Several months ago I wrote about the requirements for becoming certified as a “GD&T Professional.” (View that blog entry here.) This time, I would like to present some advanced questions. There are two levels of certification for GD&T Professionals: Technologist and Senior. You do not need to be certified at the Technologist level in order to take the Senior level exam. But you would need to be sure that you are very familiar with all the tricky nuances of GD&T! (Plus, you must submit a letter of verification that you have been regularly involved with GD&T for at least five years.) So the following are a few questions that might be representative of the more difficult stuff. Answers are at the end, along with the appropriate paragraph number from the 1994 edition of Y14.5… Sample question #1: The derived median plane of a feature can best be described as: a. a theoretically perfect plane through the center of a part’s actual mating envelope b. a plane that coincides with the centerplane of the true geometric counterpart c. an imperfect plane passing through center points of all line segments bounded by the feature d. an imperfect plane representing the average height of a surface plate used...
Learn MoreI wrote about this a long time ago, but it’s worth mentioning again as the new year approaches (for people who still do New Year’s resolutions!). Regular GD&T users should be aware of the certification process for GD&T Professionals. The American Society of Mechanical Engineers (ASME) has established a credential for GD&T proficiency, called GDTP, which stands for ‘Geometric Dimensioning and Tolerancing Professional.’ It is a testing process that measures your ability to interpret and apply tolerances correctly. It is not a license to practice GD&T (no one can legislate that) but it is something that looks nice on your resume! There are actually two certification levels: the Technologist Level, which measures your ability to read GD&T; and the Senior Level, which tests not only interpretation, but also the application of GD&T to a design. One does not necessarily need to become a Technologist first; some people go right for the Senior Level, although they are required to document at least five years of experience in GD&T (and they have a more difficult test!). If you decide to pursue either level, be aware that the questions on the test come from all sections of the 1994 Y14.5 standard. (UPDATE — summer 2017: They now offer the exam based on...
Learn MoreMany of you may know that GD&T has been around for a long time (see an earlier blog entry about the history of this system). And like anything else that’s been around for a while, things sometimes change.The current American national standard for GD&T is maintained by the American Society of Mechanical Engineers (standard number Y14.5M-1994). Prior to 1994, the previous edition was dated from 1982 (and 1973 before that). And each time, there were a few things that were changed in the rules and symbols of GD&T. So, if you look at the history of the standard, you might guess that it’s about time for another revision — and you would be correct! The Y14.5 committee has been hard at work for the past couple of years, and the next edition is in the review phase. (One sneak preview for you GD&T geeks: a new modifier to indicate unilateral profile tolerances.) It is projected that it will be released for general use in the first part of 2009. As a side note, this underscores why it is important to always mention the specific tolerancing standard in the general notes of your prints, or even as part of your company’s standard title block. If this is not mentioned, then...
Learn MoreFor those of you who actively use GD&T on a daily basis, you should be aware of the certification process for GD&T Professionals. The American Society of Mechanical Engineers (ASME) has established a credential for GD&T proficiency, called GDTP, which stands for Geometric Dimensioning and Tolerancing Professional. It is a testing process that measures your ability to interpret and apply tolerances correctly. There are actually two certification levels: the Technologist Level, which measures your ability to read GD&T; and the Senior Level, which tests not only interpretation, but also the application of GD&T to a design. One does not necessarily need to become a Technologist first; some people go right for the Senior Level, although they are required to document at least five years of experience in GD&T (and they have a more difficult test!). If you decide to pursue either level, be aware that the questions on the test can be taken from any section of the Y14.5 standard. Each chapter has a “weight” that determines the number of questions from the chapter that appear on the test. This means that there is more than just GD&T; you need to be familiar with the nuances of traditional tolerancing as well as the many definitions contained in that standard....
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