looking for a granite piece for sharpening? i have a deal for you.


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None near me.  I bought a 2'x3' piece to make a top for a sharpening cabinet for $58 from Community Forklift in Hyattsville, Md.  They always have a good selection of sizes and colors.  I think builders, remodelers, and countertop shops carry scrap there to donate, rather than having to dispose of it.  They are no where near me either, but I was going by there a couple of weeks ago, and always stop to see what they have.  I also bought four double 2-0 by 4-6  Marvin casement windows for $65 each that were taken out of some remodeling job, and weren't hurt.

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honestly unless you live in a really small town try your local counter top store. I live in a small city and a friend of mine got his for free. He said they where happy for him to take it as they didn't have to deal with disposing of it. i think his was like 12" x 30" 

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Small town livin here so no countertop option, but what we do have is memorial craftsman -headstone maker. At least around here most larger sized towns (for us that's population of +3,000) have a memorial shop. They also have cut offs but these are more for installing in your sharpening center, mine is about 6" thick and heavy. Same thing, dead flat and free but a much higher level of polish. What's nice about this is one little spritz of water and your paper really suctions down, a lot more than on the granite referencing plate I have acquired since.

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I think there may be an important point being overlooked here.

 

Granite is a good substrate for sharpening not because it's granite (there's no magic in that) but because granite surface plates are easily available for reasonable money and they're extremely flat. In other words, the thing that helps with sharpening isn't the stone, it's that someone made that stone flat to within a few ten-thousandths of an inch.

 

Granite counter tops are typically fairly flat as household objects go, but they aren't THAT flat.

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I found one pretty flat with a straightedge, and then flattened it further with a 12 x 18" surface plate upsidedown with wet-or-dry stuck to it.  The piece I checked with a straightedge turned out to be fairly flat.  I use surface plates for sharpening and flattening anything up to a jointer plane.  That gets flattened on the granite first, and finished diagonally on the 12x18.   Woodcraft has surface plates on sale twice a year.  You can get a 9x12 for 25 bucks.  I got a couple of them for different purposes.  One keeps diamond lapping film stuck to it.

 

I like the granite for a surface for the sharpening bench. Corian would have been okay too, but the granite has nice mass too.  Once you can sharpen an edge to take a shaving less than a thousandth of an inch, everything between your hands and the edge has no room for error out of flat.

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It's worth checking one with a straightedge when selecting one.  If no light shines under anywhere, it's a good start.  Most will show some humps and hollows.

 

When my best friend and I built telescope mirrors by hand when we were teenagers, an optical flat was much harder to produce, than a curved surface.  If a surface plate upside down with 600 grit leaves an evenly abraded surface, it's good enough for the first step in a flattening system.

 

I did find a 2'x3' surface plate on Craigslist for a hundred bucks, but I had already flattened by jointer planes, and didn't really need one any larger than the 12 x 18 any more.  If it was a little closer, I would have gone and picked it up, but it's a couple of hours away, and not worth the trouble to go get it right now.

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Before people go off the deep end about how flat is flat, they should probably take a look at the tolerances of the diamond plates most of us use to flatten our stones.

 

  1. Shapton Lapping Plate +/- .0002" $378
  2. DMT Dia-flat,  +/- .0005" $170
  3. Atoma Diamond stones +/- .0015" $100
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Before people go off the deep end about how flat is flat, they should probably take a look at the tolerances of the diamond plates most of us use to flatten our stones.

 

  1. Shapton Lapping Plate +/- .0002" $378
  2. DMT Dia-flat,  +/- .0005" $170
  3. Atoma Diamond stones +/- .0015" $100

 

 

Even the cheap Grizzly's are .0001 for B grade.

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Before people go off the deep end about how flat is flat, they should probably take a look at the tolerances of the diamond plates most of us use to flatten our stones.

 

  1. Shapton Lapping Plate +/- .0002" $378
  2. DMT Dia-flat,  +/- .0005" $170
  3. Atoma Diamond stones +/- .0015" $100

 

The reason I didn't buy any of those was because of their price when a 25 buck surface plate was flatter anyway.  Theory is fine, but once you tune a plane to take a shaving less than half a thou, it's close enough anyway.

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I can only speak of the memorial granite I have but it is just as flat as my surfacing plate, checked it with a straightedge before I bought it and double checked it with a friends plate and some layout dye. Not saying that all are like this but for me I couldn't be happier, except when I had to lift it!!

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Even the cheap Grizzly's are .0001 for B grade.

 

My point was that it doesn't really matter that much, because our finishing media isn't any flatter.  In my experience most chunks of granite that are the size a person would use for sharpening (say 4" x 12") are going to be flat to within +/- .0005". Another cheap option is a thick chunk of float glass.

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