This could also be called “How to trim QST blocks” – Because an hourglass block is another name for a QST, or Quarter Square Triangle unit.
I am really fan of making units a little larger than you need them, and then trimming them down to size- I find that no matter how careful I am with cutting and sewing, it’s hard to get them perfect. I like to do this with flying geese units, HSTs, and hourglass squares.
It is important to get your units accurately trimmed- if they’re not accurate after you trim them, then what’s the point, right? For hourglass squares, you really need those diagonal seams to be lined up in the corners of your squares, or your block won’t go together as well and your points will be weird. Nobody wants that!
I will show you 2 different ways to do it. First, I’ll show you how to do it with a square ruler. Then I’ll show you how to do it with a regular ruler, relying on the lines on your cutting mat.
To use a square ruler- Your ruler should be at least as big as your hourglass square, and it needs to have a 45 degree line marked on it.
I want to trim this square to 3 1/2″ (the finished size in the quilt will be 3″). I need to figure out what my center point is, so I divide 3 1/2 by 2:
3.5 divided by 2= 1.75
So now I know that 1 3/4″ is the center point of my square. I place the ruler on my square so that the center point of the square is at the 1 3/4″ mark, and the diagonal seam is lined up with the line on the ruler.
Then I trim the top and right edges:
Now I need to trim the other edges- easy peasy! Just flip the square around so your 2 untrimmed edges are at the top and right side, just like before. The edges which have already been trimmed should be lined up with the 3 1/2″ marks on the ruler (since 3 1/2″ is the size we want our trimmed square to be.) The center point will once again be at the 1 3/4″ mark, and don’t forget to line up your diagonal seam with the 45 degree mark on the ruler (this is crucial!) Now I just trim those 2 remaining edges:
Perfect hourglass square:
Now, let’s trim our square without the use of a square ruler. For this, you will be relying on the lines on your cutting mat. It’s a little more complicated than the first way.
Once again, you need to figure out the measurement for the center of your trimmed square. We will use a 3 1/2″ trimmed square, with a center point of 1 3/4″, again.
Place your hourglass square on your cutting mat, lining up a diagonal seam with the 45 degree line on your cutting mat, and lining up the vertical and horizontal center points with lines on the mat as well:
Trim 1 3/4″ away from both sides of the vertical center line (this will give you a square which is now 3 1/2″ across):
Then, trim 1 3/4″ away from each side of the horizontal center line:
That’s it! Another perfect hourglass square!