Hi Dave & Michael,

I've had situations before where a model wouldn't Boolean together & I've still been able to machine it with my mill.
In these cases, I've selected all the parts & exported them out as an STL file for the CAM program.
I used the default export settings, but increased the slider to it's maximum, which I think is a value of "3".
All of these milled models have come out fine.

Obviously you couldn't do this with a model that's for RP or to be "wax printed" or "grown", as these processes require the model to be water tight or a complete solid.

Hope this helps, Colin