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What Is GD&T?
GD&T stands for Geometric Dimensioning and Tolerancing. It is a system of symbols, rules and definitions used to define the geometry of mechanical parts.
GD&T is one of the most powerful tools available that can improve quality, reduce cost and shorten delivery time. All of this is possible when the concurrent engineering team is involved with the creation of the drawing. The drawing is a common thread that ties these groups together. They all are involved with the engineering drawing. GD&T on the drawing must first and foremost capture design intent. However, the best design in the world is worthless if it cannot be produced. That is why it is necessary for production/vendors and quality to be involved with the requirements that are placed on the drawing. When they are not involved, the drawings often have overly tight tolerances and result in non-producible parts. At least not producible at the quality level, cost and timeliness expected by industry.
Nearly every company in the United States and many companies around the world use the ASME Y14.5 standard on GD&T. There is an ISO standard but it is in a state of flux. Because of this the Y14.5 standard is recognized and used around the world.
In short, GD&T is:
- Mathematical definition (ASME Y14.5.1)
- A National Standard (ASME Y14.5)
- An International Standard (ISO 1101)
There is no other standardized way to control the geometry of parts. The old methods were never standardized. Many people thought they knew what the old method meant. The problem was that many people interpreted the drawing differently. GD&T is standardized and mathematized which means that anyone who knows the Standard, knows what the drawing means. GD&T is today's Print Reading. Anyone who creates, approves or uses the drawing should know how to read the drawing. In today's world, if you do not know GD&T, you do not know how to read!