Half Square Triangles

There are many ways to make these popular units.  This method allows you to sew many different fabrics for a large variety or to make just two.  It is completely accurate.

There are always two squares involved in making the half square unit.  One is lighter than the other.  You will draw your diagonal lines on wrong side of the lighter square. 

Use a thin ruler with gridded 1/4" lines if possible.  A rotary ruler is so thick it is hard to judge exactly where your line will fall.  In addition, you will get lead on the side of your ruler and run the risk of transferring that to your fabric while cutting.

A mechanical pencil will keep the same size point no matter how much you use it.  If you are using a regular pencil, you must place the ruler so the line drawn is going through the two corners of the block.  A fat pencil point has WIDTH.  Be aware of this.  You may want to offset your ruler a smidgen so that the LINE, not the ruler, bisects the block.

Line drawn in middle, seam already sewn on left

If you have an accurate 1/4" foot on your machine, you do not need to draw sewing lines.  If not, you will mark your square differently.

Marking Both Sewing Lines (Hand Piecers use this method)

If you are marking the two sewing lines, you can actually skip marking the center line,  letting the ruler do the work.  Set the ruler on the square so that the edge of the ruler extends 1/4" PAST the center diagonal.  In other words, you will let the ruler imagine where the center line is by placing it so the line that is 1/4" from the edge is running through the middle of the square.  Mark along the edge of the ruler.  Rotate the square and mark the other side in the same way.

You now have a square with two sewing lines, spaced 1/2" apart, on opposite sides of an imaginary center line.

Of course, you may draw the center line and then draw the two outside lines.  It will take you a little longer, but if it makes you more comfortable, do it.

Mark all of your light squares. 

Sewing the Half Squares

If you are using my method for sewing 1/4" seams, remove your Dr. Scholl's piece for this step.  It will make a lump under your square.

Sew on one side of the center of each square, chain piecing them through the machine.  Turn the chain around, leaving the pieces attached, and sew the second side.

Edge of 1/4" foot is against center line. You can see previous unit at top of picture.

Lift one edge and satisfy yourself that you have made a half square triangle.  The really great part here is that you have sewn that middle line while the fabric is whole.  The bias edge will not be exposed until the pieces are already attached.  You have nearly eliminated the stretching problem!

Hand Piecers: You may want to put in a pin or two to keep the two squares from shifting.  Stitch down each marked line, remembering to add a backstitch every 3 or 4 stitches.

I use scissors to cut my squares apart.  I find it faster than using a ruler and rotary cutter, but you may do it either way.  I cut approximately on the line, but it is not really important since the pieces are already sewn.  The exact size of the seam allowance is only important because it is subtracted from the size of your piece.  Once the piece is sewn, it makes no difference how you trim the seam allowance.

Take the stack of cut and sewn squares to the ironing board.  Lay the iron on each seam to set the stitches.   Then use your finger and the edge of the iron to open the unit and press the seam toward the appropriate side.  In many cases, this would be the dark side but in some layouts, you will want it pressed the other way, as I did below.

Rest the iron on the opened seam for a couple seconds to flatten the seam.  A hot iron should give you satisfactory results without steam.

Return to the cutting board to trim your squares.  This piece will square to 2 1/2".   See Squaring Up for details on this step.