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Rather than offsetting the seam allowances, as is sometimes done in a flat fell seam, two different seam allowances are adding during tracing: a 1” allowance (shown on the left) and the normal 5/8” allowance, shown on the right.
On the 1” seam allowance, I drew a line 5/8” away from the seam line and pressed that amount to the wrong side, making both seam allowances 5/8 “.
The satin edge stitching is done along the pressed edge. I used a width of 5 and length of 0 .7 and Bernina’s foot #2 - overlock foot to prevent the fabric from tunneling under the stitches.
Once the satin edge stitching was finished, I sewed the seam, wrong sides together. Both seam allowances were now 5/8” .
I trimmed away 3/8” on the seam allowance without satin stitching and pressed the remaining seam allowance over the trimmed allowance.
The final step was to topstitch the satin edge to the fabric.
The result is a decorative flat fell seam that, from a distance, looks a little like piping. It can be used in a number of garments where a flat fell seam already exists or added into a garment as a decorative detail.
Typical of BWOF, a simple process was obscured under awkwardly translated directions. But with persistence and help (Tany pointed out the unequal seam allowances months ago when I asked for her help. I’m sure she’s forgotten by now!) I achieved a design detail I really like!