Modelling and prototyping practice questions.

A team has two days to find out which of eight bottle-opener concepts users prefer for overall form and hand fit. There is no tooling budget. Which modelling approach fits these constraints?

• Full-size block models cut from modelling foam
• Machined aluminium samples of each concept
• A pre-production sample from a soft aluminium tool
• Photorealistic rendered images of all eight concepts

Answer: Full-size block models cut from modelling foam

At concept stage the decision is about form and hand fit across many ideas, so the model must be three-dimensional, quick and cheap. Renders cannot be held, and machined or pre-production samples answer a question that has not been asked yet.

An engineer must compare twelve internal rib layouts for a printer casing within one week, before any tooling is ordered, checking wall thickness consistency and clash-free assembly for each variant. Which modelling method is appropriate?

• Three-dimensional printed samples of every variant
• Parametric CAD models compared by virtual assembly
• Hand-cut card models of each internal layout
• A single machined prototype of the preferred layout

Answer: Parametric CAD models compared by virtual assembly

Twelve variants in one week rules out physical routes. A parametric CAD model regenerates the geometry for each variant and reports clashes and thin walls automatically, which is exactly the class of question a digital model answers best.

A designer needs one transparent lens housing with a smooth, finely detailed surface for a client presentation in four days. The part carries no load. Which rapid prototyping process best meets these criteria?

• Fused deposition modelling in ABS filament
• Computer numerical control routing of a foam block
• Stereolithography in a clear photopolymer resin
• Selective laser sintering in nylon powder

Answer: Stereolithography in a clear photopolymer resin

Stereolithography cures a liquid photopolymer with a laser, giving the smooth surface and fine detail a clear presentation part needs. Filament and powder processes leave a layered or matt surface and cannot produce transparency.

A 1:10 scale model of a bus shelter is built to present the design to a transport authority. Which requirement can this model NOT be used to check?

• Whether a seated user can reach the timetable
• The proportion of the roof to the side panels
• The visual impact of the shelter in a street scene
• The arrangement of the shelter's structural frame

Answer: Whether a seated user can reach the timetable

A scale model reproduces proportion, layout and visual impact, but no real user can be placed against it. Reach and clearance are settled on a full-size mock-up or against anthropometric data.

A cordless drill team must find out whether the grip stays comfortable for users with small hands when the tool is held at arm's length for one minute. Which prototype should be built?

• A quarter-scale resin model of the drill body
• A full-size dummy of the correct mass and shape
• A rendered image of the grip shown on screen
• A working circuit board mounted in an open frame

Answer: A full-size dummy of the correct mass and shape

Comfort under load depends on grip geometry and on the mass the hand carries, so the model must be full size and correctly weighted. A scale model, a screen image or a bare circuit board reproduces neither.

A folding scooter mechanism is unproven. There is budget for one prototype before the review that decides whether the project continues. Which prototype should the team build?

• An appearance model finished in the final colour
• A three-dimensional printed half-scale display piece
• A working full-size mechanism in machined metal
• A rendered exploded view of the folding assembly

Answer: A working full-size mechanism in machined metal

When the unproven element is a mechanism, the first prototype must work rather than look finished. Spending the single build on colour and finish would leave the project's main risk untested.