Hi Maciek - yes like Ed writes above usually you don't want to be trying to fill in an empty surface to cap something like that - if you're doing that again it usually means you're trying to build things in a "patch by patch" manner rather than using solids and booleans. With NURBS modeling you would usually get that type of cap by slicing the end of a solid off with a 2D side profile curve, that will leave the imprint of the extruded side profile as the cap.

re:
> I know I am too picky but this is the reason why I would like to switch from poly to nurbs.
> I would like to have perfect shape there.

NURBS modeling may not be the right tool for this purpose though - again as I wrote above NURBS modeling works best when you are able to describe the shape using 2D profile curves.

If the shape needs to be adjusted by a kind of sculpting approach with adjusting the shaping in some very local area, then that usually becomes more related to organic modeling where polygon modeling can work better since polygon modeling can get you that type of fine tuned local sculptural control.

So anyway since you're not working with 2D profile curves or solids very much and since you're also concerned very much with subtle shaping characteristics in a localized area of a surface, it's entirely possible that NURBS won't be the best fit for your needs, or it also may be possible that you'll need to work with the more finicky and advanced type of NURBS surface shaping which MoI is not focused on itself. You may need to take a couple of years of study with Rhino or Alias for example to do that type of thing.

- Michael