How does the three thread overlock sewing machine handle the skip needle?

The stitch formed by the three-thread overlock sewing machine is 504 chain stitch (according to the provisions of GB4515), so it is difficult to eliminate the stitch skipping fault. Different from the needle skipping fault of another lock stitch (only the needle loop is not hooked by the bobbin tip), as long as any one of the three threads in the 504 chain stitch is not hooked or does not enter the triangle coil, the needle skipping will occur.

From the viewpoint of thread tension, the needle thread tension of the overlock sewing machine is much lower than that of the lock stitch (the overlock sewing machine needs 50 g - 70 g, while the lock stitch needs 120 g - 180 g), so there are several ways to eliminate the needle skipping fault:

1. Checking whether the threading system meets the requirements is an important method to deal with the needle skipping fault.

First, check whether the threading process of the stitches is consistent with the instruction manual or the mark on the inside of the front baffle plate. The instruction manual or the mark on the inside of the front baffle plate generally has relevant graphic marks for reference; Secondly, check whether the tower line is stably placed in the wire rack tray and whether there is inclination or inversion; Thirdly, during the whole threading process from the tower line to the needle, carefully check whether the three threads of the needle and the upper and lower bending needles can be pulled freely without any obstruction; Finally, it is necessary to check whether all the thread passing parts of the three thread overlock sewing machine are smooth (without burrs, sharp edges, etc.). Once found, they should be sanded or polished immediately.

2. Needle skipping can also be handled according to different situations of the 504 stitch pattern.

As the 504 three-thread overlock sewing machine has skipped stitches and jumped on or off the curved needle thread, we should correctly judge the causes of skipped stitches, and deal with the corresponding faults according to different causes (according to the technical requirements shown in the drawing).