As you probably have surmised, a circle skirt is just a big doughnut, with the waist measurement as the circumference of the inner circle and the length as the distance between the inner and outer circles. When you change this to a skirt that is less than a full circle, you now have just a segment of a circle (an arc) as your inner and outer measurements, so instead of using the formula for the circumference of a circle to find the radius of your inner arc, you need the formula for arc length. I'm not going to bore you with derivations and reductions (although if you are interested, here is where I got my geometry refresher), but the formula you'll need to draft your pattern is this:
r(radius)=360l(arc length)/2 pi m(angle).If that makes you nervous, don't worry! I'm going to take you through the steps for a 1/2 or 3/4 circle skirt. It'll be easy! Stick with me.
OK, here is the info that you will need: Your waist measurement (That is, where you want the skirt to sit) and the final length that you want your skirt. Measure this from your waist to wherever you want the skirt to end. Let's get to work! I'm going to show you how to draft the waist part of the1/2 and 3/4 circle skirt.
If you've already watched the video on the Circle Skirt tutorial, then you are ready to start. If you haven't please go there and watch it, so that you know what I'm talking about. Don't worry, it's short. The first thing that we need to calculate is the radius of our inner arc. The formula up there will give it to us. For the 1/2 circle m=180 and for the 3/4 circle m=270. The formula you will need to use is:
r=l/pi for the 1/2 circleFor example, if your waist measurement is 26, you would have a 8.3 inch radius for your 1/2 circle skirt and a 5.5 inch radius for your 3/4 circle skirt.
r=(2l)/(3 pi) for the 3/4 circle
where l=your waist measurement.
Now, we have to draft. The first thing to do is choose a midpoint on your drafting paper, and draw lines representing the edges of your skirt. For the 1/2 circle, that would be a straight line (that is a 180 degree angle)
For the waist measurement, you already know what to do if you watched the video. Use the radius you calculated to draw the arc you need for your waist measurement. Here's what it looks like with our hypothetical 26 inch waist.
For the 1/2 circle,
Now to finish your skirt, head over to the original tutorial to see how to subdivide your pattern piece into panels, and how to construct your skirt. I hope this is helpful!