Rock Tumbler

http://www.youtube.com/watch?v=Vzuz8jFhXm8&feature=youtu.be
This is a rock tumbler that I designed as a birthday present for my daughter. It uses a 3000 RPM AC vent fan motor to drive it and the container is a mayonnaise jar. It's very powerful and spins easily with a load of rocks at 60 RPM. In my initial try with only rocks and water (no compound) the rocks were noticeably smoother in only 2 hours.
The motor gets warm so I put a fan on the motor pulley to blow air on it. The fan is thin enough that if you stick your finger in it, it will bend or break and hopefully not slice off your finger. (I did it once and I can still count to 10 without using any toes!) Someday I may add a guard.
The belt between the motor and gear pulley is a standard 3.5" rubber band.
I use thick rubber bands on the jar for traction. The rollers are also designed so a standard size wide rubber band can go on them.
The gears are true involute gears so they should not wear quickly. Except for the noise of the rocks falling, the thing is pretty quiet. I've had toy versions that wined like crazy.
This is a new design and has very few hours on it. As it gets used and I see what wears out, I'll be posting improvements.
Known challenges:

1. A good epoxy needs to be used to hold the ribs in the jar or they will come loose.
2. The motor is only held at 2 points so can tend to not be straight. I added a rubber band to counter the pull of the belt.
   An alternate use of this device could be a mini-clothes washer. Add detergent, and a pair of socks and underwear and have clean clothes for the next day. :-)
3. The rubber band can't seem to take the stress. It breaks in about 8 hours of running. I'm going design out the belt and use gears.

If you want to use a different motor, I think you could just print a motor mount and attach it using the holes I used for this motor. My motor is 1/75th hp, and is more than is needed for this purpose. If you need a different size pulley for your motor, leave me a comment. I have the pulley designs in SolidWorks and they are easily changed.
See the build instructions for details on printing.