Puckered seams

Visible loops sitting proud of the seam point to unbalanced tension, most often a bobbin thread with too little resistance. Rethread top and bobbin, adjust tension gradually, and test on scrap first.

Stitches that sit slack and don't lock into the fabric come from top tension set too low. Increase the top tension gradually and test until stitches lock in the middle of the fabric.

The bobbin thread breaking mid-seam, leaving only top stitches, often means the bobbin was wound unevenly, inserted backward, or lint has jammed the case. Rewind the bobbin evenly, reinsert correctly, and clean the case.

Thread that snaps repeatedly while sewing is usually old or low-quality thread, a burred needle eye, or tension set too tight for the thread weight. Use fresh quality thread, replace the needle, and ease the tension.

A tangled clump of thread on the fabric underside, jamming the feed, comes from unbalanced tension or starting a seam without holding the thread tails. Rethread fully, check tension, and hold tails taut when starting.