Gage R&R (Repeatability and Reproducability) - Tolerance vs. Variation

Marc

Hunkered Down for the Duration
Staff member
Admin
#1
Posted for Teguh Sujatno:

Subject: MSA and Calibration
Date: Thu, 21 Jan 1999 22:37:43 +0000

As you can see, in the MSA manual issued by the Big Three, calculation of gage R&R uses total variation instead of tolerance. Currently I have a problem in my client ( I am a consultant), since its gage R&R in several devices is more than 30%. Howeve, when I read a bool with the title "Concept for R&R studies" by Larry B Barrentine (In the book, he always mentioned the Big Three requirements as well), the calculation of gage R& R uses tolerance. And this makes more sense to me. Any body could make comments??.

Regards,
Teguh (Mr)
 
Elsmar Forum Sponsor
S

SCOTT SNYDER

#2
Teguh,
We just passed our QS9000 audit yesterday. The difference between variation results and tolerance results are as follow;
1) variation: your process must vary enough to show up with your measuring equipment. It is not always possible to get equipment that will measure your variation if your process is extremly stable. Thus;
2) tolerance: If your process repeats and is very stable the the only way to show good results is with the tolerance version.

Every auditor may not agree with this, but ours was extremly pleased with my explanation. I hope this answers your question.

Scott
 
R

Roger Eastin

#3
This explanation sounds interesting. So, if your process stability is so good that your measuring device can't measure it, you look at R&R with respect to the tolerance? And if your device is able to measure process variation, you can stop with that? If you can't measure process variation, how do you know when you've improved your process (you can't measure it)? Or does this assume that the Cpk of the process is very good, so process improvement for this process is not a priority? Or does this assume that you measure process improvement against the tolerance? I'm not sure that I completely follow your logic. Maybe you could explain your rules a little more...
 
D

Don Winton

#4
As that I have neither the MSA manual or the book mentioned in my library, perhaps I am completely off the mark here, so if I am, please, someone let me know.

As you can see, in the MSA manual issued by the Big Three, calculation of gage R&R uses total variation instead of tolerance.
The R&R studies I have done include variation as:

SIGMA(ev) = Equipment Variation (Repeatability)
SIGMA(ov) = Operator Variation (Reproducibility)
SIGMA(r&r) = Total Variation (Repeatability & Reproducibility)

This is the variation within the study itself. From that, it should be determined how this variation affects measurement uncertainty, usually by Percent Tolerance Consumed, as follows:

Percent Tolerance Consumed by Repeatability (PTCR)
Percent Tolerance Consumed by Measurements (PTCM)
Percent Tolerance Consumed by inspection Capability (PTCC)

The criteria for PTCC is normally:

< 10% Acceptable
> 10% and < 25 % Marginal
> 25% Not Acceptable

Of course, the above is from using the range method. The ANOVA method is a bit more difficult. Somewhere, I have a paper I did in the past that explains these concepts in more detail. I will try to find, dust off and forward. Marc’s MSA presentation in the pdf zone also does a good job of presenting this information.

Regards,
Don
 
S

SCOTT SNYDER

#5
Roger,
Sorry it took so long to get back to you. Our study is preformed using the AIAG method. We then have software that we plug the numbers into. The software we have is a replica of the AIAG methods. In the software there is a switch to compare results from both the variation and tolerance. The MSA manual also states that you can choose either method(chapterII-sec4pg.60). All I am stating is that depending on your process you may never get a good R&R from the variation method in this case compare it to the tolerance method. You must look at your part tolerance, measurment equipment and process. Determine if your equipment will detect enough variation or you will have to use the tolerance method. Example ; you are cutting a bore, your tol. is +/-.0005 and you measure with a bore gauge that measures to .0001. If your process runs at +/-.0001 you will not get an acceptable R&R from the variation method. You will however, providing you have repeatability get good results using the tol. method. We have checked this with our auditors and they agree. I hope this helps you understand my point.
Scott

------------------
 
S

SCOTT SNYDER

#7
Mark,
The software package we use is from The Crosby Co. We run a calibration program called Gauge Boss and MSA called Magic Windows MSA. The MSA program features results from every chart referenced in the MSA manual. You can find them at www.qualitynews.com.
Scott
 
R

Roger Eastin

#8
Yeah, Scott, your explanation helps. Obviously, your Cp is very, very good, so measuring process improvement is not a priority. I don't know your application beyond your description of measuring the bore of hole. I guess the only other question I have is about gauge resolution. Normally, the expectation is that the gauge resolution (its scaling) is 10% of either (the smaller of two)the process variation or the tolerance (rule 4, page 5 of the MSA manual). In your case, this sounds impractical. However, there are statistical methods that limit the impact of this resolution rule ("of thumb"). But with your Cp being what it is (as long as the resolution factor doesn't inflate it too much - it can do that), I doubt, for you, it is much of worry. It may be something that someone else, who has a Cp not as good as yours, needs to be careful of. Anyway, thanks for the explanation!
 
