JSS3: BASIC TECHNOLOGY  1ST TERM

Materials & Processing  Timber I  Week 15 Topics1 Quiz

Materials & Processing  Timber II  Week 23 Topics1 Quiz

Processing of Materials  Metals  Week 35 Topics1 Quiz

Processing of Clay, Ceramics and Glass  Week 45 Topics1 Quiz

Methods of Producing Plastics & Rubber  Week 52 Topics1 Quiz

Drawing Practice  Isometric Drawing  Week 64 Topics1 Quiz

Oblique Projection  Week 72 Topics1 Quiz

Orthographic Projection  Week 84 Topics1 Quiz

Perspective Drawing (One  Point Perspective Drawing)  Week 94 Topics1 Quiz
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Principal Planes of Orthographic Projection
Orthographic projection uses two main planes called the principal planes of projection, they are the vertical plane planes and the horizontal planes.
These two planes intersect, producing four quadrants. The object to be drawn is imagined to be placed in one of these quadrants, and orthographic views of it are projected onto the planes.
The object is normally positioned so that its main faces are parallel to them. This ensures that views of the faces are true sizes and shapes.
Principal Planes of Projection:
1. Vertical Plane: The views on the vertical plane are front elevation and end elevation (side elevation).
2. Horizontal plane: The plan is shown on the horizontal plane.
The figure above shows the intersection of the vertical and horizontal planes at right angles. This intersection forms four angles, the first angle, second angle, third angle, and fourth angle.
The quadrant 0 – 90Â° contains the first angle and the quadrant 180Â° 270Â° contains the third angle.
In orthographic projection, only the first and third angles are used.
Since the second and fourth quadrants would combine the two systems, we do not use them.
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