Half Square Triangles 101

Oddly enough, I found myself with a spare couple of hours on Christmas day…with not much to do!  So I decided to start cutting and sewing together the 967 (are you kidding?) half-square triangles needed for the sashings and borders for my “Friends of Baltimore”.

Here is my method for cutting half-square triangles.  Beware!  It is time-consuming but extremely accurate.

First of all, I always cut my triangles bigger than what is called for in the pattern.  In this case, the pattern called for 1 7/8″ squares to be cut.  I wanted to cut the squares 2 1/4″, so I needed to cut my strips 2 1/4″ wide.  To make the stitching go quicker, I layered a blue and a white strip on the cutting mat…

2 strips together

…then I cut my squares 2 1/4″.

cut 2 and a quarter

Next, I cut all my squares on the diagonal to make lots and lots of triangles.

bunch of triangles

Now I just pick up a set of triangles and stitch away!!

ready to stitch

Once they are stitched together, I pressed the seam open.

press seams open

Now it’s time to trim the HST down to 1 1/2″ square.  I place the HST on the cutting mat with the seam line running from the bottom left hand corner to the top right hand corner.


Then I line up the diagonal line on the ruler with the diagonal line of the seam.  All I want to do right now is to square up the top right-hand corner.

trim 1

trim 2

Next, I flip the HST triangle around and line up the diagonal line of the ruler with the seam.  But…this time, I am lining up the edge that I just squared up with the 1 1/2″ lines on the ruler….


..and trim it to the perfect size!

trim 4

The sashing consist of 15 half-square triangles stitched together.  And they have to measure exactly 15 1/2″ long, (the blocks measure 15 1/2 unfinished) so an accurate seam allowance is very important.  I did a test and realized my seam allowance could be tiny bit bigger, because the sashing  was too long.

test 1

I re-stitched a few of the seams and voila!  It fits!

test 3

Til next time…



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