Does Your Model Speak for You? Why 3D CAD Needs GD&T

Written by: Cat McClintock

Manufacturing equipment can be inexact. Sure, the radius of that gear is 40 cm according to your tape measure, but a pair of calipers might tell a different story.

 Does the difference matter?

 It depends. As a design engineer, it’s up to you to tell the manufacturer just how much play your model can allow. But how can you do that when your product and its subassemblies are produced in multiple locations? That’s where GD&T comes in. It helps your models speak for you.

 GD&T in 2D drawing

 GD&T, or geometric dimensioning and tolerancing, is a symbolically driven language used to communicate design details to the people who build the model. GD&T is a shorthand system used to convey how much imperfection a model can stand.

 It’s not a new concept. Engineering draftsmen have been using GD&T for a long time—since around the 1940s. But it’s getting renewed attention lately.

 That’s because historically you’d find this type of communication in the annotations on a 2D drawing. With the growing adoption of Model Based Definition (MBD), engineers now place GD&T data directly in the 3D models—making the 3D CAD geometry a single source of design information.

 We talked to Chris Wilkes, President and CEO of Sigmetrix, the global expert in GD&T and mechanical variation. Below, he answers the question, “Is GD&T a New Idea?” Watch:

 With MBD, your 3D data set could include enough information to manufacture and inspect the part—making 2D drawings obsolete.

 What’s even cooler? If you have IoT-enabled equipment set up, your inspection machine can then automatically read the GD&T data contained in your part file. It could inspect the manufactured part without anyone having to manually input data.

Download the MBD eBook

Ready to hear more about GD&T and model-based definition? Download the free eBook from PTC now. You’ll learn more about the limits of 2D drawings and how MBD streamlines organizational processes and reduces inefficiencies. Whenever you’re ready, it’ll also help you figure out how to get started using MBD with your team. Download your copy today.

 Download the MBD eBook

Tags: CAD Retail and Consumer Products Connected Devices

About the Author

Cat McClintock

Cat McClintock edits the Creo and Mathcad blogs for PTC.  She has been a writer and editor for 15+ years,  working for CAD, PDM, ERP, and CRM software companies. Prior to that, she edited science journals for an academic publisher and aligned optical assemblies for a medical device manufacturer. She holds degrees in Technical Journalism, Classics, and Electro-Optics. She loves talking to PTC customers and learning about the interesting work they're doing and the innovative ways they use the software.