Thursday, January 15, 2009

Does Your Hook Rotate or Oscillate?

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. You may consider checking out a sewing machine repair book for more details. 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.

A quick inspection of a sewing machine, and the technician can tell if the sewing machine hook assembly rotates or oscillates. These two types of mechanisms are very different, but perform the same basic function.

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.

Where do you put the bobbin on this machine? I could be inserted in front, or top under the needle plate, or on the left end of the machine. If it is a top loading bobbin, the machine is usually a rotary hook machine.

A bobbin installed on the left side of the sewing machine may either have a rotary hook or an oscillating hook. The same is true of front loading sewing machines. For example, while Bernina sewing machines became famous for the CB Oscillating Hook System with front loading, they continue to use front loading on the high end rotary hook sewing machines.

It is easy to tell the difference. Rotary hooks rotate around the bobbin carrier in a continuous circle again and again. Oscillating hooks move to half way around and then go back to start again. The go back and forth – back and forth.

If you have any question, answer this. Does the hook move back and forth (Oscillating Hook) or in a complete circle (Rotary 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.

Oscillating and Rotary hook systems do the same job. That job is pulling the thread from the needle around the bobbin carrier. The point of the hook slides behind and through the scarf of the needle to get the thread. Then it carries it to its destination.

In both cases, the action of the hook must precisely synchronize with the needle. Even slight variations cause problems. This synchronization is known as hook-needle timing. If you see skipped stitches, bad stitches, or none, check the 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.

You can learn more about sewing machine repair and do it yourself sewing machine repair through the sewing machine repair instructions available through out links.