Anyway, blind stitch foot. Get it. Slap it on your machine.
Stitch width: 5mm
Stitch length: 2-4mm
Needle thread tension: 0-3
Upper looper: 2-5
Lower looper: 6-9
Fold your fabric along where you want the flatlock detailing to be
Place it under presser foot, aligning needle to just at the edge of the fold
and the guide position on the foot so that some of the thread will loop over the edge of the fabric
sew, sew, sew
You'll have loose loops, that's okay. You need them so that you can open the fabric up. (granted, mine are a bit looser than they need to be...)
See, cool little ladder-like detail on the inside. But the look I've been pinning for 8 years after?
Seriously, that's it!
Note: Decide ahead of time which look, ladder or the loops, you want on the outside of your project. Fold right sides facing for the ladder look. Fold wrong sides facing for the loop/flatlock look.
And, the main reason I've been wanting to know how to do this? I love the way it looks when two pieces of fabric are butted up against each other with a flatlock stitch.
All you have to do to acheive this is:
Take your two pieces and fold the raw edge under (unless it's a non-fraying fabric like knits or fleece. This technique would rock with fleece)
Run it through the magic machine
Seriously, way too excited about this.