This invention relates to a cutting disc, designed for barking and hewing timber, and comprising a body rotatable by means of a power unit, a trimming surface surrounding the axis of rotation of the body, to be applied onto the log, and cutting blades protruding from the tr-unming surface and directed towards the outer edge of the surface.

Hewn timber is conventionally shaved off by hand by using a drawshave. The drawshave is then used to remove the bark and the outmost annual shoots from the trunk in order to prevent darkening of the finished timber. The hewn round timber thus obtained has been used in particular as a wall material in log cabins.

Nowadays log cabins are commonly built of lathed logs. Lathe operation is indeed effective, however, the logs obtained have the drawback of a surface which is excessively smooth and finished. A lathed surface does not have the living rough texture brought about by small irregularities in a surface shaved off by hand.

Besides a drawshave, it is well known to use a cutting disc rotated by a power unit in hewing operations. A cutting disc may comprise for instance a conical trimming surface, provided with cutting blades protruding from the surface. All the same, when conventional cutting discs are used to manufacture hewn timber, the timber will not have a satisfactory appearance, because the rotating blades will leave distinctly visible curved grooves in the timber surface. Such grooves are unesthetic, and do not occur in logs shaved off by hand.

The object of this invention is to improve a cutting disc so that timber hewn by means of this disc will have the same aspect as timber shaved off manually with the aid of a drawshave. The cutting disc of the invention is characterised in that the edges of the cutting blades are disposed angularly to the Irimming surface, so that, at the outmost end of each blade, facing the outer edge of the trimming surface, the cutting edge will be located in the plane of the trimming surface, and will rise from there towards the end opposite to the blade, facing the axis of rotation of the trunk.

The cutting blades in the cutting disc of the invention are characterised in cutting the log continuously starting from its outer ends, without leaving unpleasant, curved hewing traces in the surface. By contrast, conventional cutting discs with cutting

blades protruding from the tr-unming surface over their entire length will leave such undesired traces.

In the cutting disc of the invention, the trimming surface is preferably a round planear surface with its centre on the axis of rotation of the trunk. This design allows all of the cutting blades protruding from the trunk to operate simultaneously in shaving off the log. The number of cutting blades in the disc may vary, however a preferred number is for instance three cutting blades placed at different sides of the axis of rotation of the trunk at 120° intervals relative to the axis.

According to the invention, the angle between the blade edge of the cutting disc and the trimming surface is preferably in the range of 2 to 6°.

According to the invention, the cutting blades may be placed in the trimming surface such that the outmost ends of the blades are located at a distance inside the triπiming surface periphery, the opposite ends of the blades are located at roughly the same distance from the axis of rotation of the hunk, and the direction of the blades deviates somewhat from the radial direction of the trimming surface. Consequently, the angle between each cutting blade and the trimming surface radius drawn through the outer end of the blade may be in the range of 10 to 20°, preferably approx. 15 °, and the angle between each cutting blade and the trimming surface radius drawn through the inner end of the blade may be approx. 30°.

The power unit driving the cutting disc of the invention may consist of a motor saw, in which the chain is fitted to rotate around the disc body about its axis.

The invention will be described in further detail below, with the aid of an example, and referring to the accompanying drawings, in which

figure 1 is an oblique top view of a cutting disc according to the invention when connected to a power unit,

figure 2 shows the bottom surface of the disc of figure 1, which acts as a trimming surface,

figure 3 corresponding to figure 2, is a schematic view of the cutting blade edges of the disc and the angles between the blade tips and the t-rimming surface radius,

figure 4 shows the cutting blade fitted in the opening of the disc body as a section IV-IV of figure 2 and

figure 5 shows this opening including the cutting blades as a section V-V of figure 4.

The cutting disc for log barking and hewing as shown in figure 1 comprises a body 1, connected over a flange 2 to a motor saw in order to rotate the log by means of a saw chain 3 about its axis 4. As shown in figure 2, the lower surface 5 of the trunk 1, which acts as a trimming surface, is a round planear surface with its centre on the axis of rotation 4 of the log. The log 1 is provided with longitudinal openings 6 at 120° intervals relative to its axis of rotation 4, each of the openings having a cutting blade 7 protruding from the trimming surface 5. Each blade 7 is fixed to the log 1 by means of two bolts 8.

In figure 3, which shows only the blade edges 9 of three cutting blades 7 of the disc, it can be seen that the blade directions deviate to some degree from the radial directions of the trimming surface 5. In figure 3 the radii of the trimming surface 5 have been drawn with dashed lines, and these radii extend through the outer end of the blade 9, facing the outer edge 12 of the surface 5, and the inner end of the log, facing the axis 4. The angle a between the blade edge 9 and the radius 10 extending through its outer end 13 is 15° in figure 3, and the angle b between the blade edge and the radius 11 extending through its inner end 14 is 30°.

Figures 4 and 5 show that in the disc, the blade edge 9 of the cutting blade 7 protruding from the trimming surface 5 forms an approx. 5 ° angle c to the trimming surface. At the outer end 13 of the blade 7, facing the outer edge 12 of the trimming surface, the edge 9 is located in the plane of the trimming surface 5, and rises from there towards the opposite blade end 14, facing the axis of rotation 4 of the log. In this way, the blade edge 9 joins the himming surface 5 continuously at its outer end 13, so that it does not leave unpleasant, curved hewing traces in the log to be shaved off.

It is obvious to a person skilled in the art that the various embodiments of the invention are not confined to the example described above, but may vary within the scope of the enclosed claims. More specifically, variable parameters of the cutting disc claimed here include the specific number of cutting blades 7, their length and orientation relative to the radius of the trimming surface 5, and the degree of the

angle c between the trimming surface 5 and the blade edge 9. This angle can be made adjustable by means of the blade attachment 8, and it is possible to retract the outer end of the blade within the trimming surface 5, and in this position, the blade tip will be located at the point of section between the blade edge 9 and the plane of the t-rim-ming surface 5 while the cutter is operating.