Bobbin Nests
I'm having this problem with a relatively new machine (about six months old). The issue is that when sewing I get these nasty little nests of thread bunched up on the bottom layer. This seems to mostly happen when quilting but it has also occurred when doing the regular piecing as well.
Based on what I've seen, it seems like one thread doesn't get pulled up all the way or catches somewhere and then all the following threads built up around it. I'm usually able to get it to release by giving it a tug but by then the damage is done and I have to cut the thread.
I've opened the bottom plate and used a mini-vacuum to get rid of any lint built up (there was a bit of lint but not enough I would have expected it to be an issue). I also made sure the black casing is sat correctly. I upped the tension a few notches and that seemed to help at first but then it started doing it again after quilting a couple of rows.
Does anyone have advice on how to fix/prevent this? Is it that I just need to keep upping the tension until it stops doing it or is this an issue that I should take into the shop?