Mini Tutorial: How to sew a self-bound seam finish
1. To sew a self-bound seam finish, start by stitching the seam in a conventional fashion. Trim one of the seam allowance layers down to about a third of the seam allowance width.
2. Fold the untrimmed seam allowance layer toward the trimmed layer, such that the fabric edges align- iron the fold in this position as shown above
3. Fold the untrimmed layer one more time such that the folded edge from step 2 aligns with the seam stitch and all fabric raw edges are enclosed. Iron this fold to secure. It helps to insert a few pins as you iron to keep the folded edges perfectly aligned.
For added stability in the machine stitching process, replace the pins with a temporary hand basting stitch. Basting is especially helpful if the folded seam allowance is particularly narrow or/and if working with flimsy, difficult-to-control fabrics.
4. Topstitched the folded seam allowance next to the open folded edge (the fold located near the seam stitch) as shown. The temporary hand basting will provide much needed stability during this process to allow an even straight stitch application.
To complete the seam, remove the hand basting using a seam ripper and iron the final seam with the self-bound seam allowance layers pointing to a single direction. It is easiest to iron from the fabric face side but be mindful of heat sensitive materials- use a cotton cloth as an ironing buffer if needed.