Actually, using a drill is perfectly ok. A drill bit is precision ground to it's outside dimension. Where a drill can become inaccurate is when drilling a new hole (as opposed to enlarging an existing hole) because the tip pressing against the material can cause the drill to wobble which can make the hole slightly larger (although in most cases, it will only be 4 or 5 thousandths of an inch larger). But when enlarging an existing hole, the drill will follow the hole and stay within .002" (or about the diameter of a human hair).