Rich,
Do you use the 'D' bit type? I have some that are tapered from 1/4" to a point - (guessing) close to .020 and carbide is so darned brittle. I've found that 2600rpm is so much too slow that the feed must be ridiculously slow to keep from breaking the tip of the tool off. That's a job that at spindle speed and feeds such as they need to be, ya walk away from pretty quick....boring! The smallest E.M. that I have is 1/32" and it's been perfectly safe because of this slow spindle speed. Somehow I wound up with a very slow three phase motor for this mill's VFD, so stepping it up with the belt steps still makes a very slow spindle...
Thanks,
Bill C.