Linear bearings generally use a pad, bushing, or roller system to carry a load on a rail that need not be a straight line. The rail can be most any length, although that dimension is limited by the actuator.
The durability of the bearing is determined by the load and required speed. Furthermore, rails can generally be any profile – simple flat surfaces, round polished rods, or complex profiles with polished ground surfaces on which balls or cylindrical rollers can ride. Hard (Rockwell 6 and ground bearing surfaces work best.
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