Multi part question.
The answer to your first question can be found in your second.
As for how to avoid the problem outlined in your second question, other than going back and enabling the creation of an 'Intemedidate Datum CSYS', you could change the 'Plane Method' to either 'Create Plane' or 'Create Datum CSYS'. Either one should do it.
Not sure what you mean.
I don't want an intermediate Datum CSYS unless there is a compelling reason, hence my question 1.
If I create a sketch with no intermediate datum and the defaults set as described.
Make the datum external.
Then create another sketch on the same datum.
This sketch DOES NOT consume the datum because it is referenced by the first sketch.
Is it possible to set the defaults to not consume the datums?
NX9 & NX10 are different
NX9.0.3 works as I want it to.
no intermediate and no automatic internal CSYS
NX10 is the one that consumes the Datum CSYS if it isn't referenced by other features.
I found it.
The defaults are in different places.
"Automatically Make Datums Internal To Child" is in Modeling -> General -> Miscellaneous
"Create Intermediate Datum CSYS" is in Sketch -> General -> Session Settings
I had found this in NX9 last year and set it then forgot (probably should revoke my "Genius" status)
Still curious as to the thinking behind the intermediate Datums
"Still curious as to the thinking behind the intermediate Datums"
The system is trying to help you avoid unexpected errors later. For instance, if you create a block feature then pick one of its faces to sketch on, an intermediate datum csys is created on the face and the sketch is created on the datum csys. If you later delete the block feature, the sketch will give you a warning or error because its parent (the datum csys) lost its associativity to the block. If you do not create an intermediate datum csys, the sketch will be deleted when the block is deleted.
Previous releases of NX have taught me not to sketch on planar faces. So, like you, I opt to turn this feature off. I really don't need datum csys objects on top of other datum csys objects...
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