Hi Paul, yes so the problem with the DXF file is that everything in it is made up of polylines. So the areas that look like smooth curves are not actually smooth curves, they're actually hundreds of little line segments.

So that DXF data is not suitable to be used directly for constructing surfaces from, you'll need to create smooth curves from those, either by using the Rebuild command or possibly by drawing completely new curves and using the DXF data as a guide. For the Rebuild command if you join together a sequence of lines that should be smooth you could use the "Endpoints" mode of the rebuild command which will be the same as doing a "Through points" type curve through the polyline vertices.

It would be better if the DXF file contained higher level data in it like at least arcs for circular areas. It would be good to ask your friend if he has the data in that form and could send that rather than only linearized data.

re:
> But unfortunately the boolean operations still do not work or lead to unexpected results, for
> example the difference of the solid and the circle leads to outer tubes glued to the solid.

The "outer tubes glued to the solid" happening in a boolean is a result of the outside direction of the solid being oriented incorrectly. That is one of the things that can happen with degenerate geometry like I was describing earlier and the degenerate faces that I showed in the previous post here http://moi3d.com/forum/index.php?webtag=MOI&msg=9219.6 are still present in this model as well so those still need to be cleaned up before booleans will work properly.

I also noticed an additional thin slivery surface along the front side here:







That might be a remnant of one of the little tiny lines in the original polyline data. It won't be possible to do a proper boolean on a model with these degenerate faces in it.

It looks like I can figure out now what things to select to make the Network so in a bit here I'll examine those curves more closely to see what needs to be trued up to avoid the malformed faces.

- Michael