Introduction to

Mechanical Engineering
Drawing (MIC-201)
Effectiveness of Graphics Language
1. Try to write a description of
this object.

2. Test your written description

by having someone attempt
to make a sketch from your
description.

You can easily understand that …

The word languages are inadequate for describing the
size, shape and features completely as well as
concisely.
Composition of Graphic Language
Graphic language in “engineering application” use
lines to represent the surfaces, edges and contours
of objects.

The language is known as “drawing” or “drafting” .

A drawing can be done using freehand, instruments

or computer methods.
Freehand drawing (SKETCHING)
The lines are sketched without using instruments other
than pencils and erasers.

Example

4
Instrument drawing
Instruments are used to draw straight lines, circles, and
curves concisely and accurately. Thus, the drawings are
usually made to scale.

Example

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Computer drawing
The drawings are usually made by commercial software
such as AutoCAD, solid works etc.

Example

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 Elements of Engineering Drawing
Engineering drawing are made up of graphics language
and word language.

Graphics
language
Describe a shape
(mainly).

Word
language
Describe size, location and
specification of the object. 7
 Basic Knowledge for Drafting

Graphics Word
language language

Line Projection Geometric

types method construction Lettering

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PROJECTION
METHOD

9
 What is projection?
It is a process by which images are formed
by rays of light or imaginary lines taken in a
particular direction from an object to a
picture plane.

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 PROJECTION METHOD

Perspective Parallel

Oblique Orthographic

Axonometric Multiview
(Isometric) 11
 PROJECTION THEORY

The projection theory is used to graphically represent

3-D objects on 2-D media (paper, computer screen).

The projection theory is based on two variables:

1) Line of sight
2) Plane of projection

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Line of sight is an imaginary ray of light between an
observer’s eye and an object.

There are 2 types of LOS : parallel and converge

Parallel projection Perspective projection

Line of sight
Line of sight

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Plane of projection is an imaginary flat plane which
the image is created.

The image is produced by connecting the points where

the LOS pierce the projection plane.

Parallel projection Perspective projection

Plane of projection Plane of projection

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 Disadvantage of
Perspective Projection
Perspective projection is not
used by engineer for manu-
facturing of parts, because

1) It is difficult to create.
2) It does not reveal exact
shape and size.
Width is distorted

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Orthographic
Projection
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 MEANING
Orthographic projection is a parallel projection technique
in which the parallel lines of sight are perpendicular to the
projection plane

Object views from top

1

2
1 5 2 3 4

5
3

4
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Projection plane
 ORTHOGRAPHIC VIEW
Orthographic view depends on relative position of the object
to the line of sight.
Rotate

Two dimensions of an
object is shown. Tilt
More than one view is needed
to represent the object.

Multiview drawing

Three dimensions of an object is shown.

Axonometric drawing 18
 ORTHOGRAPHIC VIEW
NOTES

Orthographic projection technique can produce either

1. Multiview drawing
that each view show an object in two dimensions.
2. Axonometric drawing
that show all three dimensions of an object in one view.

Both drawing types are used in technical drawing for

communication.

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Axonometric (Isometric) Drawing
Advantage Easy to understand

Disadvantage Shape and angle distortion

Example Distortions of shape and size in isometric drawing

Circular hole
becomes ellipse.

Right angle becomes obtuse angle.

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 Multiview Drawing
Advantage It represents accurate shape and size.

Disadvantage Require practice in writing and reading.

Example Multiviews drawing (2-view drawing)

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 Perspective Projection
• Perspective (convergent)
projection
– Projection on a picture
plane from a single
view point at a specific
viewing direction.
– mostly used in graphic
presentations but not
for engineering
drawings.
Perspective Projections
 Parallel Projections
— Projectors are parallel to
each other

— Effective in technical
representation of objects
 Orthographic (parallel) Projection

Orthographic
(parallel)
projection
– The viewing
direction is
consistent with a
principal plane
of the object.
Orthographic (parallel) Projection
 Oblique Projection
Oblique projection
– Viewing direction
is at a angle to
the three
principal planes
of the object
 Parallel Projections(Oblique)
— Projectors are parallel to
each other but not
perpendicular to projection
plane

— Effective in pictorially
representing objects
 Axonometric Projection
Axonometric
projection
– All three
principal
planes of the
object are
inclined to the
plane of
projection.
 Orthographic Projection
Orthographic projection - visualising an object
by projecting its edges at right angles onto the
projection plane.
• Orthographic projection uses three main
planes, called the principal planes of
projection
Front View - Frontal Projection
Top View - Horizontal Projection
Side View - Profile Projection
 ORTHOGRAPHIC PROJECTION

Orthographic projection is a method of producing a number of

separate two-dimensional inter-related views which are mutually
at right angle to each other.

Orthographic projection is based on :

a. two principal planes - horizontal (HP) & vertical (VP)
b. an auxiliary intersect each other forming right angles & quadrants.
 Orthographic Projections
— Orthographic Projections are a collection of 2-D
drawings that work together to give an accurate
overall representation of an object.
— Used in working drawings
The Six Principal Views or
Orthographic Views
 Which Views to Present?

