Geneva Mechanism

Geneva Mechanism

The Geneva Mechanism is a rather basic intermittent motion mechanism. Some information, for the curious, can be located in this Wikipedia article and here are some designs and variations of the Geneva mechanism from an amazing site based of an amazing book.

Basic Geneva 1: Uses gear teeth to turn. This way the whole thing can be planar.

Basic Geneva 2: The cross piece looks like a ratchet wheel.

Basic Geneva Stop 1: This is a variation on the basic mechanism. This was used by watchmakers to avoid over-winding of the coil spring in mechanical watches. You would turn something that would turn the crank piece which would be attached to the spring and the cross would only control how far the crank can go.

Basic Geneva Stop 2: Similar to the above one but with more of a similar design to mine.

Here is my Thingiverse link so you can download the file and/or use the customizer app to make one.

I wanted to design a OpenSCAD version of it so I (or you) could generate any number of slots or any size pretty quickly. The file should be pretty self explanatory, but here are some pictures further explaining the parameters.

Here’s the basic mechanism. Ive changed the parameters one at a time off of this design so refer back to this photo.

GENEVA N6Lets start at the most important parameter shall we? The number of grooves. Depending on the number of divisions you want the cross to rotate through this number will change. If you want to index to 6 locations it would be 6 grooves, and 4 grooves for 4 locations.

GENEVA N4

If you want to change the size of the whole thing change the crank and cross radius. The base automatically scales to fit both parts. Something else to pay attention to is the bottom cross radius. This raises up the actual cross from the base so everything moves smoothly. I left this a manual parameter rather than a calculated one to leave it up to the designer how large they want that.

GENEVA RO2

You can change the thickness for all pieces as well. Each piece is based off the one value.

GENEVA RI18

If you want a stronger peg thickening it up may work. This is an extreme example but I’m sure you get the idea.

GENEVA W34

Depending on how large you want your mechanism you may want to change the bolt size. I used a #8 screw and nut for the one I printed at the beginning.

GENEVA B1 4

This is the original nut sizes for the #8 washer.

GENEVA NUTW 3 8

Depending on your bolt size you will need to change your nut size and thickness as well.

GENEVA NUTW 1 2

And finally, the pièce de résistance. The view mode. Until now you have been seeing the mechanism as assembled, but before generating the stl file and printing it change the view mode to 2. This lays everything out flat so the file is ready to go to your printer. No fuss.

GENEVA PRINTING

One last note is the tolerance. I changed how the parameter works since these screenshots but just use your nozzle diameter and everything should fit with little to no filing or sanding. If you are using metric units it would be easy since you don’t need to divide by 25.4 like I do since I prefer English units.

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