BALL SCREW

PROBLEM TO BE SOLVED: To provide a compact ball screw having high load capacity and suitable for oscillating motion by arranging spacers formed, on both ends with recessed parts similar to the spherical face of a ball between adjoining balls. SOLUTION: In this ball screw 8, a plurality of balls 25 are interposed in a ball circulating mechanism constituted of a screw shaft 10, the ball screw grooves 11, 13 of a ball nut 12, a through-hole 15 provided in the thick wall part 14 of the ball nut 12, and adapters 23, 24. A plurality of spacers 26 are arranged between the adjoining balls 25. The spacer 26 is columnar or disc-like, formed with recessed faces similar to the spherical face of the ball 25 on both end parts in the axial direction, and the adjoining balls 25 are respectively slidably fitted to them. Because the balls 25 can be interposed extending over almost full length of the ball nut 12, load capacity and rigidity are enhanced. Further, even at oscillating motion, since the ball 25 does not eat into the surfaces of the ball screw groove 11, 13 due to mutual friction, jamming can be prevented from generating.