Half square triangles (HST’s) are one of the most versatile quilting blocks. There are so many fun quilt designs that use HST’s. While the block is simple to construct, it can be tricky to match up the blocks. I’ve learned a few tips that have helped me level up my HST blocks. Here’s what’s helped.
Tip #1 - Trim your blocks with an HST ruler BEFORE pressing.
This tip has really helped the accuracy of my HST blocks! It seems counterintuitive to trim the block before pressing, but it really does work best to trim the block while it’s still in its triangle shape.
To get started, you’ll need a ruler to help you trim your blocks. There are specific rulers to help you cut and trim HST’s. You'll see them listed with different names - half-square ruler, triangle ruler, HST ruler. Any of these will work. The key is to find a ruler that has a 45-degree triangle. Most of these rulers have ¼” markings on the long side so you can slide the ruler and use it on the size block you are working on. Some rulers even have cutting slots.
My HST ruler is a simple one I’ve had for years. I bought this Omni Fons & Porter from my local JoAnn’s store years ago. I, too, miss JoAnn’s for the sales and affordable quilting notions! I bought this ruler during a 40% sale, and it’s been a handy purchase through the years.
You can also use a straight or square ruler that has a diagonal marking 45 degrees across the ruler. My 6” Omni grid has this and would work well.
How to Use the Ruler to Trim Your Blocks
We’ll start with the HST ruler. Place the dotted line at the bottom of the triangle (largest side) on your seam allowance and slide it to the edge you are cutting as close to the edge as you can.
This is where you’ll see the extra edges that need to be trimmed. Check both sides of the triangle and trim.
What do you do if your seam is not sewn straight? Position the ruler on the seam as close to the edge as possible. If your seam is wonky, go ahead and rip it out and resew.
Let’s use a square ruler next.
We’ll use it the same way as an HST ruler, except we’ll place the 45-degree mark on the HST seam. Again, slide the edge of the ruler as close as you can to the edge of the HST where both sides match. If there’s any extra fabric, go ahead and trim it.
Once you’ve trimmed all your blocks, it’s time to press the blocks. I’ll share my favorite technique that has made a difference in my HST quilts.
Tip #2 - Press your HST Block seams open.
I know, this goes against conventional quilting advice of pressing seams to one side. But hear me out. HST seams can get very bulky, especially where the points meet. This can make it tricky to accurately sew your blocks together. It can also affect your quilt when it’s quilted. My longarm is a heavy-duty machine and will sew right over bulky seams. But that’s not the norm for quilting on a regular sewing machine or many longarms. Those bulky seams can be tricky to quilt over and can affect the accuracy of the quilting.
To eliminate the bulky seams, I press my seams open. Worried about the seams coming apart? Just reduce your stitch length slightly. I sew my HST blocks with a 2mm stitch length.
Tip #3 - Use Best Press or starch when pressing to prevent stretching on the bias.
HST blocks are sewn and cut on the bias, or diagonal part of the block, the part of the fabric that stretches the most. The amount of stretching in your blocks can vary depending on how you make your blocks. Here are a couple of methods and ways to control the stretching along the bias:
Making 2 HST blocks at a time.
I make my HST blocks 2 at a time, sewing diagonal seams across two blocks. The seam has a little bit of stretchiness, so I find spraying the block with Best Press before I press it helps stabilize the block.
Making 1 HST block at a time.
Some of my quilting friends will use their AccuQuilt machine to cut HST blocks to make individual blocks. With these pieces, HST blocks are sewn one at a time with the seam across the bias. Since the block was cut on the bias, there’s more stretch to that seam. Again, I would use Best Press or starch when I press these blocks. You could also pre-starch your fabrics.
Tip #4 - Trim or don’t trim those extra edges at the block’s seams.
I don’t have a strong opinion about trimming the excess edges after sewing a HST block together. I know some quilters who must trim those off and others that ignore it. Most of the time I trim the edges, especially on larger blocks. But everyone once and a while I’ll leave them there. I’d say it’s up to you if you want to trim the edges.
Tip #5 - Use a rubber mallet to flatten seams.
If you end up with bulky seams where the points of your HST’s match, you can use a mallet to flatten those seams. Lay your block on a hard surface you can pound on. I use a clean cutting board. Take a rubber mallet and pound the center of your seam. You may need to do it a few times and with varying force to flatten it. Flattening the seams will make it easier and more accurate when quilting your quilt top.
Directions for Making HST Blocks
Want to try your hand at making HST blocks? I'll share the directions for making 2 at a time, my favorite technique, here.
My Favorite HST Block - Free Pattern!
I'll also share one of my favorite HST block patterns, the Colorado Block, here.
I hope these tips help making HST blocks easier and more fun. Let me know, too, what HST blocks you love making!