Every quilt pattern is different, but I often find myself trimming LOTS of half-square triangle units (HST’s). As I work on my latest pattern, I’m doing just that! This seems like the perfect time to share my favorite tools for trimming HST’s.
But first, what are HST’s?
The half-square triangle unit is common in quilting. It’s a square that is made up of two triangles. They can be made many ways, but my favorite is to start with two over-sized squares.
- I draw a line (from corner to corner) on the wrong side of the lighter square.
- Place squares right sides together and stitch 1/4″ seam on both sides of the diagonal line.
- Cut apart on the line and press towards one side.
- Trim on all four sides to the required size.
If I’m making tons of HST’s, I usually make them using the 8-at-a-time method.
- To get the size needed for each square, I multiply the cut size listed in the pattern by two. For example, if the pattern says to cut a 4″ square, I will cut a 8″ square instead.
- Draw a diagonal line on the wrong side of one of the squares in both directions, forming an “X”. Then draw a vertical and horizontal line in the center.
- Stitch 1/4″ on both sides of the diagonal lines and cut along the drawn lines.
- Then press and trim.
My favorite tools for trimming HST’s
There are two tools I use for trimming HST’s that work together for a fast and efficient process. They are the Omnigrid rotating cutting mat with scalloped edges and the Half-Square Triangle Bloc Loc Ruler. Together, they create a dynamic duo that work together beautifully. Let’s talk details.
Omnigrid rotating cutting mat with scalloped edges
I have other rotating mats, but the scalloped edges on this specific mat make it really easy to rotate. It’s a game changer. When using this mat, I don’t have to lift the HST to trim the other sides; I just rotate the mat.
The Omnigrid rotating cutting mat with scalloped edges is great for trimming anything that requires all four sides to be trimmed. It’s available in 8″ and 14″ (diameter) sizes. I’m using the 8″ size and it’s perfect for units smaller than 6 1/2″. It’s also a good size for taking to classes or retreats. The larger, 14″ size, would be great for trimming square quilt blocks up to 12 1/2″.
Of course this cutting mat is useful for trimming any kind of unit, not just HST’s. Squaring up blocks, trimming flying geese units and QST’s are just a few of the ways it can be used.
Bloc Loc Half-square Triangle Ruler
I love the Half-square Triangle Bloc Loc rulers; I’ve been using the 5 1/2″ square version. These rulers have an etched groove on the back that slides along the seamline. This makes it really fast and easy to lock the ruler into place. It also assures that the seam ends in each corner. Another advantage: the Bloc Loc ruler lays flat on the HST which prevents any rocking movement while you’re trimming.
It’s worth mentioning that using this ruler requires you to press your seams to one side, not open. If you’re an open-seam kind of gal/guy, this is not the ruler for you.
I’ve heard complaints that Bloc Loc rulers are expensive, and they are (compared to other rulers). However, this is the ruler I reach for time and again. It’s worth every penny to me. My 5 1/2″ ruler can trim squares from 5 1/2″ down to 1″ in 1/8″ increments. Of course, there are many sizes available; I suggest you choose one that will fit your needs.
It’s important to place the ruler so that the seam allowance is on the correct side for trimming. Notice if the corner of the ruler lands on the seam or if it’s offset. An easy clue for placement is to make sure the Bloc Loc label is on the flatter side of the unit (usually the lighter fabric, but not always).
See it in action
Here’s a short video that I shared on Instagram. This is helpful for those that need a good visual of the process in action.
I hope you found these tips helpful. I’m always looking for ways to make quilting more efficient (and fast) while still having fun. If you have a favorite tool/process for trimming HST units, please share in the comments. There’s always something to learn from each other!
Thanks for reading and happy quilting!