I made a combination lock out of wood, plastic, and some odds and ends. (Here is an overview of how a combination lock works.)
Here's what the inside looks like:
It has no sides or top.
I had a problem with the cams rotating due to friction with adjacent cams. This is what the blue rubber bands are for; they rub against the second and third cams to provide a competing source of friction:
It took about six hours to make. The front, back, and shackle are plywood. The cams are cut from a plastic board.
This thing is completely unsuitable for protecting anything important, so I might as well say the combination is 0-6-4.
Here are some more pictures:
I've removed the top cam in this one so you can see the second cam:
Here I've removed all three cams and put them side by side:
A closer view of the latch:
It's mostly biodegradable, which is better than most locks. But on the other hand, you can see how to open it by looking in the top. There is no point.