1. Dept. of Mechanical and Automation Engineering
2017/4/20
ENGG1100 Introduction to Engineering Design
Introduction to
Engineering Drawing
Professor Yunhui Liu
Dept. of Mechanical and Automation Engineering
Spring, 2014
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MAE Dept., The Chinese University of Hong Kong

2. 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

4. 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

5. 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

6. Bhuiyan Shameem Mahmood Ebna Hai
Freehand drawing
The lines are sketched without using instruments other than pencils and erasers.
Example
From Lec. Bhuiyan Shameem Mahmood
AE Dept. MIST

7. From Lec. Bhuiyan Shameem Mahmood
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

8. From Lec. Bhuiyan Shameem Mahmood
Computer drawing
The drawings are usually made by commercial software such as AutoCAD, SolidWorks etc.
Example
From Lec. Bhuiyan Shameem Mahmood

9. Elements of Engineering Drawing
2017/4/20
Elements of Engineering Drawing
Engineering drawing is made up of graphics language
and word language.
Graphics
language
Describe a shape (mainly by projected views).
Projections of the object
Word
language
Describe size, location and specification of the object.
From Lec. Bhuiyan Shameem Mahmood

10. PROJECTION METHOD Perspective Parallel Oblique Orthographic
Axonometric
Multiview
From Lec. Bhuiyan Shameem Mahmood

11. Bhuiyan Shameem Mahmood Ebna Hai
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
AE Dept. MIST

12. Perspective projection From Lec. Bhuiyan Shameem Mahmood
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
From Lec. Bhuiyan Shameem Mahmood

13. Perspective projection From Lec. Bhuiyan Shameem Mahmood
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

14. 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

15. 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

16. Multiview Projections
2017/4/20
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

17. Auxiliary Views Used to show true dimensions of an inclined plane.
From Lec. Bhuiyan Shameem Mahmood

18. 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

19. 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

20. 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

21. Standard on Placement of Projected Views: First Angle Projection
ISO standard
Used in Europe, etc.
Top view
Back view
Bottom view
Right view
Left view
Front view
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
(En.wikipedia.com)

22. 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

23. (Dimensions in millimeters)
Drawing Sheet A4
Trimmed paper of
a size A0 ~ A4. A3
Standard sheet size
A x 297
A x 420
A x 594
A x 841
A x 1189 A2 A1 A0
(Dimensions in millimeters)
From Lec. Bhuiyan Shameem Mahmood

24. From Lec. Bhuiyan Shameem Mahmood
Basic Line Types
Name according
to application
Types of Lines
Appearance
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

25. Types of Line
From Lec. Bhuiyan Shameem Mahmood

26. Alphabet of Lines Visible lines Hidden lines Center line Break line
Dimension & extension lines
Section lines
Cutting plane lines
Phantom lines
From MAE 2010

27. 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 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
From Lec. Bhuiyan Shameem Mahmood

28. Dimensioning
Two types of dimensioning: (1) Size and location dimensions and (2) Detail dimensioning
From Lec. Bhuiyan Shameem Mahmood

29. Bhuiyan Shameem Mahmood Ebna Hai
Units of Dimensions
Angle Dimensions
Length
English - Inches, unless otherwise stated
SI – millimeter, mm
Angle
degrees, minutes, seconds
Instructor:
While most construction of buildings and roads is done in feet and tenths of a foot, architects are working in feet and inches. A mechanical or industrial engineer may be building products that have both inches and mm.
From Bhuiyan Shameem Mahmood
AE Dept. MIST