Ah... makes sense. I thought about trying some RH cut, LF spiral carbide endmills, but never got around to it. THought they might "induce" coolant into the cut from the nozzle. But yeah, the flex from HSS in that small diameter gets kinda unruly... then add speed, and the chatter gets a little obnoxious.
But if it works, it works eh? :D
Wade