Half-Square Triangles: Four at a Time

It seems that just about every quilt I fall in love with includes half-square triangles or HSTs, so it’s no wonder that I constantly experiment with various ways of making them. I’ve learned quite a few different methods for making HSTs over the years, so I simply pull out the one that makes the most sense for the quilt I’m making at the time.

Let me stop for a moment and explain that you don’t have to use the method suggested by a particular quilt pattern when you make HSTs. A lot of patterns suggest that you make HSTs one at a time, by cutting a square diagonally and then sewing those two triangles together. I never use that method because it involves sewing along a bias edge and that makes the method tedious and slow. It is a good method to use though, if you only need one HST or you’re trying to create a quilt that uses HSTs that are each unique.

If you plan on using a different method than a pattern calls for however, you’ll most likely need to cut your fabric in a different size—the size appropriate for the method you do settle on. So decide on the method you want to use before you cut any fabric.

This particular method makes four matching HSTs. It’s an easy method, but it does come with its own unique problems. The main problem is that it's hard (okay, it's math-hard) to figure out how to use this method to make a set of particular-sized half-square triangles. Because of the mystery as to their finished size, I use this method when I'm making a quilt for which it simply doesn’t matter what size the HSTs turn out to be as long as they are all the same size, such as a chevron quilt or the quilt show here, which is basically a bunch of HSTs sewn together.

Before you choose this method, I should also warn you that the resulting HSTs will have bias edges. However, as long as you’re especially careful when pressing and you don’t handle the HSTs too much, everything should work out just fine.

1. Figure out the size of the HSTs you need

I made this quilt in answer to a challenge to use five fat quarters I was given in an exchange. I added a few fabrics of my own to round out the selection, then designed this simple pattern I call Origami Garden.

The quilt uses half-square triangles arranged in a classic barn raising setting (alternating lights and darks that radiate out from the center). The barn-raising setting is one of my favorite ways to set log cabin blocks, and I thought I’d use it in this quilt to set the half-square triangles and achieve a similar result. The HSTs can be any size in such a quilt, but in my quilt, they happen to finish at 4” (4.5” unfinished).

2. Cut two squares

Okay, this is the hard part. Take the unfinished size you need, and divide that by .64. I know, it’s a weird number, but with a calculator, it’s easily manageable. My quilt uses HSTs that are 4” finished and 4.5” unfinished, so I divided 4.5 by .64 and got 7.03, so I’ll cut two 7 1/8” squares.

3. Pin the two squares together right sides facing, and sew around the perimeter

Place the two squares together, right sides facing each other. Pin in the center of the squares so they don’t shift.

Sew along the edge of the squares, all the way around. Use a quarter-inch foot to help guide you. If your machine has the feature, set it for needle-down to help you turn the corners.

4. Cut the squares on the diagonal in both directions

Line up your ruler and cut the squares on the diagonal in one direction. Then, without picking the squares up, turn the cutting mat and cut the squares on the diagonal in the other direction.

5. Trim the HSTs to their Unfinished Size

This method does not result in HSTs in the size you often need for common quilt blocks. That’s why most peopleuse this method for quilts in which the HSTs are all the same size, even if they are not a common size. In such cases, all you need to do at this point is to trim off the dog ears (the triangles of fabric that stick out at two corners).

If however, you are trying to create HSTs that finish in a particular size, you will need to trim the HSTs more precisely. The HSTs in our block are 4” finished, 4.5” unfinished. So we’ll must trim the HSTs to exactly 4.5 inches (the unfinished size).

I use a shortcut to trim HSTs that is superfast but requires a small square ruler and either some ruler tape/dry erase marker, or the Quilt in a Day Square Up Ruler.

If you don’t own the Quilt in a Day ruler or you don’t want to mark your square ruler, you can trim your HSTs the conventional way—after pressing. Jump over here if you prefer to trim your HSTs after pressing.

Still here? OK, here goes. Again, your HSTs are not pressed yet. Mark a line on your square ruler connecting the marks on the ruler that match your HSTs unfinished size. I want to trim my HSTs to 4-1/2”, so I’ve marked a diagonal line connecting the 4-1/2” mark on two sides of the square ruler. You can mark this line with ruler tape or with a dry erase marker.

Lay the mark you've made on the SEAM of your HST and trim both sides.

Trimming both sides is a dangerous business because you cut across yourself, towards your hand. For this reason I recommend placing the ST on a turntable cutting mat or using a safety glove on your non-cutting hand.

If you have the Quilt in a Day ruler, you follow the same procedure--just line up the mark on the ruler (in this case, the 4-1/2" mark) with the seam of your HST and trim both sides.

You can save yourself even more time when trimming by aligning one edge of the ruler with the edge of the HST, placing the mark on the seam, and trimming the other side.

6. Press the HSTs

Before you press, lightly starch the HSTs to prevent stretching them. Remember, you’re dealing with bias edges here, so it helps to be cautious. Press the HSTs open or to the dark. Use good pressing methods here (an up and down pressing motion, and not a back and forth one).

After pressing you'll notice dog ears, so be sure to trim them. You can also trim the dog ears off before pressing, when your trimming your HSTs to the right size.

7. Repeat the trimming process on the other HSTs

You now have four matching half-square triangles, ready for piecing together.

To help you create HSTs using this method, here are some common finished sizes along with the size squares to cut. Remember that we’re dividing by .64 and that this method is anything but precise. If you’re trying to get an exact finished size, you’ll most likely need to trim the resulting HSTs to that size.

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