Drawing Instruments, Materials and Standards
This domain tests the drawing office itself: the instruments you choose, the sheet you work on, the scale you use and the BIS/ISO conventions that make a drawing readable.
Core rules
- Standard sheet sizes (IS 696 / ISO 216): A0 1189 × 841 mm, A1 841 × 594, A2 594 × 420, A3 420 × 297, A4 297 × 210, A5 210 × 148. A2 or A3 is usual for ITI sheets.
- Filing margin 20 mm on the left; other margins about 10 mm. Title block at bottom right, readable from the bottom or right edge.
- Pencils: 2H for construction and centre lines, H for visible outlines, HB for lettering and freehand. Keep a sharp point and light pressure.
- T-square for horizontals; set squares 45° and 30°–60° for verticals and angles; compass for circles; French curve for irregular curves.
- Scale: representative fraction = drawing length / actual length. Full scale 1:1; reduced 1:2, 1:5; enlarged 2:1, 5:1.
Worked example
An object 120 mm long is drawn 60 mm long. RF = 60/120 = 1/2, so the scale is 1:2. On an A4 sheet the drawing area is about 277 × 190 mm after margins; a 150 × 100 mm drawing at 1:2 fits, while 2:1 would need 600 × 400 mm and would not.
Traps that cost marks
Using the wrong margin side; putting the title block in a corner other than bottom right; leaving out the scale; using a thick pencil for construction lines; confusing 1:2 with 2:1.