There's a free version of Cinema 4D called Cinema 4D CE 6, which includes a gear tool that works very nicely. You can change the parameters of the gear any time after you've created it. The only thing is, I don't know how you can get this program. I got it from a CD that came with MacAddict magazine, and I've seen it on CDs from other Mac and PC magazines. It's certainly worth the cost of a magazine for all of the fine modeling tools.