Gage R & R Study "Best Practices" - More than three operators?

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bobdoering

Stop X-bar/R Madness!!
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#2
If you select your participants with care - and they represent the most experienced, the least experienced and a person with average experience, there is very little to gain from the additional overhead of adding more people.

Would you ever have more than three? Maybe if you bribed them with pizza....:tg: Usually it tough enough to get three!
 
A

adamsjm

#3
Would you ever want to have more than three operators included in a Gage R&R study?

In order to have some initial starting point, probably not.

But, when a new Associate becomes the inspector where the Gage R&R is applied, how will you know that the new Associate is performing the inspection in the manner that the first three were? How about the next 10 new auditors? How will your company / plant demonstrate a training plan? If the associate who usually performs the inspection calls in sick, how will the cell or shift leader determine who can fill in?

Additional associates should perform a Gage R&R (using the same sample parts, if possible) and analyzed for the above reasons. Tables exist for 2x2x2 through 15x15x15 Gage R&Rs, but I would just substitute the new associate for one of the original associates and see if you observe any “major” changes in the R&R results.

Joe Adams
 

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brahmaiah

#4
Would you ever want to have more than three operators included in a Gage R&R study?

In order to have some initial starting point, probably not.

But, when a new Associate becomes the inspector where the Gage R&R is applied, how will you know that the new Associate is performing the inspection in the manner that the first three were? How about the next 10 new auditors? How will your company / plant demonstrate a training plan? If the associate who usually performs the inspection calls in sick, how will the cell or shift leader determine who can fill in?

Additional associates should perform a Gage R&R (using the same sample parts, if possible) and analyzed for the above reasons. Tables exist for 2x2x2 through 15x15x15 Gage R&Rs, but I would just substitute the new associate for one of the original associates and see if you observe any “major” changes in the R&R results.

Joe Adams
In the attached excel file there is a serious error.Conversion of 1ppm is shown as 990,000.It should be 10,000 instead.The two conversion tables donot agree with each other for the same conversion.Pl. through some more light on this
V.J.Brahmaiah
 
Last edited by a moderator:
U

Umang Vidyarthi

#5
Would you ever want to have more than three operators included in a Gage R&R study?

In order to have some initial starting point, probably not.

But, when a new Associate becomes the inspector where the Gage R&R is applied, how will you know that the new Associate is performing the inspection in the manner that the first three were? How about the next 10 new auditors? How will your company / plant demonstrate a training plan? If the associate who usually performs the inspection calls in sick, how will the cell or shift leader determine who can fill in?

Additional associates should perform a Gage R&R (using the same sample parts, if possible) and analyzed for the above reasons. Tables exist for 2x2x2 through 15x15x15 Gage R&Rs, but I would just substitute the new associate for one of the original associates and see if you observe any “major” changes in the R&R results.

Joe Adams
Good response Joe, in perticular about swapping the additional apraisetr with an original, makes good sense.

Umang :D
 

bobdoering

Stop X-bar/R Madness!!
Trusted Information Resource
#6
But, when a new Associate becomes the inspector where the Gage R&R is applied, how will you know that the new Associate is performing the inspection in the manner that the first three were? How about the next 10 new auditors? How will your company / plant demonstrate a training plan? If the associate who usually performs the inspection calls in sick, how will the cell or shift leader determine who can fill in?
Certainly, performing a gage R&R is one method for verifying the training. Ongoing GR&Rs for all associates and all gages can become a consuming overhead - you may be manufacturing gage studies instead of parts. If you have infinite resources, or extreme risk, you can do it. Otherwise, one can prioritize the need for operator verification by gage r&r by some conditions:

1) If the gage is highly operator dependent

2) If, when working with the gage system to ensure the gage was appropriate gage, training became an issue.

3) The gage has a high gage R&R value, and the risk of any further variation in operator may move it to unacceptable.

If those conditions do not exist, and you chose your original gage study operators with a representative level of training - including new people - then it may be a very low priority to gage R&R the individual.

Once again, however, the conversation shows that gage R&R is a toolbox, and not a tool - for evaluating the gage system, not the gage. What you are describing is using the study to determining if the operator is the right operator for the job - and the original study was used to determine if the gage was the right gage for the job! Two different questions! Two different approaches with the same toolbox.
 
M

M Komarmy - 2012

#7
The purpose of the gauge R&R is to identify sources of variation. Operator interactions can be a very significant source of variation, particularly with gauge methods that are dependent on the skill level of the operator. For example, micrometers or calipers can easily have chordal errors if the gauge is not properly aligned with the part when measurements are taken. Within part variation such as form errors on diameters can also influence the measurement results.

When these items (operator/gauge and part/gauge interactions) show up in the R&R results, much can be done with gauge and fixture design and the inspection plans to alleviate the problems. I have seen hand snaps measuring crankshaft journal diameters with a +/- 12 micron tolerance have GR&R's of over 80% of tolerance. I have also seen computerized fixture gauges measuring the same features achieve less than 10%. Of course the price will be much higher for the computerized gauge. This cost will be recovered in lost production and scrap if the gauge is used properly to maintain the process. Using a gauge with 80% R&R will cause all kinds of disruptions due to the type 1 and type 2 errors that will occur (calling bad parts good and also calling good parts bad).

Gauging methods can be developed that present the part to the gauge in a controlled manner so the measurement can be reproduced. If there is within part variation, the part can also be measured in multiple locations and you can do the R&R on the range or average. In the 2nd edition of the AIAG MSA there is a method of performing a study to evaluate within material variation as a part of the R&R. I have attached some excel worksheets that can be used for these analysis.

The R&R evaluates the entire measurement system and will give you a feel for it's fitness for use. If used to sort parts for conformance to specifications, you want the R&R to be as small as possible. In order to protect the customer, you should also reduce the acceptance limits on each end of the tolerance by 50% of the R&R. This will prevent you from accepting bad parts due to gauge errors.

If the gauge is used for process control or spc, it can have up to 30% of tolerance for R&R without having a significant effect on the observed process variation. These concepts are explained in the AIAG MSA guideline (Automotive Industry Action Group - Measurement Systems Analysis).

If you have representative operators, i.e. appropriately trained, there is no need for more than three.

Good luck with your gauging!

Mitch
 

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Kalpol92

#8
I have used 4 operators before as i was duplicating a method in another plant.

I then analysed 2 different ways GR&R for each plant and both plants together.

This way i proved that the level of training was sufficient in the new plant and that enviroment in the new plant did not adversely affect my results.
 

Bev D

Heretical Statistician
Staff member
Super Moderator
#9
Certainly, performing a gage R&R is one method for verifying the training. Ongoing GR&Rs for all associates and all gages can become a consuming overhead - you may be manufacturing gage studies instead of parts. If you have infinite resources, or extreme risk, you can do it. Otherwise, one can prioritize the need for operator verification by gage r&r by some conditions:

1) If the gage is highly operator dependent
Bob - as usual you make some good points. However, it's important for us to remember that there are industries beyond automotive and thier derivatives and those that have large part mixes and/or are measured using standard 'gages'.

For example, my current company has a fairly low mix, highly complex product set. we don't use 'traditional gages' and our measurement systems are very complex and highly operator dependent. So we use MSA (a much more descriptive term that gage R&R) as part of our validation procedures for new systems and for our test/QC operator qualification. We even use MSA to qualify the customer support personnel who take customr calls...

Also - I might add to the OP to not confuse "best" with "popular" or "most used". They are not synonymous...
 
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