Monday, October 26, 2009

Reply to nanny2cole

Corrected 10/31/09 to add a couple of clarifications.

Reader nanny2cole is trying to figure out the formula on Leslie's Broomstick Skirt that I posted a while ago:

HELP!!! I got the formula to arive at "X=" but I don't understand how to get to "Y=". Y= (W/2 - 2X) /3. Am I suppose to double "X"? I'm a little lost.

Well, yes and no. OK, you've selected the 10 panel version.
W/2 = width of fabric divided by 2.
2x = x multiplied by 2, in other words, the width of the top edge of the panel.

Let's do an example with numbers:
W= 44"
W/2 = 22"
Let's just assume that x = 4", so 2x = 8"
22"- 8" = 14"
14"/3 = 4.67". This is Y.

So OK, you've got X = 4" and Y = 4.67" and you're ready to draw the pattern piece:

On your pattern paper, draw a long straight line equal to L, your desired skirt length plus 1 inch. This will be the center of your trapezoid and will be on the straight of grain when placed on your fabric. At one end of the line measure out at right angles your calculated distance x. Make a big dot. Do this on both sides of the line and connect the dots.

At the opposite side of line L, perform the same operation, but use your calculated y value this time. You should have a figure that looks like the capital letter "I" but with the base wider than the top. Connect each top dot with a bottom dots and you should see a trapezoid. Using the example above, the top of the trapezoid will be x times 2, or 8 inches. The bottom of the trapezoid will be y times 2, or 9.34 inches.

Yes, it's a long and skinny piece, considering that the finished length of my skirt is 35-1/2 inches. And it's designed to fit the width of your fabric, which is why the width of the fabric comes into the formula.


Claire S. said...

I've tried this as well and got hung up on the numbers.

In your example in this post, your piece will measure 8" at the top & 9.34" at the bottom -

If I use the 10 panel option and plug in a 42" hip (Ct) measurement, my X = 2.35. I get this (if you double it and multiply it by the number of panels, it equals the hip measurement)

I used 45" as the fabric width in the calculation and came up with Y = 5.93

My trapezoid is 4.7" at the top and 11.86 at the bottom which is not the long skinny piece I thought it would be.

Any idea where I went wrong, or is this, in fact, a normal shaped piece?

Thanks for your help.

Nancy (nanflan) said...

Those are the numbers I get as well. I even went back to the original print out and got the same numbers. Also, for what it's worth, I went back to the original pattern I drafted way back when and it measures 5" at the top and 11-5/8" at the bottom. This is the piece I used to make the black and turquoise skirt in the original post. Keep in mind, the finished length of that skirt is approximately 35-1/2" long, so I would describe the pattern piece as long and narrow.

Claire S. said...

I don't know why I froze when I got my X/Y values :-( The final shape of the pattern just looked 'funny'. I really want to make one of these, so thank you very much for taking the time to verify the numbers for me :-)