When making Half Square Triangles (more commonly called HST's,) the process involves cutting squares from two different fabrics, marking and sewing two lines down the diagonal of each pair of squares, then cutting them apart to create your HST's.

I used to avoid making quilts with HST blocks in the design for a few reasons. One, because I could never get them 100% accurate, and my points never matched up properly (more help on that topic later!) And two, because it was a tedious job to get a ruler and pencil and mark a diagonal line along each square. If you only had 10 or even 20 to do, then it wasn't such a big task. But when we are talking about 200 odd squares - insert exhaustion here. 

Take two Squares right sides together, make a line down the diagonal and sew on either side of the line. cut apart on the drawn line to create two half square triangle units.

Take two Squares right sides together, make a line down the diagonal and sew on either side of the line. cut apart on the drawn line to create two half square triangle units.

Instead of drawing a diagonal line on each square, I now simply fold a square in half on the diagonal (just before I'm about to sew it and it's partner,) and give a light finger press along the fold. Take care not to stretch the fabric, but this finger press will create a visible fold line for when you come to sew along either side of it. I find this method much quicker than using a pencil and ruler. The slight fold line is only there for a visual purpose, and does not interfere with your finished HST block at all. Once you've sewn either side of the two lines, simply cut apart (with scissors or a rotary cutter,) on that folded line. 

Step by Step Gallery

1. Create your line by folding a square in half on the diagonal. Use your fingers to press the line to create a visible fold line. 

2. Ensure the edges are aligned as you finger press. And in future, make a mental note to remove chippy nail polish from finger nails, and wear clothes. Not your pyjamas. 

3. Place two squares right sides together. Tip for working with stripes or directional prints. If you are making an even number of HST's, make sure that half of them are sewn with the pattern (or stripe in this case...) aligning parallel to your folded line.....

4. ...and the other half are sewn with the folded line perpindicular to the pattern/stripes. This will ensure that when you come to sew your block together all your stripes (or directional pattern) will point in the same direction. 

5. Sew 1/4" either side of the folded line, straight across the diagonal. 

6. I tend to chain piece my HST's by sewing them all at once along one side of the line, then turning and coming back down the other side. It makes for a fast procedure, and then simply snip to separate each HST, and cut apart on the folded line. 

7. Finished result with four HST units. Note the stripes all point in the same direction due to the tips above. Now the HST units are ready to be ironed flat, and then trimmed. I will follow up in detail with another tutorial on how I trim my HST units, but I highly recommend using a Bloc Loc Ruler. Another big time saver.