Terry, yes, that would be the root radius. Sorry for the confusion, but always had the hexagon in mind while doing this and assumed it was obvious. I will have to give it a bit more thought to make it multipass. Don't want it to cut air at any point.
Russ, I agree, squares may not be practical, but I believe hexagons and above should be doable in metals provided the rake angle is correct. We shall see this. Now I really think eccentrics should be next... what do you say, Terry?
Hmm... didn't notice the metal hex sneaked in - obviously they have some better ways to make hex shapes out there...