INTRODUCTION TO ENGINEERING

GRAPHICS

Prepared By:-Sagar Patel

CONTENTS DRAWING INSTRUMENTS SHEET LAYOUT SCALES LINES

INTRODUCTION Engineering drawing is a technique of creating graphical

representation that contains all necessary information such as dimensions, specifications and notes, using which an abstract concept can be transformed into real world object. Application of engineering drawing are valid for e.g.: Shipping industry, manufacturing, construction and many more.

Some important concept of engineering drawing is like projection. The word projection means to throw forward. It is a process of plotting an object in an imaginary plane. Projection has two types:

1. Parallel projection2. Perspective projection Each of these has further subtypes.

DRAWING INSTRUMENTS1. Drawing paper: The size of drawing paper should be

less than drawing board and paper should be fixed properly.

2. Drawing board: It is a plane and smooth surface use for drawing purpose.

3. T-square: It is a T shape drawing tool whose edge slide along width of drawing board with the help of stop. It is useful in drawing straight line.

4. Compass: It is used for drawing circles and arcs. The divider is little different with both legs made of steel and use for transferring distance.

DRAWING INSTRUMENTS5. French Curves: They are used to draw irregular

curves such as ellipse, hyperbola and parabola.6. Drafter: It is useful tool for drawing parallel lines at

any inclination. It has scale as well as protractor inbuilt.7. Protractor: It is use to measure and layout angles.8. Set Square: It is also known as triangle. They comes

in flavors of 30, 60, 30 and 45, 90, 45.

DRAWING INSTRUMENTS

Typical Drawing Equipment

Objectives in Drawing

1. Accuracy

2. Speed

3. Legibility

4. Neatness

DRAFTER It is useful tool for drawing parallel lines at any

inclination. It has scale as well as protractor inbuilt.

FRENCH CURVES They are used to draw irregular curves such as

ellipse, parabola and hyperbola.

DRAWING BOARDDrawing Boards

The left edge and right edge of a drawing board has a true straight edge.

For right-handed people, the left-hand edge of the board is called the working edge because the T-square head slides against it.

For left-handed people, the right-hand edge of the board is called the working edge because the T-square head slides against it.

T-Squares

The T-square is made of a long strip called the blade, fastened at right angles to a shorter piece called the head.

T-SQUAREThe drawing paper should be placed close to the working edge of the board to reduce any error resulting from the bending of the blade of the T-square.

The paper should also be placed close enough to the upper edge of the board to permit space at the bottom of the sheet for using the T-square.

Drafting tape is used to fasten the drawing paper to the drawing board.

DRAWING PENCILSDrawing Pencils

High-quality drawing pencils should be used in technical drawing, never ordinary writing pencils.

Many makes of mechanical pencils are available together with refill leads in all grades. Choose a mechanical pencil that feels comfortable in your hand.

DRAWING LEADSDrawing Leads

The first consideration in the selection of a grade of lead is the type of line work required. For light construction lines and guide lines for lettering use a hard lead. For all other line work, the lines should be BLACK. The lead chosen should be soft enough to produce jet black lines but hard enough not to smudge.

HARD MEDIUM SOFT

9H 8H 7H 6H 5H 4H 3H 2H H F HB B 2B 3B 4B 5B 6B 7B

Hard leads are used where extreme accuracy is required. Generally these leads are used for construction lines.

Medium leads are used for general purpose line work in technical drawing.

Soft leads are used for various kinds of art work. These leads are too soft to be useful in mechanical drafting.

SET SQUARETrianglesMost inclined lines are drawn at standard angles using the 45º x 45º triangle and the 30º x 60º triangle.

In addition to drawing angles of 90º, 45º, 30º, and 60º, triangles can be combined to draw angles of 15º increments.

COMPASSGiant Bow Sets

Giant bow sets contain various combinations of instruments.

Giant Bow Compass

The giant (large) bow compass has a center wheel and can be adjusted simply by opening or closing the legs of the compass while turning the center wheel.

