determine tolerance for GRR

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    Hello everyone,
    I am trying to determine if a measuring process is repeatable and reproducable.  I decided to calculate %Gage R&R based on the tolerance.  However, there are many different sources of tolerance such as the tolerance of the flatness from the measuring block, the digital machine and the pin gage itself.  Should I use the gage tolerance or add all the tolerances together?  (I’ve researched online but found nothing).  Please help! 
    Thanks everyone.


    Anirvan Sen

    Sandy, I guess I need more info to help you. What is it that you are measuring (Y), what is it that you are using to measure and then of course, how many parts and how many operators, etc. You need to be able to differentiate between your process tolerance and your measurement system tolerance.
    Your %Gage R&R should help you determine whether your the current measurement can capture the details about your Y effectively or not.
    I’ll more than glad to help you.



    The sources of variation that you’re listing are based on the measuring device, not the product.  Your product tolerance should be determined based on what is needed to meet proper form, fit, and functionality.  From getting the tolerance based on the customer requirements your R&R value is derived by evaluating the sources of measurement error such as those you mentioned (along with the human element) versus the tolerance range.
    What made you decide to use tolerance range versus study variation?


    Fernando Gutierrez, Jr.

    The Precision-to-tolerance ratio is based on the natural tolerances of the measurement process variation, this being 6 times the measurement standard deviation, compared to the tolerance of the subject product characteristic being measured.  Hence, suggest you use the tolerance of, and only of, the product characteristic you are measuring.  Hope this helps out!

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