a bobbin tension trick you may not know

Did you know that your bobbin case has its own tensioner?  Many sewers don't.  If you're experiencing difficulty with tensioning your machine, it might be that your bobbin tension is too loose (or, less frequently, too tight).  To test your bobbin tension, remove the bobbin case and bobbin from your machine and hold the end of your bobbin thread.  Swiftly pull up on the thread.  The thread should unwind just slightly and the bobbin case should drop an inch or two.  If the thread unwinds without resistance and the case slips to the floor, your bobbin tension is too loose.  If the bobbin case doesn't budge, your bobbin tension is too tight.  To tighten your bobbin tension, turn the tiny screw on the bobbin case a smidgen clockwise.  To loosen bobbin tension, turn the screw counterclockwise.  A quarter turn or less is a good place to start.