GB611879A - Improvement in thread-cutting mechanisms for sewing machines - Google Patents

Abstract

611,879. Sewing-machines. SINGER MANUFACTURING CO. May 13, 1946. No. 14347. Convention date, Aug. 21, 1945. [Class 112] Thread - cutters and thread-end holders. - The needle-thread of a buttonhole sewing-machine is trimmed and held when the work-clamp is opened. and the bobbin-thread is also trimmed at the same time; the needle-thread end at the beginning of the buttonhole is retrimmed to a shorter length during the formation of the buttonhole. Both needlethread trimming operations are produced by spring-action when a pushrod is released, the resetting of the rod for the latter operation being gradual and that for the trimming at the end of sewing being rapid so that it can be delayed until the work-clamp is approaching its initial position without risk of the blades fouling the needle. The timing of the resetting and the retrimming is adjustable according to the length of the buttonhole. The means for trimming the bobbin-thread is described in Specification 611,877. Trimming needle-thread.-A vertical rock-shaft 43, Fig. 2, actuated by a pushrod 49 which is spring-biassed to the right, carries a trimming blade 38 to cut the needle-thread against a member 46, Fig. 5, carried by the work-clamp, and a nipping blade 39 to hold the end of the thread against the underside of the upper plate 11 of the work-clamp. A cam 68, adjustably secured to the feed-cam shaft by engagement of a pin with one of a series of holes 71 in a disc on the shaft, gradually moves the push-rod 49 to the left during the sewing of the first side of the buttonhole, by means of a follower lever 63, link 62, and lever 57 engaging a member 61 on the push-rod, to open the blades 38, 39, which are then closed by the sudden drop of the cam surface to shorten the thread-end shown in Fig. 5. As the cam rotates further, a projection 75 on another part of it engages the nose 76 of a lever 77 which gives another lever 81 a sharp movement to carry the push-rod 49 far enough to the left to be held by a latch 83 engaging a notch 88 in a collar on the rod. This latch is released by a cam element 93 on a sliding member 92 actuated by depression of the treadle which opens the clamp to sever the needle thread and hold its end. Specification 378,790 also is referred to.