I'd expect 4 - 10 RPM would be about right. Slow enough to allow
sliding, fast enough to induce some tumbling.
Get a variable speed motor.

- -
Rex Burkheimer
WM Automotive
Fort Worth TX

Peter Grey wrote:
So is there a consensus about how many RPM the barrel that holds the stones
(or in my case, old bolts from a project car) should be turning?

Peter

"Christopher Tidy" wrote in message
...

Hi all,

When I was about 8 or 9 years old I really, really wanted a stone
polisher. I think they were rather expensive and also (probably wisely) my
parents thought that I would be bored having to wait months for results,
so I didn't get one for my birthday. Anyway, I woke up in the night and it
occurred to me that a stone polisher (or rock tumbler as some people call
them) would make a great home shop project.

I figure I can make a drum (probably cube-shaped) from welded 1/4" plate.
The drive is going to be more of a challenge (I don't have a great deal of
cash to spend on this). I reckon I probably need about a 30 rpm drum speed
and 50 W of power for a small polisher. But the drive needs to be sturdy
and energy efficient if I'm going to leave it running in the shed all
year. A mulit-stage belt drive will be fiddly and probably not very energy
efficient. It seems to me that the best solution would be an oil-filled
worm and wheel gearbox, but I'm not sure where to scrounge one from. Can
anyone think of pieces of industrial equipment which use a suitable
gearbox, which I could look out for in piles of junk etc? Has anyone built
one of these before? Any ideas would be welcome.

Best wishes,

Chris