Six Sigma - Gage R&R

The other common topic that I always get asked is Gage R&R.

What is Gage R&R?

Gage R&R is a formal analysis of measurement errors

Repeatability - if a single individual is consistent across repeated measurements of the same or identical items
Reproducibility - if the measurements are the same for different people measuring the  same or identical items

Crossed and Nested Gage R&R

Crossed Gage R&R is used normally
Nested Gage R&R

Nested Gage R&R is used when the act of testing a part destroys it. For example - testing airbag deployment. Nested Gage R&R does NOT suffer from the carryover effect. Disadvantage: you need more operators as the number of parts increases.

Carryover effect: experience gained by OP1 when measuring DUT1 affects the outcome of OP1 measuring DUT2
For Crossed Gage R&R
Nested GRR - only reproducibility across OPs can be measured

Accuracy v. Precision

Conducting a GRR Study

Reading GRR values:

In general:

<10%: acceptable

10%-30%: okay depending on application

>30%: unacceptable, too much measurement variation

https://sixsigmastudyguide.com/repeatability-and-reproducibility-rr/

This link showed me how to calculate GRR by hand:

Gage Repeatability and Reproducibility (R&R) | Six Sigma Study Guide
Gage Repeatability and Reproducibility is commonly referred to as Gage R&R. It’s a method that we can use to look at variability in our measurements.