After telling you to trim squares made out of half square triangles when publishing star #4 of the Block of the Month I got some enquiries how to do this the best/easiest way.
In a perfect world you would sew the two triangles together along their long sides, press them and voilà – you would have a perfect square in the perfect size. In real life you are sewing together two bias sides which will make for some stretching and/or shifting even if your cutting is absolutely precise. So especially when you have a lot of these pieces in your block it’s always a good idea to trim them all to the correct and same size.
Here is how I do it:
Sew your triangles along the long side to get a square. Press, pressing the seam allowance open or to one side as you prefer.
Put your ruler on the square.
The 45° line of your ruler should line up with your seam line.
Make sure that your square fits nicely or exceeds the final measurements of your square (don’t forget the seam allowance!). I stitched this square for this demonstration so I made it a bit larger to show the extra fabric beyond the ruler. My final square should be 5 x 5.
Remember: My square is stitched a little larger. Your square might fit exactely or you might have just a few threads exceeding your ruler.
Cut away the exceeding fabric on two sides.
Turn your square, align the ruler
and cut away the fabric on the other two sides.
And here is the perfect square.
I hope this will help you to always get perfect half-square-triangle squares. If you have any questions don’t hesitate to ask in the comments.