More of a metal working question I'd imagine but I installed a rear rack many years ago using carbon steel fasteners thinking I'd swap them for stainless in a timely fashion Needless to say I forgot all about them and they rusted in the threads of my aluminum Jamis Coda. One drilled out very easily essentially disintegrating without even using the easy out. On the other I've gone thru five drill bits and only managed to get a single 1/16" off center hole in the broken off flush threaded section of the screw. Really trying to not damage the thread in the frame so what are best practices for drilling out a machine screw ( now just a threaded stud ) from an aluminum bike frame?

Edit: My image loading skills were deficient