How To Sew Equilateral Triangles

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Last week we talked about how to cut equilateral triangles and the related math. Today we start sewing them together! 60 degree triangles can be a little daunting at first, but with these tips and a little practice you’ll be forming perfect points like a pro in no time!

If you haven’t already starched your triangles during the cutting process you may want to consider doing that now. Since we’re working with so many bias edges starch can help prevent them from stretching so much. If you don’t want to mess with starch, that’s fine too! It’s not necessary if you’re careful about how you handle your pieces. I’ve done it both ways, and because I like anything that saves me time I’m generally going to cut out starch with its extra ironing time.

Sewing Equilateral Triangles

Start by setting your first half triangle and full triangle next to each other, face up, in the same orientation you want them sewn. One triangle should be pointing up and the other down, and the grainline should run along the top and the bottom.

Remember how in the cutting tutorial I said you should keep track of which side was the grainline? This is why – it makes it so much easier to orient them correctly if you already have it marked. If you didn’t keep track and need to figure out which side is which, sometimes if you look closely you can see the direction the fabric threads run. The straight of grain will run horizontal and vertical. For the bias edge the threads will run diagonally. Otherwise you can gently pull on each side of the triangle to determine which one is the straight of grain – it won’t stretch as much as the two bias edges.

The reason this is important is so that when we sew the quilt together the grain runs along the length and the width of the quilt – just like it would if you were sewing squares. It helps keep the edges square too. Ever see or make a quilt where the edges are all wavy? It’s likely because those edges were bias edges.

Now that we’ve gotten all that sciencey stuff out of the way, let’s get back to sewing.

Place the pieces right side together matching the bias edge. When flipped, the first triangle’s grain line will stay at the top or bottom while the other grain line will have flipped to the side.

Sew along the bias edge.

Press the seam to one side.

Lay the next triangle right side up next to the sewn pair, continuing to keep the grain along the top and the bottom.

Place the triangles right side together, again matching the bias seam. If the seam has been pressed toward the first piece, the next triangle will match up perfectly.

If the seam has been pressed toward the second piece then you’ll need to align the triangle with the unsewn edges of the second. Make sure the point extends ¼” beyond the second triangle. This one little step of checking the distance on that point has saved me more headache and made my triangles more accurate than anything else I’ve done.

Sew along the bias edge. The seam should start exactly at the intersection between the two pieces.

Keep pressing seams in the same direction for each row, and alternate the direction for each row. This will allow you to create nesting seams when you sew them together.

As you sew your rows check to make sure your points are ¼” away from the edge of the strip.

If the points are too close to the edge you’re either going to sew over your points, preventing you from achieving those perfect points, or you’re not going to be able to sew a ¼” seam allowance which makes that area at risk of splitting open after the quilt is sewn. I know it sucks, but it pays off in the long run to rip out those incorrect seams and re-sew them. You’ll thank yourself later!

To match the points of your rows, poke a pin just above the points of both triangles to hold them together in the right position, then use a second pin to pin the two pieces together. Remove the first pin.

If you sew a scant ¼” seam just above the point it gives you enough room for pressing and turning making those points picture perfect!

Pressing these seams open can help reduce some of the bulk.

Looking for inspiration? My latest quilt + dye pattern, Dazzling Dream, is made entirely from equilateral triangles.

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