The situation when a sewing machine loops from below is familiar to every seamstress, from beginner to professional. Instead of an even, beautiful stitch, tangled balls of thread form on the wrong side of the fabric, which cannot be straightened out without damaging the material. This defect not only spoils the appearance of the product, but can also lead to the needle getting stuck or the mechanism breaking if the work is not stopped in time. Most often, the problem lies in incorrect threading or incorrect tension settings, and not in a serious engine malfunction.
Before disassembling the mechanism or taking the equipment to a service center, it is necessary to carry out basic diagnostics. Bottom loop often formed due to the fact that the upper thread does not receive sufficient resistance and is pulled freely to the wrong side. In other cases, the culprit is the shuttle mechanism, where dust or lint has accumulated. Understanding the working principle shuttle stroke will help you quickly localize the source of the problem and fix it in a few minutes.
In this article we will analyze all the possible reasons for the appearance of loops, from basic errors when refueling to the need to adjust the tension screws. You will learn how to properly configure bobbin case and why it is important to use quality threads. By following step-by-step instructions, you can return your machine to perfect stitching without extra costs.
The main reasons for the appearance of loops on the wrong side
The appearance of stitch defects is always a signal of desynchronization of the operation of the upper and lower thread feeders. When sewing machine loops, this means that the upper thread is not knotted in the thickness of the fabric, but lies freely in loops on the underside. The most common reason is a simple lack of upper thread in the tension disks. This happens if the presser foot was lowered when threading and the thread did not get between the regulator plates.
Another common problem is the quality of the threads. Cheap, overdried or too fluffy threads can get stuck in the grooves of the needle or get tangled in the hook. Polyester threads Poor quality ones often stretch, which upsets the tension balance. It is also important to check that the needle number matches the thickness of the thread: too large a needle eye for a thin thread will result in loops.
⚠️ Attention: Never pull the fabric with your hands while sewing to straighten the loops. This may cause the needle to break and the rack teeth to become misaligned.
Mechanical reasons also play a role. If there are burrs, scratches or rust on the surface of the shuttle, the thread will snag and form knots. Regular cleaning and lubrication of the mechanism is a prerequisite for stable work. Sometimes the problem lies in the bobbin case: If the spring plate is weakened or, conversely, too tight, the lower thread will behave unpredictably.
Checking the upper and lower threading
The correct sequence of actions when threading is the key to quality stitching. If the machine loops, the first step is to completely straighten the thread and thread it again, following all the steps. The upper thread should pass through all thread guides, tension regulator and thread take-up. It is critical that the presser foot is raised when threading the upper thread, as this is the position where the tension dials are spread apart and the thread gets caught between them.
Threading the bobbin thread requires care. The thread on the bobbin should be wound evenly, without humps or dips. When inserting the bobbin into the case, make sure the thread comes out in the correct direction (usually counterclockwise, but varies by model). After inserting the cap into the hook, pull the thread up until you feel a slight resistance from the spring.
☑️ Checklist for correct refueling
A common mistake is to pass the thread through needle thread guide. If the thread is passed directly into the eye of the needle, bypassing the last hook, the loop will not form correctly and the machine will begin to malfunction. Also check that the thread is not tangled around the winder or other protruding parts of the housing before entering the thread guide system.
Adjustment of thread tension: upper and lower
Tension balance is a fine adjustment that requires understanding the interaction of the two strands. If the top thread loops are visible on the wrong side, the top tension is too loose or the bottom tension is too tight. The top tension is adjusted using the numbered wheel on the front panel of the machine. Turning in a larger direction increases the tension, in a smaller direction weakens it.
The lower tension is adjusted by a screw on the bobbin case. This is a more delicate operation. A small screwdriver is needed for adjustment. Turning the screw clockwise increases the tension, counterclockwise decreases it. Before starting the adjustment, remember the original position of the screw so that you can return to the factory settings. The optimal tension is checked by testing: hang the cap by the thread and shake lightly. The thread should slide slightly, but not unwind freely under the weight of the cap.
| Defect symptom | Reason | Action |
|---|---|---|
| Hinges at top and bottom | The thread did not enter the tension disks | Rethread the upper thread with the foot raised |
| Hinges only at the bottom | Weak top tension | Increase the value of the top tension control |
| The stitch tightens the fabric | Both threads are too tight | Loosen the tension of the upper and lower adjusters |
| The thread breaks | Excessive tension or burrs | Check the thread path and reduce the tension |
When working with different fabrics, the settings will have to be changed. For knitwear or elastic materials, the tension often needs to be loosened, and for thick denim fabrics, the tension needs to be increased. Always do a test stitch on a scrap piece of the same fabric before starting the main project.
