We currently do a GRR every year for each gage or family of gages. My question is why. Why should we have to check the GR&R of the same gage more than once? If the gage is calibrated and maintained in the same state of repair, shouldn't the GR&R be the same over time? I do not see how the gage's ability to find bad parts will change if the gage it's self has not changed. I am bound to TS 16949 and ultimately, my customer specific requirements. I plan on checking these documents to see if they dictate that a gage be checked more than once.

Any opinions?

Two additional things that can change over time that could impact your Gage R&R results are:

Operator technique
Part form variation

Not all gages are significant impacted by either of these, but many are impacted. If you know that your gages are not affected by variation in operator technique (or are automated with no operator intervention) and you know that variation in part form does not affect your measurement results, you probably do not need annual gage R&Rs.

Unless your customer demands it.

We currently do a GRR every year for each gage or family of gages. My question is why. Why should we have to check the GR&R of the same gage more than once? If the gage is calibrated and maintained in the same state of repair, shouldn't the GR&R be the same over time? I do not see how the gage's ability to find bad parts will change if the gage it's self has not changed. I am bound to TS 16949 and ultimately, my customer specific requirements. I plan on checking these documents to see if they dictate that a gage be checked more than once.

Any opinions?

Keep in mind that GR&R is an assessment of the variation in a measurement system. The gage is only one part of that system. Systems do change over time. There is a predictable tendency of systems to deteriorate over time (entropy). If you have access to the AIAG MSA manual, look at page 15, there is very nice model of all elements that make up the measurement system and contribute to variation. In short, the measurement system variation is due to:
- Workpiece (Part)
- Instrument (Gage)
- Person (Appraiser)
- Environment
- Standard

Hope this clarifies a little.

Stijloor.

Thank you both for your comments. I do not think that Part variation will be an issue since I usually pick parts that cover the operating range of the gage. This always gives me a really high PV. I agree that operator influence is a factor but thru proper training we have been able to keep AV at or around 0.
I agree that I may be looking at this too narrowly. I just can't come up with a logical argument for decreasing the frequency. I have worked at plants that only do GRR at PPAP and never do anything with the gage except calibration after that.

I have to figure something out though, I can't get management to allocate the resources to do this many GRR and they are getting behind.

I do not think that Part variation will be an issue since I usually pick parts that cover the operating range of the gage. This always gives me a really high PV.

This is an acceptable practice if you are using the P/T Ratio and the gage is used for inspection purposes only. If you are using %GRR and the gage is used for SPC, this is not an acceptable practice. The part variation should then reflect the process variation.

If you are using %GRR and the gage is used for SPC, this is not an acceptable practice. The part variation should then reflect the process variation.

Can you elaborate on this a little bit? I am using GRR % of tolerance as the acceptance criteria. Some times I have a PV % of tolerance at 30-40 yet my GRR%tol is below %10. are you saying that this is a bad GRR?

Can you elaborate on this a little bit? I am using GRR % of tolerance as the acceptance criteria. Some times I have a PV % of tolerance at 30-40 yet my GRR%tol is below %10. are you saying that this is a bad GRR?

% of tolerance is the P/T Ratio. This is used to determine whether the gage can determine if a part is in spec or out of spec.

%GRR is % of the part(process) variation. This (along with ndc) is used to determine whether the gage can see the process variation for SPC.

These are independent indicators of a gage's suitability for a specific purpose (i.e., inspection or SPC). Do a search in this forum for posts by Miner, and you should find much greater detail on this topic.