Being able to read GD&T correctly on a drawing is a vital skill for product engineers, inspectors, CMM operators, supplier quality engineers, and many others in a large organization. The ASME Y14.5-2009 Dimensioning and Tolerancing Standard is a complex language with many nuances. A mistake in interpreting GD&T can result in throwing away good parts or using non-conforming parts in production. Not properly understanding GD&T can cost organizations millions.
I have seen widely differing estimates on how long it takes to learn GD&T. They vary from two days to two years. This article explains my thoughts on the time it takes to learn GD&T. My thoughts are based on my experience in training thousands of people over several decades. The first thing we need to clarify is what does it mean when someone says "learn to read GD&T"?
What does it mean to "Learn to read GD&T" correctly?
Simply put, to read GD&T based on the ASME Y14.5-2009 standard, a person needs to be able to interpret the following: symbols, rules, datums, concepts, and defaults on drawings. Reading drawings also includes recognizing undefined surfaces or relationships andrecognizing ambiguous or incorrect tolerance specifications.
How long does it take to learn to read GD&T correctly on drawings?
The length of time varies based on the learning ability of the person and how often they use the skill. For a person with average learning ability, and uses their GD&T reading skills at least once a week, I believe the following is a reasonable plan to learn to read GD&T properly.
- A three day class in the fundamentals of GD&T (with a comprehensive skills measurement event to determine how much the students learned in the class.)
- A three day class in advanced concepts of GD&T (with a comprehensive skills measurement event to determine how much the students learned in the class.)
- Six one-hour monthly mentoring sessions using company drawings to discuss drawings, answer questions and provide expert feedback
- Take an annual skill survey (based on your company drawings).
The span of time to take the classes should be within three months. A key event after a training class to significantly increase the retention of the class content is mentoring. Mentoring should be available between the training classes and for three to six months after the training. I also recommend an annual skill survey that uses company drawings as the basis for the questions. Based on the results of the annual skills survey additional training or mentoring may be needed.
The actual training and mentoring time to learn to read drawings with GD&T add up to about 60hrs. The calendar time to learn to read GD&T properly is about one year when training is followed by mentoring. Combining mentoring with training more than doubles the effectiveness of the training.
Training is like learning how to drive while sitting in the classroom, mentoring is like learning how to drive by driving on the road.
To be successful at learning a new skill you need both training and mentoring. Some companies do not invest the time to train their employees completely. I believe that mentoring should be used in addition to training. Companies that skip the mentoring part of skill development often end up retraining employees every few years.