while the return to the vertical position for cooperating alignment with link separation unit is obtained by the action of a tappet 36 acting on support block 28 in opposition to spring 35 tappet 36 is moved by a lever head 37 actuated by a cam not shown of shaft 30 to rotate shaft 27 on its own axis a rack 38 is provided for engaging with a corresponding toothed portion formed on shaft 27 and not shown in the figures as covered by the rack itself rack 38 is intermittently reciprocated by a lever 38a fig3 actuated by a cam not shown of shaft 30 and by a counteracting return spring 38b axial movement of shaft 27 is finally controlled by a lever 39 actuated by a cam not shown integral with shaft 30 and by a counteracting return spring 39a the operation of link take up unit 25 will be explained later chain linking unit 34 is generally shown in fig1 and in more detail in fig6 a b where it has been illustrated in cooperative alignment with link take up unit 25 chain linking unit 34 comprises a substantially upside down reversed t shaped support 40 fixed with respect to the frame of the machine and a bracket 41 pivotally connected to support 40 by means of a horizontal pivot 42 two adjustment screws 43 engaging bracket 41 to both side of pivot 42 are provided for adjusting the inclination of bracket 41 a projecting end of bracket.