I have an .STL file of a Minecraft building which I would like to 3D print. The building itself is "hollow", but I understand that in the world of 3D rendering, there is no such concept - just vertices and edges.

So the issue I'm having in Blender is that the building is made of units of blocks which themselves are solid, but together create an overall model which is hollow. Thus when attempting a 3D print, the hollow inside of the building is not being infilled which is causing problems.

I just care about the exterior of the model. How do I edit the model in Blender to in essence "fill" the interior of the model? I thought of trying to select all the exterior vertices, then invert, then delete the interior vertices, but that did not work in my case and is unreliable/tedious. I assume there is a proper way to do this anyway (I am relatively new to Blender).

Edit: (Link to file): https://pasteall.org/blend/510d7027732e4e07be713198e682c060


Exterior of model

Interor of model

The first image is the exterior, the second is the hollow interior. I just want to print the exterior shape as if the whole model were totally solid. How can I achieve this. Thanks!

  • $\begingroup$ Sorry, are you looking for the end result to be a solid block, or a hollow shell (with some thickness to the walls)? Or do you want the interior to resemble a "cubic honeycomb" (for lack of a better term)? $\endgroup$ – Christopher Bennett Mar 9 at 6:16
  • $\begingroup$ Christopher, thanks for your comment. I am looking for the interior to resemble a cubic honeycomb (I assume you are referring to 3D print infilling). $\endgroup$ – NDrummerboy087 Mar 9 at 6:23
  • $\begingroup$ Yeah, I'm not 100% familiar with how it works, but I'm getting the idea. You want every edge to connect to it's adjacent edge through the interior, crisscrossing the edges that run perpendicular. (I hope I have that eight). Your mesh is triangulated - do you want the diagonals filled as well? $\endgroup$ – Christopher Bennett Mar 9 at 6:28
  • $\begingroup$ Yeah that might me a solution. Whatever makes the object as a whole solid and not hollow is what I am looking for. I only care about the exterior since that is all you would be able to see in a 3D print of it, so I would like the inside to just be infilled. $\endgroup$ – NDrummerboy087 Mar 9 at 6:36
  • $\begingroup$ Ok. I'm not sure how the infill is supposed to be represented as far as instructions to a 3D printer. Blender is picky about faces having a direction (they are one sided as opposed to double sided), and any interior containing a multitude of one sided faces that are "interlaced" so to speak, would make the mesh "non-manifold" which is a no-go for 3D printers as far as I understand. This might mean the (infill) walls need some thickness to them, which might also be a pain to achieve. Since I don't know too much about this, I'll upvote the question so hopefully someone who knows more will see it $\endgroup$ – Christopher Bennett Mar 9 at 7:06

For 3D Printing, what you need is a "watertight" or "manifold" model. Both terms mean that there are no holes in the exterior of the geometry, but more importantly, no internal faces, which is what you have here. A great addon for checking your model is the 3D Print Toolbox, which comes standard in Blender, you just need to turn it on!

The simplest way to fix this is to use a Remesh modifier, this will recalculate the object into "voxels" (3D cubes) of a specific size that you can define based on the exterior. This, however, is VERY CPU heavy! It's REALLY slow to calculate!

There is a MUCH better remesh option though. It lives either in the tools panel in the sculpting mode, or under the Remesh tab in the Object Data Properties tab.

enter image description here

0.1mm setting is more than good enough for 3D Printing. But be warned, this is still quite CPU intensive!

For your model, you may need to leave it for a few hours depending on how powerful your PC is!

  • $\begingroup$ Thanks for the response. I am launching the calculation now and will leave it until it finishes. In the meantime I also had a chance to upload the file if you are interested. pasteall.org/blend/510d7027732e4e07be713198e682c060. I will let you know if the remesh works! $\endgroup$ – NDrummerboy087 Mar 9 at 14:27
  • $\begingroup$ So it appears to create a proper manifold volume with the shape preserved. In my case though, there are now about 8 million faces. Is there a way then to further simplify the geometry? $\endgroup$ – NDrummerboy087 Mar 9 at 16:13
  • $\begingroup$ Okay so this actually does do what I want (I tested with a less detailed remesh and then exported to Cura and the interior was solid!) So now the question is, is there a way to efficiently remesh? As this is a Minecraft build, everything is "blocky", so I certainly don't need 8 million vertices. Is there a way to either remesh more efficiently without losing detail, or reduce the vertices/edges/faces after the intial remesh without stalling the Blender program? Thanks much! $\endgroup$ – NDrummerboy087 Mar 9 at 18:21
  • $\begingroup$ After remesh, try the Decimate modifier, there is a setting to preserve the outer shape $\endgroup$ – Psyonic Mar 9 at 21:14
  • $\begingroup$ What would that setting be? Thanks. $\endgroup$ – NDrummerboy087 Mar 10 at 3:59

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