Straight or Zig Zag Stitch for Frame Bag Seams?

[justin1982z28]

I'm building a frame bag out of 400 weight cordura. Should I use a straight stitch or zigzag stitch to join the panels together? If zig zag, is wider better? This is my first sewing project. Thanks!

[sean salach]

First a straight stitch, then a zig-zag stitch with one side of the stitch in the fabric, the other just to the outside of the seam allowance. To better explain it, look at the inside seam on the side of a t-shirt. I put two lines of straight stitching on each seam because I'm paranoid that my shoddy craftsmanship will come back to bite me if I don't.

[daveB]

Straight.

Zig zag is for stretchy fabrics.  If you use a straight stitch on them and then stretch the fabric in-line with the stitching, the thread will break.

Any seam has two parts: fabric and thread.  Weight must be matched properly, within reason.  Upholstery thread on silnylon and lightweight thread on ballistics cordura are both bad: the lighter component will probably fail.  Also, more stitches are not necessarily good.  Every stitch is a perforation in the fabric; lots of perforations will cause the fabric to fail.

Note that in the field if something HAS to fail, you'd rather it be the thread, since you can repair that with needle/thread/dental floss.  Fabric that rips at the seam is pretty much a lost cause.

[jeremy11]

First a straight stitch, then a zig-zag stitch with one side of the stitch in the fabric, the other just to the outside of the seam allowance. To better explain it, look at the inside seam on the side of a t-shirt. I put two lines of straight stitching on each seam because I'm paranoid that my shoddy craftsmanship will come back to bite me if I don't.

Yep.
The two straight stitch lines are the primary structure, and one side of the zig zag goes just over the raw edge of the fabric to prevent fraying.
My first frame bag I tried to sew with flat felled seams.... never again!  Way too hard to access everything.

[DaveC]

My machine has a triple-backed straight stitch.  Bartacks on high-stress areas.   The strength of a seam has more to do with a tight stitch and a dead-straight and a even seam than anything else. 

[justin1982z28]

Thanks for the responses. I sewed a bag and wrote up how it went here: http://www.bikepacking.net/forum/index.php/topic,667.0.html Moving on to a seat bag next.