Working principle:
Like a car, the fundamentals of most sewing machines are the same. The heart of the car is the internal combustion engine, and the heart of the sewing machine is the coil stitching system.
The sewing method of the loop is very different from ordinary hand sewing. In the simplest form of hand stitching, the sewer ties a thread in the small eye at the end of the needle, then runs the needle and thread completely through two pieces of fabric, from one side to the other, and back again. This way, the needle moves the thread in and out of the fabric, stitching them together.
Although this is very simple to do by hand, it is extremely difficult to pull with a machine. The machine needs to release the needle on one side of the fabric, then instantly grab it again on the other side. Then, it involves pulling the loose thread all the way out of the fabric, reversing the direction of the needle, and repeating all steps in the opposite direction. This process is too complicated and impractical for a simple machine, and even for manual work, it only works well with shorter wires.
Instead, the sewing machine simply pushes the needle partially through the fabric. On a machine needle, the eye of the needle is just behind the point, not at the end of the needle.
The needle is fixed on the needle bar, which is pulled up and down by a motor through a series of gears and cams (more on this later).
As the tip of the needle goes through the fabric, it pulls a small loop from one side to the other. A device under the fabric grabs the loop and wraps it around another thread or another loop of the same thread. In the next two sections, we will see exactly how this system works.
The simplest form of loop stitching is chain stitching. To sew a chain stitch, the sewing machine loops the same length of thread behind the thread. The fabric sits on a metal plate under the needle and is held in place with a presser foot. At the beginning of each stitch, the needle pulls a loop through the fabric. A stitch-making device that grabs the stitch before the needle is pulled out moves synchronously with the needle. Once the needle pulls the fabric, the feed dog mechanism (described later) pulls the fabric forward.
When the needle goes through the fabric again, the new loop will go straight through the middle of the previous loop. The device that makes the coil will grab the wire again and make the coil around the next coil. This way, each coil will hold the next coil in place.
The main advantage of chain stitching is that it can be sewn very quickly. However, it is not particularly strong, and if one end of the thread loosens, the entire stitch may come loose. Most sewing machines use a stronger stitch called lockstitch. You can see how a typical overlock setup works in the animation below.
The most important elements of a lockstitch device are the hook and spool assembly. A spool is a coil of thread that is placed under the fabric. It is located in the center of the shuttle, which is rotated by a motor in synchronization with the movement of the needle.
As with chain stitching, the needle pulls one loop through the fabric, it rises again as the feed dog moves the fabric forward, and another loop is pulled in. Instead of joining the different coils together, though, this stitching mechanism joins them with another piece of thread that's unwound from the spool.
As the needle pulls the thread into the loop, the rotating shuttle catches the loop with the crochet hook. As the shuttle rotates, it pulls coils around the thread from the spool. This makes the stitching very strong.
This kind of rotary shuttle is also evolved from the straight shuttle.
The stitching principle of the sewing machine has evolved from a straight shuttle to a rotary shuttle, and it has entered a mature stage.
A sewing machine is a machine that uses one or more sewing threads to form one or more stitches on the sewing material, so that one or more layers of sewing material are interlaced or sewn together. The sewing machine can sew cotton, linen, silk, wool, man-made fibers and other fabrics and leather, plastic, paper and other products.
