i add one inch to the finished size (4 inches) and make the hst and then trim making sure my 45 degree line is on the seam.
good luck.

I do the same as NJ Quilter, I make larger and cut down to the size I need.

Thank you all very much
Am going to start with Irish Rose' (I'm an O'Shea)
Will let you know how it goes; won't happen right away though.
Am obsessed at the moment with Mile-a-Minute

I just learned a new way to make HST's . You cut your 2 fabrics 2 inches larger than your finished size. You put your fabric right sides together and sew 1/4 in around all 4 sizes. You then cut diagonal in both directions (cut an X). Here is a tutorial from Missouri Star Quilt Co. http://www.youtube.com/watch?v=ekYpJzHoW6E. Also craftsy has a free BOM that shows the 2 ways to make HST. http://www.craftsy.com/ It is a great class and FREE