Technical Drawing, Measurement and Estimating
Technical Drawing, Measurement and Estimating tests your ability to read body drawings, take accurate dimensions and calculate materials and labour. Expect orthographic views, sections, symbols, scales, tolerances, measuring tools and simple estimates.
Core rules
- Read the title block, scale, units and projection method before taking dimensions. Third-angle and first-angle views place views differently.
- Use datums and dimensions, not scaled measurements from the drawing, unless the drawing is marked "not to scale" and measurement is permitted.
- Measure with the right tool: tape for large body dimensions, vernier caliper for holes and thickness, micrometer for sheet, tram gauge for diagonals.
- Allow for material thickness, bend allowance, joint overlap and wastage in estimates.
- Calculate area and perimeter carefully; for two-sided panels, double the painted area.
- Labour estimates should separate preparation, repair, painting and reassembly.
Worked example
A panel has an area of 2.4 m² and is to receive two coats. Paint coverage is 6 m² per litre per coat. Paint needed = (2.4 × 2) ÷ 6 = 0.8 L. Add 20% for loss: 0.8 × 1.2 = 0.96 L, so order 1 L. Reasoning: both coats and wastage must be included.
Traps
Do not mix millimetres and metres. Do not scale a drawing when dimensions are given. Do not forget the reverse side or edges. Do not quote paint volume without checking coverage and coats.