What is a Half-Square Triangle and How Do You Make One?

This is the first thing we need to know before we can get started on our Year of Half-Square Triangles Block of the Month.   The HST is simply two equal sized triangles that are sewn together to make a perfect square.  Its one of the most common blocks used in pieced quilts.  It can be used alone as a basic block or combined with other units to make more complicated blocks like those in our BOM.  HSTs are frequently used in both traditional and modern quilts.

I've only made HST's using the 2-at-Once Method and I didn't like the process.  I can't imagine having to make hundreds of HST units just two at a time!  So I consulted my friend Google, who found thousands of tutorials and videos on the topic.  It turns out there is an endless number of methods to make HSTs.  And for every method, there are special rulers, templates and gadgets available.  And although every method claims to be the best, I think that really depends on how many you need to make and your personal preference.  So here's an overview of several methods and tools you may want to try.

The most common method is the 2-at-Once Method sometimes called the Sandwhich Method.  The yardage and cutting instructions for our 2015 BOM pattern are calculated using this method.  Cut two squares 1" larger than finished block size, mark a diagonal line from corner to corner, stitch 1/4" away on both sides of the marked line, cut apart on the line, open fabric, press, then trim down to a perfect square 1/2" larger than finished size.  When I used this method, I didn't like the need to cut a second time in order to square up the block after it's been sewn, so I'd only use this method if I needed a small number of HSTs.  But if I were using this method much, I'd try June Tailor's ruler for marking and cutting or Nancy's Notion Perfect Triangle Gauge for marking and the BlockLoc ruler for cutting.

If you want to make HSTs in larger batches, here are some alternate methods.  Remember that yardage requirements for our BOM are based on the 2-at-Once method, so you probably want to have a little extra fabric if using another method.

4 at Once Method - Starching is recommended because this method produces bias edges which can get stretched out of shape more easily that edges on the straight of grain.

8-at-Once Method - Almost the same as 2-at-Once Method, but faster!  To adapt for different block sizes, use this formula to determine how big to cut initial squares:  Cut size = Finished block size x 2 + 2".

Grid Method - This can make a larger number of HSTs at once.  Try pre-printed grid paper to save time on measuring and marking.

Tube Method - What I like about this method is that if you press carefully without stretching, there is no need to cut again after blocks are pressed open.  But you'll want to starch and press carefully because you'll get stretchy bias edges with this technique.

I've decided to try my own method.  It's a variation of the tube method but marked on the diagonal like the 2-at-once method bias tubes resulting in finished HSTs that have edges on straight grain. 

I've to make my BOM using the tiny 4" block size, so I need tiny 1.5" HSTs and was able to get 8 from one charm square.

Step 1 - Mark a diagonal line from corner to corner.  Mark 2 lines parallel to the first 1.75" on either side.   Now  stitch 1/4" on both sides of all marked lines.

Step 2 - Cut tubes apart on marked lines between the two stitching lines.

Step 3 - Since I'm making 1.5" HSTs, I've used painters tape to mark a diagonal line on my ruler at 1.5".  I've aligned the tape line with the stitching line, then cut the two sides the triangle.

Step 4 - Flip the ruler around and repeat Step 3 to cut a 2nd triangle from the opposite side of the tube.

Continue cutting triangles from the tubes.  Open and press carefully so that finished square does not become distorted.

Coming Soon:  Pressing Seams for Perfect Points 

by Amy Aderman