Math has never been my strong point, I've looked up the formula in the machinist handbook but can't seem to figure it out. Anyway I built a special ID bar that has a adjustable cutting angle for making spiral grooves in different sized bronze bearings but I need to know how to preset it so it won't rub, can somebody explain in plain English how to figure this angle? I included a simple drawing of the tool I made and I need the angle listed, say for a 2.2" bore and a 6.5 in. lead. I made this spiral groove yesterday and just eyeballed it to about 46 deg. and it worked great.