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Gage RR average chart control limits

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  • #48475

    Ropp
    Participant

    Hey,
    What what is the correct calculation for UCL and LCL on an average chart for a Gage R&R. I’m fairly new to doing these studies and need a little help. I thought that the standard SD would work but it seems that the control limits on these charts are much tighter, and the goal is to have points outside of these limits. I gather it’s a test to see normal random variation from part to part.

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    #163498

    Erik L
    Participant

    Dave,
     
    The control limits in the average chart are set by the standard formula:
     
    CL=Xbarbar +/- (A2*Rbar)
     
    Remember that the resulting space between the LCL and UCL is a reflection of the variation that we expect from the measurement process and then we add part-to-part variation on top of this ideal estimate of measurement variation.
     
    Regards,
    Erik

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    #163499

    Ropp
    Participant

    Thanks Erik,
    I know this is a silly question and I probably should know, but what is A2?

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    #163501

    Erik L
    Participant

    Dave,
     
    Not silly at all.  A2 is a control chart constant that is impacted by the rational subgroup size that you use in the creation of the control chart.  It is capturing numerous terms (e.g. 3, d2, ãn) from the following:
     
    ƒÊ +/- 3ƒÐ
     
     
    Xbar +/- 3 Ŝxbar
                        ãn    
     
    Xbar +/- 3 Rbar  1 
                       d2    ãn
     
    Xbar +/- A2* Rbar
     
    Hope that helps with where it came fromc
     
    Regards,
    Erik

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    #163502

    Erik L
    Participant

    Hmmm,
    Not good this is suppose to be the sqrt of n=ãn 
    ƒÊ=mu
    ƒÐ=sigma 
    I would have thought it would have converted from Word better….

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    #163505

    Ropp
    Participant

    Ahh its one of those tables you gotta look up in the MSA book ;0) just needed the direction thanks a bunch, I assume if I use 10 Parts, 3 appraisers, and 3 iterations the subgroupsize is 3, therefore the A2 value I need to use is 1.023.

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    #163506

    Erik L
    Participant

    You got it…I guess this is the proverbial telling of how the watch was built, vs telling you about the watch!!! 

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    #163507

    Ropp
    Participant

    Yes, I probably should crack that book open a little more than I do currently, thanks Erik

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    #163516

    Ropp
    Participant
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