NevadaBill
fully equipped rock polisher
Member since January 2019
Posts: 1,332
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Post by NevadaBill on Jun 28, 2019 14:22:27 GMT -5
OK, I am cabbing right now, and have interrupted my session to ask a question and ask for advice. Is the Circle shape the hardest one to create a cabochon around?? I have been creating ovals, rectangles, squares and a few other freeform shapes just fine. But my first Circle today turned out to be a lumpy guy. And I started with a round template outline. The one I am working on now started out as a larger Circle, which I thought I could not mess up. But after grinding down the template shape it is already misshapen, and starting to get lumpy.  I realize stone hardness (different hardness within the chosen slab slice) might effect this. Also, having the dop stick exactly in the center might effect this also.  The girdle on this one might look really low and not even. But that is mainly because I still suck at this. Plus, I am practicing a very domed one on this try. Sorry. But any advice on how I can begin to master this perfect geometric shape would be appreciated. Thank you. |
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Post by stardiamond on Jun 28, 2019 14:34:38 GMT -5
Circles are challenging for me. I mark the bottom and leave a little space outside the lines so corrections can be made. Unless a person is really skilled, once the circle is off it is difficult to recover. I find circles uninteresting but they are great for developing technique. I had bad technique and find the technique for cutting circles works well with any shape. Rotating the stone working toward the middle and seeing it the uncut area is dead center. I was grinding from the edge toward the center in straight lines and that caused me to have to keep making adjustments.
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Post by christopherl1234 on Jun 28, 2019 14:38:09 GMT -5
When I want to cut a circle I always cut the preform out of the slab with a hole saw. Then I make sure never to cut the bottom edge.
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Post by Pat on Jun 28, 2019 14:54:48 GMT -5
Put the dop stick in a rotary drill. Good luck!
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NevadaBill
fully equipped rock polisher
Member since January 2019
Posts: 1,332
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Post by NevadaBill on Jun 28, 2019 15:20:03 GMT -5
Oh, those are all good ideas. Thank you. Yep, it seems that once it is not a circle any more, getting it back to be a circle is a major pain. It is not a skill I possess yet. I didn't think of using a hole saw for a perfect circle. That seems nearly foolproof. Then just only touch up the outline of the circle with fine grit wheels to not ruin the perfect shape. Thank you. And the drill idea is also good. I think I might try that as I have the parts needed to pull it off. I am going to have to get better with my skills at centering the dop stick when I attach it to the slab though, before I attempt my next one. After an hour I have another lumpy circle. This is how the first turned out too. Polishing won't help. It is lumpy:  And with some of these geometric shapes, the human eye is quick to see that it is lumpy. Hmm. Animals might be tricked though. |
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jasperfanatic
spending too much on rocks
Member since January 2019
Posts: 463
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Post by jasperfanatic on Jun 28, 2019 15:28:35 GMT -5
I struggled with this as well, and learned some new approaches with this thread. Ultimately, I think the way I solved the problem is essentially the same as Pat's suggestion, I just spin the cab at a decent pace using the dop stick making sure to keep even coverage and not much pressure. I don't think an off-center dop stick matters here if you're hitting the perimeter surface equally around and keeping the pressure light. I've had to spot grind with the 280 wheel when I had a visibly ugly circle, but then the spin-to-win method cleared everything up from there. If I still feel it's just not quite right, another suggestion of the forum that's helped me verify uniformity is to throw it on a piece of graph paper.
The difficulty of circles does seem to ramp up when there are patterns or spots of translucence messing with perception.
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Post by pauls on Jun 28, 2019 16:50:51 GMT -5
Make a large dop stick the exact size of your circle, 1 inch wooden dowel, or a piece of broom handle. Grind down to the wood then stop.
I made some out of Brass on the lathe, they work a treat.
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Post by parfive on Jun 28, 2019 20:48:52 GMT -5
FWIW, Bill, a circle is the easiest shape to cab . . . the dome never varies on any axis.
I fail to see why so many have trouble cutting round cabs. Either you can cut accurately to a line, or you can’t . . . whether it’s a circle or an oval or any other shape that’s been marked out.
