BACKGROUND OF THE INVENTION AND THE PROBLEM Sawn wood e. g. boards, deals or crossbars are produced straight and are often stored before use. During this storage, the product dries and changes shape. In some cases the change in shape is so large that the product is disposed of which brings about heavy expenses. In other cases one has managed to install the product in a wood construction before the change in shape, which upon drying gives built-in stress in the installation.

Already known solutions clamp the products and force them in a straight position during the drying. This has in some cases resulted in change in shape after unclamping.

THE OBJECT OF THE INVENTION AND THE SOLUTION OF THE PROBLEM The object of the invention is to solve one or some of the problems stated above. This is obtained through a method according to claim 1 and also with a device according to claim 6.

The pertaining sub claims further describe preferred embodiments of the invention.

DESCRIPTION OF THE DRAWINGS With reference to the enclosed drawings, the invention will be described more in detail in the examples of embodiment.

Figure 1 shows the position of a log when the sawing begins according to the invention.

Figure 2 shows the position of a log when the sawing is completed according to the invention.

Figure 3 shows a fibre angle measuring device.

Figure 4 shows a twisted crossbar which is twisted an angle f3.

Figure 5 shows a twisted saw-blade.

Figure 6 shows a fibre angle on a log.

DESCRIPTION OF EXAMPLES OF EMBODIMENT Figure 6 shows a log 1 with encased fibres lc which are twisted around the pith lb of the log. The fibres la form an extended helical line through the log, see figure 6. The fibres 1c and the pith lb thus form a fibre angle a. The size of the fibre angle a inter alia depends on the tree's habitat, species, the original location of the log in the tree, and individual variations.

The log 1 and a saw are rotated relative to each other during sawing with an angle of rotation A of appr. 1°-12° per running meter to the fibre angle a and also to a cross angle 6 which depends on the fibre angle a. The cross angle 5 lies in a cut across the longitudinal direction of the log. A sawn product e. g. a board, a deal or a crossbar 2 will thus come out of the saw in a twisted form and forms an angle (3 with a straight axis, see figure 4. During a subsequent drying it will twist to an essentially straight form due to its fibre angle a. A large fibre angle a is thus compensated for by a large angle of rotation A and a small fibre angle a by a small angle of rotation A in order to give straight wood products. In a general case, an angle of rotation in the intervals 1-12°, 1-8°, 1-5° or 2-3° is used. In certain cases, e g sawing of crossbars from thinning or top logs, an angle of rotation A of approximately 1-4° or 2-3° to the fibre angle a portion per running meter has shown good results.

Figure 6 shows a straight sawn plane at the log 1. In order to make the fibre angle a more clear, the fibres lc are shown a portion in the middle along a line parallel to the pith lb. The bending of the fibres lc, due to their helical line form around the pith lb, brings about that the fibres lc are only visible a short portion on each side of the line being parallel to the pith lb. Furthermore, the fibres lc in figure 6 have further for the sake of clarity been shown somewhat longer than what they would be seen in the sawing of a log of wood.

By the wording direction of rotation to the fibre angle a is meant such a direction of the rotation of e g the log 1 that a number of fibres 1c are sawn off at the sawing. Thus, a crossbar 2 is sawn twisted according to figure 4 out of a log with fibre angle a according to figure 6 for obtaining a straight crossbar in the drying thereof. Sawing while rotating in the other direction of rotation, that is with the fibre angle a, would mean that sawing essentially takes place parallel to the fibres lc and that the drying would further increase the twisting of the product sawn.

During the sawing, the log 1 can be rotated by means of a retainer 3. Seen in the direction of sawing, it is in a first part 3a attached to the rear part of the log 1 and in its second part 3b arranged to run along a guiding rule 4. The guiding rule 4 is located along the log 1 and the rule 4 is somewhat tilted in relation to the longitudinal axis or pith lb of the log. The tilting brings about that when the log 1 is sawn, the second part 3b of the retainer moves along the guiding rule 4 and rotates the log 1 around its axis. A straight rule 4 and a straight retainer 3 according to figure 1 and 2 bring about that the distance of the point of

contact 5 to the axis varies during the sawing. This can lead to the angle of rotation varying along the log 1. To compensate for this, the rule 4 and/or the retainer 3 can be bent.

In an alternative method, the log 1 is brought through a saw by means of a fluid-driven pusher (not shown) e g an hydraulic cylinder having a built-in device for log rotation.

