Gregory
off to a rocking start
Member since April 2013
Posts: 7
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Post by Gregory on Apr 26, 2013 10:49:08 GMT -5
Hi I want to tumble some large rocks like 4-6 pound EACH by them selves, one at a time. I have a 15 pound Thumler's Model B so I can fit a single large rock in it. Rocks are like 6x5x4 inches. I was going to put a single large say 5 pound rock in it with a lot of ceramic pins and rough grit then let it tumble.
I can't find any info about do a large single 4 to 8 pound rock anywhere. Thing that's been bothering me is the basic philosophy that rocks get smooth in a rock tumbler by hitting other rocks. So should I add some pea gravel or small river rocks or maybe even some glass marbles just to give the one large rock something to hit against or will just 5/8x3/8 ceramic pins be enough?
May sound silly but I'm going to try it with a number of different large rocks I have. Any practical advice would be appreciated.
Thanks
Greg
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Post by Toad on Apr 26, 2013 10:59:17 GMT -5
Ceramics should do the trick, but any variations you can add to vary size and shape wouldn't hurt - like the pea gravel you mentioned. I like tumbling larger rocks myself, but have never tried a one-stone load. Will be interested to see how you do...
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Sabre52
Cave Dweller
Me and my gal, Rosie
Member since August 2005
Posts: 20,487
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Post by Sabre52 on Apr 26, 2013 11:38:30 GMT -5
Interesting project. I've never tumbled anything larger than maybe half a pound. I'd think that big rock is sure gonna crunch up stuff you have in with it. Might even make your barrel jump off the rails if it suddenly shifts to one side. I'd sure use a whole of of filler. I'd think a full load of filler would cushion the big'un enough to keep it's movements in the barrel regular enough. It would be cool if you'd post pics of our progress. It would be very cool to tumble large specimens for displays or paper weights, if your process works....Mel
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Gregory
off to a rocking start
Member since April 2013
Posts: 7
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Post by Gregory on Apr 26, 2013 11:39:31 GMT -5
Well I'm say "one rock load" cause I'm tiring to do the single largest rocks that will fit in the 15 pound tumbler, also the most weight the tumbler will handle for a single rock. Figure any smaller rocks added will take away from the size/weight of the large rock I want to tumble. I have a lot of single rocks in the 5 to12 pound range, even some 20-30 pounders which will have to breakup, so I'm going to make this a long term project. I'm going to try to document it, take months. But advice and experience, which I don't have, beats trail and error, which I can do.
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Post by parfive on Apr 26, 2013 12:53:57 GMT -5
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herchenx
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Member since January 2012
Posts: 3,360
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Post by herchenx on Apr 26, 2013 13:10:44 GMT -5
Another option would be to grind it in leiu of a coarse tumble, and then use a vibe to polish it (several stages as described in Randy's instructions in his vibe tumbler tutorial) I've been planning on doing this with some larger rocks I have that I think would be cool polished.
I've done this with smaller stones so I know in principle that it works.
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Post by deb193redux on Apr 26, 2013 14:01:37 GMT -5
I don't think this can be done in a rotary tumbler. At least not in less than a year or more. A tumbler is not a magic chamber where rocks magically get smooth. There is basic physics to the abrasive process. Unlike heat in an oven, tumblers require very specific movement. Abrasion is work, force times distance. The weight of the rock sliding across the other rocks in the barrel is the force and distance (Line D in the picture). Larger rocks slide less and take longer.. Huge rocks (80% barrel width) don't slide at all. In this case, I can see you are thinking the ceramic bits will slide across the rock. But, the much lighter weight of the ceramic will mean much less force. Distance is even stranger. Because the rock is curved, unlike the relatively straight "line D" the ceramic will not start to slide until lifted much higher around the barrel rim, and then will only slide to the midpoint of the rock where it will simple drop to the base of the rock. This minimal abrasion (minimal force x stunted distance) will be very slow to form mud to suspend your grit, and even slower to smooth your rock. It would be like using only 1" strokes with sandpaper and not pushing down very hard. You should try to grind as many imperfections off the surface as you can, and then use a vibrating tumbler. (Larger would be better). The physics of vibrating tumblers are different. The abrasion in the vibe is not sliding, but high frequency rubbing of two objects against each other (with grit slurry in between). The force is an average of the mass of both objects (rock + pellet) / 2. In this case the mass/size of you rock works for you not against you. The rolling action of the tumbler will still be stunted, because only the ceramic will really be rolling. The rock might spin slightly, but not circulate like the ceramic. This means the dampness to hold grit on ceramic will be critical. Too wet and it will settle and the limited circulation will not fetch grit back up off the bottom. (In a larger vibe, the rock can circulate a bit.)
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Gregory
off to a rocking start
Member since April 2013
Posts: 7
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Post by Gregory on Apr 26, 2013 14:45:42 GMT -5
Thanks for the suggestions. Definitely going to have to put some small pea sized rocks in there, maybe a little larger then peas, like the garnets idea mentioned in link. I've been looking at ways to cut off or grind down uneven spots or rinds. Not much luck so far. The 7" tile saws can't do much to a 6 pound rock, can't even get at the area's. Been thinking about a drum sander or angle grinder. Can't afford to buy a slab saw. Need a cheap way to grind off spots on large rocks. Keep idea's coming...
