Serger / Overlocker

"Serger" (mostly American) and "overlocker" (mostly British and Australian) are names for the same machine. It sews a seam, trims the raw edge with a built-in knife, and wraps thread over the edge, all in one pass. Instead of the single top thread and bobbin of a sewing machine, it uses two to five threads: one or two needle threads, plus threads carried by loopers, hooked arms that form loops around the fabric edge. The result is the neat, slightly stretchy edge seen on the inside of almost all ready-to-wear clothing.

What it does, and what it doesn't

An overlocker is a companion to a sewing machine, not a replacement for one.

It's excellent for:

• Finishing seam allowances on woven fabrics so they don't fray. It's the fastest neat finish there is.
• Sewing knit seams in one step, with stretch built into the stitch. Most T-shirts, leggings and sportswear are sewn almost entirely on overlockers.
• Rolled hems on chiffon, scarves, ruffles and napkins.
• Gathering lightweight fabric with the differential feed.

It can't: sew buttonholes, insert zips, topstitch, sew in the middle of a piece (it can only sew at an edge), or easily be unpicked. And because it trims as it sews, mistakes are cut off.

The common stitches

• 4-thread overlock: two needles and two loopers. A strong seam with a built-in safety row of stitching. The standard choice for sewing knit seams and for durable finishes.
• 3-thread overlock: one needle and two loopers. Lighter and narrower. Good for finishing edges and for seams in lightweight fabrics. Switch between wide and narrow by using the left or right needle.
• Rolled hem: the fabric edge rolls under inside a dense wrap of thread, giving a fine, narrow finish on light fabrics. Usually set up by changing the stitch finger and tensions.
• Flatlock: a seam that opens out flat, with ladder stitches on one side, used decoratively and on activewear.
• Coverstitch (two or three parallel needle rows on top, looper thread underneath, the hem seen on T-shirts) is made on a separate coverstitch machine or on combination machines. It isn't a standard overlocker function.

Differential feed

Overlockers have two sets of feed dogs, one in front of the other, and the differential feed sets their relative speed:

• Above 1 (front feeds faster): pushes fabric in, easing it. Cures wavy, stretched seams in knits, and gathers lightweight fabric at higher settings.
• Below 1 (front feeds slower): holds fabric back, stretching it slightly. Cures puckering on fine, slippery fabrics, and creates a "lettuce edge" frill on a rolled hem in stretchy knits.

Test on a scrap of the actual fabric and adjust until the seam lies flat.

Threading

Overlockers have a reputation for being hard to thread. Most modern machines have colour-coded paths, and some have air-threading loopers. The two rules that solve most problems:

1. Thread in the order the manual gives, usually upper looper, lower looper, then needles from right to left. The loopers must be threaded before the needles. If a looper thread breaks, unthread the needles, rethread the looper, then rethread the needles.
2. Seat the thread fully between the tension discs. Floss it in with a firm pull. A thread that misses the discs gives loose, loopy stitches no tension setting can fix.

To change colours quickly, cut the old threads near the cones, tie on the new threads with small knots, and pull them through gently with the needles unthreaded. Rethread the needles separately, because knots won't pass through the eyes.

Tension

Each thread has its own tension dial. In a balanced 4-thread stitch, the looper threads meet exactly at the fabric edge, and the needle threads lie flat without loops.

• Upper looper thread pulled to the underside: loosen the lower looper, or tighten the upper.
• Lower looper thread showing on top: loosen the upper looper, or tighten the lower.
• Loops at the edge: looper tensions too loose, or the stitch is too wide for the fabric.
• Needle threads loose (a ladder appears when the seam is pulled open): tighten the needle tension.

Thread a different colour in each position while learning, so you can see which thread is doing what.

Practical tips

• Pins and the knife don't mix. Pin well away from the edge, or use clips, and remove pins before they reach the knife. Hitting a pin damages the knife and can break needles.
• Guide by the edge, not the needle. Line the fabric edge up with the knife or the seam guide on the front of the machine.
• Starting a seam: sew a short thread chain, then feed the fabric in. Most machines grip it without lifting the foot.
• Securing the ends: thread the tail chain back under the stitches with a large-eyed needle, dab it with seam sealant, or sew over the end of the chain when crossing a seam.
• Curves and corners: sew curves slowly, guiding the edge to the knife. For outside corners, sew off the edge, then turn and start again.
• Thread: use overlocker thread on cones, a finer, smoother thread than regular sewing thread. Woolly nylon in the loopers makes soft, stretchy edges for swimwear and baby clothes.
• Clean out lint often. Overlockers produce a lot of it from the trimming. Brush out the knife and looper area regularly, and oil as the manual directs.

Do you need one?

You can make almost any garment without an overlocker by using zigzag finishes, French seams and flat-felled seams. But if you sew a lot of knits, or want fast, durable finishes inside everyday clothes, an overlocker saves a great deal of time.