Orthographic projection and multi-view drawing
This domain tests whether you can produce and interpret a set of related views that fully describe an object. Questions commonly give a pictorial view and ask for a front elevation, plan and end view, or ask you to identify a missing line in a supplied set.
Core rules
- Six principal views: front, top, bottom, left, right, rear. Only as many as are needed are drawn, usually three.
- First angle: the object sits between observer and plane, so the plan appears below the elevation and the left-hand view appears on the right. Third angle reverses this.
- Views align: widths project vertically, depths transfer horizontally. A 45 degree mitre line carries depth from the plan to the end view.
- Inclined faces appear foreshortened in every principal view; curved surfaces show as arcs in one view and straight lines in the adjacent ones.
- Line precedence where lines coincide: visible outline, then hidden detail, then centre line.
- Centre lines mark axes of symmetry, holes and cylinders; hidden lines are dashed thin.
Worked example
A bracket has a rectangular body 60 x 40 x 25 mm with a 20 mm square notch cut from one top corner and a 12 mm hole through the base. Draw the elevation showing the notch as a visible step. Project down to the plan, where the notch appears as a hidden line if it faces away, and the hole as a full circle with centre lines. Transfer depth with the mitre line to the end view, where the hole becomes two hidden lines 12 mm apart.
Traps
Placing the plan above the elevation while claiming first angle; omitting hidden lines for a bore; dimensioning to hidden edges; mismatched depths after projecting only part of the view; leaving out centre lines on circular features.