Summer Storm, Clue Three – Make a Triangle in a Square using the Tri-Recs Tool

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How to make a Triangle in a Square Quilt Block for the Summer Storm Quilt Mystery using the Tri-Recs ruler. Lots of tips in this tutorial!

If you just got here, you are following a summer mystery quilt.  It is being revealed in a series of weekly clues on the blog being posted every Monday from the introduction before Memorial Day and continuing every week until September  2, 2019. 

Before we get started, this tutorial is for the Tri-Recs ruler.  If you have the V Block ruler and would prefer to use that one, I have written a V Block Ruler tutorial here.  It is for an entirely different pattern, but the size is the same as this quilt so you can use those instructions if you like.


  • (2) 4-1/2″ wide orange strips (you may not need both strips)
  • (2) 4-1/2″ wide background strips
  • The Tri-Recs Tool.

In this block, you will be using a specialty ruler, called a Tri-Recs.   (You could also use the Accuquilt die #55409 ) If you prefer, you can cut draw out the block, then use heavy template plastic for these pieces.  This block measures 4-1/2″ x 4-1/2″ unfinished.

A Tri-Recs ruler actually has two pieces. There is a large isosceles triangle piece (which makes the center of the point block – in this block, orange)  and a half triangle piece (which will make the two sides – in this block, white.)  Because there is a right and left side of this block, you will need to alternate the direction of the side angle as you piece it.

To cut this block using the Tri-Recs ruler, start with a strip of fabric the same size as the unfinished size of the block for the middle triangle. In this case, it would be the 4-1/2″ wide orange strip.  Align the square edge of the ruler with the edge of the strip along the strip size line.

Cut along both sides of the ruler.  Notice that the top of the triangle block does not come to a point, but is squared off.  This makes room for the 1/4″ seam allowance.

Flip the ruler.  Place one edge along the cut line and the other along the block size line.  Cut one edge. Continue along the strip until you have cut (16) triangles.

Using the smaller ruler and the  4-1/2″ background strips, cut the half-triangle sides.  Make sure that you clip that little corner on the ruler.  It helps you line up the pieces later on.

See that little clip? Be sure to cut it.

Leave your long strips folded in half (wrong sides together) on the cutting board and cut two at a time.  You will automatically be cutting both the right and left side of this block.  Cut 16 pairs (32 triangles.)

The piecing of this block is tricky the first time. I suggest you make a practice block first.  It will give you something properly sewn to refer to while you are piecing the rest of the blocks.

Once you are comfortable with the process and know that you have a perfect 1/4″ seam allowance, you can batch sew the rest.

Lay the right side triangle on the center triangle, right sides together. That little snipped triangle will be on the lower right-hand side.  It should line up with the bottom of the block exactly.

When you sew the two triangles together using a 1/4″ seam allowance, the seam should go through the point of the snipped edge.

Set your seam.  Open your block and press to the outside triangle gently. (In this particular block, you will be pressing to the light.)  Does it seem to line up properly?

If so, add the left side block using the same seam allowance.

Open up the block again, press and measure.  It should be 4-1/2″ x 4-1/2″.   Square them up using a 4-1/2″ ruler by placing the 2-1/4″ mark on the X made by the seam allowances at the top of the triangle, then cutting around the ruler.  Resist the temptation to skip this step!  It will cause you nothing but grief later on.  Ask me how I know…

Keep an eye on that X.  Because it is 1/4″ away from the edge of the block, you will use it to guide the seam when you sew this block to another in a future clue.

Make (16), but don’t put away the ruler.  You will need it again.

This isn’t my video, but you can see how it is done here:

Summer Storm Mystery Quilt Clues and Quilt Tutorials

  • Introduction and Fabric Requirements

  • Cutting Instructions

  • Clue One: Four Patch Quilt Blocks

  • Clue Two: Using the Stripology Ruler

  • Clue Three: A Triangle-in-a-Square Quilt Block

  • Clue Four: A Reverse Triangle-in-a-Square Block

  • Clue FIve: Half Square Triangles

  • Clue Six: Quarter Square Triangle Quilt Blocks

  • Clue Seven: Cutting Squares

  • Clue Eight: Making Seams in Long Borders Disappear

  • Clue Nine: The Churn Dash Block

  • Clue Ten: The Day Star Block

  • Clue Eleven: The Night Star Quilt Block

  • Clue Twelve: Bunny in the Brambles

  • Finishing the Quilt

  • Picture Page

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