Why does my sewing machine bunch thread underneath?
The nest of loops under the fabric is almost always a top threading fault, not a bobbin fault — and the order to check things in.
- Difficulty
- beginner
- Time
- 15 min
- Read
- 3 min
Short answer
A nest of loops underneath means the top thread has no tension, which almost always means it is not sitting in the tension discs. Rethread from scratch with the presser foot raised. That fixes it far more often than anything to do with the bobbin.
The loops appear on the underside, so people go straight to the bobbin. The thread forming those loops is nearly always the top thread, being fed with no resistance because it never seated in the tension discs.
Step by step
- Stop and cut the work free carefully.Snip the threads underneath rather than pulling, which can damage the fabric or the machine. Clear every scrap of thread from around the bobbin case.
- Rethread the top completely, presser foot up.Remove the thread entirely and start again with the foot raised so the tension discs are open. This alone resolves the majority of cases.
- Check the take-up lever.The thread must pass through the moving arm near the top. Missing it produces loops immediately and consistently.
- Remove and refit the bobbin.Check it turns the way the diagram shows, that the thread runs into the tension slot, and that no thread has wrapped under the bobbin.
- Check the bobbin is wound evenly.A bobbin wound loosely, unevenly, or by hand feeds unpredictably. Rewind it on the machine at a steady speed.
- Fit a new needle.Blunt or bent needles cause skipped stitches and loops. Check it is in the right way round and pushed fully up before tightening.
- Check both threads are pulled back under the foot before starting.Around 10cm of both, drawn to the back. Starting with short tails is a common cause of a nest at the beginning of a seam.
- Clean out the bobbin area.Lint compacts under the bobbin case and interferes with tension. A small brush, not compressed air, which pushes it further in.
- Retest on scrap.Two layers of the same fabric. Only once the test stitch is even on both sides should you go back to the project.
Tips
- Loops underneath means the top thread. Loops on top means the bobbin. Counter-intuitive, and true.
- Rethread with the foot up before adjusting a single dial.
- Hold both thread tails back for the first few stitches of every seam.
Common mistakes
- Adjusting the bobbin tension screw first — The bobbin is rarely the cause of loops underneath, and once the factory setting is lost it is fiddly to restore. Rethreading the top solves it in most cases.
- Threading with the presser foot down — The tension discs are clamped closed, so the thread sits outside them and is fed with essentially no tension no matter what the dial reads.
If it doesn't work
Nest of loops under the fabric
Cause: Top thread not in the tension discs — Fix: Rethread completely with the presser foot raised.
Bunching only at the start of a seam
Cause: Thread tails not held back — Fix: Hold both tails behind the foot for the first three or four stitches.
Loops on the top surface
Cause: Bobbin thread not in its tension slot — Fix: Remove and reseat the bobbin, checking the direction of rotation.
Intermittent bunching
Cause: Lint in the bobbin case or an uneven bobbin — Fix: Clean the bobbin area with a brush and rewind the bobbin on the machine.
Questions people ask
Why does it happen underneath if the problem is the top thread?
With no top tension the machine pulls far more top thread down than it needs, and the excess collects into loops on the underside where the hook is working.
Should I use compressed air to clean it?
No — it forces lint deeper into the mechanism. Use a small stiff brush and pick out the visible lint by hand.