What Overlocks Really Do

The terms “overlock” and “serger” will be used interchangeably throughout this guide. Originally, the commercial ma chine devised to finish edges rapidly was called a serger. The stitches locked the edges of the fabric with thread to prevent raveling and this became known as an overlock stitch. By the time these machines were introduced to the home sewing market, the words “serger” and “overlock” had become synonymous.

If you look at an overlock and feel overwhelmed, you are not alone. They do look very different from traditional machines, with so many knobs, dials, threads, and other parts that seem con fusing. Yet the serger is easier to use than a traditional sewing machine, once you get the hang of it.

Overlocks are the greatest boon to home sewers since electricity. They have cut my sewing time in half. My garments are now ravel-free and professionally finished. And they make sewing on knit fabrics a breeze.

What sergers do, they do very well, but they do have limitations. Contrary to what you might hear, a serger won’t replace a traditional machine.

The overlock will speed up your sewing. It overcasts edges probably three times faster than doing a similar edge on a traditional machine, and it does a better job of it.

Stitch Formation

Both sergers and sewing machines use thread to join together pieces of fabric, but that's where the similarity ends.

An overlock creates a stitch more like crocheting or knitting than what is normally termed “sewing.” Two of the threads loop back and forth on the top and bottom of the fabric. These threads are captured by another thread to form a soft but stable overcast ( Fig. 6.1). If you can visualize the formation of a stitch, you will begin to understand how a serger works.

6-1 How a serger forms a stitch

The thread that moves under the fabric is called the lower looper. Because it’s hard to see, the lower looper can be difficult to thread. The upper looper is the thread that comes up over the fabric.

The serger’s biggest limitation is assembling woven fabrics. A traditional machine forms a knot within the fabric that anchors the seam together. With the stitch formed by a serger on woven fabrics, you notice the loose thread on the seam on the right side ( Fig. 6.2). Even if you tighten the needle tension until the seam puckers or the thread breaks, the seam will still look as if the tension is off. Sergers that have a chain stitch (safety or locking chain) will make a neater seam, but never exactly like a traditional seam.

6-2 Woven overlock seam

Knit fabrics, on the other hand, be cause of the loft and stretch of their construction, fill in the spaces between the threads. So you can make acceptable-looking seams on a serger that are less bulky and have more stretch ( Fig. 6.3).

6-3 Knit overlock seam

I believe the unrealistic expectations of what sergers can do have caused many people to become disgruntled with their machines when they should be cheering. Read on and learn to love your serger.

Two Important Facts about Sergers

When people complain about overlocks, they usually complain about a recurrent jam. I often hear this: “I’ve used an overlock, but it drives me crazy.

When I change thread, I can’t get the tension back in adjustment.” My reply is “I can cure all your problems by explaining two simple facts.”

Fact #1—When you lift up the presser foot on your traditional sewing machine, it releases the separating plates on the tension mechanism, so that you can pull the thread free. When the separating plates are not engaged, there is no pressure on the thread. That never happens on an overlock. They never open. This seems like a trivial fact, but it’s not. It’s one of the two most important and least understood facets of using your serger. Because the separating plates are not open unless the tension has been turned off (down to 0), the thread doesn't get inside where the pressure can control the thread.

Some home sewers thread an overlock in the same way as a traditional sewing machine. They just guide the thread around the tension mechanism. Unfortunately, the thread sits around the edge without being held between the plates. Remember that the plates are closed unless the tension is turned off.

So if you are working on your serger and it seems you have no tension for no reason, check to see if the thread is truly where it belongs. On the other hand, you may be right; you may not have tension.

If your stitches don’t look right, immediately check that the thread is in between the separating plates. To make sure the thread is inside the tension mechanism, you must either turn the mechanism to zero while threading or pull the thread into the slot by holding onto it with both hands and tugging lightly. Next, check that the thread is in all the little thread guides, called escapements.

Fact #2—An overlock makes a stitch in a completely different way than a traditional machine. Overlocks function sequentially, and the complicated order of stitch formation must be followed exactly in a precise order. So, to form stitches, without exception:

You must thread the needle last.

That means if one of your loopers breaks, you have to clip the threads right above the eye of the needle. You don’t have to take the thread out of the ma chine, but you do have to pull it out of the eye of the needle. This knowledge will save you hours and hours of frustration.

Obviously no one in her right mind wants to rethread the eye of the needle any more times than absolutely necessary. I know that many people will try to get around this—but don’t try it! If the thread is in the eye of the needle and you don’t thread the rest of the serger perfectly, you will end up with a knot instead of a chain.

