Hmmm.... I was just noticing something while cutting off a part yesterday. After an F20 command, and my motors set at a max for 20 I was getting diaginal cuts at 27-28 IPM. It was visibley faster than the axis parrallel cuts. Is this something I just have to live with? Obviously neither motor is exceeding its individual speed, but the net result is a much faster feedrate.
In this case I was using a full 1/8 cutter with enough rigidity and speed to handle it, but if I had been using a smaller mill and pushing my feed speed for the cut I could easily has snapped it with a sudden increase like that.