GB1354534A - Loose stitch forming mechanism for lock stitch sewing machines - Google Patents

Abstract

1354534 Loose stitch formation SINGER CO 1 July 1971 [9 July 1970] 30778/71 Heading DIG A lock stitch sewing machine having a needle thread take up 30 has means co-operating with the take up to produce lock stitches having slack thread therein, the means comprising a thread tensioning device 110, thread guiding means directing two successive lengths of thread to the influence of the take up, and a thread nipping device 140 permitting movement of the thread in one direction only. Stitches, seams. The devices disclosed permit the slackness of the stitches to be adjusted to match the shrinkages induced into threads and fabrics by subsequent treatments (e.g. permanent press finishes) so that a final flat, pucker free seam is obtained! Loose stitches, take up. The device provides a disc tensioner 110 which is employed instead of the usual tensioner 90 which is rendered ineffective by removing its spring. Thread guides 121, 126 direct the needle thread Nt below the take up lever 30, as shown, before the thread is passed through the one way device 140, around the ineffective tensioner 90 and guides 49, 95 before passing through the take up eye 32. The guide 126 is provided at one end of a lever 124 which may be rotated to vary the guide position and thus the degree of action imparted by the take up lever 30 to the length of thread passing therebelow. The lever 124 passes over a calibrated scale. The one way device 140 comprises a lever 145 having guide notches 146 at its ends engaged by the thread Nt which passes below a dog 150 having slots 151, 155 engaged respectively by a clamp screw 152 and an eccentric 156. Rotation of the head 157 supporting eccentric 156 varies the sensitivity of the device 140. A light spring 160 biasses the lever 145 towards the dog. The specification describes the movement of the marked points A, B and C of the thread during a stitching cycle resulting in the formation of loose stitches. In a modification (Figs. 7 and 8 not shown) the first length of thread is directed above the take up arm while the one way device (240) is modified to provide a fixed dog (250) the lever (245) being biassed towards the dog by an adjustable spring device (260, 270). Thread Guide. In the modified device a thread guide comprises a wire (212) around which the needle thread is twisted to provide a slight pretension and to remove kinks from the thread. Feed dog, looper thread take up. The feed dog 74 is provided with a coated slot 180 and a thread engaging wire 190 fastened therein to be positioned rearwardly of the needle aperture in the throat plate. The wire engages the bobbin thread to eliminate resistance to the passage of the needle thread loop along the bobbin thread. Tensioner operation. The stud (11 Fig. 1 not shown) of the tension device is connected to the presser foot raising lever (54) by a cable (58).