There are loads of fantastic tutorials available online for different methods of doing a bound edge with knit fabrics. I think over time I've tried nearly all of them and I use two or three different methods depending on the situation. In my mind the methods generally can fit into one of two categories either worked flat or worked in the round. I LOVE doing my binding flat (i.e with one shoulder seam of a neckline still open), because this opens up the possibilities of using a wider variety of fabrics for the binding. If you bind flat then you can simply cut the binding longer than required and then stretch as you stitch it on, later cutting the binding to length. This means the amount of stretch a fabric has isn't as important (you can even cut your binding on the bias if need be), and you don't have to do some fancy guesswork or complicated maths to work out the binding length. If you bind in the round you need to know the exact length of the binding before starting as the first step is to join the binding into a circle, and this length will vary hugely depending on the stretch and recovery of the knit used.
BUT when working flat the final step after completing the binding is to stitch the second shoulder seam and therefore close the neckline, which results in a serged seam exposed at the neck edge. This is usually stitched down with a few straight stitches across the width of the binding but my machine HATES doing this so it drives me crazy. This is avoided totally when binding in the round.
So...... as I was sewing in a sleep deprived state the other day, in my overly cramped sewing space where I have to keep changing my machines over between my standard machine and my serger, I was struck with a flash of brilliance (or something) so I thought I'd share. (For all those of you who already do your binding like this feel free to burst my brilliance bubble but why oh why haven't you told me about it!).
Here you go (note I used a cotton/lycra as my binding and it does curl slightly which shows in some of the photos, this doesn't happen with many other knit fabrics).
Step 1: Stitch one shoulder seam
Step 2: Pin you length of binding (I cut my the length of the neckline by 4cm in width) to the neck edge right sides together, stretching it as you go.This shows the fabric relaxed so you can see the binding will stretch out as you sew.
Step 3: Serge (or stitch the binding to the neck edge) to give a neck edge that looks like this.
Step 4: There will be extra binding hanging off the end of the neck edge so this can now be trimmed back.
Step 5: Now pin the other shoulder seam including through the neck binding, when doing this step you need to make sure that the seam allowance of the binding is pointing towards the binding NOT the garment.
Step 6: Serge or stitch the second shoulder seam. So now what started as flat binding is suddenly binding worked in the round!
NOTE: If you are lazy like me or have little sewing space you can now continue to serge all the other seams of the garment and put in sleeves, do side seams and attach any sleeve or hem bands. If you sew our knits on a serger you can get to this point without even turning on your sewing machine, neat eh?
Step 7: Now fold the binding over to the wrong side, covering the neck edge seam allowance and folding this towards the binding (so it is encased by the binding). Pin in place carefully putting pins on the right side of the garment.
Step 8: Carefully stitch in place, I use the inside of the left prong of the foot as a guide for stitching (it probably has a technical name but you know what I mean). I also try and hold the binding firmly underneath as I come to each pin and remove it, especially if the fabric tends to curl as this one did.
See the nicely encased seam at the second shoulder seam.
So I hope some of you might find this helpful, if you do I'd love to hear about it or to see pics of what you make :-)