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I have a bit of an odd one.

enter image description here

Consider the above face, composed of 4 vertices. 3D Print tools is informing me that it (and it's mirror image) is non-flat. All other faces are flat.

Yet for each vertex, the Y coordinates are exactly the same (-3m, manually provided), which should indicate that the whole face is flat and perpendicular to the Y plane. Indeed, in orthographic view, none of the plane can be seen as curved or twisted at all.

Is there any good reason it is 'non-flat'?

Oddly, if I form the same face from only three of the vertices, it is apparently flat. However the rectangular face adjacent to it becomes non-flat and I have a host of other issues such as introducing a tri, non-manifold edges etc. etc.

Has anyone any advice on why this might be the case?

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  • $\begingroup$ I'm not sure what "rules" your 3D Print tools follow, but it's possible it's topology related - just not in the way you think. I'm wondering whether the software doesn't like that the topmost and bottommost vertices have 5 edges connected to them (vertices are "poles"), whereas the vertices on the sides have 3 edges connected - "proper" quad based topology would have each vertex connected to exactly 4 edges, but if tri's are allowed, I would assume 3 edges would work as well. I'm just not sure how it would handle the "poles" . Not saying this is the problem - just a possibility to explore. $\endgroup$
    – Christopher Bennett
    Commented Aug 9, 2021 at 21:06
  • $\begingroup$ @Christopher Bennett - the Tool itself is just the Blender Add-on. I'm new to this, but I assume Blender Add-ons generally play nice with Blender vanilla. But that's a very good suggestion. My only quibble would be that prior to some work here and there (unrelated to those vertices) this face 'worked'. Along the way, Blender has just decided not to play ball, frustratingly. Thanks for suggestion though. $\endgroup$
    – Aethon
    Commented Aug 9, 2021 at 21:10
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    $\begingroup$ Solved it! This outer (long) edges of this face formed part of a fragmented edge loop that bisected the mesh on the x-axis. All the vertices in that loop, including these, were set to -3m, aside from 4 vertices which were part of a kinked joint in an extruded trim. Setting those two pairs of vertices had the bizarre effect of helping the 3D Print Toolbox redefine the faces as flat, even though they weren't adjacent at all. Basically, Blender being weird. Moral of the story - check all your vertices on an edge loop aren't causing faces attached to it to be... weird. $\endgroup$
    – Aethon
    Commented Aug 9, 2021 at 21:29
  • $\begingroup$ How to you check that? $\endgroup$
    – Max Appian
    Commented Jan 21, 2023 at 15:40

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