meviva
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Post by meviva on Mar 22, 2015 14:58:12 GMT -5
Sometimes when I cut slabs the thickness is not even from one end to the other. So when I cut my preforms there is a 1 mm difference from one side to the other. I have been using the flat lap with a 170 disc to trim down the thick side. Is there a better way to do this? Can it be done on the wheels while on a dop stick? Would a 60 or 100 flat lap disc be better? How do you correct the problem?
Thanks, Andrea
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Post by mohs on Mar 22, 2015 15:21:10 GMT -5
That certainly a nasty problem
Especially like on my heart halves it creates havoc from zipping the groove to epoxy uneven halves but I digress
sounds like your doing all you can I use the wheels to rough it out fast it seems faster --then lapping-- then lots of flat lapping
can't get an aggressive enough wheel or disc -or if you do-- then you might have chipping problem
rocks are hard -mohs
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lparker
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Post by lparker on Mar 22, 2015 16:03:21 GMT -5
Sometimes when I cut slabs the thickness is not even from one end to the other. So when I cut my preforms there is a 1 mm difference from one side to the other. I have been using the flat lap with a 170 disc to trim down the thick side. Is there a better way to do this? Can it be done on the wheels while on a dop stick? Would a 60 or 100 flat lap disc be better? How do you correct the problem? Thanks, Andrea Check your saw and make sure the blade is square with the vise - put a pencil in the vise, touch it to the blade, move the vise/pencil to the back of the blade - should draw a solid line on the blade. If it doesn't, adjust either the blade/arbor or vise so it does. Lee #1
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meviva
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Post by meviva on Mar 22, 2015 16:11:53 GMT -5
I'm using a tile saw and push the rock through by hand, the guide is very low (1/4") and it's hard to get it through completely straight without it tilting one way to the other a little bit. I need to try and do something to fix that.
Andrea
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Post by braders on Mar 22, 2015 16:15:23 GMT -5
I'm no pro and may be wrong but this works fine for me ... I preform it like any other cab and take the uneven out with the dome and girdle . Unless it's a super big difference . Cheers
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unclesoska
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Post by unclesoska on Mar 22, 2015 20:10:22 GMT -5
I had the same problem as you, Andrea, and pretty much wore out a 170 lap making "corrections". I bought a 60 grit lap and that made a big difference in time spent fixing. Nowadays, w/ more rocks @ my disposal, I don't waste time on corrections, I just throw the misfits in the tumbler as filler.
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Post by Peruano on Mar 22, 2015 20:22:06 GMT -5
A small difference in slab thickness will automatically go away as you dome the cab on a dob stick. As you use the circular movement just remove more material on that end than the other until your thickness is the same. Clearly this is easiest on an aggressive stone 80 or 100, but if you have soft stone you may be working at a higher grit number. By all means do not concentrate (i.e. stay on that thick end) or you will end up with a flat top or extremely thin cab. If you are holding and rotating the stone correctly it should correct itself in the doming process. Difficult to explain, but it happens for me. Tom
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victor1941
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Post by victor1941 on Mar 22, 2015 20:36:52 GMT -5
I like to use a 60 grit flat lap to both shape and flatten a rough cut preform and then correct the thickness without dopping if necessary. I have and do dop some material with equal success before vibe finishing those that are suitable. The 60 grit flat lap also works well for shaping once it becomes worn.
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Post by mohs on Mar 22, 2015 20:40:48 GMT -5
O i was going to mention that most corrections can be made on a cab in the doming process and a girdle line is helpful. But I don't do cabs so I didn't mention it mostly
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Post by Rockoonz on Mar 22, 2015 20:54:48 GMT -5
If you slab by hand and you're only about a mm off you're not doing bad. Like they said just flatten the back enough to get the saw marks off, mark your girdle line from the back, and cut your cab.
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meviva
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Post by meviva on Mar 23, 2015 0:23:54 GMT -5
Thanks everyone. Next time I will try to even it out while making the girdle and dome. I may still get a 60 or 100 grit flat lap to have on hand in case more than a mm needs trimming off.
Andrea
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lparker
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Post by lparker on Mar 23, 2015 8:09:43 GMT -5
Not sure what kind of guide you have. If it is something like bent sheet metal (the quarter inch sticking up) you could get a 3/4x2x6" piece of hard wood, cut a groove in the 3/4" side the width and depth of the guide, put epoxy in the groove, put the board on the guide, and set the guide against the blade over night. Oil the wood so it won't absorb water and start cutting.
Lee #1
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Post by rockjunquie on Mar 24, 2015 19:51:53 GMT -5
I've always just worked it out while doming. When you go to do it, it will make sense visually when you hold the cab level to the eye. You simply work the higher side more. Hard to describe, but really easy to do when you see it.
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barclay
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Post by barclay on Mar 25, 2015 21:38:35 GMT -5
When I mark out my girdle with an ultra fine point sharpie if the slab is a little off I make sure my girdle marking is true and I work it off during the shaping process.
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adrian65
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Post by adrian65 on Mar 25, 2015 23:45:36 GMT -5
Grinding either before as a slab, or during the cabbing process would work well. But you could also take advantage on the uneven thickness and cab a pear or drop shaped cab, which has the top of the dome sideways to the center of the cab. Placing the top of the dome on the thicker part will ease your doming process. This is, of course, only if the slab's pattern does not demand other cab orientation.
Adrian
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meviva
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Post by meviva on Mar 26, 2015 9:49:21 GMT -5
I have a few preforms that are uneven….I'm going to try cabbing without evening them out first. adrian65 That's a good idea…I didn't think of that. I will have to try that too. Andrea
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meviva
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Post by meviva on Mar 27, 2015 15:00:35 GMT -5
Not sure what kind of guide you have. If it is something like bent sheet metal (the quarter inch sticking up) you could get a 3/4x2x6" piece of hard wood, cut a groove in the 3/4" side the width and depth of the guide, put epoxy in the groove, put the board on the guide, and set the guide against the blade over night. Oil the wood so it won't absorb water and start cutting. Lee #1 lparker This is what the guide looks like on my saw. I put a quarter on top so you can see how wide it is. Thanks, Andrea
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Post by stardiamond on Mar 27, 2015 15:59:46 GMT -5
Like many others have said, fix the unevenness when doming. If you are doing a very low dome cab, you can try trimming the preform with your saw. Mark a line parallel to one side and cut. Sometimes I do this with thick material. I think you can easier trim a smaller piece than a larger piece. A lot of the slabs I've bought were uneven, including going to a knife edge. Sometimes this keeps the selling price of the slab down. Given an uneven slab and locating the design you need to weigh the scene vs the difference in thickness when doing the design.
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Post by deb193redux on Mar 27, 2015 16:04:08 GMT -5
A small difference in slab thickness will automatically go away as you dome the cab on a dob stick. ... Exactly. ... and for some pendant stones you might even be able to take advantage of the taper. No different than grinding an endcut or a small stone. You just grind the shape and dome and thickness you want. But I would start at 100g.
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lparker
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Post by lparker on Mar 27, 2015 19:10:37 GMT -5
a 1/2' x 2" x 7" piece of hardwood - drill and countersink 2 holes from the bottom of the guide - sized for something like #10 x 1 1/2" flat head wood screws. Screw the board flush with the edge of the guide. Have the guide by the blade when you tighten it to be sure it is parallel with the blade. Don't forget to oil the wood or otherwise seal it so it doesn't soak up water and warp. The idea here is to fix the problem at its source instead of fixing it every time you cut a cab...save time and diamonds.
Lee #1
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