode of communication. By the twelfth to thirteenth centuries ad, monks started preparing illuminated manuscripts on vellum or parchment and were us-ing lead styli to draw lines for their writings or for the outlines of illuminations. Fourteenth century onwards, we find evidences of drawings on paper.

1.2 CLASSIFICATION OF DRAWING

Drawing may be broadly classified as artwork and engineering drawing. The term technical drawing is synonymous with engineering drawing. From engi-neering point of view, engineering drawing can be further classified into:

Key Concepts

· Classification of drawing and the standard code of practice · Various drawing instruments and the corresponding code provision · Sizes and layout of drawing sheets and folding pattern as per the BIS code of

practice · Different types of lines and lettering as per the BIS code of practice · Patterns of sections and general system of dimensioning as per the BIS code

of practice · Conventional representations of threads, threaded parts, springs, and gears as

per the BIS code of practice

Introductory Concepts and BIS Conventions

(i) geometrical drawing,(ii) machine drawing or mechanical

drawing,(iii) civil drawing,(iv) architectural drawing, and(v) electrical and electronics engi-

neering drawing.Although our purview will be limited

to machine drawing, this introductory chapter is a generalized one and is com-mon to all sorts of technical drawing.

1.3 CODE OF PRACTICEDrawing is the language of engineer-ing and therefore it should follow a

1CHAPTER


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2 Machine Drawing

grammar (rules). In order to standard-ize the rules for drawing, in 1955, the Indian Standards Institution (ISI) pub-lished IS:696—1955, code of practice for general engineering drawing. Af-ter the publication of its second revi-sion in 1972, the contents of the code were harmonized with the relevant rules and regulations followed by the International Standards Organisa-tions (ISO), and so after withdrawing IS:696—1972, a series of standards were published. On July 1, 1987, the ISI was renamed as the Bureau of In-dian Standards (BIS). To serve as a ready reckoner, SP:46—1988 (a spe-cial publication containing the rules and standards of general engineering drawing) was published by the BIS. Its latest revised edition is SP:46—2003. Throughout this book we have followed this code and other relevant codes of the latest edition of BIS.

1.4 DRAWING INSTRUMENTS

When we start drawing, primarily we require a board on which the paper is attached and some other instruments for drawing lines and curves. Let us now discuss the various drawing accesso-ries (e.g., drawing board, T-square, set-square, protractor, drafting machine, ruling machine, French curves, scale, pencil, eraser, compass, and dividers) conforming to the BIS specification.

Drawing BoardIn India, the boards used for drawing are made as per the specification laid down in IS:1444—1989 (the latest BIS code of practice). The working surface of the drawing board should be made either of benteak, blue pine, fir, cypress, oak, or red cedar wood. Bat-tens at the back of the board, as shown in Fig. 1.1, should be made either of aini, anjan, bijasal, black chuglam, padauk, safed siris, salai, sissoo, teak, or walnut wood. The thickness of the

drawing board should be 20–25 mm, (generally 22 mm). The standard dimen-sions of the drawing boards as per the BIS code are given in Table. 1.1.

LengthBatt

ens

ThicknessWidth

Working edge

Strips

Fig. 1.1 Drawing board

Table 1.1 Specifications of drawing board

Designation Length ¥ Width (mm) Thickness (mm) Usable Sheet Designation

D00 1525 ¥ 1220 22 —

D0 1270 ¥ 920 22 A0

D1 920 ¥ 650 22 A1

D2 650 ¥ 470 22 A2

D3 500 ¥ 350 22 A3

T-SquareThe T-square is a frequently used drawing equipment. It is primarily used for drawing horizontal lines and for guiding the set-square to draw vertical lines or inclined lines. It is made of a thin long strip, called blade, that is fitted perpen-dicularly to a horizontal strip, called stock, in such a manner that the assembly resembles alphabet ‘T’ (Fig. 1.2). The side of the blade with which horizontal lines are drawn is called the working edge. Previously, mahogany wood was used to make T-squares, but nowadays celluloid is used. Table 1.2 lists the sizes of T-square that are available.

Blade

Working edge

90°

Stock

Fig. 1.2 T-square


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Introductory Concepts and BIS Conventions 3

Drawing board

Drawing sheetPencil moves left

to right

T-square

(a)

Drawing sheet

T-square

105°75°

15°

Drawing board

(b)

Fig. 1.3(a) Drawing parallel lines with T-square Fig. 1.3(b) Drawing inclined lines with T-square and set-squares

The procedures for drawing horizontal lines and lines at different angles with the help of a T-square and set-squares are illustrated in Figs 1.3 (a) and (b).

Set-SquareSet-squares are transparent right-angled triangular strips that are made of cel-luloid. Set-squares are of two types: (i) right-angled isosceles triangular shaped with included angles 45°–90°–45°, conventionally called 45° set-square and (ii) right-angled triangular shaped with included angles 30°–90°–60°, conven-tionally called 30°–60° set-square. The triangles may be solid or hollow (see Figs 1.4 (a) and (b)). The various sizes of a set-square are designated as per the length of the longer side of the triangle containing the right angle. Generally,

the 45° set-squares are available in 150- to 200-mm size and the 30°–60° set-squares are available in 200- to 240-mm size. A set-square alone or in combination with a T-square can be used to draw inclined and parallel lines (see Figs 1.5 and 1.3 (b)). All the external edges of a set-square are bev-elled so that when a pen is used the ink does not spread. Some set-squares also have the centimetre scale in-scribed and this helps in drawing lines of desired length.

ProtractorThe protractor (Fig. 1.6) is a semicir-cular strip that is made of transparent celluloid. It is inscribed with an an-gular scale of at least 1° subdivision along the semicircular periphery and is used to draw any angle.

Drafting MachineThe drafting machine is a modern compact instrument (Fig. 1.7) that can replace the use of T-square, set-squares, normal measuring scale, and

(a) (b)

150–200 200–240

Fig. 1.4 Solid and centrally hollow set-squares

Horizontal line

165°

150°

135°

120° 105°

90°75°

60°

45°

30°

15°

Fig. 1.5 Use of set-square to draw lines at different angles

Table 1.2 Sizes of T-square

Designation Length of Working Edge (mm)

T0 1500

T1 1000

T2 700

T3 500


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4 Machine Drawing

9080

100

70

110

60

120

50

130

40140

30150

20

160

10

170

27

0

0

18

0

160

150

140

130 120 110 100

170

0 18

0

10

20

3040

5060

70 80

Fig. 1.6 Protractor

protractor. It is attached to the draw-ing board with a clamping knob. It has two scales, generally graduated, fixed at right angles to each other but can move in any direction. A scale-fixing knob controls this movement. An an-gular scale is attached under the scale-fixing knob, which is used to draw lines at any angles.

