As soon as the final shape of the enclosure was established, we went on to actually producing it. When casting, you need molds, which were to be produced by means of a 3-axis CNC-milling machine and solid polyurethane. The mold for the base layer was simple, since there is no change in the height of the knobs that make up its surface pattern. The knobs themselves were easy to produce: they were designed to match the shape of a spherical milling tool and therefore could be created with a single touch of the tool in the mould.
The middle layer was even simpler, as it was basically just a sheet of silicone that was cut where the components were supposed to sit. It was cast on a clean, flat piece of acrylic glass and then laser-cut along the contours.
The most challenging part was the upper layer: concerning the design because of the surface pattern and the extending bumps for the bulky electronics, and concerning the production, because those bumps needed a second, inverted mould to act as a placeholder for the components, in order to prevent the liquid silicone from filling their space. The exact positioning of this inverted mould was critical, since there was only a thin layer of air (later silicone) between it and the actual mould, so any inaccuracies would inevitably lead to changes in wall thickness or, in the worst case, a hole in the silicone skin. Casting was mostly unproblematic: the viscosity of the liquid silicone was low, so we basically just poured it in, apart from the knobs that needed a bit of extra treatment – in order to avoid air to get caught under the silicone as it filled the cavities that would later become the knobs, we had to force it in with a scraper. Luckily, for the most parts we were able to avoid any defects, and, once they were dry, parts could easily be removed from the moulds on the first try.