There is also an older version of this mechanism here:
https://www.thingiverse.com/thing:5820868

And an improved version here:
https://www.thingiverse.com/thing:5888898

Here is a new variation of my safe with a mechanical system and a four-number password. This prototype has a locking mechanism that can only be opened with the correct combination of numbers.

Parts list:

• safebox_box (quantity to print: 1);
• safebox_box_A (quantity to print: 1) - optional, if you want to print the box in two parts;
• safebox_box_B (quantity to print: 1) - optional, if you want to print the box in two parts;
• safebox_box_slit (quantity to print: 1) - optional, with a slit to put coins;
• safebox_dial (quantity to print: 1);
• safebox_disk (quantity to print: 3);
• safebox_door (quantity to print: 1);
• safebox_double_marker (quantity to print: 2);
• safebox_hinge (quantity to print: 1);
• safebox_key_disk (quantity to print: 1);
• safebox_knob (quantity to print: 1);
• safebox_knob_big (quantity to print: 1) - optional with a bigger knob;
• safebox_latch (quantity to print: 1);
• safebox_latch_big (quantity to print: 1) - optional, with a bigger handle;
• safebox_lock_ring (quantity to print: 1);
• safebox_plug (quantity to print: 1);
• safebox_single_marker (quantity to print: 2);
• safebox_spacer (quantity to print: 3).

1. Use the "Instructions A" image to assemble the assembly using the printed parts;

2. Use the image "Instructions 2" to assemble the markers on the disks. The position chosen to mount the markers will define the unlock password.

Important: do not use glue to mount the markers on the disks at first. Mount the whole system on the vault door and perform the unlocking tests with the vault OPEN.

After you assemble the mechanism on the door, take time to understand how this kind of safe works. When you turn the external knob clockwise, it rotates the disk fixed on the shaft at the opposite extremity, inside the box. This disk turns and pushes, through the markers, the second disk. The second disk pushes the third disk, and the third disk pushes the fourth disk. When the indentation on the fourth disk aligns with the latch, stop the movement and take note of the number aligned on the dial with the arrow. This is your first combination number. Now reverse the rotation (counterclockwise) and proceed until the third disk is also aligned. Again, take note of the second number in your combination. Do the same for the remaining disks. Once all the disks are in the correct position, you have cleared the way to move the latch.

Here is an example of the combination shown on the attached video:

1. Rotate the knob three times clockwise to be sure that all the disks are moving together;
2. Rotate the knob clockwise until the number 04 aligns with the arrow;
3. Rotate the knob counterclockwise and pass the number 64 two times. On the third time, stop exactly at 64;
4. Rotate the knob clockwise, passing by the number 92 one time. On the second time, stop exactly at 92;
5. Rotate the knob counterclockwise, stopping exactly at 75.

Only after the tests are done and the password is written down, do the final assembly, applying glue to the disk markers. Test the code once more with the vault door open to make sure the password you wrote down is correct.

If you wish you can apply glue to the end of the hinge pin and the bottom plug.

I have made the box available in a single file and also in a split in two option for easy printing (safebox_box_A and safebox_box_B). If you choose to print the box in two parts, they must be joined with glue.

In case of difficulties, please send me a message and I can help you with further details.