SEW ... The Garment-Making Book of Knowledge
Trim the regular 5/8˝ seam allowance of the fabric layer that will be under the top- stitched seam down by a width equal to the fold area of your felling/lap foot. This will vary depending on your sewing machine foot. The foot I used to make the samples (at right) has a 3/8˝ fold area, so that’s the amount I trimmed from the top layer.
Start stitching the first pass of the seam, feeding the edge of the lower layer into the foot. The foot will just fold over that extra fabric just once and will be easy to handle; just hold the fabric up a bit so it feeds naturally. Adjust the needle position to the left, if necessary, to make sure the line of stitching lands near the left cut edge. Some sewists go to the trouble of pressing the edge of the lower layer under first, but I don’t. I actually find a pressed edge can interfere with the feed of the fabric into the foot. I trust the foot (you will, once you get the hang of it) to do an excellent job of fold- ing the fabric over on its own.