Patent GB-596142-A (GB)
Abstract: 596,142. Sewing-machines. BRITISH UNITED SHOE MACHINERY CO., Ltd. (United Shoe Machinery Corporation). Nov. 1, 1945, No. 28969. [Class 112] Relates to lock-stitch, .shoe-sewing machines having a curved hooked needle and a rotary hook, and provides improvements in the rotary hook and thread-tensioning. and pull-off arrangements of the machine described in Specification 532,026. Rotary hooks.-In order. to assist uniform movement across the thread-case of the thread-limb which lies in front thereof and which has no longitudinal movement, and to allow the action of the takeup to commence as soon as the thread-loop reaches its maximum extension round the thread case without the danger of imposing excessive tension on the thread, the rotary hook 10, Fig. 14, is. formed with a step 26, over which the thread-limb passes at the appropriate time to relieve the tension in it. In order to control the thread-loop as it slips off the thread-case and is pulled down to the work by the take-up, the hook is formed with a loop-retaining hook 28 at the back of its beak 11 to hold the loop until it is within a short distance of the work. Governing locking thread.-The thread-case has a resilient thread-engaging, member fitting in a peripheral groove 5, Fig. 18, and pressed against the thread by a tension-adjusting member 70 which has at each end lateral lugs 72 engaging grooves formed by undercutting the walls of the groove 5, the member 70 being held in adjusted position by a lateral projection 74 engaging a series of radial grooves 76 in one wall of the groove 5. Governing needle thread.-In order to avoid variations of tension in the thread between the thread-locks on either side of the pull-off device resulting in incorrect thread-measuring, the thread-lock between the pull-off and the takeup is closed before the stitch is set, and an additional tension device is provided before the thread-lock preceding the pull-off to apply the same tension as is applied by the take-up when the former thread-lock is closed. The thread locks and their operating means are similar to those of Specification 558,431, with the addition of a thread-guiding face on a stationary lug to keep the thread near the middle of the pulley face, which portion is more easily hardened to minimise wear. A tension-device similar to that of Specification 596,079 is provided, but in order to allow adjustment of its timing it is operated by a cam clamped on the take-up shaft instead of directly by the take-up arm. Tension-devices; stopping gear.-The additional tension-device comprises a thread-engaging wheel 30 mounted between friction discs 36 on a flanged sleeve 32 slidable, but not rotatable, in a part 34 of the machine frame, the discs and wheel being pressed together by the flange under the action of a spring 38 bearing on a nut 42 which is adjusted by a threaded rod 40 with a finger-knob 44. The tension is released, when the treadle of the machine is released for stopping, by an arm 96 engaging the end of the rod 40 and connected by a rod to an arm in the treadle mechanism, the connection having a spring to allow continued movement of the treadle when the arm 96 comes against a stop. Specification 23478/10, [Class 112], also is referred to.