Why does the seam allowance shrink as it approaches the top of the slit?
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.
Copyright © 2004–2009 Tasha Kelly McGann. The author of this work retains full copyright for this material. Permission is granted to make and distribute verbatim copies of this document for non-commercial private research purposes provided the author's name, the copyright notice, and this permission notice are preserved on all copies. Linking to this site is allowed without permission. Questions and comments can be directed to tasha@cottesimple.com