Sewing machine repair is an exciting and satisfying career , but it is also a great hobby or business. While, repairing sewing machines is not for everyone, it can be lots of fun.
When you decide to learn about sewing machine repair, there is a lot to learn. One of those things is understanding sewing machine hook systems.
There are two basic types of hook assemblies: The Rotary Hook assembly and the Oscillating Hook assembly. Each type has its own features and benefits, but they both do essentially the same job.
Find the bobbin on the sewing machine. Look under, around, or behind it to find the hook. Rotate the hand wheel forward and watch the hook move. How does it move? If it moves in a complete circle around the bobbin it is a rotary hook assembly. If you look closely, you can see that as the needle comes down and starts back up, the point of the hook slides behind the needle just above the eye. It picks up the thread and pulls it around the bobbin.
The bobbin may be installed just under the needle from the top, on the left end, or on the front lower arm of the machine. If the bobbin inserts from the top, it normally has a rotary hook.
If the bobbin is inserted in the left end of the sewing machine arm or on the front face of the sewing machine arm, it may be either a rotary or oscillating hook.
If you are unsure what kind of hook system your machine has, rotate the hand wheel and watch the hook Oscillating hooks travel half way and then travel back. They move back and forth. Rotary hooks travel all the way around the bobbin carrier in a continuous rotation.
To double check you thinking, does the point of the hook go all the way around the carrier (Rotary Hook) or only part way (Oscillating Hook)?
Watch closely. The point of the oscillating hook starts just a few millimeters to the left of the needle when it reaches its lowest point. As the needle rises, the hook moves behind the needle. A loop of thread forms in the small cut out on the back of the needle running above the eye called the scarf. The point of the hook grabs the thread here and pulls it around to the bottom where it releases the thread. It then oscillates back to its original position for another stitch. Bernina used their special patented CB Hook to become a premium sewing machine line.
Both systems do essentially the same thing. As the point of the hook passes behind the needle, it is positioned slightly higher than the eye of the needle. The upward travel of the needle causes a small loop of thread to form on the back side of the needle above the eye and amplified by a space called the scarf which is cut out above the eye. The point of the hook snags the thread from behind the needle and pulls it around the bobbin thread. As the needle rises, the threads are tightened into a lockstitch.
Each part must work in perfect timing and coordination. The hook assembly and needle must reach their exact connection point on every stitch precisely when as where they are suppose to. This is called hook-needle timing. When they are out of synch or time, you will see skipped or potentially no stitches formed at all.
Adjusting the hook-needle timing is a very common adjustment. If the user breaks a needle, sews on excessively thick material, or debris builds up in the gears; the timing often gets jolted out of adjustment. The specifics of making this adjustment vary considerably from one model to another. Some adjust on gears located directly below the hook. Some adjust at the side or at the end of the lower shaft. Some use timing belts. The essential adjustment is always the same, however, in that the point of the needle must reach the scarf at precisely the right time and in the right way. Check the specific service manual for details on adjusting the hook-needle timing until you gain enough experience and knowledge to adjust it on the fly.
The more you learn about how sewing machines work and how to repair them, the more sewing machine repair you can do. Just think there are millions of sewing machines just waiting to be serviced by somebody. You could be that somebody.
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