Basics of Engineering Graphics.

1. Lecture 3 Monday 10 December 2012 1
ENGINEERING GRAPHICS
1E7
Lecture 3: Orthographic
Projections

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Projections (1)
• Projections transform points from n
(here, n = 3) dimensional space into
a space of dimension less than n
(here, n = 2)
• Points to be considered,
– Location of object
– Location of observer
– Plane of projection
– Projectors

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Projections (2)
Projections
Parallel/ Perspective/
Cylindrical Conical
Oblique Orthographic One-Point Two-Point Three-Point
Cabinet Multi-view
Cavalier First-angle Fourth-angle Third-angle Second-angle
Other Axonometric
Isometric Di-metric Trimetric
(30°)

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Perspective Projections

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Parallel Projections

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Parallel Projections
• Projectors are parallel
to each other but not
perpendicular to
projection plane
• Effective in pictorially
representing objects

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Parallel Projections
• Projectors are
parallel to each other
and perpendicular to
the projection plane
• Effective in technical
representation of
objects

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Axonometric
The object is
tilted with all
three coordinate
axes are visible
in any one view
(PP projection plane)

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Orthographic (Orthogonal)
The object is at
rest and two
coordinate axes
are visible in any
one view
(PP projection plane)

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Multiview Projections

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Multiview Projections
• Front surfaces of object is parallel to
plane of projection
• Projectors or line of sights are
perpendicular to projection plane
• Projectors are parallel to each other
and originate from any point on object

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The six views

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Angles
• First angle projection – European
System
• Third angle projection – American
System

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Sketching Views (1)
STEP 1:
• Measure the overall
width, depth and
height of the object
Front View
Top View
STEP 2:
• Draw the construction
(thin) lines following
the number sequence
Right Side View

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Sketching Views (2)
STEP 3:
• Draw all the details
using blocks
STEP 4:
• Sketch the circles and
corners using compass

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Sketching Views (3)
STEP 4:
• Draw the centre lines,
hidden lines
•Lighten the construction lines and
thicken the final lines.

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First Angle Projection

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First Angle Projection 1
How to draw plan and elevation?

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First Angle Projection 2
How to draw end view?

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First Angle Projection 3
Points to remember:
• The ‘front view’ (or elevation) is the view
with maximum information.
•The ‘plan’ is below the ‘elevation’ (in
projection).
•The ‘end view’ is placed on the right if
viewed from left side of object and on the
left if viewed from right side.
•‘End view’ and plan face inwards from
‘elevation’.