Although there are many types of shoe-making sewing machines, their structure is basically the same, so the methods of use and adjustment are basically the same.
1. Selection of needles
Sewing machine needles with conical and profiled tips are suitable for sewing leather and artificial leather uppers. Special-shaped needle tips, also known as cutting needle tips, have oval, diamond, and triangle shapes. Oval needle points are used in many applications; diamond needle points are used for fabrics with higher hardness; triangular needles are used for thick and hard uppers with large stitches. The surface of the needle should be very straight, and there should be no burrs in the needle eye and groove to avoid broken needles and broken threads.
2. Gauge and stitch
Gauge and stitches are determined according to the design of the upper. The general requirements for the needle distance are: 6-6.5 needles/cm for cow leather and 5-6 needles/cm for sheep and pig leather. If the stitch length is large, the stitching strength will be reduced; if the stitch length is small, the sewing material will be easily torn. Stitches can be divided into lock seam, chain seam and double chain seam. The upper stitching is mostly lock stitching, which is formed by the upper thread and the bottom thread. It is characterized by: high stitching fastness, the same stitches on both sides, and low thread consumption.
3. Needle and suture
When the needle drives the suture into the needle plate and punctures the sewing material, the suture should be pulled, and it should fill the needle hole and the sewing material needle hole. The sewing thread shall not have defects or mildew, and the breaking strength shall meet the requirements. The upper thread is mostly silk thread and nylon thread, and the bottom thread is mostly cotton thread. When sewing, the tension force of the surface and bottom thread should be adjusted correctly to ensure the sewing strength and beautiful stitches.
4. Adjustment during sewing
The methods for dealing with broken needles during sewing are as follows: when the needles are bent, the new needles should be replaced in time and installed correctly; when the needles are broken for sewing thick materials, the verticality of the needle bars should be adjusted; when the needle plate holes have been ground If it is too large, it should be replaced with a new needle plate.
When the thread is broken, it is mostly caused by the insufficient strength of the suture, the wrong threading method, the thread clamp is too tight, the needle hole is rough, etc.; Excessive force or burrs, unsmooth needle plate holes, etc., can be eliminated by making targeted adjustments or replacing parts.
When the upper thread is turned down or the bottom thread is turned up, the tension of the upper thread and the bottom thread should be adjusted to make them even.
The poor feeding is mostly caused by insufficient thrust of the feeding dog and insufficient pressure of the presser foot. Adjust the height of the feeding dog or replace the worn parts, and increase the pressure and stroke of the presser foot to compact the sewing material.
5. Maintenance
Keep the inside and outside of the machine clean, especially the feeding and shuttle structure should not contain foreign matter such as cloth wool or thread; maintain good lubrication, and regularly refuel according to the specified grade, especially the oil of the automatic lubrication system must not be short of oil and polluted; Maintain the sensitivity of the motor speed control mechanism and the tension of the belt drive mechanism to ensure flexible operation and normal speed.