This page will give you a brief introduction to mesh repair software so you can check your STL file for errors before 3D printing.
Already checked and/or repaired your model? Head on over to Slice Your Model.
Why do I need to check my STL file for errors?
The “mesh”, or outer shell, of a 3D model must be free of errors. All faces of the object must be connected to each other without any gaps. When these faces aren’t connected, the gaps or holes in the mesh can adversely affect the quality of the print.
The default repair feature is powerful, easy to use and will fix most minor issues with ease. Students and educators can use the basic features of Autodesk's Netfabb for free after the 30 day free trial expires. You can import, analyze and repair models using the default repair tool which fixes most minor issues. Tutorials aren't as extensive as other Autodesk products, but their Getting Started page will do just that. Here is a tutorial to get you started:
From the makers of Autodesk, Meshmixer provides mesh editing, repair, and analysis features, in addition to designing models from scratch. Meshmixer also has a number of tutorials, a user manual, and a robust community forum. Lynda.com also provides a basic introduction to Meshmixer.
Here is a quick tutorial from Prusa Research:
You can check out the full Meshmixer tutorial on Prusa Research's blog.
MeshLab is “an open source, portable, and extensible system for the processing and editing of unstructured 3D triangular meshes.” While the number of tutorials are limited, MeshLab does sustain a blog and has an active community forum. Be warned! MeshLab is difficult to master, and there is no "undo" button. Here is a introduction to MeshLab from it's creator: