Engineering projects and product design: method, drawing, documentation and budget
The exam asks how a product is designed, drawn and costed: the design stages, standardisation of drawings, the content of the technical file, and a budget built from direct and indirect costs.
Design methodology
- Stages: identify the need, feasibility study, specification of requirements (constraints and weighted criteria), conceptual design, detail design, prototype and testing, production and market launch.
- Tools: functional analysis, QFD, brainstorming, morphological box, weighted decision matrix, DFM/DFA, FMEA, value engineering. Verification checks compliance with the specification; validation checks fitness for use.
Technical drawing and standards
- ISO 128 line types (continuous thick for visible edges, dashed for hidden, chain for axes and cutting planes); ISO 5457 formats A0 841×1189 down to A4 210×297.
- Scales: 2:1 is enlargement, 1:2 is reduction; the drawing states the unit in the title block.
- First-angle projection (ISO-E) places the top view below the front view; third-angle is the American convention.
- Dimensioning (ISO 129/UNE 1172): each dimension once, on visible edges, Ø for diameters, R for radii, M for metric threads, tolerances and Ra noted on the drawing.
Documentation and budget
Technical file: report, specifications, drawings with title block and revision control, parts list (BOM), assembly drawing, test reports, manual. Budget: direct costs (materials, labour, machine hours) → indirect costs → industrial cost → industrial margin → selling price → VAT.
Worked example
Material 2.4 kg × 5.5 €/kg = 13.20 €; machining 0.4 h × 45 €/h = 18.00 €; assembly 0.25 h × 30 €/h = 7.50 €. Direct total = 38.70 €. Indirect 12 % = 4.64 €, giving an industrial cost of 43.34 €. Margin 15 % on cost = 6.50 €, so the price before tax is 49.84 €. VAT 21 % = 10.47 €, final price 60.31 €.
Traps that cost marks
- Applying VAT to cost instead of to the selling price.
- Reading 1:2 as an enlargement.
- Duplicating a dimension or dimensioning a hidden edge.
- Mixing first- and third-angle view placement.
- Omitting revision control in the technical file.