Hi Steve, well it is true that Trim is a kind of lower level operation that does less work than booleans, and sometimes you can get things done with Trim where the booleans are having problems.

But I'm not sure if that was why you had success this time or not, that ZSurf generated surface is mega complex and previously when I looked at it, it seemed like things might be running into some refinement limits in the geometery kernel, like giving up when attempting to generate an intersection curve when it gets over some particularly large control point count like 100,000 control points or something along those lines.

Those sorts of super complex single surfaces are not that common in CAD usually so the geometry kernel has not really been tuned up to work on those kinds of things so much.

It could probably help to simplify the surface at least somewhat, like use half as many sample points on it or things like that.

- Michael