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…

…then I cut my squares 2 1/4″.

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

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

Once they are stitched together, I pressed the seam 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.

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!

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.