GD&T, or Geometric Dimensioning and Tolerancing, has become an industry standard as well as a different way of describing tolerance. Rather than the traditional reference frame, GD&T emulates the constraints of putting something together, based on the kinds of spatial relationships of the parts.

It’s been proposed and circulated by different organizations, but in the United States, it was ASME, the American Society of Mechanical Engineers, that formalized the standards for GD&T. The code was revised in 1994 to clarify the standards even further. A similar international standard is put out by the International Standards Organization, or ISO.

These codes create the framework for how the industry implements them.

Dave Calkins, a mechanical engineer from New River Kinematics, explained that in GD&T, the relationships are the most important. “It’s like how kinematics is the science of spatial relationships, and GD&T is a way of describing them,” he said.

The industry leading software, SpatialAnalyzer, is created by New River Kinematics and Calkins explains how GD&T is integrated into that software. “It’s an important feature of SA that it supports the engineer’s ability to read and implement GD&T design from CAD drawings,” he said.

The GD&T design gives the measurements relativity, and once those points are known, the data can be arranged. SA allows the technician to encode CAD with annotations indicating curvature, diameter or true position. “The piece needs to fit, so you are basically encoding the constraints. In SA, you go measure, then validate the code’s pass or failure. The feature checks assign and validate measurements, and you can also generate reports.”

Another feature of SA is that in addition to process flow, manual creation is allowed with imported CAD files that need to be annotated. So, not only is it compatible with GD&T notations, it can also create them on files when necessary, making it easier to implement GD&T.

With SA, engineers and mechanical technicians can more easily implement and integrate GD&T into their daily work, using the tools it provides, as well as work on their own customized annotations. GD&T has been around for the past 36 years, and it will continue to change the industry and the way that measurement is conveyed.