Searching for resources on pack/duffle/luggage seams

[Jim H]

I know this is straying from UL discussion, but I learned all my sewing knowledge here and branching out is scary!

I’d like to sew some gifts for folks, and things like cordura or ballistic nylon duffles, day-packs or carry-on bags are what I’m thinking. I’ve gotten fairly comfortable with construction of tarps, net tents, simple summit-packs other backpacking items, but haven’t worked with heavier fabric than some 4.4oz sil remnants I practiced on at the beginning.

So far I’ve got some tex 70 thread and appropriately sized leather/denim needles, but I’ve having trouble tracking down information on seam construction for bags in these heavier materials.

I’d really love to know what the seams look like on Tom Bihn bags, since something like their Aeronaut 30L convertible carry-on bag looks like a great layout to me.

Whoops. Forgot to paste the last paragraph…

Looking at my most heavy duty bag (an old Kelty Redwing), it looks like the construction is a straight stitch with right sides together, and then some bias tape to close the edges, so two rows of stitching, but only one really taking the load of a fully stuffed bag. It’s just surprising to me that there isn’t some additional reinforcement needed on heavy duty bags. Am I missing something? So if anyone has a tip on another forum more suited to this type of sewing, or any experience to share it’d be much appreciated.

Thanks!

[David Chenault]

With medium to heavy thread and tight stitches a straight stitch can hold a lot.  For some pack seams I still use a straight stitch because it doesn’t leave any threads exposed on the exterior, which is good for abrasion.  I usually sew these seams with a 1″ seam allowance.  Do the first pass with a standard stitch length (~2mm), then the second pass with a much tighter one (.8mm).   Then fold the seam allowance over and stitch a third time through what is now all four layers of fabric, again with a very short stitch.  Makes for simple, bomber and weather tight seams.

Last year I built a big duffle for an international trip using this method, and it has held up very well.

[Ken M]

Greetings. While certainly not a “pro” grade stitcher I manage to sew with a variety of fabrics. For some of my projects recently I’ve been using some vinyl coated nylon (outdoor furniture type fabric) and 1000/500 D cordura. These are probably in the range of 10 oz per yard. Not in the light weight category but still outdoor myog and they support my hike and kayak habits. I now use a Pfaff all electronic machine. A very strong machine with lots of stitch choices and versatility.

My experience/comments:

1__ I’ve not found a good reference for seam construction with heavy fabrics either. If there is such a ref it is probably in a book about upholstery or sailmaking. Google sailmaking will dredge up some potential useful info.

2__For seam construction ideas I look at what others have done. Look at those old packs and duffels. Go look at new gear and inspect the seams. I think what you will also find is that mostly they are put together with a few basic seams that you are probably already familiar with. Look at how they protect or keep the edges from fraying. Other than adhesives and welding sewing construction hasn’t changed much.

3__What I find challenging with heavy fabric is actually manipulating the fabric into the needle especially when I get to corners and tight curves. And how to manage with multiple fabric layers. I have to practice/experiment with each different fabric.

4__I have and use a few different thread types/weight. I have a cone of some Tex-69 bonded poly. My machine will sew it but I am limited to staight stitch. I bought (and recommend) a second bobbin holder. I loosen the lower tension (a lot) and increase the upper to get a nice balanced stitch with this stiff thread. Also works well for T-45 also. I find that my preference is for the T-45-50 weight thread. Also strong and can use almost any stitch so is much more versital. If I really want more strength I use two lines of stitch or other reinforced stitches.

5__Prototypes/practice… Get some heavy fabric and make a round bottom stuff sack or something else not too complicated. See what happens. I often find that my first piece of some new project is not something that I want you to see. I end up with something functional but not the quality I want. The second time is always better.

KenM    Louisville, Oh

[Nick Smolinske]

Basically duffels and packs use straight seams because they can (with thick thread) and because it’s faster.  Heavy thread and tight stitching is the key, as David said.  I use both 69 and 92 thread in my machines, depending on the fabric.

I could probably make a pack with flat felled seams, but it would be slower to sew, so I would have to charge more for it.  There would be no real increase in durability because the thread is already strong enough.  If I seam seal the bag then it’s even stronger.

That said, even with a straight seam I do reinforce any webbing, strap, etc that will emerge from a seam with a couple more lines of stitching.  Even though in theory only one line of stitching is being loaded at once, I find in practice that without a second line close behind the first, the stitching will stretch at the attachment point.  It won’t fail, but it will look ugly.  I use nylon thread and polyester thread might not exhibit this, but nylon has worked better in my machines so I’ve stuck with it.

[Jerry Adams]

“faux” flat felled seam?

Cut half of the seam allowance on the inner piece of fabric, so you’re sewing through 4 layers of fabric rather than 5.

This is the standard way of doing it, but with light fabrics there’s no need to.

[Jim H]

Thanks all. Sounds like I should make a prototype with strait stitches. I’m working with a home machine, a Singer Heavy Duty, which is advertised as being able to sew through multiple layers of heavy fabric, but I’m worried about thick seams. I’m going to have to get some sample fabric and see what my machine can handle.

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