Cutting blade and method for cutting sheet material

A blade for a sheet material cutting machine, said blade prior to use comprising:

• a piece of base material having an elongated cutting portion extending along a longitudinal axis and having a forward cutting edge parallel to said longitudinal axis,
• said cutting portion having two generally flat rear side faces located respectively in first and second spaced parallel planes and which side faces are located rearwardly of said cutting edge, and first and second forward side surfaces, said first and second forward side surfaces each extending forwardly from a respective one of said rear side faces and said first and second forward side surfaces being inclined relative to one another, as seen in a plane perpendicular to said longitudinal axis, and intersecting one another to define said cutting edge at their line of intersection,
• said cutting edge being located between said first and second planes and being laterally displaced from a reference plane located parallel to and mid-way between said first and second planes so that said first forward side surface passes through said reference plane, and
• a thin coating of hard material harder than said base material covering at least said first forward side surface of said cutting portion of said base material so that by a sharpening grinding of said second side surface said cutting edge can be made to be defined substantially entirely by said hard material, and whereby as a result of repeated sharpening grindings of said second side surface said cutting edge gradually moves toward and eventually to the other side of said reference plane.