【正文】 ward in stripping the stock from the punch fastend to the lower shoe . Stripper bolts hold and guide the stripper in its travel . On the upstroke of the ram , the upper end of the knockout rod strikes an arm on the press frame , which forces the lower end of the rod downward , through the die , and ejects the finished blank from the die cavity . A stop collar retains the rods and limits their travel . Center of Pressure If the coutour to be blanked is irregularly shaped , the summation of shearing forces on one side of the center of the ram may greatly exceed the forces the on the other side . Such irregularity results in a bending moment in the press ram , and undesirable deflections and misalignment . It is therefore necessary to find a point about which the summation of shearing forces will be symmetrical . This point is called the center of pressure , and is the center of gravity of the line that is the perimeter of the blank .It is not the center of gravity of the area . The press tool will be