Re: Total newbie, hobbyist question: Screeching with countersink in aluminium
I normally turn countersinks at 500 RPM or less except in wood. My favorites are M.A. Ford single flute, or 0 flute, pretty chatter resistant. WD-40 would be helpful. You might try countersinking with a hand drill at low speed, I do that a lot. Also a countersink pretty much lives in my drill press for quick deburring and countersinking.
I'm surprised your spindle will work at all as low as 2400 RPM, usually the floor on those is about 6000 RPM. They produce almost no torque at low RPM.
Jim Dawson
Sandy, Oregon, USA