can anyone explain this?
I have a Singer Featherweight. I start sewing. Everything is fine. Some time goes by. The tension gets out of kilter. I readjust the tension. (I have read the manual carefully.) There is no improvement. I replace the spool of thread with another spool, the same brand bought in the same store at the same time. Then the tension is fine again. Seems that when the spool of thread is more than half used, the bottom stitches get entirely flat. any explanation?