1. Cut two fabrics exactly the same sized square. 2. Fold in half and finger press. Open and fold in half the other way, finger press.
3. See the quadrant folds? 4. I used a Sharpie marker to make diagonals and then realized I was doing this wrong. The dotted lines are wrong. The solid lines are correct. Confused? Sorry.
5. I am using a 1/4" foot and lining it up along the drawn line and sewing 1/4" away from it.
6. The stitched line is on the outside of the drawn line.
7. A second line of stitching inside the drawn line also 1/4" .
8. Cut the triangles away between the stitch lines and then cut the remaining square diagonally twice, resulting in 8 half square triangles.
Ta Da! OK they really are all the same size. It's just my usual lousy foto.
To answer the question of how big to make the original square...I first tried out this idea on paper, folding and figuring out sorta where to stitch. Obviously now I realize the folding step is unnecessary. But if you work with a sheet of paper you can measure the quadrants and seam allowance and see what size the HST will be and go from there. I can honestly tell you that my only interest was in figuring out the puzzle. I will probably never use this in a quilt.
Years ago I sat in on a Mary Ellen Hopkins lecture and she said to always begin with the smallest element in the design and build on it from there. I have found this to be fabulous advice. So if your HST measures 1.5" and you double or triple or quadruple that measurement, you know what size the rest of your blocks need to be.
It's all just too much measuring for my taste.