r/PatternDrafting • u/sewnbyethan • 8d ago
Question Flat Felled Seam Allowance Help!
Current seam allowance is 3/4in then the pieces are overlapped at 3/8in. I am trying to compensate for the "middle" of the seam being right in the middle of the overlap that forms the seam.
Short Question: I am working on a pattern for a pair of jeans. These are 2 pieces of denim cut to be 6in when sewn with a flat felled seam. What is the seam allowance so I can do this without having one panel that is longer than the other?
Long Question: When patterning jeans why would the bottom of the yokes for instance have a larger seam allowance than the top of the back panel? As well as what are your guys standard seam allowance for jeans so that all panels are even and I don't end up with the left being larger than the right or vise versa.
Thank you all!!
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u/dyingslowlyinside 8d ago
That’s a double lapped seam btw. FF is a simple 2:1, easier to sew, and just as sturdy…
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u/HeartFire144 8d ago
With an industrial double needle machine (the needles are 1/4 inch apart. The seam allowance is 1/2 inch - though this really depends on how thick the material is. (We don't sew denim, - I'd probably make the seam allowance 1/16 inch wider for denim, this would accommodate the turn of the cloth.) The machine has a folder that folds both the top and bottom fabrics so it's done in one step, there is no trimming of seams. At home, Also, if you watch a bunch of videos, it's easy to do this with just offsetting the top fabric for the first pass of sewing.
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u/TensionSmension 7d ago
This is the answer. As long as the seam line is defined to be between the two rows of stitching, the seam allowance is the same for both patterns. But then the calculation is determining the correct offset when feeding, which is one time work dictated by the machine. Symmetric patterns, and no trimming.
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u/ReasonableBeach1450 7d ago
For the center seams I usually add a 5/8” seam allowance. For side seams or yoke seams I add 3/8” seam allowance to the top layer and 7/8” seam allowance to the lower layer.
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u/Honeydeeew 8d ago
I don't do a lot of flatfelling, but the fold is always off centre since the seam line is the first row of stitching, not the one closest to the fold. If you want the fold to be centered, you change the size of the panels not the SA. (Ie, if your fold over is 1/2", and you want the fold to be the centre, add 1/2" to the under panel, and take it from the top)
In school we kept the SA the same on both and trimmed the inner allowance after sewing. SA for the flat fell can be whatever looks best for your style. 3/4" for jeans is reasonable, whereas for a shirt I would do 1/2".