Lec_1 Intro Tools

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@ McGraw-Hill Education

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Engineering Drawing with an Introduction to AutoCAD, Dhananjay A Jolhe, Tata McGraw Hill, Ed. 2008

PROPRIETARY MATERIAL. 2008 The McGraw-Hill Companies, Inc. All rights reserved. No part of this PowerPoint slide may be displayed, reproduced or

distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators

permitted by McGraw-Hill for their individual course preparation. If you are a student using this PowerPoint slide, you are using it without permission.


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Chapter 1

INTRODUCTION TO ENGINEERING DRAWING

The role of engineers is to design & develop the products. In their business, engineers

have to prepare drawings to convey their ideas. The graphical language used by

engineers is called as Engineering Draw

ing. Just as a picture speaks thousands of

words, a complete technical drawing tells everything about the geometry of the product.

To draw accurate drawings, various instruments & accessories are used. These are

explained on next slide.


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1.3 DRAWING INSTRUMENTS AND ACCESSORIES

1.3.1 Drawing Sheets and Papers

Drawing sheets and papers are the canvases on which drawings arecomposed by pencils or pens. Drawing sheets are available in standard sizes

Table 1.1.


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1.3.2 Drawing Board

Drawing boards are used to support a drawing sheet or paper. They are made

up of soft wooden platens fastened together by two cross plates (battens),Fig. 1.2. The working surface of the board is planned perfectly. A shorter edge

of the board carries a hard ebony strip fitted in a groove. This straight ebony

edge, perfectly lined up with the edge of the drawing board, provides the

guide for the T-square.


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1.3.3 Mini Drafter

A mini drafter is a portable device used to draw parallel, inclined and

perpendicular lines speedily. It is mounted on a drawing board at the top leftcorner. A drafter consists of a scale, a scale screw, a scale plate, steel bars, a

bar plate and a clamping mechanism, Fig. 1.3.


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1.3.4 T-Square

A T-square is a T-shaped device used to draw straight horizontal lines. It

consists of a stock and a blade joined together at right angles, Fig. 1.4.


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Set-squares

Two set squares(i) 45 set-square and (ii) 30 60 set-square, are the most

common drawing instruments. A protractor is usually included in a 45 set-

square, Fig. 1.5(a). The 30 60 set-square may include French curves in it,

Fig. 1.5(b).

Protractor

Protractor is used to draw and measure the angles. It is available separately

or as merged in 45 set-square.


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Roller Scale

A roller scale is a handy device used to draw parallel and inclined lines. It is a

speedy device and may be used for practice in classrooms.
http://e/Jolhe/PowerPoint_Slides_Chapter_02.ppt#2.%20Slide%202


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Compasses

Compasses are used to draw circles or arcs. Two sizes of compasses(i) large

compass and (ii) small spring bow compass are in common use. A large compass

consists of a needle leg and a pencil leg hinged together at upper ends, Fig.

1.7(a). The two legs carry, respectively, a needle point and a pencil point at their

lower ends. The pencil point can be interchanged with a pen point, Fig. 1.7(b).

Lengthening bar, Fig. 1.7(c), is used to draw circles of diameter greater than 150

mm. Small spring bow compasses are of two types: bow pencil compass, Fig.

1.7(e) and Bow pen compass, Fig. 1.7(f).


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Dividers

Dividers are used to transfer lengths from one place to other. They are also

used to set-off desired distance from the scale on the paper.


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Pencils/Lead Pens

The quality of drawing largely depends on the selection and use of proper grade of

pencil. The grade of a pencil is printed near its blocked end. For technical drawing,

three grades of pencils, namely, H, 2H and HB are recommended. A lead pen, Fig.1.10, is an alternative to the pencil.

From softest to hardest they would be:

2B, B, HB, H, 2H

Soft lead giving the darkest, hard lead giving the lightest lines

when applied with the same pressure.

B for blackness, H for Hardness

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Pencil Sharpener

A pencil sharpener is a device used to mend the pencils. It conveniently removes

the wooden shell covering the lead. A common hand-held sharpener, Fig. 1.12(a),

is recommended.

Eraser

A non-dusting good quality eraser is recommended for erasing unwanted part of

the pencil drawing.

