Hi Brian, yes it's mostly meant to be used on open curves. With closed curves or solids it is more of a swiss cheese effect.

There really isn't a whole lot to it, it's just doing boolean difference with a circle as the cutting object. On an open curve just pieces of the curve are removed while on a closed curve or solid pieces of the cutting object are part of the result.

> but sometimes it works on an open curve, selected or not selected, or else "calculation fails"

The "Calculation failed" will happen if any of the candidate target curves are not on the same plane as the circle. if you run into this then select some curves that will be on the same plane as the circle so it only tries to target those.

Maybe it would be better if it automatically skipped over curves that are not on the same plane as the circle.

- Michael