Hi wim,

> how do you do that, raise the bent part up a little? I can't activate the show points command, so how is it done?

I'm not sure if it's what Brian did, but to activate the show points command for a solid made up of trimmed surfaces you first need to use Edit > Separate to break it into individual surfaces. Otherwise it would be easy in many circumstances to move surface control points in an areas where there was a joined edge and open up a hole in what is supposed to be a common edge.

There's some more info on this topic on this FAQ entry here:
http://moi3d.com/wiki/FAQ#Q:_Why_does_show_points_work_for_some_objects_but_not_others.3F

And yeah definitely if some pieces of a surface push through itself making a self-intersection that will make the object not make a clearly defined solid volume and that will tend to mess up booleans.

- Michael