If you have cleaned your machine thoroughly of any stray threads or lint build up, adjusted upper tension, and it is still not right, you can either make an appointment with your technician or you can adjust the bobbin case.
Early on, Baby Lock and Brother only shipped one bobbin case with our embroidery machines. Invariably, those machines are set for a regular sewing thread in the bobbin. They are not calibrated for embroidery so you often did not get the 30-30-30 split.
The only purpose of the bobbin thread in machine embroidery is to hold the stitches onto your fabric. The decorative thread sits on top and the bobbin thread needs to be thin so it is not sticking out and bulky underneath your project. With sewing, you want equal strength top and bottom to hold your seams together really well.
It is kind of difficult because we need two different bobbin case tensions for those two different types of sewing. We need one for balanced thread weights for regular sewing and then we need a tighter tension for embroidery, where the bobbin thread is a lighter weight than the stitching thread.
Generally, it is not recommended to adjust the bobbin tension screw on your own, unless you have an extra bobbin case. That way you can have one original and one to experiment. So Baby Lock and Brother started sending two different bobbins cases with their higher end machines, and many other manufacturers may do the same now too.
The Baby Lock and Brother sewing bobbin case has a little green paint dot on the screw.
The embroidery case has a purple or blue dot that's painted on the inside.
How to Adjust Bobbin Tension
There are two screws on the side of a bobbin case. One looks like a Philips screw and the other one looks like just your standard little tiny screw. Leave the Phillips screw alone, you do not need to touch that one. The one that you want to tweak is the little tension screw that just looks like a regular screw head.
Looking at the screw head like a clock face, take your tiny screwdriver and turn the screw 5 minutes but no more than 15 minutes of a turn. I would turn it 5 minutes, then test it. If it is still not right, turn it another 5 minutes and test again. Still not right? Try a third test of another 5 minutes making it a grand total of one-quarter of a turn and retest.
I would not do more than that. The very most I would probably ever do on something like this where I was testing is probably up to maybe a little over one-quarter of a turn to maybe almost half of a turn. But that is an awful lot. Anything more than that, you should probably take it to a dealer if you are still having issues.
On the other hand, if your bobbin case tension is set to your satisfaction, you might want to put a little dab of clear fingernail polish over the screw to help hold it in place to avoid it loosening up.
See the full video here.
Have a day blessed with perfect stitches and GlitterFlex!!