barny

I find a bad bobbin sometimes. If they are plastic, they get little pits that catch the thread. Or it happens on old metal bobbins also. Just run your finger around all of that to make sure it is smooth. Maybe an old bobbin holder.

KalamaQuilts

I put the foot down to thread the needle.

I'm talking about foot up when threading the machine. it tightens up the thread discs and messes with the tension. That is what I was taught in home ec anyway, and my manuals give the same advice.

Quilterman

Check your needle plates. On old machines they can have burrs and gouges where the thread goes through
that the thread can catch on. You sometimes can file out the damage with a jewelers file around the needle
hole or just have to get a new needle plate with no burrs or damage.

maviskw

I had that (or something like that) happen to an old machine. I had taken it in and they found nothing wrong with it. Then I was at a class at their shop and it happened again. Then they found the burr on the needle plate. They put in a new needle plate.
But I sure don't understand that happening to three machines.