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DIFFERENT TYPES OF PERFORATIONS
Modern perforating machines, as used in the produc-tion of United States stamps, are sprocket wheel puncheswhich punch continuous rows of holes between thestamps. When the stamps are produced on rotary pressesin a continuous strip, the sprockets are small wheels thatmake a continuous row of perforations in one direction.Then, a little further along on the machine, the sprocketsare on a long shaft running the complete width of the sheet to produce the cross row of perforations at eachturn of the wheel. Naturally this is a complicated devicerequiring careful coordination with the printed stampsso that the rows of holes will fall at exactly the correctplace between the stamps. Nowadays this coordinationis accomplished electrically by what collectors call the"electric eye" (see page 148). |
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