Gage R&R Results - ?Number of Distinct Categories = 1?

C

CMfgT

#1
Gage R&R Results - “Number of Distinct Categories = 1”

Can someone help me explain my Gage R&R results? I know most of my problem is I have “Number of Distinct Categories = 1”. I guess I don’t understand why I keep getting that. I attached my data and a few graphs from Minitab.

Some background info. The part feature being measure is a 1.181” OD with a tolerance of 0.001, so my UCL=1.181” and my LCL is 1.179”. I measured with the 10/1 rule so I included the 4th decimal place (tenths or .0001). Is this my problem?

I also run two different software programs and get two different results? What does everyone else use?


Any help would be appreciated.
 

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bobdoering

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#2
Re: Gage RR Results

Two questions:

1) What gage are you using and 2) Are you measuring the exact same spot on the part each and every time?
 
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A

achorste

#3
Re: Gage R&R Results - “Number of Distinct Categories = 1”

Well, I don't think it's the software you are running that is giving you your failed gauge R&R, or your gauge resolution (which, at a tenth of the tolerance, should be adequate).

If you look at all the results from each part in isolation, the ranges of results you are seeing is up to 0.0018", which is nearly the size of the tolerance itself.

Can you give us any more info on the measurement system itself?
 
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C

CMfgT

#4
Re: Gage RR Results

Look at your RESULT by part data. The error of the measurement is taking up the whole spec - even if the gage reads to .0001.

Two questions: 1) What gage are you using? 2) Are you measuring the exact same spot on the part each and every time?

How is the error taking up the whole spec. The tolerance is .001", and the normal range is .0003 or .0004.

1)Using a 1-2" OD mic. Appraisers are using the same mic and same gage block to zero the mic to thier feel. The mic is a friction mic. I think this is where the human error is coming in. Appraiser A from trial 1 to trial 2 was consistantly .0002" off. The operators zeroed the mic each time.

Thanks,
 
A

achorste

#5
Re: Gage RR Results

If you look at the top right chart on the minitab output it shows the spread of results by part, this spread covers up to 0.0018, in 3 cases 0.0015. The operators tend to average out ok, but that is masking the real problem that the amount of variation in the results obtained is too great to give you a reliable measurement system.
 
C

CMfgT

#6
Re: Gage RR Results

If you look at the top right chart on the minitab output it shows the spread of results by part, this spread covers up to 0.0018, in 3 cases 0.0015. The operators tend to average out ok, but that is masking the real problem that the amount of variation in the results obtained is too great to give you a reliable measurement system.
I am confused?? I posted some data to support my question. I see where Minitab says I have a range of .0018, but when I compare my data in excel, the biggest range an operato has is .0006"

What am i Missing here?
 

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CMfgT

#7
Re: Gage RR Results

I am confused?? I posted some data to support my question. I see where Minitab says I have a range of .0018, but when I compare my data in excel, the biggest range an operato has is .0006"

What am i Missing here?

I found an error in my excel formula converting the results to part numbers. I had the wrong part numbers assigned to results. Let me fix and repost. Sorry.
 

Jim Wynne

Staff member
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#8
Re: Gage R&R Results - “Number of Distinct Categories = 1”

The part feature being measure is a 1.181” OD with a tolerance of 0.001, so my UCL=1.181” and my LCL is 1.179”.
I'm confused. You're referring to UCL and LCL, (upper and lower control limits) but I think you mean USL and LSL (upper and lower specification limits). If this is the case, what do you mean by "a tolerance of .001"? The fact that you identify the "LCL" as 1.179 (.002 less than 1.181) indicates that the total tolerance is something other than .001. Can you clarify?
 
C

CMfgT

#9
Re: Gage R&R Results - “Number of Distinct Categories = 1”

I'm confused. You're referring to UCL and LCL, (upper and lower control limits) but I think you mean USL and LSL (upper and lower specification limits). If this is the case, what do you mean by "a tolerance of .001"? The fact that you identify the "LCL" as 1.179 (.002 less than 1.181) indicates that the total tolerance is something other than .001. Can you clarify?

I attached the new data with info. Alot better. First off I am sorry, I had a typo, so my part number results were mixed up.

Clarify, I ment to say my +/- tolerance is .001, so I have .002 overall.

Now, is my total gage R&R 28%?
 

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achorste

#10
Re: Gage R&R Results - “Number of Distinct Categories = 1”

A lot better indeed :D

Your total Gauge R&R %Tol is 46.79, the % Study variation is 28%.

From a quick skim of the data, my opinion would be that you still have an issue with operator repeatability.

We had a similar issue with a bore on one of our components with a 0.001" total tolerance - we first off tried a bore mic, but with all the variation (including human factors) we just couldn't get a repeatable measurement system.

In the end we switched to a combination of sample CMM and 100% Go / NoGo gauging. (Sample on CMM for SPC purposes - but be warned - the CMM is only as good as the fixturing, program and set up, and even then it will only give you an average - hence why we stuck with Go / NoGo gauging)
 
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