Lapidaryforum.net
Rock Art => Cabochons, Intarsias, Cameos => Topic started by: TJ333 on December 15, 2016, 08:52:51 AM
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What happens is I end up with small flat sections all over my stone. I have gotten to the point they are smaller and harder to see but I still can't get them smooth. I have tried with dop sticks and holding it by hand. The best I manged to do was make the marks smaller. I couldn't get them to show in a picture but share is a video where you can see the unevenness as the light reflects across it.
https://youtu.be/QtWQzG2TocA (https://youtu.be/QtWQzG2TocA)
That is not my best one but it shows the problem better. I have thinned a couple of my cabs noticeably from going back and trying the different grits as well as trying different motions to try and get a better result.
I'm using an Inland Swaptop (a flat disk) and started with the instructions on their site but have tried others.
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Keep the stone moving. I continuously rock the stone up and down, back and forth, while it's touching the wheel. Don't stop and reverse direction until you've reached, or gone past, the edge. Don't start contact unless the stone is moving.
I don't know if that's what you're doing wrong, but it works for me.
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Agree with Dave. Also, is your stone mixed hardness material ? If so the softer material will grind away, leaving a lumpy surface.
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I have an Ameritool flat lap and have not had the issue you are describing. I learned from the dealer who sold me the tool and spent a couple of hours showing me the technique. I use a dowel as a handle and superglue a wood screw to the stone. Right from the first coarse grit and through the finer grits, the secret is as Ranger Dave said: "Keep the stone moving". Always move the stone in an arc like a pendulum and keep rotating it. Do not try to grind out any flat. Just keep it moving in an arc and the flats will disappear.
(This is not a problem for most people using a wheel machine because the flats are taken out by the flex of the Nova wheels.)
Jerry
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Technique, technique! Keep those cabs moving. Sanding disks backed with sponge rubber help eliminate flats if they're not too big, as they allow stock removal along the curvature plane of the cab. There's also an old trick that can help. Get a small piece of silicon carbide sanding paper of the same grit as your metal cutting disk. Mold it into the palm of your hand and rub your dopped stone against it, rotating it every which-way until the flats are gone. It's surprisingly fast and leaves your cab ready for the first sanding stage.
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The softer the sanding belts or disks the faster the flat spots are removed. You want the belt/disk to deflect inward and wrap around the stone as you are sanding. It works best on the intermediate grits - 220, 400.
Bob
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Are you wearing magnifying optics when you grind??? At the least you need to dry your cab and look at it under a strong light, preferably magnified as you grind it. If you have a flat spot at 100 grit it will stay there until the end, scratches too. So start a new cabochon and watch it as you grind the first stage with coarse grit. When you do not see any flat spots or scratches it is time to move to the next step. Check the cab dry and with strong Light, at every stage. Roll the cabochon under the light as you check it. The flat spots will jump right out at you to be fixed. good luck, neal
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Thanks to everyone for the advice.
I can see how having a soft backing would be useful to finish a piece. The stone is cut from a marble floor tile so it may be mixed hardness.
From the sound of things I need to work on keeping the stone moving, most likely as I bring the stone onto and off of the disk. My smoothest sections have been when I was just working on the edge of the stone so keeping that in mind as well.
I have no optics for while I am working, might be able to get my helping hand magnifying glass to work though. I do agree that the flat spots jump out once its dry.
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The advice given above is great. I might add that using even pressure while you move the stone is very important especially on softer stones. I would suggest a light touch while you are getting started. I started out using a Genie which has diamond grit and I struggled for a bit with the diamond cutting unevenly as I would work on the cab's. Finally I decided to lighten up and quite trying to get the stone finished in 60 seconds and my problem went away.;
Keep experimenting with technique and you will find one that works for you. Try and find stone like brazilian agate to practice with. Any stone with even hardness throughout will work.
regards
Mike