I've created some relation expression between dimensions in the sketch, then I've deleted dimension. After I dimensioned again, NX create new expression.Now I've P3, P4 e P5 that are expression not used but not deletable. Why ?
The expressions belong to the point of your Datum Coordinate System(1) feature. They define the coordinates (0,0,0) of an intermediate Datum Coordinate System created when you inserted your Sketch. Right click Sketch(2) and choose Make Datums External to see the feature.
it's true and if I edit the value in the expression, the coordinates (0,0,0) of an intermediate Datum Coordinate System change. But if I change the value via interface, NX generate new p13_x, p14_y and p15_z expressions and the old P3, P4 e P5 expressions become orphan. Only a part clean up clean the part.
How a simple user can know if the part need a part clean up command to clean un-used expressions.
This is caused by the fact that the origin of the sketch in your part is not associative to the CSYS you sketched on. I do not know how this happened (associative origin turned off in an older release?), but it can be fixed by reattaching the sketch to the datum CSYS origin.
We enhanced create sketch so this will not occur in the future.
PS. You should be more careful in when selecting objects, the mid point constraints are not attached to the internal sketch origin but the the point of the datum CSYS. I assume you were not aware of that.