Beth In Alaska wrote:
Oh Beth, sorry to hear you are not getting on with your serger. I must admit that I'd looked at them a couple of times, and been put off by how complicated they seemed! Then all the posters here kept raving about them, I finally got fed up with zig-zag seam finishes, and went and bought a serger.
For me, it was a revelation - why the heck didn't I buy one sooner?? I've since up-graded to a 5 thread with cover stitch because I wanted the coverstitch feature. This is something I need to practice more - much trickier than 3 / 4 /5 thread overlocking! And it's time consuming to swap modes, but such a handy feature.
Right - tension. Too much tension causes stress, cross people and snapped threads! OK - you have 4 threads in your serger and 4 tension discs - one for each thread. They all work the same as the tension disc for the needle thread in your sewing machine. When you thread your serger, it's important to make sure the thread snaps into place between the discs properly - I find with mine they occasionally slip out mid-seam which leads to cussing. The tension on the left needle, upper and lower looper threads determine how the stitch fits and looks on your fabric. The tension on the right needle doesn't appear to do much as far as I can see to affect the overall look and interaction of the other 3 threads. The tension on your left needle thread is just like the tension on your sewing machine needle thread. The tension on your upper and lower looper threads affect how tightly the two threads wrap the edge of the fabric, and whether or not it rolls. You should aim to have the looper threads meet on the edge of the fabric. Tightening the lower looper causes the lower looper thread to be shorter in comparison, and pulls the upper lopper thread to the back of the seam, and in an extreme case causes a rolled hem. The tension on the upper looper works in the same way. You can also adjust the whole thing by altering the cutting width, shaving off a bit more or a bit less fabric. The right needle tension needs to be set similar to the left. It is great fun and very educational, and probably a standard part of any serger class to thread your machine up with four very different colours (red, yellow, blue, green seem to be favourite) and then play with your tensions on fabric samples, making a note of what change causes what effect.
Differential - the speed of the back and front feed dogs on a serger (yes you have two sets rather than the single set on a SM) can be made different, hence providing a stretching or gathering effect when you set your differential to anything other than 1. This can be used to stretch lycra as it's sewn when making swim costumes, or gather tulle to make a ballet skirt. It does take practice and I've found I have to be careful not to let the fabric move left or right as I guide it through if there is a high differential set.
HTH, lots of good diagrams and better explanations than mine in some of the serger books out there.
Regards,
Sarah