Start with the Thread Path and Bobbin

Before you touch the tension dial, re-thread the machine with the presser foot up. This opens the tension discs so the thread sits properly between them. If you thread with the foot down, the discs stay closed and the thread can catch outside, causing loops and snags. Follow your manual's path exactly, and make sure the thread is fully seated in the take-up lever.

Next, check the bobbin. A bobbin wound unevenly, or filled too full, will cause inconsistent tension. Wind bobbins at a steady speed, guiding the thread so it fills evenly. Leave a small gap at the top of the bobbin; a full-to-the-brim bobbin can rub and jam. Drop the bobbin into the case so it turns the correct way (usually anticlockwise when you pull the thread), and pull the thread through the slot and under the tension spring.

• Presser foot up when threading the upper path.
• Bobbin thread must click into the case tension spring.
• Fresh needle for every new project — a blunt needle causes skipped stitches and pulls threads.

Diagnosing Loops, Puckers and Snaps

Look at where the problem appears. Loops on the underside usually mean the upper tension is too loose, or the thread is not seated in the discs. Loops on the top side often point to bobbin tension being too loose, or the bobbin thread not being under the spring. Puckered seams can mean tension is too tight for the fabric and thread weight, or the needle is too large. Snapping thread is usually too much tension, a burr on the needle plate, or thread caught on the spool pin.

Always test on a scrap of the same fabric, with the same thread and needle. Fold a double layer and sew a diagonal line. If the stitches look balanced — no loops, no puckers, no snapping — your tension is close. If not, note which side the problem is on.

Needle Size and Thread Weight Matter

Tension problems are often needle problems in disguise. A needle that is too fine for the thread will cause the thread to fray and snap. A needle that is too large will punch holes that let the thread pull through, creating puckers. Match the needle to the fabric: a 70/10 or 80/12 universal for lightweight cottons, a 90/14 for medium denim or canvas, and a 100/16 or 110/18 for heavy upholstery. Use a ballpoint for jersey, a sharp for wovens, and a leather needle for leather.

Thread weight also matters. A thick top thread with a thin bobbin thread will never balance. Use the same thread in the bobbin as the top when you can. If you must use a different bobbin thread, adjust upper tension to compensate — but expect compromises.

Adjusting Upper Tension in Small Steps

The upper tension dial is your main control. On most machines, a higher number means more tension (tighter), and a lower number means less tension (looser). But always check your manual, because some machines are the opposite. The golden rule is to adjust in quarter-turn increments, then test. Never jump from 4 to 8.

If loops appear underneath, increase the upper tension slightly — turn a quarter step higher. Sew a test. If the loops persist, go another quarter step. If the thread starts to snap or the fabric puckers, you have gone too far; back off a quarter step. If loops appear on top, you may need to decrease upper tension, but first check the bobbin. Only adjust the bobbin tension screw if upper tension adjustments do not work, and then only by an eighth of a turn.

• Mark your starting point with a photo or a note so you can return to it.
• Test after every quarter turn on a scrap of the same fabric.
• Re-thread after any major adjustment to rule out threading errors.

When to Touch the Bobbin Tension

The bobbin tension screw is delicate and rarely needs changing. But if your upper tension is at its normal setting and you still have loops underneath, or the bobbin thread pulls out too easily, you may need a tiny adjustment. Remove the bobbin case, hold the thread, and let the case dangle. It should drop slowly, a few centimetres at a time. If it falls freely, tighten the screw an eighth of a turn. If it does not move, loosen an eighth. Always use a small screwdriver that fits the screw exactly, and never force it.

After adjusting, re-test. If the bobbin tension was fine, leave it alone. Most tension problems are solved with the upper dial, correct threading, and the right needle.

Prevention and a Quick Checklist

Clean the machine regularly. Lint in the bobbin case and under the needle plate changes tension unpredictably. Use a small brush to clear fluff, and a drop of sewing machine oil where your manual recommends. Keep your spool pin felt clean, and use a spool cap if your machine has one.

Before you start a project, run through this quick check:

• New needle in the correct size for your fabric.
• Presser foot up when threading the top path.
• Bobbin wound evenly and inserted correctly.
• Upper tension set to your usual middle number (often 4 or 5).
• Test seam on a scrap — adjust in quarter steps only.
• Clean the bobbin area and feed dogs if you have not done so recently.

With a little patience and small adjustments, your machine will reward you with balanced, beautiful stitches. Tension is not a mystery — it is a conversation between thread, needle, and fabric. Listen closely, and you will soon fix any looping, puckering or snapping without stress.