The present invention relates to a method for cutting back and forth a log fastened with clamps to a cutting apparatus, with at least two parallel cutting devices arranged in a carriage and moving in the longitudinal direction of the log, whereupon the desired measure of the sawing product is achieved with the symmetrical positioning of the mutual distance between the cutting devices, and the first cutting of the log is performed rectilinearly by locking the carriage in the lateral direction. This carriage moves along a log attached with clamps to the cutting apparatus from one end of the log to the other, returning to the starting point. The cutting device positioned in the carriage then cuts the log in moving in both directions. In the first stage of the cutting, the outer surface of the log is cut with a fixed blade setting of the cutting device.

The invention also relates to a cutting apparatus for cutting a log, comprising clamps fastening the log to the apparatus, and a carriage moving along the log via guide tracks and returning to the beginning of the log, at least two parallel cutting devices mutually positioned at a symmetrical distance from the axis of the log, being attached to the carriage by means of a slide rest.

At present, the sawing of timber is performed in plants comprising one or several fixed sawing machines or movable machine units. The aforementioned plants utilize for sawing frame sawing, circular sawing, band sawing and chain sawing machines, as well as chipping canters.

The capacity of movable sawmills is usually low, since the sawing is mainly performed with one blade, and the structure of the sawing machine or the blade only makes it possible to saw in one direction. Round cutting of large logs is difficult with a conventional single-blade circular saw. It requires a large blade which is difficult to maintain and repair. Since a blade having a larger diameter must be thicker, it also produces a wider saw kerf, and therefore the yield also decreases.

A movable band saw is applicable for the round cutting of large logs, but it is not suitable for the conventional method of double cutting, since it is not possible to edge individual board blanks. Mainly stationary sawmills are comprised of several separate sawing machines, and the conveyors and conveyor systems placed between the machines are expensive to set up and also require large and expensive spaces. It is often impossible to produce round-cut timber.

The purpose of the present invention is to eliminate the disadvantages of the prior art and to provide a new kind of solution having a higher capacity than the present single-blade sawing machines, but requiring no large conveyor arrangements for the handling of sawn timber. Furthermore, the invention enables all the most commonly used manners of sawing.

The invention is based on the idea that the logs are cut with a cutting unit when they are fixed in one place, wherefore it is possible to organize the further handling of the sawn timber in a centralized manner.

The aim of the present invention is achieved in such a way that the cutting method and the cutting

apparatus comprise the characteristics defined in the claims according to the invention.

More precisely, the method according to the invention is mainly characterized in that the carriage comprises associated guide members moved to a substantially symmetrical position with respect to the centre between the cutting devices, whereupon the guide members guide the carriage and/or the log in the lateral direction from its cut surfaces in such a way that the centre between the cutting devices remains substantially on the longitudinal axis of the log to be cut.

In the first stage the log is centered and fastened to clamps provided in the cutting apparatus. The resultant line between the clamps is called an axis of fastening. At this stage the cutting unit forms in the log at least two cuts symmetrical with respect to its axis of fastening.

In the second stage the cutting is controlled by means of the surfaces made in the preceding stage in the piece to be cut. Bends and twistings resulting from the internal stresses of the log are then taken into account. The internal stresses of the log are released during the cutting of the log surfaces in the first stage, and the log then bends and/or twists. These transformations of the log can be effectively taken into account during the cutting by controlling the cutting devices with the guide members moving along the cut surfaces of the log.

The manner of guiding the cutting apparatus by allowing it to follow the cut surfaces of the log also makes it possible to turn a log, which is to be sawn and which has a large diameter, 180° around its longitudinal axis after the carriage has passed over the log the first time. A new cut may then be performed when the cutting device returns to its starting point providing

a round cut of the log. Guiding the cutting apparatus according to the cut surfaces of the log ensures an accurate round cut.

In the apparatus according to the invention, it is sufficient to fasten and center the log only once, since the cutting is guided to follow the axis of fastening of the attached log.

