3D print /CNC mill with Wolfram Language?

Questions
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1

When I use functions such as Printout3D or Export to export 3D graphics to
“stl” or “dxf” formats, the exported geometric objects are automatically triangulated
even thought the original objects (like cubes) have no triangles. Is there any way to avoid
this automatic triangulation that generates wrong 3D objects when printed or milled?

Commands I use are like

Show[g1 = Graphics3D[Polygon /@ facets1]]

Printout3D[g1, “zono12.stl”, TargetUnits → “Centimeters”,
RegionSize → Quantity[8, “Millimeters”]]

Export[“zono12.dxf”, g1, “DXF”]

The graphic object g1 is a polyhedron without triangular faces, but the output zono12.stl
and zono12.dxf are both triangulated, unfortunately.

Any option to avoid the triangulation?

Thanks in advance for your help, Komei Fukuda

2

Perhaps, a simpler and executable notebook exposes better the problem I am talking about.
So, here I attach a notebook drawing the cube and export the graphics to both
“stl” and “dxf” formats, and then importing the exported files. You can see both
geometric models are triangulated cubes. How can we avoid adding
the diagonal edges in geometric models that are not from the cube.
(Of course, one can delete those edges manually with a proper 3D editor, but it will be
terribly cumbersome for more complex polyhedra.)