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Post by stardiamond on Nov 24, 2022 20:37:54 GMT -5
There is no need. You are cabbing preforms not the entire slab. Trim off the knife edges and areas you are not planning to use. If an area on the preform is too thick to grind, slice some off with the trim saw. One side is flat and the other isn't as long as the flat side is the bottom, nothing else to do. When you need to make the bottom the top, then grind the preform to relatively flat using a wheel; rotating or figure 8 and then make perfectly flat using a lap.
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Post by parfive on Nov 24, 2022 20:39:49 GMT -5
It’s easy to cab a wedge-shaped slab, Hefty. Trying to “fix” one by grinding is surely more effort than it’s worth and cleaning one up on a saw is a tricky job even when you have good equipment.
You’ll have a more critical eye at the next show.
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realrockhound
Cave Dweller 
Chucking leaverite at tweekers
Member since June 2020
Posts: 4,483
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Post by realrockhound on Nov 24, 2022 20:42:31 GMT -5
One thing I’ll add, is that something is off with your saw if it’s cutting wedges. See if you can figure out why it’s shifting, then there will be no need to level them on a flat lap.
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Post by stardiamond on Nov 24, 2022 20:48:04 GMT -5
What I suggested works with heels. You are not the only person who gets uneven slabs. I buy a lot of them.
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brotherbill
spending too much on rocks
Member since October 2018
Posts: 388
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Post by brotherbill on Nov 25, 2022 7:28:33 GMT -5
@hefty
The time required to flatten an uneven slab or straighten a tapered slab depends on the size of the area and the amount of correction required. So first I would suggest reducing these parameters to an absolute minimum with your saw. It also depends upon the laps available.
IMO, as parallel slabs are your objective, it probably isn't time effective for you to consider working with end cuts or wedges.
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Post by jasoninsd on Nov 25, 2022 8:08:37 GMT -5
@hefty The time required to flatten an uneven slab or straighten a tapered slab depends on the size of the area and the amount of correction required. So first I would suggest reducing these parameters to an absolute minimum with your saw. It also depends upon the laps available. IMO, as parallel slabs are your objective, it probably isn't time effective for you to consider working with end cuts or wedges.  |
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Post by stardiamond on Nov 25, 2022 10:30:04 GMT -5
The highest surface is in contact with the disk until it flat and any valleys are gone.
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herb
spending too much on rocks
Member since November 2011
Posts: 473
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Post by herb on Nov 25, 2022 11:15:49 GMT -5
@hefty Fiiine, I'll resign the idea for now  About flat lapping - I was under the impression square area didn't matter much. Wouldn't a quarter-sized cab grind or polish just as fast as a dollar-sized slab since the whole surface of each is in contact with the disc? If the larger and smaller surface area pieces are already flat and you are just taking them to the next highest grit, then yes the surface area doesnt make much difference. But if you are talking about trying to grind away a low spot then the larger piece will take longer because there is a larger quantity of material to remove. |
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