Fig. 26 shows a 3D-printed scale model of a chair placed next to a full-size drawing. The parts are all the same size. It works in rain and sun. It is safe ...

(a) Two reasons why a designer would produce a scale model rather than a full-size prototype at this stage:

1. A scale model uses less material and is cheaper to produce [1]. At 1:5 scale, the model requires only a small fraction of the material that a full-size chair would need, making it economical for early-stage evaluation before the design is finalised.
2. A scale model can be made more quickly, allowing faster evaluation of the design concept [1]. The designer can assess proportions, form, and visual appeal without waiting for a full-size build, enabling rapid iteration if changes are needed.

Other valid reasons include: it is easier to handle and transport for client presentations, and it allows the overall form to be checked without the cost and commitment of a full-size build.

(b) One advantage of using 3D printing to produce the scale model compared to shaping by hand from modelling foam is that 3D printing produces the model directly from the CAD file with precise dimensions and smooth, consistent curves that would be difficult to achieve when shaping foam by hand [1]. The digital-to-physical process ensures the model is an accurate representation of the intended design, with repeatable quality that hand carving cannot guarantee.

(c) The designer could test the ergonomics of the chair design by placing a scale human figure next to the model and checking that the seat height, backrest angle, and overall proportions are appropriate for the intended user [1]. By comparing the model against anthropometric data at the same 1:5 scale, the designer can identify whether the seat is too high, the backrest too upright, or the armrests too wide, and adjust the design accordingly before building a full-size prototype.