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I am pretty sure I am going to make more variants of this one, as it is just so much fun. The 2mm thick printed lock system is even better than my prior designs because this one uses print-in-place compliant springs for the tumblers and the lock Dial detents. The lock is reprogrammable, snap-together, and 100% printed. I love it.
The case is fairly small, but in fact, I wanted to make it smaller. In the end, the size is driven by how small I felt I could make it functional and reliable. Its a good size for a gift card, but not large enough for cash. So I’m thinking a cash size 4-digit lock will be next on the list.
The main case is a single print with the main case, the lid, and the hinge system all printed together. In the main case, there are numerous details, including posts for the gears and dials, spacers which surround the gears and dials and prevent the false bottom from squishing them and impeding their operation. Also, a sprung tumbler and detent are printed into the bottom of the main case.
The end result is a pretty quick build that does really require much discussion. Only the gears, dials and one latch bar need to be added to make it functional.
I created a simple STL version for those without an AMS, but I also made a 3MF version for those with an AMS. The 3MF version allows you to print just the floor in transparent material, and this gives the box a fun finish, allowing you to see the lock mechanism. But I added some masking rings to obscure the tumbler notch so as not to make it too easy to pick the lock.
The lock system is beautiful in its simplicity. A notch on each gear must align with its corresponding tumbler in order for the 3-point latch to be moved. Rotating each of the numbered dials controls the position of that notch and therefore creates the locking code for the case. Changing the relative rotation of the dial to the gear changes the combination lock. So users can change it over and over again at their discretion.
So, from the user’s perspective, it behaves like a classic combination lock. Turn each of the 3 dials to the correct lock combination, and the lid can be opened by sliding the latch bar to the open position. But if any one of the tumblers can not move forward, the lock latch bar can be moved.
In addition to the false bottom insert that holds a gift card, I have also made a simple blank one and also one that can hold a gift card and an AirTag. Why? I don’t know, it seemed like a fun idea. …may a treasure hunt with digital tracking for clues.
As noted above, you can print it with a clear floor if you have an AMS and want to be able to display the locking system (from the outside). If you do not have an AMS, you can still print the entire box transparent.
Print Settings
Functional designs (such as this one) generally require more strength than non-functional designs and more strength than the typical default slicer settings provide, so please review your slicer settings carefully.
This product was designed for a 0.4mm nozzle and a 0.2mm layer height. For best results, I suggest the following:
Post Printing and Assembly Notes
After printing, be sure to remove the small pieces of print support incorporated into the design as indicated in the following image.
Also, each of the compliant elements will benefit from you flexing them slightly now so they are free as you install the other components. Those elements are indicated in the following image as well.
Please follow the assembly process in the sequence of images below.
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