A guide bush adjusting device includes a drawbar (a mobile body) displaceable relative to a guide bush sleeve (cylindrical body). The drawbar is formed from a screw connection member (a connection member) which is connected to a guide bush housed in the guide bush sleeve (a cylindrical body), and an operation member configured to displace the screw connection member. The guide bush adjusting device adjusts an inner diameter of the guide bush by releasing the operation member from its fixation, displacing the drawbar, moving the guide bush with respect to the guide bush sleeve via the drawbar to thereby position the guide bush, and fixing the operation member of the drawbar (mobile body) at a predetermined position.

A main spindle located in a region of a rotary guide bush device where the rotary guide bush device (has been attached to be disposed in a position of a front (F) along an axis (C) direction when the rotary guide bush device having a guide bush, which is supported in a removable manner by a guide bush-supporting base (supporting base) provided in the front (F) along the axis (C) direction of the main spindle, is removed. A seal member (fixed to the guide bush-supporting base has contact with an outer circumferential surface of a main spindle cover over an entire circumference, so that processing with or without the guide bush can be selected and a complicated process required for switching the processing with or without the guide bush can be simplified.

A machine tool includes: a joint portion processing control for controlling the processing of the joint portion in a joined workpiece such that a first workpiece is gripped by a grip section, and a predetermined region extending from a joint portion of a joined workpiece toward a second workpiece is processed over a range of not less than a predetermined width to have an outer diameter of not more than an outer diameter of the first workpiece; and a movement control for controlling the movement of the joined workpiece so as to slidingly move the joined workpiece relative to the support section, from a state in which the first workpiece is supported by the support section, up to a state in which the second workpiece is supported by the support section.

A method of supporting a workpiece on a fixture, the workpiece having a first surface and an opposite second surface, and an aperture positioned at a center of the first surface and extending from the first surface to the second surface the fixture having a first end, an opposite second end, and a center portion, the center portion comprising a supporting surface, the second end being adapted to be mounted in a lathe, the supporting surface comprising an annular recess, the annular recess accommodating a supporting medium, the second surface of the workpiece being in intimate contact with the supporting medium, the method comprising the steps of: (i) mounting the fixture in the lathe; (ii) locating the aperture on the first end of the fixture; and (iii) securing the workpiece on the fixture, with the second surface of the workpiece being coplanar with the supporting surface of the fixture.