You flip the hoop over expecting a clean design and instead see white bobbin thread poking up through the edges of your satin columns, or speckled through the letters. It looks messy, and on dark garments it stands out badly. The good news: this is one of the most fixable problems in machine embroidery. In almost every case it comes down to the balance between top and bobbin tension, with the design file sometimes making it worse.
Here is how I check it, in the order I would check it at the machine.
What correct tension looks like
Embroidery is a tug of war. The top thread and the bobbin thread lock together inside the fabric, and where that lock sits depends on which side pulls harder. When tension is balanced, the top thread wraps slightly around to the back, so the bobbin thread never reaches the front.
The quickest way to see this is the back of a satin column (a capital "I" or "H" stitched at around 1/4 inch wide works well):
- Balanced: the white bobbin thread runs down the middle third of the column, with the top colour showing on roughly one third on each side.
- Bobbin showing on top: the back shows almost no top colour, or the bobbin strip is very narrow. The top thread is pulling too hard or the bobbin too little.
- Top thread looping on the back: the opposite problem, usually top tension too loose (and a common start of bird nesting under the fabric).
Stitch that test before you touch any dials. It tells you which way to adjust instead of guessing.
The 7 most common causes (and fixes)
1. Top thread tension is too tight
This is the number one cause. A tight upper thread drags the lock point up to the surface and pulls the bobbin thread with it. Loosen the upper tension a little at a time (a quarter turn on a commercial tension knob, or one or two steps on a home machine's tension setting) and re-stitch the test column. Small changes, one at a time.
2. Bobbin tension is too loose
If the top tension is already moderate, check the bobbin. A simple drop test: hold the bobbin case by the thread end and give a light jerk of the wrist. It should drop a short distance, an inch or two, and then stop. If it slides down freely with no resistance, the bobbin is too loose. Tighten the small screw on the bobbin case in tiny increments (think minutes on a clock face, not full turns). On drop-in home machines, check the manual before adjusting, as many are factory set and the cause is more often lint or the wrong bobbin.
3. The top thread is not seated in the tension discs
If the thread jumped out of the tension discs during threading, there is almost no upper tension, and the result can look random. Ironically, a thread caught or wrapped on a guide does the opposite and acts like extremely tight tension. Rethread the whole top path with the presser foot raised (so the discs open), and look for thread wrapped around the spool pin or a guide.
4. Lint or a thread scrap in the bobbin case
A tiny wad of lint under the bobbin tension spring changes the bobbin tension without you touching anything. Remove the bobbin case, brush out the area under the spring and around the hook, and check for broken thread ends. This is worth doing every few bobbins on busy machines.
5. Wrong bobbin thread or a badly wound bobbin
Embroidery bobbins are normally a lighter thread than the top, typically 60 or 90 weight bobbin thread. A heavy bobbin thread, or a bobbin wound loosely and unevenly, feeds inconsistently. Use proper embroidery bobbin thread or pre-wound bobbins, and make sure the bobbin is inserted the direction your machine specifies.
6. Needle problems
A burred, bent or wrong-size needle can catch the thread and add drag. Change the needle if it has been in for many hours. A 75/11 is a good general embroidery needle with 40 weight thread; very fine detail may need a smaller needle, thick or textured threads a larger one.
7. Machine speed
Running at top speed on dense or detailed work increases thread drag and makes tension problems show. If the issue only appears on certain areas, drop the speed and see if it improves before adjusting tension.
When the design file is the real problem
If your tension test column looks balanced but the bobbin still shows on certain parts of a design, the file is often the cause. After years of fixing customer files, these are the patterns I see most:
- Satin columns that are too narrow. Columns under about 1 mm wide have very short stitches that pull the bobbin up at the edges. Small details need to be widened or switched to a running stitch.
- Lettering that is too small. Below about 4–5 mm capital height, satin letters get so narrow that bobbin show-through is almost guaranteed.
- Density that is too heavy. Overly dense fills and stacked layers make the needle fight the fabric and thread, increasing drag on the top thread.
- Bad auto-converted files. Files traced automatically from artwork often have wrong stitch lengths, missing underlay and odd densities. No amount of tension adjustment fully fixes a poorly built file.
If a file keeps causing this no matter how you set the machine, it is usually faster to have it rebuilt properly. Our hand-digitized logo files are built stitch by stitch with sensible column widths and densities for the size you need, and you can read how our digitizing service works before ordering. If you are just looking for a ready-made design that has already been tested, browse our embroidery designs.
A quick troubleshooting order
- Stitch a satin test column and look at the back.
- Rethread the top with the presser foot up.
- Clean lint from the bobbin area and check the bobbin is inserted correctly.
- Change the needle.
- Adjust top tension in small steps, re-testing each time.
- Only then check and adjust bobbin tension.
- If the problem stays in specific areas of one design, look at the file.
If thread is also snapping during these tests, read our guide on why embroidery thread keeps breaking, as the causes often overlap.
Quick FAQ
Is a little bobbin thread on top ever acceptable?
On a well-tuned machine you should see none on the front. A tiny bit at the very edge of a narrow satin may be tolerable on a quick personal project, but for customer work it is a sign to adjust tension or the file.
Should I use black bobbin thread to hide it?
Matching bobbin colour can disguise the problem on dark garments, but it does not fix the tension imbalance, and the stitches will still look less raised and clean. Fix the cause first.
Why does it only happen on caps or thick items?
Thicker materials and cap frames add drag on the top thread, so a machine that is balanced for flat shirts can show bobbin on caps. Slightly loosening the top tension and slowing down usually helps, along with a file digitized for caps.
Have a design that keeps stitching badly? Order a custom embroidery digitizing service file, hand digitized, from $10, delivered by email within 12 hours.