In Reply to Parent Post by vinny
The customer is saying he would never allow samples for the GRR to be out of spec to the part tolerance. I'm saying it doesn't really matter since we are evaluating the measurement system, not my samples relative to the specification.
Of course you're right: The samples for a Gage R&R should cover the whole range (process and/or tolerance +/- something). Maybe the customer has a knowledge gap here and you can solve the issue by providing some informations.
As Stijloor already mentioned Miner's blog on MSA is very helpful, see section "Part Selection" in this entry: Intro to Measurement System Analysis (MSA) of Continuous Data – Part 5b: R&R
. Additionally Minitab's White Paper on Gage R&R
could provide further information, e.g. comments to Xbar chart on p.8.
Or you can try the "common sense approach" with your customer:
The MSA is conducted to verify that the measurement system is able to
- distinguish between good and bad parts AND
- monitor process performance accurately (enough).
For both goals the measurement system has to provide reliable results within the whole range of possible values. Since a part outside of the tolerance should be detected (reliably) by its value of the measurement system (regardless how likely it is that such an out of spec value occurs), those parts should be used within a Gage R&R. You can't prove that a measurement system works well on the whole range (tolerance+/-some more or process) if you only have parts for a smaller part of the whole range.
But if your customer doesn't want to have parts outside of the tolerance in the Gage R&R (in contrast to MSA4 requirements), just do what he suggests. The customer should get what he wants - he's paying the bill.
To avoid small ndc numbers you can use the Minitab (R16) Assistant menu for MSA ANOVA (Assistant > Measurement System Analysis). The ndc isn't part of the output
Or does the customer have specific requirements regarding the Minitab menu (ndc is part of MSA within the quality tools menu) and/or the numbers he wants to see?
The best way to get your customer happy (in case he remains ignorant to MSA requirements) and to evaluate the measurement system according to MSA guidelines would be to select enough parts of the "customer accepts"-range and additional parts of the "customer doesn't accept"-range (e.g. out of tolerance). After taking the readings you run two analyses, one for the "customer accepts"-part to get the numbers for a satisfied customer and one analysis for internal use to evaluate measurement uncertainty properly according to MSA4.