QMT News: September 2013
Editor’s comment: Time for good GD&T?

When it comes to GD&T, is model based  definition (MBD) and measurement the way forward? That was the thesis put forward by Bill Tandler, a speaker the CMSC conference held in San Diego 22-26th July.

In a CMSC Workshop: The Desperate Need for "Good" GD&T,  Bill Tandler, from Multi-Metrics,  said that the very first job of the coordinate metrologist is not to inspect parts, but to inspect the drawings and in particular the GD&T which will determine the inspection process. In the absence of any GD&T, all coordinate metrology depends entirely on tribal understandings and is essentially useless. Bad GD&T - the most common kind, - is even worse than no GD&T, because it misleads and requires “interpretation”, an exceedingly dangerous business. Only good GD&T, namely properly “encoded”, functional, fault tolerant and syntactically correct GD&T is of any value for tolerance stack-up analysis, for guiding manufacturing processes and for determining metrology processes. Since the complexity of GD&T always stands in the way of producing good GD&T, how do we get there? It is clearly time for implementation of intelligent GD&T encoding support in the Model Based Definition (MBD) environment, which is just in its infancy today.

Brendan Coyne
     - Editor QMT
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