I am in the process of adapting an ER32 collet chuck for use on a SB9A. My plan is to use a back plate for mounting to the 1.5-8 threaded spindle. My concern is with the collet chuck itself. In my mind, the registration diameter on the back of the chuck must be concentric with the collet receiver on the other side of the chuck. The chuck is of Asian quality, and it is about .006 TIR off between the registration diameter and the collet receiver. I have determined this by chucking up the threaded end of the collet chuck in a four jaw. When the collet receiver runs true, and then check the registration diameter, I get the .006 discrepancy. I am considering taking a light truing cut on the registration diameter at this point with a carbide boring bar to make sure that both readings are zero. I wanted to be sure that there is nothing I am not aware of with the ER series before making this slight modification. Thanks in advance for any insight on this. I wish to only do this once, and do it right. The first chuck I got was defective, in that the collets would not fit in the chuck at all. As a matter of fact, it is the defective chuck that I ran this test on, but I am preparing for mounting the replacement chuck when it arrives.