Saturday, May 24, 2014

SSDA 9: The side seam dilemma, or demystifying the front and back width

Let's talk about side seam placement. Should it be moved slightly to the back? or, maybe, to the front? In other words, should the front and back pattern pieces be equal, or should one of them be bigger.

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 dress form regular body.

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?

A skirt is easy to fit... and most people don't even see or care where the side seam is. However, correct side seam placement is a foundation for more complex styles, such as trousers and dresses.


BACK TO OUR EXAMPLES

Where do YOU think the (vertical) side seam should be located? I mean, before we start adding or subtracting arbitrary numbers, should not we have a visual idea how our side seam should look like?

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:


Coming up:

SSDA 10: The Measuring Session Summarized
SSDA 11: Drafting the Skirt
SSDA 12: Making a Toile and Analyzing the Fit

18 comments:

  1. Thank you so much for taking the considerable time to put this together. I am devouring every word and can't wait to muslin my draft and see the outcome.

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    Replies
    1. I am glad you are following despite my slow pace. It just takes time to find the best way to explain it all :)

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  2. You are such a great resource and so generous with your knowledge! A national (sewing) treasure.

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    1. Thank you :)) I should frame your comment!

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  3. Thinking. This would not apply to pants, would it?

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  4. It would! You are using the same hip block in pants as in a skirt, so all you need to work on is the crotch curve. I may make a few posts about it in winter.

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    1. I can totally see it for skirts from the hip up, but pant from the leg crease down wouldn't divide the same as hips, right? If I divided a waist with a large tum combined with a lesser protruding bottom, then setting the side based on an equal division at the waist might have more front on the leg. We bend our legs in the front when we walk & sit so less fabric to bunch up at the front leg break point would be preferable. As a petite plus, I have this issue with pants...usually it's the leg that's correct, and the whole hip section is at odds.
      I really want to thank you for discussing this - it's really helping me to understand how hip fit should be measured. It also happened to coincide with my discovering Lekala patterns, who does measure the hip just as you describe! The other interesting thing they do is take a second measure for the actual hip, not including the abdomen. I'm wondering if that's how they decide where to move the side seam from the hip break up.
      I look forward to anything you have to offer on engineering the crotch curve.

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  5. When I was working on getting my pant draft to fit well I learned that they were not hanging straight from the hip at the side seam.. I picked a place at my waist where I wanted my side seam to be and used a plumb bob to figure out where my the rest of my side seam needed to be. I had to move the side seam and inseam the same amount. I know that there are methods of drafting pants that use a skirt sloper to start with. If you have a perfectly hanging skirt I would think that it would be easier to get to a good pair of pants.

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    1. Interesting, Nancy. What method is this? What I am describing is the most basic way of using a reference point (mid waist from the side) as a starting point for a perpendicular side seam. Depending on a figure, the side seam can be moved either to the front or to the back at a later stage, once you can assess the look on a muslin. This can happen without any effect on the fit, as well as without any changes in dart intakes.

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    2. Claire Kennedy suggested that my pants were not hanging correctly causing some fit issue in the leg. I found that the easiest way to mark what I was seeing was with a plumb bob and my dh marking where it hit my ankle. It was in front of the seam at the ankle. I have a very flat rear end so it's easy to get the seam too far to the rear and I moved it forward for a more flattering fit. It worked.

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  6. This is a most interesting post. Thank you for sharing your sewing knowledge.

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  7. Very interesting post, Marina. Thank you so much. You are informing so many so well.

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  8. I took a week-long course with Dennic Lo on drafting patterns to your measurements, which I really enjoyed. Afterwards I bought his book to supplement it (although I've not really read through it!). So I was surprised to hear that he divides the hip circumference in half in the book. The skirt sloper I drafted during that course has a wider front than back, that is, the side seam has been moved towards the back of the skirt. This was done on his instruction, and was explained as an aesthetic feature so that the seam was not visible standing front on (as you allude to above). At the time it seemed as though this was his personal preference, so it is interesting that his book doesn't offer this as an option.

    Really enjoying this series of posts.

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  9. This series is exactly what I have been looking for. I never could figure out how to account for my belly/thighs in the front when drafting a skirt block.

    Question though, the final calculations are not working for me. Shouldn't Front Width + Back Width = Hip Circumference? To get that, I had to do

    BW = (Hip Circumference+(BI-FI))/2
    FW = (Hip Circumference-(BI-FI))/2

    I'm sure this will all make sense when you write the next post, but since I was trying to draft a block using your posts this weekend I thought I would ask.

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    1. Sorry for the typo. This is the correct formula

      BW = (Hip circumference : 4) + ((BI - FI) : 2)
      FW = (Hip circumference : 4) - ((BI -FI) : 2)

      BW and FW refer to the width of the corresponding pattern pieces for half body. When you add BW and FW you should get half hip circumference.

      I hope this explains it. I plan to finish the posts this week, hope nothing comes in-between, so wait until Thursday with drafting until I post the drafting sequence. :) ANd please let me know if the formula works now.

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