Modelling and prototyping

Isometric shows the whole object in three dimensions to communicate a concept. Orthographic gives front, plan and side in true size so a manufacturer can work to the dimensions.

Dashed is a hidden edge — real, but not visible from that direction. Chain-dotted is a centre line, marking the axis of a hole or cylinder.

Third angle places each view on the side you looked from; first angle places it on the opposite side. The symbol on the sheet says which, because reading it wrongly produces a mirror-image part.

When the question is about the ORDER of assembly — which part goes on first and which fixing goes where. An assembly drawing shows the fitted result but not the sequence.

Anything the body judges: weight, reach, grip, balance, fatigue, and fit in a real space with real obstructions.

Scale — full size wherever a body is involved. Shape — the form in the hand, weighted to the real mass. Space — whether it fits in the real place it must be used.

An aesthetic prototype tests how it looks and feels and need not work. A functional prototype tests whether it does the job and may look like nothing. One prototype doing both usually does neither.

Unweighted, it flatters every design — with no mass there is no wrist torque, so every grip shape feels comfortable and the test cannot tell them apart.

Surface knows only the skin. Solid knows the whole enclosed volume, so it can report mass and sections. Virtual knows geometry plus behaviour — motion, loads and materials.

It has no inside — only a skin with no thickness — so there is nothing for a density to act on.

The model is built from editable dimensions, so changing one updates every dependent feature. A variant costs minutes rather than a rebuild, which is what makes iterating affordable.

It cannot tell you what a product feels like to use — weight, balance, grip, fatigue or fit in a cluttered real space. Those need a weighted physical model.

A material, so stiffness and strength are known; the loads — how much, where and in what direction; and the constraints saying which faces are held still.

No. Red is the highest stress in that simulation. Failure depends on whether the peak exceeds the yield strength of the material, which the numbered scale tells you.

The load has to change direction through a small area. A generous fillet radius lets the stress flow round gradually, which is usually the cheapest fix available.

Anything outside the case described: being dropped, loaded off-centre, corroded, or fatigued over many cycles. It also assumes a perfect material, which a printed part is not.

Watertight solid, wall thickness against the nozzle or beam width, orientation, overhangs and reachable supports, and designed clearances at mating faces.

It fixes which faces print well, which surfaces overhang and need support, and the direction the part is weak in — so every other decision depends on it.

Typically 0.2 to 0.4 mm per mating face. Modelled at the exact nominal size, printed parts come off the bed fused together.

A printed part is not the production part: FDM is far weaker across its layers than a moulded part is in any direction, and SLA embrittles in sunlight.

They answer different questions — users about the body and the task, clients about budget, installation and what the organisation owns — and in one room the client talks while the users agree.

Decide the measurement before the session, give a task rather than an opinion prompt, say nothing and do not help, record behaviour as well as words, and ask the open question only at the end.

Pair it with what was observed, work out what it means about the design, then decide the change — and retest with the same task, users and measurement.

When the behaviour does not support the words: three users calling a tool heavy while nobody slows down is worth recording and watching, not redesigning for.