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knudenoggin
Feb 12, 2008, 4:24 PM
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gunkiemike wrote: jt512 wrote: Perhaps if you used enough bar tacks, with strong enough thread, then you could achieve a joint with efficiency greater than 1. You might be able to spread the force out over enough of the webbing so that the webbing wouldn't fail at the stitching, and then if the thread itself were strong enough, the joint might be stronger than the native webbing. That's all I'm saying. I don't think we disagree. Stitches are added until the above is true. If someone has a better explanation, I'm all ears.
an even transfer of load to share it w/o some slight weakening;
that AT THE POINT OF INITIAL CONTACT the pure, untouched tape
will be stronger than its entry to the stitched section. (Certainly in the
midst of overlapped, stitched-together pieces of material, it is stronger;
but how do you get from single to multiple thicknesses w/o some loss
of efficiency (unlike a swaged spoke)?!)
So, I remain skeptical of such claims (and don't know of testing to show
even an apparent contradiction (and nb: the comparison would be between
stitched (or knotted, for that matter) material vs. pure material,
not necessarily just examining where the break occurs, within/at or
outside of the joint!)).
*kN*
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knudenoggin
Feb 12, 2008, 4:55 PM
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moondog wrote: According to a 1974 article by Carl Magnussen in the Nylon Highway, the "X-in-a-box" stitch is one of the weakest patterns.
The strongest pattern, according to this testing, was a dense 'WWWW' pattern
where the 'WW' is seen on a vertical tape section, and quite narrow; where they tried a *wider* "W" pattern--and hence had less stitching--,
it was weaker. And the bar-tacking I think is vey short "W"s in series,
and this was not bad.
Turning the 'W' sideways, to be more cross-axis oriented, both the
extended
Z
Z
Z
Z
and bar-tack-like sequences of short "Z" sections were noticeably weaker.
Using the strongest pattern in thinner/weaker tape, the testing found the
splice to fail at the splice, "by webbing fracture". This is consistent
with my belief re the splice being a weakening (if only slight).
*kN*
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slacklinejoe
Feb 12, 2008, 5:21 PM
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jt512 wrote: You're not going to introduce enough friction between the two pieces of webbing, in practice, to add much to the strength of the joint. Jay
Jay,
From my understanding, actually it is possible in certain real world situations. Take a look at belay loops. The tacks are fewer than on an end loop but the resulting strength is higher. Yes the material is stronger because it is a loop but the bond on the webbing between those must support a higher bond than the non-looped counterpart would withstand.
Dunno, there is likely something at play there that I'm forgetting but my understanding was that the friction from the wrapped webbing in the belay loop was such that even with minimal sewing the friction provided adequate bonding.
The other example worth mentioning is if I run a peice of webbing through my bartacker with no thread the pushing and pulling of threads resulting form the needle in some materials can actually yeild some minor holding strength. Not all webs do that but some do.
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jt512
Feb 12, 2008, 5:43 PM
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slacklinejoe wrote: jt512 wrote: You're not going to introduce enough friction between the two pieces of webbing, in practice, to add much to the strength of the joint. Jay Jay, From my understanding, actually it is possible in certain real world situations. Take a look at belay loops. The tacks are fewer than on an end loop but the resulting strength is higher. Yes the material is stronger because it is a loop but the bond on the webbing between those must support a higher bond than the non-looped counterpart would withstand. Dunno, there is likely something at play there that I'm forgetting but my understanding was that the friction from the wrapped webbing in the belay loop was such that even with minimal sewing the friction provided adequate bonding.
I don't really follow you. I see nothing in your argument to suggest that friction between the two ends of the material that are bar tacked to form the loop adds to the strength of the joint significantly.
Jay
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slacklinejoe
Feb 12, 2008, 5:48 PM
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I shouldn't post without caffeine.
Basically in the belay loop scenario the webbing on webbing friction of the wrap adds a significant amount of strength. Similar to that of any friction hitch or the "no knot" tie off method.
Thus, less stitching can be used than a standard rabbit ear style loop and still yield a much higher break strength.
