....IS the blocks never turn out the same size.
Reasons---inadequate pattern drawing (Sorry!)
Variations in sewing seams.
Trying to fit blocks based on a division of five into a 12" block.
It is all part of the equation.
If this causes you anxiety consider a face-saving set that will disguise any inadequacies in planning, patterning or sewing.
Solution 1) FRAME EACH BLOCK WITH STRIPS.
Cut strips large and piece around each block.
When all blocks are finished cut to the same size.
Set side by side; differences will be so small no one will notice.
Set with sashing. Choose fabrics of similar value to
minimize visual differences.
Do not trim any of the blocks until the end.
Solution 2) FRAME BLOCKS WITH TRIANGLES
Cut large triangles and turn blocks on point
Make triangles large enough that blocks will float inside.
Don't forget to leave that seam allowance when you trim.
Trim the square-in-a-square blocks to the same size. Set on point and your blocks will be on the square. And you will have a very large quilt.
Again, do not trim the triangles until all the blocks are done.
Any other ideas?