I had a request for how I squared my half-square triangles, so I took a few pictures of the process.
1.
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First step in making a half-square triangle is to take one square of fabric fold it in half diagonally, press.
2.
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With right sides together pin to a second square and sew 1/4 inch on either side of fold. Having a 1/4 inch foot is helpful, but it can be marked with a ruler.
3.
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Cut through squares along fold.
4.
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Press seam to the dark side.
5.
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Take a square ruler...
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... that has a line running diagonally across.
6.
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Put that line on the seam line where the two fabrics meet. This square is supposed to be 2 inches, so I've got the bottom and the left side at 2 inches. Be sure to keep the diagonals lined up. (Note the yellow is on the bottom right.)
7.
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With a rotary trimmer trim the excess off the right side. Don't move anything yet.
8.
Trim off the top.
9.
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Turn the square so that the other color is on the right and bottom. Line everything up again.
10.
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Trim right side. Then trim the top.
Once you have a bunch of these half-square triangles you can make pinwheels or other designs.
I chose to sew these together in the pinwheel.
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The points should all match up in the center. Sometimes this works better than other times, but when I wasn't squaring them up properly they didn't match at all. Before I wasn't lining up the diagonal line on the ruler with the diagonal seam on the square I was putting the line of the ruler perpendicular to the seam line. While I still have some trouble getting them perfect, they're a whole lot better than they were.