Hello! Do you love specialized presser feet? I do. It's certainly a perk of having a Bernina. I ordered a couple of feet right away when I bought my machine, and they arrived this week!
One of my very favorite feet is the lap seam foot (AKA the flat felled seam foot) so I've put together a little tutorial on how to make seams with these feet
The Bernina Lap Seam foot #70 (top) and the Pfaff 41242 Fell Seam foot (bottom)
The two sides of a flat-felled seam
Flat felled seams are great because:
they're sturdy - the stress on the seam is distributed between two rows of stitching
they're clean - all the raw edges are enclosed
they're thrifty - the seam allowances you need are tiny
its difficult to make alterations, plus the small seam allowances mean you can't let out no matter what
they can be tricky to make on curved seams
1. Prepare you pattern. This means adjusting the seam allowances. The two sides of the seam that you want to join together with the flat felled seam require different allowances. See that little channel in the bottom of the foot? The width of the channel equals the width of the seam (in this case, 4 mm). The seam allowance must be equal to this width on one side and double this width on the other. For example, one pattern piece would have a 4 mm seam allowance and it would be joined to another pattern piece with an 8 mm seam allowance.
2. Align your seam. Because the two pieces that you're sewing together have different seam allowances from each other, the edges of the fabric will be offset by the width of the difference, in this case, 4 mm. If you start with the right sides together, the double line of stitching will be on the inside. If you start with wrong sides together, the double line of stitching will be on the outside.
3. Sew the first line of stitches. Place the fabric under the foot with the lower layer folded over the upper layer. Use a stiletto or a pin to get everything lined up just right as you lower the presser foot.
Once you start sewing, the foot will continue to guide the fabric so that the lower piece of fabric encloses the edge of the upper piece. Sew that first line of stitches! Then press the seam open.
4. Sew the second line of stitches. With the two pattern pieces spread apart and the enclosed edge raised, guide the raised seam into the foot so that it folds over the remaining raw edge. Stitch and press!