Ah, still a newbie... but it was a thread during research which led me here...

My initial calculations, using a 6mm single flute carbide end mill, I calculated 4046 RPM at 20 IPM (508 mm/min)
However, I wouldn't dare run my machine quite that fast after tests, but after watching videos since, maybe I should... Awaiting more bits for more tests. Er, cut depth was 0.2 or 0.25 mm

Tried a few drill tests yesterday on mild steel, using a 4mm bit at 1350 (ish) RPM and the spindle stalled a few times whilst jogging down at 0.5 mm bites.

Thanks