The invention also relates to a cutting apparatus for cutting the log. The apparatus is characterized in that the apparatus comprises guide members attached to the carriage and positioned substantially symmetrically with respect to the centre between the cutting devices, arranged to guide the carriage and/or the log in the lateral direction from its cut surfaces in such a way that the centre between the cutting devices remains on the longitudinal axis of the log to be cut.

The carriage of the cutting apparatus according to the invention comprises at least two units used in the cutting, provided with one or several cutting devices, and arranged to move symmetrically substantially perpendicularly to the axis of the log to be cut.

The cutting devices are arranged to follow the curvature of the log to be sawn by means of movable guide members in such a way that the distances of the cutting devices from the outer surface of the log remain substantial equal.

In the cutting apparatus according to the present invention, the log to be cut is centered and fastened with clamps in the place of cutting.

During cutting the cutting devices move over the log from one end to another in both directions and they also cut in both directions. The cutting devices are situated for example in a movable carriage over the

log and provided with turning setting keys in both cut sectors of the cutting device. The blade setting of the cutting devices may be changed each time the log has been crossed. The invention utilizes a mechanism which centers the carriage and guarantees that the distance between the cutting devices remains the same during the entire cutting procedure. The centralizing mechanism of the guide members in the apparatus also positions the carriage moving the cutting devices on the axis of the log to be cut. The cutting thereby produces timber of even thickness regardless of whether the log to be sawn is straight or curved.

The cutting apparatus also comprises a conveyor arrangement by means of which the sawn timber is removed from the apparatus in the lateral direction. For this purpose, the apparatus comprises a conveyor removing the sawn timber away from the actual cutting area and later back to the cutting area for edging. The invention comprises an edging site with a feeding device utilized in the edging and in a part of the dividing of the cants. During edging the cutting unit is fixed.

The inventionprovides considerable advantages. Therefore it is possible, by means of the method according to the invention and the apparatus realized with the method, to cut a thick log, since the log can be turned around in the apparatus. A thick log can be cut due to the movement of the sawing machine carriage, which follows the log and enables the accurate cutting of a curved log.

The apparatus according to the invention makes it possible to handle the sawn timber with a small conveyor arrangement, since the sawn timber is always gathered in the same area of the apparatus.

Since the apparatus according to the invention utilizes more than one cutting blade, it has a good sawing capacity. Still, each log is processed separately, which on the other hand makes the apparatus highly flexible when logs with different dimensions are cut.

In the following the invention will be described in greater detail by means of the accompanying drawings, in which Figure 1 is a side view of a cutting apparatus with a carriage, and

Figure 2 is a front view of the cutting apparatus.

The figures show one preferred embodiment of the cutting apparatus, comprising clamps 1, 2 with which a log to be cut 3 is fastened to the apparatus, a carriage 4 performing the cutting, and guide tracks 5, 6 supporting the carriage and guiding it from one end of the log 3 to another. In order to fasten the log 3, the clamp 1 situated opposite to the starting point, i.e. the beginning, of the carriage 4 can be moved in the longitudinal direction of the log.

The carriage 4 of the cutting apparatus can be moved substantially along the longitudinal axis of the log 3 to be cut via the guide tracks 5, 6 by means of a drive motor 7 contained in the carriage. The carriage 4 comprises one or several cutting devices 8, 9, preferably a blade of a circular saw, arranged in the longitudinal direction of the log to be cut. The cutting devices 8, 9 are arranged in slide rests 10, 11 situated in the carriage 4 and attached thereto by means of for example linear guide tracks 12, 13, 14. The cutting devices 8, 9 are arranged to move in the same direction with the slide rests 10, 11, transversely to the direction of movement of the carriage 4, and they leave

parallel saw cuts in the log 3 during the cutting. This transverse movement may be either free or mechanically controlled. The transverse movement can also be centralized and locked with a special locking means. The distance between the slide rests 10, 11 in the carriage 4 can be controlled in such a way that the movement of each slide rest brings the rest either closer to or further away from the other slide rests. This movement is preferably symmetrical. The symmetry of the movement is provided for example mechanically, by means of different combinations of joint and lever constructions or simply by means of a screw torsion device operated with an electric motor and provided with a right- and left-handed thread which are preferably constructed on the same axis 15.

