Hi MRAKGR,

re:
> Considering the edges were so far away from the cutter, why were they a problem?

It has to do with the surface structure - for the areas with 4 coplanar faces each planar face has a kind of trapezoidal control point structure. That means that even though it is a planar surface it is a generic spline surface that happens to have all its control points in a plane.

That's a little different case than planar surfaces made by Construct > Planar which are able to use a specialized plane analytic surface that has some special case handling to get tighter accuracy on various operations like intersections.

It usually helps to have planar areas use the analytic plane surface and to have just one large plane instead of multiple coplanar fragments. That's a general cleanup step that is one of the first things I do with cases that are having difficulty.

I'm not entirely sure which step it is helping in this particular case, it would probably take a few days of work doing a deep analysis to determine that.

It's also possible to go about things in a little different way to avoid the overlapping. Like you can do a boolean with just these lines selected:



That will cut up the faces but won't be able to automatically separate it into different pieces but you can do that yourself using Edit > Separate, then Join together the pieces and use Construct > Planar to fill in the remaining pieces.

If the simplified planes didn't work then that would have been another way to do it.

- Michael