Ruling MachineThe ruling machine is a typical draw-ing instrument used to draw horizon-tal parallel lines, vertical parallel lines, and inclined lines. Commercially, it is known as roll-n-draw machine. Figure 1.8 illustrates a ruling machine.

French CurvesFrench curves are templates of lines of different curvatures of different radii and are made of either wood, metal, or plastic. These are used to draw a smooth line through predetermined points or to draw curves of varying ra-dii. Figure 1.9 shows different types of French curves that are available. Let us now see how to draw a smooth curve using a French curve. Draw a line (see Fig. 1.10) from point 1 to point 3 only with one side of the curve. Then draw a line matching points 3 to 4 with the other suitable part of the curve. At the next stage, match points 4 to 6 and proceed accordingly.

Parallel bars Scale fixing knob

Angular scaleDrawing

board

Scales

Clampingknob

Parallel barsScale fixing knob

Angular scale

Drawing board

Scales

Clampingknob

Fig. 1.7 Drafting machine

(a)

(b)

Fig. 1.8 Use of ruling machine Fig. 1.9 Different types of French curves


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Pencil and EraserThe modern wood-cased graphite stick pencils were made for the first time in 1662 in Nuremberg, Germany. The most common type of pencil casing is a thin wooden jacket permanently bonded around the core. Wooden pen-cils are commonly referred to as lead pencils, though these never contained lead. The cores are mostly made of graphite mixed with a clay binder. These pencils are graded according to the European system using alpha-bets from H (for hardness) to B (for blackness) as well as F (for fine point). The standard writing pencil is graded as HB. It is believed that this grading system might have been developed in the early 1900s by Brookman, an Eng-lish pencil maker. Table 1.4 shows the different grades of pencils, ranging from a very hard light-marking pencil to a very soft black-marking pencil.

Mechanical pencils are those in which the graphite stick is not bonded to the outer casing. They are designed such that the graphite stick core is extended mechanically as its point is worn away. Mechanical pencils are broadly of two types: propelling type and clutch type. The advantage of these pencils is that they provide lines of constant thickness without requiring sharpening, making them well suited to technical drawing. The graphite sticks used in mechanical pencils are available in diameters of 0.13, 0.18, 0.25, 0.35, 0.5, 0.7, 1, 1.4, and 2 mm, conforming to the international code of practice ISO:9175 (Part I)—1988.

Eraser is a small piece of rubber (or a similar substance) that is used for removing marks of pencils and pens. Erasers have a rubbery consis-tency and may be of different colours, though mainly white. Edward Nairne (1726–1806), an English optician and instrument maker, developed the first widely marketed rubber eraser in 1770. Nowadays, wooden-cased

Table 1.4 Grades of wooden pencils

Grades

¨ Hardest ¨←Harder Medium Softer Æ Softest Æ9H 8H 7H 6H 5H 4H 3H 2H H F HB B 2B 3B 4B 5B 6B 7B 8B 9B

1

234

5

6

7

8910

11

3

4

5

3

45

6

67

7

89

11

109

(a) (b) (c)

(d) (e) (f)

Fig. 1.10 Use of French curve

Table 1.3 Recommended scales of drawing

Type of Scale Ratio of Scale

Full size 1:1

Enlargement scale 50:1 20:1 10:1

5:1 2:1

Reduction scale 1:2 1:5 1:10

1:20 1:50 1:100

1:200 1:500 1:1000

1:2000 1:5000 1:10000

ScaleIn the present context, the word scale does not refer to any length-measuring device. IS:10713—1983 (the latest BIS code conforming to ISO:5455—1979) defines a scale as the ratio of linear dimension of an object represented in origi-nal drawing to real linear dimension of the object itself. A scale where the ratio is 1:1 is called a full-size scale and where the ratio is larger than 1:1 is called an enlargement scale and is represented as X:1. A scale where the ratio is smaller than 1:1 is called a reduction scale and is represented as 1:X. The choice of the scale entirely depends on the complexity of the object and the purpose of its rep-resentation. The designation of the scale used on the drawing must be inscribed in the title block of the drawing. The recommended scales for technical drawing are given in Table 1.3.


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6 Machine Drawing

1.5 SIZE AND LAYOUT OF DRAWING SHEETS

The size and layout of preprinted drawing sheets for any fields of tech-nical drawing will be discussed with reference to IS:10711—2001, con-forming to ISO:5457—1999 and SP:46—2003.

DimensionThe drawing sheets used for draft-ing technical drawing are available in sizes of A0, A1, A2, A3, and A4. The basic principle to determine the size (trimmed) of a drawing sheet for any tech-nical product documentation is as follows: (i) Consider one right-angled isosceles triangle of equal side x (see Fig. 1.13).

Therefore, the length of the hypotenuse will be y x x x= + =2 2 2 . Ro-tate this hypotenuse anticlockwise by an angle of 45° so that it becomes vertical. Hence the size of the sheet is length y and width x. Therefore, the ratio of the two sides x y: := 1 2 .

(ii) The area of the sheet should be 1 m2, i.e., xy = ¥1 106 2mm . Hence, on substitution of ratio, we have

x x

x

y x

¥ = ¥\ = ª

\ = = ª

2 1 10

840 896 841

2 1189 2 1189

6

.

.

Thus the basic size of a drawing sheet is 1189 mm (length) ¥ 841 mm (width). This size is designated as A0. A series of successive sizes are obtained by halv-ing along the length or doubling along the width (see Figs 1.14 (a) and (b)). However, in any case the ratio of the sides of the sheet will maintain the ratio of 1 2: . The sizes of the drawing sheet as obtained are trimmed sizes. The untrimmed size of series of sheets will certainly be somewhat larger than the trimmed size. Designation of sheets with size, as per series ISO—A, is provided in Table 1.5.Fig. 1.11(a) & (b) Pencil compass

pencils are also available with erasers attached to their ends. In the United Kingdom, an eraser is very commonly called as rubber.

Compass and DividersA pair of compasses, commonly known as compass, is used for drawing cir-cles and arcs in technical drawing. It is also known as a drafting compass. A compass is usually made up of metal and consists of two legs connected by an adjustable hinge. Its one leg has a sharp spike at its end and the other leg is equipped with a holder for wooden pencils, leads, or inking pens (see Figs 1.11 (a) and (b)). The dividing com-pass (or simply divider) is used to measure distances. It looks similar to the drafting compass, but both its legs are identical and have spikes (see Figs 1.12 (a) and (b)).

