Whether you enjoy repairing sewing machines as a hobby, a job, or your own business, it can be both exciting and challenging. There are so many different models and designs, it can be difficult to keep up.
When you start tinkering with sewing machines, be ready to learn loads of information. There are literally thousands of different models and designs, but there are also some obvious similarities. One of the tricky areas of interest is the hook assembly.
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.
If your machine has a rotary hook system, it will continuously turn around. Turn the hand wheel and see it rotate. The way it works, is simple. As the needle starts back up, the hooks point catches the thread in the scarf (just above the back of the eye). It then draws the thread 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.
A rotary hook moves around in a continuous circular motion. An oscillating hook moves back and forth. How can you tell which type of sewing machine hook assembly you have?
If you have any question, answer this. Does the hook move back and forth (Oscillating Hook) or in a complete circle (Rotary Hook)?
The Oscillating Hook Assembly involves a hook that begins a few millimeters to the top left and moves to the right sliding behind the needle and past it around to the bottom of the swing. Then the hook travels back again the same way to its original position for a return oscillation. Bernina sewing machines built their superior reputation based on their advanced oscillating hook system called a CB Hook.
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.
The movement and positioning of the hook and needle must coordinate exactly. Slight variations result in skipped stitches, poorly formed stitches, or no stitches at all. The hook and needle travel through a finite pattern. For each stitch the hook and needle must align perfectly. As the needle rises, the loop must form on the back of the needle. The point of the hook must travel to precisely the right position and at the right moment for the hook to snag the upper thread. This is called Hook Needle Timing.
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.
As long as there are millions of people using sewing machines, people will need sewing machine repair. You may just be the person to meet their needs either as a hobbyist or as you own business.
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