Transcript Ch-4 Aspects of Technical Drawing

Chapter-4
Aspects of Technical Drawing
Technical Drawing
Learning Objectives
1.
Know the standard practices of
technical drawing
2.
Know the standard practices
for dimensioning
Know the related AutoCAD
commands for setting the
electronic drawing sheet and
plot the dimensioning
3.
Size of Drawing Sheet
(ISO A Series)
Designation
A0
A1
A2
A3
A4
A5
A6
Dimensions in
mm
841 x 1189
594 x 841
420 x 594
297 x 420
210 x 297
149 x 210
105 x 149
Dimensions in
inches
46.81 x 33.11
33.11 x 23.39
23.39 x 16.55
16.55 x 11.69
11.69 x 8.27
8.27 x 5.84
5.84 x 4.13
A0 and A1 Sheet
A2 and A3 Sheet
A4 and A5 Sheet
Relative Size of ‘A’ Series
Relative Size of ‘A’ Series
Oversize sheets are used when it is desirable to give extra
protection to the drawing sheets to provide a binding or trimming
margin. Table shows dimensions of oversize sheet.
Designation
Dimensions
RA0
860 mm x 1220 mm
RA1
610 mm x 860 mm
RA2
430 mm x 610 mm
RA3
305 mm x 430 mm
RA4
215 mm x 305 mm
RA5
153 mm x 215 mm
Dimensions of oversize sheet
Drawing Formats
•Drawing format depends upon the size of views
(2-D views or 3-D views).
•This also depends upon the user or company.
Drawing Formats
(A3 Sheet with
Landscape Mode)
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Drawing Formats
(A3 Sheet with
Portrait Mode)
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Setting limits for various sheet sizes
Before starting your engineering drawing you
should plan how you are going to make best use of
the space of drawing sheet.
Boundaries of a drawing sheet are set with
the help of LIMITS and ZOOM command in
AutoCAD. LIMITS and ZOOM command set the
drawing area to match the particular size of a
drawing sheet.
Setting limits for various sheet sizes
Command: LIMITS [Enter]
ON / OFF / <Lower left corner> <0.00, 0.00>: [Enter]
Upper right corner <12.00, 9.00>: 610, 430 [Enter]
Command: ZOOM [Enter]
All/Center/Dynamic/Extents/Previous/Scale(X/XP)/Window/<Realti
me>: A [Enter]
The change in drawing limits brought by these two
commands is not visible to the user. However, now the
graphic screen is set to align new drawing limits. While
drawing, user is always advised to zoom a particular portion
of drawing to edit or draw the entities in drawing. This is
because a normal monitor screen is used to accommodate a
larger size drawing. Now, the AutoCAD unit is matched with
drawing unit e.g. 1 AutoCAD unit = 1 mm. Accordingly,
grids can be set on the background to produce drawings
with a least count of 1 grid spacing = 1 mm.
Drawing Scale
Objects are not always drawn to their actual size.
They may be too large to fit a standard drawing sheet, or
too small for all details to clearly show.
For example, a microchip circuit must be drawn at several
thousand times its actual size to be seen. On the other
side, a plan view of a small town must be drawn with
reduced scale than the actual size.
This practice does not affect the dimensions of an object
since the actual dimensions are shown on the drawing. A
note for scale is placed on the drawing in a title block.
Drawing Scale
Type of scale
Reduction
scale
Enlargement
scale
Full scale
Recommended scale
1:10
1:2
1:5
1:100
1:20
1:50
1:1000
1:200
1:500
1:10000
1:2000
1:5000
10:1
20:1
50:1
2:1
5:1
1:1
Drawing Scale
•In AutoCAD, the scale is set by a SCALE command.
•The normal drawing file or an individual object can
be scaled to the defined scale.
Command: SCALE [Enter]
Select Objects: [select object]
Select Objects: [Enter]
Base point: [select appropriate]
<Scale factor>/Reference: (enter a scale value) [Enter]
Types of lines
Line for an outline of view
Projection line
Hidden line
Center line
Line to indicate section plane
Example for Types of Dimension Lines
Basic Types of Dimensioning
AutoCAD provides three basic modes of dimensioning:
• Linear
• Angular
• Radial
Linear Dimensioning
Baseline Option
Ordinate Option
Angular Dimensioning
Radial Dimensioning
Radial Option
Diameter Option
Title Block
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