Surface plate scratches

Driveslayer45

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I just picked up a 24 by 36 do all surface plate we was used years ago in a machine shop as another work area so I has a number of scratches on it that I can feel with my hands. As a hobbyist I certainly don't need a certified but what should I do lightly rub over it with a stone get some diamond lap paste...
 
Just give it a light going over with an India stone and some solvent or kerosene, going at it with diamond paste would likely embed some of the diamond in the iron, making it into a lap, causing wear on whatever tools were slid around on the plate.
 
Run a straight flat piece over the plate. If the scratch grap the stop lightly with lub. if not, leave it alone.
 
Is it a granite surface plate or cast iron?

If granite, you shouldn't need to worry about it. Chips, dings, and scratches in granite don't raise a burr. So they shouldn't matter one iota as long as they're small (i.e., not big enough for your parts or measurement equipment to 'fall' in).
 
So running a clean 1-2-3 block over it some places it glides like an air hockey puck, others it's smooth but has clear drag or friction , and a few spots it does grab.

Any suggested reading or videos on how to properly use a surface plate?
 

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I wonder if there is a surface plate calibration shop like Standridge Granite working in your area. If so, they can recondition and certify that plate for you. If I had that plate, that is what I would look for.
 
I did a Google search on my phone and none came up, but I don't trust the results
 
Call Standridge and ask if they know operators in your area. I bet the know most other shops in their industry.
 
I bet the cost to have it resurfaced would be more than a new plate.

Joe
 
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