I decided to be cheap and make ALL of the transmission's gears myself. I'd machined a few gears in the past, but I figured I had more patience than before so it wouldn't be too bad. I started off by turning a "blank" for the gear. This was just a cylinder of the gear's outside diameter. Then I had to machine the teeth into the blank. This is the nasty part. There are a set of cutters meant for involute spur gears. There are 8 cutters required to cut any number of teeth for a particular tooth size. Each cutter has a range of teeth that it can cut. This is because of the gear's tooth profile. A standard gear has what is called an involute curved tooth. This curve is essentially the path taken by the end of a string that is unwound from a spool of thread. Gear teeth require this shape for their teeth in order to have a smooth and constant rotation rate.
Cutting the teeth requires a rotary table or spin indexer and one of the involute gear cutters.