Why Does Thread Break?

Thread breaks for a number of very different reasons. Some are logical and obvious, such as threading route, thread quality, and tension, but there are other contibuting factors that can also cause embroidery thread to break.
Thread
While there are many different thread weights and types that can be used to create embroidery, most embroiderers choose either 40 weight rayon or polyester. Because polyester is a synthetic product it has a much longer shelf life than rayon, which is produced from natural celulose fibers. If you are using rayon threads try to store it in climate controlled environment, and try to use the thread that has been in your inventory the longest first.
Tension
Proper thread tension is achieved by creating a balance between the top thread and the bobbin thread. If you place too much tension on the top thread even if it in proportion to the bobbin thread it will break.
Threading
The first thing you might want to check when you are experiencing any type of stitching quality problem is the threading route, this is simple to fix and often the simplest solution is the last to be checked.
Presser Foot
A bent presser foot can hit the needle and damage the needle and break the thread.
Needle Plate
A gouge or burr in the area of the hole in your needle plate can also cause the thread to fray and break.
Needle
Needles do not last forever and if you expeience any type of needle depth, presser foot or needle plate problem change the needle also at the same time to assure that it isn't contributing to the problem.
Of course there are many other possible causes for threaad breaks but these are the most common ones that I have found and are a good point of departure when trying to sove the often fustrating problem of consistant thread breaks.