I designed a levitating top. I needed a part machined to duplicate via casting. Most shops want a .dxf file. My design was in FreeCAD, but, sadly, the DXF export feature is broke, and not likely to be fixed soon. See this discussion thread where I complain about this. So I did export, anyway, then had to re-dimension my part in LibreCAD. Now I learned my lesson: if one needs a 3D representation, FreeCAD may be useful. But if one needs a DXF file, LibreCAD is the way to go.