Position of a basic feature?
Position of a basic feature?
(OP)
Is it acceptable to apply a position tolerance to a basic feature?
The form (and orientation) is already controlled by the profile tolerance, however I need to hold tighter control on certain parts of a the profile as they approach LMC.
Something like the image below, using position of the diametric features in addition to the profile of the whole.
Thanks!

Bear with me an my hand-mouse markup.... the red boundary represents MMB of the profile, the red-dashed circle represents smallest diameter that fits within the profile boundary at worst-case position, the red cross represents the center of that red-dashed circle. Now, what I'd like, is to further restrict the center of that circle, so that it must fall within the blue-dashed circle, while simultaneously the form must fall within the profile min/max boundaries.

Hopefully that makes sense! :)
The form (and orientation) is already controlled by the profile tolerance, however I need to hold tighter control on certain parts of a the profile as they approach LMC.
Something like the image below, using position of the diametric features in addition to the profile of the whole.
Thanks!

Bear with me an my hand-mouse markup.... the red boundary represents MMB of the profile, the red-dashed circle represents smallest diameter that fits within the profile boundary at worst-case position, the red cross represents the center of that red-dashed circle. Now, what I'd like, is to further restrict the center of that circle, so that it must fall within the blue-dashed circle, while simultaneously the form must fall within the profile min/max boundaries.

Hopefully that makes sense! :)





RE: Position of a basic feature?
First, I'm assuming ASME Y14.5-2009 is the relevant drafting standard here. If that's not the case, please specify.
I think most would consider it invalid to apply a position tolerance at LMC to a feature with a basic size dimension. For the case you've described here though, I think you can dodge the issue entirely.
In the usual situation of a cylindrical feature with a directly toleranced diameter dimension, a position tolerance applied at LMC creates a cylindrical boundary that must be contained completely within the material of the part. But your profile tolerance already creates a boundary of the same sort, so only the more restrictive of the two actually matters. Why not just adjust the profile tolerance to provide the boundary you want, and forget about the position tolerance?
pylfrm
RE: Position of a basic feature?
I may be just overthinking this. I'll take a look at it with a fresh set of eyes this morning.
Thanks!
RE: Position of a basic feature?
RE: Position of a basic feature?
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Position of a basic feature?
I agree with AndrewTT's suggestion to use a non-uniform profile tolerance if appropriate. Alternately, just use different tolerance values on different segments of the profile as shown in Fig. 8-6.
pylfrm
RE: Position of a basic feature?
Certified Sr. GD&T Professional