Common Faults and Reference Repair Methods for Lead Screw Components in CNC Machine Tools
The lead screw in a CNC machine tool is an essential transmission element responsible for controlled linear motion and precise positional accuracy. During regular operation, factors such as lead screw accuracy, lubrication reliability, and maintenance protocols directly affect the system’s stability, machining precision, and service life. Therefore, upon detection of a lead screw fault, execute timely repair or replacement to prevent operational disruption and maintain high-precision machining capability. The following presents commonly encountered faults and technical troubleshooting procedures for CNC machine tool lead screw assemblies.
Lead Screw Replacement
1. To replace the lead screw, release both end supports, then loosen the fasteners securing the sliding saddle to enable removal. Use personal protective equipment while handling fasteners to avoid injury.
2. Installation sequence: First, secure the lead screw nut at the drive (motor) end; install the nut at the tail (support) end; adjust preload shim thickness; verify guide rail parallelism; and finally, install fasteners linking the lead screw to the sliding saddle.
3. After assembly, measure shaft runout at the motor interface, which must not exceed 0.02 mm. If tolerance is exceeded, correct alignment by adjusting the lock nut. Complete installation by attaching the motor shaft coupler. Note: When replacing the lead screw, position an appropriate support fixture beneath the vertical or inclined axis to mitigate damage from accidental impact.
High surface roughness value of machined parts
1. Insufficient guide rail lubrication inducing stick-slip motion: Apply suitable lubricant to restore smooth kinematic motion.
2. Localized scoring or abrasive wear on ball screw: Replace or conduct precision repair of the lead screw.
3. Faulty lead screw bearing resulting in irregular motion: Replace the defective bearing assembly.
4. Suboptimal servo parameterization with excessive gain: Recalibrate the servo drive control parameters.
Large reverse error, unstable machining accuracy
1. If the taper sleeve of the lead screw coupling is loose, tighten it and check with a dial indicator.
2. If the lead screw slide plate with the pressure plate is too tight or too loose, adjust or re-grind it.
3. Ball screw preload excessively high or low: Adjust preload and verify that total axial runout is within 0.015 mm.
4. If the ball screw support bearing preloading is wrong, fix and adjust it.
5. If the ball screw has big errors or moves along its axis, use the control system to auto-correct. Measure and adjust as needed with tools.
Poor lubrication of the ball screw nut
1. Confirm oil distributor operation: Inspect for blocked metered oil lines and clear obstructions to ensure unimpeded lubricant delivery.
2. Ball screw bearing cap not properly seated: Realign and secure bearing cap to ensure firm axial retention.
3. Inadequate lubrication of ball screw: Inspect oil distributor and flow passages; confirm adequate lubricant supply throughout the assembly.