GB1011878A - Chain stitch device for lock stitch sewing machines - Google Patents

Abstract

1,011,878. Sewing machines. SINGER CO. Aug 4, 1964 [Aug 7, 1963], No. 31655/64. Heading D1G. A lock stitch sewing machine, modified to produce stitching, comprises a work support formed with a needle aperture, a rotary looptaker disposed beneath the work support, a bobbin-supporting case journalled in the looptaker and constrained from rotating therewith, a thread loop engaging finger disposed beneath the work support in advance of the needle aperture and parallel to the path of needle reciprocation and arranged for movement substantially along the line of work feed, said finger being formed with an aperture, threaddirecting means on the bobbin case having a projection adapted to be engaged with said aperture, means operated by the work-feeding mechanism for shifting said finger to engage said aperture, with said projection during each release of thread loop by the looptaker, and a reciprocating element disposed between the needle aperture and said finger for stripping the thread loops from the latter when the needle penetrates the needle aperture. A feed dog 50, operating in slots 51 in a throat plate 52, is carried by a feed bar 54 pivoted to a crank 56 on an oscillating feed-advance shaft 55. Feed bar 54 is also connected by a pivotal link 62 to a crank 61 on an oscillating feed-lift shaft 60. A bobbin thread pull-off member 65 has a forked end 66 slidably embracing the pivot pin between feed bar 54, and crank 56. Member 65 is arranged to rise and fall with the feed bar 54 and has an arm 67 connected by a pivotal link 68 to a crank 69 on shaft 60, whereby member 65 is moved longitudinal on the feed bar in directions opposed to the directions of movement of the latter, member 65 being formed with an eye 70 for engaging the bobbin thread in lock stitching. The throat plate 52 is modified by pivoting thereunder on arm 84 having a thread loop engaging finger 86 with a aperture 87, and a ear 88 aligned with a feed dog slot 51. The vertical aris rotary hook 32 has a loop-seizing beak 33 and journals a bobbin case 34 constrained from rotation with the rotary hook. In chain stitching, the bobbin is removed and a plate 90 is positioned non-rotatably on the annular seat 38 normally supporting the upper flange of the bobbin. Plate 90 is formed with a thread-directing tongue 95 ending in a projection 96 aligned with aperture 87. At the end of a work-feeding stroke,when the feed dog is in its extreme left hand position and commences to descend, member 65 is in its extreme right hand position and the outer web 71 of eyelet 70 abuts finger 86 to maintain aperture 87 engaged with projection 96 to retain the previous loop of needle thread cast by the looptaker in engagement with finger 86, while the needle 19 descends through said loop. When the feed dog descends and moves to the right, member 65 moves to the left and also descends, whereby web 71 moves away from finger 86, the thread tension in the old loop disengages finger 86 from projection 96 by turning bar 84 clockwise, and the descending web 71 strips the old loop from finger 86. The new loop, when cast by the looptaker, is deposited on the tongue 95 and moves towards the projection 96, the latter being re-engaged in aperture 87 when the feed dog engages bar 88 to turn bar 84 counterclockwise. In a modification bar 84 is biased downwardly by a leaf spring. In a further modification. Fig. 8, a bobbin case 234 is modified by welding thereto a bracket 290 formed with an upstanding projection 292 adapted to enter the aperture in the thread loop engaging finger, and a second upstanding projection 294 adapted to guide thread loops on to projection 292. The bobbin is thus retained for chain stitching and the bobbin thread is concentrated with the needle thread loops, but lies on the undersurface of the seam and may be readily withdrawn from the seam.