Engineering ideas

Working on prototypes for a simple ‘counter’ mechanism, using 3d printing to work out size and shape and will eventually mill it on my S3. I want to add a detent so the numbers dont slide on their own too easily.

My leading idea is to drill a hole on the inside of one of the face plates and use a spring washer and ball bearing set in the hole, then milling shallow holes in the number wheels such that the ball bearing slightly seats itself as the number lines up with the window. It’s a pretty simple mechanism, but curious what other ideas might be out there?


Disc springs would be something simple like this:

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Lots of examples of commercial detent inserts, such as

Detents often work more smoothly if, rather than a hole for the mechanism to catch, you use a smooth wave-like form. Relative to just a round or conical depression, smother release and less impact on engagement can be achieved.

Another common scheme is a leaf spring pressing radially to the rotating part, the rotating part being a polygon or gear-- this is seen for soft indexing of geared drives in many small devices such as wheeled counters (think handheld clickers or old school mechanical odometer). This can also be done by setting the detents into a face.

A different scheme might use small iron slugs inset into the rotating parts for each position and a magnet set into the stationary part. Benefit: no wear. Drawback: positioning may not be as positive due to the balance between allowable force from the magnet and friction in the system

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I can’t believe I didn’t just search ‘detent’ on mcmastercarr, sigh. Yeah I’d intended a wave form I just wasn’t going to draw up a diagram or spend too much time descriving it, I figured you’d all see what I meant.

Magnets are my backup plan, trying to keep the pieces thin and I think the detent will work better but I may do a prototype with some small magnets as well.

Thanks for the pointers!

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So far having a little trouble finding a prepackaged detent module to fit in a thin ~1/8" material. Going to see about a more leaf spring design. The spring-washer/ball bearing method should work still though there too had trouble matching up sizes.

After some searching I think magnets are the easiest way to go. K&J has nice small magnets, not sure if bits of iron or just opposite facing magnets are best. The magnets would have the upside of being identically sized and all that. At 10 cents a piece it’s pretty affordable to use either.

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Not technically CNC but I decided to do a model of this using laser cutting since I can outsource this a bit, as I don’t have time to CNC it. Came out awesome. The downsides of lasering are of course evident as I can’t drill magnet holes, debating setting up a fixturing jig to CNC them but for now a drill press gives good results.


That turned out really nice! :slight_smile:

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