Our company have their verniers calibrated by Mitutoyo. On the calibration certificate, there are a number of characteristics checked.

Are the only characteristics I am interested in as a guide to is the instrument calibrated, the maximum error of reading throughout the measuring range on the imperial and metric scale?

Do I need to worry if the flatness or parallelism of internal/external faces is outside of the requirement? All of our verniers, even 1 which has just been bought new, have some kind of error on the measuring jaws. Is this acceptable from an 'is the instrument within calibration' point of view?

Thanks.

If there are anomalies that might contribute to measurement error, they should be accounted for in the calibration process. For calipers (not necessarily "verniers," a type of caliper) the condition of the jaws is important and should be verified, and the results should appear on the certificate.

Thanks Jim. The instruments to which I refer are indeed vernier callipers. The calibration certificate does quote a number of characteristics. I guess that my question is:

If the vernier calliper has good accuracy of scale throughout it's range: +0.01mm against a requirement of ±0.02mm, but has a parallelism of external measuring faces of 0.018mm against a requirement of 0.008mm, would an auditor deem the instrument to be within calibration?

Thank-you.

Thanks Jim. The instruments to which I refer are indeed vernier callipers. The calibration certificate does quote a number of characteristics. I guess that my question is:

If the vernier calliper has good accuracy of scale throughout it's range: +0.01mm against a requirement of ±0.02mm, but has a parallelism of external measuring faces of 0.018mm against a requirement of 0.008mm, would an auditor deem the instrument to be within calibration?

Thank-you.

The simple answer is another question: Is .018 > .008? If there's a requirement of .008 max, and that requirement is exceeded, there's a failure. If you're confident (and can demonstrate) that the discrepancy is acceptable, change the requirement.

Just out of curiosity, why are you using vernier calipers?

We are using vernier callipers to measure an assortment of characteristics. The tightest tolerance we are measuring is ±0.1mm. This could be the diameter of a pin, a length or a diameter.

The requirement is on the Mitutoyo certificate and is taken from a British Standard, BS887:2008, Specification for Precision Vernier Callipers.

I guess I'm just a little confused as to how we can order brand new equipment with a cal. cert., and when the cal. cert. arrives for the new item, there is an error on it. Surely if the item was outside of calibration, the company should not have sold it to us in the first place? The accuracy of the measuring scale and the checks on ring gauge and gauge block are OK, it's measuring jaw characteristics that have errors on them.

We are using vernier callipers to measure an assortment of characteristics. The tightest tolerance we are measuring is ±0.1mm. This could be the diameter of a pin, a length or a diameter.
I was pretty sure you were using the calipers to measure something. :tg: What I was asking was why you're using vernier calipers instead of dial or digital.
I guess I'm just a little confused as to how we can order brand new equipment with a cal. cert., and when the cal. cert. arrives for the new item, there is an error on it. Surely if the item was outside of calibration, the company should not have sold it to us in the first place? The accuracy of the measuring scale and the checks on ring gauge and gauge block are OK, it's measuring jaw characteristics that have errors on them.
It's not real unusual for something to go out of whack during shipment and handling. That's the reason that things should be calibrated upon receipt, prior to use. If you think that what you're seeing is unreasonable, go back to your source and let them know about it.

Thanks Jim.

We are actually using Mitutoyo digimatic callipers. Perhaps I should have been more specific.

I am struggling to get my head around the way that the instrument is calibrated. I have had the results back today for a vernier and the co-planar of outside and inside measuring jaws is flagged as not OK against BS887:2008. Requirement is 0.050mm, actual reading is 0.088mm. As mentioned earlier, the smallest tolerance we measure is ±0.1mm. What does this co-planar characteristic mean to the actual measurement the Inspector sees when using the vernier against the ±0.1mm tolerance and how do I make a decision if the instrument is OK or not?

Sorry to labour the point, but this calibration business is new to me. Again, any help you could offer would be much appreciated.

Note: I have just managed to speak to the guy at Mitutoyo who calibrates our verniers, and he said that the only reading that you really need to look at is the Maximum Error of Accuracy of Reading, as this takes into account all of the other characteristics that are checked, i.e. co-planar of outside and inside measuring jaws. Therefore, if the max. error is within the requirement, the instrument is calibrated OK.

Darren

Our company have their verniers calibrated by Mitutoyo. On the calibration certificate, there are a number of characteristics checked.

Are the only characteristics I am interested in as a guide to is the instrument calibrated, the maximum error of reading throughout the measuring range on the imperial and metric scale?

Do I need to worry if the flatness or parallelism of internal/external faces is outside of the requirement? All of our verniers, even 1 which has just been bought new, have some kind of error on the measuring jaws. Is this acceptable from an 'is the instrument within calibration' point of view?

Thanks.
Getting a vernier calibrated by Mitutoyo is too expensive and unnecessary.Instead of that you may follow use and throw method.The tolerance for variation in a used vernier vernier should be 1/10 of the job tolerance it is used to measure and not the tolerance applicable to new vernier.In the master list of your MTE you can fix your own tolerances.
V.J.Brahmaiah

Thanks Jim.

We are actually using Mitutoyo digimatic callipers. Perhaps I should have been more specific.

I am struggling to get my head around the way that the instrument is calibrated. I have had the results back today for a vernier and the co-planar of outside and inside measuring jaws is flagged as not OK against BS887:2008. Requirement is 0.050mm, actual reading is 0.088mm. As mentioned earlier, the smallest tolerance we measure is ±0.1mm. What does this co-planar characteristic mean to the actual measurement the Inspector sees when using the vernier against the ±0.1mm tolerance and how do I make a decision if the instrument is OK or not?

Sorry to labour the point, but this calibration business is new to me. Again, any help you could offer would be much appreciated.

Note: I have just managed to speak to the guy at Mitutoyo who calibrates our verniers, and he said that the only reading that you really need to look at is the Maximum Error of Accuracy of Reading, as this takes into account all of the other characteristics that are checked, i.e. co-planar of outside and inside measuring jaws. Therefore, if the max. error is within the requirement, the instrument is calibrated OK.

Darren

If you expected compliance with a specific standard, you would have needed to specify that standard in your PO for calibration. Did you ask what standard Mitutoyu is using, and ask for a copy? That's what you need to do at this point.

Thanks to both of you.

You have given me a couple of good ideas on how to move forward.

Darren