Turning a Block On Point Twice

Friday Jim and I drove down the Mississippi River from La Crosse, WI. We were returning from a two week trip to see our son, who lives in Washington state. With 2,000 miles behind us on the train, it felt great to switch to our own car.

In Prairie Du Chien, WI, we stopped for lunch. On one wall of the diner hung a quilt with a patriotic theme. It was a medallion quilt, centered by a stylized American flag. The flag block was turned on point twice, emphasizing its importance and creating a nice, large center.

I liked the setting, and especially liked that a non-square rectangle was turned that way. It’s a setting I haven’t used myself.

I’ve written plenty about turning large blocks on point to center a quilt. In one post I described the types of blocks suited for an on-point setting, if it is only turned once. In another I showed how to do that, with the math needed to cut your setting triangles large enough. I’ve also written about turning small blocks twice, creating an “economy block.”

But I’ve never written about turning a larger rectangular block twice. Here are some cool things I learned about it.

*~*~*~*~*

The Part I Already Knew
If you turn a square block twice, you’ll double its dimensions. Consider an example of a 15” block. Turn it twice with an exact (not over-large) setting, and you will create a block that is 30” wide. Using the math for diagonals,
15” x 1.414 = 21.21”.

Now turn it again:
21.21” x 1.414 = 30”.

This block setting is often called an “economy block.” It’s an especially effective way of highlighting a small centerpiece, such as a special or fussy-cut piece of fabric.

Economy block setting – a square turned on point twice.

The Part I Didn’t Think About Much, But Probably Knew, Too
As it turns out, you can do this with non-square rectangles, too.

Non-square rectangle, squared first with unequal triangles, and again with equally-sized ones.

The Part I Didn’t Know, And Figured Out Last Night
The size relationship for both types of blocks can be generalized, and is far easier than multiplying by 1.414. If the length of the inside shape is A, and the width of the inside shape is B, the distance across the diagonal of the interior square is A+B. That means the length of the exterior square is A+B.

In the economy block example above, the interior square is 15”.
The resulting block is 30” square, or 15” + 15”.

In the second example, if the interior blue rectangle is 12” x 18”,
the resulting block is 30” square, or 12” + 18”.

The next time you want to frame a rectangle with setting triangles, remember how easy it is to determine the finished size. Length plus width of the interior rectangle (square or not!) is the width of the resulting square.

Ain’t math fun? 🙂

14 thoughts on “Turning a Block On Point Twice

  1. snarkyquilter

    Oh dear, here’s where I confess that the size of a quilt center is usually a function of the size of the fabric I want to use. My fancy fabrics are often quite small so I make do with what I have. Then I build it out. I do use drafting paper at that point. I’m glad you do it the right way.

    Reply
    1. Melanie McNeil Post author

      My dear friend Mark said “….or start with a big blue cloth and cut what doesn’t fit…. There’s more ‘n one way to skin a cat…..” I don’t think there is just one right way here. For me, the excitement was mainly in figuring out how BIG the new square would be. And mostly that was the math excitement, as the quilt becomes what it will become, regardless of the math. 😉

      Reply
  2. katechiconi

    I have a math lame-brain, so it’s always good to see your lovely clear explanations. But the diagrams were what made it stick. I looked at the rectangle centre and just mentally pushed those short sides in till it was a square, and yes, it all made perfect sense. Yup, the visual explanation rules for me!

    Reply
  3. Pat T.

    Oh, *Yes!*…
    I DO love the math!!
    (I’ll often have fun creating a pattern, doing the math, and just put it away… without actually sewing it out! I can dive right into another design/math exercise!… Just pencil and graph paper!
    Actually, the quilt I’m finishing now, is an “old” idea/pattern I drew up and had set aside.)
    Pat T.

    Reply
  4. jmn111

    Love the math generalizations. Very helpful. I rarely make square quilts so this information could be helpful on some future quilt! Thanks. I haven’t played enough with squaring on-point elements to have figured any of this out.

    Reply

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