1. Field of the Invention
The present invention relates generally to horizontal bandsaw machines in which a saw head assembly carrying a bandsaw blade is lowered during a cutting operation in order to feed the bandsaw blade into an underlying material to be cut, and more particularly pertains to a feed control for controlling the feeding of a bandsaw blade in horizontal bandsaw machines.
2. Description of the Prior Art
Horizontal bandsaw machines comprise a saw head assembly in which a flexible endless bandsaw blade is trained around a pair of wheels so that it may perform cutting operations when the wheels are power rotated. In most prevailing horizontal bandsaw machines, the saw head assembly is pivotally connected by a hinge pin to a base on which a material to be cut is placed, and it is so arranged as to be pivotally raised and lowered around the hinge pin by a piston rod of a hydraulic motor or cylinder. Thus, in cutting operations, the saw head assembly is swung down around the hinge pin from a raised position toward the base so as to feed the bandsaw blade travelling therein into the material to be cut which has been placed on the base. In this arrangement, the weight of the saw head assembly will act as a feeding force to feed the bandsaw blade into the material to be cut. In this connection, the saw head assembly can be so arranged as to be vertically raised and lowered along a guide post or posts, but in most cases it is pivotally hinged to the base in the above described manner mainly for reasons of manufacturing costs.
In such horizontal bandsaw machines, the feeding force of the bandsaw blade into the material to be cut has of course to be sufficient to cut hard and tough materials which are difficult to cut. An insufficient feeding force will cause the bandsaw blade to slide on the material to be cut without performing a cutting action and as a result the bandsaw blade will not only be uselessly worn but also will cause an undesirable work hardening of the material and a decrease in cutting accuracy.
The problem is that a feeding force sufficient to cut hard and tough difficult-to-cut materials is too great to cut normal easy-to-cut materials which are generally soft and brittle. An excessive feeding force will cause the blade to work too hard, and consequently the bandsaw blade will become worn prematurely and cutting accuracy will again be decreased.
For the above reasons, it is on one hand desired when cutting easy-to-cut materials to feed the bandsaw blade into the material with a smaller feeding force so that the cutting action may be performed always at a cerain optimum cutting rate which is defined as square millimeters of cut per unit of time. On the other hand, however, it is desired when cutting difficult-to-cut materials to feed the bandsaw blade into the materials with a greater feeding force. Accordingly, it is also desired in the horizontal bandsaw machines to control the feeding (force) of the bandsaw blade according to the materials to be cut, and it is of course necessary to keep the feeding force always fixed or unchanged until a cutting cycle has been completed on a material to be cut.
Heretofore, however, there have been vexing problems in controlling the feeding force of the bandsaw blade in horizontal bandsaw machines especially of the type in which the saw head assembly is pivotally raised and lowered around the hinge pin.
One of the vexing problems with regard to horizontal bandsaw machines has been the fact that the center of gravity of the saw head assembly will be rotatingly moved in its position with regard to a material to be cut to gradually change the moment as the saw head assembly is pivotally swung down around the hinge pin toward the material. Accordingly, the force component deriving from the weight of the saw head assembly and acting on the bandsaw blade to feed the same into the material to be cut will be always gradually changed during a cutting cycle as the saw head assembly is lowered from a raised position toward the material. In other words, the weight of the saw head assembly will not fully act on the bandsaw blade to feed the same into the material to be cut when the saw head assembly is at the most raised position, but it will act on the bandsaw blade more and more greatly as the saw head assembly is pivotally lowered toward the material around the hinge pin. Thus, with no additional arrangement, the feeding force of the bandsaw blade cannot be controlled so as to be kept unchanged and optimum according to materials to be cut in horizontal bandsaw machines of the type in which the saw head assembly is pivotally raised and lowered around the hinge pin.
As a conventional attempt to keep the feeding force unchanged in horizontal bandsaw machines, a helical spring has been so used as to be biased around the piston rod in the chamber of the hydraulic motor or cylinder for moving the saw head assembly in such a manner that it will be more strongly compressed when the saw head assembly is higher raised. In this arrangement, the helical spring will act on the bandsaw blade to feed the same into a material to be cut so as to compensate for the lack of the acting component of the saw head assembly when the saw head assembly is at its higher swung position. In this manner, however, it has been impossible to keep the feeding force constant during a cutting cycle, since springs have not only generally suffered from manufacturing errors in spring force but also the spring force is linearly changed in proportion to the compression of the spring while the acting component of the saw head assembly will be curvilinearly changed as the saw head assembly is pivotally swung down.
Another problem with regard to horizontal bandsaw machines has been that the feeding force of the bandsaw blade cannot be accurately controlled according to materials to be cut so as to feed the bandsaw blade into a material to be cut with an optimum feeding force. Although various attempts have been made to feed the bandsaw blade into a material to be cut with an optimum feeding force, there have been no horizontal bandsaw machines in which the feeding force can be accurately controlled according to whether a material to be cut is easy or difficult to cut. Generally, conventional bandsaw machines are so arranged that the feeding force can be controlled mainly when cutting easy-to-cut materials, and accordingly the feeding force cannot be accurately controlled when cutting difficult-to-cut materials.