Now if I use another 1/4" seam allowance to join this nice straight edge to another piece of fabric then I am going to nip off the point of the centre triangle, because where those two lines of stitching cross is less than 1/4" from the cut edge for the seam.
This diagram shows the small square at the back where the three triangles meet, a square with sides of 1/4". Calculate the length of the diagonal of this square. Then half the length of the diagonal is the amount of fabric you have available for a seam allowance. It's much less than the 1/4" that you want to use.
I hope you can follow my maths. Think of Pythagoras Theorem in Maths at school.
Perhaps I've been reading the wrong books but I can't find any reference to it in the articles on joining points.
So what am I meant to do. Fudge it ? That's not exactly being accurate !