I haven’t been able to stop thinking about sleeve caps and armscyes since I read Kathleen Fasanella’s fascinating p0st Sleeve cap ease is bogus on Friday.
Most of my RTW (ready to wear) pieces fit poorly at this interface, which is why I hate RTW!
At church Sunday, daydreaming during communion, I saw approximately 150 RTW sleeve cap/armscye interfaces go by and estimated that 9 out of 10 of them fit poorly.
I asked Martin to explain why Kathleen’s modified sleeve cap pattern is more anatomically correct and he reminded about conic sections.
If you pretend your arms are the cones and the bisecting planes are the sides of your body where your arms attach, it’s easy to visualize how rotating the cones (keeping the planes in the same position) to approximate the way our arms move will change the shape of the armholes.
It’s hard to see in the above diagram because the planes are moving, not the cones, but you can see that any change in the angle of intersection, of either the cone or the plane, or of both, changes the shape of the intersection.
This animation (viewable using Windows Media Player — I didn’t test other players) illustrates the idea in motion.
In the case of our bodies, our core trunk is fixed. It’s our arms that move, dynamically changing the shape of intersection.
As Kathleen Fasanella points out, since our arms don’t hang at our our sides but are hanging slightly forward on our bodies, the shape of the sleeve cap/armscye intersection needs to approximate that positioning.
Let’s see how this looks in three dimensions, assuming an x, y, z axis (z is the depth, or near/far axis).
Relating Kathleen’s post back to conic sections, I see two discrete position changes, from the standard sleeve pattern, affecting shape: 1) a depth (near/far) translation of the hanging arm slightly forward along the z axis towards the front of the body (think of rolling clothes in on a clothes line), and 2) a slight x, z arm rotation forward and outward reflecting the fact that our arm pits face forward, not sideways, when our arms are raised over our heads.
To visualize these position changes in 3-D I made two 3-D paper sleeves following Kathleen’s instructions.
First, I hand sketched a copy of Kathleen’s drawing of the typical sleeve pattern and added a dotted line approximating her suggested changes to make the pattern more anatomically correct.
Second, I made two paper sleeves based on the original and modified patterns.
Obviously, in real life, the bottom of our sleeves don’t make a perfect horizontal intersection with a plane, as pictured here, but let’s pretend they do so we can stand them up (any angle at all would make them fall right over).
Can you see that the sleeve opening on the right intersects an invisible plane at a completely different angle than the more anatomically correct one on the left?
Can you see that the way the sleeve opening on the left intersects an invisible plane is a better approximation of how our arms actually hang on our bodies? You kind of have to imagine yourself doing a one-arm hand stand, on your side, with the arm ending not in your hand but in a flat surface, as pictured, to get the idea.
Since it’s not possible to design a sleeve cap/armscye for every shape our arms create as we move, pattern makers like (hopefully) us need to settle on approximating one shape, usually the shape created as our arms hang at our sides, at rest, then add some ease so our arms can move freely in the garment.