I recently built a cnc and everything works fine except the z axis isn't moving how it should. When milling the z axis will get lower every time it retracts as if it is loosing steps. Also when I jog the machine it can't jog more than about 7mm in the z without stopping for a second then moving again almost as if it is binding. I connected the x plug to the z motor and the z works perfect and doesn't bind but the x axis does exactly what the z did when connected to the z plug and driver. I've tried a different driver, checked wiring, as well as changed voltages on the driver. The only way the z axis movies smoothly for more than 7mm is if the feed rate is turned down considerably. All other axis work great. Any help would be greatly appreciated.