Why Gauge R&R 10% is acceptable for variable instruments ?

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Ninja

Looking for Reality
Trusted Information Resource
#2
Howdy VivekanandGawade,

I can't comment on the "why"...but sometimes the "what" can help...

What the 10%GRR {basically} means when using the TV=spec limits is that the error in your measurement is at most 10% of your spec range. It is a threshold of 'comfort' that your readings are accurate enough to tell good parts from bad.

If the spec is 17.5 - 18.5...the largest error (assuming GRR=10) is ~0.1...so the reading of 18.3 can be counted on to establish that the part is in spec.

Imagine the same thing with GRR = 30%...your reading of 18.3 might actually be from a part that is 18.6 and you've called a bad part good and shipped it.

Again, this isn't the "why"...just a way to look at the practical side...HTH
 

dgriffith

Quite Involved in Discussions
#3
In a similar fashion, in calibration, there is risk that you are turning out an instrument you declared in-tolerance and good, but it is not. You want to minimize this risk, so you use a calibrator that is at least 4x better than the instrument spec.
For calibration, 4.6 times better is a risk of 2%. 10x better is very small risk.
 

Bev D

Heretical Statistician
Staff member
Super Moderator
#4
10% is a rule of thumb, much like a p value < .05 means that there is a statistically significant difference.

Except that it is important to remember that the % of tolerance calculation is mathematically invalid and so it's a really fuzzy rule of thumb.
 
Z

zancky

#5
What the 10%GRR {basically} means when using the TV=spec limits is that the error in your measurement is at most 10% of your spec range. It is a threshold of 'comfort' that your readings are accurate enough to tell good parts from bad.
my modest opinion

GRR is the standard deviation of the measurement procedure error.
10%GRR means, for me, that 6 times the measurement procedure error standard deviation is 10% of TV or T according to the used formula

beacuse everything is supposed on a gaussian distribution, there is always a chance the error is above 10%. Nevertheless as long as MSA is performed on a dimension that will be controlled by X-R or X-S chart, the GRR will increase the spread of the population (R or s) so there is quite no risk in the determination of the state (good or bad)
 

Ninja

Looking for Reality
Trusted Information Resource
#6
Agreeing with both Bev and zanky...

That's why I had the {basically} in there...
 
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