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Are GRR studies affected by tolerance stack ups?

Discussion in 'Gage R&R and MSA - Measurement Systems Analysis' started by Vinny Pagano, Jun 19, 2019.

  1. Vinny Pagano

    Vinny Pagano Member

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    I was recently told by someone that the gage they were trying to get approved for a very complex assembly was seeing GRR percentages above 30%, which was the result of tolerance stack ups. I could understand how tolerance stack ups would greatly affect the capability of the parts measured on the gage, but I did not see those stack ups as affecting the GRR results. Am I missing something?
     
  2. Bev D

    Bev D Moderator Staff Member

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    Tolerance stack ups would only effect the popular Guage R&R method IF the individual feature specifications are adjusted tighter to avoid the stack up.
    ‘Someone’ doesn’t understand how the Guage R&R study works...
     
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  3. Miner

    Miner Moderator Staff Member

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    I agree with Bev. The tolerance stack up itself will not impact the R&R. Where you could see an impact would be if you were measuring an assembly dimension where the component parts making up the assembly dimension were not fixed, but free to move. This could allow the dimension to change between measurements resulting in Within Part Variation such as you would see if measuring the diameter of a shaft with lobes. I have seen issues similar to this in measuring the distance a switch moves before changing state (on/off). The number and complexity of the mechanical linkages results in a lot of within part variation.
     
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  4. Vinny Pagano

    Vinny Pagano Member

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    Thanks for your input Bev
     
  5. Vinny Pagano

    Vinny Pagano Member

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  6. Vinny Pagano

    Vinny Pagano Member

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    Thanks Miner, I agree!
     

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