Howard Atkins said:I would think that it is because 7.5.1.2- Work Instructions shall be derived from.. the control plan...The CP comes before the WI, it depends what is the meaning of derived
"Derived from" doesn't mean "verbatim copy." It means that there should be no conflict between the two with regard to customer requirements. If work instructions weren't different somehow from the control plan, there would be no need for separate work instructions. The question is one of control of the working specifications, I think, if the working specifications are different from the customer specifications
Howard Atkins said:... logically why should you be able to tighten and not be able to loosen.
Because loosening would probably violate customer requirements. If the drawing says 100 +/- 10 and the control plan says 100 +/- 15, then there's a problem, assuming that there isn't a subsequent operation that addresses the final condition of the product. But if the control plan or WI says +/- 5, and the additional control doesn't add unnecessary expense, the customer's requirements are being met. No harm, no foul.
Howard Atkins said:If there is a reason for the tolerances to be tightened then it should have been reflected in the FMEA and the CP! This has nothing to do with using narrowed tolerances but the justification for them.
This is an interesting point, and I think in most cases it's probably correct to assume that tolerances tightened beyond the customer requirements should be subject to some sort of review, and the FMEA process seems to be the correct place to do it. That being the case, it does seem that the tightened tolerances should be "flowed down" from the FMEA, and not arbitrarily assigned at a subsequent level. So I'm agreeing with Howard here, and probably the auditor, as there seems to be a system disconnect with regard to control of working specifications.