Re: Tolerance for Cpk purposes
I run into a similar situation with our biggest customer all the time.
They rubber stamp Cpk on things like ‘No Burr Allowed’ which obviously is an attribute with a Yes/No function. Try plug’n that one into MiniTab!
We also get 1.66 Minimum Cpk requirements on OD’s with +/- .001 tolerances on metal turned parts that are heat treated and plated. I guess we are supposed to be fortune tellers and oracles too!
We may at times bend the ‘rules’ a bit when calculating Cpk’s, but at the same time we have enough data on our processes that we can feel confident in our ability to deliver a product that meets the intended requirement of the customer.
Without first having a baseline or benchmark on your own processes I would be cautious.
Have you run any recent capability studies on your production?
If so, how close are you to the customers requirements?