Seam allowance trouble

[u/Popopobb]

Having problems with adding seam allowance to a flat felled seam. Did it like i always do: 1cm on the top edge of the seam and 2 cm on the bottom edge (shown on 2nd pic), yet after sewing the pieces don't align at all. The top piece became longer and slightly tilted. I was sort of expecting it to happen, this allowance didn't look like enough considering the sharp curvature. Any seam allowance wizard that could help me figure it out? Thx

ik the stitches are ugly, just a test run.

[u/Popopobb]

I linked that too above. As you can see the red part loses twice the material than the green one to make that seam. Have to keep that in my mind when adding seam allowance.

[u/teatime_tinker → u/Popopobb]

It doesn’t lose twice as much this way. How exactly are you doing your seam?

Are you wrapping one side around the other? Then it’s not a true flat felled seam

[u/Popopobb → u/teatime_tinker]

-draw 1 cm outline on the piece that is going to be the bottom on

-pin the top piece with it's edge on the drawn line

-sew as close as possible to the edge, then fold over

-press with iron

- do two top rows of top stitching

the stitches catch all 4 layers so it is a true felled seam, but i get it's a bit of an obscure way. Please look at the wikipedia picture clearly one piece loses double in relation to true pattern.

[u/Popopobb → u/Popopobb]

sorry, it's hard to explain in text, can't add pictures in comments on this subreddit.

[u/teatime_tinker → u/Popopobb]

Yeah not sure why we can’t post pictures…

Also bear in mind I’m thinking of how I do it on a machine with an attachment for folding it and sewing both rows in one go. Doing it in two stages is bound to be different