Digforcrystals
spending too much on rocks
Member since July 2008
Posts: 351
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Post by Digforcrystals on Mar 24, 2011 16:01:23 GMT -5
I bought a used ameritool flat lap grinder with the plan of polishing some slabs. Aside from the 180 grit, all the pads are in bad shape and I am thinking I need to start learning with new ones.
My question is, since the slabs are already fairly flat and smooth, which grit is best to start polishing? Is 600 too fine to begin?
Anways, anyone with experiance ,please tell me which grit steps you use to polish slabs.
THANKS! Rodney
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rocpup
spending too much on rocks
Pink Limb Iris
Member since March 2011
Posts: 465
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Post by rocpup on Mar 24, 2011 18:53:43 GMT -5
Polishing a slab on a flat lap may be a lot more difficult than you think. Polishing a cab you are working only on a small area at any one time. Polishing a slab the whole area is on the surface all the time unless you are trying to polish a very small slice. Most saws will leave some saw lines and require some heavy grinding to get to a flat surface that is required to get to the next step. If you think your slabs are true enough give the 600 a try. My guess is you will have to start with 180 or so and work up to your higher numbers.
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Post by johnjsgems on Mar 24, 2011 19:09:57 GMT -5
600 may work on softer materials. I do small flats on my Genie with a no hole 100 grit lap. No matter how smooth it seems faster to get it flat flat with uniform 100 grit scratches. I use magnetic Nova laps then in 280, 600, 1200, and 3000 followed by 14K diamond polish. On your unit if the 180 is OK I would use that followed by a 260 or 360 diamond lap, 600 and 1200. 3000 if you want to speed up polish or right to polish from 1200.
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stefan
Cave Dweller
Member since January 2005
Posts: 14,095
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Post by stefan on Mar 26, 2011 8:42:52 GMT -5
I have hand lapped t egg halves starting with 60/90 tumbling grit. Saw marks really take a toll and are difficult to remove. If your slabs have saw marks go with the coursest grit ou can
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Digforcrystals
spending too much on rocks
Member since July 2008
Posts: 351
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Post by Digforcrystals on Mar 27, 2011 21:26:03 GMT -5
I have got a new saw so it makes cuts that are incredibly smooth. It looks like they would take a polish just as they are, or with very little grinding, 600 at the most to start?
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Post by johnjsgems on Mar 28, 2011 7:15:17 GMT -5
You can try it. At worse you would have to add more. Starting too fine may show flaws that were not noticeable before. If you are only doing flats I would use diamond plated disc "toppers" rather than the colored diamond sanding discs.
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chromenut
fully equipped rock polisher
Member since December 2009
Posts: 1,971
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Post by chromenut on Mar 28, 2011 7:32:58 GMT -5
Your Ameritool, just like my Hi-Tech, normally comes with a set of flat laps: 180, 320, 600, 1200, and a polishing lap, with a tube of 14k grit diamond polish. Least that's been my experience with them. Is your's a 6" or 8"? If it's an 8" you'll have no problems polishing slabs, depending on how big they are. Me, I'm grabbing stuff that just barely fits on my lap down to pieces so small I can't hold them while polishing. Now I also have this grinder that turns between 1500 rpm's and 9500 with a 60 grit wheel, I use that with a sprinkling of water to prep rough cuts, makes it so much easier than trying to wear down bumps on your flat lap. I mount the grinder sideways on a portable workbench, keeping a bucket of water near me. I dunk the slab in the water then hit the wheel. It's a 6" Porter Cable grinder like in the photo below: Saves me tons of time on the flat lap. I use this same method to shape up my preforms, works on hard stone but don't try it on anything soft, it'll wipe it out.
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stefan
Cave Dweller
Member since January 2005
Posts: 14,095
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Post by stefan on Mar 28, 2011 12:17:05 GMT -5
600 is a little too far down IMHO. Lie stated the wost you can do is waste time (and possible wear out a 600 pad). I remember a discussion YEARS ago on this board about the grit size of a saw blade. Most people agreed that saw blades (even fine cutting new ones) leave 100 grit scratches. If you think about it it kinda makes sense as your really not "cutting" the rock but mearly grinding it apart. THink about how long it would take for a grinder to smooth a rough edge in 100 grit vs 400 grit! I honestly think your going to find that the smallest grit you can start with will be a 220 or so. Best of Luck on whatever you decide!
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mossyrockhound
fully equipped rock polisher
Member since January 2011
Posts: 1,278
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Post by mossyrockhound on Mar 30, 2011 18:59:33 GMT -5
I guess how you do it depends on what the starting material is like and what equipment you have at your disposal. I start with my rotary lap if the piece has deep saw marks (ridges) using 60-90 grit. You need to be careful though because the 60-90 can "eat out" the material around fractures or soft spots. If your slabs have fractures or soft spots, I believe it's best to start with 220 grit, and then work through the other finer grits and finish with cerium oxide or tin oxide on a wool pad. Garry
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