*How to Sew the Half Square Triangle

I first learned this "trick" around 1986 thanks to the "queen" of the "corner square", "connector square" or "half square" triangle, Mary Ellen Hopkins.  Many designers have jumped in over the years with their own "unique" designs, but don't be mislead - Mary Ellen is the actual quilt designer who came up with this trick - all other quilters have done is to use this trick to make some really fabulous and creative quilts, but the actual technique should always be credited to Mary Ellen who "uninvented" this technique in the early to mid 1980's using the rotary cutter.
If you buy no other quilt book, track down and buy Connecting Up by Mary Ellen Hopkins.  Unfortunately, she has quite a sense of humor and started naming a series of a books all starting with the title Connecting UP and then giving them a number like #4, #4 1/2....
THIS is the book you REALLY want:
It is very hard to find, so you might have to keep watching the auction sites for one to pop up.
This is one of the books you do not want (well, you want them all, but not as much as you want the first one):
The reason WHY you want her book is not only because of the Half Square Triangle technique (anyone can figure out the math for that one); it is the math for both the connector square technique that is important to know and using the Half Square Triangle technique for making Flying Geese Triangle Units.
By the "Connector Square Technique", I mean what size should you be cutting those large and small squares for making quilt blocks using connector squares.  There is a formula, but my blog is too small a format.  I will be posting lessons on using the connector square technique, but you need to find the book to help you know the rules/formula on cutting the squares for it.

Alternatively, Judy Hopkins wrote a book called "Fit to Be Tied" published by That Patchwork Place in 1990 that is more readily available than Mary Ellen's book.  The book is basically entirely on the Bowtie quilt block, but Judy uses Mary Ellen's connector square technique and does provide cutting guide lines.

Back to the focus of THIS page which is entirely on the Half Square Triangle:

On with the simplistic lesson: 2 squares of fabric, for our purposes, light and dark purple
Many people will draw their line down the middle if their squares are very large.  If you haven't done this before, draw the line, otherwise if you are lazy like me, you take your chances.
For this square the line has been drawn directly point to point which would be the natural inclination; you don't want to do this.
What you want to do is draw your line slightly off-center: note that my line is certainly a little more than "a little off center"; your drawn line should be off by about the width of a sewing thread.  After sewing you will be trimming and folding the fabric back onto itself.
NOTE: The line is shown drawn on the right side of the fabric - in actuality, you would be drawing the line on the WRONG side - the back side - of the fabric please.

Once you have your line drawn (on the backside of the lighter fabric for better visibility), sandwich the 2 fabric squares together, right sides (pretty sides) "kissing".  Sew directly on your drawn line.
In this case I have illustrated the drawn line offset to the right - onto the lighter fabric.
So the basic rule is (if you can follow me on this one) - which ever side has more fabric on either side of the drawn line (in this case the top side), that is the side that is going to be trimmed away, making sure to leave a 1/4" seam allowance along your drawn line which has now become your seam line.
The dashed line in the picture below is to help you visualize the seam allowance you are going to need to leave after the block has been trimmed.  Remember this is actually the back side and not the front side of the fabric you are looking at.
What the finished block would look like:
HINT: this is not always the most accurate way to sew this particular block.  What I do (it wastes a little fabric, but still saves time from other methods), is that I cut my blocks about 1/2" larger than the final block needs to be.  For example, if I need a 4 1/2" half square triangle block for my star quilt block and I want to use the above method, instead of cutting two 4 1/2" squares, I will cut two 5" squares.  I then proceed to mark and sew them just as described above.  When I have finished, I then square them up with a square rotary cutter ruler and cut them to a perfect 4 1/2".

Many quilters do not like this method because of the fabric waste, but I use connector squares or connector half square triangles whenever possible - they can be just as fast and accurate if done correctly.
Give it a try!
Sample Blocks Using this Method:
Same Method Used only Squares Have Been Added to Rectangles:

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