Hi Marco,

> ..well, an issue might be, that the circle(green) and the
> surface(red) are actually not on the same plane/level (check
> Top)..there's a tiny tiny gap..

That's so tiny that I don't think it's the issue - check out the message just slightly above, I posted it at the same time you were writing your other post I think.

It definitely looks to me like a display mesh generation problem - the bottom edge is just slightly curved but the display mesh just puts a straight line on it and so the outer and inner boundaries end up crossing each other in generated display mesh and that then makes for the messed up display mesh appearance.

As far as I can tell the actual result of Trim in the NURBS geometry itself is all ok.

There's more explanation and some screenshots to illustrate above.

- Michael