If your sewing machine thread is not properly threaded, the bobbin thread won't be pulled up into the fabric the way it needs to be. Occasionally the upper thread can catch on a moving part or get stuck, which impedes the easy flow of thread through the needle, creating a tangle.
How do I keep my bobbin thread from tangling?
How to Fix Bobbin Thread Bunching and Other Threading Problems
- Thread the Machine Properly. Re-thread the upper part of the sewing machine making sure the thread is passing through every single thread guide on its way to the needle. ...
- Change the Needle. ...
- Inspect the Bobbin. ...
- Clean the Machine.
Why is my bottom bobbin thread bunching up?
Your Thread Tails Are Too Short
If the thread tails that come out of your bobbin are shorter than two inches, they may get sucked into your sewing machine when you begin to sew. This can cause thread bunching underneath your fabric.