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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.

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  • Have you tried other materials? Like cardboard?
    – Willeke
    Commented Nov 3, 2018 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
    Commented Nov 3, 2018 at 9:37
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    You could spray paint the foam parts to make them slide against each other. But certain solvents dissolve foam as well.
    – Elmy
    Commented Nov 8, 2018 at 14:40
  • Let us continue this discussion in chat.
    – fixer1234
    Commented Mar 13, 2023 at 18:03

2 Answers 2

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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.

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Just to play with ideas for mechanisms, I've used corrugated cardboard. You cut out a disk for the body. For the teeth, use a sheet of "one-sided corrugated cardboard" (just the backing and corrugations; it bends), or strip off one layer of paper from corrugated cardboard, and cut long, thin strips. Glue the strip around the disk. The corrugations are very uniform and will mesh like gears. It's pretty crude, and the teeth won't hold up to stress, but it's fast to make. You can make the teeth stronger by gluing in short pieces of something that fits the hole, like a skewer (corrugation sizes vary).

enter image description here Credit: Education.com on Pinterest

Another fast solution is how gears were made before there were modern gears. One gear is a disk with pins radiating out. The mating gear is a carousel with vertical pins.

enter image description here Credit: Efunda Engineering Fundamentals

This style is fast to create and will work with cheap materials like cardboard and skewers or round toothpicks, with more reliable mating.

Here's a video combining a cardboard gear with a carousel.

But for something good enough to be permanent, actual gears (replace them with laser-cut acrylic only if you need the appearance), you can make them from PVC pipe. A good video of how to do it: How To Make Plastic Gear at Home.

enter image description here

This is the basic technique:

  • Make a flat panel of PVC from PVC pipe. There are online videos on how to do that. Basically, you cut a section of PVC pipe, slit it lengthwise, warm it with a heat gun, flatten it into a sheet, and weight it down with something flat while it cools.
  • Create a paper template for the gear. You can do that on a computer and print it. The video shows how to do it with a compass. Glue the template to the PVC panel.
  • Cut the outer disk of the gear from the panel.
  • The video shows how to make a V-shaped cutting tool from sheet metal that fastens into a soldering iron and easily cuts out the gap between the teeth. That example uses the casing from a dry cell battery, but you could use any heavyish sheet metal, or probably even a soda can if you don't apply too much pressure. The teeth can be further shaped with a file if needed.

Once you put in the work to make a gear from PVC pipe, you can make a mold of it and cast more if you need more of the same size.

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  • Cool, I think the idea in that video would have worked for my project back when I asked this. I'd be worried about fumes from the PVC though, as it's not nice stuff when burnt. I guess the soldering iron only melts it, but still, I think it would be safer to use something like PLA, which I think is readily available in sheet form. (Or acrylic, but I don't know how you'd cut out the circular shapes without a laser cutter.)
    – N. Virgo
    Commented Mar 11, 2023 at 18:18

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