3. History of GD&T Part 1


Geometric Dimensioning and Tolerancing symbols have been in use since at least the turn of the century. GDT was especially important during the Second World War in relation to extremely high volume production of Liberty Ships, aircraft, and ground vehicles. The automotive industry, with its high volumes, has also benefited from GDT. The computer industry, in particular, mass storage manufacturers, has used GDT extensively to increase their yields of high-volume and low-margin hard disk drives. Legend says a craftsman named Stanley Parker created the first GD&T concepts while working at a torpedo factory in Scotland during WWII. He started questioning traditional tolerancing techniques after noticing a situation where torpedo parts failed to meet inspection criteria but were actually functional parts. Stanley traced the discrepancy to the fact that 2 point tolerances result in a square-shaped zone of acceptability, but in reality, parts can still function if the tolerance zone is expanded into a circle that encompasses the square’s corners. This additional area allows for 57% more area of acceptability. The origin of GD&T is credited to Stanley Parker, who developed the concept of "true position". It is known that he worked at the Royal Torpedo Factory in Alexandria, West Dunbartonshire, Scotland. His work increased the production of naval weapons. In 1940, Parker published Notes on Design and Inspection of Mass Production Engineering Work, the earliest work on geometric dimensioning and tolerancing. Mr. Parker would later publish a book in 1956 entitled “Drawings and Dimensions”. Mr. Parker’s determination of position (or true position) has since grown to include other concepts including flatness, profile, runout, roundness and much more. The concept of GD&T was adopted by the military in the 1950s and is now in use in multiple industries around the world. By 1957 his idea had developed into a complete organized system of controls and a global standard. True Position and Position Tolerance True Position or Position, as it is referred to in the ASME standard, is one of the most widely used symbols in GD&T. The True Position represents the nominal value or the exact coordinate location of a feature. Any feature on a part having a True Position of 0.000 would be located exactly where it is should be. A True Position of 0.030 means the part feature or designated point is 0.030 off from where it is should be. Position can be defined as the total allowable variation a feature can have from its nominal value or its “true position”. In GD&T, the position is a versatile tolerance that can be used to control location, coaxiality, orientation or axis offset of a part feature or axis. Position tolerance is generally applied to features important to assemblies like holes or slots, and it is often included when performing a tolerance stack. Mr. Stanley Parker Father of GD&T Playlist GD & T - https://www.youtube.com/watch?v=kU2D9... PTC Creo Tutorials 4.0 & 5.0 - http://bit.ly/2LQevUc Assembly - http://bit.ly/2PyJbuF NC Assembly -https://www.youtube.com/watch?v=CPeBs... Solidworks - http://bit.ly/2sx4Jxv AutoCAD Tutorials 2D - http://bit.ly/2HcYWSZ Isometric http://bit.ly/2MJPMA3 Mobile App - http://bit.ly/2xAKN2z Engineering Drawing Tutorials http://bit.ly/2J42w7Q Production Drawing Tutorials http://bit.ly/2NxXuOj Big News http://bit.ly/2JpkP6G ***************************************************************** THANK YOU ALL for your support... ***************************************************************** Follow us on Facebook http://bit.ly/2jDTu1K Instagram http://bit.ly/2kikM1P YouTube http://bit.ly/2zFjLng Twitter http://bit.ly/2ANskAJ Cad Cam Tamil 3265 Subscribers