Third time's the charm! The third version of my 3d-printed clock is working great:
The biggest change was the winding system. It's a Huygens endless-chain maintaining power, a nifty idea from 300 years ago. The main weight and a tensioning weight both hang on pulleys, and the chain is a loop that goes over the great wheel (in my case, the hour wheel) and also a wheel with a ratchet. You can wind it up without affecting the driving force at all. It also simplifies things by putting the ratchet-and-click on its own wheel.
I've also made some nice-looking weights. The main weight, about 4 kg, is a 2x10 inch piece of stainless steel bar stock, the kind of thing you'd use if you were machining something on a metal lathe. They only machining I did, though, was to drill and tap some holes for a hook. And I'll have you know, I only broke 1 tap! It's still there, in the bottom of the main weight. The tensioning weight is the same idea, but exactly half scale.
The chain I'm using is the same sort of thing that's used for dog tags, #6 ball chain. You can make it into loops with a special connector piece. I've tried running the clock with that connector piece running through the pulleys, and it works, but we can do better. With a needle nosed pliers and some patience, you can form the chain into an endless loop, with one of the balls only slightly mangled. There is also a $100 specialized tool you can get to do a better job. I've made a 3d-printed version of this tool for much less, and it works fine - I used it to form the loop you see in the video.
Assembling this one was a bit difficult. On the previous version, the bearings fit loosely, so this time I added 0.2 mm of interference to the fit. That was way too much, though, so I needed to do a lot of sanding. This made the shafts not quite true, which gave the gears a "preferred" orientation, so I needed to sand even more so the shafts fit loosely. Also, the frame flexes considerably under the total 4.5 kg weight. I used some wire to brace it, but even still, the bearings would work themselves loose until I superglued them in place. The motion work was also a bit fragile, and I ended up gluing together the parts that are supposed to slide when setting the clock. (You can still set it by removing the pendulum and letting it run freely.) After all that gluing, though, it's been holding together fine (knock on wood).
Next version I make, I want to do away with the ball bearings entirely. (See my previous post for some thoughts about that.) The goal is, send a model in, get a working clock out, with almost no assembly.