Abstract: The present invention comprises an air cylinder which is driven by compressed air. When sewing with a spreader thread, the air cylinder drives a movable catcher and a fixed cutter to cut off a spreader thread, which is then clamped by a spring plate to facilitate the next sewing operation. When sewing without a spreader thread, compressed air is used through an air passage to blow the free end of the needle thread cut off by an under trimming mechanism away from the underside of the presser foot after the presser foot is lifted at the end of a sewing operation to facilitate the next sewing operation. The air cylinder in the present invention may also be replaced by an electromagnetic relay, which, when powered up, stretches and retracts the central shaft to drive a movable catcher and a fixed cutter and thereby cut off the spreader thread.

Abstract: An under trimming device with inclinedly movable catchers for a multi-needle sewing machine with multiple longitudinally extended loopers comprises a cutting and clamping part, a fixed cutter, a plurality of looper assemblies and a thread push plate, characterized in that: the movable catcher of the cutting and clamping part and the looper form an angle of inclination such that when performing the thread cutting, the movable catcher extends toward the looper at an angle of inclination, and extends into the needle thread loop and the looper thread loop, and when the movable catcher returns to its initial position, the looper thread and the needle thread are cut off sequentially when they pass the fixed cutter, and the free end of the looper thread after being cut is still clamped between the leaf spring and the movable catcher, and the free ends of the cut needle threads are blown sideward in the opposite direction by an air blower to facilitate a next sewing.

Abstract: An under trimming device for a multi-needle sewing machine with multiple longitudinally extended loopers mainly including a cutting part and a clamping part. Both the cutting and the clamping parts are longitudinally and reciprocatingly movable, so that multiple looper threads may be pulled by multiple movable catchers of the cutting part into the clamping part before they and corresponding needle threads are simultaneously cut by a fixed cutter of the cutting part, permitting free ends of the cut threads to have uniform length and being held at the same position.

Abstract: The present invention relates to an under trimming device mounted below a needle late of a multi-needle sewing machine which mainly comprises an under trimming subassembly and a thread-sucking subassembly. The under trimming subassembly comprises a linkage and a thread-releasing means both being capable of shifting the under trimming subassembly into a standby position, extended position, thread-catching position, retracted and cut position, thread-clamping position, and a thread-releasing position in a series of linear movements. The thread-sucking subassembly is provided at one lateral side of the under trimming subassembly such that the looper thread cut and released by the under trimming subassembly can be instantly sucked and clamped in place and then used in the next sewing operation.