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Capability calculations for True Position

VinniUSMC
Has anyone come across this as a means of calculating Cpk of a true position?

http://documentation.statsoft.com/ST...tionCapability

I think it should be possible, but I'm not sure if this is the answer or not. I was thinking about how something along the lines of the complex plane (or vectors/trig) could be used to identify grouping of a positional tolerance based on its quadrant within a unit circle, and then could be used to calculate Cpk. It's not unheard of. The normal distribution of a multivariate system is calculable, so why wouldn't a statistic that is related to the normal distribution in 1 variable work for higher dimensions?

I'm thinking that there must be a way to calculate the variance of position based on the the quadrant it falls in. Whether it's a trigonometric function, or a complex function.

Anyone have any input as I dive into this blackhole?

Curiosity killed the cat, hopefully I'm not a cat.

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  • So I use the first vb sheet, but I search the max std dev and the take the min cpk ?
    think I will have a project to use this in the other way (to calculate a tol for the designer !)

    Yes, I used VLOOKUP in cell AF4 to search the max Std Dev and then output the Cp for that angle. Cpk stays the minimum value of all Cpk1 and Cpk2. I also modified the macro to output every 1 degree.

    Yeah, if you just change the diameter tolerance from cell B3, then re-run the macro, you can "reverse engineer" the needed TP tolerance to hit certain marks given current data. That would be useful.

    Now I'm waiting for my QE to get the MiniTab macro to see how that compares to this.

    Thanks for your help Jef. (By help, I mean, doing basically everything... :squareSlight smile
    Attached Files
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  • So I use the first vb sheet, but I search the max std dev and the take the min cpk ?
    think I will have a project to use this in the other way (to calculate a tol for the designer !)

    Yes, I used VLOOKUP in cell AF4 to search the max Std Dev and then output the Cp for that angle. Cpk stays the minimum value of all Cpk1 and Cpk2. I also modified the macro to output every 1 degree.

    Yeah, if you just change the diameter tolerance from cell B3, then re-run the macro, you can "reverse engineer" the needed TP tolerance to hit certain marks given current data. That would be useful.

    Now I'm waiting for my QE to get the MiniTab macro to see how that compares to this.

    Thanks for your help Jef. (By help, I mean, doing basically everything... :squareSlight smile
    Attached Files
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