Mini Tutorial: How To Sew A Faced Armhole Finish
1. Start by cutting your facing pieces. In this example, the armhole facing is constructed of one front piece and one back piece. Cut two facing layers for the front and two for the back to cover both armhole edges. The two matching pieces, for both front and back, should be the mirror image of each other as pictured above.
2. Align the front facing piece to the its corresponding back pieces such that face sides are touching and seam edges are aligned. Insert pins horizontally at the seam edges to keep the seam layers aligned during machine stitching. The top seam (less curved area) corresponds to the shoulder seam, while the bottom seam (more curved area) corresponds to the underarm and should match the garment's side seam.
3. Machine stitch both facing seams at the designated seam allowance (1/2" in tis case) and iron the finished seams with the seam allowance open as shown.
4. Before aligning and stitching the facing compartment to the garment's armhole, it is a good idea to first clean-finish the facing's outer edge (opposite the armhole edge) using the technique of your choice. In this tutorial, a serging stitch is sued to encase the fabric raw edges. If you do not own an overlock machine, you can sue a simple zigzag stitch on your home sewing machine.
5. Keeping the garment on its face side, align the facing compartment to the garment with face sides touching and armhole edges aligning. The facing's shoulder seam and underarm seam should perfectly align with the garment's shoulder seam and respectively, side seam (underarm). Insert a few pins to keep the layers aligned in this position. If this is your first time sewing an armhole facing, it may be helpful to hand baste the two edges together as this will provide a lot more control during the machine stitching process, especially along the curved underarm area.
6. Working form the wrong side of the garment, stitch the two layers together at the designated seam allowance. In this case, the seam allowance is 1/2". Try to keep the stitch as smooth and even as possible especially when arriving the underarm area which naturally, features a more abrupt curve.
7. To eliminate excess bulk and tension in the finished armhole edge, trim the seam allowance width by about 1/8" (if needed) and clip triangle-shaped notches into the seam allowance layers. These notches play an important role in the finished faced edge laying flat and tension-free.
8. Iron the facing seam with the seam allowance layer and the facing directed away form the garment as shown. All seam allowance layers should be positioned directly underneath the facing layer. Apply a stitch through the facing and seam allowance layers underneath at about 1/8" from the seamline as shown above. This is called understitching and will ensure taht the facing layer remains flat preventing it from rolling to the outside of the finished edge.
9. To complete the faced armhole application, flip the facing to the garment's wrong side and iron the finished edge for a flat smooth finish.