to 62 hrc the cutting edge 45 of each spoke blade 41 projects above the cutting edge 43 of the annular blade 39 the blades 41 are flush with the internal circumference of the cutting edge 43 the cutting edge 45 has a peak 47 spaced outwardly from the internal circumference of the cutting edge 43 the edge 45 angles fairly quickly from the peak 47 toward the internal circumference of the cutting edge 43 approximately 5 u00b0 from vertical in the preferred embodiment creating a centering surface 48 while the edge 45 angles fairly slowly down and away from the peak 47 in the opposite direction approximately 15 u00b0 from horizontal in the preferred embodiment the peak 47 is approximately 1 8 to 1 4 inch from the internal circumference of the cutting edge 43 the centering surface 48 is itself blunt each spoke blade 41 also widens out from its cutting edge 45 to part way down the blade 41 where the thickness remains constant to the bottom of the blade 41 the cutting edge 43 of the annular blade 39 projects inwardly from a generally tubular body 51 so that the internal circumference of the cutting edge 43 is.