Smoothing angular lines or transition lines on a pattern to ensure smooth curves for sewing.
In the example below: When creating a Princess Line design line, the sharp dart points need to be changed to smooth curves. (Click on the images to see larger versions.)
The Princess Line (armhole) seam drawn in red on the Bodice Back block.
The pattern pieces are traced from the block. There are sharp corners on both pattern pieces where the dart point used to be.
The red dotted lines show the blending that is required to remove the points and create smooth curves for joining the seams.
Note: The side piece has the red dotted line extending past the original waist line. This is because the seams lengths need to match. You should "walk the seams" after the blending is done, to check the length.
A small amount needs to be added to the side pattern piece so that the seam lengths are equal.