Preload refers to applying a predetermined axial load to the ball screw under the required working conditions of a CNC machine tool, eliminating axial and backlash clearances, thereby increasing the screw’s rigidity, positioning accuracy, and servo responsiveness. So, what impact does preload adjustment have on ball screws in CNC equipment?

1. Clearance Reduction: Proper preload reduces or eliminates axial clearance in ball screws, enhancing transmission accuracy and rigidity—critical for maintaining micron-level precision during 5-axis simultaneous or turn-mill operations on machining centers.
2. Increased Rigidity: Preload boosts axial stiffness, enabling ball screws to better resist deformation under cutting forces from high-speed spindles and reaction forces from linear guideways, reducing servo motor following errors.
3. Wear Reduction: Appropriate preload optimizes the contact ellipse between balls and raceways, lowering Hertzian contact stress per unit area, thus reducing wear and extending service life within FANUC or Siemens closed-loop systems.
4. Thermal Effects: Higher preload increases friction, raising nut temperature and causing screw thermal elongation. Excessive preload raises servo motor torque demand, lowers machining efficiency, and can shorten ball screw life due to elevated heat.
5. Lubrication Considerations: Preload adjustment must align with the machine’s automatic lubrication system (intermittent or micro-oil-mist) to prevent lubricant film rupture under high pressure, avoiding premature flaking or corrosion.
6. Load Matching: Preload should match the cutting load profile of the machining center. Correct preload compensates for cutting-force-induced deflection, maintaining accuracy; however, excessive preload under high dynamic loads—such as those in turn-mill applications—accelerates ball fatigue and flaking.