3ds Max 2010 - Mesh/polygon won't use smoothing groups unless vertices are welded

I’ve got several imported meshes in Max, and when I attempt to smooth a group of faces, it won’t take effect. If I weld together all the vertices (with an extremely small threshold), the smoothing groups take effect and I can modify them freely thereafter. The trouble is that welding the vertices causes deformation of the mesh, creating smoothing errors that look as bad as no smoothing at all. The same goes for polygons.

Visually: (click to view)

  1. No smoothing applied
  2. Selected faces and applied smoothing group 8
  3. No visible smoothing
  4. Weld all vertices with .001 threshold, smoothing is now visible, deformation is circled
  5. Select faces and switch to smoothing group 5
  6. Selected faces are now in their own smoothing group

Is there a way to weld the vertices without deformation of the mesh/poly, or does someone know why this would happen to begin with, and how it can be fixed?

This might not work in your case, ( and sometimes causes other problems elsewhere), but I have ran across this problem as well. I just export the model to a different file type, import the new file, and apply smoothing groups to it. Try this with the pre-welded model first.