[RussMachine]

If it helps, I just finished circle milling a 5" diameter hole with a 1/2" 2-flute endmill, 1.25" deep.
I helical-milled it, dropping .050 per revolution.
Ramping down on every pass is less stressful on the endmill.
I was running the endmill at 3000 RPM, with a feed of 15 inches per minute (.005 per rev.)
Full flood coolant, and brushing the chips out of the groove every three or four passes.
It worked great.

[Don Clement]

I trepan holes from 3" to 4.25" diameter in 1/2" 6061-T6 plate all the time on my 1100 using a HSS 1/2" 2-flute high helix end mill. Spindle @2700 rpm and feed 15ipm cutting depth 0.1" per pass with flood coolant. I typically blow the chips off using a compressed air gun. I used to trepan these holes on the lathe (shown below) using Val-cut 6mm trepanning tool but the Tormach does that job faster nowadays. I have bucket full of 1/2" thick aluminum plugs trepanned with this method.

Don