Polishing long parts with a tumbler

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

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A transmission shop used to use an electric cement mixer as a tumler. Kinda noisey, but it worked

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On Sun, 23 Sep 2007 15:12:19 -0700, snipped-for-privacy@aol.com wrote:

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

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"Don't try this at home . . ."

When I was a kid I made a black powder mill out of a large coffee can (removable lid) with an axel running through it, end to end. Rotation was via a small motor and capstan. I would put in a "charge" of saltpeter, charcoal and sulfur along with a handful of glass marbles. It made a nice "chunk, chunk" noise as the contents bumped over the can's seam on each revolution. It would grind black power much finer than I could ever do with a mortar and pestle. Luckily (God protects children it seems) there was never a mishap.

Probably one could do the same thing with one of the HF tumblers; but I would be sure to wet the contents.

Bob Swinney

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

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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.

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