You can make great flat-felled seams if you have a feller foot. This is my feller foot. David Coffin recommends the 1/8" size, which mine is. You will be using a straight stitch, but check to make sure your needle position comes down at the far left of the foot. Mine came over too far and I broke the first needle.
1. I marked my seam allowances so that I could know how much to trim off of each SA. You will want one side trimmed to 1/8” and the other trimmed to 3/8”
2. line up the seam lines, wrong sides together 3. With the right side and shorter seam allowance facing you, fold the longer seam allowance over the shorter one, and press
4. put the seam under the felling foot and start sewing with the whole seam allowance underneath. Your fabric will be on the left and the upper and under seam allowances will be to the right of the needle. I am using red thread on top and light green thread in the bobbin just for illustration
5. After you have sewn about one inch, lift the upper seam allowance over the “toe” of the felling foot. Continue to sew the rest of the seam this way and the foot will guide your fabric.
6. Take this to the ironing board and press.
Now press your seam allowance open and flat so the seam is as it will be on the finished garment.
7. Now sew this seam in the same manner as you sewed the first seam. The difference is that you will have the under fabric on both the left and right sides of the seam allowance.
8. Take your beautiful new flat-felled seam to the ironing board and press! You, of course will have both colors of thread the same.
