Lightening a stock 440 crank

well I was planning on using a die grinder with a few carbide burrs, file and a 4 inch grinder. When chamfering the oiling holes I was gonna use a stone or maybe a sanding roll/tootsie roll. I’m not going to grind the mains nor rod journals. If that is what your thinking. Just going to remove a little excess material in uncrucial spots, radius and lighten the counter weights. I figure if the machine shop is going to have to balance it by drill holes deeper I might as well remove material before it gets to the machine shop. However I mainly am concerned with chamfering the oil holes. How “big” To make them?