Compensation rotating at sawing in order to compensate for a fibre angle a as above is preferably performed in a band saw or alternatively in a frame saw due to the saw blades of these saws have a short contact surface to the log in the kerf. A saw pulley has a long contact surface to the log in the kerf, which makes it more difficult e g to rotate the log during sawing.

The band 6 in a band saw can also be turned e g by means of guide pins or guide wheels so that the band 6a follows the kerf, which is shown in figure 5. In this way the rear part of the band 6 will not be guided by the log 1 but will follow the kerf in its middle part.

In one further alternative method the fibre angle a is measured before the sawing. In this case an individual setting of the angle of rotation A for each log is made and thus logs with large fibre angle a may also give essentially straight wood products. A fibre angle measuring device is generally designated by 10 and comprises a body 11, a tip 12 journalled in relation to the body and arranged to be introduced into a log 1 and a member 13 arranged to register the rotation of the tip 12 at the introduction.

The tip 12 is arranged to be movably attached at a point in a sawing plant e g at a measuring station so that the fibre angle a can be measured before sawing. The tip 12 is rotatory mounted in the body 11 via a pin 14 connected to the tip 12. Further, the tip has two plane surfaces which are delimited by two edges 12c and 12d, respectively, so arranged that they form a V. The edges form an angle to each other of approximately 30- 100° or preferably 70-90°. The edges are well rounded so that at the introduction they do not cut off the encased fibres 1c of the log 1. This brings about that when the tip 12 is applied to the log 1, first the outermost part 12e of the tip attaches to a point on the log 1 and the more the pin 12 penetrates into the log 1, the wider the part of the pin 12 which cuts the envelope surface of the log 1 gets. When penetrating, the plane surfaces of the tip (of which one surface 12a is shown in figure 3) thus put themselves parallel to the fibres and rotate the tip 12 according to the fibre angle a of the log. In those cases where the log 1 has bark, the tip 12 is not essentially influenced hereby as the bark essentially lacks the fibre structure of the wood. To avoid occasional variations of the fibre angle in the log, the measurement is carried out at a distance from e g twigs, branches, and trunk damages. It is possible to make many measurements on the same log, the measurements can give a mean value.

In another embodiment, the tip has a U-shape (not shown). The U-shape can give a less deep penetration and can require an increased force of penetration.

The position of rotation of the tip 12 inside the log 1 in relation e g to the position of rotation of the tip 12 outside the log 1 for instance or a known value (e g the direction of the longitudinal axis of the log 1), is registered by the registration member 13 e g electrically or mechanically and gives a value of the fibre angle. The value can be shown or be inserted directly as a parameter in the calculation of the size of the log rotation in a calculation unit (not shown).

In those cases where the moisture in the log 1 varies during sawing and influences the drying time and/or the pre-twisting of the product, this is also measured and is introduced in the calculation unit (not shown) as a parameter in the calculation of the size of the rotation of the log.

In an alternative embodiment (not shown) for hand-driven measurement of fibre angle on a living tree or a trunk, the tip 12 is resiliently attached to a plummet (not shown). In this embodiment, the tip 12 is always attached with its breadth in the vertical line and the body 11 is designed for e g a hammer blow so that the tip 12 can penetrate into the tree. In the cases where the tree stands in the vertical line, the rotation of the tip 12 in relation to the vertical line is equal to the fibre angle a. In the cases where the tree is leaning, two measurements are made on opposite sides of the trunk.

The size of the rotation during sawing can thus be adapted depending on the measured fibre angle a and the moisture so that the dried product will be essentially straight.

In one further alternative embodiment (not shown), the fibre angle measuring device is arranged to be mounted on various kinds of machines where there is a need of measuring fibre angle, e g a logging machine.

The invention shall not be considered as limited to the examples described above but can be varied within the frame of the claims, for example the form of the tip can vary depending on type of tree so that e g for soft types of trees broad tips are used and narrow tips for hard types of trees.

SUMMARY OF REFERENCE DESIGNATIONS 1 log<BR> lb pith<BR> 1c fibre 2 twisted crossbar 3 retainer 3a first part of the retainer 3b second part of the retainer 4 guiding rule 5 point of contact 6 saw band 10 fibre angle measuring device 11 body 12 tip 12a plane surface 12c edge 12d edge 12e outermost tip 13 angle registration member 14 pin 15 line parallel to the pith a fibre angle (3 twist angle angle of rotation b cross angle