Steady Rest Accuracy
by Jack Johns
I was asked to re-machine the centers, in both ends, of four 4″ diameter x 50″ long hardened rolls. The ends were plugged and soft, so they could be machined. The tolerance was .0002″ TIR on a dead center.
I set up a roll in the usual way, using a four-jaw chuck and solid steady rest jaws. After cutting the center and checking it, it ran out .0015″ TIR.
An older machinist saw that I was having difficulty and explained that the chuck jaws were deflecting the roll, even though I had indicated the roll very accurately. He told me to place a ring of 3/16″ diameter brass or other soft metal wire around the chuck jaws, making sure the wire ring is square with the chuck to prevent deflection. The results were very good; I received a number of sets to do!
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