A while back I posted about the possibility of tumbling long parts in
a mill to give them a finish. I've been experimenting with this
recently, and so far it's worked pretty well.

I went and got one of those cheap rock tumblers from the dreaded HF...
I always feel guilty after I walk out of there, thinking: 'There goes
a few more dollars to China'... But what can you do? Everybody buys
from China in my product field too, which is why I can't afford to buy
American myself.

I went to the pet store next door and picked out a few bags of
different media... Small river pebbles, walnut shells, and corn cob.
So far I've only tried the pebbles, which are basically the small
polished kind, about 1/8" to 3/16" in size. I filled the canister
about 1/3-1/2 full with the pebbles and water, and also added a couple
squirts of orange oil soap. It took a while to get the time down, but
on 6061, it looks like about 2 to 2 1/2 hours is just about right. The
parts come out looking great with a finish that is about equal to your
average fastener. Using the walnut or corn cob would I'm sure improve
that to a high shine. But for mechanical parts, just the pebbles alone
are great. I'm actually surprised how short a time I have to leave it
in there. Harder metals would obviously take longer, but this is fine
for aluminum. Mostly I've been doing 1/4" round pieces of various
lengths, but I also did some 1 1/2" angle brackets. The only real
limiting factor is the size of the container.

So next up is to build a long one so I can do parts about 2' long. I
think a 1/4 to 1/3 HP motor should do. I'll need to work out the ratio
to get the tube spinning at about one rotation per second or a little
faster. I should be able to put about 20-30 pieces in there at a time,
which sure beats polishing one at a time.

Dave

A transmission shop used to use an electric cement mixer as a tumler. Kinda
noisey, but it worked
--
--
Stupendous Man
Defender of Liberty, Advocate of Justice

On Sun, 23 Sep 2007 15:12:19 -0700, wrote:

A while back I posted about the possibility of tumbling long parts in
a mill to give them a finish. I've been experimenting with this
recently, and so far it's worked pretty well.

I went and got one of those cheap rock tumblers from the dreaded HF...
I always feel guilty after I walk out of there, thinking: 'There goes
a few more dollars to China'... But what can you do? Everybody buys
from China in my product field too, which is why I can't afford to buy
American myself.

I went to the pet store next door and picked out a few bags of
different media... Small river pebbles, walnut shells, and corn cob.
So far I've only tried the pebbles, which are basically the small
polished kind, about 1/8" to 3/16" in size. I filled the canister
about 1/3-1/2 full with the pebbles and water, and also added a couple
squirts of orange oil soap. It took a while to get the time down, but
on 6061, it looks like about 2 to 2 1/2 hours is just about right. The
parts come out looking great with a finish that is about equal to your
average fastener. Using the walnut or corn cob would I'm sure improve
that to a high shine. But for mechanical parts, just the pebbles alone
are great. I'm actually surprised how short a time I have to leave it
in there. Harder metals would obviously take longer, but this is fine
for aluminum. Mostly I've been doing 1/4" round pieces of various
lengths, but I also did some 1 1/2" angle brackets. The only real
limiting factor is the size of the container.

So next up is to build a long one so I can do parts about 2' long. I
think a 1/4 to 1/3 HP motor should do. I'll need to work out the ratio
to get the tube spinning at about one rotation per second or a little
faster. I should be able to put about 20-30 pieces in there at a time,
which sure beats polishing one at a time.

Dave

Check out
http://www.vibratoryfinishing.com/2ha18.htm

Yeah, the guys that make them for powder is where I got the idea. The
key with the tumbling from what I've learned, is that you have to have
a surface inside that will induce an actual tumbling effect. In other
words, it's like you're creating little mini avalanches over and over.
I believe this is why they make the rock tumbling canisters from
rubber. The rubber surface allows the materials to stick to the sides
just enough, that they eventually break off and tumble over
themselves. If you try it in something that's too smooth, the material
just slides along the bottom and doesn't tumble. Obviously the mill
works because you're using ball bearings. I haven't figured out how to
surface the inside of the pipe yet... maybe just take some non slip
sheet and glue it in there. I've already got my 4" ABS with caps and
also found a motor. Now I just need to order the drive parts. I'm just
hoping the average cheap AC motor will be able to stand running 2-3
hours at a time.

That big green one is radical though.