Half Square Triangles


Yesterday I was looking at pinwheel quilt blocks. They are made from four half square triangles and I linked to a video tutorial for sewing the pinwheel.

However, I was thinking that maybe I should spend a bit of time looking at the base block for this, and many other different quilt blocks. 

The Half Square Triangle.

This is often written in an abbreviated form which you will see on many web sites and tutorials as H.S.T.

Firstly,  a HST is a square that is made from two equal triangles.  Each triangle makes up half of the square.  Thus half a square triangle.

01

Two half square triangles…

02

…make 1 square

You can sew these in many different ways…

Here goes. This is a long one!

First method – one by one.

03Cut out your triangles.  To do this,  start with a fabric square that is 3/4 inch bigger than the square you want to finish with when sewn into a block.  Cut it in half diagonally.  Do this with two pieces of fabric and then place the triangles right sides together. Sew them along the longest side (the cut diagonal), open and press.  You now have one half square triangle.

Second method – two by two

04Cut two squares of fabric 3/4 inch bigger than you want the final HST to be once sewn into a block. Draw a line on the back of one fabric piece,  or iron a crease, diagonally across the square.

Place your two pieces of fabric right sides together.

05Sew a seam 1/4 inch to the right of the drawn/creased line. Then sew another seam 1/4 inch to the left of the line.

06Cut along the drawn/creased line.  Open out the fabric pieces and press seams. 

You now have two identical HSTs

Method three – four by four

This method will mean that your HSTs are cut on the bias rather than with the grain, so they could be a bit more ‘stretchy’ and prone to go out of shape. That may, or may not, concern you.

07Get two squares of fabric and place them right sides together.  Sew a 1/4 inch seam around the four outside edges of the square.

08Cut the square in half diagonally,  and then cut the opposite diagonal.

Open and press.  You now have four identical HSTs.

You might have noticed I haven’t given you any dimensions for this method and this is because the calculations include lots of fun maths like pythagoras theory – you know the one. .. Square of the hypotenuse is equal to the sum of the squares of the other two sides?  No. Ok – rule of thumb. A 10 inch square will give you, approximately, four 6 1/4 inch HSTs when sewn into a block. (Final HST size divided by 0.64 = square size of fabric required)

Method four – Eight by Eight

09Cut two squares of fabric 2 times the size you want the final HST to be once sewn into a block PLUS 1 and 1/2 inch. Draw a line on the back of one fabric piece,  or iron a crease, diagonally across the square. Then, draw another line / crease across the other diagonal.

10Place your two pieces of fabric right sides together.


Sew a seam 1/4 inch to the right of both of the drawn/creased lines. Then sew another seam 1/4 inch to the left of both of the drawn / creased lines.

11Cut along the drawn/creased lines THEN cut in half vertically and horizontally.  Open out the fabric pieces and press seams. 

12You now have eight identical HSTs

Phew!

Always check that your HSTs are square and the same size before joining them together – and press the seams.

Hope that this helps with your HSTs . You will find them in a huge amount of quilt blocks.  Some people even sew most of the block with HSTs rather than snowballing rectangles. 

Hmmm. Snowballing – now that’s a whole another topic! (Click here to learn about snowballing!)

After all that maths my head hurts, so I’m off to cool my brain with an episode of ‘Vikings!’ Raaaa!

Bye for now.

Alison

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