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Published byTristian Mollet Modified over 2 years ago

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My Personal Crusade Mark S. Rusco Innovative Corporate Training markrusco@sbcglobal.net

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Each is just a Standard Deviation. From Page 115 of the MSA (2 nd Paragraph) And from Page vi

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Page 55 reminds us to add variances, not standard deviations.

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X 020406080100

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XX 020406080100

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XXX 020406080100

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X XXX 020406080100

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X XXX XXXX 020406080100

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X XXX XXXX 020406080100

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X XXX XXXX 020406080100 78

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X XXX XXXX 020406080100 78 This Standard Deviation defines the Error of Width This distance defines Error of Location

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Bias Linearity Stability Averaging several readings does not help. Found by measuring known standards. Eliminate/minimize by calibration.

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Repeatability Reproducibility Averaging several readings reduces error. Found by repeated measurements of the same parts. Minimize by operator training, gauge improvement, etc.

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R & R are both Standard Deviations We combine them as Variances to get GRR Theres a major difference between Errors of Location and Errors of Width.

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Pg 74, in bold letter, tells us how to sample

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selected from the process is not: Consecutive parts Random Parts At least one part should be as small as normally expected, and one part should be as large as normally expected. All the other in- between parts dont really matter.

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Start with Equation for %GRRtv

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Substitute in EV and AV for RR. Substitute in RR and PV for TV

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Substitute in EV and AV for RR on the bottom %GRR tv is driven by PV.

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What drives PV? PV = R p x K 3 R p = Biggest Part – Smallest Part You want R p to be as big as possible, so %GRR tv is as small as possible.

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Sort through your parts to find the biggest and smallest part you can find. This makes R p big, which makes PV big, which makes %GRR tv small. Small %GRR tv makes your life easier.

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You know the Standard Deviation of your Gauge System. Is it a good gauge? Can the gauge discriminate between Good/Bad Parts? Can the gauge detect process variation?

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Can the gauge discriminate between Good/Bad Parts? Answered by %GRR tot tol

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Can the gauge detect process variation? Answered by %GRR tv

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Just because %GRR tv <10% and %GRR tot tol <10% doesnt mean the situation is good. Which situation is better for your company? %GRRtv = 6% and %GRRtt = 9% OR %GRRtv = 15% and %GRRtt = 9%

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Understand the difference between %GRR tot tol and %GRR tv Dont plug your data into software and blindly accept the %GRR values.

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