Drawing Instruments, Materials and Standard Practices
This domain tests whether you can choose and use drawing instruments correctly, prepare a sheet to BIS conventions, and recognise the standard line types and sizes that appear in every later drawing question. Questions often ask for the function of an instrument, the dimensions of an A-series sheet, or the line type used for a particular feature.
Instruments and materials
- Drawing board with T-square for horizontal lines; set squares 45° and 30°–60° for vertical and inclined lines.
- Compass for circles and arcs; divider for transferring lengths; French curve for irregular curves; protractor for angles.
- Pencils: 2H for construction and centre lines, H for outlines and dimension lines, HB for lettering and freehand notes. Keep leads sharpened to a conical point for lines and a chisel point for lettering.
- Eraser shield and dusting brush protect the sheet; masking tape fixes paper without tearing.
Standard sheet sizes and layout
A0 is 841 mm × 1189 mm. Each smaller size is half the preceding area: A1 594 × 841, A2 420 × 594, A3 297 × 420, A4 210 × 297 mm. The title block sits at the bottom right, and a border of about 10 mm (20 mm on the filing edge) is drawn. BIS SP 46 gives preferred scales and line widths.
Line conventions
Continuous thick lines show visible outlines; continuous thin lines show dimension, extension and leader lines; dashed lines show hidden edges; chain lines show centre lines and pitch circles. Thick lines are roughly 0.6 mm and thin lines about 0.3 mm, with a 2:1 ratio.
Worked example
A question asks for the A3 size and the number of A4 sheets in an A0 sheet. Starting from A0 = 841 × 1189 mm, halve the longer side each time: A1 = 594 × 841, A2 = 420 × 594, A3 = 297 × 420 mm. Since each step halves area, A0 contains 2^4 = 16 A4 sheets. The reasoning is area halving, not simply dividing one side by four.
Traps
Using an HB pencil for construction lines makes them too dark and hard to erase. Do not dimension to hidden lines or use a dashed line for a centre line. A common error is writing the title block in the top right, or folding a drawing so the title block is hidden.