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Circle Template

A transparent circle template made up of acrylic is used to draw circles of

different radii quickly. The circle templates should only be used to drawcircles of diameters smaller than 5 mm.

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Lettering Set-squares

Small sized transparent \set-squares without any graduations on their edges,

Fig. 1.17, may be used for lettering purposes.

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Lettering Template

Lettering template is a plastic plate on which letters are carved, Fig. 1.18. It

may be used for double stroke Gothic lettering (Section 2.3.4).

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Drawing Clips, Pins and Adhesive Tape

Drawing clips, pins and adhesive tape are used to fix drawing paper/sheet on the

drawing board. Their use is explained in Fig. 1.21.

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Sheet Container

A sheet container, Fig. 1.20, may be used to store and carry drawing sheets.

Sandpaper

Sandpaper (or sandpaper block) is used to sharpen the pencil lead and lead

sticks. Fine grade wood sandpaper, should be preferred.

Paper Napkins or Handkerchief

Paper napkins or a small handkerchief may be used to clean the drawing sheet

and drawing instruments frequently.

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PRACTICAL LESSONS

Before the start of drawing work, the drafting table and other drawing instruments should be

cleaned properly. The user should also clean his or her hands. This helps to keep the

drawing work clean.

Clamping a Drawing Sheet on Drawing Board and Setting the Drafter

Refer Fig. 1.21.

1. Place a drawing board on a table top or any other suitable surface. A specially designed

drafting table (with a drawing board as a table top) may be used. The cut edge of the

board should be on your left-hand side.

2. Place the drawing sheet on the drawing board. The bottom and right edges of the sheet

should be approximately 1 cm each from the corresponding edges of the board.

3. Fix a drawing clip (Clip 1) at bottom right corner of the board. See INSET 1 for proper clip

placement.

4. Loosen the clamping screw of the mini drafter. Carry the drafter gently over the board andplace its claming strap over the top left corner of the board such that two of the inner faces

of the strap will mate with the corresponding faces of the top edge of the board, INSET 2.

The distance of the clamp from the left edge of the board may be 5 mm to 10 mm, INSET

3. Tighten the clamping screw gently till the strap takes a firm grip on the board.

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5. Move the drafter scale to the centre of the sheet. Loosen the scale screw and match the 0

degree mark on the degree scale with the mark on the scale plate, INSET 4. You must

look directly from above the 0 degree mark to avoid the parallax error. Tighten the scale

screw gently.

6. Move the drafter scale near the bottom edge of the sheet. Match the edge with the

horizontal scale of the drafter. The sheet may be moved up and down pivoting about the

Clip 1. Once the bottom edge of the sheet is matched perfectly with the horizontal scale,

place another clip (Clip 2) near the bottom left corner of the sheet. (If the sheet has a

printed drawing frame, then the bottom horizontal line of the frame should be matched

with the horizontal scale.) Now, move the scale to the top edge of the sheet, sliding gently

over the sheet, and place the third clip (Clip 3) near the top right corner of the sheet. Use

a drawing pin, INSET 5, or adhesive tape, INSET 6, to fix the top left corner of the sheet.

The pin should be inserted at a point approximately 1 cm each from top and left edge of

the sheet. In case of a sheet with a printed drawing frame, the pin should be placed

outside the frame.

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Preparing the Pencil and Lead Sticks

A pen knife may be used to remove the wooden shell from the unlettered end

of the pencil. Initially, around 35 mm length of shell should be removed to

uncover approximately 10 mm length of lead, Fig. 1.22(a). The lead end

should then be sharpened to a conical tip using a sandpaper. The sharp

conical tip should be converted to a rounded tip. The lead sticks to be used

in compasses may be sharpened using sandpaper in a similar way.

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Preparing the Compass

Loosen the screw of the pencil point of the compass. Insert a lead stick of

appropriate length and prepared with tip as explained below. Adjust theneedle and lead so that the needle tip extends slightly more than the lead tip.

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Working with Pencil

The pencil should be gripped at an approximate distance of 35 mm from the

lead tip, Fig.1.25. The pencil is usually held inclined at about 60 with the

paper. The slope of the pencil should be in the direction of the stroke of the

line. For horizontal lines, the pencil should slope up toward the right-hand

side. For vertical lines, it should slope up toward the user. The pencil may be

rotated slightly while drawing a line to ensure the uniformity in line

thickness.

