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How flat is polished granite work top?

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  • How flat is polished granite work top?

    I was at a roofing supplier today picking up some slates and stuff when I discovered next door was a skip full of polished granite off cuts from a work top manufacturer, I asked if it was scrap and they told me it was landfill. It just looked too good to bulldoze.
    I can have as much as I like, so if I were to get say 3 plates worth then blue up and do the compare the three Whitworths principle, is that doable, or am I wasting my time
    The stuff is about 1" thick btw, so laminating seems possible?
    I hate good stuff going in the ground
    Any ideas?
    Mark

  • #2
    Not this thread again.. :P
    Good enough for basic layout, maybe even sanding something flatter that is badly warped.

    Not good enough to be usable for sanding things *flat*, or scraping reference, or any other job where you actually care about thou's of an inch.
    Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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    • #3
      No reason that you couldn't lap them to any degree of flatness that you desire. With a little epoxy you too could have a lathe with 1 micron tolerances: https://www.youtube.com/watch?v=sFrVdoOhu1Q

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      • #4
        Originally posted by boslab View Post
        ..........
        I hate good stuff going in the ground
        ..............
        Mark
        It DID come OUT of there, after all.....

        Yeah, this again....... No telling how good. Probably good enough for woodworking no matter what... getting chair legs matched, etc. One might turn out to be good enough for metalworking uses, although I would think it unlikely.

        The main issue is the thickness. At 1", it's about 1/3 the thickness, and many times less stiff than a standard granite flat. Might be fine for smaller stuff.

        It's pretty much chance. The makers were interested in visual flatness, not true flatness (although as rejects they may not have even that). Consequently you just don't know.
        1601

        Keep eye on ball.
        Hashim Khan

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        • #5
          YUP!!! I have a nice Granite board. Its 18"x18"x1.25". Nice flat stone. I do have some other stones, not as large. Bout 18"x18"x2.5" Really smooth and flat, it was ground for its purpose.

          I like that I have my granite board. It is not one of my small "flats". But works for me.

          I don't work in Tenths, not even Hundredths (.001").

          Get me to the solution that is task at hand and I am good. If a plate of stone does it, I am happy... Im a HSM,,,,,, Dont work for anyone.... JR
          My old yahoo group. Bridgeport Mill Group

          https://groups.yahoo.com/neo/groups/...port_mill/info

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          • #6
            I am really sorry to ask as it might appear a bit boring, what I'm thinking is to stick 3 or 4 layers together with epoxy as an experiment, it might work, obviously it's not going to be as good as a solid 4" slab, but if it works I see no reason that a 3 foot long table could be made, for the price of the glue,
            Another idea popped in as a top for a table saw, ok stretching the bounds a bit it know, I promise not to ask any more questions that have been covered!, but that may limit any form of communication a bit because just about everything has.
            My apologies
            Mark

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            • #7
              Originally posted by Black_Moons View Post
              Not this thread again.. :P
              Good enough for basic layout, maybe even sanding something flatter that is badly warped.

              Not good enough to be usable for sanding things *flat*, or scraping reference, or any other job where you actually care about thou's of an inch.
              Seriously.....http://bbs.homeshopmachinist.net/thr...ght=countertop

              A table saw is already being made with a granite top.

              http://steelcitytoolworks.com/index....san-fence.html

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              • #8
                Originally posted by boslab View Post
                I am really sorry to ask as it might appear a bit boring, what I'm thinking is to stick 3 or 4 layers together with epoxy as an experiment, it might work, obviously it's not going to be as good as a solid 4" slab, but if it works I see no reason that a 3 foot long table could be made, for the price of the glue,
                Another idea popped in as a top for a table saw, ok stretching the bounds a bit it know, I promise not to ask any more questions that have been covered!, but that may limit any form of communication a bit because just about everything has.
                My apologies
                Mark
                No need to apologize, this is after all a place for discussions. I'm pretty sure the "not this again" sentiment stems from the fact that this particular topic is one of those that crops up periodically and seems to get pretty contentious for some reason. But that's part of the fun.

