1. Field of the Invention
This invention relates to a linear motion ball bearing used for guiding portions which perform a linear motion such as a machine tool table, a positioning table, etc.
2 Description of the Prior Art
According to a conventional linear motion ball bearing of this type, generally a ball return hole is formed axially in a bearing body to let balls circulate in an axial direction, and a machining for curved surface is performed to connect end portions of the return hole and a loaded ball groove formed in the bearing body, and further a return cap having a ball turning groove for changing the direction of the balls by 180.degree. is applied to each end portion.
However, in order to prevent balls from falling off when the bearing body is pulled out from a rail base, it is necessary to provide a separate ball retainer. In addition, the aforementioned return caps are required which increases the number of parts.
A very different linear motion ball bearing has been proposed in U.S. Pat. No. 4,632,573, issued Dec. 30, 1986 to Katsutoshi Itoh, in which upper and lower ball circulation paths are formed surrounding a leg portion of a bearing body with loaded ball grooves. By fitting the circulation paths, one upon another, to the leg portion, upper and lower members are each formed with an opposingly J-shaped groove, and an intermediate member is formed on upper and lower sides thereof with opposingly J-shaped grooves and further grooves connecting the tips of said J-shapes.
The above-mentioned bearing does not require curved surface machining at the ends of the loaded ball grooves of the bearing body; nor separate provision of ball retainers. However, it unavoidably becomes larger widthwise, requiring larger space.
Therefore, an overall size becomes larger if one wants to increase the width of the leg with a view to increasing the rigidity of the bearing.