Use threads of the same number and quality for the top and bottom threading. Different thread thicknesses almost always lead to an unbalanced stitch.
Diagnostics of the shuttle mechanism and bobbin
The shuttle knot is the heart of the sewing machine, and this is where problems most often arise if the thread loops. The accumulation of lint, dust and thread scraps under the shuttle interferes with the free movement of the thread. To clean, you need to remove the needle plate, take out the hook and cap. Wipe all accessible surfaces with a soft brush or dry cloth. Do not use compressed air as it may drive dust deeper into the mechanism.
Inspect shuttle for mechanical damage. Scratches on the nose of the hook or on the surface of the cap can tear the thread or prevent it from flowing freely. If you find any roughness, you can carefully polish them with a suede file or fine sandpaper, but this must be done with great care so as not to disturb the geometry of the part.
⚠️ Attention: When cleaning the shuttle assembly, do not apply excessive force to the fixing parts. Plastic elements of modern cars break easily.
Also check the bobbin itself. If it's plastic, make sure it hasn't warped from heat or time. Cracks in the bobbin may cause the thread to jerk. Metal bobbins can oxidize, which also impairs thread slip. Ideally, the bobbin should rotate smoothly in the cap, without jerking or jamming.
How to check the bobbin winding quality?
The wound thread should lie tightly and evenly. If the winding is loose, with dips or a hump in the middle, the thread will feed in jerks, which will lead to loops. Rewind the bobbin, controlling the thread tension as it winds.
The influence of needle and thread quality on loop formation
The needle is a consumable item that requires regular replacement. A dull, crooked, or simply old needle may not be able to properly form a loop for the shuttle to pick up. If the needle is installed with the blunt side in the wrong direction, or is simply not fully inserted into the needle holder, looping from below guaranteed. Make sure the flat side of the needle shank is facing backward (or the direction specified in your model's instructions).
Matching the needle number to the type of fabric and thread is critical. For thin fabrics (silk, chiffon) you need needles No. 60-70, for medium fabrics (cotton, linen) - No. 80-90, for jeans - No. 100-110. Using a thick needle on thin fabric will pull the fabric into holes and loops, while using a thin needle on thick fabric will bend and skip stitches.
The quality of the thread also plays a decisive role. Old, overdried threads become brittle and produce a lot of lint. Threads with thickenings or knots get stuck in the needle. It is better to use modern synthetic or semi-synthetic threads from well-known brands that have a smooth surface and uniform twist.
Replacing the needle is the cheapest and fastest solution to 50% of stitching problems. Change the needle after every large project or after 8-10 hours of work.
Specific problems of vertical and horizontal shuttle
The design of the shuttle assembly affects the nature of the faults. In cars with horizontal shuttle (where the bobbin is visible through the transparent cover) problems are often associated with improper installation of the plastic casing or the thread getting under the guides. It is important here to ensure that the thread fits neatly into the slot on the shuttle body when threading.
Machines with vertical shuttle (classic models) are more sensitive to the quality of bobbins and caps. In such machines, the problem of the hook nose “not reaching the needle” is often encountered, which leads to skipped stitches and subsequent looping. This requires adjusting the gap between the needle and the hook, which is a more complex procedure.
In both cases, it is important to use original or high-quality compatible accessories. Cheap universal caps may have play, which will inevitably lead to stitching defects. If after all the checks the machine continues to loop, the synchronizer may be broken or the internal mechanisms may need professional lubrication.
What to do if loops appear only in certain areas of the fabric?
If looping is local, check the uniform thickness of the fabric. Perhaps, at the transition point from the thin to the thick layer, the foot warps and the thread tension is broken. Also check that the fabric conveyor (rail) is not dirty, which may cause uneven material movement.
Can an electronic failure cause looping?
In modern computerized models, software or sensor failure can cause the needle and shuttle to become out of sync. Try resetting your machine to factory settings or unplugging it for 15 minutes to reboot the system.
How often should you clean your machine to avoid loops?
It is recommended to remove dust and lint after each sewn product or every 3-4 hours of continuous work. General cleaning with removal of the needle plate and hook is required once a month during active use.
Does sewing speed affect the formation of loops?
Yes, starting or stopping too quickly can disrupt stitch formation, especially on thin fabrics. Try to start sewing at medium speeds, gradually picking up speed so that the thread has time to stretch evenly.