An apparatus for cutting discontinuous apertures in the wall of a corrugated tube moving along an axial path between inlet and outlet ends of the apparatus, the apparatus including a first feeder-cutter wheel proximate to the outlet, a second feeder-cutter wheel proximate to the inlet and spaced axially from said first feeder-cutter wheel, each said wheel being disposed about the outer surface of said tube and having a cutting surface and a helical worm for engaging the tube corrugations, and means for rotating the feeder cutter wheels, wherein the improvement comprises means for axially moving the second feeder cutter wheel axially towards and away from the first feeder cutter wheel wherein to accurately position the feeder cutter wheels relative to tubing corrugations.