More lessons learned: The mill get knocking the workpiece out of the oddball vise above, so I went back to the Sherline mill vise. Did not fix the problem. As the center of gravity (or is it center of pressure?) rises above the vise jaws, it gets harder and harder to hold theworkpiece in the jaws. So I have reduced feedrate to 2 in/min and 0.005" removed per pass. This makes it even slower. When I get into production for this part, Iwill find avendor who can give me a 2 3/4" wide workpiece.
By the way, feed rate and depth of cut are inversely related. At 1 in/min, you can cut much deeper than at 3 in/min. I need one of these.