A well fitting corset can require several mockups and fittings to get right. You can save yourself some time and frustration by creating a quick mock up in paper first so that you can look for obvious flaws and fitting issues before you do your first fabric mockup. Making this paper mockup showed me some really important things I needed to fix before trying this in fabric. Here's how I did it at TechShop Menlo Park.
Step 1: Print Pattern
I'm starting with an original pattern from 1907 (that's the crazy multiline picture!), so I just know it's going to need some fixing. I copied the pattern pieces and scaled them up in CorelDRAW, then made a few alterations to get it to approximately my size. I'm not going into details of that here, but you can get an idea of how I work with patterns in CorelDRAW from my instructable on adding seam allowance, and my one on converting paper patterns to laser-ready files. For this paper mock up, I've left my seam allowance lines showing, and I've drawn in my waistline and notches for matching. You'll see why!
I've printed it out full size using the large format printer, then cut out each individual pattern piece.
Step 2: Clip Seam Allowances
Clip along the edges of your pattern to the stitch line. I added 5/8" seam allowance, so each of my cuts is 5/8" deep. This is where it helps to have your seam allowances drawn on your pattern so you don't have to guess. Make each clip about a half inch apart on non curvy sections, and about a quarter inch apart on curvier areas. Continue until all seam allowances are clipped. My corset pieces only have seam allowance on the sides, so I've clipped all of the sides.
Fold back each "tab" created by your clipping to the wrong side of your pattern piece.
Step 3: Match Up Seams, Join Using Tabs
It's helpful to have notches or a waistline to help you figure out where your pattern pieces match up together. Begin assembling your pieces by finding that match point, then brining a tab from the back of one piece to overlap the front of the second piece. Make sure the two pieces are snuggly together along the stitch line, then tape the tab down.
Move up a little, then bring a tab from the opposite piece up to overlap the front of the other piece. Snug your edges up along the stitch line and tape the tab down. Continue alternating tabs and taping them down until you've come to the end of the seam. You don't need to pull every tab to the front; it's ok to skip a few. In the photo of the inside, you can see I skipped lots of tabs.
Continue adding pieces in this manner. You'll slowly see your corset start to take shape! Once you've got it all together, it's time to test it out and correct errors.
Step 4: Test Your Paper Mockup
I've pinned my mockup to my mannequin, which is already wearing one of my other corsets so that it is more or less squished down to size already. Now this isn't a perfect setup; the corset the mannequin is wearing is a Victorian style, and is very vertical in shape. The corset I'm mocking up in paper is Edwardian, and has an S-curve to it that my poor mannequin can't replicate. It's also meant to be much curvier. That means it isn't going to fit correctly on the mannequin, but we can still get some valuable information from it.
First off, much to my surprise all of the tops and bottoms of each piece meet correctly. I had assumed that since I'd altered the pattern a bit I'd have to true the seams, but this paper mock up shows me that I won't have too. Less work already!
It looks like the corset may be a bit big at the top and bottom edges, but I believe most of that gaping comes from the fact that this is an S-curve corset modeled over a straight Victorian one. Sure enough, holding the paper mockup against my body while standing in the proper posture shows that the sizing is about right. Of course, I can't pull it tight 'cause it's just paper, but it looks like when the corset is fully laced the gaps will disapear. I'll tweak the fit further with a fabric mock up.
The top and bottom lines of the corset are pretty smooth and hit where I want, except at the top back. The two back pieces meet in an awkward point, so I'll want to smooth the line there.
Most importantly, I discovered that my waistline and grain lines were off! I guessed at these back when I was creating the pattern, and my guess has the waistline rising strangely from the side to the front, when it should be level all around. I've marked the bad waistline in green, and I've drawn the corrected waistline in red. I'll transfer the new waistline to my pattern, and adjust the grain of each piece so that it is perpendicular to that new line.
Once you've gone back to your pattern and make your corrections, you can move on to your first fabric mockup knowing that many of the big kinks will already have been worked out!