Diagonal Corners 
Diagonal corners involve easier math calulations than some of the other techniques used to create the same shapes. This technique also eliminates alot of the problems that can result from sewing seams on the fabric bias as the fabric is cut after sewing the bias seam.
To find the correct size for the base shape, take the finished measurement of the diagonal corners unit and add 1/2" for the seam allowance
For Example:
If this Snowball block's finished size should be 6", the white base fabric square should be cut 61/2".
If a 9" finished block is required, then the white base fabric square should be cut 91/2".

The same basic formula is used to find the correct size if the base shape is a rectangle.
For Example:
If this Flying Geese unit finished size is 3" x 6", then the white base fabric rectangle should be cut 31/2" x 61/2".
6" finished width + 1/2" for seam allowances = 61/2" base rectangle width If this Flying Geese unit finished size is 2" x 4", then the white base fabric rectangle should be cut 21/2" x 41/2".
4" finished width + 1/2" for seam allowances = 41/2" base rectangle width 
After the size of the base square or rectangle is calculated, the next step is to find the size of the square or squares to cut for the diagonal corners triangle. The size of this square is calculated the same way as the size of the base shape is calculated.
First, find the finished length of the short leg of the diagonal corner triangle. Then add 1/2" for seam allowances and cut the square for the diagonal corner to this size.
For Example:
If this Snowball block's diagonal corner triangle finished size is 2" (finished block is 6"), the purple square for diagonal corner triangle should be cut 21/2".
If a 9" finished block is required, then the short leg of the purple diagonal corner triangle has a finished length of 3" so the purple square should be cut 31/2".

1) Cut the base unit (square or rectangle) and the diagonal corner square(s) to the proper size.  
2) On the wrong side of the diagonal corner square, mark a diagonal line dividing the square into two triangles as shown, This line can be marked with a pencil, chalk, or other suitable marker. If the diagonal corner square is hard to mark, this diagonal line can be marked by pressing the square in half on the diagonal.  
3) Place the diagonal corner square on the base unit being sure that the right sides of the fabrics are together and the corner edges match. Check that the diagonally marked line is placed correctly. Optional: Pin the diagonal corner square in place. Carefully sew on the marked diagonal line.  

4) After the diagonal line has been sewn, the quilter has several options for finishing the diagonal corner.


5) The sequence of placing the marked diagonal square on the base fabric unit, sewing on the marked diagonal line, trimming and pressing the corner into place is then repeated as many times as is necessary to complete the quilt block or the block unit. In this example, only two diagonal corner squares are needed to completed the flying geese block. 

Be sure to check the placement of the diagonal corner square after sewing, but before doing any trimming. As long as the base and diagonal corner square fabrics are not trimmed, the quilter has the option to repair any errors that may have been made. The two examples shown both have the first diagonal corner facing the same directions, but the second corner is placed differently in the two examples and results in two very different quilt block units. 
If the excess fabric from both the base and the diagonal corner is going to be trimmed away, the quilter may elect to sew another seam 1/2" away from the diagonally sewn seam. The excess fabric is then trimmed between the two sewn lines. This will result in a smaller half square triangle unit as well as the diagonal corner unit. The additional half square triangle block can be used in the quilt border, another quilt, or many other projects. 
© Susan E Traudt 1998