Lecture 3 Friday 21 April 2023 1

ENGINEERING GRAPHICS1E7

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/Cylindrical

Perspective/Conical

Oblique Orthographic One-Point Three-PointTwo-Point

Cabinet

Other

Cavalier

Multi-view

Axonometric

First-angle Fourth-angle Third-angle Second-angle

Isometric (30°)

Di-metric Trimetric

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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)

• Measure the overall width, depth and height of the object

STEP 1:

• Draw the construction (thin) lines following the number sequence

STEP 2: Top ViewFront View

Right Side View

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Sketching Views (2)

• Draw all the details using blocks

STEP 3:

• Sketch the circles and corners using compass

STEP 4:

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Sketching Views (3)

• Draw the centre lines, hidden lines

STEP 4:

•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’.