Thread leaves a lot of lint behind if you remove your spool of thread by pulling it back up thru the tension more is left behind. It is so important to clean & oil your machine . I am so intuned to my machine I can tell by the sound if I need to clean,oil or change the needle. We have had customer bring in their machine and you would be amazed at the ball of lint from not cleaning. That is one of the instruction classes Bernina request all dealers offer to their customers.
Thank You.