A self-centring device for supporting and guiding bars to be fed to a machine tool, including:
- a guide body having a through opening, supported rotatably and rotating in a controlled manner around an axis perpendicular to an advancement direction of the bars to be guided, so as to vary the angular orientation thereof around said axis, said guide body being configured to receive and maintain in position the rotating and advancing bars,
- a return member configured to oppose a suitable preselectable resistance to the rotation of said guide body around said axis so as to maintain a firm coupling and contact of said guide body with the advancing bar, wherein said return member comprises an elastic element including a helical torsion spring having a first end being engaged in a stationary manner with a support structure and a second end being operationally connected by a coupling and adjusting arrangement to said guide body,
- wherein said coupling and adjusting arrangement includes a hollow connecting element and an adjusting arm fitted to said hollow connecting element and configured to select the size of the elastic return force exerted by said torsion spring, on said adjusting arm a coupling seat being obtained for said second end of said spring and a seat housing a releasable fixing and adjusting screw, by which it is possible to adjust the position of said adjusting arm around said hollow connecting element to increase or decrease in a desired manner the recall force exerted by said torsion spring,
- a manual selector member configured to adjust a position and control the angular movement of said guide body, in which said selector member is fitted to a support structure suitable for being fixed to a bar-feeding apparatus and in which said manual selector member includes a screw arrangement cooperating with an oscillation limiting element to set an angular rest position of said guide body in function of the geometry of the bar to be received and guided to said machine tool, said device being WHEREIN said limiting element included in said selector member includes an adjusting plate applied to said support structure and configured to limit the oscillation of said guide body around said axis, said selector member including a positioning arrangement to adjust the position of, and releasably fix, said adjusting plate with respect to said support structure, a sliding and limiting slot cooperating with a cursor screw connected to and movable with said guide body being obtained on said adjusting plate, to set an angular rest position of said guide body as a function of the geometry of the bar to be received and guided to said machine tool, said sliding and limiting slot setting an end-stroke position for said cursor screw that is variable by modifying the position of said adjusting plate with respect to said support structure by acting on said positioning arrangement.