You’ll want to start out by making the cylinder that the discs rotate upon. This is done by taking paper and wrapping it around a pencil with Elmer’s glue. Don’t glue it to the pencil, but glue the paper so that it is a decently hard cylinder that the pencil can spin spin freely inside of. Next, cut out three circles from cardboard that are a bit over an inch in diameter. The measurements don’t matter two much in this combination mechanism, just make sure it will fit in the final box. Punch holes in two of the circles that will allow them to slide onto the paper tube. You want a little bit of friction but not too much or it will hinder the ability for the discs to rotate. On the third disc, punch a hole the size of a pencil, which should be slightly smaller than the paper tube.

Now add some teeth to the outer rim of each disc. Make sure it extrudes no more than 1/4». Use the photos above for reference. In the end, when you rotate one disc, it should meet the teeth of the other discs until all three spin. Note that the middle disc should have two teeth, one on each side. Cut a notch into each disc with random placement so the combination will end up random.

Now take some thin cardboard and cut it into strips 1/4» wide and long enough to be wrapped around the paper tube. These are the sections that separate the discs seen in the pictures above. Slide two discs into place along the tube, 1/4» apart, and glue the cardboard strips in between the discs to separate them and keep them in place. The third disc needs to be glued to a section of the pencil. The pencil should extend long enough to go through the wall in order to attach the main dial. In my reference pictures, the pencil is green.

If done correctly, spinning the end of the pencil, which is attached to one disc, will eventually spin every disc as the teeth meet up. You can now try lining up the notches.

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