I've made a grinder heres what you need

1. 2 Gatorade tops
2. Around 20 thumb tacks

Just take the thumbtacks and insert them in the top. Start around the edge and go in a circle until you reach the middle, then do the same with the other top. Now once you have the tacks in place, set one top on top of the other and make sure to turn it and if it doesn't turn figure out the problem which will probably involve moveing a tck or two. Once they fit each other, bend the outside of one so the other one can fit inside and it should work. I hope that wasn't confusing cause I'm high as shit. But there you go a homemade grinder