Half-square triangles are my nemesis. I think I've tried just about every method for making them, and still, I sometimes get mixed results. The key I think is being careful and taking your time, something I don't always want to do when I'm trying to get a quilt done. The other key is choosing a method that'll work best with the quilt you're trying to make.
Here's a handy-dandy method that makes two matching HSTs. Use this method when making blocks that require pairs of lookalike HSTs or scrappy quilts that require a lot of HSTs, like Strawberry Preserves, a quilt from my book Idiot’s Guides: Quilting.
1. Figure out the size of the HSTs you need
For example, take a look at this block. It measures 8” finished (8.5” unfinished). The four HSTs in the corners are 2” finished (2.5” unfinished).
2. Cut two squares of fabric
To figure out the size of the squares to cut, add 1 inch to the finished size of the HSTs in your block. The HSTs in our block are 2” finished, so you need to cut two 3" squares, one pink and one brown.
3. Draw a diagonal line from corner to corner on the back of the lightest square
After drawing the diagonal line, draw two sewing lines on either side of this diagonal line, 1/4-inch away. Marking the sewing lines makes it easier to be precise, especially if you’re a beginner.
A quarter-inch seam marker like the blue one shown here is a must-have for this technique--it really makes the process of marking those lines easier! You can buy them in several sizes, so consider purchasing a set so you can use them regardless of how large the HSTs are in the quilt you’re making.
4. Place the squares right sides together, pin, and sew on the two sewing lines
5. Cut the squares apart on the diagonal line
You don’t have to cut exactly in the middle—just between the two sewing lines.
6. Trim the HSTs to their unfinished size
The HSTs in our block are 2” finished, 2.5” unfinished. So you must trim your HSTs to 2.5 inches.
I use a shortcut to trim HSTs that is superfast and that’s what I’m going to show you now. For this shortcut to work, you’ll need a small square ruler and either some ruler tape or a dry erase marker. You can also use the Quilt in a Day Square Up Ruler to trim your HSTs.
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 2-1/2”, so I’ve marked a diagonal line connecting the 2-1/2” mark on two sides of the square ruler. You can mark this line with ruler tape or with a dry erase marker.
You can skip this marking business if you use a Quilt in a Day Square Up ruler to trim your HSTs, and I'll get to that method in a moment. For now, I'll show you how to trim using your marked square ruler.
Lay the mark you’ve made on the SEAM of your HST triangles and trim. Trim both sides of the HST.
Trimming both sides of a HST means you have to rotary cut horizontally (which is not safe), so I recommend placing the HST on a turntable cutting mat or using a safety glove on your non-cutting hand.
You use the Quilt in a Day ruler the same way, lining up the seam on the HST with the right mark on the ruler and trimming. You just get to skip the marking nonsense because the ruler is already marked for you. If you like, you can save yourself even more time trimming by carefully aligning the top edge of the ruler with the top edge of the HST while also placing the seam on the right ruler mark. Trim the one side and your HST is ready to use!
7. Press toward the dark triangle
Press open or to the dark. Pressing open may help the block to lay flatter--especially if a lot of seams are coming together at the intersections like they do in a pinwheel block.
Trim the dog ears. You can also trim the dog ears off before pressing.
8. Repeat the trimming process on the other HST
You now have two matching half-square triangles, ready for piecing into your block. Of course, our block requires four HSTs, so we’ll start over with two new squares and make the two additional HSTs we need.