Patent GB-548549-A (GB)
Title: Improvements in or relating to buttonhole sewing machines
IPC: D05B3/06
Filed: 1941-04-11
Abstract: 548,549. Buttonhole sewing-machines. JACKSON, L. MELLERSH-. (International Button Hole Sewing Machine Co.). April 11, 1941. No. 4851. [Class 112] In a sewing-machine for eyelet-end buttonholes, capable of being adjusted to sew buttonholes of different lengths, thread-trimming mechanism is provided below the work and is actuated at a variable position in the relative movement of the work and the stitchforming devices, so that the thread-end is properly related to the end of the buttonhole by being trimmed at a substantially constant distance from the end of the stitching. The trimming means may act on either thread or both. Provision is made for leaving a proper length of thread for starting the next buttonhole. Means are provided for trimming a stay-cord similarly. The machine shown is of the type described in Specification 437,585, for making fly-bar buttonholes. The mechanisms for severing the sewing threads, cutting the cord and positioning the cord end for a new buttonhole are carried by the lower turret and are actuated by normally stationary cams 191, 161, and 140, Fig. 5, positioned along the path of the stitching frame. Contact is made with these cams only when the turret has turned into its position for the second side of the buttonhole. The cams are adjustably secured by a bar 91 to the cam-bar which controls the starting and stopping of the stitching instrumentalities and are moved with it and the fly-bar cam plate to vary the length of the buttonhole. By these means, the cord is cut so that its end is invariably covered by the barring stitches and the free ends of the stitching threads are short and independent of the length of the buttonhole. The stitch-forming mechanism is as described in Specification 17692/07, [Class 112], comprising a pair of loopers 37, Fig. 26, one having an eye for the under-tbread, and associated spreaders. The pins which alternatively engage the fly-bar cam-plate 65 for the production of the initial and final-bar stitches respectively, are interengaged as shown in the manner described in Specification 467,055. The starting and stopping of the stitching shaft is as described in U.S.A. Specification 713,764. The cord carrier 126, Fig. 13, is mounted on an arcuate slide 128. Prior to the completion of the stitching, a lever 136 actuated by the cam 140 depresses a slide 132 and the carrier is moved downward to expose the cord above a pair of scissor cutters 151. After the cord is cut, the carrier is returned. A grip 139 permits the cord to move freely forward through the carrier and permits the carrier to move backwardly over the cord, but on the return movement of the carrier the grip holds the cord and ensures that the cut end is carried forward into position for the next buttonhole. The cord-cutters 151 are pivoted at 154, Fig. 16, and are actuated by a lever 157, carried by the turret and engaging the cam 161 on the return movement of the stitching frame. The thread cutter, or severing means, is mounted on a lever 176 having an arm 179 which is brought into line with a lever 188, mounted on the stitching frame, for the second side of the buttonhole and is actuated at the close of the stitching operation by the cam 191. After the stitchforming mechanism is stopped further movement of the stitching frame carries the threads into positions as shown in exaggerated form in Fig. 26. The needlethread loop d is held by one looper and spreader 37, 38 and both limbs of the loop lie on a shoulder 198 of the throat plate 116. The under thread t passes from the other looper 37 to the work and lies in a slot 199 in the throat plate. The thread-severing device comprises a knife blade 184, which cuts the looper thread, and a hook 182 with a beak b the edge of which engages both limbs of the needle thread loop; the limb leading to the last stitch, being under the greater tension, is severed at that edge, if the edge is sharpened, or is broken at the last stitch knot, and the limb leading to the needle provides free thread for the next buttonhole. A spring-biassed lever 207 carries a looper-thread clamping device 214 and an arm 203, Fig. 5, fixed to the thread-cutter lever 176 engages the lever 207, first closing the clamp and deflecting the thread about a guide 213 to apply a light tension for the severing operation, then moving the lever 207 further to draw off sufficient looper thread for the next stitch. If desired, the under-thread cutter 184 may be omitted, so that only the needle-thread is severed, or the hook 182 may be so formed that it does not stretch the needle-thread sufficiently to break it, only the under-thread being severed.