Worm Gear and Cam Prototyping

Sun, 1 Mar 2015

Cams are really useful in automata. One crinkly surfaced cam can be used to describe a quite intricate set of movements. Add a couple more cams to the same cam shaft and it is possible to make a automata with a quite complex set of movements.

The limitation is that all of the movement has to fit into a single rotation of the cam. For a complex sequence this means that the viewer has either to turn the handle really slowly or the cam needs to be geared down. If you are a regular reader on the blog you will know that I have been experiment quite a bit with gears with some degree of success.

If I wanted to make a story that took ten turns of the handle to perform I could use some of the gear designs I already have but for a 10:1 reduction or greater that would need either a multiple stage gear box or a really large output gear.

Enter the worm gear. In a worm gear mechanism one turn of the handle advances the gear by a single tooth of the output gear so even with quite small gears large speed reductions are possible. I made a worm gear a while ago but this is the first time I have tried it since I switched to using circular axles.

The output gear is eleven teeth. The short section of worm is turned via a crank handle resulting in the cam shaft turning round very slowly, perfect for a more complex automata.

I’ve fitted a couple of cams to the cam shaft and mounted the whole into a box. It works okay by does need a bit of tweaking with dimensions to try and smooth out the movement. In this version the handle turns roughly 3/4 turn with the gear moving smoothly then the gear stops for the next quarter turn. I’m hoping that increasing the gear size slightly should overcome that issue. It should be a useful little mechanism once it is sorted!