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Don’t Be Tricky with GD&T
(In accordance with the ASME Y14.5-2009 standard)

PDF of this Tip

There is some overlap in the geometric tolerancing symbols. For instance, position at times has the same meaning as perpendicularity. Some people will even proclaim that profile and position can be used to replace most of the other geometric tolerances. This last point could be true if the Standard had been written differently—but it wasn’t.

However, some overlap does exist.

On this part, the design intent requires that the left face of the part be controlled within the tolerance zone shown. Because of the overlap in geometric tolerances, there are four geometric tolerances that might provide this control.

There is an implied 90° basic angle so profile of a surface might work. But, profile of a surface is used to locate surfaces. On a more complex drawing with lots of basic dimensions and because of simultaneous requirements, this could be confusing.

Total runout could work.

Perpendicularity seems to be most descriptive.

In the 2009 revision of Y14.5, angularity can be used to replace perpendicularity. However, on a more complex drawing I could waste a lot of time looking for a basic angle that is close to 90°.

I don’t believe it is nice to try to trick someone else. Using the most descriptive tolerance is more likely to be understood by the people who will be reading the drawing. We have 14 geometric tolerancing symbols because they are instructive, tutorial and they guide the reader in the meaning of the drawing. So, the next time you are feeling a little tricky, save it for your magic show. On the drawing, be as clear as you possibly can.

Back to Tips Tip added Oct 2009