Linear motion guide unit

A linear motion guide unit comprising:

• a rail including a pair of first raceway grooves extending in parallel along a longitudinal direction;
• a slider straddling the rail such that the slider is movable relative to the rail, the slider including a pair of second raceway grooves respectively facing the pair of first raceway grooves;
• and
• a plurality of rolling elements,
• the rail and the slider defining an annular path in which the plurality of rolling elements circulate,
• the annular path including
• a raceway path defined by the first raceway groove and the second raceway groove,
• a first circulation path defined in the slider and extending side by side with the raceway path, and
• two second circulation paths defined in the slider and connecting the raceway path and the first circulation path to each other,
• in the linear motion guide unit, the second raceway grooves of the slider being defined in a casing of the slider, and
• each of the second raceway grooves including a first raceway surface extending along a length direction of the slider and a second raceway surface facing the first raceway surface and extending along the length direction of the slider,
• the second raceway surface including
• a first portion including a center portion in a length direction of the casing, and
• a second portion including end portions in the length direction of the casing and having a wall surface shape different from a wall surface shape of the first portion,
• in the first portion, the first raceway surface and the second raceway surface defining a symmetric Gothic arch groove,
• in the second portion, the second raceway surface having a surface recessed from a position symmetric to the first raceway surface, and
• the first raceway surface is uniform over the length direction of the casing.