How do I change 3D surfaces or 3d meshes to a solid? I will eventually simply shell out the part I am making, but the outside has a few complex curves to it that I can't do with basic extrude and subtract comands etc. I can completely enclose the object with all 6 sides if need be. But is there a command to fill the void in the surfaces or completely convet the surfaces (or meshes) to a solid object?