Why does the sewing machine loop at the bottom: diagnostics and repair

Have you noticed that the sewing machine has started to loop at the bottom, creating sloppy loops on the wrong side of the fabric instead of a straight stitch? This problem occurs in both household models (Janome, Brother, Singer), as well as on industrial machines, and can turn a simple stitch into a real puzzle. Looping of the lower thread not only spoils the appearance of the product, but also indicates a problem with the mechanism or settings.

In 80% of cases the reason lies in incorrect threading, mismatch between thread and needle numbers or contamination of the shuttle mechanism. However, sometimes more serious problems are to blame: wear of parts, tension imbalance, or even manufacturing defects. In this article, we will analyze all the possible reasons why the machine loops from below, from obvious to hidden, and give step-by-step instructions for eliminating them. You will learn how to diagnose the problem yourself and when to contact a service center.

1. Improper threading: the main cause of looping

Let's start with the most common culprit of the problem - incorrect upper or lower threading. Even experienced seamstresses sometimes miss this point, especially if the machine has not been used for a long time or has been reconfigured. Threading errors result in the thread not passing through all the necessary guides and tensioners, causing the tension of the upper thread weakens, and the lower thread is pulled to the front side, forming loops.

To check the gas station:

• 🔹 Upper thread: Make sure it goes through everything guides (usually 2-3), thread take-up and tension regulator. On most models, the thread path is indicated by arrows or numbers on the body.
• 🔹 Bottom thread: Check whether the bobbin is inserted correctly into the hook (it should rotate counterclockwise when the thread is pulled out). The thread from the bobbin should pass through the slot in the shuttle and come out without snagging.
• 🔹 General point: After threading, lower the needle to its lowest position (by turning the handwheel) and make sure that the upper thread picks up the lower thread - if this does not happen, the hook requires cleaning or adjustment.

If the problem persists after refilling, proceed to the next step. But remember: 9 out of 10 cases of looping from below are solved by correct threading!

2. Needle, thread and fabric mismatch

The second most common reason is incorrect selection of consumables. Using a thread that is too thick for a thin needle (or vice versa) upsets the tension balance, causing the bobbin thread to be pulled to the right side. The same thing happens if the needle is dull, bent or not suitable for the type of fabric.

Here's how to choose the right components:

Fabric type	Needle number	Thread thickness	Needle type
Lightweight fabrics (chiffon, silk)	60–70	40–50	Universal or "Microtex"
Cotton, linen, chintz	80–90	40–60	Universal
Jeans, drape	100–110	50–80	"Jeans" or enhanced
Leather, vinyl	110–120	60–90	"Leather" or with a rounded point

Look for signs of needle wear:

• 🔍 Blunt point — leaves puffs on the fabric.
• 🔍 Bent rod — the thread begins to cling to the shuttle.
• 🔍 Burrs on the ear - the thread breaks when sewing.

3. Violation of thread tension

Incorrect tension is another common reason why the machine loops from below. If upper thread is too loose, the lower one is pulled to the front side, forming loops. If bobbin thread too tight, the upper one cannot grab it properly, and the stitch turns out uneven.

How to adjust tension:

1. Upper thread: On most machines, the tension control is located on the front panel (a dial with numbers from 0 to 9). For standard fabrics the value is usually suitable 3–5. If the loops are from below, increase the tension by 0.5–1 unit.
2. Bottom thread: Adjustable with the screw on the bobbin case. Be careful — incorrect setting can lead to thread breakage! It's best to try adjusting the upper thread first.

Check the tension on frontal seam (a simple straight stitch on a scrap piece of fabric). The ideal stitch should look the same on both sides: neither the top nor the bottom thread should be pulled to the opposite side.

⚠️ Attention: If after adjusting the tension the loops do not disappear and the thread begins to break, return the settings to their original position. The problem may be something else (for example, a dirty shuttle or a worn needle).

4. Contamination of the shuttle mechanism

The hook mechanism is the “heart” of the sewing machine, and if it gets dirty it can cause looping at the bottom. Dust, thread fragments and fabric particles accumulate in the shuttle, preventing the bobbin thread from being properly picked up. This is especially true for machines that are used to work with fleecy fabrics (fleece, terry cloth) or without regular cleaning.

How to clean the shuttle:

1. Turn off the machine and remove the bobbin case.
2. Remove the bobbin and carefully pull out the shuttle (in some models you need to unscrew the screw to do this).
3. Clean the hook and the surrounding area from dust and threads using soft brush or compressed air (do not use metal objects!).
4. Lubricate the mechanism with 1-2 drops machine oil (only if this is provided in the instructions for your model!).

What happens if you don't clean the shuttle?