In addition to the cutting devices 8, 9, the slide rests 10, 11 comprise associated guide members 16, 17, 18, 19, such as hydraulic guide rollers. They are connected to the slide rests 10, 11 by means of guide bars 20, 21, 22, 23. The guide members 16, 17, 18, 19 are placed in the cut surfaces of the log 3 to be cut to control, via the slide rests 10, 11, the cutting devices 8, 9, as well as the log to be cut, substantially in the cutting point of the log. The guide members 16, 17, 18, 19 follow the surface of the log 3 to be cut and, by means of the guide bars 20, 21, 22, 23, force the slide rests 10, 11 arranged in the carriage 4 to move along the linear guide tracks 12, 13, 14 substantially perpendicularly to the direction of movement of the carriage 4, thus following the possible curvature of the log to be cut. The movement of the guide members is symmetrical and it is provided for example by means of a closed hydraulic circuit.

The clamps 1, 2 in the cutting apparatus can also be released to make a rotating movement in such a way that the log 3 to be cut is allowed to revolve substantially around its longitudinal axis during the cutting. The guide members 16, 17, 18, 19 then force the log to be cut to turn into a position which enables a saw cut of even thickness.

The cutting devices 8, 9 of the apparatus may be provided with turning setting keys 24, 25, which make it easier for example to cut a cant obtained from the log 3 in the longitudinal direction to provide for example boards. The setting key 24, 25 is in an off- position when it is turned away from between the cut sector of the cutting device 8, 9 and the log to be cut. The operation of the cutting apparatus is characterized in that the log 3 is centered and fastened to the clamps 1, 2, and surfaces from two opposite sides of the log are then sawn off with the fixed blade setting of the cutting devices 8, 9. When the log comprises sawn surfaces extending the full length of the log, the guide members 16, 17, 18, 19 attached to the carriage 4 are made to follow the surfaces cut in the log, whereupon they guide the slide rests 10, 11 positioned in the carriage 4 and the cutting devices 8, 9 attached thereto with respect to the longitudinal axis of the log 3. If the log is twisted, the guide members 16, 17, 18, 19 force the log to turn at the point to be cut to follow the direction of the cutting devices 8, 9, thus providing a cutting line parallel to the surface to be followed. Sawn timber of even thickness can thus be cut out of the log, even if the log were curved and/or twisted.

The cutting devices 8, 9 placed in the carriage 4 perform both back-cutting and counter cutting of the log 3, whereupon their blade settings are changed each

time they have crossed the log according to a predetermined pattern of sawing. In order to enable this sawing, the cutting devices 8, 9 comprise associated setting keys 24, 25 in both cut sectors. The sawing in both directions also comprises guide members 16, 17, 18, 19 in both cutting directions of the apparatus, if necessary. For example, when the blade of a circular saw is utilized, the guide members are formed of four guide rollers organized in pairs in such a way that the slide rests 10, 11 are always controlled by the guide rollers 16, 17, 18, 19 situated on the cutting side of the blade 8, 9, the other pair of rollers being released from the surface of the log. The guide rollers then guide the log to the blades of the circular saw substantially around the point of cutting.

The cutting apparatus according to the invention may also be used to cut thick logs, which cannot be cut through at once, by performing a so-called round cut on the log 3. This is performed in such a way that after the cutting by the cutting devices 8, 9, the log fastened with the clamps 1, 2 is turned 180° around its longitudinal axis and cut in the other direction with the same blade setting as during the preceding cutting. Due to the control of the carriage 4, the saw kerfs are accurately positioned in the same line.

The carriage 4 may also be locked in its starting position, and it may then be used as a resaw and an edging saw by performing the cutting of the log 3 in a fixed position. The invention is not restricted to the above embodiment, but it may be modified in several ways without deviating from the scope of the inventive idea defined in the appended claims.