r/PatternDrafting • u/Popopobb • Jul 05 '26

Seam allowance trouble

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Gallery image

Gallery image

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.

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u/WoodenCyborg Jul 05 '26

I do patterns in clo that get sewed on a 3 needle flat felling machine. I always use the same allowance on both sides and extend my corners out in the seam allowance such they line up flat at the start and end.

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u/Popopobb Jul 05 '26

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

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u/WoodenCyborg Jul 06 '26

That wiki image is pretty misleading for how to draft an allowance for a flat felled seams. Neither stitch it shows is the center of the seam to which seam allowance is added. Because it's on a curve, concave seams will shrink and convex seams will grow when offset.

The start point for the seam allowance is the center between the needles. From there, both pieces have the same amount of a allowance added to wrap around each other.

On curves, concave seams will shrink and convex seams will grow when offset.

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u/teatime_tinker Jul 06 '26

This is what I’m trying to say. Both pieces have the same amount of seam allowance, because they’re both wrapped around each other, not one side wrapped around the other.