[Metrology] Flatness Of Granite Counter Top

CPCaballero

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Does anyone know how flat the typical granite counter top is and its suitability for use as a surface plate? We will have a few cutouts from a kitchen remodel job and I'm looking for uses for them.
 
i'd be interested to know . Have a buddy that owns a granite business. They let me pick thru dumpsters of beautiful cut offs ...some large . Nice for making water features with ...never thought of a surface plate though .
 
Unknown quantity. Will vary from one to the next. Surface plates need to be held to very tight tolerances and counter tops do not, so they are not. If you want a surface plate, import ones are being sold at really cheap prices. Look for a free shipping deal, and pull the plug. You will likely get a good one, though quality control of Chinese surface plates, like their other stuff, is often somewhat lacking. Granite counter tops would likely make a great lapping plate for non critical work, as will plate glass.
 
I have wondered the same thing. How many of the members on this forum actually have any need to be that accurate? I can't recall seeing or reading anything about any project that required that level of accuracy. Some of the gunsmithing people might benefit from .0001 accuracy, but I am not sure it even matters that much there.
 
Bob is correct.........But, for non-critical work they would proabaly be OK. I suspect you are not doing work for NASA:grin:
 
If cost is minimal, get three and lap them all together. eventually they will all be flat, but you need three. No guarantees about how long they'd stay good, either.
 
:sherlock::nail biter:

ok ladies and gentleman
i have a 6x6 piece of counter top grade rock that seems to be polished up pretty good at my shop,
i'd be willing to give it a rub on my recently recalibrated plate and see the result.
something tells me beforehand that the counter top will blue up pretty good, but then i have been wrong before!:grin:
pictures to come!!!
 
here is the test:
calibrated surface plate to Grade A, cannode blue ink , test @72*F
https://plus.google.com/u/0/collection/E8Tpv

before:
2016-10-08.jpg

after:
2016-10-08.jpg



end result: FAIL

the marble counter top is not flat, touching in only 4 corners and hollow in the middle >.001"

your results may vary,
use only as directed, yadda yadda yadda :p
 
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Debur the corners and try again!:grin: Just kidding..:cool 2:

Be interested how many impressions it takes to get about 70% coverage from scraping.
 
I wonder how much stress relieving the rock sees when it is sawn up into smaller square pieces as you have shown?
 
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