Wow, more creative quoting here. Jay, YOU were the first to use the term "friction" in this thread.

If it were about friction, I imagine we'd be hearing the manufacturers citing stitch tension and webbing surface finish rather than stitch count and thread tensile strength (see moof's post).

You're right. I was the first to use the word friction as a succinct way to express your awkward phrase "sewn so tightly together that they won't separate." If you don't want credit for realizing that you're describing friction, so be it.


Well, now you're agreeing with me, and disagreeing with your previous claim, since I have been saying all along that friction is probably unimportant, whereas you had implied (whether you realize or not) that friction is important.

Jay

Fercryinoutloud, I can nail a couple greased boards together with a few hundred nails and you'll never pull them apart lengthwise, but friction ain't got nothing to do with that either.

Jeesis F'n Cripes...there's no end to your making up quotes, is there? I never said "tightly", let alone the rest of what you put there in quotation marks, so if that's where you INFERRED anything to do with friction, it's all in your head.
.

OK, so maybe my choice of the word "fuse" made you think of "one piece" of material, but that's silly. Webbing is a mass of thousands of interwoven filaments. Two webbings sewn so tightly together that they won't separate under the greatest stress is now 2n thousand filaments acting together. Do you really have a problem with that being much stronger?

Fercryinoutloud, I can nail a couple greased boards together with a few hundred nails and you'll never pull them apart lengthwise, but friction ain't got nothing to do with that either.

Point, Set, Thread.

Two webbings sewn so tightly together that they won't separate under the greatest stress is now 2n thousand filaments acting together. Do you really have a problem with that being much stronger?

[from Tom Moyer at www.xmission.com/~tmoyer/testing/pull_tests_11_98.html ]
Test Methods

We used a vehicle winch on a Hummvee to apply forces. A second Hummvee was initially used as an anchor. However, with an end-to-end pull, and with all four wheels locked, we were able to drag both vehicles across the concrete floor with 5000 lbs force. (good number to know if you use vehicles as anchors.) We ended up anchoring one vehicle to a tank (yes - really) and the other to eyebolts mounted in the wall. A Sensotec load cell was used to measure forces. It is calibrated internally with a shunt resistor.

Results

11/18 Test #1:
Pull an old 9/16" tubular web sling to failure. This sling was found girth hitched around a tree on Mt. Olympus and had obvious burn marks where ropes had been pulled through it. The sling was loaded with an end-to-end pull on the loop.

Result: Material failure at one of the burn marks at 4410 lbs.

11/18 Test #2:
Pull an old 1" tubular web sling to failure. This sling was found tied around a tree on Mt. Olympus. It had no obvious burn marks on it, but it has to be assumed that at least one rope had been pulled through it. The sling was cut off and retied with a water knot. It was loaded with an end-to-end pull on the loop.

Result: Material failure in the middle of the sling (presumably at an unseen burn) at 4300 lbs.

11/18 Test #3:
Pull a new 1" tubular sewn web sling to failure. One of our members sewed the sling on his home machine with a random stitching pattern (for testing purposes only!) The sling was loaded with an end-to-end pull on the loop.

Result: Failure of the stitching at 5260 lbs.

11/23 Test #3

Repeat of 11/18 Test #3
Result: Failure of the stitching at 5920 lbs.

11/18 Test #4
Pull a new 1" tubular sewn web sling to failure. The sling was sewn professionally with 5 bar tacks. The sling was loaded with an end-to-end pull on the loop.

Result: Failure of the stitching at 4720 lbs.

11/23 Test #2
Repeat of 11/18 Test #4 prof.sewing
Result: Failure of the stitching at 4730 lbs.

11/18 Test #5
Pull a new 1" tubular web sling to failure. The sling was tied with a water knot and loaded with an end-to-end pull on the loop.

Result: Material failure in the knot at 4980 lbs.

11/18 Test #6
Pull a new 1" tubular web sling to failure. The sling was tied with a [grapevine bend]and loaded with an end-to-end pull on the loop.

Result: Material failure at the bend over the shackle at 6210 lbs.

---------------------------
Discussion:
The relatively high breaking strength of the two old and burned slings surprised me. Nevertheless, don't expect to see me rapping off a single old sling any time soon. I was also surprised that the home sewing job outperformed the professional bar tacking - and that the bar tacked slings were so weak. I have always been told that sewn slings are stronger than tied ones.

The sling tied with a water knot failed at 4980 lbs. If the two sides are loaded equally, each side carries 2490 lbs of tension. The CMC Rope Rescue Manual claims a 36% strength reduction for a water knot in webbing. Mountain Search and Rescue Techniques also lists a 36% strength reduction, although in nylon rope. If these are correct, the webbing has a material strength of 3890 lbs - very close to the 4000 lb rating usually assumed for 1" webbing.

The sling tied with a [Grapevine Bend] was the strongest of all slings. It is notable that the sling did not fail at the knot.

Bar tack climbing webbing with 138 thread... Not 69.
double fishermans is strongest. Box with X next...

It's actually pretty simple. Box tacks are technically stronger because they distort the natural weave of the webbing less and spread their load bearing nature over a larger area. The reason they aren't used in our applications is that to get enough stitches to maintain strength will require a large area of the sling for sewing as well as increase labor (and thus prices). It would also make the sewn joint 5 x larger, thus making it more bulky, stiff and unmanagable.

Industrial slings are sewn with cordage, not standard thread. This cordage when used in 1" or smaller webbing would distort the weave. It has a much higher tensile strength 30+ lbs so you need far fewer stitches. Together, that makes it practical on large items to use a box tack.

At the first order, say just putting in a dozen stitches the literature says you get about 2-2.5X the threads tensile strength per stitch (due to loading in shear, and there being two strands of thread in cross section).

My office is next to that of the world's most advanced parachute manufacturer, I'm going to wander over there and ask a few questions. But it's not a priority for me, and my wife is having surgery on Thursday, so I'll get around to it when I do. I do know a bit about sewing standards and I do manufacture critical application materials in webbing and in fabric.

If you really want to find out everything there is to know about sling construction, try researching the US Military's voluminous experimentation in ways to put webbing together for climbing slings and a plethora of other applications.

moof- where is this strength estimate from (the 'literature').?