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I use Blender for creating 3D models for 3D printing, and it's great except that there is one step I have to do in an external program: hollowing. Blender's Solidify modifier only works on simple objects, but on complex objects things go bad really quick.

What I currently have to do is export my mesh as an .stl and then load it into Meshmixer because it has a fantastic Hollow feature that works perfectly and quickly. Then I export it back into Blender. This works, but it's very cumbersome, and I do not know how much longer Meshmixer will continue working on my Mac as they're no longer working on it.

Does anyone know of a way to properly hollow a mesh directly in Blender? I tried the BlendShell plugin which is supposed to do exactly what I want, but it's very buggy and doesn't work properly, not to mention it's extremely slow.

Example of the problems with the Solidify Modifier

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    $\begingroup$ I'm assuming self-intersection is the problem? Perhaps you should show exactly how the solidify modifier is failing (with screenshots for example). $\endgroup$
    – HISEROD
    Commented Aug 31, 2021 at 2:48
  • $\begingroup$ Yes, it's the self-intersection problem. Pretty much any complex geometry does this as you know, so that tool isn't really useful for hollowing out models. $\endgroup$ Commented Aug 31, 2021 at 15:29
  • $\begingroup$ Why won't a Boolean "difference" operation work to create a hollow? $\endgroup$
    – R-800
    Commented Aug 31, 2021 at 17:40
  • $\begingroup$ @BGreenstone Did you ever find a good solution to this problem? I'm struggling with the exact same thing and have yet to find a decent solution. $\endgroup$
    – NoVa
    Commented Mar 6, 2023 at 23:43
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    $\begingroup$ @NoVa No, unfortunately. I'm still having to export the file, load it into MeshMixer and do it there. It's a royal pain, and MeshMixer isn't going to work forever since eventually Apple will drop support for emulation apps. I can't believe Blender doesn't have a way to hollow objects. $\endgroup$ Commented Mar 7, 2023 at 19:21

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The "hollow" functions on the free software that usually comes with the printers are often great when they work ... but they often don't work on extremely high-poly models.

BlendShell works nicely, but very slowly.

You can solve BlendShell's self-intersection problem by taking BlendShell's generated internal object, while it is still unconnected to the outside surface, and remeshing it and perhaps smoothing it as a separate object, before making the normals point inside again, combining it with the exterior surface, and maybe manually punching some holes through (subtract cylinder) for drainage.

The other "gotcha" with BlendShell (other than speed) is scaling. You'll want to "normalise" your model first by using the menu command "Object/Apply/All Transforms", otherwise BlendShell may be using a different scale to your actual model. If you find that the shell is jumping through the exterior surface and running amok, that's probably why.

My biggest problem with BlendShell was that, last I looked, it wouldn't run on recent versions of Blender, and files saved from recent versions often won't load into older versions. So if you're using recent Blender, you might want to finalise all other aspects of your file, export an STL version, import this into an earlier version of Blender that has BlendShell installed, save, and then reload into the later version. A bit of a pain.

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You could make another object, the rough shape and size you need for an inner wall, flip the normals on it, place it inside your complex object then join the inner and outer object. (Control J, if the hotkeys for your version are the same as for mine.)

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  • $\begingroup$ Yes, and that's exactly what I used to do before I discovered the Hollow feature in Meshmixer. Unfortunately, the Boolean method is extremely rough and not an efficient way to do it - building a rough inverse of what you want to carve out takes a very long time on a complex model. With a proper Hollow option you can set how thick you want the walls, and how high resolution you want the mesh on the inside to be. That's how both Meshmixer and BlendShell work - it's just too bad BlendShell is too buggy and too slow to use. $\endgroup$ Commented Aug 31, 2021 at 21:05
  • $\begingroup$ It wouldn't take a very long time. Create a cube. Subdivide it at least twice. Apply the subdivision. make sure this new shape is bigger than the objet and use shrinkwrap to project onto your object. Vois-la, you have the rough shape of your object. Scale it down or use the shrink tool so it fits inside your object, invert normals and join. $\endgroup$ Commented Sep 2, 2021 at 20:15
  • $\begingroup$ You could also just use solidify, then use decimate to simplify the mesh of the inner island. $\endgroup$ Commented Sep 2, 2021 at 20:17
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    $\begingroup$ I appreciate the suggestion, but it's still a very manual process with no precision control. I really need an automated tool where I can tell it exactly how thick I want the walls to be and just have it do it - exactly how Meshmixer does it. Anything else will just take more time and result in a less accurate final model. Blender simply needs a proper Solidify or Hollow modifier. $\endgroup$ Commented Sep 8, 2021 at 19:51

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