I used this great edging for some of my latest T-shirts. This is a nice casual look for thin floppy knits that don't fray very much. It works really well on those fabrics that want to curl up spontaneously... and it's always a good idea to listen to what the fabric wants to do and work with it rather than struggling to force it into submission...
Firstly, when you cut out the sleeves, cut them about 2.5cm longer than you want, and then slice off this extra length.
(Oh, for the neckline, you have to measure the finished length of the edge of your neckline, and cut out a 2.5cm width strip (with the length going the stretchy way, natch) the same length, plus 2cm for seaming. I didn't take any photos of the neckline finishing, sorry.... maybe next time :) but it's essentially the same process from here on)
With right sides together, sew the sleeve seam, and the seam of the strip to form a ring.
Take your sleeve edge strip and fold it wrong sides together in half along its long length, over and enclosing the raw lower edge of the sleeve.
Pin in place.
Using a twin needle on your machine, stitch the strip down, keeping the stitching a perfectly even length from the folded edge.
So, you end up with this, which doesn't look particularly... wow. In its ironed, just-been-neatly-sewn state. But wait...
...after washing, the raw edge of the knit will curl up nicely, creating a tight little ridge over the stitching.
Then I dyed the T-shirt using iDye in Crimson, which throws the blue stitching into focus. Of course, if you don't want contrasting top-stitching to show up as a feature on your garment; you must choose a thread colour that is going to blend in with your final colour after dyeing, as I did for my "bat" shirt. In that case, I top-stitched with a black thread, since in that design I wanted the top-stitching to blend in, and the shirt was going to become a deep deep brown. But in this case I like the tiny accent of blue on an otherwise very plain shirt. And the way the raw edge of the edging has curled up and over the lower row of stitching is very pleasing. I think it looks a little bit like piping.