I’m a little bit confused on this part. Do you think you could please expand? Thanks!
There are a lot of issues with this STL. Many places, like this spot, where there are multiple overlapped polygons occupying the same space.
It’s not a non-manifold edge issue. These polygons are separate entities that overlap each other. That’s not going to slice cleanly.
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So do I have have to go through each thing, and make sure it’s not overlapping?
What setting were you on to see the frame of the object?
It’s my CAD software. I loaded the STL and displayed it as a wire frame, started looking at areas that I had seen disappear in the slicer, saw stuff like this, selected a representative example of polys and did a screengrab.
I don’t know enough about Fusion to suggest how to prevent it from doing this. But overlapping unconnected polys can definitely give a slicer a headache. You have a zero-thickness wall. So it disappears when sliced.
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There is a very long thread here recently on STL vs STEP. If you want the long version and have a few hours, read this.
To spare you the wall of words, let me simplify.
- STL files are a mesh of triangles
- STEP files are geometric descriptions of geometric shapes such as lines, circles, arcs and angles. They are far more accurate and Slicers support them as well as STL.
- After a STEP file is imported into a slicer, the model is converted into a mesh and all geometry data is lost.
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So when I say import with the lowest version, that’s only if your CAD supports versions. There are three versions. STEP AP203, AP214 and AP242. AP203 is the earliest and oldest and will not contain the same complex data that later versions might hold. Thus allowing for less information to be processed by the slicer.
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STEP files and STL files in a text editor can look remarkably similar but there are very stark differences. STEP is covered under ISO 10303-21 and was designed specifically for CAD portability. It’s predecessor was IGES. STL was designed by 3D Labs specifically for 3D printing.
In the world you’re trying to live in, CAD 
FDM, mastering the concepts between the two formats will help you develop a more intuitive understanding of what will and will not work in a 3D printing or CAD use-case. You don’t need to be an expert to get the feel of which file format performs in a specific manner. In fact, you can know nothing about the file syntax so long as you wrap your mind around the differences between a parametric geometry and a mesh. It’s been demonstrated in this forum that many who believe they understand the concepts actually do not.
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May I ask what CAD software you are using? Fusion 360’s wireframe is pretty trash.
You can ask. 
I started doing CAD a long time ago as part of generating computer animations, using a piece of software called “Lightwave”. I think I’m on the 6th or 7th version, now.
It’s not parametric like Fusion, it’s focus is editing meshes. Can be a limitation when designing something big (it’s hard to make changes after you’ve designed a section of something). But since 3D printing is all about triangle meshes, it’s great for looking for problems.
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I am very confused beacuse @RocketSled is saying that is isn’t a malifold issue, but it is just overlapping lines, but @Olias is saying that it is a mailifold issue, and that is the only way to fix it beacuse of all the holes in the model.
There are manifold errors, too. But those aren’t the reasons these walls are disappearing. The exterior walls disappear because they are coincident with an interior wall. The resulting wall has no thickness. The “inside” and “outside” are in the same place.
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You may be reading these two posts to literally. Both posts can be true at the same time. Rocketsled’s explanation focuses more on the cause, my post focuses more on the affect. One can have a CAD issue that creates a “dimensionless” object which would then be interpreted within the slicer as an open manifold. Both conditions can exist at the same time.
The bottom line here is that if you have multiple problems reported by multiple software such as the file analysis I did above, that is your red flag that your model is corrupt.
I took a second pass at the model file and if I were to hazard a guess, it looks like this model has been passed through multiple translator or import/export processes. You can almost see the pattern where objects were not correctly accounted for in the geometry. One smoking gun is that the STL file reported over 1,300 parts but most of them under examination are tiny random stuctures.
You can quickly see the damaged model if one hides all the surfaces and shows just the objects. The disconnected geometries become more obvious.
If I may ask, what was the source of this model file? It is quite curious.
This challenge admittedly has me very curious. So I took this an extra step just to see what might be possible.
Here are the steps. I tried to use as few external program as possible but the final step did require a CAD import in OnShape before bringing it back into the slicer. I use Orca Slicer which is a fork of Bambu Studio. It uses the same libraries so the import/export functions should be identical.
- Model was brought into Orca at it’s native scale.
- Using Orca, I right clicked and did the following
- Scaled the model down to 200mm which was approximately 10% of the original
- Repaired the manifold
- Right-clicked and simplified the model down to 30% of the original polygons.
- Exported from the slicer as an STL and then imported it into OnShape and then exported it as a STEP file.
Bringing in the STEP file into eDrawings showed that the most of the orphaned shapes were reconnected.
And this what the sliced model geometry looked like on the plate at 10% scale and without supports.
It’s a 7 hour print and I’m going to bed. I’m using some crappy $10 filament that I need to burn up anyway. It was one of my failed filament adventures. Tomorrow will show if I get a pile of spaghetti or an actual model. 
I’ll use supports to print it.
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This is very weird because this “fancy” design was the only thing that I took from the internet, and all I did was tessellate the model, and put it in this model. I am very confused why this object looks corrupted in this onshape anayalsis.
It’s not necessarily corrupt, What you see here is what is in the model. The colors are OnShape’s visual queue to differentiate between different parts. It sees this entire decorative facade as a series of parts.
I’ve not completed my analysis and will share later some prints but to be blunt, you are expecting too much of this model. It was not designed to be printed at scale on an FDM printer.
Getting back to your original question. If you want to be able to print this. You need to obey the suggestions the slicer is asking and repair the defective manifold. What’s more, my early tests indicated that it is not possible or practical to expect to be able to render these facade features at 0.08 layer heights. In other words, I’m afraid you’re trying to thread a needle using a rope.
Thank you so much for trying it, to try to figure out the issue!
My only issue which I have been trying to avoid at all cost was this, repairing the manifold. This is beacuse Orca slicer add infill to the big center piece, which I can’t have beacuse I will have other items inside that center piece that we need to see.
It also looks like even after you repaired the manifolds, and brought it back into Orca, it looks like it still messed up the door in the centre on top of the stairs.
Lets see how it comes out either way, since you tried to print it .
Thank you!
I’m not sure if I mentioned this, but I will be printing this at a scale of around 5x4x6 feet. It would be cut into lots of pieces and printed with multiple X1 Carbon’s over the coming months. It looks like the manifolds will need to be repaired either way beacuse when I cut it up, some walls just dissapear if I don’t repair it first as one piece.
Is there any way to repair everything besides for the center piece? What I could do, is print the courtyard, and repair those manifolds, and the print the center piece as a second whole model. Would that help?
So why are you trying to slice the entire model at once?
You have a lot more designing to do. Break your model into parts that will fit on a plate, including whatever additions are needed to connect the parts, and slice each part individually.
That is a rather important piece of information.
Having that critical information changes the conversation entirely. Put simply, you can’t do what you want to do without modifying this model. As an example, what was your plan for extracting the support material from inside the pavilion?
You do realize that you will need to support the model from within for the roof to come out correctly, right?
Also, looking at a cutaway of the non corrected model, you can see that the inner walls have no dimensions which is exactly why your model cannot be sliced without creating a sealed manifold.
I do not want to draw final conclusions until I finish printing test models but as is, you’re trying to do something with this model that is not possible with FDM. Where did you get this model? Perhaps there is another version.
I don’t believe that I will need a lot of supports because this pavilion will be cut into lots of pieces, vertically and horizontally. So it will end up being cut up in so many pieces that the roof will be on the floor, or with very little supports.
What happened with the cut? Was this just to illustrate that the walls are practically 0mm in thickness.