I need to export in dxf or stl format some 3D geometrical constructions I made in Mathematica. But when the exported files are examined in a CAD viewer I see only figures formed out of triangles. Sometimes some triangles appear in unexpected places. Here is an example.
tube = {CapForm[None], Tube[{{0, 0, 0}, {0, 0, 10}}, 5]};
cube = Cuboid[{10, 10, 0}, {20, 20, 10}];
G3D = Graphics3D[{tube, cube}];
Export["G3D.dxf", G3D];
The circle of the tube is decomposed into a polygon and the tube's surface is decomposed into rectangles and the rectangles into triangles. The cube looks better but I do not want it to be made out of triangles but out of rectangles.