elxmanct
off to a rocking start
Member since March 2010
Posts: 2
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Post by elxmanct on Mar 25, 2010 7:02:46 GMT -5
My father was getting rid of his Thumlers Tumbler Model B which he had used for polishing brass casings, so I assume it is the high-speed model. I took it off his hands. Having absolutely no experience, I stopped by a hobby store and bought a box of Thumlers grits and polish. My son and I collected some fairly smooth river rocks, filled the 15 lb. drum about 2/3 - 3/4 full, added water to almost cover the rocks, poured in the bag of the roughest grit, and away we went. After a week, the rocks were a lot smaller and a bit smoother; they were pretty smooth to start. After washing the rocks and barrel, I repeated with the next finer grit. The rocks came out quite smooth and pleasing to the touch. Then I tried it with the prepolish and the rocks came out considerably rougher. What gives? And can someone tell me how much grit and polish I am supposed to be adding. I have just used the entire bag that came with the kit. And I did not use any plastic beads.
Thanks for your help.
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Post by deb193redux on Mar 25, 2010 8:21:33 GMT -5
I think the problems are unsuitable rocks and lack of pellets.
As for how much grit in a Model B, it is 1lb in the course stage, so if the box is a 1lb box, you got it right:
Model B 12 lbs
15 lbs Coarse........................1 lb.
Fine.............................1 lb.
Prepolish......................1/2 lb.
Polish...........................1/2 lb
See the rotary tumbling guide at therockshed.com or one of the guides posted here.
I do not think you have hard enough rocks. Just the fact that the river had already rounded them so much is a clue they were soft. River agate and jasper (or other high silica rock) will be smoothed in places but still have rounded edges.
That the rocks got considerably smaller in only 1 week is another big clue. Hard agate and jasper can take multiple weeks even when shaped fairly well at the start, and upto 16 weeks in course if the starting shape is angular.
That they continued to get smaller in the finer grit is another clue they are too soft. Usually the finer grits smooth w/o changing the shape much.
Most soft rocks will not polish. If you can scratch them with a nail they are softer than MOHS 5 and will never polish.
The pre-polish is much thinner and considerably finer. I suspect the rocks shed enough mud in the courser stages that the lack of pellets was not a problem. Here less mud would have been generated and the slurry was thin enough that the rocks banged into each other too much. When the mud in the course stages made a thick slurry, ther rocks were coushioned. Even with hard stones, pellets in the later stages are pretty important.
I can't tell if you had enough smaller stones. The load in any size barrel needs to be a mix including many fairly small stones. All of the rubbing/grinding action and rules of thumb about water levels is predicated on these small stones filling in all the spaces between the bigger stones.
Maybe post a pic of the rocks so we can see if they look like agate and jasper (or flint or chert) and see if you have enough smaller ones. Also do the nail-scratch test.
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Post by johnjsgems on Mar 25, 2010 8:47:50 GMT -5
The Model B is 15 lbs. per Thumler's. The same drum is used by Diamond Pacific on their 12 lb. tumbler. If you use one tablespoon per lb. you should be ok. As far as speed, I don't think the B comes in a high speed model but you can read the motor speed on the motor. As far as I know, the reloading places sell the same model used for lapidary.
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elxmanct
off to a rocking start
Member since March 2010
Posts: 2
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Post by elxmanct on Mar 28, 2010 8:30:41 GMT -5
Wow. What an amazing amount of useful information. I had no idea that some rocks are too soft or that I needed smaller rocks in with the larger ones. I think it is time to start anew.
Thanks for your help.
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