Importance

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Abstract

A thread chain back-tacker for an overlock sewing machine eliminates defective back-tacking. The back-tacker includes a thread chain cutter, an adjuster for adjusting the length of free thread chain after the end of back-tacking, a presser foot, an air nozzle, a thread drawing nozzle, a thread clamp cylinder, a nozzle swing cylinder, a nozzle pulling cylinder, a cylinder retainer coupling the nozzle swing cylinder and nozzle pulling cylinder together, a position adjuster bolt provided on the cylinder retainer for adjusting a stop position of the thread drawing nozzle, a speed setting/releasing unit, a venturi unit, an air breaking valve, and a solenoid for on-off operating the air breaking valve. The presser foot includes a presser body, a presser foot chain shield secured to the rear end of the presser body, and a presser foot stitch tongue secured to a central portion of the presser body. The presser foot stitch tongue has its back surface provided with a groove for guiding a thread chain and also has a top guide for guiding the thread chain into the groove. Not only is it possible to eliminate curling of the cloth end at the start of back-tacking and projection of the thread chain, but also it is possible to eliminate loosening of upper looper yarn. Satisfactory back-tacking results thus are obtainable, and needle breakage or the like is prevented.

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First Claim