GB876190A - Lock stitch sewing machines - Google Patents

Abstract

876,190. Sewing machines. SINGER MANUFACTURING CO. May 12, 1959 [May 21, 1958], No. 16206/59. Class 112 A lock stitch sewing machine having a bobbin journalled in a loop-taker has means for winding needle thread on the bobbin driven by the needle and loop-taker operating means. The machine shown is a group stitch, single thread lock stitch machine having a pattern cam 21, work clamp 58, and thread cutting mechanism 74, such a machine being described in Specification 875,326. The rotary hook mechanism, Fig. 9, comprises a hook body 80 having a hub 81 secured to a bed shaft 35 in the machine, a groove 86 in the body 80 forming, together with a recess 90 in the attached gib member 87, a raceway in which is located the rib 92 of a stationary thread case carrier 91. A thread case 118 is positioned within the carrier 91 by the engagement of pins 128 on the case with bayonet slots 97 in the carrier, the arms of a spring 98 urging the pins into engagement. The bobbin 110 has a thread receiving 'V' groove 111 and arcuate slots 117, a stud 115 extending into a bore 121 in the thread case provided with a spring loaded detent which engages a groove 116 in the stud. The compression of the spring may be varied by a set screw 126 to vary the frictional drag on the bobbin and hence vary the tension of the bobbin thread. A thread cutting knife 129 is disposed at the periphery of the thread case. Disposed between the bobbin and the face of the hook is a bobbin winding member 150 secured to a rod 141 slidable within an axial bore in the bed shaft 35. The member 150 has a recess 153 facing the bobbin and a thread guiding surface 154 which tapers towards the recess. A quadrant shaped arm 156 on the bobbin winding member engages a gap 84 in the hook body so that the member 150 rotates with the hook. When the member 150 is pushed towards the bobbin by axial movement of the rod 141 as described later, a finger 157 on the quadrant arm immediately clamps one limb of a thread loop engaged by the beak 85 of the rotary hook against the latter, while a pin 161 on a leaf spring 159 secured to the bobbin winding member will enter one of the slots 117 in the bobbin as soon as it is presented, the bobbin then rotating with the loop-taker. The axial movement of the rod 141 is occasioned, at the beginning of a stitching sequence controlled by the cam 21, by lugs on the cam which engage a follower rock arm 183 and transmission members 179, 180, 170. A push rod 193 is also operated from the follower rock arm 183, by means of transmission members 190 and 192, to separate the discs of a tensioning device 51 and release the needle thread from tension. Operation. Fig. 1 and 7 show the machine at rest after a group of stitches has been performed, the work clamp being opened and the needle and bobbin thread severed beneath the work by the cutting mechanism 74. When the machine is started the lug on the cam 21 engages the arm 183 to release the needle tension and move the bobbin winding member from the position shown in Fig. 7 to that shown in Figs. 11 and 13, the needle thread loop engaged by the beak being clamped between the latter and the finger 157. As the hook revolves the pin 161 engages the slot 117 in the bobbin to drive the latter, the thread passing round the bobbin and then slipping down the face 154 to enter and be gripped in the sharp 'V' groove in the bobbin. During the first revolution of the hook the lead of the thread (see Fig. 13) avoids the knife blade 129, but during the second revolution the thread slips down the surface 154 and is wound in the groove, (see Fig. 14), the thread passing from beak to bobbin being then severed. As the thread is then jammed in the groove of the bobbin, winding continues as the bobbin rotates, and as the work feeding means of the machine is not yet operating needle loops are not formed, as the needle reciprocates, to be engaged by the beak of the hook. The extent of winding is determined by the position of a further lug which is adjustably mounted on the cam. This and the feature that the thread is severed by the blade 129 at a uniform distance from the bobbin on each successive cycle of machine operation provides a very accurate control of the amount of thread wound on the bobbin. When the lug passes the follower arm 183 the winding member moves back to the position of Fig. 7, winding ceases and other followers actuated by the cam commence to feed the work when the beak successively siezes needle thread loops to pass them around the bobbin and produce lock stitches.