(a) (b)

Fig. 1.12(a) & (b) Dividers

A4

A3

A2

A1

A0

841

594

420

297A3A4

A2

A1

A0mm

mm0 210 420 594 841 1189

Fig. 1.14(a) Halving & doubling Fig. 1.14(b) Sizes of drawing sheets

y

x=

2

x

x

y

Fig. 1.13 Proportion of drawing sheet


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Title Block Title Block

A0 to A3 size A4 size

Drawing space

Trimmed dimension

Untrimmed dimension

Fig. 1.15 Placement of title block

c

b

a

170 max

bc

a

b

c a

170 max 170 max

(a) (b) (c)

Fig. 1.16 Contents of title block

Title Block

Any technical drawing or related docu-ment must be provided with a title block following the specification as per the latest code of practice, i.e., IS:11665—1985, conforming to ISO:7200—1984. The title block should be positioned in accordance with the recommenda-tions of IS:10711—2001, conforming to ISO:5457—1999. The location of the title block for the sheets positioned horizontally (sizes A0–A3) should be at the right-hand bottom corner and for the sheets positioned vertically (sizes A4) should be at the shorter lower part (see Fig. 1.15). In both the cases, the direction of reading of drawing is same. The title block consists of one or more adjoining rectangles, which may be subdivided into boxes as per requirements (Fig. 1.16). It is man-datory to include the following three types of information in the title block: (a) registration/identification number, (b) title of the drawing, and (c) name of the legal owner of the drawing. In addition, as per requirement, the other information that can be included would be (d) symbol for the first-/third-angle projection, (e) main scale of the draw-ing, (f) linear dimension unit, if other than millimetres, (g) surface texture indication, and (h) geometrical toler-ances.

Borders and Frame

As per the recommendations of IS: 10711—2001 (conforming to ISO:5457—1999), the border should be 20 mm wide on the left edge, in-cluding frame. All other borders should be 10 mm wide. The frame for drawing space should be drawn with lines of 0.7 mm width (Fig. 1.17).

Centring MarksDuring reproduction or for microfilm-ing, four centring marks are placed

Table 1.5 Sizes of drawing sheets

Designation Untrimmed Size (mm) Trimmed Size (mm)Length Width Length Width

A0 1230 880 1189 841A1 880 625 841 594A2 625 450 594 420A3 450 330 420 297A4 330 240 297 210

1 Trimming mark

2 Trimmed format

3 Grid reference border

4 Frame of drawing space

5 Drawing space

6 Untrimmed format

20 mm

5 mm

6

3

1 2 4 5

A

1

5m

m

10

mm

Fig. 1.17 Borders and frames


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8 Machine Drawing

Fig. 1.19 Trimming marks

Table 1.6 Number of fields in the sheet

Size of sheet A0 A1 A2 A3 A4

Longer side 24 16 12 8 6

Shorter side 16 12 8 6 4

Centring marks

Title block

10

X

X

B

C

Fig. 1.18 Centring marks and grid reference system

at the ends of two axes of symmetry of the trimmed sheet with symmetry tolerance 1 mm. These marks are indi-cated with a 0.7 mm wide continuous line, starting at the grid reference bor-der and extending 10 mm beyond the drawing frame (Fig. 1.18).

Grid Reference SystemFor locating details, additions, or revisions easily, the entire sheet is divided into fields. The fields are referenced along the vertical direction with uppercase alphabets, from top to bottom (except I and O). The horizontal fields are refer-enced by numerals from left to right. The alphabets and numerals are placed in the grid reference border marked X (see Fig. 1.18). Table 1.6 gives an account of the number of fields against various paper sizes.

Trimming MarksIn order to facilitate trimming of sheets, trimming marks are provided at the bor-ders of the four edges. Each mark is in the form of two overlapping rectangles of dimensions 10 mm ¥ 5 mm (see Fig. 1.19).


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Table 1.7 Folding of sheet for filing

130 109 190 190 190 190 190

Sheetsize

Folding Pattern

A 0

A 1

1F

old

247

(297)

297

9 Fold

8 Fold

6F

old

7F

old

5F

old

4F

old

3F

old

2F

old

Lengthwise Fold Cross Fold

190 190 190146 (125)

(297)

297

5F

old

4F

old

3F

old

2F

old

1Fol

d

6 Fold

116 (96) 96 96 190

6 Fold

5F

old

4F

old

3F

old

2F

old

297

(123)

1Fol

d

125 (105) 190

297

2F

old

1F

old

A 2

A 3

1.6 FOLDING OF DRAWING SHEETS

The drawing sheets must be folded properly and be kept either (i) in fold-ed or bound condition in a file or (ii) in a folded condition in a filing cabi-net. The methods of folding must be in accordance with the latest BIS code

of practice, i.e., IS:11664—1986. The basic principles to be followed are as follows: (i) All sheets larger than A4 size should be folded to A4 size. (ii) Title blocks should appear in topmost position. (iii) The bottom right corner should be the outermost visible section having a

minimum width of 190 mm.The different types of folding patterns for either filing or keeping in a cabinet

are shown in Tables 1.7 and 1.8, respectively.


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10 Machine Drawing

Table 1.8 Folding of sheet for keeping in cabinet

139

Sheetsize

Folding Pattern

A 0

A 1

(247)

297

297

7 Fold

6 Fold

5F

old

4F

old

3F

old

2F

old

Lengthwise Fold Cross Fold

A 2

A 3

(210) 210 210 210 210

1F

old

(297)

297

4 Fold

3F

old

2F

old

211 (210) 210 210

1F

old

(123)

297

3 Fold

2F

old

174 (210) 210

1F

old

297

(210) 210

1F

old

1.7 DESCRIPTION OF DIFFERENT TYPES OF LINES

In technical drawing, a variety of lines, such as continuous, dashed, dot-ted, dash-dot type, etc., of different widths are used. Each of the different types of lines with various widths is indicative of different demarcation. Let us now briefly discuss the various aspects of lines in accordance with the latest BIS codes IS:10714 (Part

20 and 21)—2001, conforming to ISO:128-20—1996 and ISO:128-21—1997. The width (d) of any line should be constant throughout the length of the line. Depending on the type and size of drawing, the width of all types of lines will be any of the following: (i) A series of width based on a common ratio of 1 2: , i.e., 0.13, 0.18,

0.25, 0.35, 0.5, 0.7, 1, 1.4, or 2 mm. (ii) Ratio of widths of narrow, wide, and extrawide lines should be 1 2 4: : .

The basic types of lines, with their designating number, are shown in Table 1.9.The different elements within a line, i.e., dots, gaps, and dashes, are provided

in some specific dimensions. Table 1.10 gives the dimensions of the different line elements.


