08/10/2024
今天找到一份很好文章分享給大家
Math Is Everything
Ok so here's one for you that I bet most pattern designers never ever think about, and why math is so important. This one might be a bit over most people's heads, but if your mathematically inclined then you may enjoy it!
When we create a lower block for a one piece we rarely create a leg line that goes as far as the fullest hips line ... indeed it'll likely be somewhere about halfway. Take a look at the first image below ... the leg line is about halfway up the side seem between fullest hips and the waist.
When I create a swimwear block I use 12% negative ease ... all over ... but in the case of the lower half of the block, the leg hole is actually the same as a cut out, meaning we need to lower the ease or the center front and back seat will try and narrow and become rippled (parallel to where the tension anchors). So I personally (different to fashion school) create a block with only half the horizontal negative ease at the fullest hips ... or just 6%. I want some horizontal in there still because I don't want the front crotch area over extending vertically. In the image pink represents 0% negative ease at the hips, green 6% and orange 12%. In this way the angle of the side seam is generally correct for ready to wear ... for custom you'd probably contour it out to a convex line just slightly.
But what if I wanted to lower my leg line considerably, to say that of the second image below? Then we wouldn't really consider the leg hole to be much of a cut out (it still is slightly) ... so wouldn't we choose somewhere around 9% now? Indeed we would.
Take a look at image number 3. I've put a point at half-way down the side seam to fullest hips and re-angled the lower half of the orange line to 12% ... that way I have 9% at the edge of the leg line (geometry) ... so I then redraw my side seam (black dashed line) from the waist to the intersection of orange with the leg line. Bare with me.
Why is this so important? It's about micro managing tension when you change leg line heights in order to prevent shear. One only needs about 3 degrees out at a side seam for shear ripples to pop up ...and if they do you'll never find the cause if you don't understand how tension works.
So let's keep going. Image 4 shows the dotted line (now orange from black and extended to the hip line) as the new side seam with the front and back together. The angle from side seam to horizontal is 76.5 degrees. Take a look at image 5 ... this is the original blocks 6% line ... the angle to the side seam is now 71.7 degrees ... a difference of 4.8 degrees each side or 9.6 degrees total on each side .... and that's more than enough to start propagating shear ripples!
I do have a tutorial on ripples planned, but this is just to show you that the tiniest little difference can cause a huge problem that you would never be able to resolve if you don't understand how simply adding cut-outs in a particular position on the body can create shear and instability. I know this is a bit advanced for most, but next time you see a garment full of cut outs placed willy-nilly with ripples running all over the place you'll start to see tension at play ... and it's my job to get you to see it!
