I put a new ballscrew in the table slide of my machining center but I still have backlash. Why is that?
Most likely the ball screw thrust bearings were not replaced or installed correctly, or the servo motor drive mechanism is not adjusted correctly.
Many machine tool manufacturers use a servo motor with a toothed timing belt to drive the ball screw, it is important that this belt is adjusted correctly so that it doesn't cause errors in positioning.
Also, if the electronic backlash elimination built into the control has been changed, it may need to be reset for the new screw. To do this it is best to make note of the existing setting then start from zero and gradually increase the parameter settings until the best result is achieved.