ZIMSEC O Level · Technical Graphics and Design · Form 2, Form 3, Form 4
Orthographic projection shows an object as separate two-dimensional views drawn to scale: front elevation, end elevation and plan.
First angle projection
- The plan is drawn BELOW the front elevation.
- The view from the left is drawn on the RIGHT of the front elevation (and vice versa).
Third angle projection
- The plan is drawn ABOVE the front elevation.
- The view from the left is drawn on the LEFT of the front elevation.
Rules
- Views line up with each other using thin projection lines.
- Heights are the same in front and end views; lengths in front view and plan; widths in plan and end view (transfer with a 45° line or compasses).
- Show hidden edges with dashed lines and centre lines through holes and curves.
- Draw the projection symbol in the title block.
Auxiliary views
Show the true shape of a sloping surface by projecting at right angles to it.
Exam tip: Before drawing, decide which direction is the front view and mark arrows on the pictorial – it prevents views in the wrong places.
Check yourself
- In first angle projection, where is the plan placed?
- Which dimensions are shared by the front elevation and the plan?
- How is a hidden edge shown?
Show answers
- Below the front elevation.
- Lengths (widths across the page).
- With a thin short-dashed line.
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