Trimming HSTs the Fast Way

I saw this tip on the Internet somewhere a long time ago so I have no idea where I saw it, but it is so brilliant I just had to share. For me, this tip was a real deal-changer because I spend a lot of time making and trimming HSTs (half-square triangles). Apparently I’m having a love affair with them because HSTs show up so often in my quilts.

Strawberry Preserves

Star Crossed


When I read this tip the first time I hit my forehead and thought, “Man why didn’t I think of this before?” It is so time-saving, so simple, I promise—this tip will rock your world.

First, Make your HSTs

There are many ways to make HSTs, and I include three of my favorite methods here on the Answers tab. There, you’ll find tutorials for making HSTs two at a time, four at a time, and eight at a time—and those are just some of the ways you can use to make HSTs! Regardless of how you choose to make HSTs, you end up with something like this—a HST folded in half, awaiting trimming and pressing.

Mark your ruler for trimming

Next, mark your ruler with a diagonal line from corner to corner at the unfinished size you want. I just made tiny HSTs that I needed to finish at 1” when sewn into a block, or 1-1/2” unfinished. So I used some ruler tape to mark my square ruler and connect the 1-1/2” points on two sides.

After using this tip for a while to trim my HSTs, I discovered a ruler that makes this business even easier because it’s designed just for this method! This magic ruler is called the Triangle Square Up Ruler, and it’s by Quilt in a Day. Using this ruler saves me the trouble of having to mark a diagonal line on one of my square rulers. So if you make a lot of HSTs like me, you'll want to invest in this ruler, believe me. If you have this ruler, you don't need to mark it for trimming so just skip this step.

The Triangle Square Up Ruler comes in two sizes: 6-1/2" and 9-1/2". I got the larger ruler because that seemed to give me the most possibilities. But if you tend to make only smaller HSTs, I'd buy the 6-1/2" ruler because the larger one can be a bit unwieldy when trimming small HSTs.

Align the ruler and trim

To trim the HSTs using a regular ruler that you've marked, place the ruler on the unpressed HST and align this tape mark with the seam. I also align the top edge of the HST with the top edge of the ruler. Then I trim the right side. Yep, just one trim and I’m done!

If you have trouble aligning the ruler’s edge with the top edge of the ruler, you can trim two edges of the HST and get the same effect. Trimming two edges gives you a tad bit more control, but really, I don’t find that necessary.

To trim your HSTs using the Triangle Square Up Ruler by Quilt in a Day, simply line up the seam of your unpressed HST with the appropriate line on the Triangle Square Up Ruler. The appropriate line is the one that represents the unfinished size of your HSTs.

Notice that one end of the ruler helps you cut in half sizes - 1-1/2", 2-1/2" and so on. The other half of the ruler cuts even-sized HSTs - 1", 2", 3" and the like. Again, you're looking for the mark that represents the unfinished size of the HSTs.

Press the HSTs and trim the dog ears

After trimming, I press the HST open or press to the dark, whichever seems best suited to the block I'm making and the color of the fabrics I'm using.

After pressing, you’ll see that you have two dog ears sticking out from the HST.

I either trim those dog ears with scissors after pressing or before pressing by making two cuts with your rotary cutter. Cut straight across at both ends, where the seam intersects the edges.

Regardless of whether you use your own ruler or the Quilt in a Day specialty ruler, the results are the same: perfectly-sized HSTs in the speed of sound.

This tutorial was featured!

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