Abstract: A modular device for holding a workpiece or a bar of a material to be machined in a gripping chuck of a rotating spindle of a machine tool. A gripping chuck is actuated by a thrust tube coaxial with the spindle. To tighten the chuck, various forces are exerted including: a spring applying a first axial force on a thrust tube and applying a first air pressure force introduced through a duct into at least one tightening-pressure chamber. The tightening-pressure chamber is defined between at least a first wall fastened axially to the thrust tube and at least a second wall fastened axially to a regulating tube. Loosening of the chuck is obtained by a second air pressure introduced through another duct into at least one loosening-pressure chamber made between and on the other faces of the first walls fastened axially to the thrust tube and the other faces of the second walls fastened axially to a regulating tube.

Abstract: A slide (4) made up of a table (8) and a base (11) is actuated radially relative to a workpiece (M) to be machined via a stud (17) adjustable in a slot (16). The position of the stud can be regulated by means of a screw and a motor. A roller (24) borne by the stud then moves along another slot (25) in an arm (26) integral with a shaft (7f). The oscillations of the shaft are controlled by a control cam. Displacement of the stud relative to the pivot point of the arm permits the transmission ratio, hence the course of travel of the slide, to be varied. The angle .alpha. between the directions of the slots is other than zero at the end of the travel, so that the final position of a tool (29) can be adjusted by means of the control motor.

Abstract: The control device comprises a computer program. The machining of a workpiece comprises the writing of a program, the essential element of which is a step table. Starting from a predetermined profile of the workpiece, the movements of the X- and Y-axes are plotted in successive steps, and the cumulated intervals of time for obtaining the required movements, as a function of the characteristics of the machine tool and of the workpiece, are stored in the form of a table containing the movements .DELTA.t.sub.xi and the movements .DELTA.t.sub.yi. The reading of the steps, carried out as a function of an appropriate clock signal generator, brings about the successive transmission of the pulses which cause the X- and Y-axes to take their successive steps.