As many educators turn their students to 3D printers as part of their regular STEM design and fabrication routine, it is a natural consequence that not every print turns out perfectly.  Here and there, users are finding strange errors popping up that appear inexplicable when it comes time to print. At seemingly random times, what appear to be perfectly rendered .stl files will not print out without major problems.  Of course every teacher and student who is familiar with  3D printing machines knows there is a fair amount of standard troubleshooting to be done, and becoming competent at using these complex devices means being comfortable with fixing everything from mechanical glitches to experimenting with multitudes of  printing parameters. In spite of these efforts, the process of creating a mesh from an .stl file and translating it into gcode can result in error messages and a bad print-even though the rendered image and gcode look fine. Reanalyzing the original CAD file does not always provide an answer to what is wrong. One tool that you can use before investing time and plastic in a large and potentially critical print is called NetFab Cloud Service. NetFab Cloud is an online tool that you can use to analyze, check and repair your .stl files one last time before sending them to your CAM program. Just log in and upload the file. In a few seconds NetFab will render the original and repaired file for you to work with. Best of all it is free and gives you and your students one more tool to add to your repertoire of resources to help make CNC fabrication more reliable.