Carbide end mill did the job, thanks for the suggestions. However, even with a carbide end mill, i had stacked five blades to machine in one go (with teeth alternating side to side so that the stack remained flat), and the bottom blade fractured just like the blade I tried drilling with a carbide drill. I think back support is just as important as using the right tool for a job like this. I had set the blades up with a 9/16" gap around the hole location, well clamped on both sides. Probably should have used a piece of scrap aluminum under the blade stack.