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Readers Respond: GD&T Workshop: Decoding Feature Control Frames

June 21, 2012
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Quality LinkedIn group members analyze the importance of this concept. Read excerpts of the discussion and post your own feedback.

Quality columnist Bill Tandler analyzes the Greatest Design Tool (GD&T) ever by taking a detailed look at the structure of feature control frames. Quality LinkedIn discussion group members offer up their own thoughts on the subject. Post your comment today or join the Quality LinkedIn Group to read the full discussion .



Bob Matthew, principal specialist quality engineer at Boeing Co.:

“Very well explained. GD&T is the communication language of a (mechanical) design engineer and therefore the design engineer should have product knowledge and the process knowledge.”

Roy Jackson, consultant, self-employed:

“Nice to see AMSE has finally updated Y14.5...especially with the Tangent Plane modifier. Of course, that means I have to get an updated copy of Y14.5.

“As stated in the[article], too many companies use their own GD&T ‘system.’ As an SQE (and occasional source inspector), this has always been problematic. I wonder if the ISO equivalent (ISO 1100, if I recall correctly) will be updated, as well?”

Brian Chester, project general manager at Aapico Hi-Tech:

“GD&T, now there is a subject. I wonder how many people other than the design engineer understand what this is all about. I learnt GD&T as a design draftsman more years ago than I like to remember, and have kept abreast of it ever since all be it I think I may need a refresher.

“But the question I pose is: How many people outside the design office really understand what it all means? I have seen many times when an inspector or for that matter a tool maker or production engineer comes across a GD&T tolerance or reference they are lost in fully understanding what it really means.

"GD&T is used extensively throughout the auto industry but like all tools unless it is used correctly and then understood by all then it falls over.

"It is not only the design engineer that requires the knowledge but all people in the manufacturing chain, unless all understand it, it will be cast of as a symbol on a drawing that nobody understands and eventually takes little notice of thus effecting the quality of the product.

"Second question, if a GD&T tolerance is shown on the drawing what is the tool makers tolerance on the tool to comply with the requirements. It is not make the tool to meet the GD&T tolerance shown on the drawing by the way. Not from my training, anyway."

Dana Donahue, ASQ-CQE, CQA, supplier quality engineer at BSH Home Appliances:

"I wish there were more of us T-Rex's in industry, teaching and guiding the young "up and comers". I was lucky enough to have started in Mfg. in the mid 1970's, when we had lots of "old" dino's.....and if you were respectful and paid attention they would pass on their knowledge. I still can estimate the hardness of a material based on the color of the spark or use clay to get a cast of a hard to see radius in a machined casting. Hand scraping of machined surfaces using Prussian Blue and a carbide always amazed me!”

Tom Johnson, environmental health and safety director at Kirtland Products:

“While GD&T is a code, it is also appropriate to think of it as a language. That is, there may be multiple ways to specify a feature and still achieve the same result. The key factor is design intent and what the designer wanted to achieve. Designers do not always let their intent be known, trying to let the GD&T do the speaking for them. This does not always work, unfortunately.”

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Dimensining and Tolerancing

Steve Wartinger, Staff Engr, Tool & Eqpt Design, Conceptus, Inc., Mountain View, CA
July 11, 2012
Mr. Tandler and I became acquainted many years ago here in the Silicon Valley. I have the highest regard for his knowledge and skill as an engineer and instructor. I, too, taught GD/T at a local community college, for several seasons. An approach I fostered to grasping-the- essence/significance of the system, was simply to write out, long-hand, exactly the intent of the geometric conrol; just a simple statement of intent - including a noun and verb; think it through. I believe students have similar thought-process troubles with computer aided drafting and good ol' drafting practices - too much to think about at once. Currently, most drafting courses and practices are accomplished via CAD. My belief is that the individual ought to learn to think and practice with pencil in hand - FIRST; then graduate to CAD. The result would be better drafters and engineers, in my opinion. Students must acquire the thinking skills needed in many aspects of our discipline. Henry Ford once said -'Thinking is difficult, that's why so few engage in it'. Same theory should be applied to GD/T. Let's not be so enamored with immediate application of symbols - just yet. We in engineering must ask ourselves how the details relate to one-another in the Design Layout. (How many of us 'do' the Design Layout?); think thru 'real' requirements; take councel; remind ourselves of process capabilites while controlling the urge to impose tight constraints. As for tool-maker's tolerances - 30 - 50% of the product-part; for gaging - 10%; slip fit no shake (SFNS) for pins in bushings, etc. Allow the tool maker to do his job - these guys deliver, right on the money! Hope this makes some sense. ... and remember - are we teachable or 'stiff-necked'? Be teachable. Good job, Bill - keep your hand in the game. You are providing a path for the success of many.

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