I have heard of several methods to correlate gages. For each method, I have some questions and then the general question of which one should I use.1) Isoplot – Measure 20 pcs representative of production range on two gages. Plot these results on an X and Y graph and look for alignment to a 45 degree line. That makes sense, BUT to what degree do you say it is good? If I do a linear regression, I would be looking for a slope of 1 and I would get an R. What is the accepable R? What if the R is really good (say .96) but the SLOPE is not 1? If the slope was 2.5 with a good R, I think I could mathematically adjust safely.2) Gage R&R Method – Run a Gage R&R but use each gage as an appraiser. This makes sense to me. I would assume the same Gage R&R hurdles would be used. But if I were doing this on a CMM, would I not have to do this on EVERY dimension that it output? Or just the ones that don’t agree? Or representative dimensions? (A couple of TPs, a couple of Diameters, etc…)3) Percent Difference Method – Measure a couple of parts (3??) on both gages and look at the percent difference between the results. This is a little nebulous. Percent difference of what? The tolerance? How close is good? This is appealing because you are not measureing so many parts, but it just doesn’t feel statistically accurate for the same reason. But we aren’t dealing with statistics, really, are we? I don’t need statistics to tell me that “This one is higher than that one …”4) One Fifth Tolerance Rule of Thumb. Same as above, but the agreement hurdle is that no measurement is different by more than one-fifth the total tolerance.Any help would be appreciated. I need two answers: 1) The right answer. 2) The answer that will make my customer’s SQE happy.ncwalker
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