Rolled Hems - on a serger. These are my 'tricks' for success..... Learned from my years both selling sergers and teaching how to use them AND my own dressmaking experience...
1. Select a TWO Thread version - if possible. If you're looking for a serger, I recommend making SURE it can serge with only 2 threads. On a rolled hem, this especially nice. ESPECIALLY on lightweight fabrics! The thing is - with a 3 thread, the upper looper is very loose tension so tht the thread can roll around the edge - and the lower looper is VERY tight - so it lays in a straight line, right under the needle thread - but on the wrong side of the fabric. So - why have it??? With a 2 thread rolled hem you just eliminate the lower looper and that tight thread all together - so the hem is lighter without that extra tight thread. You know if you can do 2 thread stitching on your serger if there is some 'adapter' or 'plug' for the upper looper that serves to then lift the lower looper thread up to the top of the fabric.
2. Since you want the fabric to ROLL into the edge, you do NOT want to cut off alot of the fabric with the serger knife action - therefore move the cutting action (where the moving knife moves against the stationary knife) as far to the right as possible - thereby cutting off LESS - so that more fabric is rolled INTO the rolled hem. On my good old Elna 734, this is a dial on the left of the bed of the machine.
3. Engage negative differential feed - so that it is at a negative number - so that the back section of feed dogs are working faster than the front section - thereby putting some torque on the fabric - or stretching it a bit - all on purpose.
4. Play with the stitch length until you get the look you desire. For a more 'filled in' look - either decrease the stitch length or use a fatter thread - like Wooly Nylon.
5. For a narrow rolled hem, use the needle furthest to the right - as is shown in the photograph.
6. Be sure to have changed the stitch finger over which the stitch is formed - to the skinny, needle sized finger, not the fat 'regular' finger from regular stitches.
7. THIS IS MY MOST IMPORTANT HINT for 'non-hairy' rolled hems. Especially on a woven fabric, with a curve to it - whenever the hemline goes along a straight grain portion of the fabric edge, those fibers are very strong, and will not want to ROLL. this was the situation I had on the bridal gown skirt I was creating - a long full 4 gore skirt of georgette for the overskirt. When I tested it - sure enough - a hairy edge! Ughhhhh. I got my water soluble 'Solvy' type stabilizer out, cut it into 1/2" strips, and simply laid a strip of that on top of the edge and proceeded with the 2 thread rolled hem stitch as described above. The water-soluble film just wrapped around the fabric edge preventing any fibers from 'stitching' out! Very, very cool. Here is a photo of how it looked as I was laying in the Solvy. The excess to the left of the needle simply tore off. Steam pressing definitely made a BIG difference in the look of the hem. See the finished edge - off to the left in the photograph. In the photo, I had not yet torn off the excess Solvy. It very easily tears off too!