Michael Koblic wrote:

"Bob Engelhardt" wrote in message
I made one from a 20 lb propane tank & treadmill motor:
http://www.metalworking.com/dropbox/vibepolisher.jpg

... I was not clear about the
concept: The motor spins an arm which moves the bowl in a circular
eccentric fashion? I somehow expected the movement to be up and down.

Correct. Since the bowl is not actually rotating, the effect is a
back-and-forth motion. This back-and-forth against the curved sides
causes the "media" to have a rolling action: it actually flows up the
sides & middle and down in between. It was quite surprising the 1st
time that I saw it.

Presumably the adjustment would be achieved by regulating the length of
the arm and thus the amplitude of the vibration. The frequency of the
vibration is then given by the motor rpm (I guess yours is adjustable
being a treadmill motor). I see the recommended frequency is no less
than 1600 Hz so an ordinary induction motor would do.

Correct again. I read somewhere (Eastwood , I think), that their
vibrators ran at 3000 rpm, so that I what I used. The frequency makes a
huge difference. Not knowing what-the-hell was going to happen the
first time I ran mine, I started out very slowly & worked up. At some
point - the resonant frequency, I suppose - the action was VERY violent!
Increasing it further, it quieted down & at 3000, it was very smooth
(but NOISY).

I have done a ton of research on this but eventually one has to get
one's feet wet. I was reluctant to spend money only to find out that the
whole thing is completely useless for my purposes. I am actively looking
for someone who has one to tumble a couple of my parts and see if it
does the job.

Heh - I have used mine pretty much not-at-all. Another one of those
projects whose point was to build it, not have it G. It does polish
silverware nicely - corn cob media , with a touch of rouge.

Bob