Circular blade unit

A blade unit for cutting sheet material, said blade unit comprising:

• a base member including a supporting wall having a generally planar side and defining a substantially circular upper edge;
• an aperture extending through said supporting wall at a diametrical center of said supporting wall with reference to said substantially circular upper edge;
• an axis pin extending through said aperture, said axis pin including a flat portion for cooperating with a flat portion of aid aperture to prevent rotation of said axis pin in said aperture;
• a circular bearing ridge extending axially from said planar side of said supporting wall;
• said substantially circular upper edge of said supporting wall including terminal lower edges;
• said supporting wall including a straight bottom edge extending between said terminal lower edges;
• a circular cutting blade supported for rotation on said axis pin, said blade including an exposed portion extending past said bottom edge of said supporting wall;
• an elongated guide structure extending downwardly from said bottom edge of said supporting wall for engagement in guide slot of a cutting template for guiding movement of the blade unit;
• a guard flange extending around aid substantially circular upper edge of said supporting wall and protruding axially form said planar side of said supporting wall;
• a pair of elongated latching ridges protruding radially to a predetermined height from said guard flange at diametrically opposite locations;
• a plurality of elongated gripping ridges protruding radially from said guard flange to a height less than the height of said latching ridges, and located adjacent each of said latching ridges;
• a cover member including generally semi-circular front and rear walls;
• an arcuate top edge wall extending between said front and rear walls of said cover member to define a cavity bounded by said top edge wall and said front and rear walls;
• a pair of slots defined on inner surfaces of said top edge wall at diametrically opposed locations on said cover member for receiving said latching ridges of said base member;
• a plurality of elongated gripping ridges protruding radially from, an outer surface of said top edge wall and located at diametrically opposed locations adjacent the locations of said slots on said cover member;
• and
• wherein said base member is positionable in engagement within said cover member in first and second positions, said first position comprising said latching ridges located in engagement with side slots and said exposed portion of said blade located extending away from said cavity, and said second position comprising said latching ridges located in engagement with said slots and said exposed portion of said blade located into said cavity.