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GD&T: Design It Right the First Time

October 10, 2001- Six designers and engineers from Lockheed Martin's naval electronics and surveillance systems plant and two more from the Dana Corporation's Long Manufacturing plant recently came to Penn State Erie for a two-day class in geometric dimensioning and tolerancing (GD&T). What they learned in that class was GD&T according to Day-their instructor, Don Day, that is.

President of Tec-Ease, Inc. of Cherry Creek, New York, Don Day has nearly three decades of teaching experience in the area of geometric dimensioning and tolerancing. He defines GD&T as a concise language used on engineering documentation to provide one clear definition of mechanical parts. That language, which involves special symbols, rules, and vocabulary from internationally recognized standards, allows machinists and engineers to design parts correctly on the first try.

"No manufactured, mechanical part is perfect all the time," said Day. But geometric dimensioning and tolerancing allows engineers to design so that as other parts vary, a part is designed to accommodate that variation."

Using multi-media, real-life experiences, and liberal doses of humor, Day teaches his students how to create a "robust" design, one that has a better ability to accommodate variation. With a more robust design, a company will spend fewer of its financial resources on rework, repair, and analysis of the parts it manufactures.

One of the Lockheed-Martin group found the class, titled "Fundamentals of Global Geometric Dimensioning & Tolerancing," on Penn State Erie's Corporate and Adult Learning Web site. Discovering it was less expensive to send six people from their Archbald plant near Scranton, Pennsylvania, to Day's class at Penn State Erie, the six chose Erie.

"Many of the people I talked to said this is the best class around on this topic," said Christopher J. Lauffenburger, one of the two designers from the Dana Corporation. His human resources manager found the class for him and his colleague.

Geometric dimensioning and tolerancing became more important following some of the engineering disasters seen during World War II, said Day. Today most countries around the world use the American Society of Mechanical Engineers' Y14.5M-1994 standard for GD&T.

"I try to give each of my students a way to retain what they learn," said Day. "A year from now, I want them to remember a "sound byte," or a phrase that helps them remember what they learned."

The Center for Corporate and Adult Learning at Penn State Behrend offers a series of courses for design engineers and those who deal with machining parts and interpreting drawings. Advanced Geometric Dimensioning and Tolerancing is scheduled for October 30 and 31; Functional Gaging and Inspection for November 13 and 14; and Tolerance Stack-Ups for December 4 and 5.

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