Hi David,
Thanks for your quick reply!
I do only now realize that those flat parts are actually correct...
The part moves away from the YZ-plane, so at some rotations there is nothing to mill with the mill constrained to the XY-plane...
Which would mean I'd need a different solution for actually milling a shape like the one in your example. Because you'd need the mill to leave the XY-plane...
Thanks for taking the time for me though. Much appreciated. And your tool is still very helpful to me in other situations.