(This post was edited by slacklinejoe on Feb 12, 2008, 5:49 PM)
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jt512
Feb 12, 2008, 6:21 PM
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slacklinejoe wrote: I shouldn't post without caffeine. Basically in the belay loop scenario the webbing on webbing friction of the wrap adds a significant amount of strength. Similar to that of any friction hitch or the "no knot" tie off method. Thus, less stitching can be used than a standard rabbit ear style loop and still yield a much higher break strength.
First of all, the claim I was addressing is that friction between the overlapping ends of material that are bar tacked together is an important component of strength of the bar tack. Friction between the belay loop and the harness, if that's what you're referring to as the "wrap," is not relevant to the question. Second, the original question was about bar tacks in a sling, which is also a loop, so whatever effect looping has, if any, on the strength of a bar tack in a belay loop also applies to the strength of a bar tack in a sling. Finally, who says that you really can attain the same strength from a seam in a belay loop by using fewer bar tacks than would be required in a runner?
Jay
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slacklinejoe
Feb 12, 2008, 6:26 PM
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"jt512 wrote: Finally, who says that you really can attain the same strength from a seam in a belay loop by using fewer bar tacks than would be required in a runner? Jay
Real world field testing. With all due respect please keep in mind, I do design and test high tensile sewn webbing goods for my full time job.
Jay, within the confines of my intended disclaimer of loops vs rabbit runner style sewing the variable is webbing on webbing friction. My force testing has shown that a single wrap of webbing on itself adds a more than significant measurable of additional pull strength. We were able to have a single wrap of duct tape hold suprising loads in that scenario.
I do not enjoy the "great debate" pissing match. I do however dislike incorrect information being spread much more. In no way was I refering to friction between the belay loop and harness and most people with a decent reading comprehension understood that. This is the lab, if you want people from the industry with real world and professional exerience posting up information then slowing down the jabs would be a positive thing for rockclimbing.com as it would better encourage participation from field experts.
(This post was edited by slacklinejoe on Feb 12, 2008, 6:38 PM)
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jt512
Feb 12, 2008, 6:40 PM
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slacklinejoe wrote: "jt512 wrote: Finally, who says that you really can attain the same strength from a seam in a belay loop by using fewer bar tacks than would be required in a runner? Jay Real world field testing. With all due respect please keep in mind, I do design and test high tensile sewn webbing goods for my full time job.
The problem with so-called real-world field testing is that the conditions of the "test" are not controlled. In normal use a belay loop is not used in the same manner as a sewn runner. Therefore, conclusions about the relative strength of each based on actual use are contaminated by differences in how they are actually used. Furthermore, the materials aren't even the same! "With all due respect, please keep in mind" that legitimate climbing equipment companies don't determine the strength of their equipment based on anecdotal observations of field use. They perform tests under controlled conditions, as required by certificating bodies, not to mention common sense.
Jay
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slacklinejoe
Feb 12, 2008, 6:50 PM
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Jay,
Perhaps you'd be better off asking how we did the tests rather than implying that the tests were unrelated, misleading or incomplete.
It certainly might be that I've got a big old stack of real pull test data with calibrated systems with lovely control variables, denoted webbing batchs, thread types, webbing color (yes, that sometimes actually makes a difference), levels before plastic deformation, elongation levels at different loads and tons of different types of webbing that we tested (we've made and sold polyester, polypro, nylon, nylon/spectra) and in lots of different widths. It's amazing what an engineering school will do for you if you let them use your products in a study. But frankly - your ego gets in the way of learning so I've gotta get back to work instead of posting up stuff people might find very interesting.
(This post was edited by slacklinejoe on Feb 12, 2008, 6:51 PM)
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jt512
Feb 12, 2008, 6:52 PM
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slacklinejoe wrote: Jay, Perhaps you'd be better off asking how we did the tests rather than implying that the tests were unrelated, misleading or incomplete.
I didn't say you didn't have real test data. You were the one making claims based on "real world field experience." It was that I was calling bullshit.
Edit: Although the fact that you chose to try and dazzle us with a lot of technical lingo instead of just posting the data, suggests that you probably don't have relevant data.
Jay
(This post was edited by jt512 on Feb 12, 2008, 6:56 PM)
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crackers
Feb 12, 2008, 6:57 PM
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jt512 wrote: As to my "speculating" about parachute seams, as it happens, I'm an FAA licensed Senior Parachute Rigger, and though I don't understand the physics underlying greater-than-one seam efficiency parachute seams, I am not speculating when I say that they exist.
