a moving web of material having a high tendency to elongation under stress , such as woven and non - woven plastic fiber or filament webs , is cut by the combined action of a cutting knife which executes its cutting stroke generally in line with and upstream of the web and a grab knife which holds the web at a station spaced closely downstream from the path of the cutting knife and thereby isolates the small length of web between the two knives while the cutting knife completes its stroke .