Checking Your Bobbin Case Spring
Don't forget this hidden key element to great stitch quality!
Bobbin Case Springs (also known as Bobbin Tension Springs or Bobbin anti-Backlash Springs) are often forgotten about until they end up becoming a problem.
I serviced a machine yesterday, and after completing the service there were numerous stitch quality problems and an abnormal noise from the bobbin area (I normally check stitch quality before doing anything to the longarm - assuming it is running - but in this case the longarm was in a quilt shop and had not been reported to have any stitch quality issues).
Both top and bottom tension felt OK, the bobbin would stand up when thread was pulled, and there were no impairments in the thread path - what gives?
Looking closely at the bobbin in the bobbin case the edge of the bobbin was not above the rim of the bobbin case, and did not bounce up and down the way it should when light pressure was applied (see pics 1 and 2 and this short video).
I removed the bobbin to see if the spring was missing (yes....that happens...sometimes the Quilter knows, sometimes not - they can pop out if the bobbin case was dropped or during vigorous cleaning). The spring was in place, but was flat with no "springiness" (see pic 3).
The spring had worn out over time and needed to be replaced. As I did not have a spare on hand, I carefully bent the spring to provide proper lift of the bobbin and informed the Quilt Shop that they would need to order and install a replacement, and if the spring compressed before the new one came in to use a bobbin case from one of the other machines.
So...how would a flat or missing Bobbin Case Spring cause stitch quality problems? Remember, the hook shaft is rotating at twice the speed of the needle shaft, but the bobbin case is locked into place. The spring keeps friction from the rotating hook basket from being so great that it would cause the bobbin to move due to pressure from centrifugal force (think about a yo-yo spinning at rest at the end of the string - when you yank the string it allows the string to wind up on the yo-yo shaft due to pressure caused by the rotating yo-yo). If the spring is missing the bobbin moves in ways it shouldn't, causing difficulty in constant pick-up of the bobbin thread by the needle scarf and resulting poor stitch quality.
Most of you have seen the write-up I did on the top-thread Take-up Spring elsewhere on this site- and the same guidance applies - keep a spare around - the springs are only $5 or so and will fade over time.
To increase the lifespan of the bobbin case spring, if you are not going to be using the longarm for a while, you can remove the bobbin case and bobbin which will take pressure off the spring.
Two last points - as noted on pic 3, most bobbin case springs have tabs to properly lock them into place in the bobbin case - noted by the yellow lines, and the spring has to be properly installed - in this case with the center of the spring elevated but check your specific machine - some of them may install in a different manner.
Thanks so much for following this page, and please post any tech questions on Longarming - if I can't answer them maybe someone else on the site can.
Do you have questions on this topic or a suggestion for another one you are interested in?