Serger Tension Made Easy

A serger is a fantastic sewing tool that I highly recommend to any sewist that can afford one. This is especially true if you like to sew with knits (see why in my post In Praise of Sergers). But many sewists shy away from them because of the ongoing frustration of perfecting the serger tension.

Welp. That’s precisely why I decided to write this post. Serger tension can be tricky for the beginner sewist. But with a little bit of clarity, you’ll know exactly how to turn those dials or knobs to achieve the perfect tension for all of your sewing projects.

So let’s get started! To help guide you through understanding the tension on your serger, I’m pulling out my handy tension swatches.

I am using my Juki-MO654DE (p.s. If you’re shopping for a serger, this baby is my number one recommendation. It is the absolute best bang for your buck. Mine is over 15 years old and I swear has another 15 or more years to go.)

For the sake of this tutorial, I used some pretty psychedelic thread colors. In my lower looper – fuschia, upper looper – sky blue, right needle – black and left needle – neon purple.

Now depending on your serger, you will either be working with a set of knobs or a set of dials to adjust your tension. The numbers will also be unique to your particular make and model. My Juki uses a knob system with each on a scale from 1–9.

As you can imagine the higher the number the higher the tension.

---

Editor’s Note: Enjoying this sewing tutorial? Put it to use on our Nora Sweater!

---

But what exactly does tension mean?

Higher tension means there is more friction on the thread as it is being pulled through the machine. More friction means the thread will be sewn in tighter. Perfecting your tension means creating a perfect balance of “tightness” between all of the threads.

Imagine a teeny tiny game of tug of war between the threads. When the fabric is perfectly settled between all threads, you’ve got yourself a balanced stitch. With a two needle serger, this means four threads.

Let’s Begin with a Balanced Stitch

The two pictures below are of a perfectly balanced stitch.

You’ll notice that the two looper threads (the blue and the fuchsia) meet right at the fabric’s edge. There is also no puckering at the needle threads (black and purple).

Now let’s take a look at some unbalanced examples.

Troubleshooting Unbalanced Loopers

Let’s start with the loopers. In this first example, we are looking at the upper looper thread (blue) being set with too much tension. Notice how it is so tight that it is pulling down on the lower looper thread (fuchsia) which is causing the fabric to “tunnel”. You’ll also notice that since it is pulling down on the lower looper thread (fuchsia), the lower looper thread is now pulling up on the left needle thread (purple).

This second example is with the upper looper thread (blue) being set with too low of tension. In this case, there is no resistance against the lower looper thread (fuchsia) which is making it loose and wavy on the backside of the stitch.

Next, let’s check out our lower looper settings. In this next picture, we are looking at the lower looper thread (fuchsia) with too much tension. Similarly to the high upper looper example, the lower looper thread (fuchsia) is pulling down on the upper looper thread (blue). Also notice how its tightness is also pulling up the left needle thread (purple).

In the case of the lower looper thread tension being set too low, you will see the lower looper thread (fuchsia) being carried over to the front side of the stitch by the upper looper thread (blue).

Now Onto Needle Tension

Needle tension isn’t quite as finicky as looper tension, but it is still just as important. Let’s start with the right.

This first example is when your right needle thread (black) tension is set too high. There are two signs of your tension being too high. First, you’ll notice some puckering at the stitch line. My swatches are sewn with a super stiff muslin material, but if you are sewing with a lighter woven or knit, you will see this straight away. Another thing to notice is how the right needle thread (black) is so tight that it is pulling the lower looper thread (fuchsia) through the fabric onto the front side.

Now if the right needle thread (black) tension is set too low, like in the following picture, you will see the right needle thread (black) hanging out loosely on the front of the stitch and create loops on the backside of the stitch.

Lastly, let’s look at the left needle. The following picture shows the left needle thread (purple) with too much tension on it. Just like the right needle, when the left needle thread (purple) is too tight it will pucker and pull the lower looper thread (fuchsia) through to the front of the stitch. Notice how tiny the left needle stitch (purple) is on the backside of the stitch. It’s so tight you could barely pick it if you had to!

Now if the left needle thread (purple) tension is set too low you will instantly know because it will be showing through on the right side of your garment. If you’ve ever sewn something with negative ease and put it on only to see your thread showing on your seams, your left needle thread tension is too low. Just like the loose right needle thread, if the left needle thread (purple) is too loose, you will see loose stitches on the front of the stitch and little loops on the backside of your stitch.

Bird’s Eye View

I know it can be easy to get lost in all of these examples so here’s a comparison chart for you to see them all together: