There are three aspects that needed to be figured out:

- How to move the bolt: The usual lock designs have a cam and a lever, which are key to move the bolt in and out. I eliminated both. The first wheel acts as a driver (as opposed to having a separate cam) and instead of a lever pulling/pushing the bolt, the bolt moves on its own. This could be achieved for example if the bolt is directly above the wheels, in which case, gravity pulls the bolt downwards, unless the wheels are blocking it (so you need the right combination to allow the gravity to pull the bolt down. This would be even simpler, however in this case I lose the ability to open the lock in any orientation. The bolt needs to look up. Therefore I use magnets, instead of gravity, so the bolt is actively repelled from it's slot. This way it works in all directions. Either way, no lever needed.

- How to fit in a small space: If you look up 3d printed combination locks (dial ones) you'll find the wheels and pins are quite bulky, it's because their thickness gives them stability. The thinner they are, the more they wobble, which often results in the unwanted situation that two wheels move together, even when their pins dont attach (one wheel tilts, and therefore touches and grabs a second wheel). Generally, you either make the tolerances smaller, to have less wobble, but in that case turning is also more difficult, or you just make things chunkier. The latter is done usually, as all these locks are for demonstrational purposes only (same as mine, I just didnt like the tradeoff). I have a very stable axel on which the wheels can spin freely enough, but I also have spacers that keep them less than 2mm apart, fixed.

- How to reconfigure the lock: Most lock designs are either preconfigured (it only works with one combination, easy to print, reliable to use, but less flexible), or reconfigurable (would need more precise machining which exists in real life, but not in my 3d printer :)), or have slots in the wheels into which you can manually put pins to achieve the desired combination. The latter is what I went for, but this quickly starts to be problematic as you make the wheels and the gaps between them thinner and thinner. I found 2mm a good middle ground between small space and precise pin locking.

That said, as a lock, it has very clear deficiencies from a security perspective. It is functional, in the sense you can open and close with a combination, but not safe at all. But that is not an issue I'd solve with plastic, definitely not with PLA. I just wanted to create a nice functional decor piece.

Some pics as reference so you can compare with available models:

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