You can visit robives.com for a chance to win a ready made version of this planetary gear mechanism
This tactile and delightful looking mechanism is a planetary gear. So named for the four planet gears orbiting the central sun gear. I've put this project together as part of my learning-to-use-a-laser-cutter experiments.
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I've cut the parts out from 3mm acrylic sheet. (Perspex) I also used a length of 6mm diameter acrylic rod to hold everything together. There is no glue in this model. All the circular holes in the model should be a tight fit. It might be worth shrinking down the size of the circular holes to, say, 5.6mm. Try cutting one circular hole and making sure that it is a tight fit with the perspex rod before you cut out all your parts.
Tap the centre gear onto the centre peg. This gear is fixed, it should not be free to rotate.