Non-manifold edge deteceted?

[Tbayne]

I am trying to shell a multi-layered part that has been union boleaned to form a 3D solid. Once I hit shell, eliminate one face for 3D printing, set the thickness desired, command line reads "Non-manifold edge detected" and restarts the shell command. 1.) What is a non-manifold edge and 2.) How do I fix it?

[Cad64]

When you get a "non-manifold edge" error, it usually means your model is not watertight. There are either holes or additional faces or edges that shouldn't be there.

 

Take a look here for a detailed description: http://www.shapeways.com/tutorials/fixing-non-manifold-models