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Table 1.9 Basic types of lines

Line No. Description Representation

01 Continuous line

02 Dashed line

03 Dashed spaced line

04 Long-dashed dotted line

05 Long-dashed double-dotted line

06 Long-dashed triple-dotted line

07 Dotted line

08 Long-dashed short-dashed line

09 Long-dashed double short-dashed line

10 Dashed dotted line

11 Double-dashed dotted line

12 Dashed double-dotted line

13 Double-dashed double-dotted line

14 Dashed triple-dotted line

15 Double-dashed triple-dotted line

Table 1.10 Dimensions of line elements

Line No. Line Element Length

04–07 and 10–15 Dot £ 0.5d

02 and 04–15 Gap 3d

08 and 09 Short dash 6d

02, 03 and 10–15 Dash 12d

04–06, 08 and 09 Long dash 24d

03 Space 18d

Table 1.11 Width of lines used for construction drawing

Line GroupLine Width (mm)

Narrow Wide Extrawide

0.25 0.13 0.25 0.5

0.35 0.18 0.35 0.7

0.5 0.25 0.5 1

0.7 0.35 0.7 1.4

1 0.5 1 2

Lines Used in Construction DrawingLet us now discuss the different line styles used in construction drawing of civil engineering. Normally, nar-row, wide, and extrawide lines are used, with the ratio of widths being 1 : 2 : 4. The width of the line is cho-sen according to the line type (see Table 1.11).

Table 1.12 lists the application of different lines in construction draw-ing.

Lines Used in Mechanical DrawingAs in construction drawing, different line styles are also used in mechanical drawing. Normally, two line widths are used and the line widths are according to the line type (see Table 1.13).


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12 Machine Drawing

Table 1.12 Application of different lines for construction drawing

Line No. Subdivision of Line No. and Description Application of Lines

01Continuous

line

01.1

Continuous Narrow Line

01.1.1 Boundaries of different materials in view

01.1.2 Hatching

01.1.3 Diagonals for indication of openings, holes, and recesses

01.1.4 Arrow lines in stairs, ramps, and sloping areas

01.1.5 Modular grid lines, first stage

01.1.6 Short centrelines

01.1.7 Extension lines

01.1.8 Dimension lines and their terminators

01.1.9 Leader lines

01.1.10 Existing contours on landscape drawings

01.1.11 Visible outlines of parts in view

01.1.12 Simplified representations of doors, windows, stairs, fittings

01.1.13 Framing of details

Continuous Narrow Lines with Zigzags

01.1.14 Limits of partial or interrupted views (continuous narrow zigzag lines)

01.2

Continuous Wide Line

01.2.1 Visible outlines of parts in cut and section when hatching is used

01.2.2 Boundaries of different materials in view, cut, and section

01.2.3 Visible outlines of parts in view

01.2.4 Simplified representation of doors, windows, stairs, fittings, etc.

01.2.5 Modular grid lines, second stage

01.2.6 Arrow lines for marking of views, cuts, and sections

01.2.7 Proposed contours on landscape drawings

01.3

Continuous Extra-wide Line

01.3.1 Visible outlines of parts in cut and section when hatching is not used

01.3.2 Reinforcing bars

01.3.3 Lines of special importance

02Dashed line

02.1

Dashed Narrow Line

02.1.1 Existing contours on landscape drawings

02.1.2 Subdivision of plant bed or grass

02.1.3 Hidden outlines

02.2

Dashed Wide Line


02.3

Dashed Extra-wide Line

02.3.1 Reinforcing bars in bottom layer on plan and far face layer in elevation when bottom and top layers and near and far face layers are shown on the same sketch

04Long-dashed

dotted line

04.1

Long Dashed Dotted Narrow Line

04.1.1 Cutting planes

04.1.2 Centre lines

04.1.3 Lines of symmetry

04.1.4 Framing of enlarged details

04.1.5 Reference lines

04.1.6 Limits of partial or interrupted views, cuts, and sections

(Continued)


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Line No. Subdivision of Line No. and Description Application of Lines

04.2

Long Dashed Dotted Wide Line

04.2.1 Cutting planes

04.2.2 Outlines of visible parts situated in front of the cutting plane

04.3

Long Dashed Dotted Extra-wide Line

04.3.1 Secondary lines for setting out an arbitrary reference lines

04.3.2 Indication of lines of surfaces to which a special requirement applies

04.3.3 Boundary lines for contracts, stages, zones, etc.

05 Long-dashed double-dotted

line

05.1

Long Dashed Double Dotted

Narrow Line

05.1.1 Alternative and extreme positions of movable parts

05.1.2 Centroidal lines

05.1.3 Outlines of adjacent parts

05.2

Long Dashed Double Dotted Wide Line

05.2.1 Outlines of hidden parts situated in front of the cutting plane

05.3

Long Dashed Double Dotted Extra-Wide Line

05.3.1 Reinforcing prestressed bars and cables

07Dotted line

07.1

Dotted Narrow Line

07.1.1 Outlines of parts not included in the project

Table 1.12 Application of different lines for construction drawing (Continued )

(Continued)

Table 1.13 Width of lines used for mechani-cal drawing

Line Group

Line Width (mm) for Line No.

01.2, 02.2, 04.2

01.1, 02.1, 04.1, 05.1

0.25 0.25 0.13

0.35 0.35 0.18

0.5 0.5 0.25

0.7 0.7 0.35

1 1 0.5

1.4 1.4 0.7

2 2 1

Table 1.14 Application of different lines for mechanical drawing

Line

No.

Subdivision of Line No. and Description Application of Lines

01Co

ntin

uous

line

01.1

Continuous Narrow Line

01.1.1 Imaginary lines of intersection

01.1.2 Dimension lines

01.1.3 Extension lines

01.1.4 Leader lines and reference lines

01.1.5 Hatching

01.1.6 Outlines of revolved sections

01.1.7 Short centre lines

01.1.8 Root of screw threads

01.1.9 Dimension line terminations

01.1.10 Diagonals for the indication of flat surfaces

01.1.11 Bending lines on blanks and processed parts

01.1.12 Framing of details

01.1.13 Indication of repetitive details

01.1.14 Interpretation lines of tapered features

01.1.15 Location of laminations

01.1.16 Projection lines

01.1.17 Grid lines

Continuous Narrow Freehand Line

01.1.18 Preferably, manually represented termination of partial or interrupted views, cuts, and sections, if the limit is not a line of symmetry or a centreline

Continuous Narrow Lines with ZigzagsContinous Narrow Lines with Zigzags

01.1.19 Preferably, mechanically represented termination of partial or interrupted views, cuts, and sections, if the limit is not a line of symmetry or a centreline

Table 1.14 lists the application of dif-ferent lines in mechanical drawing..

