Profile vs Parallel & Perpendicular 1

[SpaciouS]

Is there a difference between the following call-outs?

A double segment FCF that states, for example:
Top segment: Perpendicular tolerance of .02 relative to datum -A-
Bottom segment: Parallel tolerance of .02 relative to datum -B-

and

A single segment FCF, for example:
Profile tolerance of .02 relative to datums -A- & -B-

I see this lot and my feeling is if the double segment FCF doesn't state 2 different tolerances, why not use a single segment profile FCF?


Thanks,
SpaciouS

 

[Belanger]

Dave -- suppose I point to the top of a flat box and use profile of a surface with a 0.2 mm tolerance and no datum reference. Also assume that the height of that box is given with plus/minus tolerancing.

This situation would be identical to flatness, and it is a legitimate use of GD&T (there's no requirement that profile be on multiple surfaces). That's all I meant: flatness or profile of a surface can be used there, and they mean the same thing.

For multiple surfaces, it's true that profile of a surface is quite different from flatness, because of the coplanarity effect. But the discussion above was which "level" of symbols to use when trying to say the same thing.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[fsincox]

We all agree really, as J-P is stating, the coplanarity can also imply location not just orientation. We need this difference because in the end you may only care only to invoke multiple flat surfaces and not a coplanarity control.
Frank