Origins and GD&T / History of GD&T
Geometric Dimensioning and Tolerancing (GD&T) [ASME] and Geometrical Dimensioning and Tolerancing (GD&T) [ISO] has been used since the 1940s. GD&T was developed to address the many problems that had been encountered over the years as companies tried to describe their part geometry. They realized that it was very difficult to describe how much variation was allowed on their part and assembly geometry. More importantly, they found that everybody that read their drawings had a different interpretation of their Dimensioning and Tolerancing specifications and the limits they created. This led to mistakes, rejected parts, non-conforming parts, wasted time and money, and costly delays in production.
Companies found that they had difficulty clearly describing the size and form limits of individual part and assembly features. For example, it wasn’t clear from their drawings how flat certain surfaces had to be, and in other cases it wasn’t clear exactly what the requirements were for the size and form requirements for a hole.
They also found that they had even greater difficulty describing how much variation was allowed between features. For example, it was even more difficult to understand how much a hole was allowed to tilt relative to a surface (or which surface it was allowed to tilt relative to), or how much variation was allowed between related surfaces. GD&T was developed specifically to address these problems and eliminate the ambiguity that using the traditional Plus and Minus Dimensioning and Tolerancing introduces. The primary purpose of GD&T is to make the drawing specifications clear and unambiguous and to eliminate the problems, confusion, scrap, rework and loss of profits that results.
We Can Help You Properly Implement GD&T in Your Enterprise and Supply Chain
Many companies ask us about their Dimensioning and Tolerancing problems, and many of them want us to help them understand why they are experiencing problems with their parts and assemblies. In most of these cases, their problems are a result of the confusion generated by using Plus and Minus Dimensions and Tolerances to locate and orient features. The majority of these problems can be solved by proper application of GD&T and making sure their staff and their suppliers are trained to understand what it means.
The ASME Y14.5-2009 Dimensioning and Tolerancing standard is the result of many years of experience in industry and research and development by various standards committees. It is the latest in a long line of U.S. Dimensioning and Tolerancing standards dating back to 1943. The standard answers many of the questions that arise from using Plus and Minus Dimensioning and Tolerancing to define Features of Size, and it contains extensive material describing how to use Geometric Dimensioning and Tolerancing to describe the form of features and the relationships between features.
Aside from cases where the process capabilities are inadequate to meet the tolerancing specifications, the vast majority of problems relating to out-of-spec parts are a result of improper Dimensioning and Tolerancing specifications. The majority of these cases are where Plus and Minus Dimensioning and Tolerancing was used to describe the relationship (orientation and/or location) between features. There is simply too much ambiguity in Plus and Minus Dimensioning and Tolerancing – it leads to multiple interpretations of what the drawing specifications mean, and there is simply no way to say which of these interpretations are correct.
Perhaps the most pressing problem that GD&T corrects is in clearly defining how Features of Size (such as holes and pins) are located or oriented to other features on the part.
GD&T Presentations and Training for Management, Procurement, and Supply Chain
We offer GD&T presentations and training for management, procurement, and supply chain managers. We work to clarify why GD&T is the only legally-valid way to dimension and tolerance parts and assemblies, so you have a clear understanding of the pitfalls of using plus and minus dimensioning and tolerancing why you need GD&T. If your organization is not using GD&T or not using GD&T properly, your ability to identify, understand, quantify, and solve problems related to variation and variation management are diminished. Simply put, you are wasting time and money. Let us help your organization do it right.
In fact, that’s our motto: Get-it-Right™.
We also offer a White Paper that presents the benefits of using GD&T versus Plus and Minus Dimensioning and Tolerancing, and it clearly explains why GD&T is so important for you to adopt.
Please Contact Us to set up a management presentation or for a complimentary copy of our White Paper.
Bryan R. Fischer is President of Advanced Dimensional Management LLC in Sherwood, Oregon, offering leading-edge training and consulting in Dimensioning and Tolerancing, GD&T, Tolerance Stackup and Analysis, Dimensional Management, Design, Standards and Quality.
Bryan and our other trainers are ASME Certified Senior Level GD&T Professionals. Bryan and others are members of several ASME sub-committees. Bryan a member of the ASME Y14.5 Sub-committee Support Group, the US TAG to ISO TC213 which develops ISO GPS (GD&T, etc. standards, and directly involved in developing the ASME Y14.5 standard and ISO 1101 and 5459 standards. He is recognized as a leading authority in the theory and application of Dimensioning and Tolerancing, GD&T, Tolerance Analysis and Stackups and Dimensional Management.
He is a published author, having written several books on Geometric Dimensioning and Tolerancing, Tolerance Stackups and Tolerance Analysis. His books “The Journeyman’s Guide to Geometric Dimensioning and Tolerancing: GD&T for the New Millennium” now in its 12th revision, the GD&T Update Guide: ASME Y14.5-2009: Changes, Improvements, and Clarifications, and the GD&T Visual Glossary will be used as the basis for the seminar. His book “Mechanical Tolerance Stackup and Analysis,” now in its second edition (CRC Press 2011) is the preeminent title on Tolerance Stackups and Tolerance Analysis available.
In 2008 Bryan revised the 11th Edition of The IHS Global Drawing Requirements Manual (the DRM), and wrote an extensive new chapter on using Digital Data as Design Deliverables and Annotating Solid Models. This is a book in itself, and is based on the ASME Y14.41-2003 and ISO 16792-2006 standards, and includes material not found in either of those standards. We are leaders in 3D Model-Based Product Definition (3D MBD) and 3D Model-Based Enterprise (3D MBE) Implementation techniques training and consulting. Check out our Books and Materials section and our 3D PMI, MBD, and Advanced Applications of Solid Modeling Seminar and other 3D MBD and 3D MBE courses for more information.