|I am so excited that I finally figured out (with the help of David Coffin's Shirtmaking book) how to use my felling foot to make a flat-felled seams. I have tried other methods, but they never looked quite good enough. This is easy to do once you know what you're doing. I have a picture tutorial at the link above. I hope the directions alone will make sense, but the pictures really tell the story.
First of all, you will need a felling foot. They come in 2 sizes, but the procedure will be the same; the measurements will just be a little different. My foot is a 1/8" foot.
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.
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!