Heather Thomas

Cutting Corner and Setting Triangles for Diagonal Sets

Heather Thomas
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Duration:   6  mins

When designing and piecing a quilt set on the diagonal you will need to have both setting triangles and corner triangles in your design. Heather Thomas shows you how to measure for and cut both kinds of triangles sharing several different cutting and measuring tips and techniques.

Quilt Design and Cutting Triangles

To begin with, Heather explains what it means to have a quilt design set on the diagonal and how this design needs to be finished around the edges in order to make them straight. Heather explains the difference between corner triangles and setting triangles and shows where they go in an example quilt design.

She then explains the math behind calculating how big of a square you need to start with in order to get the correct finished triangle size. There is a different equation used for setting triangles than there is for corner triangles and Heather shows how to use both. Similar to when determining a half square triangle size, there is a certain number you need to remember that gets used when determining the size of the initial square that is cut down and Heather explains what that is. She also explains how the final number can be rounded up in order to make measuring and cutting easier. Heather then shows how the triangles need to be cut.

Setting triangles and corner triangles are both cut differently, one by cutting a square in half and one by cutting a square into four sections. This is done because setting triangles and corner triangles require the bias edge of the triangle to be in different places. Heather explains what the bias is, shows where it is located on a fabric square and demonstrates how much stretch there is on the bias compared to the straight edges. She then explains where the bias edge needs to be on each triangle and why it’s important.

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3 Responses to “Cutting Corner and Setting Triangles for Diagonal Sets”

  1. Jenny

    Very helpful--thanks!

  2. michelle barkley

    I love the sashing on that quilt!! Is there a pattern online for it?

  3. Ruth Canterbury

    I noticed when you calculated the size of the setting triangle (multiplied 12 inches by 1.414) you rounded the 16.97 down to 16 inches. I would have rounded up to 17 inches and then added the amount for the seam allowance. My block would have been an inch wider than the one you used. Is rounding down on the setting triangles the norm?

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