I like watching craftsman and maniac Ronald Walters' woodworking videos for two reasons. Number one is his skill. Number two is because he sounds enough like Parks & Recreation's Ron Swanson that I half-expect him to say things like "Turkey can never beat cow" or "Kendra, I think I will have that third steak."
In any case, if I showed you a bunch of plywood gears like the ones pictured above, you'd probably ask where I had them CNC'd. But Walters cuts his teeth the old-fashioned way: With a freaking scroll saw, following along on a pencil line. His accuracy is pretty nuts—if he were off by a millimeter here and there, he probably wouldn't be able to rotate his pin gear and ring gear assembly at this speed:
If you're wondering why the holes around the circumference, Walters is planning to incorporate the gear into some kind of marbles machine.