What should I do if I experience thread bunching? As “thread bunching” occurs on the underside of the fabric, some people think it is due to the lower thread. They check whether the bobbin is sitting correctly in the bobbin case or even replace the bobbin. … On many models, the upper thread tension is set automatically.
Why is my sewing machine bunching up the fabric?
Cause. Tension pucker is caused while sewing with too much tension, thereby causing a stretch in the thread. After sewing, the thread relaxes. As it attempts to recover its original length, it gathers up the seam, causing the pucker, which cannot be immediately seen; and may be noticeable at a later stage.