GDT – Geometric Dimensioning and Tolerancing – An Overview
What Is GDT?
GDT is a symbolic language. It is used to specify the size, shape, form, orientation, and location of features on a part. And its defined by ASME Y14.5 standard. Features toleranced with GDT reflect the actual relationship between mating parts. Drawings with properly applied geometric tolerancing provide the best opportunity for uniform interpretation and cost-effective assembly. GDT was created to insure the proper assembly of mating parts, to improve quality, and to reduce cost. GDT is a design tool. Before designers can properly apply geometric tolerancing, they must carefully consider the fit and function of each feature of every part. GDT, in effect, serves as a checklist to remind the designers to consider all aspects of each feature. Properly applied geometric tolerancing insures that every part will assemble every time. Geometric tolerancing allows the designers to specify the maximum available tolerance and, consequently, design the most economical parts. GDT communicates design intent. This tolerancing scheme identifies all applicable datums, which are reference surfaces, and the features being controlled to these datums. A properly toleranced drawing is not only a picture that communicates the size and shape of the part, but it also tells a story that explains the tolerance relationships between features.
When GDT Is Used?
Many designers ask under what circumstances they should use GDT. Because GDT was designed to position size features, the simplest answer is, locate all size features with GDT controls. Designers should tolerance parts with GDT when Drawing delineation and interpretation need to be the same
- Features are critical to function or interchangeability
- It is important to stop scrapping perfectly good parts
- It is important to reduce drawing changes
- Automated equipment is used
- Functional gaging is required
- It is important to increase productivity
- Companies want across-the-board savings
