Hello everyone,
Recently a sewer asked me about transitioning from a flat-fell seam to a side vent. She was making a shirt from our pattern called A Subtle Twist (by the way, it is now discontinued, but this blog will apply to other shirts as well).
I was not particularly pleased with all aspects of my first experiment with solving the problem, but I'm going to show it to you so you can see the process--and what I didn't really like. Then in my next blog I'll show you what I like better. So let's get to it.
A Subtle Twist includes 5/8" wide side vents. Here's a photo of the wrong side of the Front showing you the dot where the side seam ends at the top of the side vent, the miters at the hem corners (we draft those for you), and the hem. You can see that I've already serged the side seam and hem edges.
Here you can see that I've created the back piece of the sample, serged it, and stitched it to the front piece, stitching the side seam to the dot. I've pressed the seam allowances open, continuing to press the remaining portions of the seam at 5/8" down to the corner miters, forming the vent. Finally, I trimmed the back seam allowance to 1/8" down to a point 1/2" above the dot. It's important not to trim all the way down to the dot! At the bottom of the trimmed back seam allowance, be sure you've clipped all the way to the side seam stitching. (I had to do it later!)
Now you're ready to stitch the miters. These will be uneven miters, because the side vent is 5/8" wide, but the hem is 1-1/4" wide. The thing to note is that the diagonal seam allowance for the miters is 3/8" (shown in the first photo), so the serged edges must cross at 3/8". It's simple if you can see a photo--. The top pin is at 3/8". Stitch from that top pin to the corner--we always place a dot at that corner to help you.
Once you've stitched, you'll trim the corner of the miter diagonally and press its short seam allowances open over a point press. Turn them right side out.
So this is where I started wondering just how I wanted to proceed. I tried what we often do with flat fell seams. I used my edgestitching foot and stitched (working from the wrong side), down both sides of the seam and across the bottom, right where the trimmed seam allowances end. Then I stitched across the hem, up one side of the vent till I was even with the dot, pivoted and stitched up the angle at the top of the vent, and the same on the other side of the vent.