Method and bag making machine

According to a method of manufacturing a bag from a tube (20) having transverse perforation lines defining the legs of the future bag, a rear leg (232) of a first bag (27) being opposite of a front leg (231) of the second bag (28) according to the first, - one proceeds in a first step to a separation of the first and second bag (27, 28); - in a second step, separating a waste material (26) remaining on one of the bags (28) between the two legs (231, 232). Is carried out first and the second stage between firstly a first pair of rollers (51) for separating and secondly a second pair of rollers (52), the waste (26) being gripped between the rolls of the first pair (51) during the first step to be retained on the second bag (28) and pinched and pulled by the second pair (52) during the second step, the first pair of rollers (51) being animated by a peripheral speed lower than that of the second pair (52) at least during the first and second step. Machine implementing said method.