Ed, your website post brought this back to the front of my mind. 

What type of tool attachment does your mill have?  Ours uses a Morse taper and a Jacobs chuck, and any time I try to mill for more then a few minutes, the taper will come loose and once it does it's next to impossible to accomplish anything because it will not stay in again. 

My question, how am I supposed to keep the taper seated tight?  If it is not appropriate to the milling application, why on earth do they put it on a mill/drill machine?  

Second question....what is an appropriate RPM for a 5/16" end mill in mild steel?