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Post by Bob on Oct 19, 2023 11:19:44 GMT -5
Last night it happened again. A load had tumbled for a week in 220, and instead of just correct slurry and no grit and just rock dust, the slurry was thin and some grit--a lot-- was left over.
This is my 10th year of tumbling. It doesn't happen in 50-70, or 80, or 600, or 1,000, but only in 220 and it bugs me. It doesn't always happen either.
I learned a long time ago never to use plastic pellets in any grit larger than 220, because for some reason it would decrease grinding effectiveness and grit would be leftover. So I use quartz river gravel that I purchase about 1/2" size for small filler.
With 600 and 1,000, I use plastic pellets unless there is a real nice mix including smalls.
I do use plastic pellets in 220 if there isn't sufficient smalls to be processed. So maybe 75% of 220 loads are this way. The times when some grit is left over area always times when some plastic pellets were used. I've never tried to dry it out and measure, but I would just guess that up to 1/3 of the grit has been left over. And I can feel the surface of the rocks and know that they are a bit more sandpapery in feel than if a normal week of 220 had gone on and been totally used up. I hate seeing that thin slurry with the unused grit in it wasted.
Has anyone else noticed anything like this or have any ideas what is going on? It's been going this way for years. I do go ahead and separate the rocks into piles of what needs another week in 220 and what is ready to go on for 600. I'll bet the first pile has more than it ought to because of this grit not being used up problem.
At first one might think just run the 220 for 10 days or another week, but I accidentally did that once and the grit was still there.
I'm about ready to give up on using plastic pellets in 220 and start using the quartz gravel smalls instead. But it will add another layer of complication because I will have to keep that 220 used gravel separate from the gravel used with larger grits to avoid accidentally getting large grit in my 220 loads. The gravel has crevices in it.
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jone
starting to spend too much on rocks
Member since February 2023
Posts: 112
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Post by jone on Oct 19, 2023 12:17:43 GMT -5
In general, does grit continue to break down even after the rocks are smoothed to that grit size?
If not then maybe your 50-70- or 80 grit tumbles are very efficient and there is just too much 220 grit to start with - have you tried using less 220 grit?
(I'm not sure if this makes any sense but it came to mind after reading your post...)
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Post by HankRocks on Oct 19, 2023 12:20:59 GMT -5
Bob I would say that the plastic pellets are the issue. I dis-continued using them several years back in a "simplify the process" move How much 220 grit? in what size barrel? and the mix of rocks? In my case I use about half the grit in the 220 and 600 stages as I do in the coarse runs. It might be a case of too much grit and the same may be happening in the 600 run, it's just not possible to know if there's any 600 grit un-used. Henry
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Post by Bob on Oct 19, 2023 16:16:09 GMT -5
Well, I never thought about using less grit. It the beginning, with the published teaspoons of grit guidelines, I found the following so close to that that I adopted it:
40lb barrel: 4 cups
20lb barrel: 2 cups
12lb barrel: 1 cup
6lb barrel: 1/2 cup
So that's why I've been doing and getting good results. I just run each barrel a week, but in hot weather the 40lb one 6 days and in very hot weather only 5 days. The finer grits are the most expensive, so using less of those would be nice. I'm trying to think of how one could find out if using less of any grit stage is okay...I guess the answer would be if the end results after polish look just as good.
Henry is the point you are making about not being able to tell on 600 (and I'm sure 1,000) is that the grit is so fine to begin with that it's just not possible to rub the slurry between our fingers and detect if it still contains any grit or not?
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Post by HankRocks on Oct 19, 2023 17:32:17 GMT -5
Bob Henry is the point you are making about not being able to tell on 600 (and I'm sure 1,000) is that the grit is so fine to begin with that it's just not possible to rub the slurry between our fingers and detect if it still contains any grit or not?Yes, Every once in a while I get a bit of the 600 on my hand or finger and I am unable to feel it between my fingers, blended into slurry it would be un-detectable. Maybe someone with more sensitive fingertips than I could feel it. For 1st stage you need more grit as you are grinding and shaping and you want that to continue thru the process. After you have a rock ready for 220, the rock is mostly on the way to being what needs to be shape-wise, now you have moved to more finishing. 220 is probably a transition stage grit, a bit of shaping, a bit of finishing. I use about half of the coarse grit for all my stages after coarse, including polish. It's my opinion that you could probably reduce grit amount after the coarse stage. My one qualification to my statement above is that I do use dried slurry for all my stages. It is my opinion that the 600 slurry, the pre-polish slurry, and the extra polish(saved and re-used polish) it serves as cushioning and extra finishing and in the coarse grit and 220 grit with grit suspension. Note - This is Rotary only. Vibes are another whole deal. Henry
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tkvancil
fully equipped rock polisher
Member since September 2011
Posts: 1,548
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Post by tkvancil on Oct 19, 2023 17:39:54 GMT -5
When I used to rotary tumble all stages I ditched plastic pellets in favor of ceramic media. As I recall it was due a similar problem.
