The easiest way to make a snowball block is with small corner squares that are stitched across the diagonal, trimmed, and then flipped open to form corner triangles. While this method uses more fabric than sewing triangles, I find it fast and easy. All you need is one big square and 4 small squares for the corners. No bias edges to contend with.
So you might be asking how do you know what size small square to use? Well, the size is often determined by the quilt setting you are using. Because a snowball block is frequently paired with another block in an alternating setting, the size of the corners is usually determined by the breakdown of the alternate block. In other words, If the alternate block is a 9-patch block, then the side of the snowball block is divided by three. If the alternate block is a 16-patch, then the side of the snowball block is divided by four. Here's a great source for determining the size of the corner squares for various sized snowball blocks.
The most common sizing for a snowball block calls for dividing the finished size of the block by three and then adding a half inch seam allowance. This would then align with a 9-patch block as shown above left. Whatever number you are dividing by you will still add 1/2" seam allowance. For my quilt the finished block size is 6" so the squares would be cut 2 1/2" x 2 1/2". (6 divided by 3 equals 2 plus 1/2" equals 2 1/2")
Since my quilt is made entirely of snowball blocks, the size of the small corner squares didn't matter so much. The triangles didn't need to line up with any points on an alternate block, they simply line up with each other.
I started with the typical directions and made a sample block using the 2 1/2" corner squares. It didn't really seem as much like an octagon as I wanted. All eight sides of the octagon aren't the same length. Of course they'll change a little once the seam allowances are taken into account but it still wasn't going to be a true octagon. Here's what it looked like.
Wanting a more true octagon, I turned to my computer to see if I could figure out a better size for the corners. Since I didn't know the mathematical way to draw an octagon in Illustrator, I estimated using a small grid. For my finished 6" block I found that if my corner squares were cut 2 1/4" the end result was as close to a true octagon as I could get. In other words all eight sides were of equal length. You can see the difference below between the 2 1/2" square (left) and the 2 1/4" square (right). The one on the right is closer to a true equal sided octagon.
I know this is a small thing to some of you, but it was worth the effort to me. Not to mention I could get more small squares from my yardage so I needed less fabric. All together I need 900+ of the small squares so I have a lot of cutting to do.
Until then, I'm curious, have you ever made a quilt that included snowball blocks?
I'm linking up this week to Needle and Thread Thursday at My Quilt Infatuation. It's been far too long since I've played along. Hop over and see Kelly's latest quilt finish.