All objects must have a volume. Often drawing for renderings or animations we create surfaces without any thickness: with 3D printing we will create a solid object, real, which must therefore have a thickness, even minimal.
To give a volume to the surfaces it is sufficient to extrude them, so as to obtain solids
Objects must be manifold:in a nutshell it means that the geometries must have a inside it's a out without "holes". A mesh is said non-manifoldwhen it has edges shared between more than two faces.
Errors can concern:
- faces locked in a volume
- double points
- separate volumes joined by a corner or a point
Each corner must have only two adjacent faces, no more and no less.
Points must belong to a single face. When two faces share a point, without having a common edge, then the point is non-manifold.
For example, when with SketchUp two faces are drawn and placed in an adjacent way, it is not said that the edges fit perfectly, so what on screen may seem like a solid is, in fact, a set of surfaces without volume.
To avoid problems like this it is always preferable to use the drawing tools dedicated to solids, or draw faces and then extrude them. To draw a cube, instead of drawing 6 faces and then placing them next to each other, it is advisable to draw a square and then extrude it.
All surfaces of your model must have the normals oriented in the right direction.
If your model contains normal inverted it can not be printed, because it is impossible to determine which is the "inside" and which the "outside" of the model. In SketchUp it is easy to orient the normals and it is advisable to always do this before saving the model.
Does the model contain no information about the volumes?
If loading your .skp file on Vectorealism you will get this error message trying to export your model in .dae format and repeat the upload.
Is your model not manifold?
If after uploading to Vectorealism you receive an error message that warns you that your model is not manifold you can try to temporarily delete the larger faces of your model, to watch it from the inside: in the standard view, if you have not applied any color to your model, the inside faces must be celestial, the ones on the outside white / gray.