Some results from saving cubes in MoI as .obj, and applying create subD:

Attached are the solid models 4Box01.3dm and 4Box02.3dm, created in MoI, derived from the Box tool, which appear to be identical, but are not. Saving as .obj files and then using create SubD results in different SubD models. There are at least two additional permutation models, which result in different .obj and subD results. Saving some .3dm and reloading them, then saving to .obj and applying SubD may result in different results than the pre-saved .3dm to .obj save.

Creating 4Box02.3dm:
1. Create a box.
2. Use circular array to create 4 boxes touching by their edges.
3. Change color and Separate the inner 4 faces, leaving the outer 20 faces joined into 4 open cubes.
4. Select the 4 open cubes, excluding selection of the inner 4 faces, and join.
5. Select the 20 face outer joined surface, then select the inner 4 faces one by one. (they can be selected in different orders), and join to form the 24 face solid.
6. Save as .obj.
7. Use create SubD on the .obj file to yield 2 or 3 subD objects.

Creating 4Box01.3dm:
1. Create a box.
2. Use circular array, or copy to create 4 boxes touching by their edges.
3. (May change color of the 4 inner faces.) Select all 4 cubes and Separate.
4. Select the 20 outer faces and join to a joined surface.
5. Select the outer 20 face joined surface, then select each of the 4 inner faces, one by one, and join to one solid. (Note that selecting the 4 inner faces by their color, or by their name, does not give the same result.)
6. Save as .obj.
7. Use create SubD on the .obj file to yield 1 subD object.

Using meshlab, it turns out that the 4Box solids are not manifolds, and that they have different non-manifold edges. The meshlab command:
Filters/ Cleaning&Repairing/ Remove Faces from non manifold edges,
shows the difference between the two .obj solids.

(Three boxes may be arranged around a central triangle with comparable results.)
- Brian
Deleted this old attachment, for space.