Quilting and the Diagonal Set Layout
The diagonal set layout is when blocks are placed "on point." This means that instead of the top of the block being horizontal, they are placed with the points facing upwards.
A diagonal set is harder to piece than a straight set. It requires you to place triangles around the edges of the quilt, and in the corners. These triangles can be made scrappy, so it can be done in a frugal manner.
You must cut the triangles so that the straight of grain goes along the edge of the quilt.
How to cut triangles for the diagonal placement
When you cut a square on the diagonal, the bias will be on the long side of the triangle. So you can't just cut a square in half and put it on the side. If you look at the pictures at the bottom of the page, you will see that the long side of the triangle goes along the edge of the quilt.
You must cut a square on the diagonal twice. That will give you triangles with the straight edge on the shorter sides of the triangle. See:
How to measure for the SIDE setting triangles:
First measure the size of your finished block. Multiply that number by 1.414, and then add 1 1/4 inch. Round the number up if necessary for your ruler. Cut a square to your measurement, and then cut it twice vertically.
How to measure for the CORNER setting triangles:
The corners are squares that are just cut once, on the diagonal. Measure the finished size of your block, and divide it by 1.414. Add 7/8 of an inch to that number. Round up if necessary. Cut a square to your measurement, and cut it once, vertically
When you are done attaching your side setting triangles and your corners, you will trim the outside edge of your quilt. Do not expect it to be straight until after you trim it. To trim the edge, take a long ruler, and leaving 1/4 inch for the seam allowance, even up the blocks.
Here is an example of a straight set layout
Here is an example of a diagonal set layout