An overlocker, also referred to as a serger, is a sewing machine used for enclosing the raw edge of a seam in a protective thread casing. It works on a simple principle: Upper and lower knives trim the edge of the fabric, then the needles and loopers overcast the edge with thread. At first glance, an overlocker can be intimidating as it has dials, two needles, upper and lower loopers, upper and lower knives and its mechanism looks complicated. But once you understand what causes a problem, you will be able to solve it with ease.
Adjust the thread tension. Thread your machine with different thread colours and match thread colours with the colours of the adjustment dials. This will make it easier to identify what thread needs tension adjustment. Ensure that the thread is correctly inserted between the tension disks. Stitch 6 to 8 inches of a single layer of a fabric swatch. If the lower-looper thread straggles over the edge of the fabric and is visible on the top of the fabric, tighten the lower-looper tension in small increments. If the upper-looper stitches are visible on the underside of the fabric, tighten the upper-looper tension in small increments. If needle threads form loops on the underside of the fabric, the needle threads are too loose. Tighten the appropriate needle tension slightly. If needle threads are too tight, the stitches will pucker. Loosen the appropriate tension dial.
Replace blunt or bent needles. To replace the needle, turn the hand wheel until the needle reaches its higher position. Swing the foot to the side for easier access to the needle, if your model permits. Remove the thread from the needle. Loosen the screw above the needle (using a small screwdriver) and remove the needle by hand, or with tweezers. Hold the new needle with the flat side toward the back of the machine. Insert the new needle up into the needle clamp as far as it will go. Securely tighten the screw.
Adjust the cutting width. If the fabric twists and curls underneath the stitches, the upper knife is too far from the edge of the fabric. Move the knife to the left to decrease the cutting width. If loops form outside the edge of the fabric, the cutting width is too narrow. Move the knife to the right to increase the cutting width. The cutting width is controlled by a knob or dial that moves an upper knife holder to the right or to the left. Follow the manufacturer's instructions to change the cutting width.
Replace the upper knife if it is dull and does not cut fabric properly. Open the looper and side covers. Deactivate the upper knife according to the manufacturer's instructions. Remove the hexagon bolt and remove the upper knife. Insert the new knife into the groove of the knife holder. Tighten the hexagon bolt slightly. Turn the upper knife holder to a cutting position. Turn the balance wheel toward you until the upper knife is in its lowest position. Loosen the hexagon bolt and adjust the position of the upper knife so that the edge of the upper knife slightly overlaps the lower knife. Tighten the hexagon bolt firmly. Close the looper and side covers.
Adjust the differential feed ratio that controls the speed of the front feed dog. Depending on the model, a normal setting is indicated as "N" or "1." If fabric tends to pucker, select a lower-than-normal setting. If the edge of the fabric is stretched and looks wavy, select a higher-than-normal setting.
Clean the feed dog. Open the looper and side covers. Remove the needles, presser foot and needle plate. Push any lint to the front using a lint brush. Put the needle plate, presser foot and needles back into their positions. Close the looper and side covers.
To prevent thread and fabric jams, begin and finish your stitching with a thread chain of 2 to 3 inches. If you are using conventional machine thread spools, put the small plastic disks on top of the spools to prevent threads from snagging. If you are using large cones, cover them with net sleeves to prevent threads from unreeling too quickly.
Disconnect the overlocker from the power supply when replacing knives or needles. Keep fingers away from the moving parts during sewing.