If the bobbin case in your sewing machine is malfunctioning or in bad repair, you may want to change it. After first obtaining a new bobbin case that fits your machine, this is a thing that is easily done. You will simply need to remove foot and footplate on your sewing machine. From there, you should easily be able to pry up the bobbin case using either your fingers, a flathead screwdriver, or both.
Remove the foot from your sewing machine. To do this, locate the thumbscrew that holds it in place. Rotate it counterclockwise with your thumb until the foot falls off and the thumbscrew comes out.
Raise the treadle arm to its highest point using the manual control so that it is out of the way.
Remove the footplate. On some machines the footplate can be removed by releasing a small catch with your thumbnail. Others require that you unscrew the footplate using either a small Phillips or flathead screwdriver.
Examine the cavity beneath the footplate. You should see some of the innards of your sewing machine, including the bobbin case.
Disengage the bobbin thread from anything that is holding it in place and threading it up to the footplate. Then remove the bobbin case using your fingers or a small flathead screwdriver. It should pop out easily.
Clean all lint and debris out of the bobbin case area with a small cleaning brush. Because you are replacing the bobbin case, it is best to start fresh.
Place the bobbin from the old case into the new bobbin case. Now place the new bobbin case in the machine where the old one was. Reattach the footplate and foot.
Most sewing machines come with a cleaning kit intended for use with that machine. Your cleaning kit should have a small cleaning brush that is suitable for the tiny crevices on a sewing machine. If it does not, any small brush that can get into those crevices will do. For stubborn dirt, you may wish to slightly dampen the brush first so that it picks up more of it.
You may wish to take this opportunity to clean and oil all the moving parts of your sewing machine. The cleaning kit that came with your machine may include a small bottle of sewing machine oil. If it does not, any all-purpose mechanical lubricant will do. Apply only a small amount of this lubricant to the areas specified by your sewing machine’s manual. Too much oil could cause seepage into whatever you sew next.