Bridge CourseIntroduction TO ENGINEERING ( MECHANICAL ENGINEERING )

GUJARAT TECHNOLOGICAL UNIVERSITY

Introduction

Engineering Graphics is a language of communication between engineers on international basis.

The beauty of this tool of communication is that it transfers 100% information between technical peoples.

Graphical presentation is more than an essay for describing the same thing.

Drawing Instruments

and simple geometry

Instruments for DrawingFollowing drawing instruments are required for preparing a neat and correct drawing.

Basic Instruments.

(i)        Drawing board           (ii)        Drawing sheet (iii)       Drawing pencil        (iv)       Drawing clips (v)        Eraser                        (vi)       Eraser shield

Instruments for Drawing Straight Lines. (i)         T- square.                              (ii)        Set- squares

 Instruments for Drawing Curved Lines. (i)         Large size compass          (ii)        Small bow (iii)       French curve

  Instruments for Measuring Distance.   (i)         Large size divider            (ii)        Small bow divider   (iii)       Scales

 Instruments for Measuring Angles.         (i)         Protractors                           (ii)        Set-squares

 Special Tool.            Mini drafter

Fig. 1 The top surface of the board is perfectly smooth and level. Fig. 2 Bottom of the drawing board. A drawing board is rectangular in shape and is made of well seasoned soft wood such as oak or pine. A straight ebony edge is fitted on the left side on the board against which the head of the T- square moves…

Fig. 1  Drawing Board (Top)              Fig. 2 Drawing Board (Bottom)

Drawing Board 

Mini drafter

  T- Square It is composed of a long strip called blade, which is screwed rigidly at right angle to a shorter piece called head or stock.  It is made of mahogany or pear wood, which is harder than the board wood. The head also has an ebony edge which slides against the working edge of the board. T- Square is used for making horizontal, vertical, inclined or parallel lines on the drawing sheet. 

How to Clamp Paper to Drafting Board Using Clips

1. Place the paper close to the table’s left edge.

2. Move the paper until its lower edge place about the top edge of T-

square.3. Align the top edge of the paper with T-square blade.

4. Attach the paper’s corners with tape/clips .

5. Move T-square down to smooth the paper.

6. Attach the remaining paper’s corners with tape/clips.

Clips

Neatness, quality and accuracy of the drawing greatly depends upon the type and conditions of the pencil used for drawing.

(a)          Hard               :           9H to 4H(b)          Medium       :           3H to B (3H, 2H, H, F, HB and B)(c)          Soft                 :           2B to 7B

Following pencils should be used for drawing work in class:

2H Pencil - For drawing outlines, Centre lines, Break lines, etc.

H Pencil   -  For dimensioning, arrowheads, hatching lines, lettering, sketching, circles, arcs, etc.

Micro tip pencil - 0.5mm for drawing outlines and 0.8mm for shading and sketching           

Drawing Pencil. 

ISO A Drawing Sizes (mm)

A4 210 X 297

A3 297 X 420

A2 420 X 594

A1 594 X 841

A0 841 X 1189

Sizes of drawing sheet typically comply with either of two different standards, ISO (World Standard) or ANSI/ASME Y14 (American), according to the following tables:

ISO paper sizes

1. Start circle. Apply enough pressure to the needle,

holding compass handle between thumb and index

fingers.

2. Complete circle. Revolve handle clockwise.

Using the Compass

Using a Circle Template1. Draw two perpendicular lines that pass through center

of a circle to be drawn.

2. Place the template till all marking coincide with center

lines.

3. Tracing the circle. (Hold the pencil normal to the paper.)

Center of a circle to be drawn

Draw a Horizontal Line

1. Press the T-square head against the left edge of the table.

2. Smooth the blade to the right.

Draw a Horizontal Line3. Lean the pencil at an angle about 60o with the paper in the

direction of the line and slightly “toed in”.

4. Draw the line from left to right while rotating the pencil

slowly.

Draw a line at 45o with horizontal

2. Draw the line in the direction as shown below.

1. Place 45o triangle on the T-square edge and press them

firmly against the paper.

A

B

Draw the line passing throughtwo given points

1. Place the pencil tip at one of the points.

2. Place the triangle against the pencil tip.

A

B

Given

3. Swing the triangle around the pencil tip

until its edge align with the second point.

4. Draw a line.

Applied Geometry

To Bisect a Line

1. Swing two arcs of any radius greater than half-length of

the line with the centers at the ends of the line.

2. Join the intersection points of the arcs with a line.

(not to scale)

A

B

r1

Given

A

B

r1

3. Locate the midpoint.

To Bisect an Angle

2. Swing the arcs of any radius from the intersection

points between the previous arc and the lines.

3. Draw the line.

1. Swing an arc of any radius whose centers at the vertex.

(not to scale)

r1

Given

A

B

C

A

B

C

r2

r2

PROBLEM :

To make 12 equal parts of circle.

2

3

5

4

67

8

9

10

11

121

PROBLEM :

To make 08 equal parts of circle.

3

2

8

7

4

5

6

1

PROBLEM : To make 12 equal parts of line.

1

3’2’1’

10’9’8’7’6’5’4’

0

12’11’

2 3 4 5 6 7 8 9 10 11 12

How to Keep Your Drawing CleanDo Don’t

Dimensioning and geometrical construction

Dimensioning componentsExtension lines

Dimension lines(with arrowheads)

Leader lines

Dimension figures

Notes :

- local note

- general note

Drawn with4H pencil

Lettered with2H pencil.

indicate the location on the object’s features that are dimensioned.

Extension lines

Dimension linesindicate the direction and extent of a dimension, and inscribe dimension figures.

10 27

43

13123

o

indicate details of the feature with a local note.

Leader lines

10 27

43

13123

o

10 Drill, 2 Holes

R16

30

30

30

30

30

3030

30

EXAMPLE : Dimension of length using aligned method.

30

30

30

30

3030

30

30

EXAMPLE : Dimension of length using unidirectional method.

Introduction to Orthographic

Projection

ORTHOGRAPHIC PROJECTIONS

CONCEPT OF 1ST AND 3RD ANGLE PROJECTION METHODS

Projection systems

1. First angle system

2. Third angle system

First Quadrant

ThirdQuadrant

- European country

- ISO standard India

- Canada, USA,

Japan, Thailand

Orthographic projection1st angle system 3rd angle system

Orthographic views1st angle system 3rd angle system

Foldingline

Foldingline

Foldingline

Foldingline

Orthographic views

1st angle system 3rd angle system

Front View

Front View

Right Side View

Right Side View

Top View

Top View

First angle system

Third angle system

Projection symbols

prepare Orthographic views (First angle method) for the parallel key from the isometric drawing as below

Given Iso. view

Orthographi

c views

prepare Orthographic views (First angle method) from the isometric drawing as below

Given Iso. view

Orthographic views

Given Iso. view

prepare Orthographic views (First angle method) from the isometric drawing as below

Orthographic views