Axial movement caused by insufficient preload of lead screw bearing. Screw clearance. The sliding saddle is not well matched with the guide rail and the belt pressing plate, resulting in crawling. It is the commutation error caused by the gap that makes the machine tool unable to perform the action immediately during commutation. Reverse clearance refers to the transmission clearance of ball screw pair, including the clearance between ball screw and rolling nut and the clearance between ball screw and bearing supporting it, mainly axial clearance. It will cause idle stroke in the initial stage of the reverse movement of the tray, that is, the screw rotates but the tray does not move until the gap is eliminated. Inspection method: Manually move the coordinate axis in one direction for a certain distance, then tap the support plate with the dial indicator, and then move the support plate reversely with the handwheel until both hands swing, and the handwheel moves by a reverse clearance. Input this value into the clearance compensation in the numerical control parameters. You can use the handwheel to shake the table to fix the dial indicator on the machine tool, and press the meter head to a certain shaft table for half a turn, that is, 60 lines (channels) to record the value (preferably the whole scale is convenient for observation). Select the gear position of X 100 (0. 10) with the handwheel, shake it for 2-3 squares in the direction of the gauge and then reverse it (normally it should also be 1 square). For example, if you take 0.06 and the reverse clearance is 0.04, then you can compensate the reverse clearance in the parameter 185 1 (the unit of this parameter is 0.00 1, so enter 40). Parameter 185 1 is cutting feed clearance compensation 1852. Moreover, in theory, the maximum clearance compensation is 2mm, so if the clearance is too large when measured by an instrument, it is necessary to check whether the mechanical transmission is loose first, and then make clearance compensation after mechanical adjustment. Check the ball screw before adjusting the reverse clearance. If there is nothing wrong with the ball screw, check and adjust the preload of the screw, then measure the clearance and modify the parameters.