Granite Surface Plate Calibration

E

Eloy Gomez

#1
How do you calibrate a Granite surface plate? Or what instruments would one use to calibrate a surface plate?

It has been brought to my attention that the company that does our surface plate calibration may not be doing their job thoroughly. Our calibration rep tells me that the outside calibration tech that we hired to calibrate our surface plate spends less than 3 minutes to calibrate the surface plate and he only cleans it.

I am a bit concern over this but would like to see first hand before I bring up the issue, I have seen surface plate calibration before but it has been a couple of years and may need a refresher. If any one could shed some light I would appreciate it. Thanks.
 
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Hershal

Metrologist-Auditor
Staff member
Super Moderator
#2
There are two basic sets of instruments: repeat-o-meter with the attendant bars and so forth, and autocollimators.

Your accuracies will be close with a good technician regardless of which tools, but the uncertainties should be lower with the autocollimator.

3 minutes , even for a 12" x 18" plate is not nearly enough time. It requires nearly that to set up for the cal.

You should receive a chart with your certificate that shows the actual readings taken at corners, centers, and typically either a "X" pattern or a pattern that resembles the British Union Jack, with several point on each arm. The certificate should also report the grade of the plate.


Since this is done on-site at your location, you should be watching the technician to verify what you have been told.

And this does NOT include lapping if necessary. That is a whole other thing.

Hope this helps.
 
E

Eloy Gomez

#4
You should receive a chart with your certificate that shows the actual readings taken at corners, centers, and typically either a "X" pattern or a pattern that resembles the British Union Jack, with several point on each arm. The certificate should also report the grade of the plate.

Will the calibration technician be able to print out a chart on site using either of these two instruments?
We believe our tech uses an autocollimator.
 
Last edited by a moderator:
H

Hodgepodge

#5
Will the calibration technician be able to print out a chart on site using either of these two instruments?
We believe our tech uses an autocollimator.
There are autocollimators with digital outputs that could be used for reports/certs, so what you're asking is possible. I've attached GGG-P-463. It may give you an idea of what is required to calibrate a surface plate. Government specs such as this are available for free at http://assist.daps.dla.mil/quicksearch/.

How large is your surface plate? Did you receive a calibration report/cert? What quality requirements does the purchasing document (your P.O.) specify? I wonder if you are asking for more than you are getting.
 

Attachments

E

Eloy Gomez

#6
Thanks for the useful link and PDF information. The calibration company is showing up today or tomorrow and I will observe the calibration.

We have multiple surface plates and our P.O. states to be calibrated to the Standard.
 
E

Eloy Gomez

#7
Well, Our calibration house sent a new technician and he had all the instruments referenced by you guys, it took him about two hours to do two surface plates mid size and he was able to provide a chart along with a report.

He informed me that there had been other reports by clients who also questioned the work performed by the other technician. Thank you both for the insight.
 
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