Abstract: A web slitting machine for cutting a web or roll of material includes an upper carriage assembly joined to a lower blade holder assembly by a selectively removable guide key which is milled to provide a predetermined cant angle for the blade. The blade is lowered into position by a piston which is rectangular and includes a torsion-resisting sleeve to prevent rotation of the piston about its vertical axis. A pneumatic control provides a plurality of control modes whereby the blade may be raised and lowered with or without locking the upper carriage assembly to its transverse bar and vice-versa. A unique side shift adjustment is provided whereby the blade may be shifted to a half-stroke position and the upper carriage locked when the blade is positioned against a lower knife. This ensures that the pressure of the blade against the knife is the pressure exerted at the mid point of the stroke.