A rotational force transmission mechanism includes a shaft and an engagement member. The shaft is rotatable about a first axis. The shaft includes a leading end portion having a second groove and a first groove which is configured to receive a rotatable portion of a tool holder so that the shaft rotates the rotatable portion about the first axis. The engagement member is movable along the first axis between a first position and a second position and rotatable about the first axis together with the shaft. The engagement member includes an engagement portion configured to be received in the second groove. At least one of the shaft and the engagement member has an inclined surface that moves the engagement portion in a direction toward the first axis when the engagement member moves from the first position to the second position.

A rotational force transmission mechanism includes a shaft and an engagement member. The shaft is rotatable about a first axis. The shaft includes a leading end portion having a second groove and a first groove which is configured to receive a rotatable portion of a tool holder so that the shaft rotates the rotatable portion about the first axis. The engagement member is movable along the first axis between a first position and a second position and rotatable about the first axis together with the shaft. The engagement member includes an engagement portion configured to be received in the second groove. At least one of the shaft and the engagement member has an inclined surface that moves the engagement portion in a direction toward the first axis when the engagement member moves from the first position to the second position.

A support member includes a base projection. A cover includes a press-fitting portion and a cover projection. The press-fitting portion is press-fitted to a press-fitting hole of the support member. The cover projection is placed at a location, which is spaced from the base projection in a state where the press-fitting portion is press-fitted. At time of disassembling between the support member and the cover by sliding the cover in a releasing direction, the base projection and the cover projection contact with each other to form a disassembly indication mark, which indicates the disassembling between the cover and the support member, on at least one of the base projection and the cover projection.

A spindle apparatus for use at a machine tool, having: an assembly including a workpiece spindle to receive an elongated workpiece and a motor for driving spindle rotation of the workpiece spindle about a spindle axis; a rotary guide-bush assembly being axially arranged with the workpiece spindle with respect to the spindle axis, the rotary guide-bush assembly receiving the elongated workpiece supported at the rotary guide-bush assembly to rotate about the spindle axis enabling movement of the elongated workpiece; wherein the rotary guide-bush assembly includes a portion to clamp the elongated workpiece, received in the rotary guide-bush and in the workpiece spindle, to transfer driving torque applied from the spindle motor during a driven acceleration of the rotation through the clamped elongated workpiece for rotation of the rotary guide-bush synchronized with the driven acceleration of the rotation of the workpiece spindle.

A spindle apparatus for use at a machine tool, having: an assembly including a workpiece spindle to receive an elongated workpiece and a motor for driving spindle rotation of the workpiece spindle about a spindle axis; a rotary guide-bush assembly being axially arranged with the workpiece spindle with respect to the spindle axis, the rotary guide-bush assembly receiving the elongated workpiece supported at the rotary guide-bush assembly to rotate about the spindle axis enabling movement of the elongated workpiece; wherein the rotary guide-bush assembly includes a portion to clamp the elongated workpiece, received in the rotary guide-bush and in the workpiece spindle, to transfer driving torque applied from the spindle motor during a driven acceleration of the rotation through the clamped elongated workpiece for rotation of the rotary guide-bush synchronized with the driven acceleration of the rotation of the workpiece spindle.

A tool holder for a lathe having a spindle permits improved arrangement of tools on a turret to maximize the allowable workpiece outer diameter for a given tool. A Z-axis feed mechanism moves the spindle and the turret relative to each other in a Z-axis direction along a center axis of the spindle, while an X-axis feed mechanism moves the spindle and the turret relative to each other in an X-axis direction orthogonal to the Z-axis direction. A plurality of tool holders is attached to the turret, each having a tool holding part. At least one of the tool holders holds the tool at a holding position such that, when indexed to a machining position by rotation of the turret, a cutting-edge reference point of the tool is offset with respect to an X-Z plane including a center axis of the turret.

A lathe capable of shortening a spindle with respect to a spindle axis direction. A spindle provided with a chuck at the front end thereof is rotatably supported on a support by bearings. A chuck operating apparatus includes a tilt claw and a shifter. A built-in motor is disposed between the bearings to rotate the spindle. The claw is provide outside the spindle and between the bearings. The claw has a movable end whose distance from the spindle axis varies between a first posture to bring the chuck into the opened state and a second posture to bring the chuck into the closed state. The shifter is provided outside the claw and movable in the spindle axis direction to be brought in a first position to bring the claw into the first posture and in a second position to bring the claw into the second posture.

A spindle apparatus for use at a machine tool, in particular a lathe, has: a spindle assembly including a workpiece spindle to receive an elongated workpiece and a spindle motor for driving spindle rotation; and a rotary guide-bush assembly axially arranged with the workpiece spindle, the rotary guide-bush assembly including a rotary guide-bush to receive the elongated workpiece and supported at the rotary guide-bush assembly to rotate with the elongated workpiece received in the workpiece spindle about the axis while enabling a movement of the elongated workpiece in the axial direction. The spindle and rotary guide-bush assemblies connect to each other by a torque transferring connection, between the spindle and rotary guide-bush assemblies along the axis to transfer driving torque during acceleration or deceleration of the spindle rotation driven by the spindle motor to the rotary guide-bush of the rotary guide-bush assembly.

A spindle apparatus for use at a machine tool, in particular a lathe, has: a spindle assembly including a workpiece spindle to receive an elongated workpiece and a spindle motor for driving spindle rotation; and a rotary guide-bush assembly axially arranged with the workpiece spindle, the rotary guide-bush assembly including a rotary guide-bush to receive the elongated workpiece and supported at the rotary guide-bush assembly to rotate with the elongated workpiece received in the workpiece spindle about the axis while enabling a movement of the elongated workpiece in the axial direction. The spindle and rotary guide-bush assemblies connect to each other by a torque transferring connection, between the spindle and rotary guide-bush assemblies along the axis to transfer driving torque during acceleration or deceleration of the spindle rotation driven by the spindle motor to the rotary guide-bush of the rotary guide-bush assembly.

A rotational force transmission mechanism includes a shaft and an engagement member. The shaft is rotatable about a first axis. The shaft includes a leading end portion having a second groove and a first groove which is configured to receive a rotatable portion of a tool holder so that the shaft rotates the rotatable portion about the first axis. The engagement member is movable along the first axis between a first position and a second position and rotatable about the first axis together with the shaft. The engagement member includes an engagement portion configured to be received in the second groove. At least one of the shaft and the engagement member has an inclined surface that moves the engagement portion in a direction toward the first axis when the engagement member moves from the first position to the second position.