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dillonf
fully equipped rock polisher
Hounding and tumbling
Member since February 2022
Posts: 1,622
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Post by dillonf on Oct 19, 2023 18:00:42 GMT -5
I run QT12 and QT6 barrels. I get left over grit when there is too much water and not enough smalls. I have switched to primarily ceramic media. I will use plastic on softer stones in the pre-polish and polish stages though. I do use a little less grit than you 1 tblspn per lb.
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Post by Starguy on Oct 19, 2023 21:16:38 GMT -5
The gradation of the load being tumbled is pretty important. The most efficient grind is in a dense graded load which is missing fines and sand. Hopefully at the end of the tumble, the sand (grit) you added will have made lots of fines.
A dense load will require slightly more grit than an open graded load. That’s because there is more rock to rock contact in the denser load. An open graded load allows the grit to find places that aren’t between rocks so it doesn’t break down as fast.
Adding smalls might help or you can run longer to break down the grit but that opens you to more impact damage. That would be the last thing you want in 220.
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Post by Bob on Oct 20, 2023 10:47:58 GMT -5
I run QT12 and QT6 barrels. I get left over grit when there is too much water and not enough smalls. I have switched to primarily ceramic media. I will use plastic on softer stones in the pre-polish and polish stages though. I do use a little less grit than you 1 tblspn per lb. They are expensive, and if I did that in place of all uses of plastic pellets my expenses would go up significantly. |
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Post by Bob on Oct 20, 2023 11:02:14 GMT -5
It's my opinion that you could probably reduce grit amount after the coarse stage. My one qualification to my statement above is that I do use dried slurry for all my stages. It is my opinion that the 600 slurry, the pre-polish slurry, and the extra polish(saved and re-used polish) it serves as cushioning and extra finishing and in the coarse grit and 220 grit with grit suspension. Note - This is Rotary only. Vibes are another whole deal. Thanks for those tips. Although I don't use dried slurry, I do leave up to 1/4 of the slurry in the bottom of the barrel when recharging for the next load if the grit size is the same. Since the slurry has been settling on my workbench for maybe 15 mins or more before being sealed up again, the thickest of it is probably at the bottom. This is only for loads that don't have plastic pellets because I pour off the slurry over a screen to pull out the pellets which float. I agree with you totally that I regard 220 as an intermediate stage during which there is a tiny bit of shaping as well as surface smoothing. I often leave tiny cracks or dings of less than .5mm and find they come out in 220 and save me having to do one more week in rough grind. Sometimes they don't come out and I have to repeat 220 on those one more time which doesn't matter. It appears this thread had led into two different directions. 1. No longer using plastic pellets in 220 might be good. 2. Using less grit starting in 220 and finer might be okay too. As to 1, I think I'm going to switch to keeping some quartz gravel dedicated to 220 and stop the plastic pellets. I have the gravel in a big bucket, and it won't be too bad to have a 2nd bucket. As to 2, I think I'm going to start with my 1,000 grit last stage before polish. Do you have any suggestion as to how much to cut back as my test? |
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Post by HankRocks on Oct 20, 2023 12:16:49 GMT -5
It's my opinion that you could probably reduce grit amount after the coarse stage. My one qualification to my statement above is that I do use dried slurry for all my stages. It is my opinion that the 600 slurry, the pre-polish slurry, and the extra polish(saved and re-used polish) it serves as cushioning and extra finishing and in the coarse grit and 220 grit with grit suspension. Note - This is Rotary only. Vibes are another whole deal. Thanks for those tips. Although I don't use dried slurry, I do leave up to 1/4 of the slurry in the bottom of the barrel when recharging for the next load if the grit size is the same. Since the slurry has been settling on my workbench for maybe 15 mins or more before being sealed up again, the thickest of it is probably at the bottom. This is only for loads that don't have plastic pellets because I pour off the slurry over a screen to pull out the pellets which float. I agree with you totally that I regard 220 as an intermediate stage during which there is a tiny bit of shaping as well as surface smoothing. I often leave tiny cracks or dings of less than .5mm and find they come out in 220 and save me having to do one more week in rough grind. Sometimes they don't come out and I have to repeat 220 on those one more time which doesn't matter. It appears this thread had led into two different directions. 1. No longer using plastic pellets in 220 might be good. 2. Using less grit starting in 220 and finer might be okay too. As to 1, I think I'm going to switch to keeping some quartz gravel dedicated to 220 and stop the plastic pellets. I have the gravel in a big bucket, and it won't be too bad to have a 2nd bucket. As to 2, I think I'm going to start with my 1,000 grit last stage before polish. Do you have any suggestion as to how much to cut back as my test? Maybe reduce the grit by 1/4 to start with and then see if you detect any change. If no noticeable change then maybe another 1/4 for the next batch. Your tumbles are always top shelf so I am hesitant to making too much change at once. As I mentioned I think you will be able to reduce the more expensive grits by some amount. I suspect that the recommended grit amounts, with the exception of coarse, have always been too high. Maybe someone was selling grit! |
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Post by Bob on Oct 20, 2023 16:10:54 GMT -5
Thanks Henry, I will try that recommendation on reduction.
