I have a project where I need to cut a 0.188" radius fillet for about
16" in aluminum. Unfortunately, the cut is at the bottom of a 4.5"
deep channel. I haven't been able to find a cheap ($20) ball/radius
mill that is long enough to do the job.

However I can get a .75x6" HSS two flute for about $7. Could I get
away with just grinding a radius on the end of the flutes? I don't
have a grinding jig so I'd have to do it by hand. I'm thinking that
it might be wise to grind it such that only one flute is cutting.
That way they don't have to be the same. Obviously, this is a hack
--- I realize that. That said, my tolerance is loose and my budget is
low.

Thanks for any advice,
-DC