A shop-built vacuum forming rig for producing visors and lenses for ski and cosplay helmets, developed across three revisions.

The build is deliberately simple: a wooden frame, a shop vacuum as the vacuum source, an oven for heating, and thermoplastic sheet as the stock. Commercial vacuum formers cost more than the parts they would have produced, and the underlying process is not complicated. Heat a sheet until it goes pliable, seal it over a mold, and pull the air out fast enough to draw the material down before it cools.

Executing it well is harder than describing it. Thermoforming is unforgiving on timing, since the sheet has a narrow window between too stiff to draw and too hot to hold its own shape, and that window closes quickly once the sheet leaves the heat. Seal quality around the platen matters as much as vacuum strength, because a rig that leaks will not pull a part no matter how much airflow it has.

The three revisions came from the platen and the vacuum source, which turned out to be the two things that decide whether the rig works at all. MK1 used a salvaged air hockey table as the vacuum bed, on the reasoning that it already had a uniformly perforated surface. It performed poorly. An air hockey table is built to push a small volume of air out across a very large area at low pressure, which is close to the opposite of what thermoforming needs, namely a hard pull concentrated under the part. Later versions replaced it with pegboard, giving a smaller bed area with a denser hole pattern, so the available suction was concentrated where the sheet actually needed to be drawn down. The vacuum source changed across revisions as well.

The rig produces usable visors for prop and cosplay applications. Getting to a visor that would function as real protective eyewear needs thicker stock and a material chosen for impact resistance, which is the current direction of the work.