cutting as to the length of the yarn residual piece coming out of the knitted fabric usually these saws are mounted on a disc which in a simple machine as the one now being described is not provided as there is no requirement for the operation conventionally entrusted to this disc thus in replacement of the disc there is provided a device particularly shown in fig2 to 31 which serves to cut the yarns and is caused to intervene at the moment when the yarn is to be cut this cutting device includes a supporting arm 140 projecting from the fixed annular element 7 borne by the frame 1 and extending to the area of the extension of the needle cylinder axis in an end head 140a of the support 140 there is provided a housing coaxial to the needle cylinder axis for a column 142 which can slide with respect to the head 140a and is fixed against rotation the column 142 is urged upward by a spring 144 which by pressing on the head 140a pushes upwardly a plate 146 integral to the upper end of the column 142 at the lower end of the column 142 there is an expanded head 142a below which there is provided an upper plate 148 and a lower plate 150 both borne by a shaft 142 internal and coaxial to the column 142 and assembled for rotation therein the column 142 is prevented from rotating by a groove 142b in which co acts a dowel 154 borne by the head 140a a disc 156 is mounted between the peripheries of the plates 148 150 and projects outwardly therefrom with teeth formed around its periphery the disc 156 is designed to cooperate.