We had to copy our downstairs bar key the other day because zhuoma's key broke while she was trying to open the lock. The key copying machine (used by those guys sitting next to the shoe repair guys) is completely manual. There's a crank on the right, which the guy turns to spin an axle. I assume there's a flywheel on the axle to store energy and keep it spinning at about the same speed. The axle has a grinding stone and one other protrusion on it. That's part 1 of the machine.

There's one more counterbalanced device, which is weighted to fall toward the axle. The key blank is attached in one spot, and the original is attached near the protrusion. Then both keys slowly move across the length of the axle. The protrusion follows along the teeth of the original key, and because the key blank is attached to the same arm, it gets ground at the same height.

One copy takes about 5 seconds. It's all pretty cool.