Abstract: In accordance with the invention, a wheel (16) is used as the burnishing wheel for a helical thread, the periphery of which wheel has a profile whose shape matches that of the thread to be surfaced. The wheel (16) is mounted such that it rotates freely about an axis which is inclined with respect to the axis of the screw (10) which is caused to rotate about its own axis. The wheel (16) is applied in a resilient manner to the screw (10) by means of a compression spring (56) which pushes the pivoting support (18) of the wheel (16) in the direction of the screw (10). The carriage (20) on which the support (18) is pivotably mounted is freely displaceable in translation parallel to the axis of the screw (10) on a rail (22). The invention may be used for finishing by means of burnishing of a helical thread using an automatic repetitive cycle comprising a predetermined number of passes of a burnishing wheel along the thread.

Abstract: A worm screw has two threaded portions of opposite hand cut on a single shaft, using a lathe. Several passes of the cutting tool are used to form each of these threaded portions, and in order to provide a compact and robust worm screw of this type the two threaded portions are separated by a groove having a depth shallower than that of the threads being cut and having a width at least equal to 15% of the greater axial pitch of the threaded portions.