Multi-segment FCF (refinement)
Multi-segment FCF (refinement)
(OP)
Are the segments of a multi-segment FCF to be written from top down (& not bottom up)
And if so
Does the lower segment of a multi-segment FCF have to be a refinement of the preceding segments (like a composite FCF)?
And if so
Does the lower segment of a multi-segment FCF have to be a refinement of the preceding segments (like a composite FCF)?
Thanks,
Sean





RE: Multi-segment FCF (refinement)
I think the short answers to your two questions are "yes" and "yes"...
As a matter of practice, feature control frames are stacked with the one having a larger tolerance, and more constrained tolerance zone, on top, then as you go down in the stack, the tolerance values become tighter and the tolerance zones are less constrained, based upon the type of tolerance and/or the datum features referenced.
This means a location tolerance that references datum features that constrain all 6 degrees of freedom would be listed first, then maybe a location tolerance with fewer datum features referenced, then an orientation control, then a form control.
Having said this, I don't mean to imply that such a stack of feature controls frames is a common need though... Most common is that a size tolerance provides sufficient form control, and a location tolerance provides sufficient orientation control, or if using profile, all of the needed location, orientation, form, and possibly size, control may come from a single feature control frame (as I expect you already know - I add this just for the sake of attempting to answer this completely).
Even though stacking feature control frames with tighter values as you go downward in the stack, is normal practice, and to avoid meaningless controls as you go downward in the stack there are some dependencies to consider regarding datum features referenced (for instance, identical datum reference frames would not be specified for two stacked position tolerances), the requirement imposed by each is separate and independent from all others... Technically you wouldn't really have to stack the feature control frames following a normal convention, except section 3.4.5 and figure 3-26 of ASME Y14.5-2009 (or the same section and figure 3-22 in Y14.5M-1994) imply this convention as a "shall" type of requirement.
Dean
www.d3w-engineering.com
RE: Multi-segment FCF (refinement)
Peter Truitt
Minnesota
RE: Multi-segment FCF (refinement)
Thanks,
Sean
RE: Multi-segment FCF (refinement)
Peter, do you disagree with both Dean and I?
Thanks,
Sean
RE: Multi-segment FCF (refinement)
Frank
RE: Multi-segment FCF (refinement)
Peter Truitt
Minnesota
RE: Multi-segment FCF (refinement)
Even though, to me the standard is a little unclear, I feel segments should be stacked one below the other and that the lower segment is a refined tolerance to the upper.
Thanks Fank.
Thanks,
Sean
RE: Multi-segment FCF (refinement)
Do not fret, it really did not matter until troublemakers like myself tried to actually use this stuff. We wanted datum restatement to imply orientation only. The 1982 standard was not clear on this as they were only showing restatements of the primary datum which when used traditionally implied orientation only.
FYI, It is my understanding the ISO does not agree with ASME on this point, either. Here is one area I am firmly with ASME as a composite framework vs separate statements now gives us additional options, the ISO way I do not gain anything.
Frank
RE: Multi-segment FCF (refinement)
I am specifically refering to composite tolerances. Otherwise, as I have already stated, I do not believe it functionally matters.
Thanks, Spacious.
Frank
RE: Multi-segment FCF (refinement)
Thanks,
Sean
RE: Multi-segment FCF (refinement)
I do not believe the order of the tolerance statements was that critical until the composite issue I mentioned, above.
Frank
RE: Multi-segment FCF (refinement)
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems