This is a great technique for making Half Square Triangles that eliminates the need to directly manipulate the stretchy bias of the triangle. It utilises two easy-to-cut squares.
In the Pattern
You will be given instructions to cut pairs of squares, as this technique produces two Half Square Triangles. I usually give generous measurements so you have lots of wiggle room when trimming the units to exact size (for instance if you need a 1 7/8″ square, I will tell you to cut an even 2″ x 2″).
How I will show the requirement for Half-Square Triangles in the pattern:
So that means take two squares of D and two squares of E to make 4 Half-Square Triangles, by the method that is outlined below.
So you can make your own at home:
The rule for working out the size of square to cut to make Half-Square Triangles:
Add 7/8″ to the required finished size.
On the back of the lightest fabric (or the one most likely to show a pencil mark), draw a pencil line, diagonally from corner to corner. Repeat for every square you need in this fabric. No need to draw on the dark square; you only need a line on one square in the pair.
Stack a pair of light and dark squares, right sides together. Sew a scant ¼” seam either side of the diagonal pencil line.
Hint: some books don’t give you much wiggle room when it comes to trimming the Half-Square Triangles. In this case I often make my ‘scant’ seam even ‘scantier’; but, usually don’t let it get much smaller than 1/8″.
You will end up with something like this:
Now, cut along the diagonal line.
First, press the seam together, to ‘set the seam’; then, press towards the darkest fabric.
To trim the block to the exact size: firstly, line up the diagonal (the 45° angle) on your ruler with the seam.
Then, carefully trim your block into sheer perfection.
The result: a perfect Half-Square Triangle.