Okay, I have to confess that I've been reading this whole thread in something like horror. I really think that a lot of this thread is not too informed.
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.
I know that seams in fabric with joint efficiency greater than 1 exist, but I didn't think you reproducibly sew them. As far as I know off the top of my head, LSc-4 has a seam efficiency in the high 80% range...btw LSc-4 is a variety of a felled seam used in military parachutes. I really don't know though.
With glue and other stuff, you get to 100% easily. In our non-woven dyneema packs, the seams are far far stronger than the material being bonded.
But so what? Webbing has almost none of the performance characteristics of fabric. They're totally different things. I wouldn't necessarily say it's stupid to compare the construction of the fabric in a parachute canopy to a climbing sling, but it is of limited use.
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.
In all seriousness, aviation and 'chutes have driven most of the serious research on the comparative strength of webbing and techniques of assembly. That said, not all of the research in this field has been done by parachute folks, and I really find Jay's tone objectionable.
I think that I recall that the approximate breaking strength quoted by most manufacturers of 1" tubular webbing is something like 4,000 pounds. So what precisely is your problem with a (as in one) 4700 pound break? Stress Riser? Oh jeez...
Having responded to the troll, I'm going back to my bar tack machine. Bye!
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jt512
Feb 12, 2008, 8:47 PM
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slacklinejoe wrote: ... a single wrap of webbing on itself adds a more than significant measurable of additional pull strength.
OK. One of the things that had me confused is what you meant by a "wrap" in a belay loop." I took a look at a belay loop on an old harness of mine, and now I see what you are talking about. I had never noticed that belay loops are constructed like that. I always thought they were just two loops of webbing sewn together. Anyway, I agree with you on that point. It is clear that the friction is significant in that design. But I still don't think that has much relevance to the issue that I had been addressing, which is whether the friction between the overlapping ends of a bar tacked runner is a major component of the strength of the joint. I doubt it. There's a big difference between an overlap and a full wrap.
Jay
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gunkiemike
Feb 12, 2008, 9:44 PM
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jt512 wrote: slacklinejoe wrote: Jay, Perhaps you'd be better off asking how we did the tests rather than implying that the tests were unrelated, misleading or incomplete. I didn't say you didn't have real test data. You were the one making claims based on "real world field experience." It was that I was calling bullshit. Edit: Although the fact that you chose to try and dazzle us with a lot of technical lingo instead of just posting the data, suggests that you probably don't have relevant data. Jay
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jt512
Feb 12, 2008, 10:06 PM
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gunkiemike wrote: jt512 wrote: slacklinejoe wrote: Jay, Perhaps you'd be better off asking how we did the tests rather than implying that the tests were unrelated, misleading or incomplete. I didn't say you didn't have real test data. You were the one making claims based on "real world field experience." It was that I was calling bullshit. Edit: Although the fact that you chose to try and dazzle us with a lot of technical lingo instead of just posting the data, suggests that you probably don't have relevant data. Jay Egregious mis-quote there Jay. Scroll up and see for yourself. BIG DIFFERENCE between "experience" (anecdotal, usually) and "testing" (controlled evaluation, usually). I have to wonder if you're blinded by the desire to argue.
I don't misquote. That wasn't the paragraph I was quoting. Try again.
Jay
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slacklinejoe
Feb 12, 2008, 10:07 PM
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To put my point into perspective, one should ask themselves what the difference between a full wrap as in a belay loop and a partial wrap in the case of a standard sling.
There are often only a couple bartacks (1-4) in a belay loop and longitudal stiches to keep the webbing in place and they break at a much higher level than a standard 6 tack sling made out of the same material. There are several forces at work that make that happen, friction is not negligable in the equation. Obviously the webbing being doubled makes the resulting loop stronger, but the point to ponder is how it does it with less stitches.
I personally feel the lab should be held to a higher standard than the choss pile / community forums if RC hopes to reach the goals of the forum itself, which is real progress in education and understanding. I don't post in those other forums because of the signal to noise ratio and I don't want it to happen here.
