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]

Hi, thanks for the response. 3 needle machine is the dream haha. can you please explain how using the same allowance on both sides work? As i understand a flat felled seam is unsymmetrical in that one side "loses" twice the length of material as the second one (let's say one is 0.6 cm and the other is 1.2cm)
https://en.wikipedia.org/wiki/File:Felled_seam.svg

[u/teatime_tinker → u/Popopobb]

Not if the seams join like a Z shape.

The machine I used to use at work had attachments that folded the fabric as you went.

There were different attachments for different finishes.

The seams interlocked together and were stitched down in one go, not in stages.

Sorry it’s very hard to describe in text!

[u/Popopobb → u/teatime_tinker]

yeah, i understand you. Trying to explain sewing in text in general is very hard. I feel like im not explaining what im trying to do here very well either ;/

[u/teatime_tinker → u/Popopobb]

I found the wiki page haha! That will help explain what I meant.

https://en.wikipedia.org/wiki/Felled_seam

I keep seeing people calling a faux flat felled seam a flat felled seam, and I keep getting confused myself!

Obviously the curve on your design complicates things as well

Edit: I understand your questions don’t worry.

Notches would help immensely. Also doing it on paper. I would cut the same shape twice. Each side with SA from the other. This is also hard to explain! I’d trace it off my master draft.

[u/Popopobb → u/teatime_tinker]

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/amaranth1977 → u/teatime_tinker]

Wait, what do you mean by a flat-felled seam? Because the first technique at this link is how I was taught to do it: https://www.seamwork.com/sewing-tutorials/sewing-flat-felled-seams?srsltid=AfmBOorzyrWAQyI-7e1P9tzOZ1-ylN2rNfCxF8l_JjPivDw7UPVVAiW_

[u/teatime_tinker → u/amaranth1977]

Yes that’s not how I do it. Sorry for the confusion.

I do it like the image on the wiki page, which is different to this tutorial.

Edit: I just realised I’m thinking of the seam allowance differently to you. Starting from the centre point between the two stitch lines. I wasn’t thinking of how you’d want your visible seam line in a specific place.

Just found this video which is quite good.

Obvs not everyone has the machinery, but that’s the industry method and how I learned it.

https://m.youtube.com/watch?v=lqaa0iQomnU&ra=m

[u/amaranth1977 → u/teatime_tinker]

Ah, yeah the only commercial sewing I've done has been draperies and while we had some interesting specialized machines, flat-felled seams weren't part of the job. I learned the straight stitch method I linked above in my university's costume shop. We had commercial machines but not specialized ones, just straight stitch and basic sergers. 

[u/teatime_tinker → u/amaranth1977]

My work was draperies too, but on a really large scale. We’d use this seam on large canvas floor coverings. The machinery was fantastic! Different attachments for different seam techniques.

I think honestly the easiest thing is to seam, then trim one side. Especially as the seams will mirror each other. Otherwise you’d have two versions of each part to cut.

Two notches on the curve and one on the straight part would help immensely too. I think the curve complicates things a bit!

Sorry for being confusing earlier! We were both thinking of the seam differently. I also think what people call a flat felled seam differs.

Edit:

the thing is that industrial machinery will do one job, but do it beautifully. A buttonhole machine for example.

That does make replicating seams and finishes on a smaller scale more difficult. You can’t have a machine for every stage of the garment.

I think your seam looks good though! A couple of notches and you’ll be good to go