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A linear-motion bearing is a device used to allow motion of an object in a linear direction. The bearings within the system are usually small steel balls, though other types of bearings exist to accomplish this task. The function of a linear-motion bearing is to allow smooth movement of an object in a linear fashion, unlike most bearings that facilitate movement in a round orientation or circular motion. The two major components of the system are the plane and rolling element; these components work together to facilitate smooth movement, very often in machines or industrial applications.
The rolling element consists of ball bearings contained within a sleeve or oriented along a track. A linear-motion bearing may contain ball bearings or roller bearings, which are flat cylinders. The bearings facilitate smooth, low-friction movement, and they are usually lubricated in some way to further reduce friction and encourage longer life of the linear-motion bearing system. In some cases, these bearings are fully contained within the system to protect them from dirt, grime, and even impact damage, though in other cases the bearings may be exposed along a track. The system usually involves the use of a fixed plane and a sliding plane that slide against each other with the bearings in between.
An example of a system that uses a linear-motion bearing would be a sliding table, which is commonly used in fabrication. The table itself can expand or contract as the individual pieces slide, thanks to the linear-motion bearing. Jigs mounted on the table may also be moveable along a track that uses a linear-motion bearing, allowing the user to set up stops or guides in different configurations. This is useful when cutting angles or straight lines with a saw that must be guided to keep the cut straight.
A much simpler example of linear-motion bearings is the set of bearings used in many filing cabinets. The bearing planes are mounted on each side of the cabinet drawer, and another plane is fixed to the inside of the cabinet shell. As the drawer is pulled out, the ball bearings or roller bearings move within the planes to facilitate smooth movement of the drawer. This reduced friction is important for proper functioning of the drawer, especially when it is loaded down with a significant amount of weight. Older styles of filing cabinets did not feature such systems, and the drawers had a tendency to get stuck frequently when loaded with weight.