How to make half-square triangles 8 at a time

Welcome back to the HST tutorial series! In this last half-square triangle tutorial, we're going to look at how to make HSTs eight at a time. 

This is a great time saver for when you need a lot of HSTs that have the same fabric combinations, but it doesn't have the bias-edge issues that the four-at-a-time method has. 

Making half-square triangles 8 at a time is not necessarily scrap friendly, though, because you will be starting with much larger starting squares. So this is a technique best used for fat quarters, or yardage. But generally, if a quilt pattern requires that many of the same HSTs, you are most likely not making a scrappy quilt anyways.

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Three easy ways to make HSTs

There are three main methods for making half-square triangles, and I am showing you all three in this tutorial series:

• Two at a time - the easiest method and usually the first one new quilters learn. It's perfect for scraps or patterns that have HSTs with lots of different colour combinations.
• Four at a time - This method is perfect for patterns that have many of the same HSTs, but the downside is that they have bias edges and therefore distort more easily, which makes them a bit trickier for beginners.
• Eight at a time - the method I am showing you in this tutorial. It's super-fast, and as easy as the two-at-a-time method. This technique is perfect for patterns with lots of the same HSTs, and it doesn't have the bias edge issues that the four-at-a-time method does.

A quick note on finished vs. unfinished measurements:

• Finished means the measurement of your unit or block as it is sewn into the quilt. This does not include any seam allowances, and is basically what you see once the quilt top is sewn up.
• Unfinished means the measurements of a block or unit including the seam allowances. So this is what you would see if you measured a unit on your cutting table, before sewing it into a block or quilt. Seam allowances in quilting are normally 1/4", so a quilt block or unit would be 6" x 6" finished, for example, or 6 1/2" x 6 1/2" unfinished. 

Quilt math for 8-at-a-time half-square triangles

This method is basically quadrupling the two-at-a-time method, which means the math is very similar, and easy.

Start with the finished size of your HST unit, and add 1" like you did for 2-at-a-time. Then double that measurement to find your starting square size.

For example, if you want a 4" finished HST (which is 4.5" x 4.5" unfinished), add 1" to the finished measurement, which makes 5". Then double that measurement which makes 10". So your starting square will be 10" x 10". This does give you a good amount of trimming room, but feel free to add an extra 1/4" if you're more comfortable trimming slightly larger units.

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How to make half-square triangles eight-at-a-time

Supplies needed:

• two squares of fabric
• a marking tool (I'm using a Clover Chacopel chalk pencil)
• a rectangular ruler + an optional square ruler (my favourites are Creative Grids rulers)
• rotary cutter
• cutting mat
• sewing machine

Cut two fabric squares to the size you calculated above.

Place the two squares right sides together. Pin or clip if they look like they might shift while sewing.

Mark two diagonal lines on the back of one of them (a big X).

Sew a 1/4" seam on either side of both diagonals (that's 4 seams, see red arrows).

Cut the square in half both lengthwise and widthwise. Do not move the fabric between cuts, just lift the ruler and place it down again.

Cut all four smaller squares apart on the diagonal lines. You can cut each smaller square individually, or leave the four pieces together and just move the ruler again to cut everything at once.

Open up the HSTs and press them, then trim them to size. 

How to trim half-square triangles

The easiest way to trim HSTs is by using a square ruler (I love my Creative Grids 6.5" square for smaller HSTs) but it can also be done with a rectangular one if you don't have a square. You can see which ones I use on my Resources page. There are also a number of specialty rulers designed specifically for trimming HSTs, but those are a topic for maybe another tutorial.

Line up the 45 degree line on the ruler with the diagonal seam of the half-square triangle. Check that the measurement you need (4 1/2" in our example above) is within the fabric on all 4 sides. If not, slide the ruler up or down along the diagonal seam until it fits.

Trim the top and side of the block. I am right-handed, so I am trimming the top and right-hand side of the block, but if you're left-handed, it works the same way on the left, just turn the block around. There are even left-handed rulers that have all the markings the other way around so you're not having to read things upside down.

Turn the block around so the two untrimmed sides are now at the top and right. Line up the 45 degree line again on the diagonal seam, then line up the edges you just cut with the exact measurement you need.

Trim the other two sides.

And there you go, eight half-square triangles done and dusted.

If you don't have a square ruler and are using your rectangular one, here's how that looks. I'm using my 8.5" x 24" Creative Grids one here. It's lined up exactly like the square ruler, with the diagonal line on the seam and the edges on your chosen markings. I like that the Creative Grids ruler has markings all the way around, but if yours doesn't, just use some masking tape on the ruler to mark the line you need. That should help to keep your eye from slipping to the wrong line.

Quilt patterns that use 8-at-a-time HSTs

Block Adventures is a pattern I co-designed with my friend Katy that uses both 4-at-a-time and 8-at-a-time HSTs to make the various blocks. It was published in Make Modern issue 40 here. There is also a colouring page available if you click on the pattern title above, which takes you to the blog post I wrote about the pattern.