Technical drawing, communication and CAD
What this domain tests
Drawing questions test standard conventions, spatial reasoning and the ability to specify a part so it can be made without asking questions.
Conventions
- Line types: continuous thick for visible outlines, dashed for hidden detail, chain thin for centre lines, thin continuous for dimension and projection lines.
- Projection: first-angle (European, usual in Malta) puts the plan below the front view and the view from the left on the right. Third-angle puts the plan above the front view and the left view on the left.
- Isometric: axes at 30° to the horizontal, vertical lines vertical, true lengths along the axes.
- Dimensioning: millimetres without units, dimension lines parallel to the feature, projection lines from the feature, arrowheads touching, no duplicated or closed dimensions, smallest dimensions nearest the outline.
- CAD: parametric sketches, constraints, layers, orthographic views generated from a 3D model, dimensions linked to geometry; export DXF for CAM.
Worked example
A rectangular plate 60 × 40 × 10 mm with one 10 mm hole, 15 mm from the left edge and 20 mm from the bottom edge. In first-angle projection, draw the front view (60 × 10) with the hole as hidden lines, the plan below (60 × 40) with the hole as a circle, and dimension the overall 60 and 40 once, the thickness once, and the hole position from the two datum edges. The hole diameter is given once as Ø10. The reasoning: dimensions are taken from datums, not from each other, so errors cannot accumulate.
Traps
- Putting the plan above the front view in first-angle.
- Adding “mm” after every number when the standard already states millimetres.
- Double-dimensioning a feature.
- Drawing isometric lines at 45°.