While not quite as bad as some non-euclidean projective geometry, the geometry of 3D printed parts must be manifold and the spice must flow.
A 3D model is considered manifold if it is water tight and there are no holes in the geometry.While there are no obvious holes in the mesh below, at the point indicated it looks like the surface is not differentiable and is causing a problem.
Avoiding intersections like this will help ensure that your parts can be produced. Usually just moving the feature slightly will fix the problem.
Selecting Thrown Together from the View menu in OpenSCAD can also help trouble shoot problems. The patterned areas in the image above are indeterminate and will cause problems.
So, when performing composite solid geometry operations, it is important to remember that the piece you are subtracting must extend past the original part.
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