Originally Posted by
Sewnoma
These are tricky for me, too! I don't have any good solutions for you, but you're definitely not alone in this. I'm awful with these.
I tend to not end up with the straightest seam (even if I draw lines to sew directly on) and so I end up with weird puckers and curved-up pieces when I try to press them flat. Argh! I think for ME, I'm better off cutting the triangles first and then sewing, so I can use my quarter-inch foot to keep me in line. Which is disappointing, so I keep trying to do it the more efficient way, telling myself I just need to keep practicing...but I keep getting aggravating results.
This is why most of my quilts are made with squares and rectangles! LOL
If you prefer cutting first and then sewing, I'd suggest the Easy Angle Ruler:
http://www.amazon.com/Quilting-Angle.../dp/B005KC3L4U
You can find it just about anywhere and it's really helpful. Using the ruler, you won't need to add 7/8" to get the proper finished size. It's designed to cut triangles from strips. If you have 2 1/2" strips, you'll be able to get 2 inch finished triangles. One end of the triangle is blunt when you cut them, and you'll be able to feed that end into your sewing machine using your 1/4" foot. It avoids having to start sewing on a point.
Here's a video on this method:
https://www.youtube.com/watch?v=HKrTj-d5ryI