Patent GB-521640-A (GB)
Title: Improvements in or relating to sewing machines
IPC: D05B73/12
Filed: 1938-11-19
Abstract: 521,640. Sewing-machines. WILLCOX & GIBBS SEWING-MACHINE CO., Ltd., SLATER, H., and SUMMERS, G. L. Nov. 19, 1938, No. 33712. [Class 112] The invention comprises improved threadhandling means for overedge-sewing machines of the kind described in Specification 464,773, having an under looper and an overedge looper, either, neither or each looper being threaded according to the type of seam required, as described in that Specification; a single take-up member acts on needle and looper threads, being adapted to engage one of the threads during only a part of its movement. The needle-driving mechanism is also modified, the remainder of the machine being substantially as described in the above Specification. Needles, driving; presser-feet; work-supports.-. The curved needle 76, Fig. 6, is carried by an arm 69 on a rock-shaft 70 actuated from the main crankshaft through an arm 74 and a link 75 which is in tension instead of compression during the work-entering stroke. The needle rises beneath the work more slowly than in machines such as that of Specification 468,032, and it can thus be shorter and stronger. The presser-bar mechanism is substantially the same as that described in Specification 464,773. The presser-foot and work-plate 78 may be provided with complementary thread-engaging fingers such as 104 to assist in the formation of the stitches. Threads, controlling.-The threads, 99 for the curved needle 76, Fig. 1, 102 for the lower looper 79, and 103 for the overedge looper 93, are led to their respective tension, devices 109 through a guide 115 which provides friction to prevent the threads being jerked through the tension devices. The guide 115 has rounded ends, so that loops of thread cannot catch on it, and has four holes for each thread, the threads passing through the lowest both to and from the tension devices; the threads may be passed through two holes instead of the four if less friction is required. A single take-up arm 126, fixed to the upper end of the link actuating the under looper as described in Specification 464,773, acts upon all three threads and works within a thread guiding casing 124 which comprises a pair of side walls 134, 135, Figs. 9 and 10, joined together at the front end and by a top portion 140 and adjustably fixed to the machine housing by a screw 143 bearing on the top edges of the walls 134, 135; the casing 124 fits in a channel in the machine housing to prevent lateral movement. The casing 124 is cut away at the front end at '147 to form a thread aperture and a thread-guiding eye 150 is adjustably fixed to the wall 135 and cranked to lie in the plane of the latter in the aperture 147. An inverted channel-shaped member 161, embracing the upper edges of the casing 124 and adjustably fixed to the part 140 thereof by a screw 164, carries bent-out lugs 166, 168, having thread-guiding eyes 167, 169, the latter being elongated; a member 170, adjustably fixed to the side of the member 161, carries a thread-controlling finger 173 lying above the wall 135. The members 161 and 124 and the machine housing are marked to indicate their correct setting for different types of seam. The needle thread 99 passes from the guide 115 through the eye 167, an eye 129 in the top end of the takeup arm 126, the slot 169 and eyes 177, 179, Fig. 1, which bring it into the plane of the needle 76 so that it can lie in a groove in the needle; the guiding eyes are so positioned that the thread is substantially straight between the tension device 109 and the eye 177 when the take-up arm 126 is in an intermediate position. The under looper thread 102 passes from the guide 115 through an eye 145 in the wall 134 of casing 124, over a forwardly-projecting part 127 of the take-up arm, which is formed with a notch 131 to receive the thread during part of its operation, through an eye 146 in the wall 135, the eye 150 and an eye 130 in the end 127 of the take-up arm, through the aperture 147 and a guide 'tube 151 to the underneath of the work plate, and behind a guide 152 on a slide member 153 and through an eye 154 in the latter to the looper eye. The eyes are so arranged that the thread is substantially straight between the tension device 109 and the eye 146 when the take-up arm 126 is in its rearmost position, and the eyes 150, 130 are substantially in line when the arm 126 is in its most forward position. The overedge looper thread 103 passes from the guide 115 through one of a series of eyes 156 in the wall 134 of the casing 124, behind the take-up arm 126, through one of a pair of eyes 157 in the wall 135 of the casing, through a guide tube 158 and under a guide 159 to the eye of the looper; the alternative eyes 156, 157 allow the action of the take-up arm on this thread to be varied. As the needle moves downwardly towards the work, the takeup finger, moving forward from an intermediate position, pulls off just enough thread for it to reach its lowest position and, engaging the lower looper thread in the notch 131, tightens this thread, and pulls off more of it, after its engagement by the overedge looper. As the needle finishes its descent and begins to rise, its thread being engaged by the lower looper, the looper thread leaves the notch 131 but its slack is taken up by the eye 130 as the take-up moves backwards; thread for the overedge looper is pulled off, and the needle thread is laid over the control finger 173 so that it is pulled just sufficiently to keep it in the needle groove and rising with the needle. As the needle proceeds upwards and the lower looper forwards the overedge looper and the take-up start to advance, the take-up disengaging the overedge thread and releasing the lower thread and the needle thread, which latter slides off the control finger. The effects on the threads are described in detail.