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Understanding Gauge R&R

My Personal Crusade. Understanding Gauge R&R. Mark S. Rusco Innovative Corporate Training markrusco@sbcglobal.net. Each is just a Standard Deviation . From Page 115 of the MSA (2 nd Paragraph) And from Page vi. What do EV, AV, RR represent? .

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Understanding Gauge R&R

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  1. My Personal Crusade Understanding Gauge R&R Mark S. Rusco Innovative Corporate Training markrusco@sbcglobal.net

  2. Each is just a Standard Deviation. From Page 115 of the MSA (2nd Paragraph) And from Page vi What do EV, AV, RR represent?

  3. Page 55 reminds us to add variances, not standard deviations. You can add variances, but not S.D.

  4. A simple example

  5. A simple example

  6. A simple example

  7. A simple example

  8. A simple example

  9. A simple example

  10. A simple example 78

  11. A simple example This Standard Deviation defines the Error of Width This distance defines Error of Location 78

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

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

  14. R & R are both Standard Deviations We combine them as Variances to get GRR There’s a major difference between Errors of Location and Errors of Width. Summary so far

  15. Pg 74, in bold letter, tells us how to sample You’re not sampling correctly

  16. “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 don’t really matter. You’re not sampling correctly

  17. Start with Equation for %GRRtv You’re not sampling correctly

  18. Substitute in EV and AV for RR. Substitute in RR and PV for TV You’re not sampling correctly

  19. Substitute in EV and AV for RR on the bottom • %GRRtv is driven by PV. You’re not sampling correctly

  20. What drives PV? PV = Rp x K3 Rp = Biggest Part – Smallest Part You want Rp to be as big as possible, so %GRRtv is as small as possible. You’re not sampling correctly

  21. Sort through your parts to find the biggest and smallest part you can find. This makes Rp big, which makes PV big, which makes %GRRtv small. Small %GRRtv makes your life easier. Summary of sampling

  22. 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? Interpreting the results

  23. Can the gauge discriminate between Good/Bad Parts? Answered by %GRRtot tol Interpreting the results

  24. Can the gauge detect process variation? Answered by %GRRtv Interpreting the results

  25. Just because %GRRtv <10% and %GRRtottol <10% doesn’t mean the situation is good. • Which situation is better for your company? • %GRRtv = 6% and %GRRtt = 9% • OR • %GRRtv = 15% and %GRRtt = 9% Interpreting the results

  26. Interpreting the results

  27. Interpreting the results

  28. Understand the difference between %GRRtot tol and %GRRtv Don’t plug your data into software and blindly accept the %GRR values. Summary of interpreting results

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