I just got in a Shars 6" 2 piece jaw, 3 jaw chuck with back plate, for my SB9A. I mounted it up and chucked up an arbor and found it to be over .015" tro. I may have isolated some of the problem to the back plate. It's got a .007" warp on the face and about the same on the edge. I've contacted Shars, but am waiting for a reply. I was wondering if I should turn the back plate true, or just let them send me another if they will. I appreciate any ideas here. The best I can tell, my spindle is <.0005" tro. It's hard to check it with the threads, but with the stock faceplate, that's what I got.