Mystery Quilt Block #3 - Shoo Fly with a Lesson on HSTs

Block #3 – Shoo Fly – Quilt Assembly Tricks – The Half-Square Triangle (HST)

What is a HST?

Half square triangle units are possibly the most commonly used patchwork component. Sometimes abbreviated as HST or called a triangle square, the units are squares that are composed of two triangles. Each triangle occupies half of the square's space, leading to the name half square triangle unit.

Why Learn this Technique?

You can sew two triangles together to create a HST unit, but it's easier, and often more accurate to quick piece them, since it eliminates the need to handle the stretchy bias edges of individual triangles.

Is this Lunch or Quilting?

One way to piece HSTs is the easy sandwich method, where two squares of fabric are sewn together along the diagonal and then cut apart to create two identical HSTs.

The sandwich method is a perfect technique to use when you're making a scrap quilt or need a few HST units in specific color combos -- it helps you make great use of fabric scraps or small yardages. However, I use it even when I'm making lots and lots of identical units.

Cut the Squares and Mark the Diagonals

1.Use the square size called for in your pattern. If you are drafting your own pattern, cut squares that are 7/8" larger than the finished size of the units (unless you want to make them oversize and then cut back for complete accuracy, see page 5).

2.Use a pencil or permanent marker to draw a diagonal line (from one corner to the opposite corner) on the reverse side of the lightest square.

3.If you do not have a quarter-inch presser foot, draw two more lines, each one 1/4" from the original diagonal line (extra lines not shown)

 

4.Pair the marked square with the same size darker square, edges matched and right sides together.

5.Sew two seams, each one 1/4" from the marked center line (measure and draw seam lines before sewing if you do not have a quarter-inch presser foot to guide you).

 

6.Use scissors or rotary cutting equipment to cut through both layers of the square on the marked center diagonal.

Press the Half Square Triangle Units

1.Place the cut units on your ironing board, the darkest fabric up. Press a medium iron directly onto the units to set the seams.

2.Open up one unit and carefully move the iron into the diagonal that separates the dark half from the light half. Let the weight and heat of the iron press the unit, because ironing with vigorous back and forth movements will stretch it out of shape. Repeat to press the second unit.

3.Trim the "dog ears" from the ends of seam allowances. Measure the units. If they are too small, make sure they were pressed adequately. If squares are still slightly small, try sewing the next squares together with seams that are slightly less than 1/4" from the marked center line.

4.Now you have two identical half square triangle units that should measure 1/2" wider and taller than its finished size. The straight grain of each triangle lies along the outer edges of the square.

5.Once you know your seams are accurate, speed up assembly time by chain piecing the squares.