Martin Eastburn wrote in
:

Remember Al expands on heating - and you will be hearing as you
cut or mill on it - thereby cutting off or milling off more than you
plan. The metal will have to be flooded as you cut - to keep cool
and make the cut in the right place.

Al isn't all that easy to work with if you want a precision final.
It is for the most part and alloys easy enough to cut, but precision
is tough.

That's pretty much a general issue with holding tight tolerances in the
stuff. My big concern is not that the depth & width of the slot are
within a thousandth, but that the angle of the slots on each end is
within a degree or better.

I've typically used my collet block for working on round stuff this size,
but I should have a Vee block or small vise that will allow me to
reposition the work without losing my reference.

Using a keyslot cutter has the advantage that with appropriate clamping,
I don't have to move the workpiece at all.

Doug White