3-Plate Method, Surface Plates?

Did any of the local companies get back to you on calibrating them?
 
NCjeeper said:
Did any of the local companies get back to you on calibrating them?
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Nope. Wish we were near SoCal about now, I know where I'd go...
And if you watch Stan's BarZ shop tour of Standridge out in SoCal from (5) years ago, The dude Mike made an interesting comment
about some companies that offer 'calibration' services... So time to do a bit more in-depth research.

What I would like to find, is a couple of those hooks he's using when placing the plate on the SG.

 
I'm fairly ignorant when it comes to surface plates but how does a giant chunk of granite go out of calibration?
 
Weldo said:
I'm fairly ignorant when it comes to surface plates but how does a giant chunk of granite go out of calibration?
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By use. If used carefully and kept clean and the grit kept cleaned off the plate, it will stay in calibration for a long time. Temperature warps the plated, but will return to true when the temperature returns to the same as before. Grit will wear the surface. If the top of the plate is warmer than the bottom, it will warp out of true, but will return to the previous shape when the temperatures change back to the same gradients. In clean rooms that do do high accuracy work and testing, they are quite anal about controlling all the things that can change the size and shapes of the measuring equipment. In a home hobby shop it is a lot more difficult to make the environment stabilized, and we will need to settle for a lower tolerance, even if we are quite careful with our setups and work.
 
For something as hard and stable as granite to warp or wear, I'm guessing we're talking about tenths of thousandths of an inch, right? I'd imagine the wearing and warping to very miniscule.
 
Weldo said:
For something as hard and stable as granite to warp or wear, I'm guessing we're talking about tenths of thousandths of an inch, right? I'd imagine the wearing and warping to very miniscule.
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Wearing can get pretty bad. Have a look at ROBRENZ's video. He scored a large Starrett pink for nothing because it had wore beyond the point of being economically feasible to bring it back into tolerance.
Temp changes, as Bob mentions, straighten out after the plate has 'soaked' at the temp it was certified at.

(never did see a Part II...)
 
From the 'Just when you think you've got it clean dept.'
I took one of the 24x36"ers last night after the sun had set and wheeled it to the end of my apron.
('wheeling' these around is a bit challenging...)
Sprayed some Dawn on it and let it soak for half-a-Cerveza.
Made up a bucket and used a soft brush on it and gave it a good cleaning. Figured that Dawn is good for cleaning injured wildlife, oughta work for granite... :grin:
Rinsed it down with a pressure nozzle, and let it run off for the other half-a-Cerveza.
Took a clean white bath towel and dried it off, and _still_ it had a light brown tint to it.
I believe that shows how embedded the dirt and grime can become when they are not maintained properly.
 
Wow, this is all very surprising to me! Thanks for the education. I know some surface plates are cast iron, any benefit or detriments to cast over granite?
 
Weldo said:
Wow, this is all very surprising to me! Thanks for the education. I know some surface plates are cast iron, any benefit or detriments to cast over granite?
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Cast Iron ruled the roost until WWII. When metal was needed elsewhere granite became more prevalent.
Granite is more stable than CI and lasts longer - if maintained properly. There's the catch, as I have found out this past month. :cool 2:
Just as with most anything, it as to be taken care of.
 
I watched some of the video you posted and I was amazed to see how the precision level actually showed a change when he slid the counter balance weight from side to side. I would have never guessed in a million years that moving a 10lb chunk of steel across an 8" thick slab of granite would cause any change whatsoever. Interesting stuff!
 
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