Run your max rpm  at 1.5 inches per minute taking .03 depths of cuts for each pass to start. Use a 3 flute carbide end mill and be sure to use the air blast to clear the chips. Also try to get TiN Coated tooling. If at all possible try to drill a line of holes about .093 in diameter and .125 apart.
Copper is gummy material so use quality sharp end mills like DuraMill, or OSG.
This are starting recommendations that may have to be increased or decreased.