Geometry is important in pattern making. I know I go off about that a lot, but it’s true, and it’s why I’m obsessive about squaring corners. Here’s the thing: if your corners aren’t square, then your seams won’t meet squarely. When your seams don’t meet squarely, you get weird looking edges on your sewn piece.
Here are examples of the two most common mistakes I see from students truing up drafts. Check the waistline action:
And here is what happens: when seams don’t meet squarely, you get peaks and valleys.
How many of us have done this with bodice straps? *sheepishly-raises-hand* I was young! I was new at this!
This is annoying at a waist or a strap, but imagine it happening at the side seam/armscye area. Try setting that sleeve! It’s not awesome, people. :( To prevent it, make sure that the corners of your draft are square. It’s easy to check with a gridded ruler. The whole line doesn’t have to be square, as you can see in our waistline examples – it’s better for a straighter line to be square for some length (like our waistline), but a curve (like an armscye) just needs to be square for a moment at the corner.
For my fellow geometry nerds, there’s a caveat: technically, as long as the angles of the two pieces in the seam add up to 180 degrees, you’re fine. Go nuts, dare to be festive, draft dangerously! If you’re not sure what that means, of you can’t quite remember why 180 is important in geometry, then stick with squares. You can’t go wrong when your seams meet squarely, and also you won’t need a protractor; just your gridded ruler. ;)
So, can you just guess how insane it makes me that the 1/2 scale slopers in the text we use aren’t squared at the side seam and center front neck? Nnnnngggggrrrrr!!!!! *falls-on-hands-and-knees-pounding-the-earth-shouting-why-god-why?!?* (Yes, it really is that dramatic of a thing for me.) I keep reflexively squaring them. I try to stop myself, especially when I’m doing a demo, but it so hurts my OCD. :/