There is a long-standing practice in the computer aided inspection industry that includes CMMs to report in-tolerance values in green and out-of-tolerance values in red.

Typical answers include: cheaper, faster, most accurate, none of which would pass a technical smell test. On reflection, many might say they want calibration to tell them if the item to be calibrated is any good or not while not defining what ‘good’ means from a technical point of view.

Many factors may play into your scrap nightmare: wrong or misread tolerances, incorrect materials, and in precise measurements. These nonconformance nightmares will cost you plenty. It’s the call from your customer, or the news from the shop floor no one wants to get: “The part doesn’t fit.” The amount of time and effort for a redo is a tremendous drain and distraction.

In my last column I noted that I would give some hints to help you avoid problems with assigning and applying acceptance limits, so let’s go back to square one.

Some of the data I’ve noted from the AMTMA studies make it very clear that measurement disputes will continue. When the range of readings is close to or exceeds the tolerances of the gages being calibrated, it is a certainty. Further problems will occur due to unrealistic expectations by all the parties involved in a dispute.

When testing the properties of a material or component, a range of options are available for examining, reporting and tracking tensile data.

I took a cursory look at this subject in a recent column but with the increasing number of companies expecting their calibration sources to make such decisions on their behalf, I thought a little more detail was in order. 

I offered some comments that relate to gaging problems in the last column but thought it would be worth giving measuring instruments the same treatment.

Air gaging has many advantages as an inspection method. It is quick and easy to use, and requires little skill on the part of the operator.

Gage manufacturers and calibration laboratories often find themselves in this minefield. New gages or instruments are supplied or calibrated and immediately returned by the customer because they aren’t correct.