(This post was edited by slacklinejoe on Feb 12, 2008, 10:10 PM)
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russwalling
Feb 12, 2008, 10:16 PM
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Strength comes from: total area of friction (more in a belay loop, less in simple overlap), thread strength, and saturation pattern Vs. the physical limits of the material being sewn. Bar tacks will also "series load" to spread out the force from each end of the lap towards the center.
Now what was the original Q?
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gunkiemike
Feb 12, 2008, 10:51 PM
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jt512 wrote: gunkiemike wrote: jt512 wrote: slacklinejoe wrote: Jay, Perhaps you'd be better off asking how we did the tests rather than implying that the tests were unrelated, misleading or incomplete. I didn't say you didn't have real test data. You were the one making claims based on "real world field experience." It was that I was calling bullshit. Edit: Although the fact that you chose to try and dazzle us with a lot of technical lingo instead of just posting the data, suggests that you probably don't have relevant data. Jay Egregious mis-quote there Jay. Scroll up and see for yourself. BIG DIFFERENCE between "experience" (anecdotal, usually) and "testing" (controlled evaluation, usually). I have to wonder if you're blinded by the desire to argue. I don't misquote. That wasn't the paragraph I was quoting. Try again. Jay
Nope, sorry...can't find where SLJ ever used in this thread the phrase you put in quotes. What'd I miss?
(Just trying to referee the dialog here...not fan the conflagration)
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jt512
Feb 12, 2008, 11:24 PM
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gunkiemike wrote: jt512 wrote: gunkiemike wrote: jt512 wrote: slacklinejoe wrote: Jay, Perhaps you'd be better off asking how we did the tests rather than implying that the tests were unrelated, misleading or incomplete. I didn't say you didn't have real test data. You were the one making claims based on "real world field experience." It was that I was calling bullshit. Edit: Although the fact that you chose to try and dazzle us with a lot of technical lingo instead of just posting the data, suggests that you probably don't have relevant data. Jay Egregious mis-quote there Jay. Scroll up and see for yourself. BIG DIFFERENCE between "experience" (anecdotal, usually) and "testing" (controlled evaluation, usually). I have to wonder if you're blinded by the desire to argue. I don't misquote. That wasn't the paragraph I was quoting. Try again. Jay Nope, sorry...can't find where SLJ ever used in this thread the phrase you put in quotes. What'd I miss? (Just trying to referee the dialog here...not fan the conflagration)
You're right. He said "real world field testing." I interpreted that to mean that he's never seen one break in the field. If he's hooked up quantitative testing equipment and tested it in the field under controlled conditions, than, well, I'd be surprised. "Real world" usually means the antithesis of this.
BTW, the first time I quoted him I did quote the word "testing." The second time I quoted him, I did inadvertently quote him incorrectly. The guy's profile says he's a college student, so I assume he does not have much experience in technical writing. I'm used to reading scientific literature, where a phrase like "real world field testing" would be never be used. Maybe my fault for interpreting "real world field testing" to mean little more than "I've never seen one break in the real world." On the other hand, if you want your "tests" to be taken seriously, you should learn how to be precise in your descriptions of them.
But it's all practically a moot point anyway, because his claims are about friction in a wrap being significant, which no one is contesting. The claim that is being contested is whether the friction in the overlap of a the bar tacked section of a runner is a major contributor to the strength of the bar tack.
Jay
(This post was edited by jt512 on Feb 12, 2008, 11:40 PM)
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jt512
Feb 13, 2008, 1:34 AM
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slacklinejoe wrote: "jt512 wrote: The guy's profile says he's a college student, so I assume he does not have much experience in technical writing. I'm used to reading scientific literature, where a phrase like "real world field testing" would be never be used. Comments like these belong in a different forum. It's semi-personal stuff, not related to the question. Not that it matters - Graduate actually. Masters in Communication/Administrative Studies 2005, undergrad degrees in business / computer information systems 2003. My brother in law is wrapping up his PHD program as an mechanical enginneer and one of my employees is a engineering student at CU. I like to leave self stimulating academia where I left it.
Yeah, I know. Every comment except yours belongs in a different forum. You keep harping on about how this forum should be held to a higher standard, yet you've yet to present any of this supposedly relevant-to-the-question "real world field testing" data of yours. Why don't you post it, along with a description of the study design and the data collection and analysis protocol, and then we'll critically review it, like real scientists do. OK?
