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The proper way to adjust jaws in the 3 jaw chuck is to close the jaws on a ring at the back of the jaws. Then grind with a tool post grinder all but the ring, then take out the ring and grind that section of the jaws a little further. Before you go so wild, .001 out of center is really good for a chuck. When you check with a different diameter test rod, you will find it different. If you take the chuck off the spindle and put it back on you probably will find it bit different in magnitude and in a different position on the chuck. Remember the jaw centering depends on the manufacturing of a spiral and that can and will vary. Once you crank down hard on a piece of slipping hard steel, you will add further variations. REAL machinists use a 3 jaw self centering chuck only when they don't care for precision centering. When they want to center work precisely they use the dial gauge and a 4 jaw chuck. With practice they can center the work nearly as fast as you can tighten the three jaw chuck and check it for error. And the extra jaw of the 4 jaw often grips hard material better. There are 3 jaw chucks with adjustable mountings, but they gain you little since the error of the 3 jaw is always going to depend on the diameter of the work piece, so you have to check for error and adjust the back plate again. Might as well use a 4 jaw and adjust every time unless you are doing repeat work with the same size stock for days at a time. Gerald J.
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