When sewing Why does the thread bunches underneath?
If your bobbin tension is too loose, extra thread may unwind from the bobbin, which causes a buildup of thread underneath the needle plate. Try tightening the bobbin tension by turning the tension screw on the bobbin case a quarter turn clockwise. The top thread isn’t threaded correctly.
Why does my top stitch look wrong?
Poor thread tension on a machine-sewn seam can result in an unstable seam, puckering, or just plain unattractive stitching. Perfect machine stitches interlock smoothly and look the same on both sides of the fabric. If you see small loops on the right or wrong side, the thread tension isn’t correct.