Full definition
Deliberately applied axial load on a pair of angular contact or tapered roller bearings to eliminate internal clearance, increase system stiffness and improve rotational accuracy. Types: spring preload (soft, constant force) or positional preload (rigid, via shims). Typical values: 20–500 N in machining spindles. Excessive preload raises temperature and reduces bearing life. ISO 15 standard. Critical in CNC spindles and precision gearboxes. Brands: SKF, FAG, NSK.