So a spot weld is super hard stuff, right? I busted several cobalt bits trying to bore through a spot weld on the old trigger guard I'm reusing. I was about to break down and purchase a carbide bit from my local Grainger. Before I did I asked one of my instructors if he happened to have any in our shop tool closet. He didn't but he did offer me an unconventional solution. Burn it with an EDM machine. So this afternoon he set up the EDM and burned a perfectly clean, round hole for me.