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Author Topic: Flat felled seams  (Read 8764 times)
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Will Sturdy
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« Reply #15 on: June 29, 2012, 05:43 PM »

I believe you have correctly identified the seam on the WM.

Straight stitch in any type of seam creates a 'tear here' line in hard coated fabric. This will be more obvious in hard fabrics like PC-31 or mylar than softer fabrics.

Straight stitching does not elongate with the movement of the fabric like a triple step lap seam does, so it can create odd lumps in the sail. The extra layers of material concentrated in one strip also are no good for the sail shape. These effects are more obvious in softer fabrics than harder fabrics.

PC-31 is extremely fray resistant, so I would not worry about raw edges fraying. Cutting down on the width of seams so the stitches completely cover the seam and/or using a tape such as 1/4" seamstick or ATG 924 with a seam of the exact width of the tape will prevent the edges from lifting.

 Unless you value visual appeal over structure, lapped seams are the way to go.
« Last Edit: June 29, 2012, 05:44 PM by Will S » Logged
Ca Ike
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« Reply #16 on: June 29, 2012, 05:50 PM »

THe WM is done with Flat felled seams and when done right they can be just as strong or stronger than lapped seams.  Common mistake with flat felled seams is to use too short of a stitch length and thats what weakens them.  YOU want a length of 1/8 inch minimum when doing flat felled seams if strength is an issue.
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« Reply #17 on: June 29, 2012, 05:53 PM »

good to know.  I have never worried about my lapped seams and zigzag stitching (I'm partial to a serpentine stitch as well).  Mostly just looking to try something new.  I do value structural integrity, but also appreciate the visual appeal (I would be fooling myself if I said the look/finish didn't appeal to me).  My thoughts are that if the Widowmaker holds up, so would whatever I build (in theory).  It is my intent to give it a shot on one sail pattern (I've been playing around with a few straight seamed patterns that would lend themselves to the flat felled seam).  In the long run, I'm sure I'll prefer the straight forwardness of the lapped seam.  We'll see!
Ca Ike
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« Reply #18 on: June 29, 2012, 06:09 PM »

YEa just remember when dealing with plastic cloth (nylon, poly, mylar) the closer the needle holes the weaker the cloth will be when using a straight stitch or single step zig zag.  ITs the perforated paper syndrome.
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« Reply #19 on: June 29, 2012, 07:15 PM »

A flat fell seam is said to be the strongest seam when talking about regular woven fabrics. On our hard coated thin sail fabrics the number of seams/holes may make a difference but we really shouldn't be breaking or cutting any of the threads when sewing so do we really weaken the fabric?  No doubt a taped seam with sewing is the strongest for PC31 & 9460 or Nylon & C3 Sailtape since the tape alone is enough for most of the seams on a kite, the triple step zig zag just adds another level of security and assures there won't be any issues with creep.

But I am always impressed by a well done flat fell seam. The Skyburner Delta Drive with its half width flat fell seams is a true work of art & craftsmanship.


"Living is easy with eyes closed, misunderstanding all you see" John W Lennon

"People do not quit playing because they grow old, they grow old because they quit playing" George Bernard Shaw
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« Reply #20 on: June 29, 2012, 09:57 PM »

TNT is done with flat felled seams and a straight stitch from what I can tell.  It is gorgeous and I haven't heard of failed seams.

It this one of those things that is theoretically weaker, but practically no different?


6 kite tom
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