Patent GB-386543-A (GB)
Title: Thread-cutting mechanism for sewing machines
IPC: D05B65/00
Filed: 1932-06-16
Abstract: 386,543. Sewing-machines. FAIRWEATHER, W. C., 65, Chancery Lane, London.-(Singer Manufacturing Co. ; Elizabeth, New Jersey, U.S.A.) June 16, 1932, No. 17027. [Class 112.] Buttonhole-sewing machines ; thread cutters and thread-end holders.-In machines for sewing a group of stitches and then coming to rest, means are provided for ensuring the shortest possible end of needle-thread on the underside of the finished work. Means are also provided for controlling the needle and under threads to ensure perfect stitches. Also, means are provided for ensuring the proper co-operation of the working parts. The invention is illustrated as applied to a " straight " buttonhole sewing- machine. The cycle of operations is as follows. Starting with the machine at rest, the workclamp and needle-thread cutter operating levers are unlocked by the arm 111, Figs. 4 and 11. The thread end is held by the nipper 67 above the work. The under-thread is held by the nipper blades 120, 123, Fig. 18. The movable throat-plate is in its rearward position with its first-stritch aperture 43 in register with the needle 6. After placing the work in the work clamp, the operator pulls down the starting-rod 18 to tilt the stop-motion lever 10 into running position, Fig. 12. This motion causes the catch 64 to engage and swing the bell-crank latch-lever 60, 61 to release the plunger 57 which enters the cam groove 58 of the barrel cam 59 on the main shaft and receives one back-and-forth movement. The first part of the cam-groove causes a dwell to give the needle time to make its first descent and present its loop to the shuttle 28. As soon as the needle rises out of the work, an inclined part of the cam 58 starts to move the plunger 57 and its carrier 56 to open the upper thread nipper and release the needle-thread end, at the same time shifting the throad-plate 39 from its first-stitch position to normal sewing position. The shuttle 28 in its continued movement pulls down the released needle-thread end and the usual take-up (not shown) draws this end to a final position between the spring- plate insert 45 and the under surface of the work. The latch 153 locks the throat-plate shifting-bar 151 in its forward position. After three or four stitches have been sewn, a cam on the feed-wheel 25 actuates the slide bar 144 to release the bobbin-thread from its nipper and reset the bobbin-thread-cutter and nipper operating-bar 126. At the end of the sewing operation, the final rise of the stop-motion plunger 12 into the notch of the stop-cam 13 rocks the shaft 81 which functions only to release the needle-thread tension (not shown) and to shift the clamp-lock 111 to the full line position, Fig. 11, to unlock the work clamp and needle-thread-cutter release mechanism. The operator now exerts a downward pull on the lever 96. The first motion rocks the lever 96 upon the lever 90 to release the needle-threadcutter and nipper by tripping the latch 74. A further movement shifts the latch 153 to release the needle-throat shifting-bar 151. A still further movement causes the arm 154 to engage and return the bar 151 to its rearward position and at the same time the underthread-cutting and nipping mechanism is actuated. In the operation of the under-threadcutting and nipping mechanism, the pull exerted on the bobbin-thread by the threadcatching hook 130 draws down the severed end of needle-thread just before the bobbinthread is severed. The inclined tail 135 of the bobbinthreadcutter actuator-bar 126 causes this bar to swing sufficiently to permit the end wall 141 of the safety-latch 140 to drop into position, Fig. 21, to prevent reopening of the under-thread-nipper by repeated operations of the clamp lifter. During the downward motion of the clamp-lifter lever 90, the roller stud 94 depresses the tail 33<1> of the work clamp lever 33 and raises the clamp-foot 341 to release the work. Starting and stopping gear.-A safety device for preventing starting of the machine until after the work-clamp has been closed and the needle-thread-cutter and nipper tripping device 88 are restricted to initial position is provided. A lever 107, Fig. 11, is connected by a link 108 to an arm 109 integral with the stop-motionlever 10. The lever 107 has an inclined portion 1071 which will strike the arm 102 in the position this occupies when the clamp-opening and thread-cutter operating pedal is depressed, and block the movement of the lever 10 till pressure in the pedal is relieved.