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  Gauge Repeatibility and Reproducibility

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Author Topic:   Gauge Repeatibility and Reproducibility
Ram narayan
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posted 15 July 1998 04:38 AM     Click Here to See the Profile for Ram narayan   Click Here to Email Ram narayan     Edit/Delete Message   Reply w/Quote
I want to know whether GR&R studies had to be conducted on all gauges used in the shop floor or only for a family of gauges. (Like 0-25mm Mics, 0-150mm Verniers etc..) ie.. one instrument from that family. I think that it make sense to conduct GR&R for one instrument from one family because what we are trying to conclude is whether that instrument is suitable for measuring a product characteristic.

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Marc Smith
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posted 15 July 1998 08:13 AM     Click Here to See the Profile for Marc Smith   Click Here to Email Marc Smith     Edit/Delete Message   Reply w/Quote
You don't have to *do* gage R&R on anything. You can use other studies.

The point is MSA as a high level system has to be considered. Basically you address all gages, etc., which you take measurements with which 'affect quality'. In the case of inspection and test gages, typically Gage R&R is part of the standard studies.

You start hitting touchy ground when you want to do an R&R on one gage as evidence of family 'compliance'. If you want to get down to the nitty gritty it can be, and often is, argued that a study has to be done on each gage used for inspection and test on the actual parts and with the actual operators - this is quite often the case.

And you have to look at the family of which you speak. Are they all the same brand from the same manufacturer and are they the same model (etc.)? I saw one situation where a 'qualification by similarity' failed.Same gage and model but one was 5 years older than the first. From that there were/are a lot of reasons why they may *not* be alike.

We come back to common sense and an implied understanding of MSA. As you go through design (APQP) youi have to look at the situation as a whole - What precision is necessary, etc. This is where you decide what you have to do to 'prove' your measurement and test equipment as well as the environment it is used in and such.

You have to be ready to explain to the auditor what you're doing and why. Proof (studies) may or may not be in order, but it appears auditors are wanting more and more evidence - so specific, extended studies will probably be more important in the future.

Can you 'qualify by similarity or family'? Yes - if you have good evidence that your hypothesis is true.

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Christian Lupo
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posted 15 July 1998 08:21 AM     Click Here to See the Profile for Christian Lupo   Click Here to Email Christian Lupo     Edit/Delete Message   Reply w/Quote
If you are a QS-9000 certified company or you have plans to be the answer is simple. All equipment defined in the control plan must have MSA, which includes GRR. Calipers and mics will need GRR. It is not acceptable to perform MSA on one gage, and have it represent a family of gages of the same type. Remember GRR measures the total variation in a specific gage not a family of gages. No two gages are the same, therefore they will have different levels of variation.

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Marc Smith
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posted 23 July 1998 03:02 AM     Click Here to See the Profile for Marc Smith   Click Here to Email Marc Smith     Edit/Delete Message   Reply w/Quote
Christian - I disagree with you here. Some common sense is involved. You do not have to do a gage R&R on every instrument on the control plan. It was not long ago that all the big 3 wanted was a gage R&R - it was a defacto standard. Now it came to pass that the big 3 found out about Measurement Systems Analysis. Well, they knew it was there (sorta) 'cause there was this great AIAG manual.

When auditors came and checked out the requirement of QS9000, they really (early on) just looked for common sense, a base understanding of MSA (is the rightr equipment chosen, and such), a strong calibration system and gage R&R. Over the last year most of the registrars are stressing MSA more. I'm not sure why. I know the first report to come to me was that UL was acting an ass again (I get lots of 'complaints' about UL).

I just went thru this with LRQA at Motorola in May. We did not graph studies of bias and such. I'd go into detail but I've typed responses to these MSA issues several times already that I refuse to do it again.

If you take a cruise to The Old Message Base Threads Listing you will find this discussed a number of places.

In the 'new' QS9000 MSA is addressed in 4.11.4 where it states: "Appropriate statistical studies shall be performed..." Keyword = APPROPRIATE

This leaves it to you to do what you can justify as 'appropriate'. If an R&R is not approprite, then it's not appropriate.

We come back to this: Can you explain what you are doing and why?

Hell - most of the auditors I've come up against are MSA stupid anyway. At best most understand one part of MSA as a high level system - they understand Calibration Systems Requirements - NOT MSA. One of the most important parts of the whole thing is upfront - determination of appropriate M&TE - how many autitors have you heard ask to be taken thru the selection process?

My 10 cents....

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Steven Sulkin
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posted 23 July 1998 04:30 PM     Click Here to See the Profile for Steven Sulkin   Click Here to Email Steven Sulkin     Edit/Delete Message   Reply w/Quote
The question was asked, do all gages have to be studied? My question is, do all products have to be studied? We have gages that are used for a bazillion products, many having different specs. Our data collection is also unusually expensive.

Is there a simple approach to this? Going back to Marc's comments, "what percision is necessary," we need a percision that is enough to prevent significant type I and type II errors. I define this as, "RR cant be more than 30% of tolerance." If my definition holds, I should only have to do studies for the products with the tightest specs. As long as they meet my rule (<30%), I should be ok right?

Also, if I find that many gages are above 30%, but I have action plans in place and work being done to get to the below 30% mark, can I still be certified?

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Christian Lupo
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posted 24 July 1998 08:27 AM     Click Here to See the Profile for Christian Lupo   Click Here to Email Christian Lupo     Edit/Delete Message   Reply w/Quote
Marc-

Actually you do agree with me; I guess I didn't make the distinction between MSA and GRR. What I meant to say is that a compny must use MSA on all IM&TE in the control plan. MSA not necessarily means GRR. As an example of what I mean, the last QS-9000 registration audit I performed I wrote the company up for not following the MSA manual eventhough they had done GRR studies. Their equipment was mostly calipers. Upon further investigation this particular company did not evaluate linearity, bias, stability, resoultion, range of use etc... How could they evaluate total variation (GRR) if they did not even know the variation inherent in their equipment?

