More Triangle Magic: Split Square Triangles, Hourglass, and Quarter Square Triangles

If you have ever tried to sew along a bias cut (not straight with the grain), you have probably wondered why your measurements seem to be off. It isn’t you. The bias s-t-r-e-t-c-h-e-s, which causes us to question our sanity or our ability to properly use a ruler.

Starch helps, so I generally recommend it, but it isn’t foolproof, unless you use so much it is like stitching through cardstock.

That is why I love making half square triangles (HSTs) several at a time (see 2, 4, 6, 8 – Half Square Triangles). It minimizes that bias issue and my level of frustration.

But what do you do for blocks that have more than two triangles? Three of the more troublesome ones are split square triangles, hourglass, and quarter square triangles. That triangle magic we learned earlier works here, with a few modifications.

Get your cheat sheet here

Split Square Triangles (SST)

Let’s take these one at a time, starting with split square triangles (SST). An SST looks a lot like an HST, but the triangle on one side is made of two smaller triangles. How does that happen? We start with an HST and a plain square.

1. Trim your HST to 1 inch larger than the finished size and cut a plain square the same size. No 1/8 inches to fuss with! Place them right sides together.
2. On the back of the square, draw a diagonal line. Make sure it is perpendicular to the original seam. That’s the trick!
3. Sew 1/4″ on both sides of the line, then cut on the line.
4. Now look what happens when you open them up: two split square triangles! They’re not identical. They’re mirror images, so check your pattern before you sew to see which one you need, or plan to use both.
5. Press and trim to the unfinished size.

Those mirror images are the trick to the Pages Upon Pages pattern.

Watch it at the start of the video above.

Hourglass

What happens if you sew two identical HSTs together? They make two identical quarter square triangles (QST): the hourglass.

1. Place two identical HSTs right sides together, making sure the like fabrics are not together. Nest your seams.
2. Draw a line on the back, corner to corner, perpendicular to the original seam.
3. Sew 1/4″ on both sides of the line, then cut on the line.
4. Open them up, and what do we get? Two identical QSTs, often called hourglasses! Spin the seams so each one goes in the opposite direction, making a little pinwheel on the back. It helps them lay flatter.
5. Press and trim to the unfinished size, centering the seam intersection.

Watch it at 0:52 in the video above.

Quarter Square Triangles (QST)

What happens if we put two different HSTs together? Let’s find out! Use the same steps as the hourglass. This time the two QSTs are not the same. They are mirror images of each other – like the SST.

So lay them out before you sew and check which one your design needs. If you need identical QST for your project, make sure to double the number of HST you need. Use the extra as bonus blocks for another quilt – or maybe a pillow sham.

Watch it at 1:56 in the video above.

Trimming Tip

Trimming is ALWAYS best. Seam allowances are unreliable no matter how many gizmos you use to keep them straight: a 1/4″ foot, guards, laser lights. We are human, for goodness sake! We aren’t perfect, and neither are our seams.

Line the ruler’s 45-degree line up with one diagonal seam and make sure the seam crossing sits at the center before you cut. That’s half the unfinished size: for a 3 1/2-inch unit, the crossing sits at 1 3/4 inches.

Sizes and Cutting Chart

Cut your squares 1 1/2″ larger than the desired finished unit. It is the same math as the 2, 4, 6, 8 article, just doubled. You need 1/2″ for the straight seams plus another 3/8″ for each diagonal seam, which we round to 1/2″ for easy math. Three times 1/2″ is 1 1/2″. Trim the blocks as needed to get the right size. Just make sure to center the seam intersection when trimming.

Make your HSTs two at a time from these squares using the two at a time method. You can use other methods for more blocks at a time. Just make your HSTs at least 1” larger than the finished unit, using that method’s chart.

I usually don’t trim them at this point. But if you’re uncomfortable with that, or want to be sure, trim them to at least 1 inch larger than the finished size. That still leaves room to trim after the second seam. Just like with HSTs, put the diagonal line of your quilting square on the seam to keep the square balanced. For split square triangles, trim the HST and cut the plain square to the same size.

All sizes in inches. Two HSTs make two hourglasses or two QSTs. One HST plus a plain square makes two split square triangles.

Get your cheat sheet here!

 

 

Happy Quilting!