Justification for not doing Gage R&R Studies

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cuadra - 2010

#12
Re: Justifying not doing Gage R&R Studies

Dear Mnavarro:

The Gage R&R is perform to get an estimate of the precision of your measurement system.

In other words, if your measurement system is perfect and you measure the same part multiple times, you will always get the same number. In practice, since measurement systems are not perfect, the observed variation coming from measuring the same part will provide you with an estimate of the measurement system error (During a real gage study you use several parts in order to improve the confidence interval of your estimate).

When you calibrate a measurement system, you are adjusting its bias. In other words, you are adjusting its accuracy.

General Note:
When you don’t have a gage R&R study, you don’t have any information with regards the precision of the measurement system. The implications are uncertainty in your pass/fail criteria. You could end up accepting bad parts and rejecting good parts.

The only way that you could justify not doing a Gage study is to somehow show objective evidence that you are protecting the customer.
 
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K

Karen R

#13
Re: Justifying not doing Gage R&R Studies

I think you may be confusing the various studies. R & R is to determine the variation caused a) from repeated measurements using the equipment and b) from different operators using the equipment.

What you guys described (IMHO) are more in line with stability studies, the study of variability due to long term 'drift' of equipment caused by use etc. Dependingon the equipment type, linearity and bias studies are often performed too, to characterize the measurement system.
I think you may have clarified a concern of mine - but I'd like to confirm. I have a couple of measurement processes on my control plan that don't fit into a nice R&R, and I've been looking for an adequate explanation to address this.

One is a fixed ircon measuring strip temperature at a critical point on our galv line. We have evidence of acceptable linearity and bias over multiple calibrations. These calibrations also indicate there are no concerns with stability. So... if I have demonstrated via the calibration / stability protocol that there is no issue from "repeated measurements over time" and by nature of the device (permanently fixed gauge) there is no effect from "different operators using the equipment" -- can I not stop there in the MSA process?
 
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