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Procedure or Specification For Extending Gages Calibration

Hello All:
I have been assigned the task from my Quality Director to see if there are ANY procedures or specifications regarding extending any calibrated gages especially thread ring and thread plug gages. We have micrometers, calipers, micro-hites etc.
We recently had a FAA audit and he wanted us to show him we had a standard or specification stating we can extend gages.

Can anyone help please??

John Predmore

Quite Involved in Discussions
An organization is allowed to establish the frequency of calibration, but the basis of that decision should be recorded (and withstand scrutiny of the decision by a knowledgeable auditor). One machine shop I know scheduled calibration based on a log of how many cumulative hours a gauge was in use, meaning operators had to check the gauge in and out of a gauge crib. The rationale is, if a gauge lies in a drawer 51 out of 52 weeks, it is less likely to go out of calibration due to wear or handling than a gauge in daily use. The basis for your decision to extend the calibration cycle should be based on data, such as how far from nominal was the as-found condition of the gauge the last 7-10 times the gauge was calibrated. The risk of having extended duration is how you react when you someday discover a gauge exceeds its allowable limits. Will you recall product and notify your customers going back so many years since the gauge was last known to be in-calibration? Many companies decide it is more economical to have a default frequency and stick to it.

Mike S.

An Early 'Cover'
How do you establish your intervals to start with? Is consideration of risk involved? It should be. Same with changing intervals.

Do you ever reduce an interval? You should use the same kind of criteria when determining whether to extend as to reduce an interval. Consider factors like usage levels, as John said, as well as history, manufacturer's recommendations, environment, whether or not this gage being OOT could cause a recall or other severe risk, etc.

Depending on the kind of gage, implementing some kind of between-interval check like using a check-standard to verify a gage may help reduce risk.
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