Gage R&R study questions answered

Matt SavageWe frequently entertain questions about MSA and specifically, gage R&R. Below are two questions we recently received:

Question #1: “What are the requirements for the parts chosen in a study? Do the parts have to have the same specification?”

Answer: The parts selected should be representative of the process variation that is producing them. This implies that selecting 10 consecutive pieces (parts) is not as good as using 10 parts obtained throughout the day or week. Part of what you are trying to do with an R&R study is determine whether your measurement system is capable of distinguishing parts made on the same process to the same specification. In summary, you want to select the parts in a way that represents the minimum sized part, the maximum sized part and those in between. If the selected parts have different specifications, they are different by design, not by random variation.

Question #2: “Results can be calculated in several ways: using study parameters, specifications and others. Which is most acceptable for gage R&R?”

Answer: The industry trend is to use study/process parameters, however, how you calculate the results of a gage R&R study depends on the purpose for doing the study. Before the study begins, you should decide what the primary purpose for conducting the study is. If you are trying to control your process, you need to be able to detect changes in the process. To do this, you should use study parameters or process parameters. If your focus is being able to compare a part to specifications, then you should use the specification method. Using the specification method suggests that you are trying to prove that your measurement system can distinguish between good and bad parts.

If you have any other questions or concerns about MSA or gage R&R, please contact us at support@pqsystems.com or by phone at 800-777-5060 or just post them below.

7 thoughts on “Gage R&R study questions answered

  1. Hello,

    For complex assemblies utilizing complex fixtures and then inspected on a CMM, is it necessary to load and unload the part in and out of the fixture petween trials for gage RR studies?

    • Hi Kelly,

      The study is supposed to mimic what happens on the floor. I would assume that there is more than one appraiser/operator of the CMM and that they measure parts they have loaded uniquely. The loading and any fixtures are sources of variation. In my opinion the part will need to be loaded and unloaded for repeated measurements.

      Gordon K. Constable, PhD
      PQ Systems

  2. I need to validate an equipment,Good and Bad parts are going to be tested in order to know if this machine is able to reject damaged parts.

    -The gage R&R should include only the good parts?
    – I only have an acceptance criteria, lower limit = 80 “x”, good parts usually 120 – 180 “x”, bad parts usually 0 “x”.

  3. Hi Ernesto,

    In respect to the good and bad parts, there needs to be bad parts or how would you know if you can find them? This says in essence that you should not be checking (doing R&Rs) processes that do not make bad parts. In the MSA manual they indicate in their example that 25% of the parts selected for the study were in the gray area close to the lower specification and 25% were in the gray area close to the upper specification. If you have only a one sided specification, I would recommend at least 25% and probably closer to 50% of the items to be in the gray area close to the specification.

    Gordon K. Constable, PhD
    PQ Systems

  4. For the older software Gage R&R 4.0.106, what was the K-sigma used by the software? Was it 5.15 sigma? What does the newer GagePack use for its calculations? Thanks.

    • Although we no longer support GAGEpack 4.0 (this version is about a decade old now) GAGEpack 4.0 and GAGEpack 5.0 up to release 5.0.34 perform the calculations for the R&R percentages consistently with the 2nd edition of the MSA manual.

      What the MSA 3rd edition recommends is that the specification range be divided by 6 and this figure used to determine the percentages. The new standard appeared in release 5.0.40 and above.

      GAGEpack 9.0, the current release, is compliant with the methods shown in the MSA Fourth edition.

      Matt Savage
      PQ Systems

  5. Can you perform a Gage R&R for one part number and say it applies to another part number too if the gage is the same and the feature(s) geomotry is identical? (i.e. a diameter 12.15 ± 0.15) I Does the standard forbid this?

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