Precision Linear Bearings

Precision Linear Bearings

Precision linear bearings allow objects to be moved in one straight direction at high speeds with superior accuracy, low noise and vibration, and maximum life. Linear bearings in general are not capable of consistently accomplishing those tasks, and precision bearings are used in demanding situations for high-performance work with the least amount of machine downtime. Precision linear bearings must meet certain regulated standards to be approved by ABEC, the Annular Bearing Engineers’ Committee, who rates the accuracy and tolerance of bearings. These bearings are made from the same materials—stainless steel, ceramic, aluminum—that regular bearings are made from as well as being in the same circular or disk-like shapes. Precision bearings are designed to meet the most demanding tool requirements and can be found on heavy load or high speed assembly lines, in the hard drives of computers, for high-speed grinding, boring and milling and other applications. The four main types of bearings are available at the precision level, including ball bearing slides, roller slides, bushings and dovetail bearings. Special finishes on the raceways, or grooves in which ball bearings travel, aid in achieving the highest possible operating speeds.

Often cited as the most precise are linear air bearings. Because the bearing itself does not have contact with any surface, the bearings are frictionless and do not generate heat, which could cause distortion and wear to both the housing and bearing. Since the bearing never degrades, air bearings need to be calibrated only once; they never lose precision or accuracy. To ensure the best performance for air bearings and precision linear bearings alike, bearings can be preloaded which maximizes the rigidity of the system, eliminates radial and axial movement and prevents the balls (if present) from skidding under very high acceleration. Preload is the application of a thrust load to the bearings which removes any internal clearance or undesirable spaces between parts. There are four types, mainly weight, vacuum, magnetic and opposing air bearing preload. Weight preload adds mass to the system as it compresses air inside the bearings so it rides stiffer; vacuum preload accomplishes the same goal without adding any physical weight. Adding magnets to the stationary part and to the moving part of the bearing adds stiffness to the system although at high speeds, the magnets could generate currents that would oppose the motion of the machine. The final method is solely for air bearings as it uses another set of air bearings to preload each other. This provides twice the stiffness of a single bearing but reduces the load capacity by half.