# Gage RR % of contribution

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Viewing 8 posts - 1 through 8 (of 8 total)
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• #41187

michel
Participant

Can someone tell me where do the following specs for the Gage R&R % of contribution:  less than 2% = good, more than 8% = unacceptable   come from ?

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#128881

Summerfield
Participant

As per the AIAG Standards (Automotive industry action group) your Gage R&R % contribution value should be =5 for accepting Gage R&R.

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#128889

CT
Participant

What Ash said, assuming Normal Distribution with 99% of area under normal curve or 5.15 standard deviations. Also recall that %Contribution is a ratio of the Variances, so you would want this % to be as low as possible. Were as P/TV is the ratio of the measurement system standard deviation to the total observed standard deviation and thus this % can be higher (less than 30% considered ok)
CT

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#128903

Doc
Participant

Careful here … you are mixing up on the indices.
The AIAG MSA Reference Manual uses the following accpetance criteria for %GRR and %Tolerance. Note that these are standard deviation-based metrics:
<10% – generally acceptable
10%-30% – may be acceptable based upon importance of application, cost of measurement device, cost of repairs, etc.
>30% – not acceptable
Use %GRR when the measurement will be used for process control situations (SPC, process capaiblity, and process improvement)
Use %Tolerance when the measurement will be compared to a specification (inspection or end-of-line comparison to specs).
For a capable process (where Pp>1) the %Tolerance will always be smaller than the %GRR, since the Tolerance width is larger than the 6sigma width. Note that AIAG MSA 3rd Edition now uses 6.00 as the multiplier rather than the old 5.15.
The %Contribution, on the other hand, is a variance-based metric.
AIAG does not specify acceptance criteria for %Contribution. It is usually used to provide an understanding of the respective sources of variation. If %GRR or %Tolerance are too high, you can use %Contribution to determine if the problem is with the operators or the gage itself.
Regardless, %Contribution is actually the square of the respective %StudyVar. So to convert the standard deviation-based acceptance criteria for use with %Contribution we take the square of the cutoffs:
<1% – generally acceptable  (.10^2 = .01)
1%-9% – may be acceptable based upon importance of application, cost of measurement device, cost of repairs, etc.
>9% – not acceptable (.30^2 = .09)
Again, these squared metrics are ONLY for %Contribution.

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#128904

Sweta / Mintu
Participant

Hi! None has responded Michel’s question. AIAG guidelines are fine and are well estalished. Where did Mikel get GRR % 8 not accetable has been determined. Michel please send reference document, if any
Praveen

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#128905

Doc
Participant

I’m not sure where he got 2% and 8%.
I suspect these are mutated acceptance criteria taken from the 10%^2=1% and 30%^2=9% metrics I mentioned in the earlier post. These are calculated using the AIAG MSA Reference Manual acceptance criteria for %GRR and %Tolerance.
Some people have rounded the 9% up to 10% for ease-of-use/presentaiton.

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#128915

CT
Participant
#128916

CT
Participant
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