I actually had a similar problem this past weekend while working building my diy cnc. I bought thomson rod and needed to drill and tap it for support rails. Well, let me tell you, my first attempt frustrated me for hours. I created flats on the shaft with a grinding stone on a mill. I went in about .05 inches thinking it was enogh. Went to drill the holes and nothing, still hard, ruined one end mill and 2 drill. The next morning a professor saw what I was doing(I'm a student at Rutgers University and have access to the machine shop) and told me he once had the same problem and that he went to Home Depot and bought a carbide masonary bit to drill through hardend shafting like thomson rod. He said that the carbide bit would build up heat high enogh to locally soften the material and cut it and not effect the bit. I was skeptical but went out and bought a 5/16 bit for $5 and WOW, it worked like a charm!!!!!!! The chips flew off dark blue and at times glowed red hot, but the area being drilled showed no signs of heat. I used it to drill through the hardened case up to the soft steel, about .12" in 1" rod. From that point, a #7 drill and 1/4-20 tapped. The drill lasted me for 18 holes, with plenty of life left.  |