Closing sweeps
I haven't worked with Vellum's DXF files, so I can't speak from
experience here. From the symptoms you describe I suspect the DXF
segments are not fully joined together.
MacroModel will create endcaps for solid shapes, not open shapes. Even
if endpoints for two different lines are coincident, they will not be
necessarily joined. The DXF stage complicates things greatly.
I'd try a couple of things:
** Marquee-select all profile segments and choose "Join" from the
object menu.
** If that does not work, open the profile for editing and try to
tease apart the endpoints. It may be that only one vertice is left
open — MacroModel will not "join" these, as it's already a single
line. Solution: option-click anywhere on the profile with the Trim
tool to make two distinct segments, then join them.
** It may be that the DXF is totally funky. I try to avoid the
format, myself. If you can export as PostScript curves from Vellum,
this might be more robust.
** You can always use the Vellum DXF as a template for 2D MacroModel
drawing, or design from scratch in MacroModel itself.
Hope one of these does the trick!