Rotary cutting blade

1. A rotary cutting blade, comprising:

a leaf comprising two opposite surfaces forming between them a smooth cutting edge extending along at least a portion of their periphery;

a single smooth inclined cutting surface extending inwardly and inclined at varying angles from the cutting edge at one of the two opposite surfaces, the inclination varying from at least one minimum angle to at least one maximum angle, wherein a distance between said at least one minimum angle to a closest maximum angle, measured along the cutting edge, is larger than any radial distance from the cutting edge to a center of the blade;

a smooth inclined surface extending inwardly from the cutting surface, said smooth inclined surface being disposed on the same one of the two opposite surfaces as the cutting surface; and

a substantially planar surface extending inwardly from the inclined surface and provided with means for mounting the blade for rotation about an axis disposed at a predetermined relationship to the cutting edge.

2. The rotary cutting blade of claim 1 , wherein the angles of inclination within the cutting blade vary between 15° and 40°.

3. The rotary cutting blade of claim 2 , wherein the minimum angle is about 20° and the maximum angle is about 33°.

4. The rotary cutting blade of claim 3 , wherein the maximum and minimum angles are arranged in a regular sequence along the cutting edge.

5. The rotary cutting blade of claim 3 , wherein the maximum and minimum angles are arranged in an irregular sequence along the cutting edge.

6. The rotary cutting blade of claim 1 , wherein the periphery increases from a radial minimum to a radial maximum relative to the axis of rotation of the blade.

7. The rotary cutting blade of claim 6 , wherein the radial maximum and radial minimum are interrupted by a cut-out section in the blade.

8. The rotary cutting blade of claim 1 , wherein the periphery of the blade is disposed at a substantially uniform distance from the axis of rotation.