I learned the hard way (2 trips for expensive repair) that if you are using invisible thread -- no matter the brand -- in the bobbin, and you have plastic bobbins, you absolutely have to wind the bobbin slowly -- like at half-speed -- and don't fill it all the way. Maybe half to 3/4 full. When going full speed, heat is generated on the threads which tightens everything up and the bobbin will seize to the bobbin winder spindle. I broke TWO bobbin mechanisms trying to get the bobbin off the spindle. Since slowing down and not totally filling the bobbin, no more problems. Hope this helps.