Marking Diagonal for QSTs

Marking Diagonal Lines for QSTs

One of my favorite aspects of teaching workshops is that it makes me really think through what I do. In the process of preparing to teach the Sunburst workshop with the Las Vegas Modern Quilt Guild a little over a week ago, I was making samples to show my process for making quarter-square triangles (QSTs), and I realized that I haven’t discussed QSTs or shared this particular tip on my blog yet. So, let’s take a look!


Quarter Square Triangles

Quarter-Square Triangles – Piecing Illustration

First, let me give a top level summary on my approach to making QSTs.

  1. Begin with (2) untrimmed HSTs. Press the HST seams to the side. In the example illustrated above, each HST contains navy, so the HSTs were both pressed toward the navy.
  2. On the wrong side of one untrimmed HST, mark a diagonal line perpendicular to the sewn seam line.
  3. Place the untrimmed HSTs right sides together, and make sure the seams nest neatly.
  4. Sew a scant ¼” on either side of the marked diagonal line.
  5. Cut apart along the marked line.
  6. Press seams open.
  7. Trim to desire size.

To know what size square to start with to make the initial untrimmed HSTs (if making the HSTs using the two-at-a-time method), I recommend adding 1½” to the finished size block. So if you want a QST that will finish at 4″ square, start with 5½” squares to make the untrimmed HSTs and trim the QST to 4½” square.

Marking Diagonal for QSTs

Marking Diagonal for QSTs

Which brings me to my tip: when marking the diagonal line on the wrong side of one of the untrimmed HSTs, I do not suggest marking the line from corner to corner of the HST. Because the HST is untrimmed, you cannot be sure that the two points are perpendicular to the sewn seam. Instead, I recommend lining up a ruler with the sewn seam (large red oval above) and sliding the ruler along the seam until it also intersects with one of the two corners of the untrimmed HST, which is the white corner in the photo above. Then mark the diagonal line.

Marking Diagonal for QSTs

Marking Diagonal for QSTs

As you can see in the above detail photograph, the diagonal line might not run perfectly through the second corner, but that is okay. It is much better that the marked line be perpendicular to the sewn seam. By marking the diagonal line perpendicular to the seam line, all four triangles of the QST should come out to be the same size, so after sewing a scant ¼” on either side of the marked diagonal line, cutting, and pressing, you will find that the QSTs sewn using this approach, rather than marking corner to corner on an untrimmed HST, will be easier to trim square.

9 thoughts on “Marking Diagonal Lines for QSTs

  1. Betty Lee Angle says:

    Thank you for this tip. It solves a problem that has frustrated me.

  2. This is a great tip, Yvonne, and thanks for the table too.

  3. Rochelle Summers says:

    Thank you, Yvonne. I think using this technique will give me greater accuracy in my piecing.

  4. Patti Howard says:

    I enjoy your tutorials! Thank you. I am curious, you specified untrimmed HSTs…is this because you will be trimming later anyway?

    1. The reason for not trimming is multifold:

      1. Sew, press, trim, sew, press, trim are a lot of steps. Removing one trim helps shorten the process of making the block.
      2. If you do trim the HSTs square, then the starting square would need to be larger so that the trim size can be a bit oversized so the final trim can be done. By skipping the intermediate trim, it saves a bit of fabric waste.
      3. Reduction in risk of injury. Rotary cutting is a bit dangerous, and while trimming can add precision, adding lots of trimming steps can lead to mis-cuts, hurting yourself, and overall frustration. Miscutting something and not having enough fabric to re-do it or the energy to re-do it could lead to a project not getting finished.

      And those are just my thoughts. 🙂 I’m sure there are good reasons for trimming as well, but when hourglass or QST blocks are made, all the instructions I’ve seen (and I see quite a few because I work as a technical editor in the industry) call for using untrimmed HSTs.

  5. Debbie says:

    I had never ever considered marking as you suggest so I will definitely try it. Thanks!

  6. What a great tutorial! Thanks so much for making it available to all of us. I have learned so much from your well written tutorials!

  7. allisonwp says:

    Thank you for another clear and helpful tutorial. I think I could create an entire Pinterest board just for your tutorials! You are very generous with your time and expertise.

  8. Liz says:

    Next time I have to make some of these blocks I’m going to try this method, thank you!

I really appreciate the time and thought you take to comment, and I look forward to conversing with you. :)