Mini Tutorial: How To Sew A Centered Zipper Application
1. Align the seam edges housing the zipper with face sides touching as you would any conventional seam. Insert pins horizontally to secure the edges together.
2. Using the zipper, mark the bottom of the zipper opening using the zipper's bottom stop as a guide. Use tailors chalk or a quilting pencil to mark directly on the seam allowance edge as pictured above.
3. Starting at the bottom, machine stitch the seam at the designated seam allowance. In this case the seam allowance is 1". When arriving at the marked location, backstitch to reinforce and switch your stitch setting to the longest stitch available on your sewing machine (or a basting stitch). Continue stitching at the same seam allowance until you reach the top of the seam. The basting should only cover the zipper opening area.
4. Using a seam ripper, clip every 5-6 stitches along the a basting area only (above the backstitch).
5. From the wrong side of the seam, iron the seam allowance layers open being careful not to accidentally pull the seam edges apart at the clipped area.
6. Open the zipper all the way and align the left zipper tape portion with the left seam allowance layer such that the zipper teeth fall directly on the seamline. The zipper should be placed face down and the two layers pinned perpendicularly as pictured above. It also helps to hand baste the two layers for extra security during the machine stitching process, especially if you don't quite feel comfortable sewing zippers yet. It also helps to move all garment layers away from the seam as you should only stitching through the seam allowance edge.
7. Starting form the bottom, machine stitch down the center of the zipper tape using a zipper presser foot.
8. Close the zipper fully and align the unstitched zipper tape portion to the other seam allowance layer underneath. Insert pins horizontally to secure the edges together. The zipper should lay completely flat against the two seam allowance layers. Again, it helps to move the garment layers out of the way during the alignment and pining process.
9. Starting form the bottom again, stitch down the center of the zipper tape using a zipper presser foot and removing each pin as you approach it.
10. Flip the zipper application on its right side, and hand baste the exact placket lines on both sides of the seam. This hand basting should be applied through the zipper tape and seam allowance layers underneath and provide an exact guide in the topstitching process below.
11. Starting at the bottom of the zipper closure and using a zipper presser foot, stitch horizontally form the seamline outward then pivot the stitch vertically following the hand basting as a guide.
12. Repeat the stitching process on the other side of the seamline to achieve two equally placed topstitched plackets. Remove the hand basting using a seam ripper once both sides of the zipper are complete.
13. To release the zipper opening, simply pull the seam edges apart- this will release the clipped basting exposing the zipper underneath. Remove any loose threads that are stuck within the seam edges.
The end result should be a zipper that is fully covered by the abutting seam edges and two equally spaced and evenly-applied topstitched plackets, one on each side of the seam/zipper.