megalotis
starting to spend too much on rocks
Member since April 2009
Posts: 226
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Post by megalotis on Dec 5, 2014 11:14:21 GMT -5
I'm a newbie to tumbling, and this may seem just plain foolish to you long-time tumblers, but I've observed what I feel is a strange phenomenon after running a few batches through my 3 pound rotary tumbler. From what I see, the coarser grits don't do much to the stones. I understand the theory, and I have some years of experience grinding and polishing on wheels, so this doesn't make much sense to me. However, I see what I see. After 2 weeks in 60/90 grit, I see very little difference in the stones. Ditto after a week using 120/220. It's only after I move to 500 and 1000 grits that the stones really start to round out and take shape. Why this would be, I don't know, but I do know that I'm starting my next batch in 500 grit to see if I can abbreviate the tumbling time and obtain the same results. Could it have something to do with the larger volume of small grit particles having a greater abrasive effect? I'm kind of at a loss to explain it, other than that. I've been filling the tumbler about 3/4 to 7/8 full of stones and smalls, and using relatively little water in the tumbling mix, as recommended by others on this forum, which does seem to increase the abrasion on the stones. I've been tumbling mixed material, mostly jasper, agate, hickoryite, and other harder material. I probably over-do it when it comes to grit, usually adding 3 to 4 heaping tablespoons per load. I'm getting a real nice polish using .05 micron AO. Any thoughts on the coarse grit issue? Am I doing something wrong that might make the coarse grit less effective? I'm loving my tumbler, but the way. Now I need a bigger one!
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Post by captbob on Dec 5, 2014 11:19:47 GMT -5
TWO weeks in 60/90 ??
A week of 120/220 ?
yer funny...
get back to us after a month or two.
7/8s full is pretty darn full unless you are tumbling soft stones in the latter stages.
My thoughts...? PATIENCE
adding: Don't move on to the next stage until you are happy with the results of the stage you are on. If you take stones out of 60/90 and put them in a jar of water and you wouldn't be happy with them right then and there (wet), put them back in the 60/90 for another run. This takes time!
also: to answer your thread title question - there's not much that grit can't wear away to nothingness given time. It can surely round your stones - - - given time.
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bsky4463
fully equipped rock polisher
Member since September 2013
Posts: 1,696
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Post by bsky4463 on Dec 5, 2014 11:31:05 GMT -5
Duration on coarse grind is all dependent on material hardness and condition of the rough. Likely months for true rough, can be a week to several weeks on rough that you work on the grinder or wheel first.... There are lot of threads to search and read on slurry thickness, speed of rotation, etc for optimizing the rough grind. Best advice is consider it a journey not a destination and enjoy the ride. Sage wisdom from captbob - patience.... Cheers
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tkvancil
fully equipped rock polisher
Member since September 2011
Posts: 1,546
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Post by tkvancil on Dec 5, 2014 11:35:03 GMT -5
That is a stumper. I see the opposite in my tumbles. The coarse grit removing the most material and the finer grits removing less.
When you open the barrel of coarse is there any grit left over? If there are easily seen grit particles left over then there is something off in your formula. Too much rock or too much grit are possibilities.
In my lortone 3 pounders I prefer 2/3rds volume. At 3/4 or more volume of rough rock I never got a good grind. Here is my formula .... barrel filled to 2/3rds, 1/2 cup water and 2 or 3 level tbs. grit. Run for 7 days then clean out add rock to make up volume and repeat.
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Post by Jugglerguy on Dec 5, 2014 11:35:10 GMT -5
I agree that 7/8 is too full. If you want a gentle tumble on more sensitive rocks like quartz or obsidian, full can protect them from banging together so much. Try 2/3 to 3/4 full.
Did you mean that you tumble for two weeks total in 60/90? Or do you do clean outs every two weeks? I do full clean outs weekly. I run hard rocks like agate and jasper for months in 60/90. In my weekly clean outs, I remove rocks that are ready for the next step and replace them with new ones. I start collecting rocks for the 220 stage and only start it when I have enough to fill my barrel again. Don't expect to see any shine after 60/90. You're just trying to shape the rocks and remove holes and cracks in the first stage. I like to keep mine here for so long because I want my rocks as perfect as I can get them. I also don't want any holes trapping grit and carrying it to later stages. A little contamination in later stages will ruin the whole batch.
I use 3 to 4 level tablespoons of grit in a three pound barrel, so what you're doing sounds ok.
If you want more advice, pictures are always helpful. I post mine on Flickr and then link to them here.
