Hi all,

I want to hollow out the inside of my model and have been using Meshmixer to try and do this. However after I enter all the hollowing settings and hitting accept, if I do a cut on the model so I can view the inside, I am seeing red (literally). Apparently STL files can have outside faces and inside faces, and Meshmixer is making the hollow an inside face. The problem with this is that the model is no longer a closed ‘solid’ STL. If I open it in Netfab the faces are red, even after I do a repair. And the slicing software I use doesn’t recognise these ‘inside’ faces and the model becomes buggy (I actually don’t know where this method would ever be useful).

Does anyone know how I can hollow a model in Meshmixer or another program without the whole inside/outside face thing. I just want a normal STL file that I can slice properly.


Just curious, why are you trying to hollow that? Maybe there is an alternate solution.

That’s just an example. At the moment I am just experimenting with print settings (SLA machine). I purchased Meshmixer Pro with the intention to use their hollowing function, but it doesn’t seem to work how I thought it would.

Ah, I see. Curious, can you tell the slicer to do perimeters with no infill? That would produce a hollow print without any prework on the model.

Yes we do that at the moment, but the slicer works in 2D. So, viewing from the top, the outside line thickness will be uniform. But when the model surface approaches zero degrees with the build platform, so does the actual thickness of the walls. That is why I want to hollow in 3D first.

Instead of hollowing in Meshmixer, you can have Netfabb do the hollowing. Strictly, you would have Netfabb create a new part, then combine it with your original part in some way to arrive at your properly hollowed part.

Presuming you to employ Autodesk Netfabb Standard (30-day free trial, or paid subscription), do:

1. From Extras menu (main menu or the part’s context menu), pick Create Shell.

2. In the pop-up, specify the mode of creating the new shell (technically, it’s a new part). Your options are:

a) Hollow Part - generates a hollowed copy of your original

b) Inner Offset - generates a shell that is “leaner” than your original

c) Outer Offset - generates a shell that is “fatter” than your original

d) Hollowing Shell - generates a shell that is “leaner” than your original, but with all its faces turned inside out.

e) Hollow Part Improved - generates a hollowed copy of your original, like a, but with a fancier algorithm. See which one works best for you.

3. Specify shell thickness and click OK.

Depending on what option you chose, you should then:

For a or e, continue to work on the generated model,

for b, use Boolean Ops to SUBTRACT the created shell from the original,

for c, … undo and pick the right option next time,

for d, use Boolean Ops to ADD the created shell to the original. Alternatively, use Merge Selected Parts.

(Part: An individual collection of one or more shells. Shell: A collection of one or more triangles, adjacent or not.)

Thanks a lot, that’s very helpful to save some resin !