I've learnt over the years to use tootsie rolls to do this.. on my B1 I
could use the mill and a end mill but I had a lot to take out.. seldom
do I ever use a alum cutter in a air grinder.. its to easy for it to wobble
around the hole and it takes too much material off to quickly(I would
rather use a steel cutting bit which is much easier to control
I tried to tell him that in my post but others insisted on telling him to buy the single cut aluminum burrs. After a grinder wings out of control and you bend the burr it teaches you the right way. Slow and easy and it ends up looking like a professional did the job instead of a HACK. LOL
I agree 100% with ya
don't forget to use a grease of your choice when using burrs. it will prevent them from clogging up.
tootsie rolls come in lots of grits, so start out with a rather course grit, then finish with 80 or 100. even finer if you are after a polished appearance.
if starting as a nu-be, grab a chunk of scrap material to practice on, so you learn the nuances of your grinder, and the way a burr or tootsie roll cuts.
use the shortest cutter you need to get the results you are after. this will prevent the dreaded bent cutter and out of control grinder.
however, 6" long cutters are made for a reason. slow and steady beats 100k RPM and hackin' away every time.