Fastening system for a circular saw blade
FIELD OF THE INVENTION 
     The present invention relates to a fastening system for a circular saw blade, in which the circular saw blade is fastened by means of a screw/screws to a fastening flange on the turning arbor, to a chipping edger in a hewing saw, or to a chipping cutter. 
     BACKGROUND OF THE INVENTION 
     In prior-art systems, the steel frame requires reinforcement, i.e. additional thickness, in order for the screw fastening to be sufficiently sturdy. In these systems it is necessary to use a plurality of countersunk screws, the opening and fastening of which in connection with servicing is cumbersome and very time-consuming. When the blade is of the same material in the area of the reinforcement, it reacts immediately to heat, which in turn causes distortions in the actual blade. The prior-art systems in which there are reinforcements are also very expensive. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to eliminate the disadvantages described above. The fastening system according to the invention is characterized in that the fastening part of the circular saw blade is made frustoconical and that the circular saw blade is fastened between two corresponding frustoconical surfaces. A blade such as this is considerably more economical to manufacture, since areas of different thickness are not necessary in it. The blade is considerably more rapid to detach and fasten in connection with servicing, since the fastening system does not require as many screws as do the prior-art systems. The blade is tightened evenly by its frustoconical surface. The blade may even be in a plurality of segments, since owing to the frustum it centers in place. The frustoconical part also provides additional sturdiness for the blade, and it is therefore also easier to handle in connection with servicing. By using the system according to the invention, a so-called smooth frontal surface is obtained, i.e. one side of the circular saw blade is left free as far as the hub; this is required in chipping cutters and in chipping canters. 
     One embodiment of the invention is characterized in that the fastening flange, which may be a chipping edger or a chipping cutter, has a frustoconical recess in which the frustoconical part of the circular saw blade is placed, and that the circular saw blade is tightened in place by means of a tightening flange which has a frustoconical edge. Frustoconical fastening such as this is easy and economical in terms of manufacturing technique and reliable in terms of fastening. 
     Another embodiment of the invention is characterized in that the tightening flange is tightened in place by means of a screw in its hub. This is a very rapid fastening system in terms of servicing. 
     A third embodiment of the invention is characterized in that the tightening flange is tightened in place by means of screws passing through the fastening flange. In this system the tightening flange may be circular, and its tightening also does not require many screws. 
     A further embodiment of the invention is characterized in that the frustum angle is 30°-60° relative to the plane of the circular saw blade. The frustum angle will probably be 45°. 
     One embodiment is further characterized in that the tightening flange is of a different material than the circular saw blade, for example of cast steel. The tightening flange is heated up considerably by friction in the frontal surface and, for example, cast steel does not become easily distorted regardless of heating up. Heat generated by friction will not react directly on the actual circular saw blade, as it does in prior-art systems. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described below with the help of examples, with reference to the accompanying drawings, in which 
     FIG. 1 is a cross-sectional representation of the fastening system for a circular saw blade, according to one embodiment, 
     FIG. 2 depicts the circular saw blade belonging to the fastening system, 
     FIG. 3 depicts the fastening system for a circular saw blade, according to another embodiment, and 
     FIG. 4 depicts a circular saw blade of this fastening system. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the embodiment shown in FIG. 1, the circular saw blade 1 is fastened by means of a screw 2 so that the circular saw blade is tightened between a chipping edger 3 and a fastening flange 4. The fastening part 5 of the circular saw blade 1 has been made frustoconical, and the tightening surfaces in the chipping edger 3 and the fastening flange 4 are corresponding frustoconical surfaces. The tightening screw 2 tightens to the turning arbor 6, whereby the chipping edger 3 is also tightened in place by the same tightening screw. 
     In the embodiment shown in FIG. 3, the fastening flange 7 is circular, and it is tightened in place by means of screws 9 passing through a chipping cutter 8. The frustoconical fastening part 11 of the circular saw blade 10 is tightened between the frustoconical surfaces in the chipping cutter 8 and the fastening flange 7. 
     In both embodiments, the cone angle α is 45°. The detaching and fastening of the circular saw blade is easy and rapid owing to the large size and small number of the screws.