find and buy a tungsten carbide drill bit... They will not bend at all... they will shatter. go watch some utube videos about tungsten carbide drill.... go about 3/8" about 9mm or 10mm. buy two, you are likely to break one. also consider dremel tool with "reinforced" cutting discs.. slow but will get the job done.... try using what is called an "impact driver" that uses 5/16" bits as a first resort... you use a hammer to make an impact driver work..... Proto brand is my go to ... harbor frieght ought to be fine but the bits suck... spend the pennies for good bits, they are considered consumables so buy several.
1) impact driver
2) carbide drills
3) dremel tool
4) cutting torch
start with one and work your way down the list..