Patent GB-290476-A (GB)
Title: Thread controlling mechanism for buttonhole sewing machines
IPC: D05B3/06
Filed: 1927-08-18
Abstract: 290,476. Fairweather, W., (Singer Manufacturing Co.). Aug. 18, 1927. Buttonhole sewing-machines.-In machine in which, at the end of the stitching cycle, all threads and cord are severed below the workclamp close to the last stitch, a pull-off device is arranged to operate on the needle thread between the needle and the work, while the work remains clamped, in order to provide for the next sewing operation a needle thread-end of sufficient length which need not be gripped. A thread pull-back device may also be arranged to shorten the needle thread-end so as to take it clear of the clamping feet after being severed. A thread slackener may operate, at the end of a stitching cycle, between the tension device and the supply spool to provide slack thread for the pull-off device referred to above, and both upper and lower thread tension devices may be released automatically. The machine described comprises an upper straight depth-stitch needle 5, a lower curved slit-stitch needle 6, and a feed wheel 12 to which movements are imparted from the main shaft 13 in usual manner. The work-clamp comprising clamping feet 17, clamp-plates 16, and a cross slide plate 26 is moved rapidly to and from sewing position by the feed wheel 12 which is driven during this part of the operation from a rapid feed shaft 32 through gearing 33, 37, and a clutch. The clutch is actuated to initiate the rapid feed to and from sewing position by a cam 70, Fig. 1, on the cuttershaft clutch-disc 71 which rocks an arm 69 on a shaft 67 to trip a latch. The drive is declutched when sewing position is reached by tripping points 63 on the pattern-wheel 60 which controls the starting and stopping of the stitch-forming devices. An arm 72 on the shaft 67 is adapted to be actuated by the stop-motion device S. The work-clamp is closed and spread, and subsequently opened and unspread in usual manner. The button-hole cutters 74, 75 are actuated by cams on the cutter-shaft 23. Thread-cutters. - When the work-clamp has been returned to cutting position after the sewing operation, but before the clamp is opened, all threads and cord are cut below the work close to the last stitch. The scissors 91 are carried by a lever 92 which is actuated by a cam-groove 97 in the gear-wheel 37 through lever 95 and link 94. The movable scissors blade is actuated by a pin 108 engaging a fixed cam groove 109, Fig. 4. The scissors 91 carry a waste needle-loop gripper 99, 100, the jaw 100 of which is moved in one direction to grip the thread by a post 102 on the turret 8, and in the other direction to release the waste loop by a fixed bracket 104. Threads controlling otherwise than in stitchforming.-A pull-off is provided to pull a measured amount of thread through the eye of the needle to ensure that the thread end will be long enough for the initial stitches of the next operation. The pull-off acts before the clamp is opened and before the thread cutter acts. It comprises a pivoted bell-crank lever 111, 111<1>, Fig. 14, having a thread-engaging hook 115 against which bears the end of a light flat threadretaining spring. The lever is actuated by a cam projection 121 on the gear 9 which actuates the needle turret, the cam and the finger 118 which it engages being arranged so that the cam is operative only when the gear makes its return movement. A thread-slackener, comprising a pivoted arm 125, Fig. 2, is arranged to pull off thread from the supply spool at the end of a sewing operation. It is actuated through a lever 127 by a projection 133, Fig. 3, on the work-clamp frame 27. In order to take the severed needle thread-end clear of the clamping feet 17, a thread pull-back, consisting of an adjustable rod 145 having a thread-engaging end 148, is provided. It is actuated by the work-clamp closing lever. The needle-thread tension 136 is released automatically at the end of an operation by a lever 139, Fig. 3, which is actuated by an adjustable plate 137 on the work-clamp frame 27. The under thread tension 152, Fig. 4, is released at the end of an operation by a lever 156 actuated by a stop on the work-clamp plate 26. Specification 18245/09 is referred to.