Hi blankidea,

> Thanks again for your tip. Works great a few second and
> the boolean operation was done. Even if I don't know
> what the operation does...

Check out here for some more general information on how "underlying surfaces" work with NURBS objects:

http://moi3d.com/faq#Q:_Why_does_show_points_work_for_some_objects_but_not_others.3F


But it might be better if boolean union used some different method to get the bounding box rather than one that included the full underlying surface size - the reason why it uses that one right now is because it's very quick to get it.

- Michael