winterwinds
off to a rocking start
Member since October 2022
Posts: 7
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Post by winterwinds on Apr 11, 2024 12:47:50 GMT -5
I've been tumbling self collected rocks for over a year now with lots of learning and often am very pleased with my results. Occasionally though rocks will come out of polish stage with undercutting, fine chipping, cracking and just generally rougher than they came out of pre-polish. Usually the whole batch is less than satisfactory but sometimes it's only one or two rocks. Most of my rocks are jasper/agate variations collected on west coast beaches.
I inspect & clean the rocks closely & remove those that appear to failing before moving to next stages so I'm really confused. How can rocks come through 60/90, 120/220 & pre-polish grits sucessfully intact and smooth only to fall apart in polish?
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winterwinds
off to a rocking start
Member since October 2022
Posts: 7
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Post by winterwinds on Apr 11, 2024 13:58:55 GMT -5
  Here’s an example of rocks from the same batch which were all smooth and blemish free coming out of prepolish. The rocks in the top photo all went bad to various degrees but the bottom ones and most of the rest of the batch were fine. |
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Post by jasoninsd on Apr 11, 2024 14:41:35 GMT -5
I'm throwing this out there as a guess...so take it with a grain of grit!  Possibly you don't have enough cushioning material to prevent them from banging together in the polishing stages. Slurry is thicker in the earlier stages...and a LOT thinner in the prepolish and polish stages. Without enough ceramic media or smalls, the larger rocks are "banging" into each other more in the later stages. If you do have a ton of smalls in there...then that shoots my theory out the window! |
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chaosdsm
starting to spend too much on rocks
Member since April 2024
Posts: 162
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Post by chaosdsm on Apr 11, 2024 17:07:16 GMT -5
I'm thinking along the lines of jasoninsd not enough cushion in the mix. I see lots of talk about small rocks, plastic beads, and ceramics as cushioning.... but to me, those are all still hard materials (except the plastic beads) that could cause damage.
Not sure if it's Good, Bad, or Ugly but my Nat Geo tumbler included some cut foam pieces for the polishing stage. It's supposed to last through several polish stages, though replacement foam is pretty expensive. Softer than soapstone, they won't directly damage any rocks.
I'm going to hold off using them for now, & try 1/2" Wool Felt polishing wheels that are used with a Dremel as a cushion agent in the polish stage. They're less than half the cost of the replacement Nat Geo foam for about the same volume of product, plus, they can also be used on my Dremel for tight spaces, touch ups, etc....
In theory, tiny stone chips could get lodged into either of these soft materials, which could then potentially scratch the stones....
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brybry
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Member since October 2021
Posts: 1,221
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Post by brybry on Apr 11, 2024 18:46:41 GMT -5
The small don't really cushion as much as they get between the larger rocks and reduce impact damage by taking up extra space.
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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 Apr 11, 2024 20:47:08 GMT -5
This won't answer your question exactly, but may provide some insight.
I'm not sure if you are polishing in a vibe, but this is my experience with a vibe - a Lot-O
I have found that material prone to undercutting like Leopard Jasper, Llanite, pet wood ect. . . Tends to exhibit undercutting in the polish stage - not pre-polish. Now this isn't true 100% of the time, but seems more common than not. I have found I can limit this and achieve better results with this type of material by not using the vibe and going 100% rotary. The polish in the vibe seems to accentuate differences in hardness and exaggerate undercutting.
When I polish in the rotary I make sure the barrel is 75-80% full, and I let it roll for 2 weeks with no clean out. I aim for a gentle tumble for a longer period of time.
Not sure this helps, but it seems related.
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titaniumkid
spending too much on rocks
Member since June 2023
Posts: 499
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Post by titaniumkid on Apr 11, 2024 22:32:57 GMT -5
Without grit and with little grinding, the slurry in the polish stage is probably a lot thinner than in earlier stages. You could try adding something like sugar to help thicken the slurry so the rocks don't tumble as roughly (in addition to the other suggestions here). If you search the forum, you will read about other people's experiences and recommendations for the polish stage.
Note: I've never done this. I don't know how effective it is.
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winterwinds
off to a rocking start
Member since October 2022
Posts: 7
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Post by winterwinds on Apr 12, 2024 12:11:23 GMT -5
Thanks for sharing your thoughts. I do use plenty of media/smalls in my rotary 3lb barrels. Looking at some of the failed rocks more closely, I'm thinking I might be overfilling and the rocks are getting stuck and not tumbling freely. Essentially getting stuck in one spot and that area gets worn differently so think I'll play around with that next time.
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Post by Bob on Apr 24, 2024 11:22:41 GMT -5
Well, it's not so simple. I have this happen too. What I do is first redo them all in 600 or 1,000. But then I split them up into different batches for polish--kind of a 2nd chance thing for them. Most of the time, they come out fine. But sometimes, one of them just won't polish well and that's it. You would think that if only 1 the others would not be affected by it when they had been done together. But my experience is that it maybe doesn't work that way.
Sometimes if I like the rock a lot I'll give it a 3rd chance, not that it but rarely helps.
In other words, the unique combination of other rocks in a polish run affects things in ways we don't understand. Or at least I don't understand.
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quartz
Cave Dweller
breakin' rocks in the hot sun
Member since February 2010
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Post by quartz on Apr 24, 2024 22:16:44 GMT -5
I've had good result using scraps of leather for padding in the polish stage, whole leather, not thin split. I cut up anything I can find at garage/estate sales, for a three pound tumbler about 3/8 to 1/2 inch pieces, roughly square [easier to cut that shape}. I put in about 1/3 of the load as leather pieces, it gets a little slimy, that does turn some people off.
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Post by Bob on Apr 25, 2024 16:12:11 GMT -5
I've had good result using scraps of leather for padding in the polish stage, whole leather, not thin split. I cut up anything I can find at garage/estate sales, for a three pound tumbler about 3/8 to 1/2 inch pieces, roughly square [easier to cut that shape}. I put in about 1/3 of the load as leather pieces, it gets a little slimy, that does turn some people off. I've been saving up some leather odds and ends for a few months now and plan on trying this myself, especially with delicate stuff like crystal quartzs and obsidian. |
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