True position to one datum11/6/2022 ![]() ![]() Through application of GD&T in your designs the symbolic language soon becomes familiar. When you first examine the GD&T system and the many symbols used for defining part dimensions and tolerances it may seem overwhelming. Why Implement Geometric Dimensioning & Tolerancing (GD&T) The concept of GD&T was adopted by the military in the 1950s and is now in use in multiple industries around the world. Parker’s determination of position (or true position) has since grown to include other concepts including flatness, profile, runout, roundness and much more. Parker would later publish a book in 1956 entitled “Drawings and Dimensions”. He surmised that if the corners were in spec, in most cases the parts that fell within that circular zone resulting from the application of the same tolerance were just as functional. Some of the dimensions of the working parts fell slightly outside of this zone but were within a circle that encompassed the square’s corners. Upon further investigation, he determined that the standard X-Y coordinate tolerances resulted in a square tolerance zone. However, he found that many were functional parts and were being sent to production even though they were technically out of specification tolerance. During his time there he encountered parts for torpedoes that were rejected when inspected using traditional tolerances. ![]() Parker, by all accounts, worked in a munitions facility in Great Britain. The origin of GD&T has been credited to a man named Stanley Parker, who in 1938 developed the concept of position or “true position” as it is referred to today. The standard used in the United States for defining GD&T methodology is ASME Y14.5-2009. The GD&T methodology is currently used in Automotive, Heavy Equipment, Aviation and several other industries. The result is an improvement in communication and part quality. Geometric Dimensioning and Tolerancing (GD&T) is a precise language of engineering symbols that clearly communicate the design intent of the part. It is imperative that the design intent and functionality of the part be clearly communicated between the design engineer and the manufacturing plant. The need for accuracy in part design and manufacture is greater now than ever before. To reduce cost many component parts are currently being sourced from suppliers all over the world. In manufacturing, quality is paramount, costs must be controlled and the processes must minimize waste and use resources wisely. Introduction to Geometric Dimensioning & Tolerancing (GD&T) ![]()
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