Gage Block Grade 1 - Calibration


Hello there !

I have a gage block set Grade 1 which is due to calibration. My boss does not wanted to send out to be calibrated because she wants to save money. She has decided to do it internally. However, We do not have a master part to compare with but we have a Zeiss CMM machine. Would it be valid to measure the gage block with the Zeiss and use the MPE vale of it to calculate the Uncertainty ? Our Zeiss has two mode available : Optical and Probing, I am thinking to use Optical mode ?

can someone help me on this task ? I have not do it before and I am not 100 % sure if may works ?
Thanks a lot !

Johnny Quality

Quite Involved in Discussions

What do you use the gage block set for? How often do you use it? How often is it calibrated?

You may be able to justify extending the calibration frequency.


Hello Johnny,

thanks for your replay. I am new in the company but I have been told that it is the first time that the gage blocks need to be calibrated after they bought. They are not used very often, very rare I would say. They use the gage block to calibrate other instruments such as electronic calipers, gage drops and electronic micrometers that's all.

the calibration of gage block must be done every 5 yes according to the system.


Quite Involved in Discussions
I have a carbide gauge block set that I use for micrometers, calipers etc that I send away to a UKAS lab for calibration every 5 years.

I'm not being rude, but how much are you actually saving each year by not sending your gauge block set off to be calibrated every 5 years, and how does this cost compare against the resource you will use doing it yourself and the uncertainty of measurement you will now be throwing into the mix?

In my experience trying to cut these types of costs will end up biting you (individually and your company) in the backside and will cost you more in the long run.


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There is an old saying in Calibration:
"You can use a gauge block to calibrate a yardstick, and a yardstick to calibrate a gauge block, but only one of them is the right way".

With Grade 1 gauge blocks you are talking a tolerance of ±2 µinch.
For a valid calibration your CMM would need to be 4 times more accurate.
Your CMM is nowhere near accurate enough, even if you were just doing comparison readings to a master gauge block set.
That's why you use gauge blocks to calibrate a CMM, not a CMM to calibrate gauge blocks.

As for extending the calibration, I would not go longer than 5 years. Even when not used, the steel in hard gauges like gauge blocks can change value due to changes in their molecular structure.

Ron Rompen

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Chrifter: I am in much the same position as you are - with the financial constraints on our company due to Covid and the chip crisis (now finally resolving) we are cutting corners as much as possible.
I have revised our calibration procedure to show the CMM as the 'master' reference, and it is calibrated annually by a 3rd party. Our gauge blocks are used to verify/calibration calipers and micrometers, and the CMM is used to validate the gauge blocks - because of the nature of our business, and the tolerances that we work to (± 0.010mm is considered a very tight tolerance for us) this suffices.
In most QMS systems, (ISO 9001 IATF 16949) it is left to YOU to determine how you set up your calibration frequency and methods. Make sure it is clearly documented, and make sure there is traceability back to a NIST standard.


Ron Rompen, Yes exactly, I will try to calibrate them with the Zeiss machine we have in the lab. My boss totally refuses to send the Gage block to any calibration center. So I will give a try and measure with the Zeiss and use its MPE ( Maximum Permissible Error ) to calculate the Uncertainty somehow. However, I am aware that the Uncertainty might be larger in this case. What method do you use to calculate the uncertainty (U) and how ? Thanks a lot


Scanton, It is not that expensive, I actually found a very good price to do so, but unfortunately my boss does not understand that. She believes is so simple and can be done with a caliper or micrometer in our lab :( . I told her several times that there is a procedure to follow and it is normalized as well and still she doesn't care at all. So, I will give a try with the Zeiss machine and see what I can obtain . However, I am fully aware that Uncertainty will be larger in this case thought .
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