Upper thread keeps breaking

Why the top thread breaks

A top thread that snaps every few inches is being caught or pinched somewhere between the spool and the fabric. The manuals list the same handful of causes for almost every machine: threaded wrong, tension too tight, a needle too small for the thread, a damaged or wrongly inserted needle, thread snagging at the spool, and a burr on the needle plate, foot or hook that slices it.

Work through these in order

1. Rethread the whole top path with the presser foot up. Check the thread did not jump out of a guide, especially the one just above the needle.
2. Look at the spool. Thread wrapped around the spool pin, a spool cap on the wrong size spool, or a notch in the spool's rim catching the thread all break it. Singer's 4423 table lists thread wrapped around the spool holder pin.
3. Turn the top tension down a step. Too tight is in every table.
4. Fit a new needle a size larger. Thread too thick for the needle's eye shreds and breaks.
5. Check for knots and for old, brittle thread. Pull a length between your hands; if it snaps easily, change the spool.
6. Feel the needle plate hole, the presser foot and the hook or bobbin case for a burr or rough spot. Brother and Singer both list it; on a modern machine a scratched part means a service center or a replacement plate.

If it is the bobbin thread breaking

• Rethread the bobbin case: through the slit and under the tension spring.
• Rewind an unevenly wound bobbin, and replace one that is scratched or does not spin freely.
• On machines with an adjustable bobbin case (Featherweight, 15-91, 401A, Juki TL-2010Q), loosen the bobbin tension slightly. On the Juki a spring that has worn a groove means a new case.
• Use only the bobbin the machine was designed for. Brother says other bobbins can damage its machines.

On your machine

• Brother XM2701, LX3817, CS7000X: SA156 bobbins only.
• Brother 1034D serger: rethread in the full order; if the lower looper thread broke, take the needle threads out first.
• Singer Heavy Duty 4423, Janome HD3000, Juki TL-2010Q
• Featherweight 221, Singer 15-91, Singer 401A