The molds I make are fiberglass. You can ask questions on it in the composit section. Molds for gears would be quite different.

I have broken one gear on a heli in the last 10 years, why would you want to mess with making them? They are so cheap, unless you get the metal ones, which I use. They would be a lot more cost to make. You would need a CNC machine, which is over $10,000 for the model we were looking at, and it was tiny