Re-install the X/Y carriage within the assembly by gently slipping the 12mm linear rails into the bearings and engaging the X-axis lead screw. With the lead screw engaged within the carriage, slowly thread the lead screw through the carriage and capture the spring-loaded X-axis lead screw nut (refer to the original product assembly notes if you are not familiar with the lead screw ant-backlash nut assembly process).