Why is my bobbin case moving?
There could be several reasons why the bobbin is jumping in the bobbin case. … The thread was not wound properly on the bobbin. Wind the bobbin thread properly.
A: Looping on the underside, or back of the fabric, means the top tension is too loose compared to the bobbin tension, so the bobbin thread is pulling too much top thread underneath. By tightening the top tension, the loops will stop, but the added tension may cause breakage, especially with sensitive threads.
What happens if you use the wrong bobbin?
The short answer is YES! Filling a sewing machine bobbin too tightly can make a plastic bobbin bulge or stretch the thread if you are using a metal bobbin. This may be hard to see but can cause all kinds of problems. Plastic bobbins can become compressed in the center causing the bobbin to distort.