Ball screw device

A ball screw device, comprising:

• a screw shaft having in its outer peripheral surface a spiral ball rolling groove;
• a metal nut main body formed substantially as a cylinder with a through-hole through which the screw shaft is to be passed, the metal nut main body being threadedly engaged with the screw shaft through a number of balls, having in its inner peripheral surface a spiral load rolling groove facing the ball rolling groove of the screw shaft to form a load ball passage, and having in its inner peripheral surface a recess cut out in correspondence with both ends of the load rolling groove;
• a synthetic resin pipe member mounted in the nut main body and forming a ball return hole substantially parallel to the screw shaft;
• a return piece fit-engaged with the recess of the nut main body, the return piece being equipped with a scoop portion for dislodging the balls from the ball rolling groove of the screw shaft and a direction switching passage for guiding the dislodged balls to an entrance of the ball return hole, and cooperating with the pipe member to form an endless circulation route for the balls;
• and
• a cover plate formed substantially in a doughnut shape and fixed to each of both axial end surfaces of the nut main body to cover the return piece fit-engaged with the recess of the nut main body,
• characterized in that the return piece is divided into a first piece and a second piece by a curved plane including a center line of the direction switching passage and
• characterized in that the first piece is formed integrally with the cover plate, whereas the second piece is fixed to the first piece.