if any body can help? the z movement stutters mostly when traveling at 25% override in the plus direction.I removed the belt and ran the motor with the hand wheel seemed smooth. when the jerking starts the pulley on the motor jumps back & forth as it turns. could this be an incoder problem? feedback?or amplifier problem? this machine has been running fine up until it started breaking taps. because the movement was not steady. seems to be losing position.