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Howard Atkins
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posted 07 August 1998 04:46 AM     Click Here to See the Profile for Howard Atkins   Click Here to Email Howard Atkins     Edit/Delete Message   Reply w/Quote
When it says in QS 4.11.4 that "this requirement shall apply to the measurement system referenced in the Control Plan" can I submit results of a system that I have used in another submission or does it have to be specific to the part I am submitting?

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Marc Smith
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posted 07 August 1998 03:36 PM     Click Here to See the Profile for Marc Smith   Click Here to Email Marc Smith     Edit/Delete Message   Reply w/Quote
Typically R&R is done (or other validation of the system or instrument) on the item as is on the control plan. But - you have to look at frequency and such as to what studies you have to do at all.

And - depends upon the measurement being taken and the system as a whole with consideration to the techniques you are using to validate. For example, R&R is on a specific dimension of a specific part (or multiple dimensions in cases such as a with a CMM - which is really an R since there's only one operator) per the control plan line item number.

I think, Howard, we're back to some common sense. As an auditor I typically expect to see a match with the control plan, though.

Why don't you start a new thread with some details and we can bandy it about.

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Batman
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posted 19 August 1998 08:19 PM     Click Here to See the Profile for Batman   Click Here to Email Batman     Edit/Delete Message   Reply w/Quote
Regarding GRR, we have had success with our QS9000 auditors demonstrating "family of gages" as they apply to "family of parts." Also we have multiple gages of similar type, and we select random gages within the family when GRR are performed. Our control plans are primarily for the "family of parts," so a "family of gages" approach fits.
Re frequency of GRR, our Ford STE was in today and stated we need to "update our GRR every year, as stated in the AIAG."

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Marc Smith
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posted 22 August 1998 06:39 AM     Click Here to See the Profile for Marc Smith   Click Here to Email Marc Smith     Edit/Delete Message   Reply w/Quote
I wouldn't have a problem with that approach. You can prove statistically that which gage of the family of gages makes no different in the result. I think some auditors would not have this paradigm, however.

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Dr Gage
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posted 03 March 2001 02:04 PM     Click Here to See the Profile for Dr Gage     Edit/Delete Message   Reply w/Quote
According to the MSA, all MEASUREMENT SYSTEMS must be tested so the amount of variation is known. A measurement system is not A GAGE or a FAMILY OF GAGES. A measurement system is the combination of 6 elements. 1)The gage 2)The part (or part characteristic) 3)The operator 4)The method 5)The environment & 6)The SIZE of the tolerance. Any time one of the 6 changes, you have created a DIFFERANT measurement system. All of the 6 induce differant amounts of variation. If you are using a micrometer on a rectangular part with a tolerance of +/-.005", you'll probably get great R%R. Does that mean you can claim that R&R study when you turn around and use the same micrometer on a round part with a tolerance of +/-.001" ... No, even though the same gage was used, their are 2 completely differant MEASUREMENT SYSTEMS.

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Dan Larsen
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posted 03 March 2001 03:43 PM     Click Here to See the Profile for Dan Larsen   Click Here to Email Dan Larsen     Edit/Delete Message   Reply w/Quote
I'm starting to see this approach in auditors with respect to gage R&R. I work with a number of heat treaters that tend to use test blocks to perform GRR for hardness. This is the "classic" approach for a destructive test, and seems to be used across the industry.

In a recent audit, this was not considered good GRR because the effect of the gage on the actual process variation for a specific part was not being considered.

We ended up performing a "gage capability study" with a test block and then using this data in conjunction with a capability study on the part to define the GRR for the part.

The statistics followed a published model, and the results were interesting (Concepts for R&R Studies, Larry Barrentine, ASQ Press).

I think the emphasis on GRR is shifting in the direction that Dr Gage is describing.

Any thoughts?

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Sam
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posted 05 March 2001 10:31 AM     Click Here to See the Profile for Sam   Click Here to Email Sam     Edit/Delete Message   Reply w/Quote
Although I can't find it in the MSA hdbk, I agree with the definition of the measurement system as described by Dr Gage.
As far as using test samples vs process samples; the standard is quite clear on selection. Refer to chap. II sec. 3 para 4 pg 39.

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D.Scott
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posted 06 March 2001 08:18 AM     Click Here to See the Profile for D.Scott   Click Here to Email D.Scott     Edit/Delete Message   Reply w/Quote
MSA defines a measurement system as "the collection of operations, procedures, gages and other equipment, software, and personnel used to assign a number to the characteristic being measured; the complete process used to obtain measurements".
QS-9000 states "Appropriate statistical studies shall be conducted to analyze the variation present in the results of each TYPE of measuring and test equipment system".
We have had no problem with auditors on this issue. When it comes to specific parts, our customers have the final say on what they will accept as an R&R. Most of our customers use the "family of parts" approach.
Right or wrong? Who knows? Untill it is a concern of the customer, we can't afford the time or the resources trying to do R&Rs for every gage, employee and part we have.
Just my opinion.

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RonSmith
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posted 16 March 2001 06:10 AM           Edit/Delete Message   Reply w/Quote
Hi,
Not related to this, but did you guys hear about the latest MSA Software called MSA Pro 2000 developed by Omnex? I had a demo and that looks great! It simplifies things for we, quality managers

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