quilterscache.com They have a bunch of wonderful borders, including the one above, and it is all free. I use them frequently.
I have done this and the best way is to make half square triangles using your favorite method. Then add a triangle to two sides. Looking at the pattern at an angle you can see the piece. Sew them in the strip.
Of course you must do the math!
Last edited by Grammahunt; 08-28-2018 at 10:37 AM.
Reason: additional info