The larger HST is the classic "draw a line from corner to corner on the wrong side of the background fabric. Sew 1/4" away from each side of the line and cut on the line." I like to use this nifty tool, the Quick Quarter ruler. It comes in two sizes, 8" long or 12" long. Just slap this puppy on your right-sides-together squares diagonally and draw a line along each side of the ruler:
Sew right on each line:
The smaller pinwheels are made by sewing all the way around two 5" squares placed right sides together with a 1/4" seam. Then cut corner-to-corner one direction:
And the other direction:
Four HSTs at once!
To make a pinwheel block, first press the HSTs carefully toward the darker fabric. This is a bias seam, so don't be over-energetic or you'll mis-shape your HST. Lay them out in the pinwheel -- notice that since I am using a directional print, I have the opposite HSTs going in the same direction:
Sew the top two HSTs, then the bottom two. Because the HSTs are pressed toward the dark fabric, the diagonal seams will snuggle nicely together.
Then flip the left two HSTs up and the right two down, like this:
Finger-press the seam on the left down, and the one on the right up. Then when you sew them together, the top seam will face toward your presser foot. This will make the seams snuggle up nice and tight:
When you press, if you open the last two or three stitches on the crossing seam, it will make a mini pinwheel, like this:
Which will result in a nice, flat center to your pinwheel!
Of course, if I had read the directions first, I would have realized there was supposed to be sashing between the large pinwheels -- oops.
I'm posting to Freshly Pieced's WIP Wednesday -- go look at some other great Works In Progress!