Brian wrote:

I find drilling small holes in the kerf really helps on the chip clearance
with holesaws in aluminium. If I had that mill, I'd be tempted to put a
trepanning tool together and try that.


I've never done one quite this big, but before I had CNC, I did set up
to trepan
out some 2.5" or so holes. At very low RPM, it cut long, stringy chips that
were mostly pulled up out of the hole, so chip clearance was not a big
problem.
It went through on power feed rather quickly. I just ground a special tool
to use in my boring head.

Jon