What is an acceptable Gage R&R (Repeatability and Reproducability) system?

J

jaker

#1
What is an acceptable Gage R&R system? Do you have to have a study on each instrument or can in be done by family (calipers, ht gauges, etc.)? Does it have to be done on production parts or can it be done on gage blocks used for calibration?

Forgive my ignorance!!!

[This message has been edited by jaker (edited 06 June 2000).]
 
Elsmar Forum Sponsor

Marc

Hunkered Down for the Duration
Staff member
Admin
#2
As I understand the requirement....

Typically QS auditors expect to see an R&R done with production parts on each instrument cited in the control plan.

However, if you are really MSA savvy and are ready to explain how you address each part of your uncertainty budget, you can use other methods. For example, if you have 100 sets of 6" calipers of the same model from the same manufacturer and they were maufactured within a 'reasonable' relative time frame (say - all were manufactured in 1997 and 1998) - you can make an arguement that all have nearly the same uncertainty in so far as the instrument its self goes. You had best have a study to prove this is, in fact, the case.

Yup - you can use gage blocks.

But - in both of these you had best be able and ready to explain how you address the uncertainty associated with surfaces being measured. If you use the calipers on an edge to edge measurement where they will be seated much like on a gage block, you will probably have a lower uncertainty factor than if you are measuring an 'unstable' part feature such as a diameter on a gently grooved feature. The fact that the instrument is stable and precise does not address several other parts of your uncertainty budget for that measurement.

The bottom line is if you do an R&R on the specific instrument at the station where the part is being measured, on the feature being measured on the part which is being measured, by the techincians who will/are actually be doing the measurement you are addressing all of the uncertainty budget and fulfilling the auditors paradigm (you are showing the auditor what s/he expects to see).
 
D

David Bear - 2010

#3
I am also relatively new to Gage R&Rs.

During our last QS9000 audit, our auditor said his interpretation is that Gage R&Rs only need to be done on an "as needed" basis. The need occurs whenever a modifciation is made to a gage or if you have a new operator. Any requirements from your customer would override that frequency.

I have two questions I can't seem to get answered. Can someone help me with them?

1. If I add a new operator, can I add their measurements to an existing Gage R&R? ex. I already did a Gage R&R with 3 operators. Can I add a 4th operator and recalculate the variation by adding the newest measurements to the already existing measurements?

2. How many operators do I have to use and what does my sample size need to be? I have been told: a) 3rd edition requires 15 samples for a variability study and 50 samples for an attribute study, b) my company's intranet example uses 10 samples for variability and 30 samples for attibute, c) there are no set sample sizes - the sample size is based on what is reasonable (i.e. 50 samples with a pin gage is easy, 50 samples that take 20 minutes each is unreasonable) d) you must have 3 operators (all must be from production), e) you can use 2 or 3 operators f) all operators using the gage must be tested.

I am receiving a lot of conflicting opinions.:confused:

I appreciate any help!:thanks:
 
L

lee01

#4
GRR on gauge blocks? This is a no no right?

The whole idea about a GRR is to ascertain the gauges' ability at measuring production parts in a production environment.

Measuring some gauge blocks at your desk all nice and comfortable, your bound to get better results as if your measuring production parts, say a large composite skin of an aircraft? You’ll be on the shop floor, you’ll be rushed, you could be stretching in some instances, the part could be un-washed, the part may be difficult to hold, all this provides an element of measurement uncertainty, which is exactly what GRR is trying to find out. That’s why it used production tolerances.

I have found this out by conducting GRR within an inspection facility at final inspection stages, the parts fully cleaned and the inspector sat at his desk, and during production by the random inspectors. The differences are great.
 
B

bmccabe - 2006

#5
I echo Marc's comments.
Planning, rational, and MSA's are the way to go. GR&R's are pathology, MSA's forecast. In fact, I really despise R&R's, I think they're flawed and a waist of time: Especially true for automated equipment, where Appraiser/Operator error = 0 by definition. R&R’s will assign a substantial measurement error to the monkey who pushed the run button.

