To start off, we need to do a little math. It's very handy that the waist/hip ratio in my example is exactly the same as the waist/hip ratio on my chart: 10" difference. If your ratio is different, I will mention what to do about that in a few steps, but for now we are going to need only the waist numbers.
We need to find out how much difference there is between the waist measurement and the chart. Subtract the chart size 18 (38") from your measurement and divide the difference by 4.
The result is how much we need to add to the pattern, both front and back.
Make a long strip, 3 3/4" wide (per my example, your number may be different) that we can tape to our pattern. I used my cutting board grid to draw the first line, and then I'll measure across and make some dash marks to follow all the way down. Don't trust your board to measure for you. They are great for making straight lines, but as you can see, the squares on my board are not accurate.
Now connect your dash marks, creating two parallel lines.
Here are my two lines with 3 3/4" between them.
With the yoke front, match up the first line with the center front line on the yoke. Tape in place.
Using the grid board and your ruler, square off the top and bottom, extending the yoke pattern.
Relabel your pattern markings. Cross out the old labeling so you will know what to do if you use this pattern again in the future. Your pattern should look like this. In my example, I need to cut from the extension and follow the size 18 cut line.
If your waist hip ratio is smaller than 10", cut the size 18 and make any needed changes during fittings. If your waist/hip ratio is larger, it is at this point you would reshape the hip curve at the side seam, adding width to the bottom of the pattern (1/4 of the
ratio difference), tapering from nothing at the waist. For example, if your waist/hip difference is 12" (2" more than the 10" pattern ratio), 2" divided by 4 = 1/2" needs to be added to the hip at the side seam.
Follow the same procedure for the back yoke. Use the grid board and the ruler to line up and move the notches to the new location.
The grain line stays the same. Cross out the old center back and cut line. Make any needed adjustment to the hip at the side seam as you did with the front yoke.
Now we move on to the skirt pattern. I've taped on the 3 3/4" strip to the pattern center front.
In order to keep the skirt flare evenly divided, I'm going to split the extension more or less in half by drawing a line down the middle. Mine is divided into 2" and 1 3/4" strips.
To sew the skirt, I recommend a different order of operations from the booklet that comes with your pattern. Sew the skirt front to the yoke front, and the skirt back to the yoke back first. Then sew the side seams and center back seam so that you'll be better able to test the fit and alter it at the side seam in one step. I also recommend a full 9" or 12" zipper, which will provide for easier access in and out of your spin skirt.
I'm excited, so sent me photos! Let me know this tutorial was useful to you.
Happy Sewing Day!