Re: centering
135 deg drills are a bit stronger than 118 deg and seems like I can push them harder and they work better in some steels. Split-point drills help prevent walking the most.
Running the tool a bit above center probably does 2 things for you. First as the tool flexes it moves to be on center rather than below, and 2nd being above center makes the tool edge a bit more of a positive rake which aluminum like better
__________________
Jeff
|