COMMON PATTERNMAKING METHODS
Patternmaking books don't help much either. Most authors don't explain the drafting process, which makes drafting for individual figure rather difficult.
Kenneth D. King drafts front half an inch (1.2 cm) wider than the back.
Mueller & Son, a major European patternmaking and publishing company, works with equal back and front measurements, for a
Helen Joseph Armstrong (Patternmaking for Fashion Design) measures the back and the front hip width on a dress form, which makes it a little more accurate, but doesn't guarantee a straight side seam in the top portion of the skirt sloper.
Dennic Chunman Lo (Patternmaking, Portfolio Series) also divides the hip circumference in half.
WHY SHOULD WE CARE AT ALL?
BACK TO OUR EXAMPLES
A. It should be straight and perpendicular to the floor, all the way from the waist to the hem. Common patternmaking methods give you a straight side seam from the hip line, but the top portion is often distorted.
B. To get a perfectly straight seam, we will place so it divides the waist in half (as in illustration below).
Moving the side seam to the front or to the back is a personal design decision, which doesn't affect the fit as long as it is not moved too far from the original position. If you want to know more, read this post. It will give you an idea. For now, to make things easier, we will not be moving the seam anywhere.
Since we have an accurate starting point for the side seam, all we need to do is determine the front and the back width. And because we have measured and adjusted our dart values, we can now very easily and accurately calculate the exact placement of the side seam.
Let's look carefully at some of the important points in the above illustration. Front waist section is equal the back waist section. If we drop down perpendicular lines from the waist, we will see that the blue-shaded rectangular areas are as wide as our dart intakes. Logically, the difference between the front and back pattern pieces is the same as the difference between the front and back dart intakes.
Back width - front width = BI - FI ( see the Dart Calculation post)
When calculating back and front width, we will need to add or subtract only half of this difference (since we have to distribute this difference between two pieces). This will take care of an accurately perpendicular side seam, all the way from the waist, through hips, to the skirt hem.
BW = (Hip circumference : 4) + ((BI - FI) : 2)
FW = (Hip circumference : 4) - ((BI -FI) : 2)
Note: BW and FW refer to the width of the back and front pattern pieces, which is only half of the Back or Front body circumference. When you add BW and FW you should get half hip circumference - it's always useful to cross check, as one of my readers did and found the typo in this post, which is now corrected. Thanks!
You don't need to worry if your tummy is bigger than your buttocks. This formula takes care of it by producing a negative value for the dart intake difference and, consequently, changing the plus and minus signs in the formula.
Phew, that was our last calculation post, readers. Do review the previous installments, as we will be doing our full measurement session next. A measurement and calculations sheet will be included.
Previous Straight Skirt Draft Along (SSDA) posts:
SSDA 10: The Measuring Session Summarized
SSDA 11: Drafting the Skirt
SSDA 12: Making a Toile and Analyzing the Fit