My wife recently started making beads and other things from polymer clay, and wasn't getting quite the finish she wanted using sandpaper. It turns out that even children's toy rock tumblers are relatively expensive and the professional models are definitely out of our price range, so she asked me to see if I could assemble something from old bits and pieces we had laying around.
The kind of tumbler I've seen before seemed like a fairly simple arrangement - some kind of barrel turned by horizontal rollers, similar to a tumble dryer, so that's what I set out to build.
Parts list - these parts all came from my junk pile. Nothing was purchased for this project, so technically it cost $0 to build.
1) electric motor from Grand Am electric window lifter.
2) old PC power supply. This one happens to be a 90W supply.
3) rollers - could be broom handle or any round pole. These are actually mini rolling pins from my wife's craft supplies.
4) various bits of wood to make a frame and base board.
5) 2 inches of garden hose.
6) power switch.
7) screws, coach bolts w/ nuts
8) anti-slip shelf liner
3) Drill + appropriate sized bits
5) Sharp knife
6) Soldering iron (or use crimp-on spade connectors)
Step 2: Initial sizing
Cut several length of plank to make the ends of the frame, then stand them in their approximate locations. The position of the driven roller depends on the size of the motor mount. The position of the other roller is variable, depending on the size of the drum. The rollers here are 5" apart on centers. Later I decided to add a third roller at 3.5" to accomodate smaller drums.