>>coming from a Rhino 3 perspective, booleans aren't
>>always my friend, so I'm in the habit of making sure that objects
>>extend past the edge of where they have to cut..
>>that's why it didn't even occur to me to use the semi circles as boolean cutters

Hi Jesse, ...in some cases, Rhino V4 has trouble to make this kind of booleans with overlapping/sharing surfaces as well.. MoI seems to have more powerful geometry kernel related to booleans.... -Petr