Three-piece triangle square


I have a new pattern coming soon. Before release the pattern, I’d like to show you the easy way to trim using useful tools! It might make sense for you if you had the instructions though… But I hope you get the idea!

So you make a half square triangle (HST) first. (I will not explain how to make HST here since it’s mentioned in my pattern) Draw a diagonal line on the wrong side of a piece of square.

With the right side together, layer the marked square onto HST. Make sure that marked line and HST pieced line are crossed. Sew two seams, each ¼” away from the marked line.

The other side looks as shown in the photo above.

Cut on the marked line.

Trim the three-piece triangle square using the ruler. I used Clearly Perfect Slotted Trimmers by New Leaf Stitches ruler. I want to make 3-1/2″ square (unfinished), so I aligned 3-1/2″ dash line of the ruler onto the stitched line.

If you don’t have this ruler, DON’T WORRY! I will show you how to use the regular quilting ruler to trim the three-piece triangle square!

Before showing that, here is the three-piece triangle square after trimmed.

Okay, now I will show you an alternative way . You need the quilting ruler with 45 degree line and the masking tape. (painter’s tapes work as well) I used 6-1/2″ square ruler.

Place the masking tape on the ruler. Again I want to make 3-1/2″ square (unfinished), so I placed the edge of masking tape from 3-1/2″ mark to other 3-1/2″ mark on the ruler as shown in the photo above.

Close up. The tape is meeting 3-1/2″ on both sides.

Place the ruler onto the triangle. Align the edge of the masking tape (3-1/2″ side) onto the stitched line as shown in the photo above.

Close up. Both tape and stitched line are meeting 3-1/2″ on the ruler.

Trim the block and cut the dog ears.

You can trim any size of the three-piece triangle squares easily with the regular quilting ruler! You just need the masking or painter’s tape.

I hope it’s helpful for you!

Happy Quilting!


3 thoughts on “Three-piece triangle square

  1. Question. When making the three-piece triangle square, it’s right to have the long side of the large triangle running opposite directions, correct? If you need four, would you recommend making two and have different directions? Or would you suggest make 4 and wasting 4 halves? Hope that makes sense.

    1. Leanne – Thank you for the question! The way I suggested here, you will have (2) three-piece triangles from one set of a HST and a square. And yes, the long side of the large triangle running opposite directions. If you need (4) three-piece triangles, you make from two sets of a HST and a square. I used this method in my pattern MILKY WAY which I needed to make (4) three-pieces triangles. It worked perfectly since it didn’t matter which directions the long side of the large triangle running. Because the color for the star is same. I hope I answered for your question! Please let me know if you have more questions! Thank you! Satomi

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