Lapidaryforum.net
Rock Art => Cabochons, Intarsias, Cameos => Topic started by: drnihili on March 12, 2015, 11:54:32 AM
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So, I'm slowly trying to make a cab. Of course my choice of stone is probably terrible, but let's leave that aside for the moment.
I got the basic shape out and worked up through putting a polish on. However, after getting to this stage, I'm noticing some roughness in the stone that wasn't apparent earlier (at least to my noob eyes). The roughness seems to be a matter of differences in the stone, not leftover grinding marks. My suspicion is that I used too heavy a hand on the polishing wheel and that I should now go back a stage or two (to 1000 or 3000 grit) and use a very light touch to smooth things out, followed by a much lighter touch when buffing.
Is that largely right or is there some other process I should use? Is this a stone that needs something higher than 3k grit?
Unfortunately, I am not the sort to make myself carefully practice using easy stones until I get the knack of things. So I'm hoping to muddle through as best I can with this. I did make myself start with an end piece so that when I inevitably screwed it up there would be some rock left for Teresa to actually do a good job with. :blob1:
Here's a closeup showing the texture problem I'm having and a shot of the overall cab for context. The cab is 1.5 inches long.
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I would try backing up a couple of stages to a rougher grit before anything else and re-work the areas that are not uniform. I like the colors in the material, it's pretty.
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I would try backing up a couple of stages to a rougher grit before anything else and re-work the areas that are not uniform. I like the colors in the material, it's pretty.
That was my thinking. Alas, the rough areas comprise nearly the entire cab except for the vein of quartz. There are several lovely spots of exposed metal that may be alright too. How far back would you go? 3k? 1k? 600?
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1200 or 600. The cutting needs to be fast and aggressive enough that both the soft and hard areas are cut at approximately the same rate. this is classic undercutting and the piece may not yield a decent polish. Badly undercutting rocks are usually ignored by lapidaries for good reason unless they have an inherent quality that is very special. No felt or muslin buffs on undercutters and 3000 may be as far as you can go on the polish without recreating the problem.
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Thanks, Frank.
I'll hop back to 600 and work my way up to 3k gently. Our only buff is leather, so that's good, though depending on how it looks at 3k, I may opt for another route. Would a higher grit sanding belt likely yield better or worse results than going from 3k to buffing?
While we're talking about buffing pads, the vast majority of the leather I have is tanned dark rather than light. Is there a problem using it for buffing in general?
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Leather is capable of causing undercutting at times. Jumping from 3000 if it looks good to 14,000 is what I would do. I have seen 14,000 softback wheel cause undercutting but it is rare.
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Are you sure you have enough fluid running to keep the stone cool too? Sometimes if the stone gets hot you can see results like that too. Frank is right, that could just be the way it is- I'd go back to 600 if it were me.