When it comes to learning geometric tolerancing, some people opt for buying a book to read, or nowadays they can sign up for an online self-study course. The advantages to this are twofold: the ability to study at your own pace, and it is usually less expensive for an individual than a full training seminar. Traditional training with an instructor in the same room is sometimes more expensive (not always, depending on the number of students) but the huge advantage here is the ability to ask questions and have the instructor relate the concepts to your specific needs. If people from different areas attend the class together (design, CMM inspection, manufacturing), then they can also learn from each other and be in sync when GD&T issues come up in the future. I have dabbled in online training in the past, but we have not pursued that option in depth because we have found that the best service to our clients is to work with them directly to help digest and retain the material. Numerous times people have told me, “I have tried learning about bonus tolerance in the past, but the way you explained it made sense instantly!” While teaching a GD&T concept, I can get feedback — someone...
Learn MoreAnother question came in recently, having to do with basic dimensions and their use with datum targets. If you are up to speed on GD&T, you should know that a basic dimension is any number enclosed in a box: The purpose of this is to show a theoretical dimension, without any tolerance. (Even a general title block tolerance does not apply!) Instead, the feature that is being dimensioned will have some GD&T that provides the actual tolerance for manufacturing. Now here’s the question: datum targets are usually located using basic dimensions, but there is no GD&T to provide a tolerance: Is this legal? What governs the accuracy of where those datum targets are? Yes, it is legal, and here is the key: Geometric tolerances are applied to features of a part. A datum target is an imaginary point, line, or area that is simply used for fixturing or gage setup. It’s not the responsibility of a product drawing to worry about the tolerancing of a gage or fixture! The ASME Y14.5 standard says it this way in paragraph 4.6.2: “The location and size, where applicable, of datum targets are defined with either basic or toleranced dimensions. If defined with basic dimensions, established tooling or gaging tolerances apply.” Thus, most GD&T...
Learn MoreSAE International (the Society of Automotive Engineers) has recently announced its winners for this year’s awards, and among them is John-Paul Belanger, from Geometric Learning Systems. Mr. Belanger is receiving the Forest R. McFarland Award for outstanding contributions toward the work of the SAE Engineering Meetings Board in the planning, development, and dissemination of technical information through technical meetings, conferences, and professional development programs. This is in recognition of his years of involvement in GD&T training for SAE to their network of members and clients. “I am proud of my membership in SAE, and am happy to be able to work with them as an instructor in GD&T. They serve as a valuable resource for the automotive industry, and I am grateful for this recognition.” John-Paul has been involved in training for GD&T and Tolerance Stacks for over fifteen years. He is a principal for Geometric Learning Systems, a consulting firm specializing in GD&T...
Learn MoreWhen investigating training in the topic of geometric tolerancing, one thing you’ll probably notice is the various options for the format of a class. The two major types are public classes, sometimes referred to as “open enrollment,” and on-site training. There are advantages to each. A public class is ideal for individuals seeking to learn GD&T. Some companies may only have one or two people that need training, and sending them to a public class is a great way to deepen their knowledge (and it’s nice to get a couple of days out of the office). An on-site class is dedicated to a company or a group within that company. This has two distinct advantages: First, because an on-site is targeted to one group, the instructor is able to customize the presentation. I always invite participants to bring sample drawings to class to help generate discussion and get them to think more about the correct application of GD&T to their actual parts. The second advantage is cost. The on-site package is usually less expensive as compared to individual tuitions at a public course, although there is a threshold number (usually around 5 or 6 people) needed to make the savings apparent. If you are considering any type of GD&T...
Learn MoreIf you are familiar with GD&T, you’ve probably heard of “virtual condition.” It is a number that represents a worst-case combination of a feature’s size along with its geometric tolerance. For instance, suppose we have the following example of a hole, with a size tolerance of 6 ± 0.2 mm: The worst case for assembly purposes would be the smallest hole that is also out of position: 5.8 – 0.3 = 5.5. This virtual condition represents the “usable” area that the mating pin must fit within: Now, virtual condition is usually easy to identify with — think of assembling pins and holes together. But sometimes I may be concerned about the outside boundary, created by the largest hole that is also off center: This outer boundary, called resultant condition, is calculated as: LMC + stated geo tol + any bonus, or: 6.2 + 0.3 + 0.4 = 6.9 mm. This represents the area where any portion of the hole’s edge may possibly fall.This resultant condition is not of concern when dealing with assembly of holes and pins! But suppose we are simply punching...
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Watch John-Paul talk about the benefits of GD&T training courses.