Frenchy,

The nurbs file created from the obj may still present a problem for a few reasons. Its possible there are now intersecting surfaces, even if there were none in the original polygon model. Also, the number of surfaces as well as very sharp, thin areas can present a problem as well.

Typically, when a nurbs model is required it is due to the type of CAM system used to create the mold. Mold makers will typically refuse a polygonal file, but a straight conversion to nurbs may not be acceptable either.