1.8 PATTERNS OF LETTERING

The pattern of lettering is a vital part for the preparation of a complete tech-nical drawing. Writing of all texts in-cluding numerical items of the draw-ing should be in accordance with the general requirements as laid down in the latest BIS code IS:9609 (Part 0)—2001, conforming to ISO:3098-


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14 Machine Drawing

01.2

Continuous Wide Line

01.2.1 Visible edges

01.2.2 Visible outlines

01.2.3 Crests of screw threads

01.2.4 Limit of depth of full-depth thread

01.2.5 Main representations in diagrams, maps, flow charts

01.2.6 System lines

01.2.7 Parting lines of moulds in view

01.2.8 Lines of cuts and section arrows

02Da

shed

line

02.1

Dashed Narrow Line

02.1.1 Hidden edges


02.2

Dashed Wide Line

02.2.1 Indication of permissible areas of surface treat-ment

04Lo

ng-d

ashe

d do

tted

line 04.1

Long Dashed Dotted Narrow Line

04.1.1 Centrelines

04.1.2 Lines of symmetry

04.1.3 Pitch circle of gears

04.1.4 Pitch circle of holes

04.2

Long Dashed Dotted Wide Line

04.2.1 Indication of required areas of surface treatment

04.2.2 Indication of cutting planes

05

Long

-das

hed

doub

le-d

otte

d lin

e 05.1

Long Dashed Double Dotted

Narrow Line

05.1.1 Outlines of adjacent parts

05.1.2 Extreme positions of movable parts

05.1.3 Centroidal lines

05.1.4 Initial outlines prior to forming

05.1.5 Parts situated in front of a cutting plane

05.1.6 Outlines of alternative executions

05.1.7 Outlines of the finished part within blanks

05.1.8 Framing of particular fields

05.1.9 Projected tolerance zone

Table 1.14 Application of different lines for mechanical drawing (Continued )0—1997. For numerically controlled lettering, either of the two types, namely, ‘type A’ and ‘type B’, should be used. Each of these two types can be written either in a vertical fashion or in an inclined fashion at an angle of 75° with the base line. Heights of all alphanumeric characters are defined by the proportion of the height of any uppercase alphabet. The height of the uppercase alphabet is called nominal size (h). The range of nominal sizes are in a series of ratio of 1 2: , such as 1.8, 2.5, 3.5, 5, 7, 10, 14, and 20 mm. The line width (d) of any sort of character is constant and the spacing between successive characters will be twice the line width. The intercharac-ter spacing for some specific combina-tion of alphabets, such as ‘LA’, ‘TV’, ‘Tr’, etc., will only be the line width. Different heights related to lettering are shown in Fig. 1.20. These dimen-sions in terms of nominal size (h) for letters of type A and type B are pro-vided in Table 1.15

Some Latin alphabets, numerals, and marks, both in vertical and inclined style, in accordance with IS:9609 (Part 1)—2006, conforming to ISO:3098-2—2000, are shown in Fig. 1. 21.

Table 1.15 Relative dimensions for letters of type A and type B

Characteristics Type A Type B

Line width (d ) (1/14)h (1/10)h

Height of uppercase letters (h) (14/14)h (10/10)h

Height of lowercase letters (c1) (10/14)h (7/10)h

Tail of lowercase letters (c2) (4/14)h (3/10)h

Stem of lowercase letters (c3) (4/14)h (3/10)h

Height of diacritical marks (f ) (5/14)h (4/10)h

Spacing between characters (a) (2/14)h (2/10)h

Minimum spacing between baselines [uppercase and lowercase with diacritical marks] (b1) (25/14)h (19/10)h

Minimum spacing between baselines [uppercase and lowercase without diacritical marks] (b2) (21/14)h (15/10)h

Minimum spacing between baselines [uppercase only] (b3) (17/14)h (13/10)h

Spacing between words (e) (6/14)h (6/10)h


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c2dea

h

c3b3

f

a1

Baseline

h1

b1

c1

b2

Baseline

Fig. 1.20 Dimensions for lettering

Fig. 1.21(a) Letter type ‘A’, vertical fashion

Fig. 1.21(c) Letter type ‘A’, inclined fashion

Fig. 1.21(b) Letter type ‘B’, vertical fashion

Fig. 1.21(d) Letter type ‘B’, inclined fashion

Fig. 1.22 Spacing between hatching lines

1.9 PATTERNS OF SECTION AND OTHER CONVENTIONS

The basic methods of presentation of sectioned part of elements by means of hatching, in accordance with SP:46—2003, are as follows: (i) The lines for hatching should

be continuous narrow lines (e.g., line no. 01.1).

(ii) The space between successive hatching lines should be pro-portionate to the hatching area, but in no case should it be less than 0.7 mm (see Fig. 1.22).

(iii) Hatching lines should be in-clined preferably 45° to the principal outline of the area (see Fig. 1.23 (a)) or 45° to the lines of symmetry of the area (see Figs 1.23 (b) and (c)).

(a) (b) (c)

Fig. 1.23 Basic pattern of hatching

(iv) For any large area, instead of hatching within entire area, hatching along the contour will be indicative (see Fig. 1.24).

(v) In a case where sections of the same part in parallel planes are shown side by side, the hatch-ing should be identical but the


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16 Machine Drawing

propriate units of measurement and is indicated graphically with lines, sym-bols, and notes. All dimensional infor-mation, which is required to define a component or part completely, should be clearly shown within the technical drawing, unless mentioned in related documents. The general system of di-mensioning will be discussed here in

accordance with the latest BIS code of practice, i.e., IS:11669—1986, conform-ing to ISO:129—1985. Broadly speaking, dimensioning is of two types:

Functional DimensionThese dimensions are very essential for the functioning of the element and for the production of the drawing (see Fig. 1.28).

Nonfunctional DimensionThese dimensions are not essential for the functioning of the element.

Basic Rules of Placement of DimensionsThe basic rules to be followed during dimensioning are as follows:. (i) Dimensions should be placed on that particular view or on that particular

section which most clearly shows the corresponding feature. (ii) Each feature should be dimensioned only once in a technical drawing. (iii) Within the drawing, all linear dimensions should be provided in the same

unit, preferably millimetres. Hence there is no necessity to write ‘mm’ at the end of each dimension. Only one note, such as ‘all dimensions are in millimetre’, placed at the end of the drawing sheet will be sufficiently indicative. If other units like ‘Nm’ or ‘MPa’ appear, dimensions should be placed with proper mention of units.

(iv) Functional dimensions, wherever possible, should be shown directly on the drawing.

(v) Generally, the process of production or the method of inspection is not mentioned within the drawing if not otherwise compelled for ensuring satisfactory functioning or interchangeability.

(vi) Nonfunctional dimensions should be placed in way that is most convenient for inspection and production.

Elements of DimensioningThe major elements of dimensioning, other than the dimension itself, are the projection line, the dimension line, and the leader line. These are continuous lines, and their code-specified conventions are as follows:

Fig. 1.24 Hatching of large area

A

A

A-A

Fig. 1.25 Hatching in parallel sectional plane

50

Fig. 1.26 Interruption of hatching

(a) (b)

Fig. 1.27 Thin sections

25 ± 0.06 15 ± 0.01

Fig. 1.28 Functional dimension

lines in two parts should not be collinear. This convention is followed for greater clarity (see Fig. 1.25).

