It looks like only RAW triangle format is supported by Megacut 3d, so someone must be converting the STP file to RAW.

Converting from a nurbs surface (STP) to a mesh has some variables that could end up producing different result depending on which application is doing the conversion, and how the conversion parameters are set.

Its just a thought, but try exporting as an STL. You could check it in netfabb as hep suggested to be sure it is a solid. I would think STL triangles would convert directly to RAW triangles. So theoretically, if you have a good STL, then the RAW triangulated file converted from the STL might be a better method.