Gage R&R (Repeatability and Reproducibility) for Dummies

Miner

Forum Moderator
Staff member
Admin
#51
Please enter your data into one of the many GRR worksheets that may be found here at the cove. The graphs and detailed analysis of these worksheet will help diagnose your issue.
 
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Jim Wynne

Staff member
Admin
#52
Good Morning,

Attached you can find an example of a RR study that I have performed. The specification is 11.2 and the tolerance is +0.2 to -0.45.
The study has 2 operatores, 3 trials. The difference between operators is very small but the result is too high. If it is possible can you explain this situation?

I thank you in advance.
There seems to be one data point that's throwing everything off. Look at Part #3 and Operator A. I'm thinking that 11.86 must be a typo, and should be 10.86.
 
A

Avelar

#53
Hello again,

Attached there is a screen shot of the study for these values, the RR is 37% is to high. In my understanding, we can see similar measures between operators and we can see also parts with different values between the tolerance, I do not understand why the R&R study is to high.
 

Attachments

Jim Wynne

Staff member
Admin
#54
Hello again,

Attached there is a screen shot of the study for these values, the RR is 37% is to high. In my understanding, we can see similar measures between operators and we can see also parts with different values between the tolerance, I do not understand why the R&R study is to high.
Look at part #3 and operator A. There seems to be a typo. It looks like 11.86 should be 10.86.
 
A

Avelar

#55
Hello,

In the last example there was a mistake for sure, the value might be 10,86.

Attached you can see another study, in this time the values are all correct, the tolerance is from 0 to 0,1 and the values between appraisers are all with a good repeatability and the R&R is too high and I do not understand this huge value if the difference between appraisers is very small.

Many thanks again
 

Attachments

Miner

Forum Moderator
Staff member
Admin
#56
Your problem is not with the Appraiser Variation (Reproducibility), but with the Equipment Variation (Repeatability). Repeatability can be caused by a number of things that are easily diagnosed by the GRR graphs, which you did not include. These include the gauge resolution and the inherent variability of the gauge itself.
 
A

Avelar

#57
Dear all,

I have one more doubt regarding the gage study R&R. I am performing the studies for the gages and when I have specifications with a two sided tolerance (I mean for example 13,5 +/- 0,5), in this cases the studies are well, below 10%. But, when I am doing the same study for gages single sided (I mean for example run out 0,2 or perpendicularity 0.1) I introduce in the minitab the lower spec 0 and the upper spec 0.2 or 0.1 depending the case. When I run the test I always face values too high. Am I doing the test in the minitab correctly (Gage R&R study Crossed) or when I have single sided specifications, there is another way to do?

Many Thanks for your support
 

Miner

Forum Moderator
Staff member
Admin
#59
The first thing that leaps out at me is the range chart. Your gauge only has 2 possible levels of measure within the upper control limit. There should be a minimum of 5 possible levels, AND no more than 25% of the ranges should be equal to zero. Your range chart is indicative of insufficient resolution in your gauge.

Low gauge resolution can distort the R&R results. Too many zero values and the R&R looks better than reality, but it typically will make the R&R appear worse.
 
G

GoRingo

#60
Hi!

I need some help :)
I have a discussion now with Customer about GRR. Maybe it is stupid question (and therefore answer will be short :)) but I need to know something about sample selection.

We will make %tolerance GRR (ANOVA crossed and nested) for incoming material. This material we get is a powder. We have a several types of powders, each with unique chemical and physical properties. We are testing them e.g. for density using lab densimeter. Each powder has own -+ tolerance for density.

Now, the question is for "entire process variability" can I run GRR using different powders (Sample 1 - Powder type A, Sample 2 - Powder type B ...) and using the lowest and highest tolerance for density? Or I need to select one type of powder, use tolerance for that powder and if needed, repeat GRR for each powder?

Thank you.
 
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