The gd&t and engineer

Geometric Dimensioning and Tolerancing (GD&T)
What Is GD&T?
Geometric Dimensioning and Tolerancing (GD&T), when made an integral part of the Product Development/Delivery Process through drawing previews/reviews, is the tool that can have the greatest impact on improving quality, cost and delivery of your product. GD&T is not new, but there is newness about it. Recent developments in CAD and CMM technology, ISO Standards and Statistical Process Control have brought GD&T once again to the forefront of design, quality and manufacturing. GD&T is a common language that may be used to improve communication between design, quality, manufacturing, suppliers and customers. For nearly two hundred years, industry has been struggling with the problem of clear part definition. The latest and most successful approach has been to employ Geometric Dimensioning and Tolerancing (GD&T). After nearly sixty years of refinement, industry now has a Standard which will handle virtually every situation. The Standard is published by the American Society of Mechanical Engineers and is designated ASME Y14.5M-1994. Some of the advantages of using GD&T on engineering drawings and product data sheets are that it: • • • • • Uses datums and datum systems to define dimensional requirements with respect to part interfaces. Specifies dimensions and related tolerances based on functional relationships. Removes ambiguity by applying universally accepted symbols and syntax. Provides information that can be used to control tooling and assembly interfaces. Expresses dimensional tolerance requirements using methods that decrease tolerance accumulation.

Why Do I Need GD&T?
The craftsmen of old could fashion parts in a way that would allow them to slide together and give the impression that the parts fit "perfectly." Today, with the concept of interchangeable parts, credited to Eli Whitney, it is expected that parts will assemble the first time and perform their intended function. Interchangeability