New serger owners sometimes are uncertain where to place their fabrics when their pattern calls for a 5/8" seam allowance. Here is a little exercise to learn where your serger will cut, and where the seam line will be. Set up your serger for a basic 4 thread overlock stitch.
Method One: Without trimming any fabric, serge sleeve cap with your differential feed at its standard setting (normal or 1) to the first notch of the sleeve cap. Then adjust the differential upwards, try 1.5. Ease in fabric to other notch. Lower differential feed back to standard setting for the rest of the sleeve cap. If the ease is not gathered enough, go back over the sleeve cap again with the differential set higher to make a little more ease. Pin eased sleeve to armscye and serge.
Method Two: Similar to method one, but set the differential for too much easing, say a 2.0 setting. Ease the sleeve cap, then use a seam ripper to break the needle threads here and there, so sleeve can be smoothed into the armscye properly. Serge or sew the sleeve to garment.
These stitches work best with firm medium to heavier weight fabric (e.g. polar fleece). –Not a stitch to try late at night, but it makes a lovely edge stitch. Depending on your fabric you may want to fold under the edge about 3/8ths of an inch. Serge slowly. –Test Test Test.
3 Thread Version: Use decorative thread (thread you want to highlight) in the needle. Buttonhole twist works well with a 90/14 needle. Use your left needle only (right needle removed). Use Woolly Nylon in the upper and lower loopers. Use a long stitch length (3.5 to 5). This stitch works by tightening up both looper threads so that they run along the fabric edge with the needle thread very loose and visible from both sides. Thread the loopers with the wooly nylon and tighten the tension. Start with a 7.5 and adjust from there. Thread the deco thread through the needle. Set tension to 1 or 0. If you are feeling bold try a thicker thread skipping the needle tension disc all together. Sew a test sample. Sometimes the stitch will "form" on top of the fabric and you can just run your fingernail down it to get it to sit on the edge of the fabric. The heavier the needle thread, the greater the looper tensions need to be. If there is not enough tension on the wooly nylon the stitch will not work. Try adding thread nets to the woolly nylon cones to get more tension on the thread.
2 Thread Version: Decorative thread is in the left needle, (right needle removed) regular thread in lower looper. (Upper looper is disengaged.) Set up will be similar to a 2 thread flatlock. Needle tension will be 1 to 0. Lower looper tension 7-9. Use a long stitch length (3.5 to 5). Now: cut long strips of water soluble stabilizer 1 to 4" wide. Lay the stabilizer on top of the fabric, lined up with or slightly overlapping the cutting edge. (Your needle must penetrate the stabilizer.) Place the fabric with your fold (if you have one) or raw against the knife. Serge along the edge. When finished stitching, grab the Solvy at its inner edge (away from your stitching/cutting line) and pull up and then towards the edge of the fabric. This will pull the needle thread to the very edge of the fabric. Remove any extra Solvy. (Note: you can start with wider strips of Solvy, then just used the leftover strip for your next length of serging.)
Adapting a Pattern
Before starting construction, review your pattern instructions. 1) Look for places where your serger will improve/ease construction (e.g. serging raw seam allowances or facing edges). 2) Decide where you want to change the order of construction to take advantage of the serger. For example, if you serge a sleeve to the body of a shirt before the sleeve has been serged into a tube, it can be somewhat quicker and easier. After attaching the sleeve then you serge a single seam from the start of the sleeve to the end of the garment.