Instruments, Standards, Lettering and Sheet Layout
Instruments and their set-up
A drawing board's working edge is the datum: the stock of the T-square slides along it and every horizontal is drawn with the blade. Set squares (45°–45°–90° and 30°–60°–90°) are used in pairs - one edge on the T-square blade, the other giving 30°, 45°, 60° and, combined, 15° and 75°. A mini-drafter replaces both and locks at any angle; a protractor sets inclined lines, French curves fair irregular curves, and the compass and dividers carry circles and equal lengths.
Standards to quote
IS 10711 fixes sheet sizes from A0 (1189 × 841 mm) down to A4 (297 × 210 mm), each half the area of the previous. A 25 mm filing margin is left on the left edge and 10 mm on the other three, with the title block in the bottom-right corner. IS 10714 governs line work: continuous thick (about 0.5–0.7 mm) for visible outlines, continuous thin for dimension, projection and hatching lines, dashed for hidden edges, chain thin for centre lines. IS 9609 lettering is single-stroke Gothic with heights from the series 2.5, 3.5, 5, 7, 10, 14, 20 mm, stroke roughly h/14 and width about 0.7h.
Worked example
An A3 sheet is 420 × 297 mm. Deducting the 25 mm filing edge and 10 mm elsewhere leaves (420 − 25 − 10) = 385 mm width and (297 − 10 − 10) = 277 mm height. That 385 × 277 mm block is all the space available for views, dimensions and notes.
Traps
Filing margin drawn on the right; hidden edges drawn continuous; centre lines drawn thick; lettering smaller than 2.5 mm; title block placed anywhere but bottom-right; dimension lines drawn with the same weight as outlines.