A normal way of decomposing logs into boards and planks is that in a first step in the so-called log saw, a rectangular block (cant) is produced by cutting off the sides (slabs) of the log.
The rectangular cant that then remains to be split is usually more or less curved in the longitudinal direction depending on the log crook. This cant is taken into a second saw (resaw).
Curve sawing is today a normal cutting manner to decompose curved cants and thus gain advantages (quality and yield is increased) compared to straight sawing. Curve sawing involves feeding the curved cant in a curved path through the resaw, see the figures on the left for resawing with double arbor saw blades.
Measurements and theoretical simulations show that the cant decomposition shown in figures above, give oblique and curved sawkerfs. The magnitude of the kerf error can be 0.2-1 mm for the relatively large radius of cants that are sawn today. The errors give wider sawkerfs and backsawing. The cross sections of the sawn boards become distorted, see figures on the left.
New patented method for correcting kerf errors
By tilting the saw blade / blades in a vertical plane oblique saw kerfs can be avoided (for single blades) and for double blades both blades are tilted towards each other. Further, blades (double blades) are skewed towards each other in a horizontal plane so that the intersection of arbor extensions is located in the center of curvature of the cant. With this correction backsawing is eliminated and thus also the saw kerf widening. Typical angles are practically <1 °. The angles are variable as a function of the curve radius, cant height, blade diameter and other parameters via an algorithm.
Advantages of the method
- Straighter kerf
- No backsawing
- No kerf widening
- No reduction in thickness of the cross sections
- Reduced standard deviation of sawn timber
- Opportunity to handle more crooked logs
- Reduced lateral forces on the blades
- Reduced blade vibrations
- Opportunity to reduce blade thicknesses
- Lower energy consumption
- Possibility to avoid clean cutting grooves
- Higher yield
- Better surface quality of sawn timber