Hi WN & Stefano, thanks for the example files. The DXF spline output from CorelDRAW is having problems because of 2 things - one is control points that are stacked up on top of each other and the other is their conversion from beziers to NURBS has one more duplicated knot than what is necessary to chain beziers together.

The stacked up control points means that the curve has a 0 length first derivative. The additional knot making a knot multiplicity greater than the degree of the curve means the curve has degenerate spans in it. CAD programs are generally not expecting to work with NURBS curves that have either of these conditions in them.

However both of these are things I can compensate for and remove during the import. I have got that set up so the next beta will be able to use these curves ok without weird stuff happening although I would not recommend using the PolyArc variation for construction of 3D geometry because it has a lot of little pieces which are close to being tangent to each other but off by just a few degrees. So if you try to construct something off of that you'll end up with lots of little surface fragments. But that's to be expected, it's just that you should consider that to be used only for CNC transfer and not for CAD transfer.

- Michael