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(In accordance with the ASME Y14.5-2009 standard)

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Drawings are changing. The ASME Y14.100 standard defines a drawing as "an engineering document or digital data file(s)". The ASME Y14.41 standard defines how to embed tolerancing in the digital data file. This data may be transferred to CAM equipment to produce the part or tool. Once the part is produced, the digital data file may be used to assure that the part meets the drawing requirements. Point clouds of data from part measurements may be merged with the digital data file to determine part conformance. This last step is only possible if tolerancing has been applied to the features in the digital data file. The software that evaluates the data should be compliant with the ASME Y14.5 and Y14.5.1 standards. This is where the system is breaking down. We have a lot of folks who are good at creating CAD files. However, far too many do not understand how to apply GD&T to part features.

The CAD models are perfect out to 24 significant figures. Unfortunately, we cannot make perfect parts.

Most engineering colleges are not teaching geometric tolerancing! Graduate engineers are pretty good "CAD Jockeys" but do not know how to tolerance. They get jobs where they sign off on drawings that they cannot read.

When I train, I first wear a shirt that asks the question "Got Tolerance?" to make people aware of what they do not know. Later in the training I switch to a shirt or hat that says "GD&T Rules!" because, if you are reading this Tip, you know it does.

Let’s work to create an awareness that without GD&T the new technology will not work.

Back to Tips Tip added Sep 2011