This invention relates generally to apparatus for cutting threaded rods to any required lengths without ruining the threads thereon, and more specifically to a machine comprising a fixed and a movable cutting bit, the latter being power driven for linear travel past the fixed cutting bit for shearing threaded rods. Still more specifically, the invention deals with provisions in such shearing machines for preventing the jamming engagement of the movable cutting bit with the threaded rod when the rod is sheared.
Portable, power-driven shearing machines for threaded rods have been known in which both fixed and movable cutting bits have each a semicircular recess bearing a series of internal screw threads of the same pitch as that of the thread on the rod to be cut. The internal threads on the cutting bits are designed to mate with the thread on the rod being cut. As the movable cutting bit is thrust past the fixed cutting bit, as by a hydraulic cylinder of the familiar single acting, spring return type built into the machine, the threaded rod is cut by shearing action between the parallel cutting faces of the two cutting bits.
The shearing machines of the foregoing general construction offers the advantage that threaded rods can be readily cut to any required lengths without ruining the threads thereon, with the result that mating nuts can be smoothly turned onto such rod lengths. Conventionally, however, this advantage was limited only to cases where the machines were put to use with relatively small diameter rods. The machines had a serious drawback with larger diameter rods.
Any threaded rod undergoes elastic deformation when sheared, to an extent depending upon the diameter of the rod and the shearing force exerted thereon. The elastic deformation includes a component in the longitudinal direction of the rod, which component initially causes either of the separated sections of the rod to travel longitudinally away from the other rod section. Then the rod section in question recoils and, conventionally, has butted fast against either of the cutting bits. For this reason, the movable cutting bit has so far been easy to stick to either of the separated rod sections.
As has been mentioned, the shearing machines of the class under consideration usually employ a single acting, spring return hydraulic cylinder for driving the movable cutting bit back and forth past the fixed cutting bit because this type of cylinder is far less expensive than the double acting type. Consequently, on sticking to either of the rod sections as above, the movable cutting bit has conventionally been prone to become unretractable to its initial position under the force of the return spring, particularly when the rod is of relatively large diameter.