General Guidelines
— Pick a Front View that is most descriptive of object
— Normally the longest dimension is chosen as the width
(or depth)
— Most common combination of views is to use:
— Front, Top, and Side View
— Any other view different from the Principal Views is
called an Auxiliary View.
 Angles

— First angle projection – European System

— Third angle projection – American System
Planes of Projection
 Orthographic Projection
— Three principal views in orthographic
projection:
— Elevation (front elevation)
— Plan
— End view (side view, side elevation)
 Orthographic projection - First angle orthographic projection
- Third angle orthographic projection
B

tion
El eva
A
First angle
VP C

D HP F
n
Pla

Third angle E
 Third Angle Projection
— Third Angle Projection - object positioned in
space in the 3rd Quadrant.
— In Third Angle projection, the planes are imagined
to be transparent and the object is viewed through
them.
— ELEVATION - projection onto vertical plane
— PLAN - projection onto the horizontal plane
— To obtain the views appear on a sheet of paper,
the horizontal plane is opened out about the
folding line.
 Introduction
Standards are set of rules that govern how technical
drawings are represented.

Drawing standards are used so that drawings convey

the same meaning to everyone who reads them.
 Drawing Sheet
A4
Trimmed paper of
a size A0 ~ A4.
A3
Standard sheet size
(ISO- A Series) A2

A4 210 x 297
A3 297 x 420 A1
A2 420 x 594
A1 594 x 841
A0 841 x 1189
(Dimensions in millimeters) A0
 Drawing Scales
Length, size
Scale is the ratio of the linear dimension of an element
of an object shown in the drawing to the real linear
dimension of the same element of the object.

Size in drawing Actual size

:
 Drawing Scales
Designation of a scale consists of the word “SCALE”
followed by the indication of its ratio, as follow

SCALE 1:1 for full size

SCALE X:1 for enlargement scales (X > 1)
SCALE 1:X for reduction scales (X > 1)

Dimension numbers shown in the drawing are correspond

to “true size” of the object and they are independent of
the scale used in creating that drawing.

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 Basic Line Types
Name according
Types of Lines Appearance
to application

Continuous thick line Visible line

Continuous thin line Dimension line

Extension line
Leader line

Dash thick line Hidden line

Chain thin line Center line

NOTE : We will learn other types of line in later chapters.

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 Meaning of Lines
Visible lines represent features that can be seen in the
current view
Hidden lines represent features that can not be seen in
the current view

Center line represents symmetry, path of motion, centers

of circles, axis of axisymmetrical parts

Dimension and Extension lines indicate the sizes and

location of features on a drawing

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Example : Line conventions in engineering drawing
 First Angle Projection
— Fist Angle Projection - object positioned in space in the
First Quadrant.
— View on the vertical plane - ELEVATION
— View on the horizontal plane -PLAN
— View projected on the profile plane -END VIEW.
— To obtain the views as they would appear on a sheet of
paper,
Ø Horizontal plane is opened out about the intersection of the
planes.
Ø line of intersection is called the XY line, ground line or folding
line.
— Relative position of the three principal views:
END VIEW ELEVATION END VIEW

PLAN
First Angle Projection
Example

Vi
ew
in
g
Di
re
c tio
n
Elevation

El
ev
at
io
n
Elevation

Plan

Plan

El
ev
at
io
n
Elevation End View 1

Plan

Plan

w 1 El
Vi e ev
d at
En io
n
 End View 2 Elevation End View 1

Plan
2
w
d Vie
En
First angle Plan
orthographic projection

i ew1 El
ev
ndV at
io
E n
 First Angle Projection

Bottom Bottom

Rear Left

Right Front Left Rear

Top
Third Angle Projection
Third Angle Projection
 Third Angle Projection

Top Top

Front Right

Rear Left Front Right

Bottom
Frontal Plane (Vertical Plane) ORTHOGRAPHIC PROJECTION

F PP PATTERN OF PLANES & VIEWS (First Angle Method)

P Y A) HP IS ROTATED 900 DOWNWARD

B) PP, 900 IN RIGHT SIDE DIRECTION.
THIS WAY BOTH PLANES ARE BROUGHT IN THE SAME PLANE CONTAINING FP.
X
Horizontal Plane (Top Plane)
HP

FP PP
Y
FV LSV

X Y
X TV

HP

ACTUAL PATTERN OF PLANES & VIEWS

HP IS ROTATED DOWNWARD 900 PP IS ROTATED IN RIGHT SIDE 900 OF ORTHOGRAPHIC PROJECTIONS
AND AND DRAWN IN
BROUGHT IN THE PLANE OF FP. BROUGHT IN THE PLANE OF FP. FIRST ANGLE METHOD OF PROJECTIONS
SHOWN BELOW IS A SHAPED BLOCK POSITIONED IN
SPACE IN THE FIRST QUADRANT (1ST ANGLE)
PLAN VIEW

ELEVATION VIEW
END VIEW
How to draw plan and elevation?
Example

Projection of Front View

 First Angle Projection

Projection of top view

Projection of left side view
Placement of the six principal
views in 1st angle projection
Glass Box Model(First Angle Projection)
B.V

R.S.
V
F.V

F.V

R.S.
V

T.V

Transparent (glass) box model

T.V
REA
F.V - FRONT VIEW R
T.V – TOP VIEW

B.V – BOTTOM VIEW Opening of the glass box

L.S.V – LEFT SIDE VIEW

R.S.V – RIGHT SIDE VIEW

 First Angle Projection

B.V

F.V

R.S.V L.S.V REAR

T.V

Placement of the six principal views in

1st angle projection
First Angle Projection
THANK YOU

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