Boning channel alignment can be a tricky thing. In most cases on modern corsets the boning is aligned to the seams of a corset, but not always. In many historic styles it almost never aligns with the seams. Ideally, the boning of a corset is placed vertical to the body, so it holds the corset firm against compression along the waist. When the seams of the corset do not lay on the vertical, it can be difficult to determine exactly where the boning channels should be.
This demo shows one trick you can use to find the vertical placement of boning on a corset, regardless of piecing.
For the vast majority of construction methods, the boning is inserted long before the grommets, so it is necessary to find a way to lace the corset without the grommets. I decided to try binder clips. If you grommet before inserting the boning, lace using the grommets instead.
In order to give the binder clips the best possible grip on the corset, sew the boning channels around the grommets and then fold over the edge boning channel.
Fold a strip of scrap fabric over the edge to protect it from the binder clip, and then add the clip. Use small clips, because they are stronger than the larger ones. spread them out evenly along the edge of the corset.
The binder clips cannot take much pressure so take a soft pillow or two to lace it on. I used two soft feather pillows for this corset. A poly-fill corset may work for you, but such pillows are usually much firmer, and the binder clips may pull free.
Compress the pillow(s) by hand and then tighten the lacing to match. The binder clips can hold once tightened, but they are not good at pulling the corset tight.
Mark the boning channels with your preferred method. I used loose chalk dispensed from a roller (usually sold with quilting supplies). I like the loose chalk because it can be removed with an air can, leaving no residual marks and I don’t have to brush the surface of the fabric.
I will be using double-boning on most of this corset, so I marked the center of each pair that did not fall along a seam line, and at the top marked where the other seams should fall in relation to those center lines.
Mark only one half of the corset.
After removing the corset from the pillow, copy the marks to the unmarked half of the corset.
Sew all the channels by your preferred method, following the marks.