When my needle thread kept snapping every few inches it was because a tiny piece of thread had caught in the bobbin case holder area. I tried every thing like rethread, change needle, clean, oil and finally in desperation tried canned air especially in the bobbin area. That tiny thread wiggled and I saw it. I had quite a time getting it out, but finally did. No more problems. I think that thread would tighten up on the needle thread as the needle went up and down causing it to pop. I truly thought I would go crazy. Yes I know canned air can cause problems. I'm not advocating it's use.