The accumulation of dust and threads can lead to jamming of the mechanism, thread breakage and even breakage of the shuttle. In advanced cases, expensive repairs or replacement of parts will be required.

After cleaning, check how the shuttle moves - it should rotate smoothly, without jamming. If the contamination was severe, you may need to repeat the procedure after 1-2 days of work.

5. Worn or damaged parts

If all the previous steps did not help, the problem may lie in physical wear and tear of parts. Over time, even high-quality sewing machines require replacement of consumables. Here's what to look for:

• 🔧 Needle: As mentioned, a blunt or bent needle can cause looping. It is recommended to change the needle after 8–10 hours of operation or at the first sign of wear.
• 🔧 Shuttle: If it has nicks or scratches, it may snag the thread, disrupting its tension. In this case, the shuttle must be replaced.
• 🔧 Bobbin case: Cracks or deformation of the cap will cause uneven tension on the bobbin thread.
• 🔧 Presser foot: If it does not adhere tightly to the fabric, it can cause shifting of the layers and, as a result, looping.

To diagnose wear of parts:

1. Inspect the hook and bobbin case for scratches or chips.
2. Check if there is any play in the movement of the shuttle (it should not dangle).
3. Make sure the presser foot lowers evenly and with sufficient force.

⚠️ Attention: If you find mechanical damage to the shuttle or other parts, do not try to repair them yourself - this may lead to even greater damage. Contact your service center to replace parts.

6. Malfunctions in the mechanism or electronics

In rare cases, looping underneath may be caused by serious malfunctions, such as:

• 🛠️ Shuttle stroke imbalance - Occurs after the machine falls or undergoes strong vibration.
• 🛠️ Broken thread take-up - it may not lift the thread completely, which leads to skipped stitches.
• 🛠️ Failure in the electronic control unit (relevant for computerized models, for example, Brother Innov-is or Janome Memory Craft).

Signs of serious problems:

• The car is zigzagging regardless of fabric type and settings.
• Appear extraneous sounds (creaking, knocking) during operation.
• Electronic display shows errors (for example, E6 on typewriters Singer).

In such cases, independent repair is not recommended. Contact an authorized service center, especially if the machine is under warranty. Trying to disassemble a mechanism without experience can lead to complete failure.

7. Features of industrial sewing machines

Industrial sewing machines (eg Juki DDL-8700 or Typical GC6-2) can also loop from below, but the reasons often differ from household models. Here's what to check:

• 🏭 Presser foot pressure: In industrial machines it is regulated separately. If the pressure is too light, the fabric will move and the stitch will be uneven.
• 🏭 Hook and needle synchronization: At high speeds, even the slightest mismatch in timing can cause looping. Adjustment requires special tools.
• 🏭 Oil pump: Insufficient lubrication of the shuttle mechanism accelerates wear of parts.

For industrial machines it is recommended:

1. Clean the shuttle passage daily from production debris.
2. Use only special industrial threads (for example, Gütermann Mara 120 or Amann Mettler).
3. Perform preventative maintenance every 3–6 months (depending on intensity of use).

FAQ: Frequently asked questions about sewing machine looping

The machine loops only on thin fabrics. What's the matter?

Most likely the problem is needle and thread mismatch. For thin fabrics (chiffon, cambric), use a needle 60–70 and thread 40–50. Also check the tension of the upper thread - for light materials it can be loosened slightly (set to 2–3).

After replacing the bobbin, the machine began to loop. What to do?

Probably a new bobbin not compatible with your model or not inserted correctly. Make sure that:

• The bobbin is suitable in size and shape (for example, for Brother and Janome bobbins are not interchangeable!).
• The thread is wound onto the bobbin evenly, without humps.
• The bobbin is inserted into the shuttle so that the thread comes off counterclockwise.

Can I adjust the bobbin thread tension myself?

Yes, but with caution. There is a small screw on the bobbin case - you can tighten it slightly with a screwdriver (clockwise to increase tension, counterclockwise to loosen). However It is not recommended to change the factory settings by more than 1/4 turn, otherwise the thread may begin to break. It's better to adjust the upper thread first.

The machine only loops at high sewing speeds. Why?

This is a sign shuttle mechanism wear or insufficient lubrication. At high speeds, the parts do not have time to interact correctly, which is why the thread is not captured in time. Try:

• Clean and lubricate the shuttle.
• Reduce sewing speed.
• If the problem persists, contact the service to diagnose the shuttle stroke.

The new machine has been running smoothly since the first days. What's wrong?

Possible reasons:

• Factory defect - Contact the store for a replacement under warranty.
• Incorrect assembly — check that all parts (especially the shuttle) are installed correctly.
• Transport mode - some models (for example, Bernina) have a shuttle lock for transportation, which must be removed before use.

Do not attempt to repair a new machine yourself - this may void the warranty.