Planetary Gear Desk Toy - a free 3D model from Shapekit

A desk toy that is also a real gearbox. Turn the crank and the sun gear drives three planets round the inside of the ring; the carrier and its pointer follow at a fifth of the speed, so five turns of the crank take the pointer once round the dial (a 5 : 1 ratio). The herringbone teeth run smoothly and hold every gear in place, and it all clicks together without screws or glue. Nine printed parts, no supports.

Parts (each STL is already placed the right way up for printing)
- planetary-gears-housing.stl: The back half of the ring gear (72 teeth), the back wall with an 8 mm axle pin for the sun, a groove for the cover's hooks and a foot that runs forward under the crank. Print: Back face on the bed, no supports.
- planetary-gears-sun.stl: 18 herringbone teeth on an 8 mm shaft. It turns on the axle pin, and the crank presses onto the flat at the front. Print: Back face on the bed, shaft up. No supports.
- planetary-gears-planet.stl (print 3): 27 herringbone teeth, with a bore that runs on a carrier pin with 0.3 mm of play. Print: Flat, either face down. No supports.
- planetary-gears-carrier.stl: Three arms with a pin for each planet and a hex socket for the pointer. It turns once for every five turns of the crank. Print: Front face on the bed, pins up. No supports.
- planetary-gears-cover.stl: The front half of the ring gear on a sleeve, and the bezel with the dial: five big marks, one for each turn of the crank. Three springy hooks click into the groove round the housing. Print: Bezel face on the bed, hooks up. No supports.
- planetary-gears-pointer.stl: The output hand. Its hex peg plugs into the carrier, and it sweeps round the dial. Print: Face down, peg up. No supports.
- planetary-gears-crank.stl: A knurled knob with a handle. Its D-shaped hole presses onto the end of the sun shaft. Print: Back face on the bed, handle up. No supports.

Also needed (not printed)
- Nothing to buy: no screws, no bearings and no glue. The cover's hooks and the herringbone teeth hold it all together.
- Optional: a little dry PTFE lubricant or silicone grease on the teeth, for an even smoother turn.
- Optional: four small self-adhesive rubber feet under the foot, so it doesn't slide while you crank.

Print settings: 0.4 mm nozzle, 0.20 mm layer height (0.12 mm makes the gears smoother), 3 walls, 15% gyroid infill, PLA or PETG material.

Assembly
1. Print and clean up: Nothing needs supports. The teeth have 0.2 mm of play per side and the pins 0.3 mm, so turn on elephant's foot compensation or scrape the bottom edges of the teeth, and check that each planet turns freely on a carrier pin.
2. Build the gear bundle: Stand the sun on the table, shaft up, and set the three planets round it so their teeth mesh. Lower the carrier over them, pins down and the shaft through its middle, so a pin goes into each planet.
3. Drop it into the housing: Lay the housing on its back. Hold the bundle by the carrier (the herringbone teeth keep the sun from dropping out) and lower it in, with the sun's bore over the axle pin. Herringbone teeth only go in with a slight twist, so let the gears turn as they slide into the ring until the bundle sits on the bottom.
4. Click on the cover: Set the cover on, hooks down, and push: let it turn a little as its teeth find the planets, until the three hooks click into the groove round the housing.
5. Fit the pointer and crank: Push the pointer's hex peg into the carrier. Then press the crank onto the end of the sun shaft, flat to flat, until it stops. It is a tight fit; if yours turns loose, add a drop of glue.
6. Crank it: Stand it up and turn the crank: the pointer goes round once for every five turns. Each big mark on the dial is one turn of the crank, each small mark a fifth. To take it apart, pull the hooks out and lift the cover off with a twist.

Safety: Small parts: keep the gears and the pointer away from young children.

License: Creative Commons Attribution-NonCommercial 4.0 (CC BY-NC 4.0)
https://creativecommons.org/licenses/by-nc/4.0/
Print it, remix it and share it, as long as you credit Shapekit and don't sell the files or the prints.
