As one of my first projects I was making a flycutter to fit in the R-8 spindle of my mill. Spent lots of hours turning, milling, drilling and tapping. I was quite proud of my new flycutter. Went to try it out and it would not pull in with the draw bar. Some investigating and I discovered that I had tapped the drawbar hole 1/2-20. Duh R-8 standard is 7/16-20. What to do, plug and weld, make a unique drawbar, and some other wild ideas. Thought that maybe I could Heli-coil it. Of all the good luck the tap size for a 7/16-20 Heli-coil is 1/2-20. I installed the Heli and all has been good for years.
dumb luck wins again.
lg
dumb luck wins again.
lg