Interlock/ Flat Lock Sewing Machine Thread Trimmer Debugging & Maintenance Skills

The three-needle five-thread interlock sewing machine is divided into two types in terms of appearance: platform type and cylinder type (Figure 1).


With the comprehensive popularization of mechatronics, today’s interlock sewing machines have the function of automatic thread trimming. This article combines the specific problems encountered in practice with the currently widely used 720 horizontal cylinder high-speed three-needle interlock sewing machine as an example. I will talk about some debugging and maintenance skills of the automatic thread trimming mechanism, hoping to bring some help to colleagues who are new to this type of machine.

The following adjustments are all based on the sharpness of the blade. To judge whether the blade is sharp, you only need to put a piece of wire into the movable knife edge, and push and pull the connecting rod by hand to make the moving knife coincide with the fixed knife. As long as it can be cut off, the knife edge is sharp. When encountering poor thread trimming when the knife edge is sharp, it is necessary to focus on checking the mechanical installation position of the thread trimming mechanism.

Check whether the movement of the cutter is normal. Firstly, push the driving link of the cutter by hand, and observe whether the moving knife is just on the right side of the lower looper when it starts to move to the left(Fig. 5). This time point can be adjusted by the stop plate of the fixed knife bracket(Fig. 6). If the knife is pulled out too early, the end of the needle thread will be too long, and if the knife is pulled out too late, the bottom thread clamp reed will collide with the looper. Also note that the movable knife tip is located in the center of the width of the looper, that is, the front and rear 1/2 position. This position can be adjusted by combining the eccentricity of the two cutter guide rocker arms(Fig.7). Generally, when the mark on the eccentric wheel on the right is at the 3 o’clock direction normal.


Then observe whether the right knife edge of the moving knife exceeds the center of the left needle by about 1-1.5 mm when the moving knife moves to the left fixed point (Fig. 8). , this problem can be adjusted by the adjustment screw on the connection block (Fig. 9).



Finally, observe whether the right tip of the moving knife is aligned with the front end of the fixed knife when the moving knife and the fixed knife return to the rightmost origin, and whether the left tip of the moving knife and the front end of the fixed knife have an engagement degree of about 1mm (Figure 10). The adjustment is relatively simple, just loosen the fastening screw of the fixed knife. In actual use, if garbage accumulates on the edge of the two eccentric wheel screws, it will also affect the degree of engagement between the moving knife and the fixed knife at the origin and the movement of the moving knife. Itinerary, be sure to pay attention to this detail.

Generally, in actual maintenance, it is necessary to pay attention to the trajectory of the moving knife when it comes out of the knife. If the trajectory of the moving knife tip moves to the left from the tail of the looper to the left dead point is parallel to the looper, the moving knife tip just starts from 3 The thread trimming effect is good if it passes through the middle of the needle thread loop (Figure 11). If the knife is not drawn out along the track of the back of the looper, the thread trimming stability is not good. The correct movement track of the moving knife must pass the above mentioned The two eccentric wheels and a stop block that have been passed are adjusted to achieve the ideal state. When only cutting the needle thread but not the bottom thread, it is often caused by the moving knife being too close to the operator’s side. On the contrary, if it is biased to the other side There will be a situation where only the bottom thread is cut off and the needle thread is cut off on one side. The ideal thread trimming effect is that the thread left on the needle hole can form a normal stitch without leaving a thread tail on the surface of the fabric when the sewing starts. The length of the thread can be adjusted by the amount of loose thread and the amount of thread. This is relatively simple. .


As for the cutting of the needle thread, it is easier to observe and adjust, so I won’t repeat it here. Finally, I would like to mention a phenomenon that the author once encountered: when using the thread pulling device (Figure 12) for double-needle work, sometimes the It is found that the thread trimming is not good, but if the thread removal device is turned off, the thread trimming is normal. At this time, it is only necessary to adjust the parameter of the thread removal action time in the electric control, without any mechanical adjustment. I don’t know who said: It is easy to repair a machine, but it is difficult to repair a knife. For the automatic thread trimming type interlock sewing machine, in fact, as long as you understand the ins and outs of the thread trimming process, any problems will be easily solved.


Post time: Dec-12-2022