I have always wondered about grit recommendations, though maybe not for the reasons of worrying about wasting money or grit.
A. If suddenly we were to double the grit we put in, doesn't that merely imply twice the grinding would occur before the grit starting getting smaller and smaller? There's probably some reason why that isn't true. If it was true, it implies it might be a good idea for those rocks you already know in advance will need more than one week in rough grind. On the other hand, if the rocks are pretty nice and you know that one week in rough grind would be enough, it would result in removing more of their surface than is necessary.
B. It seems like just the opposite might also be true. If we half the grit, doesn't that imply one week might not be enough for those rocks you know are in such good shape that one week normally would be enough? So it might require another week with another grit charge. There is probably some reason why that isn't true.
If I'm wrong and it is true, then A could result in wasting grit and rock surface needlessly. But B, would not waste anything other than maybe a bit of electricity and a bit of one's time because it would take two weeks to accomplish the work of one week before. So if one is going to err in too much or too little, if my thinking has any validity whatsoever, your recommendation to try less seems to wisest way to experiment to me.
It's often valuable to think in terms of extremes in working on an issue. In this case, one extreme would be a barrel full of grit with a thumbnail size rock put in it. What would happen in a week? Well, I suppose the rock might disappear and with plenty of grit leftover too. But nothing might happen w/o other rocks to press against. So maybe 2 rocks would be that extreme end. The other extreme I guess would be a barrel full of rocks with a single grain of grit. In a week, the grit is gone and I doubt if you could see any grit work on any rock. So perhaps someone long ago started experimenting and finding that happy spot in between.
I enjoy knowing that it takes right at a week for a barrel to need recharging. It's convenient for me to know that this barrel I did last Saturday, will come due the following Saturday. The timing is just about right.
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stefan
Cave Dweller 
Member since January 2005
Posts: 14,113
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Post by stefan on Oct 22, 2023 14:26:10 GMT -5
I never run plastics in 220. I use dollar store decorative gravel filler, or make sure I have enough mix to not need filler (I have been tumbling a lot of Moroccan agates and these are great filler that move along with every batch). I even stopped using plastics with 500 grit as I have some potentially contaminated 500 (it foams up real bad and the pellets just make it unbearable to deal with) I run my 220 for 2 weeks and never have issues. I think the plastics must be slowing down the grinding process too much and are causing the issues.
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Post by Bob on Oct 24, 2023 9:51:04 GMT -5
Started 20lb barrel 220 with quartz gravel filler instead of plastic pellets last night. Will see if a week how it goes. Something tells me it's going to get well.
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geoff59
spending too much on rocks
Member since October 2022
Posts: 288
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Post by geoff59 on Oct 25, 2023 19:48:22 GMT -5
Bob said:
”A. If suddenly we were to double the grit we put in, doesn't that merely imply twice the grinding would occur before the grit starting getting smaller and smaller?”
I hesitate to chime in, ‘cuz I’ve never worked with a drum of that size. I would say no. Because there is only so much surface area on a rock you can have grit-contact on. I think it’s likely that you have too much grit in the drum-but it largely depends on the other variables inside the drum that you can control, such as time. I’ve never rolled anything bigger than a 12 lb drum, and I’ll add that I think larger drums are a science of their own (compared to 3 or 6 pound tumbler drums) If I were in your shoes, I think I’d try cutting back the amount of grit before I tried anything else. Or started thinking too much. 25% back as a start, and keep good notes.
