Impervious Globoid Tuning Peg

Long ago I wanted to make a dulcimer. Oh boy where did we end up.

Why?

I needed a lot of tuning pegs but commercial ones were too expensive.

So I made my own, in a previous post. They worked, but they weren't up to my standards. I later improved on my design and made them quite capable (not published, very recent), but they still were bulky and a little hard to manufacture since they needed a sort-of-precise metal part.

Then I remembered a design by noamtsvi that was very similar to a commercial one and it did work to an extent but then the thread of the worm sheared (maybe I should have used a stronger material, but I want to use pla if possible) and I thought I wanted to make my own. While I don't consider this a remix, I did take a few design decisions from his design that he surely found through a bunch of work. Link to his design.

Globoid gears

Globoid gears are a type of worm gear that envelops the wheel. This ensures good teeth contact and strength. It is a more robust geometry that magically increases resistance at the cost of design complexity. This is a notoriously difficult to cad and manufacture geometry but 3d printing bypasses the hard to manufacture part. I designed it in Solidworks using my own method, and I struggled a bit. It even isn't quite perfect since the wheel doesn't envelop the worm too much but I found it works well nevertheless.

My work

Drawing some inspiration from noamtsvi's design, I incorporated its general shape and neat 4 piece structure and tried to make something really robust. Here's what I did:
 - I used a globoid gear for the worm and wheel. This makes it so that there is always 2-3 teeth from the wheel touching the worm, with remarkably good teeth contact. Very robust.
 - I used a 5mm stainless steel rod for the wheel axle and string tie point. This not only makes it impossible to fail there, but reduces load on the mechanism by making the torque arm on it of the string smaller. This metal piece is easy to make and can be manufactured with just an angle grinder or file and a drill (I didn't even use a vice, although use one if you can).
 - I designed the worm differently, making it come through both sides of the thing and also made the case symmetrical. This is kind of a big deal because it makes it so that you can mirror the whole assembly by just taking the worm out and flipping it. No mirrored printing needed.
 - I also made it bigger, sort of by accident. But that is in part a tradeoff I made for robustness.

In general, the design works very well. If well greased, it feels real good to use, without jumping or ugly noises. I managed to break a mystery metal wire I found on my house with it, which might actually be nichrome and that is not too resistant but I think it could hold my weight. In any case just using it I could tell it wasn't struggling, it felt quite robust.

Also, I'm not using standard tuning peg screws. I couldn't get those so I used the ones they sell on my local hardware store. I've uploaded step files for the case so you can modify mounting if you want.

Assembly

Assembly is pretty simple with basically just putting the pieces where they go and thats it. But you do have to hammer the metal rod in. It needs a very strong pressfit onto the gear (and superglue if you are using really heavy strings) and it might be a little hard on the case at first. Then, when you get it all assembled youll maybe need to turn it a bunch of times and then dissasemble, clean the extra plastic that shaved off the parts and reassemble; it can be really tough to turn at first so id recommend screwing it on a scrap piece then turning with a wrench. Before installing, you should grease them carefully, trying to get the grease deep into the grooves of the worm and the teeth of the wheel.