BALL SCREW AND MACHINE TOOL USING BALL SCREW

To reduce thermal displacement in an axial direction of a ball screw for driving used in a feed shaft in a linear direction of a machine tool with a simple constitution.SOLUTION: A ball screw 150 includes a fastening tool 70 constituted by inserting a shaft 60 composed of a carbon fiber-reinforced plastic material having thermal expansion coefficient smaller than that of a metallic material, into a hollow portion 50 of a screw shaft 12 composed of the metallic material having a prescribed thermal expansion coefficient, and having a diameter reduction portion 70a of which a diameter is reduced into the taper shape toward a central portion side of the ball screw, and a uniform diameter portion 70b disposed at a central portion side of the ball screw with respect to the diameter reduction portion 70a and including an inner peripheral face to which an end portion 12a of the screw shaft 12 can be fitted. At an end portion 150L of the ball screw 150, the end portion 12a of the screw shaft 12 is fitted to the uniform diameter portion 70b, and an end portion 60a of the shaft 60 projected from the end portion of the screw shaft 12 is fitted to the diameter reduction portion 70a of the fastening tool 70, and fixed by a bolt 801 (802).SELECTED DRAWING: Figure 4 【課題】簡単な構成で工作機械の直線方向の送り軸に用いられる駆動用のボールねじの軸線方向の熱変位を低減する。【解決手段】ボールねじ１５０は、所定の熱膨張率を有する金属材料から成るねじ軸１２の中空部５０に上記金属材料よりも小さい熱膨張率を有する炭素繊維強化プラスチック材料から成るシャフト６０を挿入して成り、ボールねじの中央部側に向ってテーパ状に縮径する内周面を含む縮径部７０ａと縮径部７０ａよりボールねじの中央部側に配置されねじ軸１２の端部１２ａを嵌合可能な内周面を含む均径部７０ｂとを有する締め付け具７０を備える。ボールねじ１５０の端部１５０Ｌにおいて、ねじ軸１２の端部１２ａを均径部７０ｂに嵌合し、締め付け具７０の縮径部７０ａにねじ軸１２の端部より突出させたシャフト６０の端部６０ａを嵌め込み、且つボルト８０１（８０２）により固定する。【選択図】 図４