With functional assemblies, multi-part products, or parts with complex functionality, it is crucial that all components work well together. It concerns mostly the overall geometry of the product, while other standards describe specific features such as surface roughness, texture, and screw threads. Once proven as a better operational method, the new system became a military standard in the 1950s.Ĭurrently, the GD&T standard is defined by the American Society of Mechanical Engineers ( ASME Y14.5-2018) for the USA and ISO 1101-2017 for the rest of the world. Driven by the need for cost-effective manufacturing and meeting deadlines, he worked out a new system through several publications. Stanley Parker, an engineer who was developing naval weapons during World War II, noticed this failure in 1940. X-Y tolerancing leaves a zone in which inspection would have produced a false negative because while the hole is not within the X-Y square, it would fall within the circumscribed circle. For example, when drilling a mounting hole, the hole had to be within a specified X-Y area.Īn accurate tolerancing specification, however, would define the position of the hole in relation to the intended position, the accepted area being a circle. ![]() Before GD&T, manufacturing features were specified by X-Y areas.
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