Half Square Triangles (HSTs)
Two 90 degree triangles, or half square triangles (HSTs), are created when a square is cut in half diagonally. Cut in this manner, the short sides of the triangle are on the straight grain and the longest side of the triangle is cut on the bias, so attention is needed not to stretch or distort the triangle shape when you assemble HST. Sewn together, half square triangles create a square with color that varies along the diagonal. Knowing how to make half square triangles allows you to make many new patterns and blocks and opens up many new possibilities!
There are several methods to create half square triangles:
1. Cut Then Sew: With your rotary cutter and ruler, slice each square from corner to corner to make two triangles of each color. Layer color 1 on color 2 with right sides together and stitch a 1/4″ seam along the long side. Repeat with the second pair of triangles. Press seam toward the darker fabric and trim points. You now have two half-square triangles that measure 2-1/2″ on all sides. They will measure 2″ when sewn into the block and then into the quilt. This method works fine, but you do have to handle stretchy bias edges. If you use this method and your half-square triangles turn out to be not exactly the right size, you might want to give Method 2 (below) a try.
2. Sew Then Cut: You can make perfect half square triangles by sewing squares of two different fabrics together. The trick is to know how to calculate the finished size of the block.
1. First, determine your finished block size. Then you add the “magic number” of 7/8″.
2. If you want a 4″ (finished size) half-square triangle unit, you need to cut two squares that measure 4 and 7/8″ each.
3. Place the two squares together and mark a line diagonally from corner to corner. Sew ¼ inch on either side of this line.
4. Cut along the diagonal line and open the blocks and press the seam toward the dark fabric. Trim. Two nice half square triangles! Very quick and precise and stretch along the diagonal of the triangle is minimized. (My preferred method!)
3. Diagonal (Bias) Method – makes many half square triangles quickly! This method requires a triangle ruler, worth the investment.
1. Cut two layers of fabric into bias strips, using the size table below.
-
Width of bias strips (inches) Finished size of square (composed of two half square triangles)(inches) 1.5 1 2 1.5 2.25 2 2.75 2.5 3 3 3.25 3.5 3.75 4 4 4.5 4.5 5 4.75 5.5 5.25 6
2. Without separating the fabric layers, sew a 1/4 inch seam along both outter edges of each pair of bias strips.
3. If your finished square is 3 inches, and using the triangle ruler, place the 3 inch line along the sewn seam and cut along each side of the triangle with your rotary cutter. Move from bottom to top of the strip, to minimzr fabric waste.
4. Open along the sewn line and press the seam toward the darker fabric.
4. Gridded Fabric: I just learned this method from Annie Smith! This method involves marking a grid on the wrong side of one of the fabrics that you’ll be using in your half-square triangles. Using a 2″ finished size for example. Cut a 8″ x 12.5″ rectangle from each of the two fabrics that you will be using for your half-square triangles. With a ruler and a pencil (or your favorite marking method), draw a line 1″ from the left short side. Draw another line exactly 2-7/8″ from the first line. Continue until five vertical lines are drawn. Next, draw a line 1″ from the bottom (long) side. Draw another line exactly 2-7/8″ from the first line. Draw one more line 2-7/8″ from the second one and your grid is completed. Now draw diagonal lines through each square as shown below. With right sides together, layer the marked fabric on the unmarked fabric. Stitch a 1/4″ seam on both sides of each diagonal line as shown below. Using your rotary cutter and a ruler, cut apart on the drawn lines. Press the seam allowances toward the darker fabric and trim points. You will have sixteen half-square triangles!
Wow! Impressive technique, right? Very helpful when you need to mass produce half square triangles.
To advance your quilting skills, try a quilt patten that requires HST to produce beautiful quilts! And for those of you who are “afraid” of stars, I suggest you push yourself to learn methods 2 or 3, because you need HSTs to make “stars”. You will be amazed how easy these methods are. When you are comfortable with these metods, try methods 1 and 4. If you get confused, write the Blog or come into the shop, we’re glad to help!
Barbara