According to the weight of  leather and sewing thread track is usually around 3-4 pin per centimeter. At the same time,people should  check the pressure of the foot.the pressure should be smaller than the standard. the sewing speed should be slow and  the leather should not be tighten, Also,in order to prevent tearing the leather. people should not return the needle to sewing the leather, knot must be the last step in the sewing production .