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Working with Set-squares

The set-squares, in combination with T-square, can be conveniently used to

draw lines inclined at 15, 30

, 45

and so on. The positions of the set-squares are shown in Fig. 1.26.

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Drawing Margins and Title Block

Sufficient margins should be kept on all the sides of the drawing sheet. The

margin widths at the four sides of A2 size (trimmed) sheet are shown in Fig.

1.27. A thick drawing frame should be drawn after fixing the margin width.Often, a longer frame line, say the bottom line, is drawn parallel to the

corresponding edge of the sheet.

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The title block is located at the bottom right corner of the frame attached to

the frame lines, Fig. 1.27. It typically includes information like, name of the

organization, name of the designer or draftsman, drawing title, scale of the

drawing, etc. The projection method symbol is also included in the titleblock.

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TIPS FOR GOOD QUALITY DRAWING

1. Sharpen the tip of the pencil from time to time by using a penknife and sandpaper.

2. Sharpen the lead tip inserted in the compass frequently by sandpaper.

3. Use a proper grade of the pencil and/or lead, i.e., H, 2H or HB as the case may be.

4. Avoid frequent use of eraser.

5. Complete a line, circle or arc in one stroke only. Avoid overdrawing.

6. Maintain constant hand pressure while drawing a particular line, circle or arc.

7. Check frequently the 0 setting of the drafter scale.

8. Dont use a drafter to draw measured inclinations. Use a protractor for this purpose.

9. While moving the drafter scale from one point to another, care should be taken that it

does not rub with the drawing sheet.

10. Use a bow compass to draw smaller circles or arcs. A circle template should only beused to draw circles or arcs having a diameter less than 5 mm.

11. Draw smooth curves (e.g., engineering curves, loci of points, sections of solids,

development, curves of intersection, etc.,) initially very lightly by freehand and then use

the French curve to make them sufficiently thick and uniform.

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12. Use a paper napkin or clean handkerchief to clean away the rubbed particles from drawing

sheet.

13. Avoid the contact of drawing instruments with drawing sheet except during their actual

use.

14. Your drawing sheet gets stained by dirt on the drawing instruments, drawing board and

your hands. Keep all these always clean.

15. Protect your drawing sheet from all external factors which may spoil or make it dirty.

16. Before placing the drawing sheet inside the container, roll it properly and place a rubber-

band over it.

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Drawing Sheets Sizes

ISO USA Sizes

LetterWidth Length

Letter inches

mm inches mm inches

F 28.0 x 40.0

A0 841 33.11 1189 46.81 E 34.0 x 44.0

A1 594 23.39 841 33.11 D 22.0 x 34.0

A2 420 16.54 594 23.39 C 17.0 x 22.0

A3 297 11.69 420 16.54 B 11.0 x 17.0

A4 210 8.27 297 11.69 A 8.5 x 11.0

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Planning your engineering drawing Before starting your engineering drawing you should

plan how you are going to make best use of the space. It

is important to think about the number of views your

drawing will have and how much space you will use of

the paper.

Try to make maximum use of the available space.

If a view has lots of detail, try and make that view as

large as possible. If necessary, draw that view on a

separate sheet.

If you intend to add dimensions to the drawing,

remember to leave enough space around the drawing forthem to be added later.

If you are working with inks on film, plan the order in

which you are drawing the lines. For example you don't

want to have to place your ruler on wet ink

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LINE TYPES

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Line Conventions Visible Lines solid thick lines that represent visible edges or contours

Hidden Lines short evenly spaced dashes that depict hidden features

Section Lines solid thin lines that indicate cut surfaces

Center Lines alternating long and short dashes

Dimensioning

Dimension Lines - solid thin lines showing dimension extent/direction

Extension Lines - solid thin lines showing point or line to which dimension applies

Leaders direct notes, dimensions, symbols, part numbers, etc. to features on

drawing

Cutting-Plane and Viewing-Plane Lines indicate location of cutting planes for

sectional views and the viewing position for removed partial views

Break Lines indicate only portion of object is drawn. May be randomsquiggled line or thin dashes joined by zigzags.

Phantom Lines long thin dashes separated by pairs of short dashes indicate

alternate positions of moving parts, adjacent position of related parts and

repeated detail

Chain Line Lines or surfaces with special requirements

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