You can't tell the beginning of a chain from the beginning of a knot. It helps to start your chain by turning the hand-wheel by hand for the first few stitches.

This information is in the manuals, but it may be hidden among other, not-so-important information. You must be conscious of these two facts every single time you approach your serger.

Proofing the Threading

When beginning to thread an overlock from scratch, start with the lower looper. Next thread the upper looper.

When you have the loopers threaded, you must proof the looper paths before you do anything with the needles. To proof the loopers, put your thumb or finger over the threads that you have guided to the back under the foot ( Fig. 6.4). Make three complete revolutions of the handwheel. The needle will catch the thread as it descends. As the needle goes up again, it will completely release the threads.

Fig. 6.4 Proofing the loopers

If you thread the overlock wrong, the threads become tangled on or around the loopers or needles. It makes no difference where it happens. It’s the beginning of a problem. Yet if the thread were in the needle, it would look to you like the beginning of the usual chain.

A most frustrating aspect of these machines is that problems rarely show up when they occur. They usually show up an inch or so later. About 1” into a seam, the machine starts to make a raspy noise; then the thread breaks. Unless you unthread the needles and proof the thread path before continuing, this will happen over and over until you go crazy. So when this happens, don’t fool with it; just proof it. Now and only now do you thread the needles.

One of the differences between a traditional sewing machine and an overlock is what happens to the thread when the seam ends. A sewing machine stops and the thread simply pulls free. On a serger, as you sew off the end of the fabric, you must continue sewing, leaving a little tail of thread that resembles a chain; hence, the term “chaining off.”

Stitch Width

The width of the stitch of an overlock is determined by the size of the finger over which the stitch is made ( Fig. 6.5). On a sewing machine, the needle swings back and forth. The distance of the movement creates different widths. On a serger, the needle doesn’t swing. The stitch finger over which the looper moves and forms the stitch decides the width. The stitch finger is a small prong that sits immediately to the right of the needle. The loopers arc over and under the finger, and then the thread and fabric slide off the back of the prong.

6-5 Stitch finger determines chain width

The different brands and models of sergers have a variety of methods for changing the stitch width. Some have a different plate for each width. Others have a movable projection that's held in place by screws, knobs, dials, or sliders. Each type has advantages and drawbacks. The changeable plates take extra storage and changing space, but they are very secure. The movable type is speedy to change, but isn’t as fool proof.

No matter how the overcast stitch is formed, it remains exactly as wide as the width of the finger over which it’s formed.


Prepare to adjust the tensions on your serger more than you do on your sewing machine. On your traditional machine, you have two mechanisms that control the amount of thread the ma chine feeds out: an uptake (the thing that goes up and down) and the bobbin. An overlock doesn’t have either of these mechanisms. Therefore, you have to account for all the vagaries in fabric and thread by adjusting the tension mechanisms.

Note: If a big stub comes off the spool and hits the tension wrong, it will slide around the dial and pull the thread out of the separating plates instead of through if. This is why the tension occasionally goes haywire in mid-seam.

Cuffing Blades

A serger also functions as a cutter. It can either shear away pieces of fabric and seam allowances or simply trim away the fuzzy edges.

An overlock has two cutters ( Fig. 6.6). One is the movable cutter, which can come from above the machine surface or from below. This blade moves up and down with each stitch the ma chine makes. The other is a fixed (stationary) cutter that the movable blade rubs against. These blades slice against each other to cut. The movable cutter is made of a softer metal than the fixed cutter and can be replaced when it gets dull.

6-6 Cuffing blades

Rolled Hem

One of the advantages of a serger is the ability to do narrow satin-stitched edges fast. This edge can be used on many items, from table linens to fancy ruffles.

To achieve a narrow overcast, you must change the width of the stitch finger by adjusting or by changing the plate ( Fig. 6.7). To make a smooth narrow edge, the tension on the loopers must be increased to double, triple, or even more.

6-7 Adjust tension on lower loopers for a rolled edge

Check Springs

Check springs, found on some overlocks, are small wires that come from the tension mechanism ( Fig. 6.8). Not all brands use them, but be sure to check your machine and read your manual. The spring adds additional tension on the thread. Some sergers always use them and others use them only to in crease the tension when the width is decreased.

6-8 Tension mechanism

This section has laid the foundation for your journey to successful overlocking. Keep these basic functions and facts in mind as you continue to learn and understand your serger.

Hint: If you can’t get the tension tight enough, loop the thread around the tension mechanism twice.
PREV: Sewing Machine Gremlins NEXT: Overlock Choices and Options Home

Friday, 2016-12-30 8:17