Abstract: The apparatus comprises a bearing plate (1), a slideway (2) and a girder (3) which are perpendicular to the bearing plane of the bearing plate, a slide (4) with tracer head (5) movable along the slideway and a drive plate (7) located in front of the slide and stabilized by guides (8, 9) independent of the slide. The plate (7) and the slide (4) are connected by balancing (10) and damping (11) springs. A drive device by cable (13) and return pulleys (15-18) which is moved by a movement generator (19) is connected to the plate (7) and is entirely supported by the girder (3) and the bearing plate (1). A counterweight (14) inserted in the circuit of the cable (13) balances the weight itself of the movable elements (4, 7). A body (63) for protection against impacts is fastened to the girder (3) and to the bearing plate (1).