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Have you ever sewn a garment in single jersey fabric and experienced that the seams tore when in use? I have! My youngest daughter has a bodysuit with lots of cute little holes along the seams. Here is a photo of a sleeve:
What has happened here? Answer is: I have forgotten to lower the needle thread tension compared to what I use daily. Keywords are: Thin fabric. And that it is (very) elastic. I’ll explain:
When the fabric is being stretched, the way the overlock seam copes with it, is that it has extra length of thread to offer. The looper threads goes kind of zigzag and are a lot longer than the seam. Plenty of thread! But what about the needle threads? They’re not that long. They run straight forward on top of the fabric, just to dive through the fabric now and then, giving the looper thread on the bottom a little kiss before they go up again. I’ll go get my electronic pen and paper:
Imagine the cross section of two layers of THIN fabric (black) along the seam. Only one of the two needle threads is shown (blue):
The only extra length this thread has to offer when stretching the fabric, is what goes through the fabric. And as the fabric is thin, the extra available length is short.
Let’s take a look at the seam in thicker knit fabrics, like velour:
That’s better! The needle thread is longer! There is another thing; thicker knits are often less elastic than thinner jersey knits, and doesn’t demand that elastic seam.)
WHAT TO DO?
Loosen the needle thread tension a little bit (i.e. turn to a lower number on the wheel), and by that, the overlock machine gives the seam some more thread!
Voila! Longer thread!
Another thing you can do, is to make sure that the stitch length is not too long, and perhaps lower it a little bit. This follows from the same principle; lowering the stitch length gives more stitches, and more thread going up and down through the fabric, helping to lengthen the seam when fabric is stretched.
These principles also applies to sewing with COVERSTITCH MACHINE in thin elastic fabrics or thick very elastic fabrics.
Another thing I’ve experienced, is holes in armholes and crotch (i skrittet) in a jersey garment, shown here (only armhole holes shown):
This is basically the same phenomenon as above, but with a slight different mechanism. The vertically-running seams on the picture are sealed by the horisontally-running seam. But, the seam wasn’t elastic enough, needle thread tension too high. Then, when the fabric was being stretched, instead of tearing the needle threads, they were pulled out of the crossing seam. When the needle threads are gone, there is nothing to hold the looper threads in place, hence, the whole seam loosened.
*Phew* Writing english is quite demanding! This post was my friday evening… But it’s fun too, writing english again, after many years almost only reading english ( and listening to, on the TV) My husband is sitting next to me in the sofa, playing Civ 4, watching TV and helping me out when I was needing english words. Thank you, My Love!