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About GD&T



What is GD&T?
Geometric dimensioning and tolerancing (GD&T) is an international language that provides clarity in drawing specifications and interpretation. The proper use of GD&T will reduce vague drawings, and the resulting controversy, guesswork and assumptions they cause throughout the manufacturing and inspection process.

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What are the benefits of using GD&T?
Geometric tolerancing encourages a dimensioning philosophy called "functional dimensioning" which defines a part based on how it functions in the final product. It also works well with "simultaneous engineering," a process where design is a result of input from marketing, manufacturing, inspection, assembly, and service. This results in better products at lower cost.

  1. GD&T Improves Communication
    It provides
    uniformity in drawing specifications and interpretation. It reduces controversy, guesswork and assumptions so design, production, and inspection all work in the same language.
  2. GD&T Provides Better Product Design
    It provides designers with the tool to "say what they mean," and by following the functional dimensioning philosophy.
  3. GD&T Increases Product Tolerances
    Under certain conditions, it provides "bonus tolerance" for manufacturing. Through functional dimensioning tolerances are assigned to the part based on its functional requirements which often results in a larger tolerance for manufacturing.

GD&T eliminates the problems that result when designers copy existing tolerances, or assign tight tolerances, because they don't know how to determine a reasonable (functional) tolerance. [Krulikowski, Alex, Fundamentals of Geometric Dimensioning and Tolerancing, 2nd Edition. Albany: Delmar 1998.]

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How does GD&T save money?
Vague drawings lead to errors that become more costly to an organization at each stage of the product development process. If found at the design stage, a vague drawing can be corrected for a few dollars. In the model shop, it can cost hundreds of dollars. However, once a vague drawing gets to production, the expenses escalate quickly. Gaging, tooling, and scrap costs can bring the expense to several hundreds of thousands of dollars.

The proper use of geometric dimensioning and tolerancing will reduce:

  • Drawing revisions
  • Gaging costs
  • Scrap costs
  • Design time
  • Disputes over drawing interpretation
  • High manufacturing costs

Using GD&T correctly improves productivity and will save your organization time and money. Learning to interpret and apply GD&T properly will help you and your company:

  • Save money at the design stage
  • Enable global sourcing
  • Reduce drawing errors
  • Increase productivity
  • Increase part tolerances
  • Assure that mating parts will assemble
  • Eliminate scrap
  • Improve inspection accuracy

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Why is it important to receive proper GD&T training?
GD&T is a complex language. As with any language, it must be specified and interpreted correctly to communicate well. Improper implementation of geometric tolerancing on drawings can cost your company money. However, the right training can provide your employees with an understanding of GD&T and its correct application on the job.

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How does GD&T compare to coordinate tolerancing?
Coordinate tolerancing has several shortcomings when compared with geometric tolerancing, some of those are:

  1. Square tolerance zones
    GD&T eliminates square tolerance zones through the use of cylindrical tolerance zones. The additional tolerance gained can reduce manufacturing costs.
  2. Fixed-size tolerance zones
    GD&T eliminates this shortcoming and provides an additional tolerance that reduces manufacturing costs.
  3. Ambiguous instructions for inspection
    GD&T eliminates ambiguous instructions through the datum system. This allows the designer to communicate the appropriate method of part setup to the inspector.

GD&T communicates precisely and efficiently. Take a look at how a drawing with coordinate tolerancing compares to a drawing with the same level of completeness using GD&T. Click on either drawing for a larger view.

Drawing using coordinate tolerancing

Drawing using GD&T

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Read more about it—

Read more about GD&T and how it will help your organization save money through better communication and increased productivity:

GD&T Resources (Including technical papers that discuss GD&T)

What is GD&T?

A GD&T glossary

"The Tao of Tolerancing," by Alex Krulikowski (ETImail Volume 1, Issue 5)

ETI Provides More GD&T Training Options Than Any Other Company

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This file last modified 07/28/16