The invention relates to a device for making cribs in round timber, which device comprises a saw chain for cutting wood and a power unit for driving the chain as well as support means for fastening the flange of the saw chain to turn transversely to the timber.

At present cribs are made mechanically by using a cutter plane or by replacing the saw chain of a chain saw by a blade of cutter type. The latter al¬ ternative is practicable in field use, but requires a change of blade always when the size of the crib or the timber changes. A large part of the cribs are made in the field in such a way that the cutting is drawn on the timber and accomplished by a chain saw. Generally used cribmaking machines are poorly suited for field use and have a high purchase price.

From U.S. Patent 4067368 is known a device for making cribs in round timber by a chain saw. However, the supporting of the saw blade is complicated be¬ cause of tightening bands to be fastened on both sides of each crib of the round timber and unstable especially in the longitudinal direction of the blade flange. Therefore, it is not easy to make cribs with dimensional accuracy by means of this solution.

The object of the present invention is to pro¬ vide such a device for making cribs in a round timber which is well-suited for field use and does not have the abovementioned drawbacks. To provide this, the device according to the invention, comprising a saw chain for cutting wood and a power unit driving the chain as well as support means for fastening the flange of the saw chain to turn transversely to the timber, is characterized in that the support means-

comprise at least two slotted guide plates positioned opposite to each other, between which the timber to be cribbed is placed, and guide discs supported turn¬ ably in the slots of the guide plates, which guide discs have slits receiving the flange of the saw chain and fastening means for guiding the saw chain by means of the guide discs to make a crib in the timber.

The other preferred embodiments of the inven- tion are characterized in what is set forth in the attached claims.

The invention will be described in the follow¬ ing in greater detail by means of an example with reference to the enclosed drawings, in which Figure 1 shows support means of a device ac¬ cording to the invention, i.e. a guide plate and a guide disc supported turnably in a slot of the plate, Figure 2 shows the support means of the device according to the invention seen from the end of a round timber to be cribbed,

^' Figure 3 shows a fastening of guide discs to the flange of a chain saw blade, and

Figure 4 shows one preferred embodiment of the device of the invention. According to Figures 1 and 2, a device of the invention comprises guide plates, mounted e.g. on a common base in such a way that the portion of a tim¬ ber 2 which is to be cribbed can be placed between them, and guide discs 3 to be fastened to the blade flange of a chain saw, along the periphery of which discs there is a groove 4 (cf. Figure 3). When the guide discs 3 are pressed in slots 5 of the guide plates 1 (cf. Figure 4), they can be rotated together by means of the flange 7 of the chain saw blade, which flange is pushed through slits 6 in the discs

and fastened to the discs. The guide plates and discs then fully determine the path of movement of the chain saw blade.

The guide discs 3 shall have a considerably larger diameter than the largest diameter of the crib in order that the radius of the crib may be adjusted. The adjustment is carried out by displacing the blade flange by means of its fastening means 11 in a direc¬ tion a of the radius of the guide disc in Figures 1 and 3. The depth of the crib is adjusted by changing the position of the guide plates 1 with respect to the round timber in a vertical direction b in Figures 1 and 2.

A crib is made in such a manner that a rotating saw chain 9 of a chain saw 8, which is driven elec¬ trically or by a combustion motor, is according to Figure 3 pressed with its guide discs 3 vertically down against the guide plates (Figure 1 ) , af er which the crib can be sawn and its bottom can be made even and smooth by lifting and rotating the saw and the blade flange 10 at the same time in both directions. The guide discs 3 are guided and kept in place in the guide plates 1 by the groove 4 in the periphery of the discs. In the embodiment of Figure 4, several pairs of guide plates receiving guide discs and a saw chain are positioned on the same base in order to make sev¬ eral cribs 12 in one and the same round timber 2 at fixed distances. it is clear to one skilled in the art that the various embodiments of the invention are not re¬ stricted to the above examples, but they may vary within the scope of the claims presented in the fol¬ lowing.