Sewing Tension Troubleshooter
A nest of loops underneath is a TOP thread problem, not a bobbin one. The stitch junction always moves towards whichever thread pulls harder.
Work through these first
Before touching a dial. The first one fixes more problems than the other five together, and it is the one people skip because they are certain they threaded it properly — so tick them off rather than reading past them.
Half of what gets blamed on tension is the wrong needle for the cloth, and that is a different question from this one — needle size, point type, stitch length and thread by fabric all live on the Sewing Machine Settings Guide. Rule the cloth out there first; everything below assumes the setup is already right.
Write down which way you turned it
The advice further down is an eighth of a turn at a time, and to record it — because the way back to a working machine is knowing where you started. This is that record. It stays in this browser.
The threads meet in the middle — or they should
A balanced stitch has the top and bobbin threads meeting inside the fabric, where the join is hidden. Whichever thread pulls harder drags that meeting point towards its own side, and that single fact diagnoses every tension fault there is:
| If the top tension is… | The junction… | So you see… | Fix |
|---|---|---|---|
| Too tight | pulls up | bobbin thread showing on the top surface | lower the top tension |
| Balanced | sits in the middle | neither thread on the wrong side | nothing |
| Too loose | sinks down | top thread, then loops, on the underside | raise the top tension |
So the side you can see the fault on is the opposite of the side that is winning. This is why a nest of loose thread underneath is a top-thread problem, not a bobbin one — it is a top thread barely tensioned at all, usually because it never went between the tension discs. People see the mess on the bottom, adjust the bobbin, and make it harder to find.
Adjust the top tension, essentially always
Whichever way it has gone wrong, the top dial is the one to move. It is calibrated, it is reversible, it is on the outside of the machine, and it is the culprit far more often than the bobbin. The bobbin screw is a tiny fiddly thing with no markings, easy to lose, and hard to put back where it was. Leave it alone until everything else is exhausted, and if you do move it, an eighth of a turn at a time and write down which way.
Test on a doubled scrap of the actual fabric with contrasting thread top and bottom — a different colour in the bobbin makes the junction visible immediately. Tension that balances on one layer of calico tells you nothing about two layers of what you are sewing.
Every symptom
| Symptom | Shows on | Actually caused by |
|---|---|---|
| Loops or a nest of loose thread underneath | the underside | the TOP thread |
| Top thread visible as a line on the underside | the underside | the TOP thread |
| Bobbin thread pulled up and visible on top | the top | the TOP thread |
| Loops or loose thread on the top surface | the top | the BOBBIN thread |
| Skipped stitches | either side | not tension at all |
| Top thread keeps breaking | either side | not tension at all |
| Seams pucker | either side | not tension at all |
| Fabric pulled down into the machine at the start | either side | not tension at all |
How to use
- Rethread completely with the presser foot UP before anything else.
- Fit a new needle — it is faster than diagnosing an old one.
- Use contrasting thread top and bottom so you can see the junction.
- Adjust the top dial, not the bobbin screw.
Frequently asked questions
Why is there a nest of loops under my fabric?
The top thread is barely tensioned, so all the slack ends up on the underside. It looks like a bobbin fault because that is where the mess is, but it is not. Nine times in ten the thread never went between the tension discs at all — rethread completely with the presser foot raised.
Why does the presser foot have to be up when threading?
Because the tension discs are sprung shut and only open when the foot is raised. Thread the machine with the foot down and the thread lies outside the discs rather than between them, which is effectively zero top tension. It is the single most common cause of what looks like a tension fault, and the one people are most certain they did not do.
Should I adjust the top tension or the bobbin?
The top, essentially always. It is calibrated, marked, reversible and on the outside of the machine. The bobbin screw is a tiny unmarked thing that is easy to lose and hard to put back where it was. Leave it alone until everything else is exhausted, and if you must, turn it an eighth at a time and write down which way.
How do I know which thread is at fault?
Look at where the two threads meet. A balanced stitch has them joining in the middle of the fabric, hidden. Whichever thread pulls harder drags that junction towards its own side — so bobbin thread appearing on the top means the top tension is too tight, and top thread appearing underneath means it is too loose.
Bobbin thread is showing on the top of my seam. Why?
The top tension is too tight, so it is winning the tug of war and pulling the junction up through the fabric. Lower the top tension by about half a number and test again. Counter-intuitively the fault is the top thread even though the bobbin thread is the one you can see.
What if the loops are on the top surface instead?
That is the genuine bobbin case, and it is the rarer one. Either the bobbin tension is too loose or the thread was wound onto the bobbin without passing under its tension spring. Take the bobbin out and re-seat it properly before touching any screws.
Why do my seams pucker?
Usually both tensions too tight, a stitch too short for the fabric, or a fine fabric being dragged down into the needle plate hole. Lengthen the stitch, ease both tensions, and if your machine has a straight-stitch needle plate with a small round hole, use it.
The fabric gets pulled down into the machine at the start. What do I do?
The feed dogs cannot grip a fine fabric right at its edge, so it is pushed into the needle hole instead. Start a few millimetres in and reverse back, hold both thread tails as you begin, or sew onto a scrap of fabric first and feed straight from it onto your piece.
My thread keeps breaking. Is that tension?
Sometimes, but check simpler things first. A burr on the needle plate or in the thread path, a needle in the wrong way round, or old thread that has gone brittle with age. Thread from a charity shop or an inherited box is a common and rarely suspected culprit.
How should I test the tension?
On a doubled scrap of the actual fabric, with contrasting thread in the bobbin so you can see exactly where the junction sits. Not a single layer and not a different fabric — tension that balances on one layer of calico tells you nothing about two layers of what you are sewing.
What tension number should I use?
Whatever balances on your fabric. The mid-range mark, usually around 4, is where most machines sit for ordinary sewing, but the number itself means nothing across machines and very little across fabrics. Adjust from the default and judge by the stitch rather than by the dial.
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