To keep the bobbin case from bouncing about in the hook race, There is a small circular indentation on the outside of the case which belongs in the right hand bottom corner of the race {5:00}, fitting snuggly Around the upper left hand corner of the stopper on your machine {small metal rectangular device also at the 5:00 location}.
This ought keep your bobbin case in check & nicely balanced in operation while the race is whizzing around it! Never give up, much sewing trouble is caused by simple mechanical operations gone awry.
Holly Lucination
September 2007