Introduction to GD&T

A 3D CAD model is an idealized representation of a designer’s intent. However, the theortically perfect form of that model cannot adequately define the design due to downstream manufacturing imperfections. Equally important to dimentions of a drawing that describe the features of a part is the specified tolerance for manufacturing deviation from perfect form.

Geometric dimentioning and tolerancng(GD&T) is a symbolic language used to fully define the designer’s intent as well as the allowable deviation of feature geometry. This language consists of dimesions, tolerances, rules and conventions used on drawings to precisely communicate the functional requirements for size, location, and orientation of forms and surfaces. GD&T allows designers to “say what they mean” with exactness, leaving no ambiguity for interpretation by Manufacturing and Inspection.

This course presents uniform practices for stating and interpreting dimensioning, tolerancing, and related requirements for use on engineering drawings and in related documents. The simple and most practical reason to use GD&T is that it saves money.