Friday, April 15, 2016

Geometric Dimensioning and Tolerancing 101 for Manufacturers

Geometric Dimensioning and Tolerancing 101 for Manufacturers

It would be wonderful if we lived in a world where each part perfectly matched the design model. Unfortunately, there is no such thing as a perfect world! Although imperfections are a reality in the manufacturing world, it’s crucial to work towards continuously reducing project inadequacies. It is equally as important to specify a tolerable level of deviation from the ideal before a part becomes no longer usable. The problem many manufacturers face involves the lack of a common language to arrive at acceptable deviations and reduce imperfections.  

Understanding Geometric Dimensioning and Tolerancing (GD&T)

Geometrical Dimensioning and Tolerancing (GD&T) is a systematic way of defining and communicating tolerances. It uses a symbolic language with rules and principles for engineering drawings and computer-generated 3-D solid models to explicitly describe nominal geometry and allowable variations.

The language of GD&T consists of dimensions, tolerances, symbols, definitions, rules, and conventions precisely communicating the functional requirements for the location, orientation, size, and form of each feature of the design model. It ensures everyone is speaking the same language, including common definitions of the features or parts being discussed.

GD&T Benefits Manufacturers 

GD&T provides manufacturers with:
  • Increased Cost Savings
  • Lower Rejection Rates  
  • Centralized Record Keeping
  • Improved Design Clarity, Fit and Inspection Methods
  • More Realistic Tolerances
  • An Easily Understandable Compact Language

The common language enables designers to express themselves with greater accuracy when designing models. The production department understands the designer’s specification and intent because it uses the same language. Quality inspectors use the language to determine setup requirements. GD&T delivers the level of quality required and is a great insurance policy against shoddy fabrication, expensive rework and costly delays.

Getting Started

The critical first step in the implementation of GD&T is providing training to all employees who interpret engineering drawings. It is critical that everyone involved has a sufficient understanding of the GD&T because a system is only as strong as its weakest link. Designate and train experts from the design, manufacturing and quality control departments. These internal experts help resolve tolerance issues and provide guidance to the rest of the employees.

BOTTOM LINE: Implementing GD&T helps improve output. GD&T is rumored to be complex but the process is actually simple. The complexity of your parts drives the complexity of GD&T. Consider this - many complex interrelated features require a precise language capable of describing allowable variation in size, form orientation and location relationships. The more intricate your output is, the more it begs for GD&T!

Let MMTC Help

MMTC offers GD&T services and training to Michigan manufacturers. For more information, call 888.414.6682, visit or email Start reducing inadequacies in this imperfect world!

Since 1991, MMTC has assisted Michigan’s small and medium-sized businesses successfully compete and grow. Through personalized services fitted to meet the needs of clients, we develop more effective business leaders, drive product and process innovation, promote company-wide operational excellence and foster creative strategies for business growth and greater profitability. Find us at on the web at

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