(vi) In a case where inscribing di-mension is inevitable within the hatched area, lines of hatch-ing should be interrupted near zone of dimensions for better clarity (see Fig. 1.26).

(vii) Thin sections should be shown entirely in black (see Fig. 1.27 (a)) and a gap of not less than 0.7 mm should be maintained between adjacent thin sections (see Fig. 1.27 (b)).

See Chapter 2 for a detailed discussion of sectioning pattern.

1.10 GENERAL SYSTEM OF DIMENSIONING

The dimension of a technical drawing is a numerical value expressed in ap-


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2 45°¥Leader line

Origin indication Dimension line Termination (Arrowhead)

Projection line

Value of the dimension1500

3500

4500

(a)

4240 Value of the dimension

Dimension line Termination (Oblique stroke)

(b)

Projection line

Fig. 1.29 Projection line, dimension line and leader line

Fig. 1.30 Oblique projection line Fig. 1.31 Origin indication of dimension line

Arrowheads

Oblique stroke

Fig. 1.32 Termination of dimension line Fig. 1.33 Unbroken dimension line

(a) (b)

16 18

26

28 12

6

13 2

1

Fig. 1.34 Projection line and dimension line

(a)

(b)

Fig. 1.35 Arrowhead termination

(i) The projection line should be extended slightly beyond the respective dimension line (see Figs 1.29 (a) and (b)).

(ii) Generally, the projection lines are drawn perpendicular to the feature being dimensioned. If it is found necessary, a projection line may be

drawn in an oblique pattern, but parallel to each other (see Fig. 1.30).

(iii) The indication of origin of a di-mension line should be drawn as an open circle of approximately 3 mm diameter (see Fig. 1.31).

(iv) The dimension line should be terminated with an open arrow or closed arrow (filled or unfilled) or an oblique stroke inclined at 45° angle. The in-cluded angle of the arrowhead is variable from 15° to 90° (see Fig. 1.32).

(v) The dimension line should be shown unbroken for the feature that is shown in broken line (see Fig. 1.33).

(vi) In principle, the projection line and the dimension line should not intersect each other. Where it is unavoidable, neither the projection line nor the dimen-sion line should be shown with a break (see Figs 1.34 (a) and (b)).

(vii) Arrowheads of the dimension line generally terminate within limits of projection line. In case of scarcity of space, the ter-mination of arrowheads may be shown outside the intended limits of dimension line (see Figs 1.35 (a) and (b).

System of DimensioningEither of the following two systems is followed in the placement style of di-mensional values:


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18 Machine Drawing

System I In this system, the dimen-sional values are placed parallel to the dimension line and preferably near the middle, above, and clear of the dimen-sion line. All indicated dimensional values should be readable from the bottom or the right-hand side of the drawing (see Fig. 1. 36).

System II In this system, only the non-horizontal dimensional values are inserted within the dimension line. The horizontal dimensional values are placed parallel to the dimension line and preferably near the middle, above, and clear of the dimension line. All indicated dimensional values should be readable from the bottom only (see Fig. 1.37).

Arrangement of Dimensions

The arrangement of dimensioning on a drawing clearly indicates the pur-pose of the design. Following are the different types of arrangements:

Chain dimensioning This arrange-ment of dimensioning is used only where possible accumulation of toler-ances does not affect the functional re-quirements of the part (see Fig. 1.38 for details).

Dimensioning from a common feature This arrangement is used where a number of dimensions of the same direction relate to a common feature. When a number of paral-lel dimension lines with dimensional values are used, it is called parallel dimensioning (see Fig. 1.39). To sim-plify this process, sometimes we use superimposed running dimensioning (see Figs 1.40 (a) and (b)). Often it is advantageous to use superimposed running dimensioning in two direc-tions (see Fig. 1.41).

Dimensioning by coordinates Sometimes dimensioning indicated

30°

30°

(a)

20

(b)

60°

(c) (d)

3930

20

20

20 20 20

20

20

20 2020

60° 60°

60°30°

60°

30°

60°

60° 60°

60°

60°

20

70

Fig. 1.36 Dimensioning as per System I

(c)

30°

60°

60°60°

60°

60°

f20f30

f50

26 10

75

(a)

70

30

(b)

39

30°

Fig. 1.37 Dimensioning as per System II

160 20070 30

100

150

Fig. 1.38 Chain dimensioning

160

420

640

Fig. 1.39 Parallel dimensioning


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by coordinates, with or without tabu-lated explanation, are found to be very convenient. Various patterns of this procedure are shown in Fig. 1.42.

Combined dimensioning Although not recommendable, if necessary, chain dimensioning, single dimension, and dimensioning from a common fea-ture can be combined (see Fig. 1.43).

Special Indications in Dimensioning

For proper identification of shape and improvement of interpretation of drawing, the following types of spe-cial symbols and indications are pro-vided:

Symbols The uppercase alpha-bets ‘R’ and ‘SR’ indicate radius and spherical radius, respectively. f and Sf stand for diameter and spherical diameter, respectively. Sometimes a square symbol is used. The applica-tions are explained pictorially in Fig. 1.44. Chords, arcs, and angles can be shown unambiguously with symbols as shown in Fig. 1.45.

0 150 420 640

(a)

150

(b)

420 6400

Fig. 1.40 Superimposed running dimensioning

15.5

15.5

15.5

11

26

26

13.5

13.5

13.5

0 20 60 100 140 180 200

20

0

60

90

120

160

13.5

Fig. 1.41 Superimposed running dimensioning in two directions

X Y f123456789

10

20206060

100

16020

1206090

15.513.51113.526

1

3

5

4

2Y

X (c)

X = 70

Y = 80

X = 20

Y = 60

X = 10

X = 80

Y = 40

(a)

1X Y10 20

2 80 403 70 804 20 60

3

4

1

2

(b)

00

Fig. 1.42 Dimensioning by coordinates

(a)

(b)

Fig. 1.43 Combined dimensioning


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20 Machine Drawing

f40

f30

(a)

R10R15

SR12

SR

60

(d)

S 50f

(e)

(b)

(c)

40

Fig. 1.44 Use of symbols in dimensioning

Equidistant features When equi-distant features or uniformly arranged elements are available on a drawing, dimensioning system may be simpli-fied. Simplified linear spacing and angular spacing are illustrated in Figs 1.46 and 1.47, respectively.

Repeated features If it is possible to define a quantity of elements of the same size so as to avoid repeating the same dimensional value, they may be shown as depicted in Fig. 1.48.

