A friend just told me that a new tecnique to calculate r&r involving 6 sigma ( no from g.e.concept) so, somebody hear about that ?

Only that i know is when you relations is with RTT( total Spec ).

thanks

I''m not an R&R expert. Maybe one of the other folks can pick up on this.

I have not heard anything "new" regarding R&R either.

Regards,

Don

I am not a statistamagician, but on occasion I have used a 6 sigma vs total tolerance when using a CMM or similar instrument and only needed the "R" repeatability part of the Gage error.

I take one part and measure it 20 times (not sure how significant THAT value is - 15 may be enough) and calculate the 6 sigma of those values. Theoretically, this give the error of the measurement device, which is then compared to the total tolerance.

I don't recall reading this anywhere, but no one ever complained.

yeahhhhhh, thanks

I just talk with a friend statical man and he give the same aswer that you batman.

The only issue is : if you use a gage for SPC chart you should be use a 6 sigma, if not use the regular calculation.

For what ? only the impact the readings and more exacly which error is permissible on this instrument.

thanks

Not sure of your question, Chuy, but when you perform a GR&R, you are qualifying the gage to either accept readings from it or not. SPC is separate from GR&R in that, given the gage is acceptable, the actual readings from the process are charted, and any other [correct] data analysis is accepted since the data were collected and accepted by an acceptable gage.

I have a silly question, does the G R&R mean 5.15¦Òm ( Standard deviation of measurement system)?

Thanks!

Allen

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Allen Lee

A gage R&R is a method of evaluating several potential sources of variation in a measurement system. The typical gage R&R quantifies the variation due to differences between parts, between operators, and between units treated identically (gage variation).

The idea is that the variation between operators and the gage variation should be small compared to the total variation observed. If it is not, you can use the gage R&R to determine whether you need to retrain your operators or improve your gage, or both.

If you haven't already, I strongly suggest you purchase a copy of the AIAG Measurement System Analysis Reference Manual, available at http://www.aiag.org/

Only $11 for non-members. It is well written.

I also strongly suggest you invest in statistical software capable of analyzing the results properly. Your best bets are MINITAB, StatGraphics, and JMP. I prefer MINITAB.

Ken K.

Ken,

You opened the door for another question. Why do you prefer Minitab over StatGraphics or JMP?Regards,

Rick

Thanks for your response. But my question is whether the G R&R is the 90% of the measurement system distribution (5.15 sigma of measurement system). For I see, in the formula calculating EV and AV, it includes the constent index 5.15, am I right?

Thanks!

Allen

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Allen Lee

The formulas use 5.15, which reprsents the number of standard deviations that contain the central 99% of the normal distribution.

The only way to make a realistic statement regarding the %-contribution of the variation is to obtain variance components using the ANOVA-method (these are the variances as opposed to the std. deviations). The variances can be added to calculate percentages of the total observed variation. By dividing the R&R variance by the sum of ALL the variances you can determine the %-contribution of the measurement system.

That is one reason I like MINITAB better than JMP. MINITAB provides both the average & range and ANOVA methods. I prefer the ANOVA method. JMP can do the ANOVA method, but more handwork needs to be done.

I used to have the demo for StatGraphics 5, but it has expired and I can't remember much about its GR&R tool.

I tend to like MINITAB because overall it has a better laid out set of tools. With respect to the GR&R, StatGraphic's latest version added a one-page report much like MINITAB has had for several years, but I still like MINITAB's better.

Ken K.

Ken,

Thanks for the input! Always nice to get the users point of view when evaluating software.

Rick

If MINITAB was "taken away from me" I'd probably have a tough time deciding between JMP and StatGraphics. I'd probably have to go with SG, since JMP's tools aren't really AIAG (Automotive Industry Action Group) complient for Process Capability, and I work for an automotive industry company.

We've used both in the past - StatGraphics through their Windows version 2, and then JMP 3.x.

It wasn't until I looked at the StatGraphics 5 Demo that I realized how poor SG's data manipulation tools are. Now that I think of it I did end up using Excel for most of my manipulation when I used SG. MINITAB just rolls over SG in that category. JMP's data manipulation tools are a little better, but not much.

The other real advantage MINITAB has is in the area of reliability/survival analysis - their tools are becoming really near-world class. I'm told their goal is to have world class reliability tools by version 14, which should roll out in 2002. From what I've seen in version 13.3 I'm sure they'll do it. High marks for implementation and ease of use.

Ken K.