I have made several attempts at making clocks using a 3D printer, always ending in a clock that didn't run at all or that would only run for a short time. Some of this is attributable to the quality of the prints. My first two printers really weren't up to the level of precision that is needed. Another source of problems is my inexperience with debugging clocks, and mechanisms in general. I know how to think about solving software problems, but I don't have a good feel for where to start with mechanical ones. I've gotten better at this over time, and in the case of clocks I have a better understanding of them as physical systems than I did at first; I mean things like how power is transmitted through the system and how it interacts with the elements that control the timing. And finally, some of the designs that I tried just weren't as good as they might be. I don't mean that the designer was negligent, just that you find many objects on 3D printing sites which worked when the designer made then and so they generously shared the design with the community, but they didn't test them to allow for variation in printers, materials and the abilities of the person making the clock.
I recently came across a design by Steve Peterson for a clock intended to be easy to make and get going. He accompanies the design with detailed videos on assembling and debugging the clock. It has variants for different run times, from 7 days up to 32 days, with 10 days being the recommended starting point. (Strictly speaking, the run time depends on how long it takes the weights that drive the clock to reach the ground; if hung in a deep stairwell, it would run for longer.) I successfully built this clock and have it running, and enjoyed the process.
Here are some pictures and a video of my build of it:
Huge credit goes to Steve Peterson. It's a good design with good supporting information. There are many thoughtful decisions, such as using gear teeth with a profile that makes them easier to print. I'm really happy with it, and plan to move on to some more challenging clock models next.