GB476943A - Fret-saw machines - Google Patents

Abstract

476,943. Fret - saws. CARWARDINE, G. June 18, 1936, No. 16926. [Class 145 (ii)] The blade is connected at its ends to springs both of which are strained in all positions of the blade, the resultant of the forces exerted by them being zero at mid-point so that the tension is constant when the machine is driven at a rate equal to the natural frequency of the system. The blade 7 is secured to chains 12, 13 passing over pulleys, and attached to rods 16, 17. One of the latter is connected by a spring 8 to the frame, and the distant end of the other rod is caused to execute harmonic oscillations ; it also is connected by a spring 9 with the frrme. Harmful vibrations are eliminated when the forced oscillations have the same frequency, as the natural oscillations of the reciprocating system. In a modified machine, Fig. 4, the blade 7 is secured to a spring-pressed rod 10 and to a rod 11 fast to the upper end of a flexible strip 35. A rotatable crank-pin 19 gives harmonic oscillations to a coupling between the strip 35 and a flexible strip 37 connected by a spring 9 with the frame. To prevent damage to the machine shown in Fig. 1, if a blade breaks, part of the rod 17 is made in the form of a telescopic link L, in which a pin 22 on the part 17 projects through slots 23, and is connected by springs with a pin 25 on the part 171. If a blade breaks the parts 17, 171 telescope and a stop pin 26 on the jaw 11 seats in recesses 27 in the head 6, where it becomes motionless. In mounting a new blade the jaw 10 is depressed by means of a lever 28 pivoted at 29 to links 30, which are pivoted by a pin 31 in a recess in the head 5. If the lever be raised the jaw 10 is lowered by a. pin 32 acting on its upper end. The connection between the pin 19, Fig. 4, and the strips 35, 37 is shown in Fig. 5, in which a collar 36a is clamped between plates 36b riveted as shown to the strips.