[ginger]

Are you using a drill chuck to hold an end mill?

Please don t do that- drill chucks are made to hold drills, and to drill holes. End mill holders or colletts are made to hold end mills. There is nothing you can do to a drill chuck and its morse taper socket to make it hold well enough to use for milling.

In addition, drill chucks never run dead true, so holding an end mill in one causes it to become a one tooth cutter.