Trying to make angled corners, but the triangles are too short and not lining up with the blocks or at the seams. Blocks are 6"x6", and the triangles are 6" on the hypotenuse. HELP!

Yikes, a lot of misinformation here.

Here's a primer for you to get started. Print it out so you can reference it to what follows below.

I can't tell if you're trying to make HST or QST blocks. Your picture looks like QST blocks, but Google led me to this pattern, which used HST blocks.

Let's go back to basics:

You can't just cut a plain 6" block into triangles, sew them together and have it come out the same size as the plain block. You need to account for the inside seam allowances down the center, plus the angle of the inside seam. So you need to start with a bigger square so that when you sew those triangles back together, they are the same size as your plain blocks.

Also, you should learn the terminology - not just to ask questions, but to understand patterns and instructions.

Desired FINISHED size of block = 5.5"

Plain block CUT size = 6" = UNFINISHED size.

HST = Half Square Triangle unit and block. This is a block made up of TWO triangles, preferably with the bias edge on the inside. The triangle units are made by cutting a square in half once along the diagonal. The straight (on grain) edges are on the two shorter equal sides, and the bias edge is the longer side.

The magic number is 7/8". You add this to your desired FINISHED size. So in your case that would be 5.5" + 7/8" = 6-3/8". That would be the cutting size for your starting squares. You would then put two squares right sides together, draw a line down the center, sew 1/4" on each side of the line, then cut it apart on the line. Open up and you've got 2 HST blocks each measuring 6" UNFINISHED.

QST = Quarter Square Triangle unit and block. This is a block made up of FOUR triangles. The triangle units are made by cutting a square twice, along each diagonal. The straight edges are on the long edge, and the two shorter sides have bias edges. These are used for setting triangles, because the last thing you want if to have bias edge all around your quilt.

They are NOT interchangeable and play different roles within a block.

The magic number is 7/8". You add this to your desired FINISHED size. So in your case that would be 5.5" + 7/8" = 6-3/8". That would be cutting size for your starting squares. You would then put two squares right sides together, draw a line down the center, sew 1/4" on each side of the line, then cut on the line. Open up and you've got 2 HST blocks each measuring 6" UNFINISHED.

QST = FINISHED size + 1=14" = cutting size for starting squares - cut on both diagonals, results in 4 triangles, with one on-grain side on the long side, which you want on the OUTSIDE of your block, the other two sides have bias edges.

These are not interchangeable, and serve different purposes.

Personally, I prefer to cut my starting squares a big bigger make the HST or QST blocks, then trim them down to my UNFINISHED size. YMMV.

There are shortcuts to piecing that unit, but you don't mention if it's scrappy or you're using the same fabrics for each one.

Before you cut the squares, I would starch them as you'll be working with a lot of exposed bias.

Now, as far as those two numbers I used above - the 7/8" and 1-1/4" - those are the exact measurements needed. However, who among us actually sews exactly, or needs that pressure? I personally prefer to cut those starting squares for HST/QST blocks a bit larger than required, make the blocks, and then trim them down to my desired UNFINISHED size. I find then that when I'm ready to join the blocks together, it goes very smoothly, and they fit together perfectly. So just add 1/2-ish to the numbers - it doesn't have to be exact, because you're just going to trim them down anyway.

I suggest you find some scrap fabric - two colors - and just make sample HST and QST blocks. That way you can see in front of you how they're put together, and why it's important to use the right one in the correct position.

TL;DR - you need to understand the basics of HST and QST triangles. ;)

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