In college, one of my lab courses required us to learn manufacturing techniques. We covered a wide range of methods for machining and shaping things, all out of metal.
Making gears was interesting, we had to first turn a rough blank of metal on a lathe to make a steel gear blank (about 12cm in diameter and 2cm thick) then drill out the center and broach a keyway for the axle that would go through the gear. This was all pretty straightforward, but the final piece of work was more difficult, it was cutting the teeth of the gear. The teeth of a properly made gear require complex shapes.
There are, as I recall, two ways to cut the teeth. Hobbing uses a helical cutting head turning on an axis that is roughly perpendicular to the axis of the gear. The cutting head and gear turn at the same time in a synchronized manner and the teeth are eventually cut out by the cutting head. See [1] for a video of a large complex gear being made this way.
The other method, broaching, uses a straight bar of tool steel that has thick straight across cutting teeth. The bar is pushed past the disk shaped gear blank. The cutting bar moves in a straight line parallel to the axis of the gear blank. Repeated passes over the gear blank cuts out the spaces between the gears teeth.
Master machinists taught us how to make these kinds of projects. They would produce a finished gear in about 15 minutes of instruction; then we would have something like two weeks to make the gear. They made everything look easy; it definitely wasn’t easy for me.
Making gears was interesting, we had to first turn a rough blank of metal on a lathe to make a steel gear blank (about 12cm in diameter and 2cm thick) then drill out the center and broach a keyway for the axle that would go through the gear. This was all pretty straightforward, but the final piece of work was more difficult, it was cutting the teeth of the gear. The teeth of a properly made gear require complex shapes.
There are, as I recall, two ways to cut the teeth. Hobbing uses a helical cutting head turning on an axis that is roughly perpendicular to the axis of the gear. The cutting head and gear turn at the same time in a synchronized manner and the teeth are eventually cut out by the cutting head. See [1] for a video of a large complex gear being made this way.
The other method, broaching, uses a straight bar of tool steel that has thick straight across cutting teeth. The bar is pushed past the disk shaped gear blank. The cutting bar moves in a straight line parallel to the axis of the gear blank. Repeated passes over the gear blank cuts out the spaces between the gears teeth.
Master machinists taught us how to make these kinds of projects. They would produce a finished gear in about 15 minutes of instruction; then we would have something like two weeks to make the gear. They made everything look easy; it definitely wasn’t easy for me.
[1] https://www.youtube.com/watch?v=0rnTh6c19HM&feature=share