Abstract: A lathe carriage unit displaceably mounted on a bed for carrying and moving a tool post in a z-axis or x-axis direction comprises a saddle body having a guide slot extending along the length thereof and first and second bearing housings spaced apart from each other. A cross slider is slidably fitted to the guide slot of the saddle body for movement between an extended position and a retracted position. The cross slider can be caused to move by a drive mechanism into the extended or retracted position along the guide slot of the saddle body. The drive mechanism includes a ball screw rotatably supported at its opposite ends on the first and second bearing housings of the saddle body, a ball nut threadedly engaged with the ball screw and fixedly attached to the cross slider and a servo motor operatively connected to the ball screw for causing forward or reverse rotation of the ball screw.