Maybe it is the export or something. I run the 3D toolbox and often models are not manifold.

I see things like two circles in slightly different positions but both are connected in different ways to the surrounding "single" instance model. Things like this mean you end up with "infinitely small volumes". There is no fully enclosed "volume" and so mathematically there is "nothing to 3D print".

As a model this makes no sense to do, and so it irks me.

But clearly the slicer software doesn't care or autocorrects and people make their 3D print happen just fine.

>Mesh formats like stl cannot represent a circle by its position and radius, while a parametric format like step can.

This is where I think the Geometry nodes can help. A node (function) can be used to represent the circle with inputs and outputs set or changed as required.[0]

I have not fully explored this space though and so my "hopes and dreams" may well be as useful as thoughts and prayers...

[0] https://docs.blender.org/manual/en/latest/modeling/geometry_...