GD&T Q&A session - Interpreting FCF (Feature Control Frame)

[CycleMike]

In Reply to Parent Post by CycleMike

This print wouldn't have made it past our advance quality planning review. If the print isn't clear enough, or we don't know which standard the print was drawn to, we'd have to find that out first.

I'll leave it at this.

[justncredible]

And I would have never questioned it to begin with.

[ewh3356 - 2010]

Wow... much ado about nothing.
I'm in the camp that claims that a diametric true position is a legitimate control for the square hole and the slots. The FCF is locating the center of the feature to be within a certain diameter. Can the center be determined? Then why can't it be controlled to within a diameter? The orientation of the feature could be controlled by an angular block tolerance. Perhaps it was designed allowing for a circular tolerance zone, and a rectangular tolerance zone using the same tolerance would be too large. You may not be able to imagine a situation where this could be the case, but this would definitely be something to check out with the designer before casually ignoring the diameter symbol.
That said, I do agree that this is probably not the intent of the design, and is a poor way to locate the features.
It is a yellow flag to me when "old pros" fall back on their years of experience instead of using specifics in the standard to prove their point.