Anticipatory crack at cutting wood anticipatory crack is formed already at the initial stage of the tool. When introducing the tool into the timber after sealing a chip rake face starts pulling the cutter shavings from the rest of the wood. Odnovrmenno chip bends. When communication between the fibers of wood to reach the tensile strength of wood to break across the grain, starts peeling chips and cracks advanced education. The length of the crack advance increases with increasing chip thickness.
The propagation velocity of the crack advance is always higher cutting speeds. Therefore, after the formation of advance the crack edge is not working. During this period the surface of the cutting tool rake face is formed by the separation of chips from the workpiece, the cutting edge formed only smooths the edge surface. Because the chip is formed margin, and not just cut the blade, the quality of surface treatment produces high; In addition, when cutting the fibers against forestalling a crack located in plane fibers can cause tear-out of the wood fibers, which leads to marriage. To reduce the harmful effects of crack advance in the quality of surface treatment, it is necessary to create a back pressure of the wood fibers near blade. As a result of backwater grain of the wood shavings nadlamyvaetsya as you move the tool.
Chip fracture occurs near the edge retaining element, so the smaller the gap between the edge and the tool edge, the less boundary of the crack advance. This method is used, for example, when planing a manual plane. The highest surface quality is obtained by processing a thin chip, when the length of the element chip is small. At carving along the fibers without the formation of advanced fracture surface quality of processing produces a high, as the surface formed by cutting the cutting edge. If you cut the fibers and parallel to them, then cutting of thin chips and a small angle of the cutting anticipatory crack does not appear, because the chisel is easier to bend the chip than break the timber. In this case, the surface quality of processing increases with decreasing angle of cut. However, the workpiece has a nonuniform structure of wood grain, so for large values of the angle between, especially in areas with defects of the structure of wood, there will be tear-out fibers leading to marriage. Furthermore, the decrease of the cutting angle is associated with a decrease in the angle of sharpening, which reduces the strength of the blade. Cutting without advanced education may also fracture displacement with respect to chip layers layers wood beneath the surface of cut, ie, the longitudinal shrinkage of the chip. Longitudinal shrinkage chips occurs when the face of tool, moving in front of a chip, compresses it along the grain and turns into isolated from compacted layer of the workpiece. Cutting capacity is the tool used to its full extent, when the cutting angle is 70 , and the chip thickness is small. Under these conditions, the high quality of the surface cutting at different values of the angle between the blade with the fibers. Cutting to the longitudinal shrinkage of chips used, such as planing manual plane-shliftikom.Pri cutting wood in the end the quality of surface treatment turns out to be low. Beneath the surface treatment of fibers in the fiber direction obrazuyuts cracks. The processing quality of ceteris paribus higher when the chip thickness and cutting angle are small.