cilindrosolido=Cylinder[{{0,0,0},  {173,0,0}},8.5];
huecocilindrico1=Cylinder[{{85,0,0},{85,0,9}},5];
cilindroagujerado1=RegionDifference[cilindrosolido,huecocilindrico1];
region3dfinal=RegionPlot3D[cilindroagujerado1,PlotPoints->100]

Printout3D[region3dfinal,"miflauta.stl"]

FileNames["*.stl"]

Directory[]