Gage R&R %Tolerance NDC

bobdoering

Stop X-bar/R Madness!!
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#11
Can anyone tell me why, in the AIAG manual/4th ed. page 129, it shows an example of ANOVA with ndc=4 and states "Measurement System is acceptable for process control analysis."?
I thought this was a clear distinction that anything less than 5 ndc was basis for NOT approving a system for process control.
First of all, good catch! You are correct, to AIAG's suggestion ndc>=5 is necessary for process control. Even so, it is woefully too low for SPC. For SPC, ndc>=10. Otherewise, your data is too "chunky" to be of any value in SPC.
 
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#12
Can anyone take a look at the file attached and help with a couple of Q's?
First, why would the NDC compute at different levels when using the exact same data to run both styles of R&R reports?
Secondly, am I incorrect in thinking that these two studies usually come into closer agreement than what is shown here?
Trying to figure out why the major differences are shown.
The operator* Part component seems to stick out as concerning, as these are fixtured pieces with automated gage system doing the rest.
Thanks for any help.
 

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bobdoering

Stop X-bar/R Madness!!
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#13
Let me answer the second question first:
Secondly, am I incorrect in thinking that these two studies usually come into closer agreement than what is shown here?
Per the description by AIAG, X-bar R technique was developed as a simple shop-floor version of the GR&R evaluation, because it did not require a computer (think back at what was available in 1994). Now that computers are far more accessible, ANOVA is the recommended approach.

First, why would the NDC compute at different levels when using the exact same data to run both styles of R&R reports?
The key factor in the equation is the GR&R value itself. Since they differ between the methods, ndc result will also.
 
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