Have you ever had two pieces of fabric that looked perfectly matched on the cutting table, only to finish with an uneven seam? The fabric layers shifted while you were sewing. One layer moved quicker, or slower, than the other.
The result might be a creeping edge, mismatched corners, or the bottom layer extending past the top layer.
Some fabrics and seams are more likely to shift than others. Longer seams and small pieces can be challenging to manage. Slippery surfaces, loose weaves, stretch fabrics, and contrasting weights all make shifting more likely.
However you like to hold the fabric in place (pins, clips, or other), try these tips to keep the layers of fabric evenly aligned while you sew.
Prepare and pin the two pieces so their raw edges are aligned. It’s helpful to do this right sides together, in preparation for sewing. This is also an opportunity to verify the two shapes are identical, as cut. If the two don’t match, don’t try to force them together. Take a second look at your cutting and marking process. You might be cutting uneven shapes or not marking well.
Use an adequate number of pins or clips. Use as many as you need to hold the fabric securely, but not so many as to make handling the fabric more difficult. A useful rule of thumb is to space pins in proportion to the length of the seam.
Pin strategically to prevent shifting. It’s critical to catch corners, markings, and ends. In between those points, it makes sense to add pins at even intervals along the length of the seam.
Pay particular attention to the middle of the seam. You’ll likely have the most confidence at the beginning, and again near the end of a seam. But small errors at the middle point can add up to a significant mismatch by the time you reach the end.
As you sew, let the machine do the work. Don’t tug on the fabric from behind or push it toward the needle. Both actions can cause the fabric to stretch unevenly, letting one layer race ahead of the other. Keep your hands on either side of the seam, and allow them to lightly guide the fabric, but don’t interfere with the feed.
Keep your eyes off the needle. A seam guide or a line drawn on your machine bed will help you maintain an even seam allowance, and avoid shifts. This is a good reminder that the quality of a sewn seam is not in the speed of stitching but in your control of the fabric.
Be confident to stop and adjust. You can stop at any time while you sew. Make sure the needle is down. Then, lift the presser foot, and adjust the fabric to make sure the layers are smooth with no folds, or creeping. Lower the presser foot, and continue on.
Sew at a pace that will allow time to remove pins or clips. Make sure you have the ability to stop at any time, and remove pins safely before they reach the presser foot.
Practice on stable fabrics. Take a couple of rectangles of woven fabric, and sew two sample pairs. Pin one pair densely, but unevenly, along the seam line. Pin the other pair sparsely, but at even intervals. When complete, press the samples, and compare them. Pressing always helps, but if a seam is badly shifted, the iron won’t save it.
This exercise gives you a tactile sense of what the fabric is doing while you stitch. And it’s helpful to develop these skills on a stable woven cotton, before trying them out on a slippery silk or stretchy jersey.