Just a thought...when we get a lot of thread breaks, and its on the same colors we normally use, I found that when my wife is changing from hats to flat again, she doesn't get the 'plate' above the bobbin lined up right! Don't know if she is looking at it from a slight angle-or not enough light-but I set to 'center needle head down' and then double check WITH my reading glasses on-and I can also 'feel' the plate on one side-my fingertips are more sensitive. Usually its just that 'half a hair' off to one side and I reset it. Thread breaks disappear! She can't explain it-will set it, ask me to check, and she says it is perfectly aligned (and she has much better eyesight than me!) I just rub my finger on the side, and can tell right off!