Over on the WIP drag page, Daniel Himmel AKA Straightliner is figuring out how to make a cogged blower belt. He made a gear of sorts and rolled it on lead foil. Check it out.
I needed a small air filter element, so I found a picture hanging nail with a brass gear on the end slid it into a good fitting K&S tube then rolled it over some aluminum ducting tape. Then I wrapped the adhesive backed variegated foil around some styrene rod. It will get painted and shaded later. I might make another run at the "element" part because I pulled on it a bit and pulled out the pattern a little.
Anyway, it's easy, cheap, and does not take any special tools.