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LECTURE 1ENGINEERING GRAPHICS 232
Fundamentals of Engineering Drawing
Introduction
Engineering graphics is is a graphical communication language of engineers, a system of communication, which employs lines,
characters and symbols to represent three-dimensional objects two-dimensionally
used to represent initial concepts and final working drawings
Methods for producing engineering drawings: Sketching Manual Drafting Computer-Aided Drafting / Drawing (CAD)
Sketching/freehand drawing
is one of the quickest ways to graphically express ideas, concepts and designs.
is an integral part of the design and development process.
Materials required for sketching Sketching paper(Graph paper) Lead pencils and erasers Trigonometry set (compass, triangles and ruler) Templates (circles, curves)
Manual Drafting
is created on a paper or polyester film using manual drawing instruments and equipment.
Instruments used Drawing board and T-square or Drafting machine Compass set squares ( 45, 30-60) Protractor Lead pencils Eraser
Widely replaced by CADD in industry
Fig. 1 Manual drafting equipments
Fig. 1 Manual drafting equipments cont’d
Computer-Aided Drafting/Drawing
includes 2D projections and 3D solid modelling.
Some of popular software used for drawing and design of products are: AutoCAD and Inventor (Autodesk, Inc.). CATIA (Dassault Systems) MicroStation (Bentley Systems, Inc.) SolidWorks (SolidWorks Corporation, InterCAD) Solid Edge (UGS, The PLM Company) ArchiCAD Design / Building Series (GraphiSoft)
Drawing Standards
Importance of drawing standardsISO standardAustralian Standard related to engineering
drawing:
Basics of Engineering Drawing
Drawing sheets
Sizes: Factors that affect the selection of drawing sheets size
includes: the complexity of drawing, amount of information contained and the drawing equipment.Table 1: Dimensions of preferred sheets
Layout
Fig 2. Layout of a drawing sheet for detail drawing
Layout
Fig 3. Layout of a drawing sheet for assembly drawing
Borders/Frames
The drawing area on a drawing sheet is enclosed by a border (frame).
Borders/Frames
Table 2: Dimensions for drawing frames and margins
Elements of a drawing sheet
1. Title BlockIts recommended position is in the lower right-
hand corner. It is also allowed to be placed in the upper-right
hand corner if required. The contents of a title block include
drawing identification, company name, confidential statement, sheet size, scale, drafter and engineer’s names, and history of construction and revisions etc.
Recommended dimensions of title blocks
Fig 4. Title blocks for various size sheets
LOCATION INFORMATION
A Name of company, e.g. Curtin University, ABC Engineering, etc.
B Title of drawing, e.g. Crank shaft, bearing pedestal etc.
C Drawing identification number
D Information regarding drawing preparation, e.g. names / signatures of drafter, checker and approver, etc.
E Code identification number of the design authority (if needed)
F Drawing sheet size
G Scale of drawing, e.g. SCALE 1:1, SCALE 1:2, SCALE 5:1, etc
H Miscellaneous information
…. More blocks can be added for general information, such as tolerancing and finishing notes
Table 3: Location of contents of a title block
Elements of a drawing sheet
2. System of Projection: Method of project must be shown in a prominent
position. It could be an appropriate projection symbol or
words .
Fig 5: Method of projection a) third angle projection, b) first angle projection
a b
Elements of a drawing sheet
3. Prohibition of Scaling: Scaling dimensions directly from a drawing is extremely dangerous
and must be prohibited using the phrase “DO NOT SCALE”.
4. Dimensional Units: The correct dimensional units must be indicated on a drawing. For
metric units, this is done by including the phrase “ALL DIMENSIONS IN MILLIMETRES”.
5. Drafting Standard: Conformance to the particular edition of a drafting standard should
be shown. For example, DRAFTING STANDARD AS 1100 – 1992
6. Other Information: Where it is appropriate, space in the area to the left of title block
should be provided for other relevant information such as tolerance notes, heat treatment and machining requirements etc.
Drawing Scale
Why scale?Types of scale1. Full Size:
In this case, the drawing size is equal to the size of the object. This scale is indicated as SCALE 1:1.
2. Reduction Ratios (Scaling down): In this case, the drawing size is smaller than the size of
the object.
3. Enlargement Ratios (Scaling up): In this case, the drawing size is greater than the size of
the object. For small objects, drawn using large scales, a full-size view of the object should be added to the drawing.
Drawing Scale
recommended scales for mechanical engineering drawings are shown below.
Table 4: Engineering drawing scales
Full size and enlargement ratios
5:1 2:1 10:11:1
Reduction ratios
1:2 1:2.5 1:5 1:10
1:20 1:25 1:50 1:100
1:200 1:250 1:500 1:1 000
1:2 000 1:2 500 1:5 000 1:10 000
1:25 000 1:50 000 1:100 000
Drawing Scale
Indicating scale on drawingThe scale of a drawing should be shown by:
Block or graduated scale The “SCALE” word followed by the ratio. For
example, SCALE 1:100. “NOT TO SCALE” words in or near the title block or a
diagonal line through the space reserved for the indication of scale ratio specifies that the drawing is not drawn to any consistent scale.
NOTE: Regardless of the scale used, the actual values of dimensions are indicated on the drawing.
Line styles and application
Lines on a drawing illustrate the shape and size of objects that will later become real parts.
A particular line type is defined by two essential features shape of the line, and thickness (or line weight) of the line.
Fig 6: Commonly used line types
Note that:• Lines on drawing sheets
should be clear, uniform in thickness, dark and must be of a quality that reproduces easily.
• There should be no variation in darkness
Fig 7: Definition and application of the standard line types
Fig 7: Definition and application of the standard line types cont’d
Line styles and application cont’d
Notes on definition and application of the standard line types (Fig 7):
1. It is desired to restrict line thickness to two on any one drawing. A medium thickness line may be used by some drafting disciplines.
2. It is recommended that only one thickness of dashed line be used.
3. Proportion of spaces is as specified for type G. Order of Precedence
Visible outlines and edges Hidden lines Cutting plane lines Centre line Centroidal lines Projection lines
Fig 8: Application of Line types
Fig 9: Poor definition of line types
Letters and Numbers
Letters and numbers are used to represent notes, dimensions, and specifications, which can not be represented graphically.
According to AS 1100.101, the basic form of letters and characters on a drawing should be similar to either Gothic or ISO Type B character sets.
Upper case letters should be used except for conventional applications such as mm, kg etc.
Only one style of characters should be used through a drawing
Vertical characters should be used for titles, drawing and reference numbers
Fig 10: Lettering and numerals suggested by Standards Australia
References: Lecture Note- week 1 Fundamentals of Engineering
Drawing
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