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Post by Jugglerguy on Dec 5, 2014 11:36:37 GMT -5
Wow rapid fire responses!
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Post by captbob on Dec 5, 2014 11:46:53 GMT -5
I'm thinking he is seeing shape change after moving on simply due to the time the rocks have been tumbling against themselves with whatever grit. No question that a coarse grit will remove more material given the same time to tumble vs a finer grit.
We all go through a learning curve when starting out. Again, patience is the key to rocks worth being proud of.
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Post by deb193redux on Dec 5, 2014 11:51:39 GMT -5
What is puzzling is that the 500g is rounding the stones. If it just started shining them w/o rounding I would understand. There is some mystery. I do think the barrels are too full at 7/8 to allow enough sliding action. See the 3/5th barrel in this image: Usually I would say too much water was letting the heavy grits fall to the bottom instead of forming slurry. But you report fairly little water. next I would think of too many larger stones and not enough smalls to provide abrasion surface, but you do mention smalls. So to cover bases, do you see any evidence of 60/90 grit breakdown when you wash out barrel? Any mud? Is a slurry forming? Also, when you say smalls, can you give a picture of what you think is a balanced load?
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Post by Jugglerguy on Dec 5, 2014 11:53:25 GMT -5
I actually see the biggest change in the rocks in the very first week. They go from being very rough to somewhat smooth. The outer crust and/or dirt is also cleaned off to show the color of the rocks better. The next eight weeks are painfully slow though.
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Post by Starguy on Dec 5, 2014 11:58:23 GMT -5
megalotisJugglerguy pretty much hit the nail on the head. His recipe is pretty much the standard. If you have enough rock, a larger tumbler will be a little more efficient. You will get a heavier mass of rock sliding over each other effectively increasing the grinding pressure on the lower rocks in the batch. Larger tumblers also have flat sides in the barrel that keep stones from sliding along the inner surface of the tumbler barrel. I use Lortone rotary tumblers. I've found that a 12 lb tumbler and a 3 lb tumbler are a pretty good match. The 12 pounder runs exclusively with 60/90 or coarser. The 3 pounder runs fine, pre-polish and polish. After three weeks of fine through polish, the 12 pounder has usually rough ground enough to fill the three pounder again. Occasionally the the small tumbler will have to wait a week or two for the 12 pounder to catch up but that doesn't happen too often. I've been producing a 3 pounder of polished stones every 3-4 weeks. It will take a month or two for the big tumbler to produce enough "ready for fine" stones when you recharge with all new rocks. Hope this helps. Post some photos when you get a chance. Later, Brent
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megalotis
starting to spend too much on rocks
Member since April 2009
Posts: 226
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Post by megalotis on Dec 5, 2014 12:14:42 GMT -5
Rapid indeed! Gosh, I thought I was being really patient using a 2-week stage for the coarsest grit! I have seen the error of my ways! Smaller loads, at least a month in 60/90 grit and maybe another in 120/220 with 2-week interim cleanouts and grit refresh.
Thanks much for sharing your hard-earned wisdom, it is greatly appreciated!
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Post by captbob on Dec 5, 2014 12:26:28 GMT -5
Can't use a calender when tumbling. They are ready to move on when they are ready. The hardest thing about tumbling may be the time that quality takes
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Post by Starguy on Dec 5, 2014 12:32:15 GMT -5
megalotisWhen silicon carbide grit wears out, it doesn't disappear, it just turns into finer grit. I usually change the grit weekly to keep the batch working in truly coarse grit. For softer or already rounded rock, you can sometimes skip stages by letting the stones run longer. 60/90 seems to break down into roughly 120/220 in two weeks or so. It takes a little experimentation to see what works because it seems to depend on the hardness and durability of the rocks.
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megalotis
starting to spend too much on rocks
Member since April 2009
Posts: 226
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Post by megalotis on Dec 5, 2014 12:34:06 GMT -5
deb193redux, I do get a slurry, there's sometimes quite a bit of grit left, and sometimes none is detectable after 2 weeks.
By the balanced load question, I just load the tumbler up with stone, than put in a few handfuls of smalls, shake it down a bit, then add the grit, then the water. I don't have a specific measurement that I use to determine the amount of smalls.
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Post by captbob on Dec 5, 2014 12:45:12 GMT -5
It ain't rocket science, so I never measure grits or water. Maybe there is a "perfect" blend, but I'm anal (picky) about enough other things in my life to be too concerned if I put in half a teaspoon too much grit. I measured early on, but now figure it will all work itself out in the wash...
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