Feature Control Frame composite vs multiple single segments

[Vindicit]

Whats the difference in the feature control frame of a composite tolerance vs multiple single segment tolerances? I got this on a drawing and these 2 flatness tolerances are considered Datum A. To me the bottom example feels like it was a mistake by the drafter as most of the drawings that came in at the same time by the same people looked like the above example.

 

[3DDave]

There's no definition for interpreting composite flatness tolerances under Y14.5. The lower version, with separate single callouts looks correct, but there should be a note indicating the flatness requires part restraint. There is no way to generally refine a flatness tolerance.

 

[Belanger]

Agree with Dave, except to say that there is a way to "refine" a flatness tolerance with what they call a unit-basis control (a smaller flatness tolerance for every random section of 10x10, for instance).

Your question is valid, but it's just that the term composite is more for position and profile controls.

 

[3DDave]

That's a local refinement, not a general refinement; it doesn't affect the overall flatness.

 

[mkcski]

1.4(m) Unless otherwise specified, all dimensions and
tolerances apply in a free-state condition. For exceptions
to this rule see paras. 4.20 and 5.5.

Given Fundemental Rule 1.4 (m): I thinking the upper frame is the max "free state" flatness effor based on (F) symbol from paragraph 3.3.20 and the lower frame is the max flatness error in a restrained condion that is not defined - at least from the info given. Maybe??

Certified Sr. GD&T Professional

 

[drawoh]

Vindicit,

The single flatness window symbol could mean something. This can be significant when you specify positional tolerances. I would guess that in this application, both are valid and that both mean the same thing.

There should be a note explaining how your datum face is being clamped. Otherwise, your .005 has no meaning.

--
JHG

 

[Vindicit]

Thanks guys, your comments have been helpful.

 

[Belanger]

3DDave.... uh, OK.
I didn't know your use of the term "general refinement" was so particular.