100

(a)

105

(b)

(c)

42°

Angle

Arc

Chord

Fig. 1.45 Special indication in dimensioning

15 5 18 ( = 90)¥

(a)

18

15 17 18 ( = 306)¥

(b)

Fig. 1.46 Equidistant linear dimensioning

5 10° (= 50°)¥

(a)

(b)

50

9

Fig. 1.47 Equidistant angular dimensioning

1.11 CONVENTIONAL REPRESENTATION OF THREADS AND THREADED PARTS

In this section, we will discuss the conventional representation of threads and threaded parts in accordance with the latest BIS code of practice, i.e., IS:10715 (Part 1)—1999, conforming to ISO:6410-1—1993.

Representation of Single EntityIn the side view and the section of visible screw threads alone, the crests should be drawn with a continuous wide line (e.g., line no. 01.2) and the roots with a


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continuous narrow line (e.g., line no. 01.1) (see Fig. 1.49). At the end view, the roots of the thread are represented with a three-quarters circle, open at the top right quadrant. The circle is drawn with a continuous narrow line (e.g., line no. 01.1). These are illustrated in Figs 1.49 and 1.50. When it is neces-sary to show hidden screw threads, the crests and roots are represented by dashed narrow line (e.g., line no. 02.1) (see Fig. 1.51).

Representation of Assembled PartsThe conventions as followed for sin-gle entity are equally applicable for assembled threaded parts. The exter-nally threaded parts should always be shown covering the internally thread-ed parts and without any hidden lines. The wide line representing the limit of the useful length of the internal screw thread should be drawn to the root of the internal thread (see Fig. 1.52).

45°

45°

60°

6 (or 6 holes 8)¥ f f8

8 (or 8 holes 8)¥ f f8

(a)

60°

60°

Fig. 1.48 Repeated feature dimensioning

Fig. 1.49 Continuous boundary of visible screw thread

or

Fig. 1.50 End view of screw thread

Fig. 1.51 Hidden screw thread

Fig. 1.52 Assembled threaded part

Designation and Dimensioning of Threaded PartsGenerally, a few alphanumeric charac-ters are used to designate the threads. First, the kind of thread is mentioned with abbreviated alphabets, such as M (for metric thread), G (for one type of British Standard Pipe thread), HA, Tr, etc. The nominal diameter is written just after the type of thread. Sometimes the lead (L) and pitch (P) are mentioned in millimetres. For the


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22 Machine Drawing

right-hand threads, the direction of lead need not be mentioned. But for the left-hand threads, the direction of lead must be mentioned with ‘LH’. If required, the tolerance information is also provided within the designation of the thread. As per the requirement, the thread engagement type (N, nor-mal; S, short; L, long) may need to be mentioned. See Figs 1.53 (a) and (b) for a better understanding. Regarding dimension, the nominal diameter (d) refers to the crest of the external thread or the root of the inter-nal thread. The thread length (b) nor-mally refers to the length of the full-depth thread (see Fig. 1.54).

1.12 CONVENTIONAL REPRESENTATION OF SPRINGS

The conventional simplified repre-sentation of compression springs, ex-tension springs, torsion springs, disc springs, spiral springs, and leaf springs are briefed here in accordance with the latest BIS code of practice, i.e., IS:10716 (Part 1)—1999, conforming to ISO:2162-1—1993.

M20 L3 – P1.5 – 6H – S¥

Metric thread

20 mm nominal diameter

3 mm lead1.5 mm pitch

Short thread engagement

M20 2 – 6G/6h – LH¥

(a)

Metric thread

20 mm nominal diameter

2 mm pitchTolerance class

Left-hand threads

(b)

Fig. 1.53 Designation of screw thread

b

d

(a)

d

(b)

Fig. 1.54 Dimensioning of screw thread

Cylindrical helical Conical helical Cylindrical helicalwith square c/s

Fig. 1.55(a) Sectional views of some helical compression springs

Cylindrical helical Conical helical Cylindrical helicalwith square c/s

Fig. 1.55(b) Simplified presentation of Fig. (a)

Helical Compression SpringsThese springs are of two types, namely, cylindrical helical compression spring and conical helical compression spring. The cross section may be circular or noncircular. When it is noncircular type, a small square or a small rectangle will have to be provided as a symbol to indicate the cross section square type or rectangular type, respectively. The helix of the spring is considered as right-hand type, by default. If it is left-hand type, then it is to be specified with ‘LH’. Figures 1.55 (a) and (b) represent the sectional views and simplified presenta-tion, respectively, of some helical compression springs.


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Sectional view Simplfied view

Fig. 1.56 Helical extension spring

View

Sectional View

Simplified View

Fig. 1.57 Torsion springs

Sectional and simplfied view of single disc spring

Sectional and simplfied view of multi-disc spring

Fig. 1.58 Disc springs

View and simplfied view of spiral with rectangular c/s

View and simplfied view of constant force spiral extension spring

Fig. 1.59 Spiral springs

View and simplfied view of laminated leaf spring without eyes

View and simplified view of laminated leaf spring with eyes

Fig. 1.60 Leaf spring

Helical Extension SpringsIn these springs, the requirements for the indication of cross section and direction of helix are identical to that of helical compression springs. The sec-tional and simplified views of some helical extension springs are represented in Fig. 1.56.

Torsion SpringsIn these springs, the requirements for the indication of cross section and di-rection of helix are identical to that of helical compression springs. The sec-

tional and simplified views of some torsion springs are represented in Fig. 1.57.

Disc Springs

The sectional and simplified views of some disc springs are represented in Fig. 1.58.

Spiral Springs

The sectional and simplified views of some spiral springs are represented in Fig. 1.59.

Leaf Springs

The sectional and simplified views of some leaf springs are represented in Fig. 1.60.


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24 Machine Drawing

1.13 CONVENTIONAL REPRESENTATION OF GEARS

Let us now discuss the conventional representation of gears in accordance with the latest BIS code of practice, i.e., IS:10717—1983, conforming to ISO:2203—1973.

ContoursFigure 1.61 represents the contours and edges of each gear, as if (a) in an unsectioned view, a solid gear bound-ed by tip surface, (b) in axial section, a spur gear having two diametrically op-posite teeth, represented unsectioned, and (c) even in case of a gear without spur teeth or with an odd number of teeth.

PitchThe pitch is indicated with a pitch circle with long dashed dotted narrow line, when the view is normal to the axis. In case of a projection parallel to the axis, the pitch is indicated by its apparent contour, by means of extend-ing the line beyond the gear contour on each side (see Fig. 1.61).

Root SurfaceGenerally, root surface is indicated in sectional views. If really necessary to

(a)

(b)

(c)

Fig. 1.61 Contours and pitch indications in gears

(a)

(b)

Fig. 1.62 Root surface and teeth indications in gears

RECAPITULATION

· In India, the boards used for drawing are made as per the speci-fications of IS:1444—1989.

· The scale of drawing is the ratio of linear dimension of an object represented in original drawing to real linear dimension of the object itself. The choice of scale should be in accordance with IS:10713—1983, conforming to ISO:5455—1979.

