Building the wooden combination lock
Before that, I had also laid this template onto the back piece and punched the hole centers through with an awl. The back only has a few holes, so I didn't bother to print that template. The holes are in the same place front and back.
I punched divots through the centers of the holes, then peeled off the front template and drilled the holes with Forstner bits. This way, I don't get the drill chewing up the template. The divots naturally guide the point of the Forstner bit to the exact location.
After that, I drilled the correct size holes using the pilot holes as a guide.
A spacer needs to go between the two L-shaped pieces of plywood. This spacer goes against the 5/8" (16 mm) dowel, so it needs a round curve cut out of it to match the dowel's radius. I carved that out using a gouge (a curved chisel)
And a thin wooden strip also goes between them. I cut this from some solid hardwood. It's only a few millimeters thick, but by not cutting all the way to the end, the thin piece doesn't end up flying into the saw or getting kicked back. After that, I cut off the length that I needed.
After that, I put some clamps on it and let the glue dry.
Two strips of wood that go on the bottom have an arc cut out to clear the L-bracket as it rotates. I cut out the template, laid it on the wood (without gluing) and traced the curve with a pencil. It wasn't worth gluing the template on.
The three rotors and the front dial are all circles of the same diameter. I figured it was more convenient to just use a compass to draw the circles on some plywood than to paste on the templates. Then I cut them out with a bandsaw.
One of the small circles is glued on the back of the dial. I used a piece of dowel to help line up the holes, then applied clamps. Then, before the glue fully dried, I pulled out the dowel to make sure it doesn't get glued in place.
The rotors all need to turn freely on a dowel. My dowels fit very tightly in the 5/8" holes, so I used my belt sander to sand the dowel down a bit to make a looser fit.
This piece of dowel gets glued into the back panel, with one of the rings to help reinforce this connection. It's important that this dowel is square in the panel. I ended up placing two squares next to it to hold it square while the glue dried.
I lined it up with the dial and disk on the back, again with a dowel in the hole, then applied clamps,then removed the dowel before the glue fully set.
The front and back rotors have a tab that sticks out on one side, while the middle rotor has a longer tab that sticks out both sides.
Cutting out the open lever. I cut the sides of the point, but didn't cut them all the way off. I then flipped it on its side and cut the pointer end to be less thick, I then flipped it back again and finished cutting out the shape.
When attaching the back, it's important that the dowel attached to the back ends up centered in the large hole on the front. I lined it up and held it in place with some spring clamps, then used a drill to mark a small divot for where the holes line up.
I then used those divots to line up the pilot hole locations, which I drilled on the drill press.
I messed up when I glued together the L-bracket. I should have positioned the dowel further towards the front (for the knob). Rather than make it again, I just glued another short piece of dowel onto the end of the one that's there. End grain to end grain joints, if done with enough glue, can be surprisingly strong.
If you build one, I'd recommend using a longer dowel when gluing up this bracket, that way you don't have to worry about positioning it just right. After it's glued up, cut the dowel to the right length.
The dowel that the L-bracket rotates on fits very tightly in the holes I drilled in the front and back panel. So I wrapped some sand paper around a 1/2" dowel and used that to sand the holes larger until the dowel could rotate freely.
A pin through both pieces transfers rotation. Here drilling the hole in the front rotor part.
Here's how the front knob fits on. Note that in this photo, the front rotor is pushed way forward. The back of the knob actually protrudes through the front panel (whereas this shows the front rotor part protruding through).
I also had to make two thinner washers to go on either side of the L-shaped bracket to center it in the lock. You can make these out of 1/8" (3 mm) plywood, or use 1/4" plywood and then sand them down to the right thickness.
I then assembled the lock temporarily. The dials still don't have notches in them. To figure out where to put the notches, I simply dialled in the combination and then marked where the notches line up with the coat hanger wire. I based the combination on the mathematical constant e, which is 2.7182818284... so the numbers are 27, 18, 28. I first wanted to use Pi(π), but the dial only goes up to 39, so 31,41,59 would not have worked.
A screw behind the bolt then prevents the bolt from sliding out the right side.
As it is, I have to dial the combination slowly. If I dial too fast, the rotors will overshoot their position from momentum.
But the whole lock is really not that practical. It's more there to demonstrate how a combination lock works.
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