mae dept., the chinese university of hong kong 1 introduction to engineering drawing engg1100...
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MAE Dept., The Chinese University of Hong Kong MAE Dept., The Chinese University of Hong Kong 11
Introduction to
Engineering Drawing
ENGG1100 Introduction to Engineering DesignENGG1100 Introduction to Engineering Design
Professor Yunhui LiuProfessor Yunhui Liu
Dept. of Mechanical and Automation EngineeringDept. of Mechanical and Automation Engineering
Spring, 2014Spring, 2014
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)
MAE Dept., The Chinese University of Hong Kong MAE Dept., The Chinese University of Hong Kong 22
• 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!
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.
Why ? Effectiveness of Engineering Drawing
The word languages are inadequate for describing the
sizesize, shapeshape and featuresfeatures completely as well as
concisely.
You can easily understand that …
MAE, CUHK From Lec. Bhuiyan Shameem MahmoodMAE, CUHK From Lec. Bhuiyan Shameem Mahmood
Graphic language in “engineering applications” uses
llinesines to represent the surfacessurfaces, edgesedges and contourscontours
of objects.
A drawing can be done using freehandfreehand, instrumentsinstruments or computercomputer methods.
Graphic Language
The language is known as “drawingdrawing” or “draftingdrafting” .
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Freehand drawingFreehand drawing The lines are sketched without using instruments other
than pencils and erasers.
Example
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Instrument drawingInstrument 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 drawingComputer drawing The drawings are usually made by commercial software
such as AutoCAD, SolidWorks etc.
Example
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Elements of Engineering Drawing
Engineering drawing is made up of graphics languagegraphics language
and word languageword language.
Graphics
languageDescribe a shape
(mainly by projected views).
Word
languageDescribe size, location andspecification of the object.
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Projections of the object
PROJECTION METHOD
Perspective
Oblique Orthographic
Axonometric Multiview
Parallel
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PROJECTION THEORY
The projection theory is based on two variables:
1) Line of sight
2) Plane of projection (image plane or picture plane)
The projection theory is used to graphically represent
3-D objects on 2-D media (paper, computer screen).
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Line of sightLine of sight is an imaginary ray of light between an
observer’s eye and an object.
Line of sight
Parallel projectionParallel projection
Line of sight
Perspective projectionPerspective projection
There are 2 types of LOS : parallel convergeand
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Plane of projectionPlane 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 projectionParallel projection Perspective projectionPerspective projection
Plane of projection Plane of projection
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5
Orthographic projectionOrthographic projection is a parallel projection technique
in which the parallel lines of sight are perpendicular to the
projection plane
Orthographic Projection
Object views from top
Projection plane
1
2
3
4
51 2 3 4
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ORTHOGRAPHIC VIEW
Orthographic view Orthographic view depends on relative position of the object
to the line of sight.
Two dimensions of an
object is shown.
Three dimensions of an object is shown.
Rotate
Tilt
More than one view is needed
to represent the object.
Multiview drawingMultiview drawing
Axonometric drawingAxonometric drawing15
From Lec. Bhuiyan Shameem MahmoodFrom Lec. Bhuiyan Shameem Mahmood
Multiview Projections
Project an object from six principal directions (front, back, top, bottom, right, left)
MAE Dept., The Chinese University of Hong Kong MAE Dept., The Chinese University of Hong Kong 1616
(From lecture notes of course MAEG2010)
Auxiliary Views
Used to show true dimensions of an inclined plane.
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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
MAE Dept., The Chinese University of Hong Kong MAE Dept., The Chinese University of Hong Kong 1818
Circular hole becomes ellipse.
Right angle becomes obtuse angle.
Drawing Standards
StandardsStandards 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.
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Drawing Standards
Standards on Sizes and Format of DrawingsSizes and Format of Drawings LinesLines ScalesScales Projection methodsProjection methods Presentation of view and sectionsPresentation of view and sections LetteringLettering DimensioningDimensioning …
MAE Dept., The Chinese University of Hong Kong MAE Dept., The Chinese University of Hong Kong 2020
Standard on Placement of Projected Views: First Angle Projection
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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
ISO standard
Used in Europe, etc.
(En.wikipedia.com)
Top view
Back view
Bottom view
Right view
Left view
Front view
From mytvmoments.com
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 MAE Dept., The Chinese University of Hong Kong 2222
Drawing Sheet
Trimmed paper of
a size A0 ~ A4.
Standard sheet size
A4 210 x 297
A3 297 x 420
A2 420 x 594
A1 594 x 841
A0 841 x 1189
A4
A3
A2
A1
A0(Dimensions in millimeters)
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Basic Line Types
Types of Lines AppearanceName 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
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Types of Line
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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 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
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DimensioningTwo types of dimensioning: (1) Size and location dimensions and (2) Detail dimensioning
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Units of Dimensions
Length English - Inches, unless otherwise
stated SI – millimeter, mm
Angle degrees, minutes, seconds
Angle Dimensions
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