Jay
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slacklinejoe
Feb 13, 2008, 4:03 AM
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Jay, I've withstood a lot of personal attacks on this forum for my mere existance at what I do. I don't have enough invested in this particular debate to make it worth it. Thus, I am drawing the line and saying no - you've dished out too much disrespect, been too discourtious and your desire to argue has blinded your better judgement. I know very well what will probably be said at my expense following this but I am going to unsubscribe myself from this thread and tell you to shove it.
I also want to let you and the RC admins know I have received emails from other industry professionals who have decided not to post up, basically saying you, or people's posts like yours, are the reason it isn't worth it to them to post potentially valuable information. Goodnight.
(This post was edited by slacklinejoe on Feb 13, 2008, 4:18 AM)
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jt512
Feb 13, 2008, 4:23 AM
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slacklinejoe wrote: Jay, I've withstood a lot of personal attacks on this forum for my mere existance at what I do. I don't have enough invested in this particular debate to make it worth it. Thus, I am drawing the line and saying no - you've dished out too much disrespect, been too discourtious and your desire to argue has blinded your better judgement. I know very well what will probably be said at my expense following this but I am going to unsubscribe myself from this thread and tell you to shove it. I also want to let you and the RC admins know I have received emails from other industry professionals who have decided not to post up, basically saying you, or people's posts like yours, are the reason it isn't worth it to them to post potentially valuable information. Goodnight.
Honestly, I don't think I've been disrespectful at all in this thread. You and your supposed industry professionals who have supposedly decided not to post their supposed data need to get a thicker skin.
There is a difference between being critical of claims and being disrespectful of the individual making the claim. When you make claims whose relevance to the question is unclear, and claim, without explanation, or data, that they are relevant, you should expect that your claims will be criticized.
Jay
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crackers
Feb 13, 2008, 6:19 PM
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Jay, I disagree with you.
This is supposed to be a highly moderated technical discussion.
If russ or joe are willing to share the results of their proprietary testing programs or experience with everybody, maybe that should happen. After all, they're paying for their testing and for their insurance.
I don't see your comments as adding anything to a discussion of how bar tacked slings failed above the webbing's mean breaking strength.
If you want to start a methodology thread, go for it.
If you want to buy Joe's dataset, maybe he'll supply you a copy...
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kai_da_klimba
Feb 13, 2008, 6:39 PM
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Just for the record:
I, too, feel that Jay has been disrespectful in this thread without supplying useful information himself.
I totally understand how other "industry professionals", who don't have time to constantly justify themselves against attacks, would decide not to post any more.
I've seen the signal to noise ratio on rc.com go down a lot over the time I've been visiting, and it's an unfortunate development in my eyes.
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jt512
Feb 13, 2008, 6:40 PM
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crackers wrote: Jay, I disagree with you. This is supposed to be a highly moderated technical discussion
Fine with me. Then maybe someone should fucking moderate it.
In reply to: I don't see your comments as adding anything to a discussion of how bar tacked slings failed above the webbing's mean breaking strength.
I think it is completely obvious why my comments are relevant, but If you don't see it, I'll be happy (well, not really) to explain it to you, step by step:
1. The original question was, "do bar tacks fail."
2. Someone responded, "no, they're stronger than the webbing itself."
3. Someone responded, "I don't see how that's possible."
4. Someone responded, "It's possible if there's enough friction between the overlapping sections of webbing in the bar tack.
5. I responded, "no, in practice, you can't generate that much friction by bar tacking. Therefore the friction in a bar-tacked runner is not an important component of the strength of the joint.
6. Slacklinejoe responded, but if you make a complete wrap of webbing, like in a belay loop, then there is significant friction.
7. Once I figured out what he was talking about, I responded, I agree, but it's not relevant to the bar tacks in slings, because there is no such wrap.
In case you still don't get it, we are discussing what physical mechanisms underlie the strength of the bar tack. If you do not understand why that is relevant to the original question, well, what can I say.
In reply to: If you want to start a methodology thread, go for it.
That comment apparently implies that you do not think that the methodology by which data is collected is relevant to how the data are interpreted. If that is what you believe, again, there is not much I can say.
Jay
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