I made another ball mill that I think will be more efficient than the one I have been using so far. it is a 9 inch OD jar, 7.5 ID and 8 inches long. The ideal RPM should be 68, I have it at 60. This is simply because of what was available for pulleys, I can increase it to exactly 68 by adding some electrical tape to the shaft where the jar rests but I think its pretty good now. As you can see though, the jar isn't half full with media so I will have to cast some more of those balls or maybe fill the rest with ceramic media. This is a very nice jar.
Attachment 292951
Attachment 292952
You cant see them in the pictures but there are stoppers on the driving shaft preventing lateral movement so the jar wont slip off the casters. The 1/2 drive shaft has a plastic tube sleeve that fits over it to ad friction. I gave it a run and the rubber lining in that jar makes things very quiet.