Two fundamental flaws in the math used in R&R’s are first: The assumption that Operator, Equipment, and Part variation exist simultaneously in every data set. And second, that it IS possible to reproduce the same measurement on a given object.

Try this for fun:
Conduct an R&R using 10 parts, 3 operators, and 3 measurements of each part. Compare the capability of two measuring devices: A six inch steel scale graduated in 1/32nds of an inch, and a set of calipers with .0005 graduations. Measure the length of the part, to see which device passes the GR&R.

Which do you think will pass? Now, what I didn’t tell you was the nature of the part we’re going to use for the test. Compare now, the same R&R methods on two different parts. First measure the thickness of a precision ground gage block. Second measure the length of a human hair.

Do you believe the results would change? Would you believe calipers fail both tests? Would you believe the steel scale passes both tests? Now, ask why.
 

Miner

Forum Moderator
Staff member
Admin
#6
bmccabe said:
I echo Marc's comments.
Planning, rational, and MSA's are the way to go. GR&R's are pathology, MSA's forecast. In fact, I really despise R&R's, I think they're flawed and a waist of time: Especially true for automated equipment, where Appraiser/Operator error = 0 by definition. R&R’s will assign a substantial measurement error to the monkey who pushed the run button.

Two fundamental flaws in the math used in R&R’s are first: The assumption that Operator, Equipment, and Part variation exist simultaneously in every data set. And second, that it IS possible to reproduce the same measurement on a given object.

Try this for fun:
Conduct an R&R using 10 parts, 3 operators, and 3 measurements of each part. Compare the capability of two measuring devices: A six inch steel scale graduated in 1/32nds of an inch, and a set of calipers with .0005 graduations. Measure the length of the part, to see which device passes the GR&R.

Which do you think will pass? Now, what I didn’t tell you was the nature of the part we’re going to use for the test. Compare now, the same R&R methods on two different parts. First measure the thickness of a precision ground gage block. Second measure the length of a human hair.

Do you believe the results would change? Would you believe calipers fail both tests? Would you believe the steel scale passes both tests? Now, ask why.
The steel scale would fail the very first test that should be performed, namely does the gauge have adequate discrimination. If it does not have adequate discrimination, STOP!, Do Not pass GO!, Do not perform any more MSA tests!, Get a gauge with adequate discrimination, then perform the MSA.
 
B

bmccabe - 2006

#7
Yes; we all know the scale has insufficient resolution. You may have missed the "for fun" part, and my point:truce: . My point is, the R&R rewards inferior measuring devices. As the quantity (not quality) variability decreases, the greater the chances the R&R will pass. The R&R places absolutely no relevance to the significant digits (number of decimal places) in which the variability occurs. It needs some percentage of the data to have the exact same value. As a greater quantity of data points vary, the more likely it is that the R&R will not succeed. Up until you get the "insufficient variability" error message, and mistakenly believe your good to go.
 

Jim Wynne

Staff member
Admin
#8
bmccabe said:
I echo Marc's comments.
Planning, rational, and MSA's are the way to go.
GR&R and MSA are not mutually exclusive; GR&R is a type of MSA.
And: did you mean rationale, or rationalism?

bmccabe said:
GR&R's are pathology, MSA's forecast. In fact, I really despise R&R's, I think they're flawed and a waist of time
Properly executed GR&R analysis provides predictive value. What's flawed and a "waist" of time is GR&Rs improperly done, or properly done and improperly evaluated.

bmccabe said:
Especially true for automated equipment, where Appraiser/Operator error = 0 by definition. R&R’s will assign a substantial measurement error to the monkey who pushed the run button.
If a GR&R study is done in a situation where other forms of analysis would be more appropriate, the fault lies with the person who decided to use GR&R, not with GR&R itself. You wouldn't use a sledge hammer to drive a finishing nail and then, when the inevitable happens, opine that hammers shouldn't be used to drive nails.

