1. Field of the Invention
This invention relates to severing devices for fibrous material, and more particularly relates to a combination shear-saw used for felling or otherwise cutting through the bole of a tree.
2. Description of the Prior Art
It is well known in the tree cutting art that felling or bole slashing shears cause high longitudinal compressive forces in the tree as the shear blade progresses transversely through the wood resulting in severe wood splitting. Increasing demands by government and industry to extract all good saw timber from felled trees, including the large diameter portions of almost all pulpwood, requires that care be taken to minimize splitting of trees when they are felled. Although shears are the fastest and most durable means of felling trees, the tree splitting problem is so great that industry is looking to chain saws in order to comply with government standards.
Chain saws operated manually provide good nonsplitting cuts, but locating the labor force to handle the saws presents a substantial problem. Using chain saws in mechanical felling heads has presented difficulties due to uncontrolled conditions in felling trees frequently resulting in binding of the chain saw blade within the cut of the tree. In many cases an attempt to back the bound chain out of the saw cut in the tree results in breaking of the chain.
A vehicle supported scissors type felling head which uses a hydraulically actuated chain saw and resisting anvil is disclosed in U.S. Pat. No. 3,612,115 which issued to Albright on Oct. 12, 1971. The chain saw blade, however, is exposed to the solid wood and is subject to binding within the saw cut in the event the tree sways during cutting.
U.S. Pat. No. 3,672,412 which issued to Albright on June 27, 1972 discloses a similar felling head with chain saw. The patentee, however, provides a pusher which operates in conjunction with a chain saw in an attempt to prevent binding of the saw as it cuts through the solid wood of the tree.
A third U.S. Pat. No. 3,796,242 dated Mar. 12, 1974 discloses the combination of a pair of dogleg jaws which clamp the tree being cut at four points so that a chain saw may be swung through the tree without binding in the cut. The patentee also discloses a pair of shear blades on the dogleg jaws for cutting trees of small diameter. A flow divider is used in the system to control the feed rate or swinging of the chain saw through the log inversely with the size of the opening of the jaws.
U.S. Pat. No. 3,726,326 to Coleman which issued on Apr. 10, 1973 discloses a vehicle mounted felling head provided with a first pivoted chain saw which is swung partially through the tree from the side opposite the vehicle. The first chain saw is then pivotally retracted and a reciprocating second chain saw cuts through the uncut portion of the tree while a pusher forces the tree away from the tractor thereby preventing binding.
U.S. Pat. No. 3,854,510 to Matlik which issued on Dec. 17, 1974 discloses a felling head having a pair of pivoted tree supporting jaws with arcuate cross sections. Each jaw has a chain saw incorporated therewith with the tree engaging section of the saw projecting outwardly of the tree supporting jaw in position to precede the jaw through an undisturbed solid portion of the tree. The leading edge and arcuate flutes of each jaw are slightly larger in cross section than the chain saw and are forced into the saw cut to prevent binding of the saw blade as it cuts through the tree.
U.S. Pat. No. 3,902,538 which issued to Muirhead on Sept. 2, 1975 discloses a felling head having a stationary buttress blade and an opposed pivotal blade which carries a sharpened auger-type rotary cutter. As the driven rotary auger is moved with the pivotal blade against a tree, the exposed cutter cuts through the solid wood of the tree toward the buttress blade. During this time clamping means support the tree.