Patent GB-656920-A (GB)
Title: Thread-trimming mechanism for sewing machines
IPC: D05B65/00
Filed: 1949-01-14
Abstract: 656,920. Sewing-machines. F A I RWEATHER, W. C. (Singer Manufacturing Co.). Jan. 14, 1949, No. 1030. [Class 112] Thread-cutters and thread-end holders.- A needle-thread cutting device, particularly for a buttonhole-sewing machine in which the thread may extend from the needle to the work at various inclinations at the end of the operating cycle according to the length of the buttonhole, comprises a pair of relatively-movable blades which are moved to a position where they straddle the needle and then to a position clear of the needle (below it), where they are actuated to cut the thread; by these movements engagement with the thread is ensured. In the arrangement shown, in the position of rest, the device comprises a lower fixed blade 73 and a movable blade 75 (shown dotted in the open position) pivoted at 77 to a plate 78 with which the blade 75 co-operates to hold the cut end of the thread until the start of the next stitching cycle. It is carried by an arm 71 projecting from a boss 69 on a hollow spindle carried in a bearing 67 on a lever 66 pivoted at 65 to a depending plate 64 on a base member 58 which is fixed to the stationary stud 61 carrying the usual toothed sector for rotating the needle turret; the rear end of the spindle of the boss 69 carries an arm 102 with a pin engaging a cam slot 104 in the plate 64 to control the position of the arm 71. The blade 75 is actuated by a slide 85 on the arm 71, engaged by a ball-ended pin 88 projecting laterally from a spindle bearing in the bore of the spindle of the boss 69 and carrying at its rear end an arm 107, with a roller 106 for engaging a cam surface 105 on the plate 64 to close the cutter as it reaches its operative position, and a radial pin 119, for engagement by a finger 117 on a slide 114 to open the cutter at the appropriate time, as described below. The lever 66 is engaged by a slide-block universally mounted on the end of an arm 92 on a shaft 93, journalled in the member 58, which carries at its other end a block 95 with a spring-pressed plunger 96 adapted to engage a finger 98 carried by the usual link 33 actuating the needle-turret-rotating sector. The finger 98 snaps past the plunger 96 during the rotation of the needleturret while the eye of the buttonhole is being formed, but during the return rotation after completion of the buttonhole the finger rocks the shaft 93 to raise the arm 92 and thus lower the thread-cutter, the cam slot 104 guiding it to bring it first to a position in which the open blades lie on either side of the needle and then vertically downwards to a position below the needle, where the thread is cut and nipped by the action of the cam 105. The cutter is lifted by a spring surrounding the shaft 93 when the finger 98 passes clear of the plunger 96, the blades remaining closed to hold the threadend until the stitching of the next buttonhole begins, when the stop-mechanism moves a rod 108 against one arm 111 of a crank pivoted at 112 to the base 58 so that its other arm moves the slide 114 to open the cutter as described above; the crank 111 and slide 114 are returned to their initial position, so that the pin 119 moves into proper relation with the finger 117 when the cutter is lifted after the next operation, by engagement of the block 95 with the crank arm 111 as it depresses the cutter into operation. Specifications 179,278, [Class 112], 183,873, [Class 80(ii)], 549,425 and 549,563, are referred to.