bmccabe said:
Two fundamental flaws in the math used in R&R’s are first: The assumption that Operator, Equipment, and Part variation exist simultaneously in every data set. And second, that it IS possible to reproduce the same measurement on a given object.
GR&R makes neither of these assumptions.

bmccabe said:
Try this for fun:
Conduct an R&R using 10 parts, 3 operators, and 3 measurements of each part. Compare the capability of two measuring devices: A six inch steel scale graduated in 1/32nds of an inch, and a set of calipers with .0005 graduations. Measure the length of the part, to see which device passes the GR&R.

Which do you think will pass? Now, what I didn’t tell you was the nature of the part we’re going to use for the test. Compare now, the same R&R methods on two different parts. First measure the thickness of a precision ground gage block. Second measure the length of a human hair.

Do you believe the results would change? Would you believe calipers fail both tests? Would you believe the steel scale passes both tests? Now, ask why.
Building strawmen isn't my idea of fun. What you're suggesting is that if it's possible to find a certain set of circumstances under which GR&R (or any sort of statistical analysis, for that matter) might prove inefficacious, then GR&R will be inefficacious under all possible sets of circumstances.
 
D

David Bear - 2010

#9
Properly executed GR&R analysis provides predictive value. What's flawed and a "waist" of time is GR&Rs improperly done, or properly done and improperly evaluated.:yes:

I agree with JSW05. GR&R, done properly appears to be an excellent tool.

Does anyone use GR&R to test operators? Should other methods be used instead? I want to ensure people doing the measuring really know what they are doing. A GR&R seems to be a good way to test their knowledge and capabilities. :horse:
 

Miner

Forum Moderator
Staff member
Admin
#10
bmccabe said:
Yes; we all know the scale has insufficient resolution. You may have missed the "for fun" part, and my point:truce: . My point is, the R&R rewards inferior measuring devices. As the quantity (not quality) variability decreases, the greater the chances the R&R will pass. The R&R places absolutely no relevance to the significant digits (number of decimal places) in which the variability occurs. It needs some percentage of the data to have the exact same value. As a greater quantity of data points vary, the more likely it is that the R&R will not succeed. Up until you get the "insufficient variability" error message, and mistakenly believe your good to go.
My point was that you should never perform a GRR study if the discrimination was not adequate. All statistical tools have basic conditions that must be met before the results have any meaning. GRR is no different.
 
