Does an Unequally Disposed Profile FCF have to point to a surface?

[Blue33]

The question came up to me if it was allowed to attach a profile FCF to a Basic dimension. In ASME Y14.5 -2009 - 8.3.1.1, it clearly states that it must be directed to a surface or extension line. But why is that statement only mentioned in 8.3.1.1 ? why is it not repeated in 8.3.1.2 ? Is there some assumption that these statements in the standard are meant to build on each other and the statement in 8.3.1.1 continues to apply in 8.3.1.2 ?

To me the statement doesn't even need to be there, I feel like it just makes sense that it should be pointing to a surface. If you attach it to a dimension, how do you know which end of the dimension it applies to. I saw in one other post they talk about applying it to a diameter dimension, I can see the exception there if you wanted to, the diameter is only one surface so it's easy to understand what surface the profile applies to. But the standard says what it says, so we comply. I'm good with that. But when it makes a statement in one paragraph and not another, I feel like there is a reason. Why not put this statement in 8.3.1 so that it applies to the entire section?

any help is appreciated.
thanks

 

[Garland23]

I suspect that statement in 8.3.1.1 wasn't repeated in 8.3.1.2 because that 2009 version still allowed an unequal/unilateral profile tolerance to be shown graphically with phantom lines. In that case, the leader wouldn't be "pointing to the surface."

 

[3DDave]

Probably because the committee ... sigh. The closest I can figure is that in the olden times when the offsets were unequally disposed the arrows from the FCF would not terminate on the surface, as they show in the "alternate practice" but then they also show the Model Based Definition depiction that does not have explicit geometry to show the offsets.

Given any fork in the road of description the committee will take it.

 

[greenimi]

Blue33,

Did you notice that in 2018 version they are trying to divorce size dimension from the runout callout? Probably it is the same idea that the runout should be applied to the surface.

 

[greenimi]

https://www.eng-tips.com/viewthread.cfm?qid=464253

Agree or disagree....as you wish