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

bobdoering

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#21
Re: Gage R&R Results - “Number of Distinct Categories = 1”

Yes, as stated above, I used a friction mic which minimizes this error. I believe this error is a main cause when setting or zeroing the mic. We ordered a snap gage, so hopefully another gage r r will yield better results and will justify spending the money on snap gages.
Good idea. Even a friction mic can create error by impact. If an operator spins down at a different speed each time, it can still create error. Standard micrometers are generally just bad news. I have seen huge GR&R improvements with snap micrometers.
 
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Miner

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#22
Re: Gage R&R Results - “Number of Distinct Categories = 1”

Can you clarify what you mean by "Your total Gauge R&R %Tol is 46.79, the % Study variation is 28%." What is the difference? I know my gage rr value must be below 30%. If a customer called and asked for my gage r and r value, what value are they looking for? what is the difference.

thanks,

  • %Tol = 46.79% means that gage variation consumes 46.79% of your tolerance. Use this if your gage is used only for inspection to tolerance.
  • % Study Variation = 28% means that the gage variation consumes 28% of the variation seen in your study which theoretically includes your process variation. Use this if you gage is used only for SPC or statistical studies.
  • Use both if your gage is used for both inspection and SPC.
BTW, these questions are related to another thread that you started. They should be part of the same thread, not separate.
 
R

ROOPA KODE

#23
Re: Gage R&R Results - “Number of Distinct Categories = 1”

Hi all
Last week we had a survilence audit where the auditor has gone thru one of the R&R studes done with optical comparator.The ndc obtained in this case is 425.Onseeing that he said that its impossible to get an higher ndc like that and said that this report is definetly a fake one.But actually its a valid r&r carried on.Can anny one suggest how to manually interpret the ndc and what could be the maximum limit for ndc
 
B

Barbara B

#24
Re: Gage R&R Results - “Number of Distinct Categories = 1”

Welcome to the Cove :bigwave:

A huge ndc is rare, but possible. If you have a %SV (study variation) of 0.11%, you'll get ndc=425. %SV depends on the ration between VarComp(gage) and VarComp(total):
%SV/100 = VarComp(gage)/VarComp(total)

If the variation of the gage is tiny compared to the total variance, you'll get a high ndc (see Minitab knowledgebase ID 2393: Relationship between the number of distinct categories and % Study Variation for details).

This will happen if the selected parts are really different and cover a broad interval comparing to a gage with a minimal measurement uncertainty and no operator effects.
 

Bev D

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#25
Re: Gage R&R Results - “Number of Distinct Categories = 1”

I have seen large NDC values in that range before and they can be valid...

the best help we can give you is if you post your data and explain the characteristic and how it is measured...
 
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