Originally Posted by bulgie

True but lots of people are not great at drilling holes, can make it worse. Drilling at the top of a slit, the lack of any metal on one side of the hole makes the drill want to wander to that side. Do-able of course but some drilling knowledge and experience is required. One option is drilling just above the slit so the drill doesn't have as much desire to wander, then connect the slit up to the hole, but that has its challenges too, and it's reducing the amount of un-slit quill, lengthening the slit. Drill the smallest hole you can (that still removes the sharp corners) because any metal removed is likely reducing the strength of the quill.