Patent GB-738610-A (GB)
Title: Improvements in or relating to sewing machines
IPC: D05B15/08
Filed: 1953-03-13
Abstract: 738,610. Sewing-machines. BRITISH UNITED SHOE MACHINERY CO., Ltd. (United Shoe Machinery Corporation). March 12, 1954 [March 13, 1953], No. 6931/53. Class 112. Lock-stitching by hooked needles; work-supports, boot-sole type.-In order to control the slack thread while it is being drawn up by the needle in a machine of the kind described in Specification 532,026, in order that the stitches may lie in line with one another, the needle opening in the worksupport has a restricted portion at one end; the work-support may also have other threadconfining surfaces on its upper part. A measured length of thread is laid round a thread finger by the looper before the thread is laid in the needle hook, and this thread is released by the finger when the needle begins to rise. In the worksupport shown in plan in Fig. 5, the needle penetrates the opening 46 close to the left-hand end, and a narrow extension 62 of the opening receives the thread extending from the previous stitch. The upper surface of the support has at its left-hand end a shoulder 64, which is pressed against the seam during back-feed of the support, and a complementary shoulder 66 providing a groove slightly narrower than the needle-slot extension 62 but with a flaring outlet to provide for movement of the shoe in a curve. The upper surface of the work-support is slightly inclined upwardly to the left as far as the end of the slot extension 62, so that the pressure of the presserfoot is concentrated in the region of the latter, and the part 68 of the surface is slightly lower (though still higher than the other end), the thread being clamped on this part by the presserfcot. In a modification, for stitching close to the surface of the shoe upper, the front wall of the needle-slot extension is in line with that of the slot, and the shoulder 66 is omitted, the shoulder 64 being made to extend somewhat forwardly of the rear wall of the slot extension. Feed by co-operating jaws.-The work-support 22 and presser-foot 24, Fig. 14, are mounted on a feed carriage 26 oscillated about a pivot 28 by a cam 40 which is so shaped that the support and foot exert a relatively slow rearward pull on the work during the feeding movement and a relatively quick forward thrust during back-feed (which takes place while the awl is in the work). The feed-carriage is connected by toggle-links 30, 32 to a yoke 36, pivoted at 37, and is oscillated by the cam 40 through a crank 38 and link 34; the feed is adjusted by means of a lever 184 acting through a link 182, crank 180 and link 178 on an arm 176 of the yoke 36. The arrangement is such that at the end of the back-feed the joint between the toggle links 30, 32 is close to the axis of the yoke pivot 37, so that the position of the work-support at this time is independent of the feed adjustment; this position is such that the needle is close to the left-hand end of the slot in the work-support. Presser-bars.-Relatively heavy pressure is applied to the work while the stitch is set, so the stitch is tightened by expansion of the work on release of the pressure, but to avoid the possibility of the work being squeezed from between the presser-foot and work-support during feed the pressure is lessened at other times in the cycle of operation. The presser-foot 24 is carried by a lever 86 pivoted to the feed-carriage 26 at 88, and is actuated and locked by mechanism similar to that described in Specification 558,431. The spring which applies normal pressure to it is attached at its forward end to an arm which is adjustable by a hand wheel through worm gear. The presser-foot is unlocked while the needle enters the work to take up its position under the pressure of the spring, and is then locked until after the stitch is set, when it is lifted for the backfeed: while the stitch is being set and the awl is entering the work the heavy pressure is applied.