Acceptable Criteria for Variable Gage R&R according to the MSA Manual 3rd Edition

The Acceptable Criteria for Variable Gage R&R study according to the MSA Manual 3rd Edition for %Study Variation and %Tolerance is:

< 10% - The measurement system is acceptable

between 10% and 30% - The measurement system is acceptable depending on the application, the cost of the measuring device, cost of repair, or other factors

>30% - The measurement system is unacceptable and should be improved

Everybody says MSA is the Standard that is used for the Gage R&R's but I want to know whether there is any reasoning behind the Acceptable Criteria. How did MSA come up with such numbers?

Thanks

Re: Acceptable Criteria for Variable Gage R&R

you quote the "standard" for the automotive industry - it is not the standard for everyone or every industry. Miner is probably the best source for the history. But there is really no substantial reason for using 10, 20 adn 30. These were in all liklihood anatomically derived. I refer you to Wheeler's work and the many posts here on this topic.

Re: Acceptable Criteria for Variable Gage R&R

Ditto on Bev's comment!!!

While I tend to agree with Bev D. that “… there is really no substantial reason for using 10, 20 and 30%”, there are some reasons these values are sited. It mostly deals with the ability to pass the Gage R&R vs. Cpk correlation.

A good reference source on this is RESOLVING DILEMMAS THAT OCCUR WHEN USING QUALITY MEASURES by Karl D. Majeske and Richard W. Andrews

http://deepblue.lib.umich.edu/bitstream/2027.42/35878/2/b2035029.0001.001.pdf

They state, “Automobile manufacturers and suppliers that follow Automobile Industries Action Group (1995) guidelines use a cutoff of Co = 1.67, i.e., processes with Cp >1.67 are approved for production.”

With this condition a capability of Cpk > 1.67, Gage R&R most likely must be less than 30% to be confident of the process capability. With a condition of capability, Cpk > 2.00, Gage R&R most likely must be less than 10% to be confident of the capability. The confidence that the process is that capable is more complicated but these are some guidelines.

Per Majeske and Andrews, “… Therefore, the more capable a process, the more precise a gage must be to pass the correlation criteria (i.e.: Gage R&R vs. Cpk).”