Understanding Quilt Block Patterns
Sewing Half-Square Triangles
The half-square triangle is a basic piece used in many quilt blocks. Very simply, it is a square that is cut in half from corner to corner (diagonally) to create two triangles within one patch.
As amazing as it sounds, there are several ways to sew these units together. Some of these methods increase the accuracy of the resulting patch (for example Methods 2 and 4). Other methods increase the speed or convenience of sewing many half-square triangles (Methods 5 and 6).
Which method you use depends upon personal preference.
Method 1 – Individual Triangles
If you are going to cut individual triangles, be sure to use a template that has the seam allowance added to it. You can also cut squares, and then cut the squares into triangles. You can easily use the chain piecing method of sewing to sew your triangles together (refer to Chapter 4 in The Beginners Guide to Quilting for detailed instructions).
Step 1 – Cut your fabric into squares or triangles. If you are beginning with squares, in order to determine the correct size of square, start with the finished size you want your square to be (for example, 2” after the square is sewn into the block), and add ⅞” to each side. In the example of a 2” finished square, you will cut squares 2⅞” and then cut each of those squares in half diagonally (from corner to corner).
An alternative is to cut strips from your larger fabric, and then cut squares from the strips. Using the above example, cut 2⅞” wide strips, then cut the strips into 2⅞” squares.
If you are cutting triangles, it is easiest to use or make a template that is the size of the triangle including the seam allowances. Mark your fabric (on the wrong side) around the template, then cut. Or place the template on your fabric and cut around the template using a rotary cutter. Generally it is best to place the square sides of the triangle on the straight and cross grain of the fabric, leaving the long side of the triangle for the bias. (The bias side stretches, and when you sew these triangles together, the bias will be sewn together and be stabilized.)
Step 2 - With the right sides of the fabric together (facing each other), sew the triangles together along the diagonal edge, from corner to corner. Since this is a bias edge of the fabric, take care not to stretch the fabric as you sew, otherwise your triangles will be different sizes and will not fit into your block correctly.
Step 3 - Open the half-square triangle, and press (preferable press the seam allowance so it is under the darker fabric).
Method 2 – Two Squares = One Triangle
This method calls for cutting squares, and then sewing through the diagonal center of the squares. There is some wasted fabric with this method, however, there is no need to mark the cutting or sewing lines, and sewing through the diagonal adds stability to the triangles.
Step 1 – Cut your fabric into squares. To determine the cut size, take the finished size and add ½ ”to both sides. For example, if you are using 2” squares (finished size), cut 2 ½ ”squares, just as in the above step.
Step 2 – Draw a sewing line from corner to corner on the light fabric. With the right sides of the fabric together (facing each other), sew the squares together from corner to corner.
Step 4 - Open each half-square triangle, and press (preferable press the seam allowance so it is under the darker fabric).