so this will be something I've never tried before. need help with some dimensions . I don't have my machinist handbook yet. it's on the way. I bought a 4 jaw chuck and the back plate is 2-1/8" x 8tpi .. I need 2-1/4" 8tpi . so bore it out and re-thread it. ok this might be beyond my skill level. maybe someone can talk me through it .