Patent GB-233812-A (GB)
Title: Lock-stitch sewing machine
IPC: D05B57/18
Filed: 1924-02-26
Abstract: 233,812. Fairweather, W., (Singer Manufacturing Co.). Feb. 26, 1921. Sewing-machines; lock-stitching by hooks; governing needle thread. - A bobbin-case of greater capacity than usual is supported within a rotary hook by a stationary support on which it rests and from which it is lifted periodically, because of its increased weight, to allow the passage of the needle-loop. The bobbin-case 43, Fig. 3, is mounted within on open raceway 37, Fig. 3, in the hook and has lateral peripheral flanges 63, Fig. 18, which rest on a disc 64, Figs. 4 and 5, carried by a member 67 which is pivoted at 90, Fig. 4, in a support 88, Fig. 22, on the bed of the machine. An arm 71 pivoted to a feed-lift, actuating-lever 25 at 72, and adjustably fixed thereto by screws 74, 75, engages underneath the bobbin-case and lifts it periodically from the disc 64. The disc 64 carries a pin 65, Fig. 4, adjustably fixed in a hole in the member 67, Fig. 9, and a lug 76 which loosely engages in a notch 52<1>, Fig. 5, in the bobbin-case. A lug 77 on a lever 77<1>, which is pivoted at 77<11>, Fig. 9, to the member 67 also engages in the notch 52 and is normally pressed against the lug 76 by a spring 80 surrounding the pivot 77". A lever 83 pivoted at 84 to a slot in the member 67 carries a pin 82 and has a notch 86 at its lower end to rest on the support 88, Fig. 22, and lock the member 67 in position. A spring 91 is positioned within the slot in the member 67 by a screw 92 which also acts as an adjustable stop for the pin 65. When the lever 83 is manually shifted against the spring 91 to disengage from the support 88, the pin 82 actuates the lever 77<1> to separate the lugs 76, 77 which grip the bobbin-case and withdraw it from the hook-race when the member 67 is turned out of position. In this way, the underthread b, Fig. 4, may be cut and the bobbin replaced without disturbing the needle-thread. The hook, which is rotated three times for each needle-reciprocation, is gapped at 35<1>, Fig. 3, to form a beak 36 which has a transversely-convexed outer surface and the heel of which is formed with a loop-arresting notch 42. A bridgepiece 39 over the gap 35<1> is spaced from the hook and has a concave edge 40, Fig. 5, which deflects the work-limb of the needle-loop over the outer face of the bobbin-case. The bobbincase bridge 44, Fig. 18, carries a tubular pin 45, Fig. 16, within which is expanded a longitudinally split and slotted hollow pin 46, Fig. 19, by a taper-headed screw. The pin 46 is taper flanged outwardly at the free end to retain the bobbin. The bobbin-case has three sectional race-flanges 53<a>, 53<b>, 53<c>, Fig. 18, the first of which has the usual loop-detaining hook 54, Fig. 16, while the last prevents the escape of the limb a, Fig. 22, until the hook-gap passes the end 55, Fig. 16. thereof. A guard-flange 59 prevents the beak 36, Fig. 3, from re-seizing the needle-loop, which is ejected from the notch 42 by the periphery of the flange. An adjustable tension spring 56, Fig. 18, bears on the bobbin-thread between the threading slots 57, 58, from which the thread passes through the notch 52, one wall of which is formed with a ledge 60 to guard the thread against seizure by the beak 36. An undercut loop-detaining horn 61 holds the loop until the limb a has passed through the notch 52 and so prevents twisting of the loop. A raised surface 69 on the bobbin-case rests against the disc 64 and provides thread-clearance between the case 43 and the disc 64 for most of the circumference. A take-up 93, 94, Fig. 29, is actuated by a crank 7 and anchored by a link 96. It acts in conjunction with a tension 99 and a light check-spring 101, which normally rests on an arm 102 of the presser-bar, the position of which varies in accordance with the work thickness. The take-up does not start until the needle has risen more than 5/16 ths of an inch above the work-plate to allow of sewing work of any thickness without adjustment. The stitch is set before the needle starts its downward motion and before the take-up reaches its upper limit, and further movement of the take-up first lifts the check-spring to its upper limit and then pulls off thread equal to that used in the last stitch, whatever the work-thickness. The take-up gives slack very early in the needle-descent, thus allowing of working on thick material without increasing the needle-stroke. Feed by dogs.-A feed-bar 27, Fig. 22, is pivoted to an arm 29 of a feed-advancing rockshaft 24, and is connected by a ball-ended link 26 and by a spring 30 to an L-shaped arm 25 on a feed-lift rock-shaft 23.