GD&T is difficult to get right even though it is very logical. What does “right” mean? Right means several things, but mainly that it imposes achievable, fully function based and only necessary permissible limits of imperfection using absolutely syntactically correct code. But right also means that controls are complete and logical. Many call-outs in the following drawing are syntactically correct but flawed in that they 1) fail to impose the necessary constraints, 2) utilize Datum Features in non-functional ways, or 3) misuse Geometry Control Tools and modifiers. Some are syntactically incorrect as well.
Take some time to study the call-outs below and make notes on each numbered item to log any problems you discover. Then put your notes away and only return to them for a second go at least one day later. When you feel you have a good handle on things, read through the numbered comments to compare your insights with ours. If you differ with our take, please email us your comments, and look for follow-up comments at www.qualitymag.com or in the forthcoming April issue. (This column will now appear quarterly.)