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Unexpected shell and red areas

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Posted · Unexpected shell and red areas


I am new to 3D printing and facing some problems.
I downloaded a model and tried to fix some problem areas causing new problems. I attached the stl file.
1) Please tell me why the bottom of the mouth is red.


2) Please tell me why the bottom the pot is red.


3) The biggest problem is that when I slice it cura thinks that the cup should be closed and adds a face on the top!


The following picture shows the helpers.


I appreciate any help. If I made any major mistakes please tell me so that I can avoid them in the future.



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    Posted · Unexpected shell and red areas

    The red areas would normally indicate overhanging geometry that needs supports. In this case it looks like the surface normals are inconsistent, which breaks the visualisation of overhangs. 


    The model likely doesn’t slice as expected because it has small holes or internal geometry. The model needs to be “repaired” before it can be sliced correctly.



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    Posted · Unexpected shell and red areas

    @raldone01 - what cad software did you use to create this?  If it was sketchup I can help you out.


    The quickest thing to do is "fix" the model with netfabb.

    netfabb free repair service is here (you have to create a free account first):


    You could also experiment with the 8 options in the "mesh fixes" section.  In particular uncheck "merge overlapping volumes".  That might make it even worse though.  But try that.


    The best solution is to not create these errors in CAD in the first place. 99% of cad software out there will not let you create these errors - it's impossible.


    A "normal" as ahoeben calls it indicates which side of each triangle in the STL file is facing "air" and which side faces "internal".  Many cad programes (like sketchup) make the user set this value manually.  It's very easy to fix in sketchup.

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    Posted · Unexpected shell and red areas

    @gr5 I used blender to adapt it. @ahoeben mentioned normals and I checked them out in the blender documentation. I didn't know that each face has a direction. The problem was easily fixed by pressing ctrl+N (in blender edit mode) which recalculates the normals.
    Thanks for your fast and helpful replies.

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