An overlocker is a specialist machine for raw edges and stretch seams. Known as a serger in North American sewing, it trims the edge with a knife while needles and loopers wrap several threads around it. Depending on the stitch, it can join and finish fabric layers in a single pass.
How an overlocker forms stitches
Unlike a domestic sewing machine, an overlocker mainly uses looper threads rather than a bobbin. Three- and four-thread overlock stitches are common: a three-thread setup can finish an edge, while the additional needle line in a four-thread stitch makes it more suitable for many construction seams.
Differential feed uses independently controlled front and rear feed dogs. Correct adjustment can stop knits from stretching into waves or lightweight fabric from puckering. Deliberate adjustment can also create gathers.
Common uses
- stretch seams in jersey and knit fabrics
- fast finishing of open seam allowances
- rolled hems on lightweight fabric
- decorative flatlock effects, depending on the machine and setup
Because the knife removes fabric, a misplaced seam cannot simply be unpicked and resewn at its original width. Test tension, cutting width, stitch length, and differential feed on a scrap first.
Overlocker, sewing machine, and coverstitch
An overlocker does not replace every sewing-machine function: buttonholes, darts, corners, and much topstitching still require a conventional machine. A dedicated coverstitch machine normally sews without trimming and can stitch within the fabric rather than only at a cut edge. Combination machines provide both families of stitches but usually require conversion and rethreading between modes.