A sheet folding apparatus, which may be used in conjunction with a printer
or copier, includes a set of rollers forming a buckle zone, in which
sheets are caused to buckle for creasing by a folding nip formed by the
rollers. A blade is selectably positionable in and out of the buckle zone.
When the blade is positioned in the buckle zone, any previously-folded
portion of the sheet (such as in C-folding of the sheet) is prevented from
being drawn away from the folding nip.
