The easiest way to make a test bar to align centers is to use a 12 inch piece of 1/2 x 13 threaded rod. centerdrill each end. At each end screw on a nut , a large washer and another nut to lock the washer. Place between centers, take a light cut on each washer(don't change depth of cut). If the diameters of the washers are equal, the centers are aligned.