the lower cam enclosing housing 230 so that the punch member is capable of moving from its retracted position of fig1 to its extended position of fig1 a movement of cam follower 170 is limited to radial movement relative to housing 230 by slide bearing surfaces on guide lug portions 229 of housing 230 engaging a cross bar 181 attached to cam follower 170 by bolts 193 received in threaded openings 190 provided in follower 170 and also engaging facing surface 227 of the cam follower and surfaces 228 of shoulders 183 and 185 fig1 of cam follower 170 punch 171 includes diametrically opposite arcuate side slots 264 only one of which is shown in fig4 a the outer surface of the punch is hardened and it is machined so that a vertical cutting edge 270 is defined by the intersection of forwardly facing planar surfaces 268 also the forwardly facing planar punch surfaces 268 are oriented 450 from the horizontal axis and are therefore oriented at 90 u00b0 with respect to each other it would also be possible to use a punch such as punch 280 shown in fig4 b which has a side profile like that shown in fig4 of u s pat no 4 932 129 punch 280 has curved forward surfaces 282 and does not have side slots however it is identical to punch 171 in all other respects curved forward.