skewed planes as datum features

[cjccmc]

I'm working on a set of curvey parts that do not have the easy orthogonal surfaces to pick as datum features. There are flat surfaces that are functional but they are at skewed angles to each other. If I pick one for A and one for B does that lock up all degress of freedom? Also, how do you determine the origin and orientation of the datum ref frames from such datum features?

 

[CheckerHater]

Somehow like this:

 

[cjccmc]

CH: that provides some insight as to how ASME says it needs to be done. If you were to follow that example in the case of two "skewed" planes, one being datum A and the other B, then it would mean that another datum feature is needed to define the remaining plane for the DRF. Since A & B intersection is a line, I guess movement along that line means that two non perpendicular planes do not lock up all degrees of freedom and a third feature is needed for the tertiary datum.

Can a hole whose axis does not intersect the line of intersection of A & B function as a tertiary datum feature? If so how would you locate the third plane of the DRF?

 

[Tarator]

Also remember, any mathematically defined feature can be used as a datum (even in the 1994 version). So if it is in the CAD, it is mathematically defined.