Toy Lockbox with keys (fidget toy)

I have a toddler son, and he loves mechanical stuff. He got a set of toy keys, and I realized he had no “locks” for them. Oh no! Good thing he has a dad with a 3D printer. :)

This project is a small box with three “lock” cylinders mounted to the face/top. The face has provision for spring detents for each cylinder, which make for a wonderful (seriously - it makes me smile) click-click feel when turning the cylinders. Included are three variants of the cylinders that do slightly different things when turned: All three have a detent at 90 degrees from the start position. Type two has two additional detents. Type three has mini-detents that feel and sound like a ratchet.

The box face should snap into place on the box, depending on your printer and filament tolerances. If it's loose, little glue will fix it right up. The detents require springs: I used 5x15mm, but you can use longer and really jam them in there to make a harder-to-turn lock, or a weaker spring for a softer click. You might be able to get away with using standard ballpoint pen springs in this. Amazingly enough, I couldn't find any to test with, but the detent is completely enclosed, so smaller diameter springs won't escape.

The cylinders are held in by retaining rings on the face, and these need a few dabs of glue to keep them in place. I found that gluing on the seam between the ring and the cylinder gives a strong enough connection without gluing the rotating assembly to the face plate, which of course would be bad.

Since I assume most people don't have the same keys as my son, I've included color-matched keys with small compliant mechanisms built into them to provide friction so they click into the cylinders and then stay in place without falling out even if the box is turned upside-down. I found this to be an important feature during testing.

Originally designed and printed on a H2D, where everything fits on one plate and prints by object to massively cut down on time and material use for the multiple colors used for the lock assemblies. I'll also include a print profile for monotone per-layer printing for smaller printers, and a two-plate print for AMS use on smaller printers.

If you end up building this, I'd love feedback on your experience and any suggestions for improvement. Remixes are welcome, if you know a better method of holding the cylinders in, for instance.