ENGG1100 Introduction to Engineering Design
Introduction to
Engineering Drawing
Professor Yunhui Liu
Dept. of Mechanical and Automation Engineering
Spring, 2014
MAE Dept., The Chinese University of Hong Kong
1
What is Engineering Drawing?
 An engineering drawing is a type of technical
drawing used to fully and clearly define
requirements for engineered items (from
en.wikipedia.org)
• a formal and precise way (graphic
language) for communicating
information about the shape and size of
physical objects.
• a mean for specifying the precision of
physical objects.
Important as it is a legal document, i.e., if
the drawings are wrong, it is the fault of the
engineers!
MAE Dept., The Chinese University of Hong Kong
2
Why ? Effectiveness of Engineering Drawing
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.
MAE, CUHK
From Lec. Bhuiyan Shameem Mahmood
Graphic Language
Graphic language in “engineering applications” uses
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.
From Lec. Bhuiyan Shameem Mahmood
5
Freehand drawing
The lines are sketched without using instruments other
than pencils and erasers.
Example
From Lec. Bhuiyan Shameem Mahmood
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Instrument drawing
Instruments are used to draw straight lines, circles, and
curves concisely and accurately. Thus, the drawings are
usually made to scale.
Example
From Lec. Bhuiyan Shameem Mahmood
7
Computer drawing
The drawings are usually made by commercial software
such as AutoCAD, SolidWorks etc.
Example
From Lec. Bhuiyan Shameem Mahmood
8
Elements of Engineering Drawing
Engineering drawing is made up of graphics language
and word language.
Projections of the object
Graphics
language
Describe a shape
(mainly by projected views).
Word
language
Describe size, location and
specification of the object.
From Lec. Bhuiyan Shameem Mahmood
9
PROJECTION METHOD
Perspective
Parallel
Oblique
Axonometric
From Lec. Bhuiyan Shameem Mahmood
Orthographic
Multiview
10
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 (image plane or picture plane)
From Lec. Bhuiyan Shameem Mahmood
11
Line of sight
is an imaginary ray of light between an
observer’s eye and an object.
There are 2 types of LOS :
Parallel projection
parallel and converge
Perspective projection
Line of sight
Line of sight
From Lec. Bhuiyan Shameem Mahmood
12
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
From Lec. Bhuiyan Shameem Mahmood
13
Orthographic Projection
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
Projection plane
From Lec. Bhuiyan Shameem Mahmood
14
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
From Lec. Bhuiyan Shameem Mahmood
15
Multiview Projections
 Project an object from six principal directions (front, back,
top, bottom, right, left)
(From lecture notes of course MAEG2010)
MAE Dept., The Chinese University of Hong Kong
16
Auxiliary Views
 Used to show true dimensions of an inclined plane.
From Lec. Bhuiyan Shameem Mahmood
17
Isometric Drawing
• Represent 3-D objects by a 2D view in the projection in
which the coordinate axes appear equally foreshortened.
• It is easy to understand the 3-D shape
• However, the projection causes shape and angle distortions
Circular hole
becomes ellipse.
Right angle becomes obtuse angle.
MAE Dept., The Chinese University of Hong Kong
18
Drawing Standards
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.
From Lec. Bhuiyan Shameem Mahmood
19
Drawing Standards
 Standards on








Sizes and Format of Drawings
Lines
Scales
Projection methods
Presentation of view and sections
Lettering
Dimensioning
…
MAE Dept., The Chinese University of Hong Kong
20
Standard on Placement of Projected Views:
First Angle Projection
ISO standard
Used in Europe, etc
From mytvmoments.com
Directly project images
along the line of sight
- Front view is put at the
middle
- Top view is put at the
bottom
- Right view is put on the left
Bottom view
Left view
Right view
(En.wikipedia.com)
Back view
Front view
Top view
21
Standard on Placement of Views:
Third Angle Projection

The positions of the viewpoint and location of the projection view are
the same




Right side view is located at right
Left side view is located at left
…
Mainly used in US
MAE Dept., The Chinese University of Hong Kong
22
Drawing Sheet
Trimmed paper of
a size A0 ~ A4.
A4
A3
Standard sheet size
A4
210 x 297
A3
297 x 420
A2
420 x 594
A1
594 x 841
A0
841 x 1189
A2
A1
A0
(Dimensions in millimeters)
From Lec. Bhuiyan Shameem Mahmood
23
Basic Line Types
Types of Lines
Appearance
Name according
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
From Lec. Bhuiyan Shameem Mahmood
24
Types of Line
25
From Lec. Bhuiyan Shameem Mahmood
Alphabet of Lines
Visible lines
Hidden lines
Center line
Break line
Dimension & extension lines
Section lines
Cutting plane lines
Phantom lines
From MAE 2010
Line Conventions
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
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
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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 random “squiggled”
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
27
From Lec. Bhuiyan Shameem Mahmood
Dimensioning
Two types of dimensioning: (1) Size and location
dimensions and (2) Detail dimensioning
From Lec. Bhuiyan Shameem Mahmood
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Units of Dimensions
Angle Dimensions
 Length
 English - Inches, unless otherwise
stated
 SI – millimeter, mm
 Angle
 degrees, minutes, seconds
From Bhuiyan Shameem Mahmood
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