How to construct a unit (3-1/2" square) that has a half-square triangle on one side and a quarter-square triangle on the other (using colors white, blue and brown, for the example)
Step 1. Start with a 4-1/4" White (Background) square, a 4-1/4" Blue Square, and two (2) 3-7/8" Brown squares
Step 2. Layer the White Square on top of the Blue Square
Step 2. Mark lines on both diagonals from corner to corner
Step 3. The background should have an "X" drawn as shown below
Step 4. Using a 1/4" foot and starting with the diagonal line which begins at the upper left corner, sew 1/4" to the right of the line, stopping at the intersecting diagonal line (if you don't have a 1/4" foot, draw sewing lines 1/4" to the right and left of each diagonal line to mark the stitching line)
Step 5. Lift presser foot and jog over 1/4" to the left side of the diagonal line and sew to lower right corner
Step 6. The sewn first diagonal line (blue thread)
Step 7. Turn square a quarter turn and sew the second diagonal line in the same way as the first--to the right of the first half of the diagonal line and to the left of the second half (red thread)
Step 8. Cut apart on both diagonal lines
Step 9. Press to Blue fabric
Step 10. This creates four (4) partial Units (the quarter-square half of the finished unit) "QSH"
Step 11. Cut the two (2) 3-7/8" C2 Brown squares in half on one diagonal
creating 4 half-square triangles
Step 12. Sew each QSH unit to a Brown triangle
Step 13. Press toward Brown triangle
Step 14. Cut off "dog-ears"
Step 15. Each set will produce four (4) Split Quarter Square/Half Square Triangle Units
A new (to me) tool for creating these units and a tutorial for using the tool and creating the units may be found at Nancy's Quilt Designs here:
No affiliation, and I don't have this tool, but it looks like it would make the process of making these units very straightforward. I may need to order one!