Fig 4-4 in ASME 2009

[waqasmalik]

Hi all, please find the attached figure naming waqas, its from ASME 2009 Version of the standard.
Since Rule # 1 does not control perpendicularity so our part could be produced as a parallelogram.Hence perpendicularity control must be specified.In the attached figure, what prevents the part from becoming parallelogram? Profile of surface i guess. Am i right?

My second question is that " Position tolerance on datum feature D has been applied with respect to datum feature reference A and B.Datum axis B is the axis of the related actual mating envelope( orientation constrained minimum inscribed cylinder with
respect to A) so the circular tolerance zone of 0.8 is centered on datum axis B.When i omit datum feature reference A from the feature control frame of datum feature D them my datum axis ( lets say its B1) is the axis of unrelated actual mating envelope and circular tolerance zone of 0.8 will be centered on this B1 axis.If datum feature B tilts in its worst case to 0.060 then the axis BI will be tilted at certain angle to B and this angle will continue to increase as it proceeds towards the datum feature D.Am i right in all this? Plz correct me if i am wrong.Sketch naming waqas 2 has been attached of all this description.
Bundle of Thanx in advance

Regards

waqas

 

[waqasmalik]

second image

 

[pmarc]

Waqas,
This part can't be extreme parallelogram, because datum feature B is controlled by perpendicularity tolerance wrt A. Profile of surface controls distance between right and left face of the part. Orientation of two faces is controlled by parallelism tolerance 0.5 wrt A.

You are right about second part of your question - no A in position feature control frame for datum feature D means the perpendicularity of that feature's axis wrt datum plane A is not controlled at all.