Abstract: A bag forming machine of the top stacking type has means at the stacking station whereby a stack (12) of bags are clamped during high acceleration arising in their transfer from the stacking position at the station to a discharge conveyor (11). By employing high accelerations and clamping the stack can be transferred without interrupting the rhythm of delivery of bags to the stacking station. The bags are clamped at their "cut" ends by a first clamp (14, 15) during stacking and are then clamped at a second clamp (22, 24), moving transversely to the stack so as to apply dragging motions to the stack to move the "cut" ends of the bags away from the first clamp and to present the "weld" ends of the bags at a roll nip (30, 31) which feeds to the conveyor.