@mcdanlj a mill would be great but I currently have no room for one. Btw, I ended up brute force drilling the broken taps out with a solid tungsten carbide bit (which broke twice), then I was able to drill & tap for 6-32. There was enough slack in the copper spreader to handle some misalignment. The rest of the 4-40 were done very carefully with a form tap and tap magic. I’ll try the spiral flute next.