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Post by Bob on Oct 27, 2023 15:56:03 GMT -5
...As to 1, I think I'm going to switch to keeping some quartz gravel dedicated to 220 and stop the plastic pellets. I have the gravel in a big bucket, and it won't be too bad to have a 2nd bucket. I forgot when I wrote that that merely I can keep the gravel to be used in 220 in the same container that I had been keeping the plastic pellets for 220 because I wont' be needing those plastic pellets anymore. One new complication I realized only after throwing in this gravel in a few days ago. I also have rocks in 220 that can be small and kind of hard to tell from the gravel. In fact, I pick every now and then a nice looking piece of gravel from rough grind and put it in the "need 220 next" box with other rocks. One advantage of the plastic pellets in 220 is I never could confuse the small pieces I'm wanting to keep from the gravel I'm putting in there now just for filler and to help grinding. I'd pour off the floating pellets, and everything left were rocks in process no matter how small. Now, dang it, the gravel being added to help filler and grinding in 220 can't be separated from the small rocks in process in 220 because they look alike in many instances. So in this first test batch, I had to make sure no small rocks to be kept were in the batch. After thinking about this problem for a day or two, I came upon a decent solution. The quartz gravel I buy is a mix of white, black, and mostly browns. Some are striped and kind of pretty. It would not be very hard for me to divided this new gravel in 3 separate ways. Black vs. white vs. brown. If I use just black, or white, in this 220 filling/grinding purpose I can quickly tell it from the rocks to keep. If most of what I'm processing in 220 is dark, I'll use the white, and vice-versa. |
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stefan
Cave Dweller
Member since January 2005
Posts: 14,113
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Post by stefan on Oct 28, 2023 7:33:17 GMT -5
The stuff I use is so cheap, that even if it gets moved on (because some of it does turn out very nice)Its no big deal. But if you are processing a specific batch of smaller rocks, I can see where the issue would be frustrating to work with.
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Post by Bob on Nov 8, 2023 10:55:04 GMT -5
"After thinking about this problem for a day or two, I came upon a decent solution. The quartz gravel I buy is a mix of white, black, and mostly browns. Some are striped and kind of pretty. It would not be very hard for me to divided this new gravel in 3 separate ways. Black vs. white vs. brown. If I use just black, or white, in this 220 filling/grinding purpose I can quickly tell it from the rocks to keep. If most of what I'm processing in 220 is dark, I'll use the white, and vice-versa."
Well, doing that was kind of peaceful actually. I sat down and sorted it out into blacks or mostly black, whites/clears or mostly so, and anything else went into another box. Doing this caused me to find some pretty neat pieces of black or black striped with something else. And I won't have to do this sorting very often, maybe once per year, because this gravel being used only in 220 will last a long time.
Also, I've had two finished batches now of 220 using this gravel instead of the plastic pellets and the results have been fantastic! Good slurry, good grinding. I'm completely sold and doing that now going forward. Thanks to all who helped me figure this out.
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Post by Bob on Feb 29, 2024 17:36:05 GMT -5
I just want to thank everyone that contributed to the suggestions in this thread. I've since had quite a few batches, in 6lb, 12lb and 20lb barrels using quartz gravel filler instead of plastic pellets in 220 grit. It solved the problem of the leftover grit--period. It's been so easy to have a container of quartz smalls (one white, and one black) to use. At times, I have to make sure I have no white rocks going in the batch using white filler, and have no black rocks going in the batch using black filler, but that is very easy to do.
I have only used plastic pellets in 220 2-3 times since, and it has been because it's hard for me to let go of needing to cushion extra some expensive and sensitive materials, like lapis, rhodonite, and unakite. But instead of using only plastic pellets in those batches, I used maybe half of what I used to and the rest with quartz smalls, to no negative effects.
I've only experimented a little bit with the suggestion to cut back on the amount of grit used in 220 and finer grit batches. I've probably done quite a few batches using only 2/3 to 3/4 of what I usually use. It's hard to tell if this has proven good or not. I've noticed slurries tend to be thinner, and this may be because the grinding has been less in my runs which are one week long. But the grinding may still be adequate--I just haven't had the time to do some control comparisons and find out.
Although 1,000 grit is rather expensive and 600 a bit less, and so forth as one gets larger, by far my biggest grit expense is coarse grind. I probably go through 10 to 20x as much of that grit, which is the cheapest, than say 600 or 1,000. So I'm not too concerned about using up a lot of expensive grit because I really don't. Each time my 40lb barrel comes due each week, and one of my 20lb barrels, which are almost always doing coarse grit, I go through therefore 6 cups of coarse grit a week. This scooping takes down the grit level in a plastic bucket quite a bit each month. But this hobby makes me happy with modest cost overall!
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