Mini Tutorial: Sewing a bias seam
In a bias seam, both seam edges are cut on the bias grain thus they both have the same amount of stretch. Considering the stretch in a bias-cut edge, a bias seam is handled similar to a knit seam.
Note: The bias seam described below applies to non-stretch, woven fabrics.
1. Start by aligning and the top and bottom edge and inserting a pin horizontally at to keep both fabric layers in place at each point.
2. Continue aligning and pinning the remainder of the seam, keeping the layer flat on the table to prevent them form stretching in the alignment process. Insert the pins perpendicular to the edge for easy removal.
3. For a smoother machine stitching process, replace the pins with a large hand basting stitch. The hand basting will prevent unwanted puckers and prevent the seam from stretching out of shape in the sewing steps to follow.
Hold the hand basted seam up and make sure the edges have not stretched out. If the seam appears to have compressed, leave it hanging for some time before machine stitching it,
4. Carefully machine stitch the bias seam, holding the layers down but not stretching them in them in the process. The hand basting should help keep the layers more secure.
If you notice that the seam begins to ripple or pucker, lift the presser foot and smooth out the layers with your hand. Drop the presser foot and continue stitching. Repeat this process as needed.
Once the stitch is complete, remove the and basting using a seam ripper.
The final bias seam should lay completely smooth and flat, with no unwanted puckers in the seam. It is also important that the seam has not stretched out during the stitching process. Hold the garment up and check that the bottom edge is perfectly horizontal straight line.