[MichaelA]

One thing that I have found with stl files is that you need to refine the facets on the faces before you export. I have done b spline surfaces in the past that look terrible in stl until they have been refined. I've done the refinement in steps of factor of 4 and then redo the export and evaluate. the more you refine the larger the stl gets so you may not want or need to refine to the max allowed. try that and see if that helps.