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Gage R&R according to customer spec

Discussion in 'Gage R&R and MSA - Measurement Systems Analysis' started by laffranchinis, Sep 10, 2020.

  1. laffranchinis

    laffranchinis Member

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    Hi Everybody,

    I am a rookie in MSA. I just run few of them (both internal and for customers) but I still have some doubts regarding the correct way to run a Gage R&R when we have a tolerance given by our customers, and I hope you can help me to dissolve these doubts.
    Here below two approaches to run a MSA:

    1) Sample selection: samples taken on purpose over the entire tolerance field given by customer.
    --> We consider the %Study Var to assess if the Measurement System is OK for the intended application.

    2)sample selection: random from our process. In Minitab we will insert manually the customer tolerances.
    --> We consider %Tolerance to asses if the Measurement System is OK for the intended application.

    Which one is a more correct approach? With the first case, for some processes, oft is very difficult to prepare samples scattered over the entire tolerance field given by the customer.


    BR
    Samuele
     
  2. Miner

    Miner Moderator Staff Member

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    Samuele,

    Neither one is correct. First decide how the gage will be used (inspection to a tolerance, SPC or both).

    If the gage will be used for inspection to a tolerance, you may select the parts as you wish, because the variation of the parts will not affect the results of the correct metric, which is % Tolerance. Ignore % Study Variation and ndc, because they are irrelevant in this case.

    If the gage will be used for SPC, you should either randomly select the parts from actual process variation and used % Study Variation or ndc, or you should use the variation from a capability study/control chart and use % Process Variation (preferred). Ignore % Tolerance in this case.

    If the gage will be used for both SPC and inspection, you should either randomly select the parts from actual process variation and used % Study Variation or ndc, or you should use the variation from a capability study/control chart and use % Process Variation (preferred). In this case you will also consider the results of % Tolerance.
     
  3. laffranchinis

    laffranchinis Member

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    Hi Miner,


    As usual, thanks a lot for your quick reply! this really help me to understand how to run such gage R&R in a correct way. I do not know why, but on the web you find many times statements that the samples should be have the characteristic to be measured scattered over the tolerance field.


    Samuele
     
  4. Miner

    Miner Moderator Staff Member

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    There is a lot of misinformation spread over the web. Some of it is from people that honestly don't know better passing on what they were told, and some of it is from people that know selecting samples in that manner will usually make their metrics appear better than they would otherwise look.
     
    Bev D likes this.

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