Unless you own a serger (also known as an overlock machine) you may not be familiar with the term Differential Feed. There are no home sewing machines that have this feature, though the effect of a differential feed may be imitated, to a certain degree, on a home sewing machine by changing the presser foot pressure or the presser foot itself. The true differential feed feature can only be achieved by having two sets of feed teeth, one in front of the other, that can move at independent speeds to move the fabric at different rates. Home sewing machines have one set of feed teeth (sometimes referred to as feed dogs), some with more rows of feed teeth than others, but one group of feed teeth that always move at the same speed together. Feed teeth on a home sewing machine are either up or down, but they always move together. A serger has two sets of feed teeth, one set in the back under the foot and one set in the front, that can move together or at different rates depending upon how the differential feed adjustment is set. The back set of feed teeth on a serger always move at a constant speed, but the front set of teeth can change speed to bring fabric into the feed teeth faster or slower. If, for example, you have your differential feed set at 1 (or on some sergers on “N”) both front and back feed teeth will be moving at the same speed (a 1:1 ratio). If you change the setting to 1.5 or 2.0, the front set of feed teeth will be going faster than the back set and will bring more material into the feed teeth area faster. This can create gathers if you are serging lightweight material or can get rid of waviness in knit fabrics. If you set the differential feed in the other direction, more like 0.7, the front feed teeth will move slower than the back teeth and will cause the fabric to stretch as it moves through the machine. Using this differential feed feature can cure problems with fabric puckering when creating a rolled edge as well as create beautiful effects, such as a lettuce edge for your projects, depending upon the fabric you’re using. Once you really understand how this feature works, you will find yourself using it often. Happy Sewing!
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