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Pretty new to Blender and modeling in general and I've spent a couple days trying to figure out this problem. Can someone more knowledgeable take a look and give me some direction?

Background

Been working on modifying a 3d model in preparation to print, but have been running into what's become an insurmountable problem for me.

I've divided the model up into sections and added keys to help printing and assembly later. Have then exported each section as individual stl files to test importing and slicing in the print utility. All of the parts are fine except for one.

Issue The problem section seems to have some geometry issues that I haven't been able to fix. There appear to be some non-manifold sections but I haven't been able to find a way to fix them. Have spent hours tinkering with the model manually to no avail. I've ran the section through Mesh -> Cleanup, as well as trying to apply a combo of remesh and decimate modifiers. (The last 2 kept crashing Blender so couldn't make progress that way.)

The key hole on the bottom may be causing problems. The stl file that gets generated sometimes has errors in the slicer or completely disappears when I change the rotation of the section model.

Here's an image of the non-manifold sections selected.

enter image description here

Here's a link to the blend file of the model https://drive.google.com/file/d/1ESKfCxDuTgUELPmL98NK5f8HZFfpfKw9/view?usp=sharing.

In the blend file, each model section is labeled like "sword-0", "sword-1", etc. The problem section is "sword-0" and should be the only one visible on opening the file.

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    $\begingroup$ Hello :). The non-manifold parts are technically easy to repair, but it's rather hard to explain :). The main issue are faces going through other faces, and simple holes (you probably just forgot to fill them) $\endgroup$ Aug 1 '20 at 20:05
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    $\begingroup$ I repaired the mesh, and uploaded it here on GDrive so you can check it against the old one. I also included a version with a Mirror Modifier, so you can better see the final geometry. $\endgroup$ Aug 1 '20 at 20:46
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    $\begingroup$ Since your mesh contained many examples of non-manifold geometry, be sure to check out what it is and how to avoid it :). You can start here: What is non-manifold geometry?. $\endgroup$ Aug 1 '20 at 20:47
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    $\begingroup$ @JachymMichal you're my f-ing hero right now. Man I wish I could watch how you fixed the mesh. I'd learn a lot from that. How did you get the large side faces to intersect the curved parts so the large face didn't continue behind curves? $\endgroup$
    – Geuis
    Aug 2 '20 at 5:56
  • $\begingroup$ Hey, np :). I'll add an answer with some examples of what I did. The file also contains the repaired mesh with a Mirror Modifier - if you disable the modifier, you can see the topology more clearly. $\endgroup$ Aug 2 '20 at 6:08
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There were three main issues with you non-manifold mesh:

  1. Faces going through other faces - You need to reconnect them vertex to vertex.
  2. Disconnected edges (with gaps) - hard to notice, check for non-manifold vertices
  3. Holes in mesh - just fill them through Vertex > New Face (F)

To check for non-manifold geometry try this:

  1. Select > All by trait > Non-Manifold. This will highlight all non-manifold vertices. There should be none.
  2. Check face orientation - this will also reveal small holes and missing faces

Faces going through other faces

enter image description here

Disconnected edges (with gaps)

enter image description here

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    $\begingroup$ Thanks for gifs. I think I see what you did. Really appreciate this. $\endgroup$
    – Geuis
    Aug 2 '20 at 9:21
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    $\begingroup$ Glad to be of help :). Good luck with your project. $\endgroup$ Aug 2 '20 at 9:23
  • $\begingroup$ Hey @JachymMichal, one other question. How did you turn the model blue in the updated file? I haven't been able to figure out how to set it back to grey. $\endgroup$
    – Geuis
    Aug 3 '20 at 4:55
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    $\begingroup$ Sure :). That's Face orientation, check my answer, there's a link :). $\endgroup$ Aug 3 '20 at 6:38

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