Hey, just a thought here. This may sound obvious, but, is the drill centered correctly in your tailstock? Are you holding it in a drill chuck? I would check this first if it is wandering at all. The next check would be the cutting faces of the drill bit. I have found some cheap drill bits with unequal length cutting faces, causing chatter, wander, breakage, etc. Maybe trying a good drill bit would help determine if it is setup or tooling.
As far as centre drills are concerned, in Al, geometry of the centre drill doesn't much matter, as long as it's in the centre! There is no worry about work hardening of the pilot area that you would get with other materials such as stainless. Even 7075 Al is soft enough that no matter what centre you choose, the drill bit will cut through it with ease.
I think the idea of using an open web (the spiral part of the drill bit body) is a good idea for chip evacuation. Find a good tool supplier in your area. Maybe visit a machine shop and ask the guys which suppliers they use? Oh, and the way that I learned was to read as many catalogues as possible, and try as many different tools as possible. Oh, and keep notes - the time you spend here will pay dividends in the long run.
Good luck.
Adam  |