Using an overlocker, also called a serger, is very similar to using a sewing machine. Both can sew a seam, but an overlocker goes beyond simply sewing to also trim the seam to an even width and cast a series of threads over the edge to keep the fabric from ravelling. And these three steps are accomplished with only one pass of the fabric through the overlocker, saving you a lot of time when sewing. Although specific directions for operating an overlocker will vary depending on the model of machine and its features, the following directions for two-needle, four-thread overlock sewing, a common overlock technique, will help you become familiar with the basic operation of an overlocker.
Insert the needles. Turn the hand wheel on the side of the machine to raise the needle holder to its highest position. Loosen the clamp that holds the needles by either turning a hand screw or using a small Allen wrench, usually provided with the machine. One at a time, push the needles up into the holes or slots of the needle holder, with the eyes of the needles facing forward. Tighten securely.
Thread the machine. Unlike a sewing machine, which has an upper thread and a lower bobbin, an overlocker uses four cones of thread--for two upper loopers and two lower loopers--all of which are located above and to the rear of the machine. Locate the diagram on your machine that shows the route each thread must take through the guides in the machine. The diagram is often located inside a flip-open door on the machine. It is very important to follow the exact paths as shown, as well as the order in which each looper must be threaded. Changing the order of threading will result in the thread's not looping correctly, and the overlocker will not cast on stitches.
Set the stitch length. Many overlockers have a numbered dial on the side of the machine. The smallest number will produce the shortest stitch. Generally, use a shorter stitch on lightweight fabrics and a longer stitch on heavy fabrics.
Adjust the differential feed. This feature controls the operation of the feed dogs on the overlocker, ensuring that seams are not wavy or puckered. Like the stitch length, the feed is typically adjusted by turning a dial. On an overlocker having three settings, normal is for average-weight fabrics, 0.7 is used for delicate fabrics and 2 is used for stretchy fabrics.
Ensure the blades are in place. An overlocker has both an upper and a lower blade. The lower blade is stationary and is located even with the plate on which you place your fabric when sewing. The upper blade moves and is located near the needles. As you sew, the blades will cut through the fabric to trim the seam.
Place the fabric under the presser foot and lower the foot to hold the fabric in place.
Step on the power pedal to begin overlock stitching. When you reach the end of the area you wish to overlock, keep your foot on the pedal to keep the machine stitching while guiding the fabric out from under the presser foot. Unlike a sewing machine, which will tangle and knot the thread if operated without fabric, an overlocker can stitch without fabric in place. When fabric is removed and the machine is still operating, the threads will create a chain that you snip to release the fabric from the machine.
If your overlocker is already threaded and you want to change the thread colour, use the easy tie-on method. Snip the old thread near the cone and tie on the new colour of thread with a common overhand knot. Then just run the machine until the new colour works its way through all the guides and the needles, which are large enough to allow the knot to pass through smoothly.
Always make sure the fabric you are working with is lying smooth. If it is bunched up or folded over and you mistakenly sew over it, you will also slice through the fabric underneath.