How to trim half square triangles is a basic quilting skill that, at least at some point in your quilting career, you will probably have to figure out. There are different ways to sew, press and trim half square triangles, but let me tell you, as someone who has made thousands of these wonderful blocks, I have recently landed on a favorite way to do it.
What makes this technique the best way to trim half square triangles? Easy – it's fast and accurate, saving me time and making me look good in the process. Double win!
Most quilt patterns will instruct you on how to sew half square triangles, but the trimming and pressing is more or less up to you and your prefered method. So how does one take some cut squares like this...
...and turn them into a beautiful quilt like this?
The quilt featured here is the Gather quilt pattern and can be purchased in the shop!
The answer is not a wag of the finger telling you to go slowly and always measure twice before you trim. Oh no, no, no. Please don't measure each of your blocks twice! The answer, is in fact, switching up the order in which we typically make these blocks.
In a past blog post on trimming HSTs (half square triangles) I sewed my blocks, pressed my blocks, and then trimmed my blocks. This method is still great and will also result in beautifully accurate quilt blocks. The one factor it doesn't take into account, however, is time. It's just not the fastest trimming method.
With this new method, as seen in the video below, my steps look like this:
- Sew the half square triangles.
- Trim the blocks.
- Press them open.
I know what you're thinking. That's the exact same amount of steps, how could it be faster? Well, it's faster because with a single HST still folded on top of itself, you trim all four sides without moving your ruler and by making only two cuts.
Previously, you needed to either rotate your mat and/or yourself and cut all four sides individually. Am I making sense? The video above will make it really clear.
You May Also Like...
Supplies to Trim Half Square Triangles
Technically you only need a very basic ruler (square is the easiest), rotary cutter and cutting mat. However, in this tutorial I am using a really helpful HST-specific ruler that allows you to trim the dog ears off your half square triangle during the trimming process (so you don't have to go back and do it after pressing all of your blocks.)
When you buy a pack of Clearly Perfect Slotted Trimmers they come in sets of two. One question I had immediately after opening these rulers was, "Why is this frosted paper so difficult to remove?"
The answer is that you're not supposed to remove it. 😉 These rulers are designed with frosted paper on the back. Which actually turned out to be a nice feature because it helps the ruler not slide around as much as if it were just plain plastic on top of your HST.
EDIT! You ARE supposed to remove the paper, it's just kinda hard and takes some fingernail power, which I don't have! So remove that frosted paper, people! Sorry to steer you wrong initially. Blame it on my addled pregnancy brain!
In the video I also show you an alternate trimming method that does not use the Clearly Perfect Slotted Trimmer. Instead, I use a square ruler I had on hand and a piece of masking tape to give myself an obvious guideline.
The only major difference with not using the Clearly Perfect Slotted Trimmer is that I will have to trim the dog ears off after each block is pressed open. The supplies used in the video for this method includes:
Step 1: Line up the HST seam with the ruler.
This is actually something I messed up on a few practice blocks. Here's the truth – we don't always sew a perfect 1/4" seam (whaaaat?!?! I mean, obviously YOU do, but I don't.) So I initially made the mistake of lining up the edge of the ruler with the edge of my seam.
According to the size of your unfinished HST (in my case that would be 6"), line up the dotted seam line of the ruler with your sewn seam. This may mean that the edge of your seam and the edge of the ruler are off a little. That's OK! Ignore them. They don't matter.
See how my edges are ever so slightly off? What matters is that the seam and the dotten seam line on the ruler is lined up.
Step 2: Trim.
Hold down firmly with one hand, and with the other use your rotary cutter to trim all of the excess bits, including those dog ears.
Step 3: Press the HST
I like to use my tailor's clapper when pressing, but the important thing to notice here is that once you open up and press your half square triangle it's perfectly trimmed! See that?
For a full tutorial on how I press quilt seams, check out How to Press Seams in a Quilt (with Video Tutorial!)
Now go forth and make all of the HST quilts!
SQ HST Quilts!
And that's all there is on how to trim half square triangles! What do you think of this technique? Do you have a favorite trimming method? Share it with us in the comments!