Thread Tension
A high level of upper thread tension or bobbin tension can cause thread breakage. The fix for this problem is loosening the upper tension knob or bobbin. Loosening the thread a great deal to begin with and then testing stitches until you reach the right fit is an effective way of finding the best tension level. This particular problem is another reason why test stitches are so important before tackling a new project.Thread Quality
One of the simplest answers could be that the thread being used is either too old, or it could be of poor quality. Old thread quite often dries out and becomes more fragile. An old thread can be revitalised using thread lubricant, although a simpler answer may be just to replace any thread that begins to become brittle with age. If you have a newer thread that is repeatedly breaking for no apparent reason this may just be a section of the thread that needs to be removed and discarded or the whole thing may need to be replaced. Delicate or weaker thread material is obviously more likely to break than heavier materials, so it is important to test multiple thread cones to differentiate between one bad batch and possibly the wrong choice for the current project.
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Needle
It’s important to ensure the needle is installed in the machine correctly as this can cause the thread to break. If an incorrect or damaged needle is being used this could also be at fault. To read a blog outlining which needle to use for which thread/material click HERE. The size of the needle eye can also become a factor, as too small an eye will slice the thread causing frequent thread breakage.
Thread Installation
Possibly the most common cause of thread breakage is incorrect threading. Check the path the thread is taking through your machine to ensure that it is not catching on anything, as friction and edges can cause a break.
Be sure to follow the arrows on your machine correctly.