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I'm using Cura and it removes my holes and deletes sections of the print and disconnects parts. In Blender it looks as it should be, as I designed it. I know there are a few mishaps inside (not manifold) but is there a way to fill in everything on the inside. I only care about the externally facing faces. This is extremely infuriating I hope someone can tell me how to force Cura to print what is originally seen in the .stl.

Blender as it should look

Again how I designed it.

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These are photos of how it should look.

Now these next photos are how Cura previews it. Not only does it fill in the holes (no, fill holes isn't enabled) it adds huge gaps in the side and bottom of the print as can be seen.

All messed up.

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How can I force Cura to print what I see in blender in the original .stl?

I am exporting in Blender to .stl and opening that in Cura.

I was able to fix it partially by fixing normals in Blender but there is still this:

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It's common for modeling software to flip normals, causing what you describe. You said,

I only care about the externally facing faces.

But are you sure they are truly externally facing? Turn on normals in Blender and ensure that all the arrows/pointers are external.

Another problem that can generate the results you're seeing are self-intersecting surfaces, non-manifold edges, and a couple others that are explained in a 3dhubs article. Correcting those problems involve a bit more examination and trouble shooting.

The slicing software prefers to have clean, well defined triangular surfaces in order to create a print file. When something is amiss, you get results you've presented.

With the STL in hand, I opened it in Meshmixer (free) and immediately was given a clue.

STL image in meshmixer

The zebra-stripes are reversed normals.

Here's another error point, difficult to see clearly in flat 2D image, but panning and zooming and orbiting and all those 3D manipulating things shows there's nothing there:

broken corner

The other end of this not-joined area shows a bit better:

other broken corner

After selecting all I could find/locate, I did the reverse normals and here's a slightly improved result:

corrected part

Unfortunately, the other borked up portions prevented meshmixer from performing a suitable auto-repair, completely destroying the model in the process.

Those joint corners and any other colored lines have to be addressed individually.

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  • $\begingroup$ [alt]+[N] -> Recalculate Normals Outside $\endgroup$
    – Trish
    Mar 15, 2021 at 20:24
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There are several problems at work here:

  • Internal Geometry & unjoined parts

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  • Missing Surfaces

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  • Generally inverted surfaces: every surface is inside out!

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Fixing it!

Step 1: add missing surfaces.

Select the vertices around the hole that has no bottom surface and then pres F to create a surface. Use several steps, making roughly triangle surfaces. For example: select the red marked vertices, then F and then the next set.

![enter image description here

Step 2: Internal Geometry

Let's now hunt for purely internal surfaces. Select them and delete them with Del, and select Delete Face.

Step 3: Superflous surface geometry

Some areas have remnants from areas where you worked. Merge those vertices to prevent new artifacts from cropping up. Select the vertices, M and then collapse for each circle, like the red one. Some might need to be collapsed at a specific vertex to prevent surfaces from getting ripped or intersecting badly - in the lower picture the green circled one.

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Step 4: Normals

Last but not least: Alt+N and then Recalculate Outside

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Export to look for other errors...

Everything should look much better now: The "checkered" areas are gaps are gaps in the walls... which stem from bad geometry in the big walls I selected in the lower picture.

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So, I select one of these areas - then change to vertex mode, deselect the vertex I don't want the face to connect to (red) but the ones that should define the edge instead (green) and then press F to make a new face. Then I select the old one and delete it.

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DONE!

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  • $\begingroup$ Thank you so much! I already fixed it with 3D builder but this will be very helpful for me later if 3D builder fails in the future and for others looks for solutions to similar problems! Thanks for taking the time to do this, much appreciated! 😊 $\endgroup$
    – techset
    Mar 16, 2021 at 22:44
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Rhino gives the following output for MeshRepair

  • Mesh has 3 degenerate faces. (a face that's actually a line or a point)
  • Mesh has 42 non manifold edges. (a line where 3 or more faces meet, possibly caused by degenerate faces)
  • Mesh has 6 duplicate faces. (faces that share the same coordinates)
  • Mesh has 148 naked edges (edges that have only one face)

All of these things are indicators that it might be difficult to distinguish inside from outside.

Naked edges

I have encountered these problems after changing a model a lot during it's lifetime (adding/removing stuff). Since there are 200 errors and it's a relatively simple model, I advice you to fix these kind of problems by starting with a new clean model, using some of the coordinates of the old model as reference.

Also: be sure to check out blender's 3d printing wiki, they seem to have quite some tools similar to rhino's meshrepair

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Okay, so like suggested I put it into 3D Builder (A free Windows 3D modeling program). I imported it as an stl, then exported it as an stl and imported that stl into Cura. And lo and behold all problems were gone! If you are having a similar issue give that a try! The 3D Builder program and similar ones are designed to export for the sole purpose of 3D printing so it automatically fixes these issues! If this doesn't work try editing yours in edit mode (Blender) a bit so it makes it easier for 3D Builder to fix it.

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