After half a dozen iterations, this was the first reasonably working, acceptable feeling, and good-sounding ratchet mechanism.
allows clockwise rotation blocks counterclockwise rotation
design features:
- allows for a large inner bore (e.g. rotary encoder shaft or 5.2mm screwdriver bit)
- printable with 0.4mm nozzle
- 2cm diameter
- no assembly required. Print in place.
To get a full ratchet: mirror the assembly and add a mechanism/part that pushes one of the springs out. In neutral both leavers are engaged and the ratchet is completely locked.
Btw. Good luck copying it without going through half a dozen of iterations. Going from it barely works to this isn't easy. For my part: Version 5 was working and close to the final design. It took another 10 rounds to get it usable and from there some more to fine-tune it.
Here you go: https://www.thingiverse.com/thing:6595547
v10 should still be 0.4mm tolerances (easy to print) on all sides and working. Otherwise not a great design but enough for you to understand that there are dozens of parameters to tune in such a "simple" mechanism and it is (nearly) impossible to nail it on the first try. Have we started talking about optimizing the force required to break it loose? That's one more thing that needs to be accounted for.