Small surface plate tester

Take the surface plate to a pro shop and let them do the calibration and certification. My 18x24x4" 2 ledge plate cost me just over $100 for the job, took them about 20-25 minutes to get it correct, from a .003" hole in the plate center error. We had Standridge Granite from So. Cal. come here on one of their road trips, and we had 5 plates that belonged to 4 of us for them to do. Without the quantity we did, the minimum order charge and travel fee would have killed the deal. If you live close to a shop that does the work in house, you can take it there and get it calibrated while you wait. Call first to get price, availability, and other information. Those guys can do the work in their sleep and get it right after calibrating hundreds or thousands of them. Friendly workers, fun group collaboration.
 
FYI - This RoM design was driven by "on hand" material, none of my ideas are cast in concrete. US Marine motto: Improvise, Adapt, Overcome.
 
Per Bob's comments, a long gradual trough will lead you astray or produce confounding readings. Found this on a recent used surface plate purchase. Surfing for reconditioning quotes.
 
Brownells has 1/2-40 taps, typically used for tactical tupperware.
 
Bob Korves said:
Note that the Repeat-O-Meter is only half of the equation to check a surface plate. It only shows if you have hills or valleys. It does not give their relative heights. Typically, a autocollimator is also used to test the actual geometry of the plate from one position to another. Neither of these tools will do the job of calibrating a surface plate by itself. Beyond the tools, a clear understanding and interpretation of what the tools are telling you is also necessary, along with the skills, tools, and knowledge of how to use the information to actually make the plate flat.
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Good points, many autocolimators give angular readings, alignment scopes are metric or Imperial and others have no internal micrometers so you have to use targets that have micrometers attached, this is the type I have.
 
Bob Korves said:
Note that the Repeat-O-Meter is only half of the equation to check a surface plate. It only shows if you have hills or valleys. It does not give their relative heights. Typically, a autocollimator is also used to test the actual geometry of the plate from one position to another. Neither of these tools will do the job of calibrating a surface plate by itself. Beyond the tools, a clear understanding and interpretation of what the tools are telling you is also necessary, along with the skills, tools, and knowledge of how to use the information to actually make the plate flat.
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Bingo, no true reference plane, the Feds use a Mahr indicator and a heavy base, then you check by indicating a pattern, if the readings are acceptable you are OK for checking Govt. parts, again this magnifies error but does not give a measurement of the outage.
 
Bob Korves said:
Take the surface plate to a pro shop and let them do the calibration and certification. My 18x24x4" 2 ledge plate cost me just over $100 for the job, took them about 20-25 minutes to get it correct, from a .003" hole in the plate center error. We had Standridge Granite from So. Cal. come here on one of their road trips, and we had 5 plates that belonged to 4 of us for them to do. Without the quantity we did, the minimum order charge and travel fee would have killed the deal. If you live close to a shop that does the work in house, you can take it there and get it calibrated while you wait. Call first to get price, availability, and other information. Those guys can do the work in their sleep and get it right after calibrating hundreds or thousands of them. Friendly workers, fun group collaboration.
Click to expand...
I'd really be interested in any tips for finding someone to lap and qualify a granite plate. If I could get my 18x24 done for ~$100 I would do it in a heartbeat.
 
Couldn’t agree more, Know a guy who bought a TruStone lab grade. I bought an Enco shop grade for a tenth of the price, neither one could get the Mahr indicator to move
 
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