jimgsmith
starting to shine!
Member since September 2022
Posts: 37
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Post by jimgsmith on Dec 14, 2022 11:01:03 GMT -5
I have several pieces of Gabbro (mohs 7ish) that I collected on a beach, and after stage 1 in the rotary, they looked great. Perfectly smooth all over, no undercutting and no cracks or pits. After stages 2 through 4 in the Lot-O, there is undercutting on all of them, and they did not take a good polish. I get that the lack of polish is likely a result of the undercutting, with rock debris mixing with the grit/polish and not letting them take a nice shine, but I'm surprised that this only happened in the vibe. Is there a reason that stage 1 in the rotary would leave them looking good, but the vibe would cause the undercutting? If I do stages 2-4 in the rotary, would this solve the problem?
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geoff59
spending too much on rocks
Member since October 2022
Posts: 288
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Post by geoff59 on Dec 14, 2022 12:55:26 GMT -5
With the more aggressive grind of step 1, the entire rock is more or less sanded down evenly; when you get to the later stages, with the progressive finer grits/polish and resulting reduction in the level of grind, the difference in mineral hardness can then come out and be seen within the rock much better, and unfortunately it comes out at these later stages, such as the undercutting you see. Another perfect example of this occurs with leopard skin.
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Post by jasoninsd on Dec 14, 2022 13:19:15 GMT -5
With the more aggressive grind of step 1, the entire rock is more or less sanded down evenly; when you get to the later stages, with the progressive finer grits/polish and resulting reduction in the level of grind, the difference in mineral hardness can then come out and be seen within the rock much better, and unfortunately it comes out at these later stages, such as the undercutting you see. Another perfect example of this occurs with leopard skin. That's very well put. I do more cabbing than tumbling...and after the initial grind (80 grit) and then the second hard wheel (220 grit), I don't see the undercutting at all...because it basically hasn't happened yet.
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jimgsmith
starting to shine!
Member since September 2022
Posts: 37
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Post by jimgsmith on Dec 14, 2022 14:55:28 GMT -5
Thank you for the replies! And here I was thinking it was smooth sailing after they came out of the rotary.
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