Thread starter Similar threads Forum Replies Date
B Gage R&R Acceptable (10-30%), deduct Total Variation from Tolerance Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 12
C Lowest Acceptable Grade for Master Gage Set Calibration and Metrology Software and Hardware 1
A Help with acceptable screw gage values per standard BS 919 for Go/ No Go gage General Measurement Device and Calibration Topics 4
G Ford - Type 1 Gage Study MSA (Measurement Systems Analysis) acceptable? Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 7
D Acceptable % on a Gage R Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 9
A Gage Block Repair - What type of stone is acceptable for removing burrs General Measurement Device and Calibration Topics 5
A Acceptable Criteria for Variable Gage R&R according to the MSA Manual 3rd Edition Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 3
C Is this GR&R (Gage R&R) acceptable on the surface Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 36
Sean Kelley What are Acceptable Limits for Gage R&R Results Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 6
J Acceptable Gage R&R - What is acceptable %error for Gage R&R Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 3
J Acceptable Gage R&R Output Results - EV, AV, R&R, PV, and TV Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 5
W Misinterpretation of requirement acceptable as root cause? Problem Solving, Root Cause Fault and Failure Analysis 19
J Standard used to determine if check fixture gauge is acceptable Reliability Analysis - Predictions, Testing and Standards 2
M Measurement Error - How to determine what is acceptable? Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 3
M Are Fungal counts acceptable in class 1000 clean rooms? Other ISO and International Standards and European Regulations 2
T ISO 14971-2019 doubt - Evaluate if estimated risks are acceptable ISO 14971 - Medical Device Risk Management 9
samer Acceptable limits for Spills - Tracking Hydraulic Spills ISO 14001:2015 Specific Discussions 3
V Acceptable maximum RSD (relative standard deviation) for an sample size Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 1
Q Acceptable calibration accuracy of a 60" linear measuring device General Measurement Device and Calibration Topics 16
F It is acceptable moving remote locations staff to manufacturing plant for auditing? IATF 16949 - Automotive Quality Systems Standard 3
Q Is it acceptable to mix components from two different lots into an assembly? ISO 13485:2016 - Medical Device Quality Management Systems 1
C Acceptable NDC for %GR&R part inspection to Tolerance (%Tolerance) Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 3
D Risk Register - have we considered enough and is the format acceptable? ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 8
K Operator Checks - How to show that they were completed on a checklist as acceptable IATF 16949 - Automotive Quality Systems Standard 2
C Example Work Instruction/Procedure for AQL (Acceptable Quality Level) AQL - Acceptable Quality Level 4
S Dates on Labels acceptable to the USA - GS1 General Specification 3.4.4 Other US Medical Device Regulations 3
E Root Cause Analysis - Is Insufficient Understanding an acceptable Root Cause? General Auditing Discussions 9
W Unattached (stand-alone) Forms acceptable for AS9100C? AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 7
V Why Gauge R&R 10% is acceptable for variable instruments ? Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 5
X Acceptable methods to store and archive records ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 7
M Is it acceptable to audit to the Nuclear Principles? Quality Manager and Management Related Issues 9
I Is it acceptable it is to list new products under an existing 510(k)? Other US Medical Device Regulations 14
S If this EN ISO 11137 certificate acceptable for Contract Sterilization? ISO 13485:2016 - Medical Device Quality Management Systems 2
D What is satisfactory & acceptable for Coliform - Staphylococcus - Hands and Surfaces Food Safety - ISO 22000, HACCP (21 CFR 120) 3
S Is a Dynamic Controlled Form acceptable per 21CFR820 Document Control Systems, Procedures, Forms and Templates 3
B Digital Signature Solutions acceptable to use in an FDA Medical Device Environment 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 4
J Is a ndc less than five is also acceptable? Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 6
T Technical regulations that determine the acceptable limits of cigarettes General Measurement Device and Calibration Topics 4
L IEC 60601-1 3rd edition Clause 9.2.2 Trapping Zone (Acceptable Gaps) IEC 60601 - Medical Electrical Equipment Safety Standards Series 5
N Is it acceptable to sterilize products without claiming and labeling "sterile" ? ISO 13485:2016 - Medical Device Quality Management Systems 6
M Quality Objectives - Acceptable Levels and Functions ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 37
C What is an acceptable bioburden level or count when working in cleanroom ISO class7 ISO 13485:2016 - Medical Device Quality Management Systems 1
D Is embedding documents within a Contract an acceptable practice ? Contract Review Process 9
B Non Acceptable % Tolerance Result - Decrease Sorting Limits Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 3
F ANSI ASQ Z1.4 - Is the following process acceptable? Inspection, Prints (Drawings), Testing, Sampling and Related Topics 4
C Maximum acceptable Tolerance - Uncertainty Ratio (TUR) General Measurement Device and Calibration Topics 2
S Is it acceptable to have an ASL for Critical suppliers alone? Supplier Quality Assurance and other Supplier Issues 4
S Is this Quality Policy acceptable in the context of ISO 13485? ISO 13485:2016 - Medical Device Quality Management Systems 24
S What are typical Acceptable Quality Levels (AQL) adopted in Food industry? Food Safety - ISO 22000, HACCP (21 CFR 120) 1
somashekar Who can provide a WHO GMP certificate in India acceptable to the CDSCO Other Medical Device Regulations World-Wide 6

Similar threads

Top Bottom