SCALEScalesScales are instruments used in making technical drawings full size or at a given reduction or enlargement.

Types of scales include metric scales, engineers’ scales, decimal scales, mechanical engineers’ scales, and architects’ scales.

Scales are usually made of plastic or boxwood and are either triangular of flat in shape.

SHEET LAYOUT Sheet size: The preferred

sizes of drawing sheet as recommended by the bureau of Indian standards are given below as per SP:46(2003).

Sheet Designation Trimmed size (mm)

Untrimmed size (mm)

A0 841*1189

880*1230

A1 594*841

625*880

A2 420*594

450*625

A3 297*420

330*450

A4 210*297

240*330

A5 148*210

165*240

SHEET LAYOUT Margin: Margin is provided in the drawing sheet by

drawing margin lines. Prints are trimmed along this lines. Border lines: Clear working space is obtained by

drawing border lines. More space is kept on the left-hand side for the purpose of filling or binding if necessary.

Borders and frames: SP:46(2003) recommends the borders of 20mm width for the sheet sizes A0 and A1, and 10mm for sizes A2, A3, A4 and A5.

SHEET LAYOUT Title Block: Space for title

block must be provided in the bottom right-hand corner of the drawing sheet. The size of the title block as recommended by the B.I.S is 185mm*65mm for all designations of the drawing sheet. All title blocks should contain at least the particulars as shown in the figure:

SCALES A scale is defined as the

ratio of the linear dimensions of element of the object as represented in a drawing to the actual dimensions of the same element of the object itself.

The scales generally used for general engineering drawings are:

1) Reducing scales

1:2 1:10 1:5

1:20 1:50 1:100

1:200 1:500 1:1000

1:2000

1:5000

1:10000

2) Enlarging scales

50:1 20:1 10:1

5:1 2:1

3) Full size scales

1:1

SCALES Representative fraction: The ratio of length

of the object represented on drawing to the actual length of the object represented is called RF.

If RF>1 then the drawing is enlarged. If RF<1 then the drawing is reduced view. The different types of scales are:1. Plain scale2. Diagonal scale3. Comparative scale4. Vernier scale5. Scale of chords

LINES Lines are predominant and fundamental drawing

element in every drawing. Various types of lines are used to represent different

objects like visible lines are used for drawing outlines of visible edges and surface line which represent the object. These are drawn in bold dark and continuous lines.

Hidden lines are shown with medium thick lines consisting of short dashes and use to represent invisible ages and surface boundary.

Centre lines are thin lines drawn with ultimate long dashes and dots and are used for representing symmetrical objects. Then there are dimension and cutting lines.

Main Line Types

Lines

Hidden Lines

Center Lines

Dimension Lines

Extension Lines

Leader LinesCutting Planes

Section Lines

Phantom Lines

Viewing Planes

Break Lines

Visible Lines

LINES

Cutting Plane Lines

• Thick broken line that is terminated with short 90 degree arrowheads.

• Shows where a part is mentally cut in half to better see the interior detail.

Extension Lines• Thin lines used to establish the extent of a dimension.• Can also be used to show extension of a surface to a

theoretical intersection as shown in (b).• Begin 1.5mm from the object and extend to 3mm

beyond the last dimension.• They should not cross dimension lines.

Dimension Lines• Thin lines capped on the ends with arrowheads and

broken along their length to provide a space for the dimension numeral.

• They indicate length.

Center Lines• Thin line consisting of alternating long and short

dashes.• Used to represent the center of round or cylindrical

features, or the symmetry of a feature.

Section Lines

• Thin line usually drawn at a 45 degree angle.• Indicates the material that has been cut through in a

sectional view.

Section Line

Hidden Lines• Light, narrow, short, dashed lines.• Shows the outline of a feature that can not be seen in

a particular view.• Used to help clarify a feature, but can be omitted if

they clutter a drawing.

Visible/Object Lines• Dark, heavy lines.• Used to represent the outline or contour of the object

being drawn.• Define features you can see in a particular view.