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herchenx
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Member since January 2012
Posts: 3,360
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Post by herchenx on Apr 26, 2013 14:51:19 GMT -5
jamesp seems to be a master at getting really good results with inexpensive harware. I have an old Lortone combination unit that I put an 80 grit diamond wheel on and it chews through almost anything. The wheel was not super cheap, but given how long it has lasted and the time I save and cost of comparable grit and electricity to try and get similar results in a tumbler I'd say I came out way ahead.
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Post by johnjsgems on Apr 26, 2013 15:01:30 GMT -5
If the rock won't6 roll you won't have much success. You need a 40 lb. or larger tumbler to roll big rocks.
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Post by deb193redux on Apr 26, 2013 16:52:42 GMT -5
Put all the pea size you want. if the rock cannot slide it will not work. I would gestimate that diameter of rock should be less than 1/4 of barrel diameter. That will work slowly. As you increase diameter of rock, slow got to forever at an exponential rate.
An 80g wheel like mentioned above or a gang for 7" blades to make a super grinder can rough out rock. But then you need 15" diameter rotary barrel or a UV10 or UV18 vibe.
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Post by johnjsgems on Apr 26, 2013 20:57:19 GMT -5
Rocks rotate in vibes too. Rocks I've had that get stuck in one place just beat up the bowl.
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Post by Toad on Apr 26, 2013 21:13:25 GMT -5
thought the idea was to tumble, not slide??
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Post by deb193redux on Apr 26, 2013 23:31:44 GMT -5
not sure why it is called tumble instead of slide. no abrasion happens when the rock is tumbling over other rocks. it has to slide. just like tire rolls on road with little friction, but drags along road with lots of friction.
but something larger than 1/2 the barrel diameter will neither rumble nor slide.
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Post by deb193redux on Apr 26, 2013 23:32:58 GMT -5
Rocks rotate in vibes too. Rocks I've had that get stuck in one place just beat up the bowl. barrel damage is a good point. I was just speaking to the physics of the abrasion. but I did tumble a 3" t-egg in a Lot-O
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quartz
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breakin' rocks in the hot sun
Member since February 2010
Posts: 3,352
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Post by quartz on Apr 26, 2013 23:33:29 GMT -5
Our mid-size tumbler is a pair of 7" across inside x 10" long homemade octagons made of UHMW plastic, giving about a 15 lb. capacity. I just weighed the biggest rock we have run in it at 3lb. 6.6 oz. finished. It was originally close to the size you described. We ran it with a bunch of small agates such as those found at the beach. The one thing to watch, be wary of running a rock of a length that could go crosswise and get stuck in the barrel.
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rollingstone
starting to spend too much on rocks
Member since July 2009
Posts: 236
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Post by rollingstone on Apr 27, 2013 1:24:50 GMT -5
I came across this thread and noticed that that Parfive had referenced an old thread where I ran a one-pound chunk of Stone Canyon jasper in a 6 lb barrel. He noted that most of the photos had been lost from that thread, and I have now gone and added them in again in a new reply to that old thread.
That Stone Canyon chunk initially had the rock's longest dimension about half the inside diameter of the barrel. At that size, I found that brutal action in the barrel was the concern, not sluggish action. The solution was to surround the big chunk entirely with pea-sized garnets, everything went smoothly after that.
A 4-6 lb rock is an entirely different ball game, but if I were to try it I would use one big rock and a lot of small filler, whether that be ceramic media, small garnets, small beach gravel, or something similar.
My one-pound piece took 60 days in coarse grind. A 4-6 pound rock will definitely take longer, unless carefully pre-shaped in advance.
- Don
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Post by Toad on Apr 27, 2013 7:54:32 GMT -5
Don, was it one-pound at start or finish?
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Steve
has rocks in the head
Member since June 2005
Posts: 506
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Post by Steve on Apr 27, 2013 9:55:29 GMT -5
Here's a link to the largest rock I've polished in a tumbler - a partial sphere preform. home.comcast.net/~sscarbor/steves_spheres/pictures/img_0456.html This was done in a Lortone. It took long 2 polish runs, as the bottom siphoned to the bottom of the barrel, so I turned it over and did another run. I packed it with small beach agates that had already been run up to the pre polish stage and added a lot of plastic pellets for the polish run to make up for lost volume. All together this was a 6 month plus project.
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rollingstone
starting to spend too much on rocks
Member since July 2009
Posts: 236
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Post by rollingstone on Apr 27, 2013 12:27:45 GMT -5
Toad, it was 480 grams at the start, just over one pound. The polished stone was 310 grams, so it lost 1/3 of its mass from start to finish.
Steve, impressive. When you say it took 6 months, how much of that time was in the polish stage? And did you run all the tumbling stages including coarse after cutting the hexagonal shape?
- Don
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