The Quarter Square Triangle Quilting Block or The Hourglass Quilt Block
The quarter square triangle is different than the half square triangle in that it has 4 triangles.
It is also very important that all the outer edges are on the straight grain. All of the diagonal lines are on the bias, even though the this time the hypotenuse, or long side of the triangle, is on the outer edge. (The hypotenuse is the center seam in a half square triangle)
Note: This page will teach you how to make the Quarter Square Triangle Block. If you just need a single quarter square triangle, you will be cutting the square as illustrated in the section below, and then cutting it in half twice diagonally. All 4 pieces will be the same.
Once again you make this block out of squares. Again, working with squares puts as little pressure as possible on the delicate and stretchy bias edges.
The first step in making the quarter square triangle is the same as the half square triangle. However the size of the squares because you will be cutting them twice.
The number to remember here for a finished block is 1 1/4 inches. If you want a 6 inch triangle, you would cut 7 1/4 inches.
If you were working with raw blocks (without the seam allowance), you would just take away 1/2 inch, so the cut would be 6 6/8 or you would add an additional 3/4 inch.
Cut on the line down the middle, and press the seams toward the dark fabric.
To avoid confusion, try and always think in terms of the finished block. Memorize the 7/8 number for the half square triangle, and the 1 1/4 inch number for the quarter square triangles.
I've made the picture a little bigger so you can clearly see what is happening in the second step.
You are to place the squares that you have just made (which are actually half square triangles) right sides together.
However, notice that they are placed with the dark side against the white side.
Again, draw a line from corner to corner as in the above block.
When you open them up, you will have your quarter square triangle. The straight grain will all be on the edges, and you can see the four triangles.
Again, be careful with the pressing.
One thing to note about quarter square triangles - because the straight grain is on the edges, when you set fabric triangles on the end of the rows with blocks placed on a quilt diagonally, you will always be using a quarter square triangle. You will not have to piece it, but you will be cutting a square, and then cutting it in half diagonally, twice.
Just be aware that the most important difference in the half square triangle and the quarter square triangle is actually the line of the bias.