you know I have the same question as the OP. (perhaps for a different reason)
Why take just the lower value? what if you have parts out of spec both high and low? are the defects that are less frequently out of spec not of any importance? won't they feel left out?
what if there are 2 machines making the same parts: both have the same Ppk value for the high end of the spec (.5) but one has a very good Ppk value (>2) for the low end of the spec and the other machine has a poor Ppk (.9) for the low end of the spec. How do we judge these two machines? They certainly aren't equal...
Hi Bev D
Your questions seem designed to provoke a response, so if I was your customer I'd be "unhappy"
For parts out of spec I hope you are sorting (not shipping me the OOS) and working hard to get in spec or negotiating with me the customer to open up the spec?
For two machines it comes down to the overall out the door capability, and it will be pretty bad when you combine two processes, one targeted and high and the other targeted low.
The customer gets all these parts, so again I hope you are working to target both machines, or get customer relief on the spec....
All this assumes the customer even knows anything about capability and that they have actually put tolerances on the print that make sense.
Sometimes customers just copy old prints without understanding. It is always good to talk to them to understand.