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Post by Pat on Jun 28, 2019 20:58:05 GMT -5
FWIW, Bill, a circle is the easiest shape to cab . . . the dome never varies on any axis. I fail to see why so many have trouble cutting round cabs. Either you can cut accurately to a line, or you can’t . . . whether it’s a circle or an oval or any other shape that’s been marked out. I use a core drill in the rotary drill to cut out the circle, then dop the circle and put the dop in the rotary drill. Works. |
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gemfeller
Cave Dweller 
Member since June 2011
Posts: 4,064 
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Post by gemfeller on Jun 28, 2019 22:51:44 GMT -5
FWIW, Bill, a circle is the easiest shape to cab . . . the dome never varies on any axis. I fail to see why so many have trouble cutting round cabs. Either you can cut accurately to a line, or you can’t . . . whether it’s a circle or an oval or any other shape that’s been marked out. I use a core drill in the rotary drill to cut out the circle, then dop the circle and put the dop in the rotary drill. Works. How do you make certain the dop's centered Pat ? If I want to make a near-perfect circle I spin the preform on my faceting machine. I use a coarse lap after removing as much extra stock as possible with the Genie after the stone's dopped. They used to make cab rests on the old Lortone and other arbors. I found they gave a more precise control when grinding to the outline, and you could also adjust them for about any girdle angle you desired. The one that comes with the Genie's a pain to use and you can't adjust for girdle angle without some modification. |
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Post by Pat on Jun 28, 2019 23:13:59 GMT -5
Centering the dop is the hardest part.
As I recall—- draw a good square on the backside. Draw two diagonal lines from corner to corner to form an X.
Where they intersect, is the center of the square, and therefore the circle.
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gemfeller
Cave Dweller
Member since June 2011
Posts: 4,064
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Post by gemfeller on Jun 29, 2019 0:17:50 GMT -5
Centering the dop is the hardest part. As I recall—- draw a good square on the backside. Draw two diagonal lines from corner to corner to form an X. Where they intersect, is the center of the square, and therefore the circle. Now if I could only figure out how to mate the center of the dop with the center of the preform! Trust me to get it wrong. |
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Post by rockjunquie on Jun 29, 2019 6:29:33 GMT -5
FWIW, Bill, a circle is the easiest shape to cab . . . the dome never varies on any axis. I fail to see why so many have trouble cutting round cabs. Either you can cut accurately to a line, or you can’t . . . whether it’s a circle or an oval or any other shape that’s been marked out. Absolutely agree. I don't even need a centered dop if I have a line. The trouble is when you get real uneven hardnesses and hit a soft spot, knocking it out of round. THAT cab be difficult to recover from. I'm getting better, though, just doing it by eye. I don't do a lot of circles. Mostly because I don't care to work with finished rounds. I have a beautiful wingate agate circle to finish which I keep putting off because of the hardness issue. The absolute best shape for the rough I had was a circle. |
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Post by stardiamond on Jun 29, 2019 20:59:19 GMT -5
I was looking for something to give my first Etsy customer. I was kind of shocked how it snugly fit the template. Circles have never been a strong point for me.  |
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Post by rmf on Jun 30, 2019 7:30:47 GMT -5
NevadaBill I have been cabbing since 1972 and YES! rounds are the most difficult to get eye perfect. A machine has no problem but a human has too many things to control. the correct pressure, the speed you turn, how square you were able to get it dopped. The use of CA on metal dops has helped with the last one. the key is to spend time on the 220 grit diamond to get the girdle just right. The stones pattern can also cause optical illusions where it does not look right but is when you put it to a caliper.
