I will use no mill before it's time...
Had to mill a 1/8th inch slot across a 7/8 x 14 bolt. Put it into a V block, indicated down the shaft where there were no threads (kinda sorta close), then milled it.
The Cutting Speed for HSS is 60-100 SFM, diameter of the cutter is .125, should be 1920 RPM. I don't think it got that fast...
CS x 4 RPM = ------- D
This formula doesn't include the feed speed. Just fed it slow. No snap, no flying shards...
I see the worth of a Weldon Shank end mill holder. It lowers the mill about 1" or so away from the quill, so it's easier to move the table without the quill running into something, like the strap clamp bolts...