                If we restricted the discussions to only stuff that has not been discussed before this place would be pretty quiet. I'd fall into the "if it's flat enough for what you do it's flat enough" camp. Not sure how easy that is to quantify independently however. Experiment, have some interesting fun and post your results.

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                • #9
                  Originally posted by alanganes View Post
                  I'd fall into the "if it's flat enough for what you do it's flat enough" camp. Not sure how easy that is to quantify independently however. Experiment, have some interesting fun and post your results.
                  It's not the flatness issue as much as the stiffness of such a thin piece. I believe Forrest has pointed this fact out on several occasions. For a sanding plate, maybe.

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                  • #10
                    have you guys actually done any measurements? i did on a 80 x 50 cm plate. it was within 0.03 mm. there was a line that was absolutely flat. compare that to the lesser grade "real" plates. for general shop use its good enough. as to the stifness, if you put it on some foam, do you think it going to bend because of a surface gage or something similar on it?

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                    • #11
                      Originally posted by dian View Post
                      have you guys actually done any measurements? i did on a 80 x 50 cm plate. it was within 0.03 mm. there was a line that was absolutely flat. compare that to the lesser grade "real" plates. for general shop use its good enough. as to the stifness, if you put it on some foam, do you think it going to bend because of a surface gage or something similar on it?
                      Do you mean mapping Chinese plates? Yes, someone imported a dozen or so plates. None of the plates matched any of the included certification maps.

                      Support a countertop cutout on foam rubber?? Ignore the standard of supporting the plate on it "airy" points.

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                      • #12
                        It's an interesting subject, we had surface tables in work that compensated for the earths curvature, I think the big one was 20m long, oddly I never saw anything that long on it, the 4 ' tables in the machine shop were the most used size.
                        I'm repeating myself but I remember being given a plate mapping exercise with an auto colometer that was badly messed up by the sun coming through the roof windows and shining on the table, I should have guessed but the bump in the map was moving at the same speed as the earths rotation, 15 degrees an hour, the instructor was amused.
                        I wonder if a granite welding table would be handy lol, beats my sheet of 3/4 ply, omg I've said it
                        Oh well it is a home shop after all
                        Mark

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                        • #13
                          Originally posted by Rosco-P View Post
                          Do you mean mapping Chinese plates? Yes, someone imported a dozen or so plates. None of the plates matched any of the included certification maps.

                          Support a countertop cutout on foam rubber?? Ignore the standard of supporting the plate on it "airy" points.
                          where did i say chinese? btw, my chinese din 00 surface plate is right on the money, 0.003 mm high in the middle. the airy points stuff is bs. you have to support it where it serves the purpose. flexible stuff you support on something soft. e.g., if you want to use a piece of glass to tram the mill, you put it on foam. as my surface plate is high in the middle, its supported on the four corners and according to my measurements its now din 000 standart. 0.002 mm high.

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                          • #14
                            Originally posted by dian View Post
                            where did i say chinese? btw, my chinese din 00 surface plate is right on the money, 0.003 mm high in the middle. the airy points stuff is bs. you have to support it where it serves the purpose. flexible stuff you support on something soft. e.g., if you want to use a piece of glass to tram the mill, you put it on foam. as my surface plate is high in the middle, its supported on the four corners and according to my measurements its now din 000 standart. 0.002 mm high.
                            You didn't, but I can see where this thread is going....

                            Really? .......tram you mill with a piece of glass sitting on a piece of foam.

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                            • #15
                              Hey, there are high quality certified flats from good US and other makers. Known flat to whatever tolerance.

                              There are chinese ones with mass-printed specifications... many of which are quite flat. I have two that blue up well against one another, which means they are either perfect complements, or they are flat.

                              After that you get to glass, countertop, etc.

                              The big issue with the glass and countertop is thickness, and the total lack of info and even lack of maker's intent to make them truly "flat".
                              1601

                              Keep eye on ball.
                              Hashim Khan

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