For fun, I started designing some two-dimensional mechanisms with parts that rotate, slide and gear against each other. Ultimately these will be made from laser-cut acrylic, but since I don't have easy access to a laser cutter I would like to find a way to prototype them at home.

I tried using foam board, the kind used for architectural models. This is great because I can cut it accurately with an X-Acto knife or a circle cutting tool, but unfortunately the cut edges don't slide against each other very well - there's too much friction for my design to work.

So I'm wondering if there is another material that would be more suitable. That is:

  • easy to cut accurately at home

  • at least a couple of millimetres thick

  • can be sanded smooth so the edges will slide well against each other

  • doesn't need any bending strength, since all parts will rest against a flat surface and only move in the XY directions

I don't mind buying tools to cut the material, but I don't have any working space apart from a carpeted living room and a small balcony, so I can't install anything that will take up space or make a mess. Potentially I could use a Dremel or something out on the balcony if that's the right approach, but I'd be a bit worried about the noise.

  • Have you tried other materials? Like cardboard?
    – Willeke
    Nov 3 '18 at 9:08
  • @Willeke I haven't tried cardboard, purely because I didn't find any that would be thick enough. If it's too thin then the gears will just overlap each other instead of staying flat against the surface and meshing with each other. I imagine that 2mm thick solid card would actually be quite difficult to cut, but if I find some I will try it. (I'm fairly sure corrugated cardboard won't work, since the cut surface will not be smooth even if I can cut it accurately.)
    – N. Virgo
    Nov 3 '18 at 9:37
  • 1
    You could spray paint the foam parts to make them slide against each other. But certain solvents dissolve foam as well.
    – Elmy
    Nov 8 '18 at 14:40

Balsa wood is available from many sources and can often be found at local outlets. Various thickness panels are usually presented in shelf units or organizer caddies, typically in 24" or 36" lengths (0.6/0.9m) and varying widths.

Balsa wood is quite soft and easily cut, more easily than foam core as it is consistent throughout the thickness. There will be weakness parallel to the grain, however, which means gear teeth will break off if too much force is applied.

One could create the model components and then apply a thin layer of PVA glue along with a paper reinforcement layer to mitigate the grain-parallel weakness.

1/8" balsa (3mm) can be cut with a sharp razor knife, but I believe you'll have better strength with 3/16" to 1/4" material (4.75 to 6.35mm), especially if you apply paper reinforcement. If one layer on one side appears insufficient, apply a second layer on the other side. It would then be the equivalent of foam core board with a much stronger inner ply.

Balsa sands to a very smooth surface. You could then apply a thin layer of glue if you require a harder contact area for reduced friction.

  • This is a great suggestion - I will see if I can get some balsa wood and try it. Thanks also for the glue layer idea - I will also try that with the foam board, because that idea might solve my problem by itself.
    – N. Virgo
    Nov 3 '18 at 13:36

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