Reasonable GRR result for a 0-1" micrometer with a total tolerance of .002"

D

dickgent

#11
You may want to break out the "R" from the GR&R. Take a single part with a single operator and measure it 10 times at the same dimension. Do this for each operator and calculate the variance. This will give you a proportional variance that you can use to narrow contributors down. This is based on producing an Anova to measure the interaction effects.
 
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Ninja

Looking for Reality
Staff member
Super Moderator
#12
Ninja:

The total spec range was .002"
You've got great advice and questions up above.

FWIW, I make a slightly compressible material that (sometimes) has a spec range that large (+/- 25um = +/- 0.001")...usually it's smaller (+/- 5um)

I have thrown out all of our micrometers after they failed trial after trial. Micrometers were simply not up to the job for a spec range as tight as 0.002".

While you are considering the questions and suggestions above (and posting data so we can look into it further), you may also want to start considering what other tools might be used for this measurement.

Micrometers reading in inches typically have a resolution of 0.0001". That gives you only 21 discrete values in spec. While this can work, you might be better off with a gage with higher resolution (and equivalent or better accuracy).

My product is flexible and can be laid flat...so I use a vertical drop gage now with resolution to 1um and accuracy of 1um. Passed GRR with flying colors (%GRR = 0.6 on a spec range of 50um). For X-Y measurements I use a CMM.

All the same, if you are measuring machined metal (not really compressible) ...micrometers may be appropriate.

HTH,
 
5

57jeeper

#13
Good morning all,

Thanks for all the advice.

Would someone have a list or site with standard expect gauge RR values with total tolerance from .0005" to .005" for 0-1" micrometers, comparators (25x), 0-1" blade micrometer, vision system (flash 5000) and CMM?

The gauge RR was performed with a 0-1" micrometer to match the customer's inspection method. I'm trying to avoid using a CMM or vision system due to the lack of resources and time compared to a mic.

The ten parts used were from a 30 piece lot, and had little variation and didn't cover the .002 total tolerance.


I attached a copy of the data. Using your suggestions I could get the gauge RR under 10% thanks.

Also I attached a copy of a second gauge RR performed on a CMM with a total tolerance of .001". 3 operators, 10 parts (same lot) 3 trails. The parts were removed from the fixture and reloaded. Total gauge RR %tolerance was 19.72 and I don't think I can get it under 10%.

At what point is the total tolerance too tight that getting under 10% not realistic?
Thanks
 

Attachments

S

shorttimeQE

#14
What do you do when you cannot get parts that are "bad", out of the upper and lower tolerance zones?
 
R

Roscoe Splevins

#17
Open Question on R&R results.

Please consider my comments below. My interpretation of the results may be flawed. Normally we use an X-R method to calculate R&R. ANOVA adds interaction calculations I cannot beging to calculate (or appreciate).

Your results have two (2) distinct categories. That may indicate very good consistancy in parts OR insufficienct distrimination. You've measured to 4 decimial places so there should be sufficient discrimination for justification of the instrument used. But may be going to the fifth decimal may be needed.

Looking at the 16.42% and the formula (SV/Toler); That tells me your gage error is 16.42% of your tolerance. Would that give 46.46% as GRR? Repeating the same set of calculations without entering the 0.002" tolerance into the MiniTab set-up yeilds a similar set of calculations but with % Study Var as end result. Is this not your GRR?

Try the same MiniTab set-up but with the X-R method and compare results.

The AIAG has a book to explain all this. I don't have it and the company won't spend the 150.00 to buy it. I'd like to compare my interpretation of the MiniTab explanation to my observations.
 
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