86 mounted to upper plate 88 of slide frame 86 is a pneumatic power means 104 while this is described herein as being a pneumatic power means hydraulic cylinders and the like may also be used without detracting from the invention power means 104 drives a vertically reciprocating ram 106 ram 106 includes a downwardly extending telescope member 108 which is connected at its lower end to a die block 110 telescoping member 108 is adapted to telescope inwardly and outwardly as ram 106 reciprocates upwardly and downwardly with respect to die block 110 thus member 108 holds ram 106 and die block 110 in predetermined vertical registered alignment with respect to one another fixed to ram 106 for movement in unison therewith is a punch 112 which is trapezoidal in cross section a wiper plate 114 is slidably mounted around punch 112 and is spring mounted with respect to ram 106 by a spring 116 die block 110 is provided with a die opening 118 fig3 which conforms to the cross sectional configuration of punch 112 in operation movable notcher 78 is positioned so that the outer edge of punch 112 coincides with the lateral edge of sheet metal strip 22 as it passes through window 68 driving machine 12 stops sheet metal strip 22 and notcher 78 is actuated upon actuation power means 104 causes ram 106 and punch 112 to descend downwardly to engage the upper surface of sheet 22 and to pierce sheet 22 thereby forming the trapezoidal notch designated by 26 in fig1 upon engaging sheet metal strip 22 lost motion occurs between wiper plate 114 and punch 112 so that punch 112 continues downward movement whereas wiper plate 14 depresses spring 116 and remains stationary.