Like I said here, armholes and sleeves are very tricky. Their tricky not so much because of the sewing, although distributing the 1/2″-3/4″ of sleeve cap ease evenly can be challenging, but because there are so many components that have to “fit” together in order for a sleeve and an armhole to look impeccable. One component is the shape of the sleeve cap. From shoulder to underarm, it changes from a concave curve to a convex curve. How much it curves and the length of the curve determines sleeve cap ease.
Another component, and the topic of this post, is the balance of the armhole. When drafting the front and back bodice block, the back armhole should be ½”-5/8” longer/bigger than the front armhole (measuring along the curve). Everyone’s body is different, yes, but there are certain guidelines to consider – but not live by – when it comes to armholes and this is one of them. The back armhole should be longer because it covers the hump over the back.
Achieving a balanced armhole usually isn’t a problem when drafting a front and a back bodice block. It’s when darts on a block are manipulated when things get hairy. As you can see on Liz’s block, there are many darts that can be manipulated to create different designs or silhouettes. A common mistake is to raise the front armhole when “darting” out the bust dart (this is done a lot on knits as knits don’t need bust darts due to the nature of the fabric). As shown on the sketch, this is wrong and throws off the balance of the armhole. It results in the front armhole being higher than the back armhole and because of this, the back armhole is pulled up to meet the front armhole, causing diagonal drag lines on the back.
The correction is easy. There are several ways to determine if the balance of the your armhole is off. First, check to see if there are diagonal draglines on the back. Diagonal draglines could be a sign of many pattern making problems but the draglines for this problem will “originate” or “point” to the armhole base. As a fitter, you’ll want to “pick up” or “take out” excess at the center back near the lower back. Another way to determine if the balance is off is to measure the front and the back armhole – along the curve – and see if the back armhole is more than 1/2″ to 5/8″ longer than the front armhole. The best way to determine if the balance is off is to cut the side seam from bottom opening to armhole base and let the fabric fall naturally. It’s super cool to see, and I sound like a total pattern making geek saying that, but the front panel will shift up, the back panel will shift down, and the drag lines will disappear. This is where the garment wants to be. This will also tell you how much to lower the back armhole and reduce the front panel at bottom opening, which is the correction for such this problem (shown in diagram above).
Oh sleeves and armholes! What are we going to do with you?