invention blade 66 having a radial split 70 may be spread apart in the manner illustrated in fig1 this permits the blade to be slipped over the shaft 14 after which it will resume its circular configuration as shown in fig9 then the blade 66 may be slipped over the shoulder portion 30 of head 84 and clamped against side face 88 by clamp ring 92 by using screws 42 clamp ring and screws not shown in fig1 which will result in the assembly of the parts as shown in fig6 nevertheless if desired the blade 66 may be made in two halves 76 or 78 such as described in connection with fig1 thus both halves of the blade may be placed around the shoulder 30 and clamped in place as previously described it will be appreciated that if the blade is made in two halves it will have to be cracked along lines 80 and 82 so that its outer edge will be continuous when the halves are clamped to the head it can be seen that when a length of band 62 is cut to form a blade 66 the exact length may be cut off so that no cracking is necessary the operation of the apparatus of this invention is believed to be clear from the foregoing description suffice to say that blades 66 or 76 or 78 as the case may be are clamped to.