Sewing Diagonals BEFORE Cutting to Make ½ Square Triangles

Sewing diagonals before cutting to make half square triangles


Learn another method that makes it easier to deal with the bias while sewing half square triangles together into squares.

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download transcripts Video Transcript: CUTTING AND SEWING HALF SQUARE TRIANGLES – Sewing Diagonals BEFORE Cutting to Make 1/2 Square Triangles (#6 of 8 videos)

Here’s another quick way to cut and sew half square triangles. Instead of cutting first and then sewing, you sew first and then you cut this diagonal. This is a good method to use if you will be sewing triangles together to form a square like this as seen in the corners of this block. It wouldn’t work if you just needed one single triangle like here in this block.

The first step is to find out the finished size of your triangle. You will need to measure one of the shorter sides of the triangle. In this case, that’s 2 inches. Then you add an inch to the finished side – 2 plus 1 equals 3 inches. That’s the size of square that you will need to cut, so I cut my squares here. I made sure that my fabric was pressed with right sides together and I cut this out on the straight of grain and cross grain.

Take a marking pen/pencil and draw a straight line through the diagonal. I’m using my mat here to help me find that line but you can just take a ruler and put it up there. I’m also going very gently or softly through this line as it is on the bias. If I were to go like this I’m going to be stretching that line. I f you stretch that bias then the fabric gets distorted and this will throw off your accuracy.

So here’s my line. I will take this to the machine and sew ¼” on this side and on that side. I have a ¼” foot on my sewing machine so the distance from here to here is a ¼ of an inch. So that makes it easy. If you don’t have a ¼” foot on your sewing machine, then you can take your ruler and draw a line ¼” over on this side and ¼” over on that side.

Here’s my sewn piece. Now I’m ready to cut the diagonal. Let me get my ruler. It’s going to come right over here. I don’t have to worry about that ¼” seam. I could cut right here if I wanted to because I’ve already sewn the fabric BUT I like to stay as close as I can to that marked line because it helps with the pressing later on. There – I’ve cut – and now I have 2 sets of ½ square triangles.

Now I’m ready to “Square Up”. So I want to make sure that the diagonal on the fabric piece is underneath the diagonal on my ruler. I want a little extra all the way around. Let me trim. Yup, I moved a little. So that’s OK since it’s the first trim I can get set back in there. Let me trim that off. I want to turn this around and now I am ready. I am cutting a 2 ½ inch square. The ½ inch marks – whoops – the ½ inch mark is here; the ½ inch mark is there. I’m going to line up my cut edge with that mark. I want to make sure that my diagonal is lined up. And I have a 2 ½ inch square where the diagonal runs out on the corner.

You can find more information about cutting and sewing half square triangles at under “Beginner Basics” – “Cutting” and “Sewing”.

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