I loosened the carriages that ride the x rails a bit...that is, the bolts that attach the carriages to the lower gantry. Then I backed up the gantry under power until it was at the x=o end of the table (I placed two equal sized blocks of MDF between the legs and where the gantry would hit). So with the gantry jammed against the MDF blocks, I figured the gantry was as square to the x axis as the table was square. Then I tightened the x axis carriages to the gantry. If you find you cannot get quite enough adjustment that way, you may have to loosen the fasteners holding your gantry together, and go through the same sequence.