IMG 5790

Last step in the milling operation is to drill (4) 1-1/4" holes in the plate. This is used in an oil well and they need to circulate cement or drilling mud past the nut. The holes are for circulation. The problem is the plate is held in a 3-jaw chuck. That means no matter how you line it up one of the holes will hit a jaw. The solution is to center drill all four holes then drill the three that are clear of the jaws. Now I loosen the chuck and rotate the plate and line the center drilled hole up with the center drill. It's not super accurate, but generally within 1/64" and, since it's just a fluid hole, that's plenty close. I will pilot the hole with a 13/16" S&D bit followed by a 1" and then finish with 1-1/4" drill.