Hi ska234,

> I tried Boolean, or projekt,
> the results are inpredictable...

Is it with this curve here? :



It looks like the problem is that curve is not planar, it swoops around in 3D space a bit, I think because this particular control point is just slightly not in the same plane as the others:


I drew in a plane using Draw solid > Plane > 3pt, then enlarged it slightly using the edit frame in the corner, then I projected the curve onto that plane:



The result is in the attached 3DM file, it should now do a boolean with it - the booleans won't work with non-planar 3D bending curves because they don't know which direction they should be extruded out into with the automatic extrusion processing.

You may need to use View > CPlane to set your drawing plane, or put in a plane like I've done above and draw on that to make sure the points you are placing are all on one plane. Hope this helps!

- Michael