Friday, October 24, 2014

Crossover Pleat Circle Skirt Draft Along 3: Math & Measurements


DREADED MATH

Circle skirts have varying fullness depending on whether we use the full circle for drafting, or only a part (segment) of it.

Most common variations are a full circle skirt, a three-quarter skirt, a half-circle skirt and a quarter-circle skirt, with the last one having the least fullness.


The waistline is defined by the inner circle, and the hem line by the larger outer circle. The distance from the circle center to the circle's edge, or radius, is calculated using a simple mathematic formula
r = C / 2π
r = radius 
C = circle circumference (in our draft-along - the waist circumference) 
π = 3,14 (which, by definition, is a constant number that represents the ratio of the circle circumference to its diameter)

The last formula is used to draw a full circle skirt. But what if we want to draft only a 1/2 circle skirt?
r = C / π  (which is derived from r = 2C / 2π)

A 1/4 circle:
r = 2C / π (from r = 4C / 2π)
As you can see that we need larger radius for less flare.


But what do we do about 3/4 circle?
r = 2C / 3π (from r  = 4C / (3 x 2π)

What we got here is a fraction that represent the part of the circle, which in our formula is turned around.  For quarter circle, for example, we could also write  1/4 r = C / 2 π, which is the same as r = 4C / 2π. Understanding this principle helps you draft a skirt with any amount of flare you want.

Now, our skirt is 3/8 circle

Note that the radii and, accordingly, the circles here will be much larger than the ones for the circle skirt, even though they appear to be are the same size as on the previous illustration
r = 8C / (3 x 2π), or r = 4C / 3π

I apologize for the nerdy language here. If you are fed up with the math this is the only formula we will use for our 3/8 circle skirt:
r = 4C / 3π 


MEASUREMENTS:

For the master pattern, which can be then used for lining or petticoat as is, we will need the following measurements (I am using mine as an example):
W (waist circumference without ease) = 71 cm 
H (hip circumference) = 105 cm 
Lf (length front) = 58 cm 
Lb (length back) = 59 cm 
Ls (length side) = 60 cm
I am using the waist circumference without the ease (2cm as a rule for other skirt styles) here. The reason is that when handling the fabric we will inevitably end up with slightly wider waistline because most of it is on the bias. Most formulas I have seen in pattern drafting books accommodate for this stretching in some way. In addition, I usually stay the waistline before cutting off the fabric wedges next to the waistline.

CALCULATIONS

We need to calculate the radius for our smaller 'waistline' circle.
r = (4 x 71) / (3 x 3.14) = 284 / 9.42 = 30.1
Please use decimal numbers for accuracy and speed! I am rounding down the final result, keeping only tenths

In the next post, I will show how I draft the 3/8 master pattern, as well as explain the grainline options. Leave a comment with any questions here, or, preferably, in a dedicated thread on the Couture Collective forum. Please, also let me know if you noticed any typos  - I am lacking sleep lately 

P.S. Thanks to Nancy K for a great tip on where to get a cheaper tracing paper: http://www.nationwidedrafting.com/store/sketchandartpaper.html. This is a less durable light-weigh sketch paper. She buys 24" wide x 50 yards

8 comments:

  1. Right, the first part was quite confusing for me as a maths-fobic person, I think if I were folding a piece of paper and working it all out physically it would be easier. But I have managed to follow and complete the calculation, so it's all good. Thank you. I would never have worked this out for myself. I will read it all again when I have had some more coffee!

    ReplyDelete
  2. Thanks for doing this draft along. Your explanation of the math is very clear, and I didn't have any problem figuring out the waistline. My question is how you decided on the length of approximately 60 cm and why the front, back, and side are all slightly different.

    ReplyDelete

LinkWithin

Related Posts Plugin for WordPress, Blogger...