It looks like flex in your machine is causing the slight curve in those lines. I'd make sure that new spindle bracket was rigid, and that your whole machine wasn't susceptible to motion when the spindle is stressed. With the machine turned on and the motors locked, try putting a pen in the spindle, touching it down to a piece of paper on the bed, and then pushing on the spindle in various directions. Does the mark on the paper remain a dot, or is it turning into a dash, or a comma?