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NevadaBill
fully equipped rock polisher
Member since January 2019
Posts: 1,332
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Post by NevadaBill on Jul 4, 2019 10:07:07 GMT -5
FWIW, Bill, a circle is the easiest shape to cab . . . the dome never varies on any axis. I fail to see why so many have trouble cutting round cabs. Either you can cut accurately to a line, or you can’t . . . whether it’s a circle or an oval or any other shape that’s been marked out. Absolutely agree. I don't even need a centered dop if I have a line. The trouble is when you get real uneven hardnesses and hit a soft spot, knocking it out of round. THAT cab be difficult to recover from. I'm getting better, though, just doing it by eye. I don't do a lot of circles. Mostly because I don't care to work with finished rounds. I have a beautiful wingate agate circle to finish which I keep putting off because of the hardness issue. The absolute best shape for the rough I had was a circle. This. Uneven rock hardness on a slab piece is part of what is happening to me. Well, it is a problem with one of mine at least. Once you start to try to fix the problem, it just seems to get more lumpy. For me at least. I tried another circle, freehand and had trouble again. I didn't try to attach to a power drill. But will try it this weekend. I like the power drill idea, when used with a light pressure. I wish I had come back to this forum topic sooner, because there are some more great ideas. - Using graph paper to help find the perfect center. Or a ruler. - Having a dop stick rest, such as on those Lortones, eliminating one axis of movement. - Using a thick 1" broom handle as a template, and grinding down to it. And, yes, I also think that a circle should be the easiest form to cab. In my mind. It makes perfect sense. I was thinking the same thing when cabbing my 2nd one. In practice, I'm having trouble though. stardiamond, I also think that your circle looks perfect to me. Great material also. I would love to end up with results like that. All great ideas folks. Thank you all very much! |
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Post by rockjunquie on Jul 4, 2019 10:18:19 GMT -5
Absolutely agree. I don't even need a centered dop if I have a line. The trouble is when you get real uneven hardnesses and hit a soft spot, knocking it out of round. THAT cab be difficult to recover from. I'm getting better, though, just doing it by eye. I don't do a lot of circles. Mostly because I don't care to work with finished rounds. I have a beautiful wingate agate circle to finish which I keep putting off because of the hardness issue. The absolute best shape for the rough I had was a circle. This. Uneven rock hardness on a slab piece is part of what is happening to me. Well, it is a problem with one of mine at least. Once you start to try to fix the problem, it just seems to get more lumpy. For me at least. I tried another circle, freehand and had trouble again. I didn't try to attach to a power drill. But will try it this weekend. I like the power drill idea, when used with a light pressure. I wish I had come back to this forum topic sooner, because there are some more great ideas. - Using graph paper to help find the perfect center. Or a ruler. - Having a dop stick rest, such as on those Lortones, eliminating one axis of movement. - Using a thick 1" broom handle as a template, and grinding down to it. And, yes, I also think that a circle should be the easiest form to cab. In my mind. It makes perfect sense. I was thinking the same thing when cabbing my 2nd one. In practice, I'm having trouble though. stardiamond , I also think that your circle looks perfect to me. Great material also. I would love to end up with results like that. All great ideas folks. Thank you all very much!
I had something go terribly out of round once because of the hardness issue. I undopped it, used a template and drew a new slightly smaller circle on the precab. The second time worked fine.  |
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Post by stardiamond on Jul 4, 2019 10:36:17 GMT -5
This. Uneven rock hardness on a slab piece is part of what is happening to me. Well, it is a problem with one of mine at least. Once you start to try to fix the problem, it just seems to get more lumpy. For me at least. I tried another circle, freehand and had trouble again. I didn't try to attach to a power drill. But will try it this weekend. I like the power drill idea, when used with a light pressure. I wish I had come back to this forum topic sooner, because there are some more great ideas. - Using graph paper to help find the perfect center. Or a ruler. - Having a dop stick rest, such as on those Lortones, eliminating one axis of movement. - Using a thick 1" broom handle as a template, and grinding down to it. And, yes, I also think that a circle should be the easiest form to cab. In my mind. It makes perfect sense. I was thinking the same thing when cabbing my 2nd one. In practice, I'm having trouble though. stardiamond , I also think that your circle looks perfect to me. Great material also. I would love to end up with results like that. All great ideas folks. Thank you all very much! I had something go terribly out of round once because of the hardness issue. I undopped it, used a template and drew a new slightly smaller circle on the precab. The second time worked fine. That's why the templates have progressively smaller circle sizes. |
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Post by rockjunquie on Jul 4, 2019 11:03:51 GMT -5
I had something go terribly out of round once because of the hardness issue. I undopped it, used a template and drew a new slightly smaller circle on the precab. The second time worked fine. That's why the templates have progressively smaller circle sizes.
Funny, but true. LOL!
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Post by bobby1 on Jul 6, 2019 0:07:31 GMT -5
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