A surface is added to my .stl file when slicing, even when neither supports nor adhesion are enabled.

[CuraGuy 1]

 

Hello, Cura forum! I have recently encountered a very strange issue with Cura, to the point where someone I know who is very experienced with the software was unable to figure out what was happening. Naturally, I decided to ask you fine people.

 

I'm trying to print a small item (.stl file attached), and, when slicing the file, a thin surface appears in the middle of it. This surface is removable, though not easily. I'd like to delete it from the slice file, but I'm not sure how - it doesn't appear to fall under either of the categories that can be disabled, and I'm not quite sure what purpose it's intended to serve. Has anyone encountered this problem before?

 

The .stl file I intend to print, before slicing. Note that the corridor on top goes all the way through the model.

The .stl file, after slicing. Note that supports and adhesion are both disabled - should this not be the (broadly speaking) unaltered model, then? Previous iterations of this design didn't have this issue.

A better view of the mysterious surface that is added.

attempt5.stl

Edited July 19 by CuraGuy

[GregValiant 1,112]

When you see things like that (extra surface or missing surfaces) you need to check the model.  I used MS 3D Builder and it was able to effect a repair.  There is likely a "flipped surface" which was telling Cura that the inside had become the outside.  As the lady said "...and that's when all the confusion jumped up".

Your model is on the right and the repaired model on the left.

fixed attempt5.stl

Edited July 19 by GregValiant

[CuraGuy 1]

5 hours ago, GregValiant said:

When you see things like that (extra surface or missing surfaces) you need to check the model.  I used MS 3D Builder and it was able to effect a repair.  There is likely a "flipped surface" which was telling Cura that the inside had become the outside.  As the lady said "...and that's when all the confusion jumped up".

Your model is on the right and the repaired model on the left.

fixed attempt5.stl 111.7 kB · 0 downloads

 

Thanks for the reply! I'm using Blender, and, after checking the model over several times, I'm having trouble identifying the rogue surface. Do you remember which vertices it was attached to?

Edited July 20 by CuraGuy

[gr5 2,069]

Greg described backwards normals which is different from missing faces.  Most CAD software takes care of this automatically but blender is for photos and movies, not for making real life parts so it lets you do things that are impossible to print.  Anyway here is a nice blender article about what the issues are and how to fix them in blender.

 

https://www.sculpteo.com/en/tutorial/prepare-your-model-3d-printing-blender/

 

Read the sections 3.1 - 3.6 and search for "recalculate" to fix inverted faces (aka backwards normals).

[CuraGuy 1]

6 hours ago, gr5 said:

Greg described backwards normals which is different from missing faces.  Most CAD software takes care of this automatically but blender is for photos and movies, not for making real life parts so it lets you do things that are impossible to print.  Anyway here is a nice blender article about what the issues are and how to fix them in blender.

 

https://www.sculpteo.com/en/tutorial/prepare-your-model-3d-printing-blender/

 

Read the sections 3.1 - 3.6 and search for "recalculate" to fix inverted faces (aka backwards normals).

Looks to have worked. A -> Shift+N -> Recalculate Normals -> Inside did the trick.