A

AJLenarz

#9
As posted in previous messages, the MSA manual does list the tolerance method as an acceptable method (pg. 60). However they also state (pg. 15) "The long-standing tradition of reporting measurement error only as a percent of tolerance spread is inadequate for the challenges of the market place of the future in which emphasis will be upon continual process improvement.”

I have found that most people are not familiar with the tolerance method. And if that is the preferred method, be prepared to argue and justify your approach.

Keep in mind rule 4 (pg. 39) when doing a R&R. “The sample parts must be selected from the process and represent its entire operating range.” In situations where my CP has been very tight, I have actually altered the process slightly to produce product at both ends of the spec to qualify the measurement system. As far as I can see it’s legal, the result is usually within a couple percent of the tolerance method and no argument or justification for the method selected.

Let me know what you think. I am still a young buck in the world of quality with a lot to learn.
 
Thread starter Similar threads Forum Replies Date
P Gage R&R (Repeatability and Reproducability): What are the calculation restrictions Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 6
J What is an acceptable Gage R&R (Repeatability and Reproducability) system? Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 9
S GRR (Gage Repeatability and Reproducibility) for Material Strength Tester Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 6
M Repeatability issue in Gage R&R study for inner diameter of a bushing Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 16
T Gage Repeatability for an Automated Leak Tester Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 10
S Weight Scale Gage R&R (Gage Repeatability and Reproducibility) Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 2
U Gauge repeatability and reproducibility (Gage R&R) worksheets Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 0
M Determining Repeatability without Gage R&R Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 22
D Gage R&R Repeatability - How do I know my gauge is in specification Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 4
A Gage Reproducibility & Repeatability for POKA-YOKE (pass/fail) gage? Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 12
M Gage R&R (Reproducibility and Repeatability) using Minitab 14 Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 3
U Gage R&R (Reproducibility and Repeatability) Understanding for the Layperson Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 3
S Operator Capability - Gage R&R Poor Repeatability Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 8
M Gage repeatability and reproducibility - GRP% Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 3
R MSA Attribute gage repeatability and reproducibility IATF 16949 - Automotive Quality Systems Standard 1
R How to Determine CMM Gage R&R - Accuracy, Repeatability, Reproducibility? Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 2
Y Product Stability (Machine Capability) vs. Equipment Repeatability (Gage R&R) Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 7
A Gage R&R - Repeatability and Reproducibility of a newly bought CMM machine Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 8
D Gage R&R (Repeatability and Reproducibility) for Dummies Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 67
P Gage Repeatability (1x1x10) form - 1 part measured 10 times by 1 appraiser Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 7
A Automated Testing Gage R&R (Repeatability and Reproducibility) Issues Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 4
Courier Gage R&R (Reproducibility and Repeatability) - Automotive Requirements Basics Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 2
M Gage R&R (Repeatability and Reproducibility) Study with one appraiser Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 2
B Gage R&R (Repeatability and Reproducibility) Destructive Test Method Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 2
R Gauge Repeatability and Reproducibility (Gage R&R) on all shop floor gages? Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 15
K Gage R&R with more than 3 appraisers Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 2
Anerol C Gage R&R Template AIAG 4th Edition IATF 16949 - Automotive Quality Systems Standard 3
T Attributes SPC study - Attributive control (Go gage) Statistical Analysis Tools, Techniques and SPC 5
S Capability or Gage R&R Study for Leak Tester? Reliability Analysis - Predictions, Testing and Standards 15
N % Tolerance - Type 1 study on the gages, then a gage R&R (ANOVA) Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 4
M Definitive answer on Type 1 vs Type 2 vs Type 3 Gage Study Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 0
V Gage Management and Gage R&R Software General Measurement Device and Calibration Topics 1
D Gage R&R Study on Load Cells - Large chemical blending tanks IATF 16949 - Automotive Quality Systems Standard 1
B Minitab Type 1 Gage Study on True Position Question Measurement Uncertainty (MU) 1
S Gage R&R on alloy Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 10
8 Need Help - Runout - Function Gage Inspection, Prints (Drawings), Testing, Sampling and Related Topics 7
L Gage R&R studies for identical Devices - Need to confirm the requirement to perform them Reliability Analysis - Predictions, Testing and Standards 2
G Stab Pin Size For Check Gage Inspection, Prints (Drawings), Testing, Sampling and Related Topics 3
E Functional Gage for TOP applied at RFS Design and Development of Products and Processes 5
F No reproducibility Error in Gage R&R? Reliability Analysis - Predictions, Testing and Standards 4
M Template for Attribute Gage R & R wanted Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 3
G Warning about Deltronic Gage Pins - The "Certification of Accuracy" document General Measurement Device and Calibration Topics 13
A Gage type 1 study on CMM Capability, Accuracy and Stability - Processes, Machines, etc. 2
Q Gage R&R for Instant Measurement Machine Manufacturing and Related Processes 6
M Gage R&R with large inter part variance - Torque Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 7
D Do we need normal data for gage r&r studies? Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 5
D Do I need part variation while doing Destructive Variable Gage R&R MSA study Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 19
S Gage R&R Standard Deviations Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 6
J Informational Gage R&R: Swapping operators Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 5
S Gage R & R for large amount of inspections IATF 16949 - Automotive Quality Systems Standard 10
Similar threads


















































Top Bottom