How to trim Half Square Triangles
This week, I've been teaching Peter the basics of sewing. Honestly, I never thought I'd see the day that he'd sit at a sewing machine, haha. However, he hasn't worked in over a month due to the coronavirus quarantine, so he's had a lot of free time on his hands. He's always had a strong aversion to sewing and quilting, claiming that it's my "cup of tea", not his. Well, the other week we asked if he could learn....which was like music to my ears!
After much thought, I decided that a good first quilt for him would be Christmas Joy. It has a simple block construction, as well as half square triangles (HSTs), which are a fundamental quilting skill (in my opinion). As we've been working through the pattern together, I decided to whip up a blog post to share the 3 ways that I like to trim my HSTs.
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First of all, why do we need to trim them?
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This is such a great question. When Peter asked me this, I simply responded...."we just do!" haha. But really, here's why:
When sewing two squares together to form your HSTs, sometimes there can be shifting in the fabric. We try to minimize the shifting as much as possible with pins and such, but sometimes it's unavoidable. Also, our seam allowances can sometimes get a little "off"...espeically if our starting square is a little large. To combat human imperfections and to give ourself a little grace and wiggle room, most patterns will have you create your HST units, then trim them down to the desired size.
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In order to accurately trim HSTs, you'll want to trim them with that middle seam in mind. That seam should run corner to corner. Once you're finished trimming, the seam should still run corner to corner. This ensures that once you piece your HSTs together using a 1/4" seam on all four sides, you'll keep the points of your HST nice and crisp.
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HSTs are arguably one of the key fundamentals of quilting. They are extremely versatile, relatively easy to create and offer a wide variety of effects. I have three quilt patterns with HSTs and they're all quite different from each other!
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Lo & Behold Patterns with HSTs
- Valley Song
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There are a few different ways to trim HSTs but these are the three that I'm the most familiar with: a traditional square ruler (I really like Omnigrid), a Bloc Loc Ruler, and a Quilt-in-a-Day Ruler. Lets take a closer look at each.
Square Ruler
When it comes down to it, you don't need anything fancy to trim these blocks. If your ruler does not have a 45 degree line, consider creating one by either using a permanent marker to draw a line form one corner to the other, or use a piece of tape to create a diagonal line.
Align your 45 degree line with your seam on your HST. Using the measurements on your ruler, extend your HST a little past the designated size that you're trimming to. I am trimming my HSTs to measure 2.5" square. My initial cut will be to square up the top and right side of my HST. Notice how the bottom and left sides extend a little past 2.5".
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2. Next, flip your HST to the other side. Align your diagonal seam with the 45 degree line on your ruler. This time, align the left and bottom sides of the HST with your desired HST size. Trim the top and right edges.
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There you have it! Keeping your seam directly under your 45 degree line will help you keep your points every time!
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One thing to note: you might notice that the square ruler can easily slip while you are cutting. Since it's so important that the diagonal seam stays directly under the 45 degree line, you'll want to prevent this from happening. You can use something like ruler grips to help keep your ruler from slipping, or....you can consider upgrading to a Bloc-Loc.
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Bloc-Loc Ruler
The Bloc-Loc ruler has a groove along the 45 degree axis, which help to grip your seam as you are trimming your HST. You use it the same way as your square ruler. People who have these rulers LOVE THEM.
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One thing to note: if you press your HST seams open, the Bloc-Loc might not "grip" that middle seam as well. I've noticed that when I press my HST seams to one side, the Bloc-Loc is the most useful.
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Quilt-in-a-Day Ruler
The idea is that you use this PRIOR to pressing your HST open. Align your seam with the designated line on the ruler. Since I want my HST to be 2.5" square, I will align my seam with the 2.5" line. Then trim the two sides that are exposed from the ruler. Some people like to align one side of the ruler with one side of the HST, meaning you'd only have to trim one side. Play around with both options and choose whichever works best for you. Note that you will still have to trim the dog ears, but it's nice to only have to trim 1-2 sides!
When you then go to press your HST open, make sure that you don't stretch your fabric and that you get your seam as flat as possible. I would measure one or two HSTs after you press them open, just to check your accuracy.
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What's your favorite way to trim half square triangles? Let me know in the comments!
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This post may contain some affiliate links meaning I may receive a small commission from each sell. Rest assured, I only share my favorite items with you!.
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