At some time almost every sewing machine user will encounter problems with their sewing machine tensions. When you understand how the tension system is suppose to work, you will have far less trouble and resolve the problems much quicker.
When you sew, thread from the top of your machine and thread from the bobbin lock together to form a stitch. As the thread moves through the sewing machine, drag is created which we call tension. When the drag from the top correctly balances the bobbin drag, the lockstitch will form in the middle of the fabric without extra thread on top or bottom of the fabric.
On top you can see the thread go through the various guides. It then goes through a tension assembly and the take up lever. Finally, it is threaded through the needle. To adjust, turn the tension knob right to tighten or left to loosen.
Under the arm of your sewing machine is a bobbin carrier where you put your bobbin. You might not have thought much about the tension system here, but it is very important. Antique machines used an elongated shuttle, but basically served the same purpose. Today machines have carriers loaded from the front, top, or left side.
While there are a variety of different designs, the essentials are the same. Thread is wound on a bobbin The bobbin is placed into a case or holder. (Older machines used shuttles the same way). The thread in the bobbin is drawn through a tension device and up to the top of the sewing platform.
First, always use the proper bobbin for your sewing machine. This is vital. The bobbins often look very much alike, but their subtle differences can make the difference between smooth sewing and junk sewing.
Second, be sure the bobbin thread is properly wound with no loops or loose threads and not too tight either. The thread should be smoothly wound around the bobbin.
The third step is to insert the bobbin into its holder. If you are new to your sewing machine, get the manual and double check the correct procedure. If you do not have a manual, take the machine to your nearest sewing machine technician and have them show you. Follow the procedure exactly every time. If the bobbin and carrier are not inserted properly, they will mess up. Note too, the thread must then go under the tension spring.
The fourth step, is to thread the bobbin tension. If you look closely, the thread goes under a small piece of metal which is actually the tension spring. This part is crucial. If the thread fails to slide under the tension spring, it will flop around, get tangled up, or appear on top of your fabric as puckers as you sew.
Tension on the bobbin thread can be adjusted with the small screw that you sew on the tension spring. Turn it right to tighten or left to loosen.
There are many different types of bobbin carriers, find out how yours is suppose to work and always use it the same way. Some machines have carriers that are already installed on the machine, and all you have to do is put your bobbin into it. Other machines have detachable carriers that you put your bobbin into. Then put the carrier into its socket.
If you have a bobbin case that detaches from the machine, test the tension by doing the following. Pull off about six inches of bobbin thread through the tension. Dangle the bobbin carrier with the bobbin in it while holding the thread above it. The lower tension should hold the carrier so that it does not drop. If it does, just turn the screw a quarter turn to the right. If it does not drop, try bouncing the carrier a little. If the tension is properly set, the carrier will drop a little and stop. If it does drop a couple of inches and stops, all is good. If the carrier does not drop at all even after pretty good bounce, the tension is too tight. Turn the screw a quarter turn to the left. Try again.
Test drop in bobbins by using the draw test. Pull the thread through the bobbin tension until it flows freely with a gently tug. Adjust the spring as needed.
Double check to identify any worn parts that might snag the thread. If you find a rough spot, burr, or other such spot; correct the problem before bringing the thread up through the needle plate hole and preparing to sew. Generally, once the bobbin tension is set, it should only need to be adjusted if you change the size of thread you use.
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