Cutter for square timber hewing machine

A cutter for square timber hewing, which consists of a cutter disk shaped like a truncated cone and on the mantle surface of which have been affixed cutter bits arranged after each other in helical configuration, so that cutting takes place with each cutter bit in its turn, starting at the outer periphery of the cutter cone and proceeding inward. The cutter bit has two cutting edges which lie on each other's extension and define an obtuse angle. One bit edge moves in parallel with the grain of the timber and the other bit edge moves obliquely with reference to the grain of the timber, hewing of the square timber being effected by feeding the trunk in between two opposing cutters or pairs of cutters. The cutter bit has been affixed to the cutter disk by the extension, pointing towards the center of the cutter disk, of the cutter bit's bit edge cutting in the direction of the grain.

BACKGROUND OF INVENTION 
The present invention concerns a cutter for a square timber hewing machine, 
consisting of a cutter disk shaped liked a truncated cone and on the 
mantle surface of which have been affixed cutter bits in consecutive 
succession in helical configuration so that the cutting takes place with 
each bit in turn, starting at the outer periphery of the cutter disk and 
proceeding inward. The cutter bit has one curved cutting edge, or two or 
more cutting edges located on each other's extension and define an obtuse 
angle, part of the cutting edge (edges) moving parallel to the wood grain 
and another part moving obliquely against the grain orientation, the 
square timber hewing operation being accomplished by feeding the trunk 
into the interstice of opposing cutters or pairs of cutters. 
The object of this invention is to provide a new type of cutter by which 
several advantages are gained over cutters of prior art. 
SUMMARY OF INVENTION 
The cutter of the invention is characterized in that the cutter bit has 
been affixed to the cutter disk by an extension, pointing toward the 
centre of the cutter disk, with a first part of the cutting edge cutting 
in the direction of the grain of the timber being hewed and a second part 
of the cutting edge cutting obliquely to the grain. 
The mode of affixing the cutter bit to the cutter disk as taught by the 
invention enables both the cutter and the square timber hewing machine to 
be constructed about two-thirds smaller and lighter than any solutions 
known at present. Other advantages include that, one achieves firm 
attachment of the cutter bits to the cutter disk, simple and rapid cutter 
bit servicing and replacing, changability of bits in accordance with the 
hewing behaviour of each timber species, lower energy consumption due to 
the cutter's small rotating mass, and the possibility to construct the 
square timber hewing machine to operate with one feeding means, thus 
enabling the hewing also to be done with observation of the trunk's 
curvature. The cutter of the invention produces an excellent surface of 
the finished timber and it detaches chips which are of uniform quality and 
have a fibre length suitable for instance with a view to their use in the 
cellulose industry. 
When the cutter of the invention is employed, the chips fly to one side, 
owing to centrifugal force, without catching anywhere or accumulating on 
projections of the cutter bit and cutter disk, because that cutting edge 
which is doing cutting work at any given time is, at the point where it is 
cutting, the outermost part of the cutter bit. 
An advantageous embodiment of the invention is characterized in that in the 
mantle surface of the cutter disk has been made a recess adjacent to the 
bits edges, to serve as chip accommodation. 
Another embodiment of the invention is characterized in that the cutter 
disk presents, for the cutter bit, a recess conforming to the base of the 
cutter bit. As a consequence, the cutter bit is held firmly in its place, 
and invariably in the same place, by one single screw.

The cutter 1 consists of a cutter disk 2 shaped like a truncated cone and 
to the mantle surface of which cutter bits 3 are affixed. The square 
timber hewing is accomplished by feeding the trunk 4 in between two 
opposed cutters 1 or between two opposed pairs of cutters. The cutter bits 
3 have been affixed to the conical surface of the cutter disk 2 in 
consecutive succession in a helical arrangement so that cutting will take 
place with each cutter bit 3 in turn, starting at the outer periphery of 
the cutter disk 2 and proceeding inward. The cutter bits 3 form one or 
several helices on the mantle surface of the cutter disk 2. 
The cutter bit 3 has cutting bit edges 5, 6 lying on each other's extension 
and defining an obtuse angle therebetween. One bit edge 5 moves in the 
grain direction of the timber trunk 4 and the other bit edge 6 moves 
obliquely with reference to the grain of the timber 4. It is seen in FIG. 
7 that the cutter bit 3 has been affixed to the cutter disk 2 by that 
extension 3a of the bit edge 5 cutting parallel to the grain and which 
points toward the centre of the cutter disk 2. The cutter 1 may then be 
constructed to be of small size and low weight and to operate with only 
one single tree trunk feeding means. 
In the mantle surface of the cutter disk 2, a recess 7 has been provided 
adjacent to the bit edges 5,6 to serve as chip accommodation. Since the 
cutting edges 5,6 of the cutter bit 3 are the outermost point of the 
cutter bit 3 at the point where cutting is in progress at any particular 
time, the chips will be flung out by centrifugal force action, without 
sticking and without accumulating on projections of the cutter bit 3 or 
cutter disk 2. For firm atachment of the cutter bit 3 by the extension 
towards the cutter disk's 2 centre of the bit edge 5, one screw 8 inserted 
through hole 9 in cutter bit 3 for instance is sufficient, whereby the 
servicing and replacement of the cutter bits 3 are fast and simple 
operations. 
It is obvious to a person skilled in the art that different embodiments of 
the invention may vary within the scope of the claims following below. For 
instance, the obtuse angle between the cutter bit's bit edges need not 
necessarily be as shown in the figures: it may equally well be gently 
curving.