a stitching head is provided having a cam connected to the bender rail rail , the cam operates to redirect the staple driving force being applied by the driver rail to the driver and upon the staple during the staple driving step of stitching head operation ; the force - redirecting position of the cam is automatically adjusted in response to the thickness of each workpiece as the cam is connected to the bender rail rail and the contacting of the workpiece by the bender rail repositions the cam at the desired distance above the workpiece to reestablish the set - point for the redirection of the staple driving force being applied to the driver rail upon as staple head contacts each variable thickness workpiece .