Re: Bobbin Case Jumping

Jim Stutsman
 

Most of the time when the bobbin case starts "jumping" it's because there is damage to the case itself and/or the hook race. Usually this happens as the result of something like a thread nest or a broken needle. As the thread slips under the bobbin case to make a stitch it catches on burrs on the case or the hook race that the case sits in. This causes the thread to catch. Instead of the thread sliding freely, the stitch is held until the thread can pull free from the damaged area. This causes it to pull the bobbin case up. If the damage is not repaired, this will eventually cause the case to pull up past the stopper, which is a small metal spring that the case rests against at about the 5 o'clock position. Once it spins out it usually gets penetrated by the needle and more damage occurs.

Remove the bobbin case and inspect it carefully, top, bottom, and edges. Any roughness will catch the thread. While it's out take a look at the thin metal shelf that it sits on. Use bright light and magnification if you can. Look for pits, notches, scratches, or any sign of damage from a needle strike. I'm attaching a photo of hook race damage, as well one with an arrow pointing to the legendary stopper. If yours looks different from this in any way you need to have the machine serviced.

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