Automatic Tension on Sewing Machines
Automatic Tension on Sewing Machines: What It Is, How It Works, and Is It Really Automatic?
A sewing machine technician’s honest take on one of the most misunderstood settings on the tension dial.
Many modern sewing machines tout “automatic tension” as a feature.
On the upper tension dial — typically numbered 1 through 9 or 10, with 1 being the lightest tension and 9 or 10 the heaviest — you’ll see a slot on the dial that says “auto” or “automatic.”
The other day, I logged onto my LinkedIn profile for the first time in months, and I was happy to see a message from the owner of a sewing machine dealership in Sweden. He asked me the following question:
I am a Janome and Baby Lock sewing machine shop owner from Sweden. I really like your articles. It would be interesting to hear about your view on automatic tension. Some has Electronic tension but for exemple Janome S5 and s3 and even cheaper models it is also called auto. Is it really a difference in this setting compared to a specific number? for example number 4. In what way is it automatic?
Great question — it had been on my mind for a while. Here is my response.
What Is Automatic Tension on a Sewing Machine?
My honest opinion is that the manufacturer choosing to call it “automatic tension” is a slightly misleading choice of words. The tension dial does not automatically adjust itself if the tension is poor. The machine has no way of seeing what the stitch actually looks like. So why do they call it “automatic tension”? Probably because it makes for good marketing.
But how does a machine with “automatic tension” differ from machines that don’t offer it? And how does “automatic tension” actually work?
With “automatic tension,” the manufacturer has done enough research to make an educated guess of the best tension setting in relation to the stitch pattern being used.
Here is an example. Assume we are using a tension scale of 1–10, as most modern machines do, with 1 being light tension and 10 being heavy tension. If my tension is set to “automatic” and I select a straight stitch, the machine will set the tension to what the manufacturer’s research has determined is typically the best upper tension for a straight stitch. Let’s say it’s a 4 on the dial. Though the tension dial shows “auto,” internally the tension discs will adjust to a 4. If I select a zig-zag stitch, the machine will set the tension to what the manufacturer’s research has determined is typically the best upper tension for a zig-zag. Maybe that is 5 or 5.5.
If you were to go through all the different stitches, I bet the tension adjusts slightly for each category — for example, I think with “automatic tension” selected, the tension changes slightly for all stitches in the buttonhole category, all stitches in the appliqué category, the monogramming category, and so on.
How Does Automatic Tension Work?
How does the tension change without turning the dial on these machines? The tension system on machines with “automatic tension” is not purely mechanical. There is a stepper motor attached to the upper tension mechanism that adjusts the tension discs according to the stitch pattern selected, as long as the tension dial is set to automatic. Once you go off automatic tension and turn the dial to a specific number, I believe the stepper motor (and therefore “automatic tension”) is no longer in play.
You can actually see the tension change on some Janome and Baby Lock machines with touchscreens. These machines tell you exactly what the tension is set at on the screen (you have to press the tension icon to see it). If you take a picture of the tension setting on a straight stitch, then select a decorative stitch and take a picture of the tension again, you’ll see the exact change being made by the “automatic tension” feature.
Bernina Machines Go One Step Further
Modern Bernina machines have a feature called “Creative Consultant.” With this feature, the machine essentially asks the user what fabric they are sewing and what sewing technique they are going to use on that fabric.
- Fabric options are quite wide — more than 10 in total, including leather, denim, light woven, heavy woven, toweling, pile fabrics, and more.
- Technique options include zipper, buttonhole, embroidery, decorative, and more.
Once you tell the machine the fabric and technique, the Bernina will recommend a specific needle (size and type) and a specific thread (weight and material). Then it adjusts tension based on your fabric and technique, along with the Creative Consultant’s recommended needle and thread.
This Creative Consultant feature actually helps prove my earlier point about how “automatic tension” is misleading terminology. The stitch type we’ve selected (straight, zig-zag, decorative, etc.) is not sufficient information for the machine to know how much to adjust the upper tension. Stitch type matters, but so do the fabric, thread, and needle — I think of them as the four ingredients of the “stitch recipe.” I’ve written about how these four ingredients affect one another:
Is Automatic Tension Really Automatic?
This is why “automatic tension” isn’t actually automatic. My stitch quality will look perfect when using high-quality thread like Mettler, Isacord, or Aurifil. But if I switch to something of poor quality like Coats & Clark, or to a significantly heavier thread (say, from 50 wt to 12 wt), the tension will become poor because the thread changed. “Automatic tension” has no way to see or feel the thread change, and it will not adjust on its own. As mentioned before, the machine is making an educated guess of what upper tension is best, and it assumes you’re using quality thread and the correct needle for the fabric you’re sewing.
Another reason the term is misleading: it only applies to the upper tension discs. When we talk about tension, we’re really talking about the balance between the needle thread and the bobbin thread — and there is no mechanism in place to adjust the bobbin case tension automatically.
The Closest Thing to Truly Automatic Tension: Baby Lock ATD
Small aside — the closest thing we have to real “automatic tension” in the sewing world is the Automatic Thread Delivery (ATD) system found on most Baby Lock serger and coverstitch machines. ATD is a beautiful mechanical system of sliding metal blocks and wires (no electronics involved) that measures the amount of thread needed to make a perfect stitch. Tension dials are eliminated, and any brand or type of thread can be used without adjustments.
ATD works by sensing the thread feed and making precise adjustments in real time, giving you even, professional-quality stitches every time you sew. Whether you’re working with delicate silk, stretchy knits, or heavy denim, ATD delivers consistent results without constant fine-tuning of tension — so you can focus more on creativity and less on fussy details.
Frequently Asked Questions
What does “auto” mean on a sewing machine tension dial?
It means the machine sets the upper thread tension for you based on the stitch you’ve selected, using a preset value the manufacturer has determined works best for that stitch type. A stepper motor moves the tension discs to that preset whenever the dial is on “auto.”
Is automatic tension different from setting the dial to a number like 4?
Only in that it changes with the stitch. On a straight stitch, “auto” might be the same as a 4; on a zig-zag or decorative stitch, it might shift to 5 or 5.5. Once you turn the dial to a specific number, the machine holds that number regardless of stitch.
Does automatic tension adjust for different thread or fabric?
No. It can’t see or feel the thread, needle, or fabric. If you switch to a lower-quality or much heavier thread, you’ll still need to adjust tension yourself.
Does automatic tension adjust the bobbin tension?
No. It only controls the upper tension discs. Bobbin case tension is adjusted separately, by hand.
Is there a sewing machine with truly automatic tension?
The closest is Baby Lock’s Automatic Thread Delivery (ATD) system on their sergers and coverstitch machines, which mechanically measures thread feed in real time and eliminates tension dials entirely.
Have questions about tension on your machine? Reach out — my dad and I are always happy to help.
