Springs

The take-up spring is used for three things. One of its jobs is to act as an electrical contact for the upper thread break detector (above). It also holds the thread as the needle goes down into the fabric until the eye of the needle goes through the fabric. So, the thread can't just flop in front of the needle. In the third function, the take-up spring acts like a little shock absorber while the stitch is being made. When the hook is in the six o'clock position (below), the take-up spring lets out the thread being pulled by the hook, easing the strain on the thread. As the take-up lever pulls the loop of the upper thread into the fabric, the spring keeps acting like a shock absorber (bottom). So, the take-up lever can't pull on the thread too hard.