To keep the look of two straight lines meeting each other at a point, both stitch lines must appear straight, not curved or bent at a sharp angle. Take a look at the first diagram below. It represents a slit in a piece of fabric:
If you try to stitch around the slit exactly 1/2″ (or 5/8″) away from it, here are examples of what you might get:
On the outside, gores stitched these ways would look like this, respectively:
If you stitch around the slit as seen below, you will get the appearance of two straight lines meeting in a point on the front of the fabric:
This is why your seam allowance is tiny at the beginning of the slit and large at the end.
2 thoughts on “Why does the seam allowance shrink as it approaches the top of the slit?”
Thank you! This is very helpful for inserting flared gussets into tops as well.
I’m glad you found it helpful!