how high are the RPM's. Generally, a good starting point is 1200 SFM. You shoud use a 2 flute high shear Endmill. If the RPM's are too high, youll just rub and not cut. I would start at 1/3 dia of endmill for DOC. Just take Your time, and you should be fine. Also, Magafor makes a good spotting/V-groove tool for your starter holes.