· The size and layout of preprinted drawing sheets follows IS: 10711—2001, conforming to ISO:5457—1999 and SP:46—2003.

· The title block of a drawing sheet should be as per IS:11665—1985, conforming to ISO:7200—1984.

· The folding of drawing sheets for preservation should be done in accordance with IS:11664—1986.

· The use of a variety of lines in technical drawing should be as per IS:10714 (Part 20 and 21)—2001, conforming to ISO:128-20—1996 and ISO:128-21—1997.

· All texts including numerical items of the drawing should follow the general requirements as laid down in IS:9609 (Part 0)—2001,

conforming to ISO:3098-0—1997. · Latin alphabets, numerals, and marks, both in vertical and in-

clined style, should follow IS:9609 (Part 1)—2006, conforming to ISO:3098-2—2000.

· The basic methods of presentation of sectioned part of elements by means of hatching should follow SP:46—2003.

· The general system of dimensioning should be done in accor-dance with IS:11669—1986, conforming to ISO:129—1985.

· The conventional representation of threads and threaded parts should be done in accordance with IS:10715 (Part 1)—1999, conforming to ISO:6410-1—1993.

· The conventional simplified representation of different types springs should be in accordance with IS:10716 (Part 1)—1999, conforming to ISO:2162-1—1993.

· The conventional representation of gears should follow IS:10717—1983, conforming to ISO:2203—1973.

show in unsectioned view, it can be shown with a continuous narrow line (see Fig. 1.62).

TeethThe profile of teeth must be speci-fied with reference to a standard or by a drawing. If it is essential to show one or two teeth on the drawing, these should be drawn with a continuous wide line (see Fig. 1.62). It is vital to indicate the direction of teeth. Normally, teeth are symbolically indicated with three continuous narrow lines as shown in Fig. 1.63.

Right helical Left helical

Double helical Spiral

Fig. 1.63 Indications of direction of teeth in gears


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MULTIPLE-CHOICE QUESTIONS

Pick out the best possible alternative(s).

1. What was the year of the latest revision of special publication no. 46 (SP:46) published by BIS?

(a) 2003 (b) 1972 (c) 2010 (d) 2005

2. What are the dimensions of D1 type drawing boards as per IS specification?

(a) 1525 ¥ 1220 (b) 920 ¥ 650 (c) 1270 ¥ 920 (d) 500 ¥ 350

3. Parallel lines can be drawn with (a) T-square only (b) T-square and/or set-square (c) set-square only (d) divider

4. Which of the following equipments are used for drawing curves of different radii?

(a) French curves (b) set-square (c) T-square (d) protractor

5. Drafting machine can draw (a) parallel lines (b) perpendicular lines (c) lines at any angle (d) curves of different radii

6. X:1 represents (a) a reduction scale (b) a full-size scale (c) a comparative scale (d) an enlargement scale

7. 1:X represents (a) an enlargement scale (b) a full-size scale (c) a comparative scale (d) a reduction scale 8. 1:1 represents (a) a full-size scale (b) an enlargement scale (c) a comparative scale (d) a reduction scale

9. What is the area of trimmed A0 size drawing sheet? (a) 1.5 m2 (b) 2.0 m2

(c) 0.1 m2 (d) 1 m2

10. State the correct ratio of length to width of any trimmed drawing sheet conforming to the BIS code of practice

(a) 1 2: (b) 1:1

(c) 2 1: (d) 3 2: 11. As per the BIS code of practice, which of the following information

is mandatory for the title block? (a) the main scale of the drawing (b) the surface texture indication (c) geometrical tolerances (d) the title of the drawing

12. The line width used to draw the frame-enclosing space of draw-ing in a standard trimmed drawing sheet is

(a) 0.7 mm (b) 0.8 mm (c) 0.9 mm (d) 1 mm

13. How many number of drawing fields bounded by grid lines are there in an A4 size trimmed drawing sheet?

(a) 36 (b) 30 (c) 24 (d) 20

14. As per the BIS code of specification, maximum width of the title block will be

(a) 190 mm (b) 180 mm (c) 175 mm (d) 170 mm

15. All larger size drawing sheets should be folded, following the BIS code of practice, into a size of

(a) A4 (b) B4 (c) A2 (d) foolscap size

16. As per the guidelines of BIS, the specific ratio to be maintained for the widths of narrow, wide, and extrawide lines is

(a) 1:2:4 (b) 1:2:3 (c) 1: 1.5:2.5 (d) 10:11:12

17. Which of the following types of lines is used as the dimension line?

(a) continuous narrow line (b) continuous wide line (c) continuous extrawide line (d) dotted narrow line

18. Which of the following types of lines is used in hatching? (a) continuous narrow line (b) long-dashed dotted wide line (c) continuous extrawide line (d) dashed wide line

19. Which of the following types of lines is used as hidden outlines? (a) hidden narrow line (b) long-dashed dotted wide line (c) continuous extrawide line (d) hidden wide line

20. Which of the following types of lines is used as leader lines? (a) hidden narrow line (b) long-dashed dotted wide line (c) continuous narrow line (d) hidden wide line

21. Which of the following types of lines is used as leader lines? (a) hidden narrow line (b) long-dashed dotted narrow line (c) continuous narrow line (d) hidden wide line 22. What is the preferable inclination of hatching lines? (a) 30 (b) 60 (c) 75 (d) 45° 23. What is the possible angle included within the arrowhead of a

dimension line? (a) 30 (b) 60 (c) 45 (d) all of these 24. What does ‘SR’ indicate in dimensioning? (a) spherical radius (b) simple radius (c) separated diameter (d) short radius 25. What does the alphabet ‘M’ stand for the conventional represen-

tation of threads? (a) pitch expressed in millimetre (b) lead expressed in millimetre (c) multiple thread (d) metric thread


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26 Machine Drawing

ANSWERS 1. (a) 2. (b) 3. (b) 4. (a) 5. (a), (b), and (c) 6. (d) 7. (d) 8. (a) 9. (d) 10. (c) 11. (d) 12. (a) 13. (c) 14. (d) 15. (a) 16. (a) 17. (a) 18. (a) 19. (a) and (d) 20. (c) 21. (b) 22. (d) 23. (d) 24. (a) 25. (d)

REVIEW QUESTIONS

1. Explain in detail the methodology for deriving the basic size of trimmed drawing sheets.

2. Write short notes on (i) enlargement scale and (ii) reduction scale.

3. What is the utility of a title block in a drawing?

4. State the basic principles of sectioning in brief.

5. Differentiate between the functional dimension and the nonfunc-tional dimension.

6. What are the basic rules to follow for the placement of dimen-sions in a technical drawing?

7. What are two systems of dimensions generally followed?

8. Explain the different types of arrangements of dimensions.

9. Draw the examples of simplified representation of helical springs and leaf springs.


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