I've made more progress on these blocks, I'm up to 36 now, I've sewn more since I took this photo.  They go together really quickly once the HST are made.  I've been making the triangles in sets of two, and making lots of these units.  The block is just four of these, rotated so that the lights and darks alternate.

To make sure the seam allowances all nest nest together, in the blocks themselves and in adjoining blocks, I always lay out the pieces for each unit the same way, with the dark square in the top left corner.  When I press the seam allowances I press the first seams towards the squares, and twirl the centre insection once the two halves are sewn together.

 It doesn't mattern which way these units are rotated, the seam intersections will nest together, so long as you make them all identically.

Four units make a block.

You can see how the seam allowances swirl at all the intersections.

The final block looks like this on the back; I like to press the seams on my HSTs open, but this pressing scheme works even if they are ironed to one side.  I love it when  blocks go together nicely, I hate having to mash seam allowances together in a big lump.

Once I put the blocks together I will be dealing with pinwheels formed by the intersections of all those triangles.  I'm not going to worry too much about making them meet exactly; I don't have time to be unpicking things on a scrap quilt like this.