next question:

How can I use a "curve on surface" to detach the surface it is projected to exactly along this curve?

------
edit

more precisely said: projecting a curve on surface and trimming away one side of geometry isn´t a prob. but if I project a curve on a allready trimmed surface the surface cannot be trimmed again. also i found no way to trimm a surface after creating a circular fillet with "create curve on surface" checked.

SE says: Warning: Trim: changed to keep originals on; curves on surface have construction history with the dependency on the surface itself.


after deleting history on the circular fillet the 2 surfaces I want to trimm don´t even get highlighted anymore..