Why is the slicer changing the geometry of the model I want to print?

[NeverDie]

First of all, this is where the part came from:

X3D-v3 Riser | Bambu Lab X1/P1 AMS Stand by DutchWorkX3D

So, if you want, you can download and slice it to see whether or not you get the same result I did. The specific part is AMS_stand_v3_RB.stl.

Here is how the part looks in Prepare mode:

And this is how it looks after slicing it:

If it isn’t already obvious, here is a zoom in on where the deforming occurs:

I thought the tree support on the other side would help hold its form:

but plainly it did not.

I printed it, and the print is faithful to what the slicer shows, not the model as it appears in prepare mode.

So, what’s going on here?

[JayZay]

Hi.
Strange thing, indeed.
Can you confirm that the mesh has no errors, or can you try the repair model to see if it is correct?
Are you using default slicer settings?

[NeverDie]

It saw no error messages relating to a mesh problem. Is there a way I can “repair” it anyway, even if no error is evident?

By default settings, do you mean process settings? I think it’s probably close to that, with maybe some small changes. I’ll try plain vanilla and report back.

[JayZay]

I want to eliminate that the model or process settings are not the cause, as I can’t replicate this.
If you press the mouse right-click on the model, you will find the fix model option.

[NeverDie]

You had an excellent suggestion. Going to full vanilla both changed the support and preserved the geometry:

Making the support invisible shows the geometry was preserved:

So, evidently, it was something “non-vanilla” in my settings that led to the trouble.

[ovityons]

If you right click on the model there should be a fix model option just under clone.
I can’t seem to replicate the issue, I get totally different tree support I tried different angle settings. I wonder if it could be caused by the graphics card. I have printed vertical Hex panels in ABS without support and they printed fine.

[NeverDie]

Thanks for that guidance.

Reporting back: I ran a fix on the model with my previous slicer settings, and it made no difference.

So, it must be some variance between my slicer settings and vanilla that’s causing the problem.

[Obfuscated]

I’ve seen this when the model was non manifold or had faces that werent joined. Using the thd model repair sometimes makes it worse but it looks like you found a solution

[JayZay]

It happens… I never faced something as in your case, but when facing strange layers, I found trying the fixing tool to be a valuable practice.
If it is your model, you can use the .step format, avoiding any slicing problems.
The important is that the problem is solved.

@Obfuscated

Using the thd model repair sometimes makes it worse

You´re right, but in that case, makers add some notes about it, or the non-manifold faces are expected (e.g., lithophane).
From my experience, the Windows-built service works quite well; I only recommend avoiding it if the shape and mesh are significantly complex.

[NeverDie]

REPORTING BACK: I found the problem. I had checked “Make Overhangs Printable,” and this is what caused the problem. When doing so it actually does warn you that it might change the model’s geometry, but I had forgotten that warning. Frankly, I don’t actually remember setting it in the first place, so maybe it was just a haphazard mistake I made in the past without realizing what it did and that followed me around up until now. Well, thanks to this breakdown, now I know what it does and what the trade-offs are.

[NeverDie]

@ovityons

I have printed vertical Hex panels in ABS without support and they printed fine.

Apparently, with the revised settings, the slicer agrees with you!

Actually, I wouldn’t mind the extra support if it guaranteed a good outcome. It’s so disappointing to do a long print only to find drooping afterward due to inadequate support.