Quality Digest

If you are trying to certify gauges and masters, then your CMM is probably not the proper place to accomplish this. Typical production and plant layout CMM's are only able to measure to about .001-.002 mm (.0004"-.0008"), and there is a lot of additional variation due to part cleanliness, temperature, part measurement programs or algorithms, filters specified, choice of stylus used, speed measured, and on and on.

Many quality standards (such as QS-9000) require that the methods/gauges used to verify part or process quality are tracable to national or international standards (such as NIST in the U.S.). It is typical for gauge manufacturers to provide certification documents with gauges and masters as a part of terms of the order. They either send the gauges or masters to a certified inspection lab, or they use their own inspection lab that is maintained to the necessary standards to be NIST certified. Certification documents should show the measured values of the gauge or master, along with the uncertainty budget (the uncertainty or confidence intervals of the measured values). It should also make note of the measurement conditions (temperature, humidity, etc.) to insure the standards are met. These values are the ones that should be used when inputting master values into the floor gauges.

If the masters are subject to wear or damage, say from dropping them, they should be sent out periodically or when damage occurs to a certified lab for re-verification and rework if necessary. In some cases this will require more than one master to be purchased so production is not interrupted while the masters are being checked.