The curved straight panel is the final shape you need to understand regarding the pleating of fabric. This shape is sort of an amalgamation between the square panel and the half circle panel I discussed in this post. (See picture below.)
I can imagine what you must be thinking…WHAT is he talking about????
Let me explain. If you take a square or rectangular panel and fold it slightly deeper (or more) along one side of the panel, the opposite side will begin to curve up.
The curvature (C) of the pleated panel will increase the deeper the fold is on the top (A).
As you look at this picture you might think, what’s the big deal? This looks just like a sunburst panel. Well, it kind of does but sunburst is pleated along all 3 grain lines whereas this panel is pleated along only one grain line.
When considering whether or not to use this panel shape for your pleating project, there are several variables to consider. There are technical as well as aesthetic reasons, but the technical reasons will ultimately dictate procedure.
You want to pleat along one grain line so you can have a folded hem on your garment before you pleat.
You don’t want the fabric to stretch along the bias as it would if it is sunburst pleating (half circle panel).
You want to create an Aline effect, as you like the way it looks. The amount of Aline can be controlled by amount of depth (or curvature) you give to the pleating panel.
You are using a striped or checkered fabric that you don’t want to distort as you would in sunburst pleating. For example, below is a photo of a wool plaid fabric on our cutting table.
Below is a photo of the same wool plaid fabric pleated in our curved pattern. Notice how the checks all line up.
Below is a photo of the same fabric pleated in a sunburst half circle panel. Again, notice the checks in the fabric. Since you are pleating along all three grain lines, the pattern of the fabric will be distorted. For more info on this read my post The Anatomy of Bias Circle Skirts.