Belanger
Automotive
- Oct 5, 2009
- 2,450
I promise that I won't bring up the thing about directly opposed/calipers. ![[smile] [smile] [smile]](/data/assets/smilies/smile.gif)
Last week I had a discussion with a colleague about some of the changes in the 2009 ASME standard. He pointed out something that changed, but I wonder if he's interpreting it as it was intended:
The new standard defines a feature of size (FOS) as "one cylindrical or spherical surface, a circular element, and a set of two opposed parallel elements or opposed parallel surfaces, each of which is associated with a directly toleranced dimension."
His contention is that you can't just look at a drawing of a part with a hole and say that it's a feature of size, because it may lack a "directly toleranced dimension." For instance: a hole might be dimensioned as Ø18, but is has no plus/minus tolerance. We would of course look to the title block tolerance, but GOTCHA -- this is not a "directly toleranced dimension," so the hole isn't a FOS.
I say that's stupid (not to his face) because that leads to the conclusion that we can't put a position tolerance on the hole, because the standard also says that position must be applied to a FOS.
Of course I could be wrong. But any thoughts on why they added the business about "directly toleranced dimension"?
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
![[smile] [smile] [smile]](/data/assets/smilies/smile.gif)
Last week I had a discussion with a colleague about some of the changes in the 2009 ASME standard. He pointed out something that changed, but I wonder if he's interpreting it as it was intended:
The new standard defines a feature of size (FOS) as "one cylindrical or spherical surface, a circular element, and a set of two opposed parallel elements or opposed parallel surfaces, each of which is associated with a directly toleranced dimension."
His contention is that you can't just look at a drawing of a part with a hole and say that it's a feature of size, because it may lack a "directly toleranced dimension." For instance: a hole might be dimensioned as Ø18, but is has no plus/minus tolerance. We would of course look to the title block tolerance, but GOTCHA -- this is not a "directly toleranced dimension," so the hole isn't a FOS.
I say that's stupid (not to his face) because that leads to the conclusion that we can't put a position tolerance on the hole, because the standard also says that position must be applied to a FOS.
Of course I could be wrong. But any thoughts on why they added the business about "directly toleranced dimension"?
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems