Design, Drawing and Estimation
Drawing conventions
Freehand sketch → orthographic views → isometric for the client. Indian practice is first-angle projection: the object sits between observer and plane, so the view from the front appears above the plan. Lines: continuous thick for visible edges, dashed for hidden, chain for centre lines. Dimensioning: millimetres with no unit written, dimension lines outside the outline, no repeated or closed dimensions, arrowheads touching the extension lines. Always give a title block, scale and bill of materials.
Design for a school project
Consider function, ergonomics (seat height 450 mm, table top 750 mm), strength, grain direction, standard sheet sizes (plywood 2440 × 1220 mm), hardware, finish and cost. A good design uses the fewest cuts and the least waste.
Estimation
Make a cutting list; volume = L × W × T in consistent units; add 10–15% wastage; multiply by the rate per m³ or cft; then add hardware, adhesive, finish, labour, overheads and margin. 1 m³ = 35.31 cft; one board foot = 144 in³.
Worked example
Stool: seat 350 × 350 × 25 mm = 0.00306 m³; four legs 45 × 45 × 430 mm = 4 × 0.000871 = 0.00348 m³. Total = 0.00655 m³. Add 15% → 0.00753 m³ (0.266 cft). At ₹60,000 per m³ the timber costs about ₹452.
Traps
Mixing mm and m in one formula; forgetting wastage; counting a part twice; ignoring grain direction; using third-angle in an Indian drawing; leaving critical sizes off the cutting list.