Instrument Use, Linework, and Drafting Standards
Instrument Use, Linework, and Drafting Standards
This domain tests correct tools, line conventions, sheet layout and legibility. A technically correct drawing can still lose marks for poor linework.
Core rules
- Use a T-square for horizontal lines, set squares for 30°, 45°, 60° and perpendiculars, and a compass for circles. Set radii from a scale rule, not by guesswork.
- Pencil grades: 2H for construction and projection lines, H or HB for visible outlines, B for lettering. Keep leads sharpened and instruments clean.
- Standard linework: continuous thick for visible outlines, evenly dashed for hidden detail, thin chain for centre lines, continuous thin for dimension and extension lines, wavy thin for break lines.
- Keep a 2:1 contrast between thick and thin lines; do not mix weights arbitrarily.
- Letter in upright, single-stroke capitals. Use a title block and border on every sheet.
Worked example
To draw a 30° line through point P, place the 30-60 set square on the T-square with its 30° edge through P and draw once. For a circle of radius 25 mm, open the compass to 25 mm using the scale rule, place the needle at the centre, and rotate the compass by the top knurled handle. Reasoning: the set square gives an exact angle without a protractor, and setting the compass from the scale avoids cumulative error.
Traps
- Using a soft pencil for construction lines.
- Dashes that are too long or uneven.
- Drawing centre lines as visible outlines.
- Pricking the paper with dividers.
- Crowding the title block or running lines through it.