I have a large stone that I need to lap quite a bit. On the advise of many of you I have purchased some SIC powder. Now I have this bag of powder and do not know how to use it to lap a 19" stone. Can anyone please help.
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I have a large stone that I need to lap quite a bit. On the advise of many of you I have purchased some SIC powder. Now I have this bag of powder and do not know how to use it to lap a 19" stone. Can anyone please help.
You need a large flat surface to put the sic on.
I recommend a large glass cutting board from Walmart or target or something similar.
Sprinkle an amount on the smooth side of the glass board and add a bit of water.
Now put your stone you want to lap flat on it and do figure eights and circles also rotate the stone end to end often.
I recommend buying a machinests rule to use as a straight edge to check for flatness.
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Step one- Cut 19 inch stone in half!
Heck, I want to see a pic of the stone?
Mike, are there any Lapidary outfits in your area? For a reasonable fee, you might get it lapped and save you time and $$?
Also, is it a Hard stone or more of an slate?
Pick up a large steel cookie sheet, try a thrift store, Dollar store, Sam’s or Costco. I usually get them from a Dollar Store.
Put the sheet on a flat piece of cement floor, sprinkle a teaspoon of loose grit, start with 60 and add a squirt of water.
Mark a grid on your stone with a sharpie, pencil will just wash off with the slurry.
Now rub the stone in the grit alternating patterns until all the sharpie ink is removed from the stone. Add grit as needed, you don’t need much. Once you removed the ink grid, rinse the stone and do it again to make sure you are flat.
You will feel when the grit stops cutting and you need to add more.
Once you get it flat, the other grits go quickly up to 500, then move to Wet & Dry, just wet the sheet and stick the paper to the wet sheet. Rub the stone until you remove the ink grid.
I buy my grit from GotGrit.com. You can buy a, 60-500 loose Silicone Carbide progression, ¼ pound of each for about $15. That will do several stones.
thank you very much. This seemsQuote:
Originally Posted by Euclid440
easy. I will post pics once this slab is flat and nice with no gouges
I like doing big large circles for troublesome hones. keeps everything moving.
Also, be sure to incorporate the water into the powder before you start lapping. Do not lap in thick mud. I've seen powder clump up and gouge the stone before. Always do a quick mix with your finger to make sure it's even.
Glass is better. Flat cookie sheets too! I have a granite plate, and while its both hard and flat, granite has some pockets in it, and the grit can get stuck in there. Not good. Glass/cookie sheets are the way to go!
For a basic idea on how it's done, this video does the trick. I just skimmed through it and I never turned on the audio, but he has the amount of grit and water right, a nice big piece of glass to work on and the figure 8 movement is what I do for the most part. I always try to bring back in the grit from the edges to attempt to keep all the grit about the same size, instead of the stuff in the centre getting finer and finer with the grit on the outside getting in on the act now and then, causing deeper scratches.
Note, as he progresses, the grit/water starts to look thick and grey, but that is actually particles from the stone he's working on, getting added to the mix. When it starts to thicken up... I clean the glass off and start over with fresh grit/water, if I need to keep going.
https://www.youtube.com/watch?v=0_vpMtppbkU
Regards
Christian
Glass, marble and granite work, but deform rather quickly, especially with low grit Silicon Oxide grits and body weight pressure. A steel cookie sheet will stay flat much longer, you can use it over a sheet of glass, large tile or piece of marble or granite counter top, (Habitat for Humanity)
You will feel when the grit stops cutting, start with a teaspoon full and just add more grit and water from a water bottle or squirt bottle, as needed. You want it a little runnier than tooth paste, more like gravy. Depending on the stone it will thicken up. Slates thicken more quickly than hard stones like arks and other noviculites.
No need to wash it off until you change grits. Or just squeegee it to the bottom of the pan. A wide plastic putty knife works well for this.
Alternate your strokes, X’s, circles and back and forth, spin your stone 180 degrees after a few laps.
Once flat 60 or 80 grit, polishing grit goes quickly, you don’t need much grit. Make sure to wash the stone and sheet well, in soapy water, when moving up in grits or you will fight deep scratches all the way up in grit.