you can create an associative Vector or an associative CSYS in the intersection of the two planes. These can then be used for referencing in a sketch or creating additional geometry like lines.
A Datum Axis is a 'vector', and vectors have a direction. And the direction of a vector is important for things like projections and other vector-related tasks.
The sort of short answer is that if you create and associative line from to plane, it would result in an infinite line, messing up a lot of stuff. Instead as Sebastian5050 suggested, you can create an axis.
An other way to do it (sometime you need to snap on something)would be to zoom out a bit to give you space before you create the line so it's long enough to snap onto.
Hope this Help!
François Bergeron Advance NX User and Surface Expert
When using the intersection curve command and selecting two planes, why is the resulting geometry a non associative line (as it explicitly states)? How can I make it associative?
There are some enhancement requests present already requesting this behaviour/functionality
You can contact GTAC and request to get added for existing ER 2128719.
Sorry to bring an old thread back to life. But one of the main reasons for creating an intersection of two planes is to create a line, or in your case the datum axis. The problem is the datum axis isn't recognized as a curve, so when I try to create a intersection point from a surface and the datum axis I can't do it. I guess you could split up the steps, but it would make the tree messier and if there are multiple intersections, you have to manually select which one you want in a complex curve.
You can use a sketch as per below picture instead of datum axis or intersection line. In this picture I have line on first plane which is collinear with second plane. It is in fact an associative intersection line between first and second plane. Then I extend the line enough to have a real intersection with third plane. Then I create intersection point.