[MrForbes]

That probably depends on what type of gearbox you are planning to use. If it's a planetary gearbox, it's kind of difficult. If it's a spur gear type then it's a little easier, but making a gearbox of any kind takes some precision work.

It might be helpful for you to post some pictures of what it is you're trying to make turn, and give some specifications about how much torque you need, and what speed it has to turn at. Without these details, it's pretty hard to for us to know how to help you.