the machine includes a horizontal support for a plastic bag and a vertically movable heat - sealing head pivoted to the support for upward movement through an aperture in the support to contact the plastic bag . a vertically movable pressure platen having a vacuum head for holding a patch thereon is mounted directly above the heat - sealing head and is adapted to be moved into engagement with the plastic bag so that the patch can be heat - sealed to the bag . a cutter is mounted adjacent the pressure platen for reciprocating movement along an oblique path to intersect the aperture in the support directly beneath the pressure platen to provide a slit in the plastic bag prior to the heat - sealing of the patch on the bag over the slit .