I'm trying to drill a .3970 diameter hole .375 deep into 6005 T5 Aluminum using a spindle that lacks power in the lower rpms so I have to feed the cutter into the material at nearly 18,000 rpms. I'm plunging the cutter at 50 ipm which was a feed recommended to me by a representative at Onsrud.

During my first attempts at this I used a single O Flute cutter from Onsrud. They worked great with no re-weld and good chip formation. But the cutter kept breaking about halfway up the shank after about 100 holes. My guess that this break is due to the un-tapered router cutters' flute edge contacting the material throughout the entire plunge, which is putting intolerable stresses on the brittle carbide. With these cutters being nearly 80 bucks a piece, each time one breaks I can't eat dinner that day and I'm getting kinda skinny. So back to the drawing board.

My next idea was to use a tapered Drill cutter and try to slow the rpms down as low as I can. But i'm guessing i'll only be able to get it down to about 15,000 rpms, 10,000 if i'm lucky. This seems to me to be way to fast and that I'll get real short tool life to no tool life at all.

Does anyone have any experience with anything similar to this and have any advice for me?

I appreciate any input. Thank you!