Non manifold hollow object

[Ssiri 0]

I'm trynna print a bong so obviously it has to be hollow but whenever I import it into cura it says it's not manifold and highlights the open spot on the mouthpiece and inside wherever there's an edge. If I go into blender and press the "make manifold" button it just fills in all the holes but I need it to be hollow so it will function correctly. I don't want to try to print it and risk wasting material just for it to print incorrectly and I can't find anybody online with the same problem. When I slice it and watch the preview it fills in wherever I extruded because there's a missing face but I need there to be no face so it's hollow.

[Ssiri 0]

Here's the file I'm using.

Bong Beaker.stl

[gr5 1,427]

if using blender - here's how to fix your model

Quote

I went into edit mode with the object in Blender 2.83 and pressed "a" which selects all faces / vertices / edges, depending on what select mode you are in. The entire object should be highlighted. I then went to "Mesh" (see images), went to the "Normals" section, and selected "Recalculate Outside". This probably will not fix any edges that are not merged, but it will fix the faces that are inverted on the object. 

 

[gr5 1,427]

I'm guessing your normals are backwards.  If so, the post above should hopefully fix it.  It's possible you also have missing surfaces.  In blender - did you put inner *and* outer walls in the tube of the bong?  You specify the wall thickness by having two cylindrical surfaces.  If you only have one surface then the bong is infinitely thin.

 

So in summary, there are two critical things:

1) Make sure the part is manifold (no holes).

2) Make sure all the normals are correct.  Here's another explanation of normals.  Normals tell you which side of a surface faces air and which side faces plastic:

https://www.sculpteo.com/en/tutorial/prepare-your-model-3d-printing-blender/