Cura Errors

[WaltP 0]

Where do we find explanations for errors in Cura 4? And how to correct them? Including what the errors are/mean?

 

I created a box with a sphere inside and the bottom face and the top of the sphere are both red for some unexplained reason.

 

Thanks,

Walt

 

[ahoeben 1,886]

The red is intended to show areas that need support. The fact that the sphere shows red on top means that the normals of that part of the mesh are reversed.

[WaltP 0]

Why does the bottom face need support?

 

What are "normals"? How did they get reversed?

 

I'm new to this stuff...

 

[johnse 31]

The bottom needs support...but that is supplied by the build plate.

 

the 3D design is represented by a mesh of infinitely thin triangles that describe the surface of object. If you zoom into the mesh of the sphere, you will get to a point where rect triangle is a flat surface, or “face”. Associated with that triangle is a “normal” vector that is perpendicular to the face. But does that normal point outward or inward? Properly described (by convention) the normals point outward.

 

Cura uses the normals for its display (the slicer doesn’t care and uses a different mechanism). If the face normals point downward by a steep angle, it colors red as a hint. If the sphere normals point inward, the ones on the top faces are pointing down...thus why Cura colors it red.

[WaltP 0]

22 hours ago, johnse said:

The bottom needs support...but that is supplied by the build plate.

 

the 3D design is represented by a mesh of infinitely thin triangles that describe the surface of object. If you zoom into the mesh of the sphere, you will get to a point where rect triangle is a flat surface, or “face”. Associated with that triangle is a “normal” vector that is perpendicular to the face. But does that normal point outward or inward? Properly described (by convention) the normals point outward.

 

Cura uses the normals for its display (the slicer doesn’t care and uses a different mechanism). If the face normals point downward by a steep angle, it colors red as a hint. If the sphere normals point inward, the ones on the top faces are pointing down...thus why Cura colors it red.

So I can ignore a red bottom.

 

I still have no understanding as to

1) how the normals came to be pointing inward

2) how to correct it

 

All I did was create the sphere in Sketchup.(and the box of course) and exported it into an STL. What do I do to prevent the normals from being reversed?

 

[ahoeben 1,886]

Yes, you can ignore the red here. You can even turn it off if it bothers you in the General preferences.

 

Sketchup is generally not a great tool to make models for 3d printing. It will very easily let you create models that won't print well, or at all. The normals thing though is fairly easy to see and fix in Sketchup; in Sketchup normals that face the "wrong" direction get a blue-ish grey color (as opposed to the regular white). You can right-click on a face and choose "Reverse Faces" to flip the normal from facing inward to outward (and vice-versa).

[WaltP 0]

So THAT's what that color means! Thanks! The color looks good in Cura now. Let's see if the top and bottom print correctly this time.

 

[ahoeben 1,886]

The bottom of the sphere will need support to print.

[WaltP 0]

I just tried a print and this happened before abort:

 

It's a reverse of the actual design.

Do I have to add the support myself or do the settings in preferences  take care of it?

I do have Generate Support checked. What else would I need? There are so many settings that say Support... and I have no idea what most of them do.

Just found Drop Down Support Mesh - that looks promising...

 

I appreciate the time and info. Thanks again.

 

Edited August 19, 2019 by WaltP

[ahoeben 1,886]

1 hour ago, WaltP said:

I do have Generate Support checked.

You are set then. Supports will be added automatically.

 

See the Preview "tab" in the header. It will show you what will be printed without actually printing.

 

1 hour ago, WaltP said:

Just found Drop Down Support Mesh - that looks promising...

All settings have tooltips. Read them. This setting is useful for advanced users, but it will not help you with what you are doing now.

[johnse 31]

10 hours ago, WaltP said:

It's a reverse of the actual design.

Sketchup is also known for creating objects with “internal geometry” that messes with slicing.

 

if, for example, the side walls overlap with the bottom, it can cause something like that result. The slicer sees the outer wall surface and starts considering that “inside”. It then sees the inner wall of the sidewall that overlaps the bottom and thinks it has found the transition to outside. then it finds the circle that should have been the real edge and toggles again to “inside”.

 

It looks like you want to use Sketchup’s “Outer Shell” command as per this article: https://help.sketchup.com/en/sketchup/modeling-complex-3d-shapes-solid-tools