Can't print my model (non manifold edges)

[pylou]

Hi,
I'm desperate. I have a plan to make a knife (specifically the Reaver Karambit from Valorant, if you know it) with some electronics inside (LEDs, maybe a mini smoke machine). I took an online model and modified it to create a hole in the blade. I've tried many solutions (I'm a beginner at 3D modeling), including manually drawing triangles in Blender, but my model still has many non-manifold edges and empty faces. I don't understand this because I made sure there was thickness everywhere.Here’s the model (half of the blade).

Thanks in advance if you can help me.

[fred_dot_u]

At first glance, it looks like a zero thickness set of walls. When you suggest that it's half of the blade, are you planning to print it in halves, then join it together? There are a tremendous number of reversed normals in the model as well. A reversed normal is a triangle that has the outside surface pointing inward and they are far too plentiful in the model you've provided. On second glance, I see it has thickness. That makes things much easier.

I'm about to move on to non-computer activities, but tomorrow afternoon, I'll fire up my other machine and load the model into it. A quick solution is to load it into Windows 10 (or 11) 3D Builder and run an automatic fix. It may destroy the model in the same manner that Meshmixer does, by removing all the reversed normal facets, but it might not, as I've found that it's a decent program for fixing broken designs.

I took a shot at it with Meshmixer and reversed all the reversed normals I could find. There's at least one non-manifold corner, with self-intersecting planes for which I am ill-equipped to resolve. I'll return to it tomorrow afternoon.

Consider also that Blender has a plug-in or maybe a built-in feature for checking and repairing 3D models for printing suitability. I'm nearly at zero capability with Blender, other than to have noted that this feature should be available.

I'd suggest that you try this attached repair attempt to see how the Blender repair feature manages, or if you have Windows 10 or 11, how 3D builder sees it.

[OG56]

Did a quick look see.

Three issues with the model.

The worst is the normal face orientations on the model is terrible (as mentioned by fred_dot_u). Half the faces are pointing out and the other in. It really confuses the software on what it is supposed to do when that happens.

Second you have intersecting geometry at one of the corners. Again, that confuses the software to determine what is supposed to be watertight.

Third, at the intersecting section you may have a missing face/s which again defeats it being water tight.

Model is completely salvageable with a little work.

You want to change all the red faces to blue. Select and hightlight and use Shift-N and if doesn't change to blue automatically click on the box labeled inside to switch orientation. For the intersecting geometry area just box model so there is no longer any intersection and if there is a hole and not just messed up geometry fill in the hole.

Also for box modeling you don't really want to triangulate a model unless there is a very specific use case. It makes it 10 times harder to work on it. When you save to STL format it will automatically triangulate the model.

[pylou]

Hey,
I want to say a big thanks you both saved the project! (i was close to give up)
it works, now i just have to fix some minor issues like too thin walls but it's all fine.
Again, im very grateful for your help, you made my week without exagerating!

[fred_dot_u]

here's the latest result, but it's not what you want. 3D Builder in Win10 joined the entire perimeter, probably because the perimeter lines were not properly joined to the walls that make up the sides of the model. Again, because my Blender skills are zero, I can't attack those weak points to make repairs, but maybe you can. I'm glad we've been able to assist.

Good luck.