conflicts of interest, stitches, and eggs

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conflicts of interest, stitches, and eggs

Postby hank moon » Oct 24, 2005 2:06 am

Leftover stuff from another thread

I'm coming to the inexorable conclusion that awl stitching is at least as strong as machine stitching. But as I said, I am interested in reality, and not being in the adventure gear manufacturing bidness I very much appreciate you and Bruce and Scott coming here and sharing your experiences.


I kinda doubt it...but if you really want to find out, sew up some sample loops (at least 5) and I'll have 'em broken. Might take awhile, but I'll have it done eventually. OTOH, might contact PMI to do the tests...they have the equipment and I don't (would have to send them off to Petzl or elsewhere). BTW, don't you think this is the kind of testing that the NSS should be sponsoring?

But make no mistake, regardless of what's in your heart, you most certainly are in a conflict of interest every time you discuss the pros and cons of gear that competes with your employer's.


I agree with you in principle, but in this case I was not discussing anything that competes with Petzl stuff...unless you consider a speedy stitcher to be somehow competing with Petzl. :roll: If I had said, "you should buy the Petzl harness that has a machine-sewn FW loop on it" that would be different. In any event, I would not recommend anyone use any kind of loop (factory sewn or otherwise) to attach a FW to a leg loop. Fine for a pinch, but not for regular use.

You say that the data is at PMI? Hmmm, maybe there are ways of getting that data. Maybe there are ways of generating such data in another shop.


This test was just something I did in my spare time with the assistance of Chuck Weber. I doubt he kept the data and I didn't. It wasn't a full test series anyway, just one or two loops broken (can't remember). The test simply left me with an impression: my (not so) speedy stitching ain't good enough for life safety applications. YMMV.

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Postby hunter » Oct 24, 2005 2:46 pm

Seems like this discussuion could just lead to some slightly hard feelings but from an observers stand point I would be really interested in seeing results posted if someone does test this. My instinct says machine sewn webbing is way stronger but I'm very curious. On testing, it seems like you could sew something up and pull an object of known weight with a truck. Crude, but I've seen a few vehicles pulled out of the mud with old climbing gear and it always held.

On a different line, it seems like Hank has taken some flak that really isn't deserved. I don't know anyone involved but just from looking at the posts it sounds like Hank shouldn't post on vertical at all. This seems wrong to me. I like to see different opinons and Hank clearly states that this is his opinion and not Petzls, which in and of itself tells me he works for petzl and I can consider that his opinion might be different due to this.
Conflict of interest is serious when a contract is being put out ( or when a government official's vote is being considered) but telling someone their opinion doesn't count on a discussion board because of conflict of interest is going kind of far.

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P.S. I'm not trying to throw rocks at anyone, just putting in my .02
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conflict of interest, but no eggs or stitches

Postby ian mckenzie » Oct 24, 2005 2:48 pm

I appreciate having input from someone who works with an equipment manufacturer; his so-called conflict is no more concern to me than the amateur opinions that the rest of us offer up. This Board would be poorer without Hank's calm and considered input. There may be a potential conflict due to his employment but I say, so what? I trust him.
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Postby Scott McCrea » Oct 24, 2005 3:09 pm

Whether Hank works at Petzl, makes pretzels or drives Edsels, his opinions can be just as wrong as anyone elses. :roll: :rofl:

I, for one, would like to thank Hank for taking the time to share what he knows. :bow:

I think this is appropriate here: LINK. (2.4mb MPG video) :woohoo:
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Postby Buford Pruitt » Oct 24, 2005 4:09 pm

Hank, that's a very interesting offer. Now, for the details...

I use 40-lb test braided nylon fishing line. Can your machine stitch that thread? To make it a comparable test, I would buy a new spool of that twine and a sufficient length of webbing to make 10 loops. I would make 5 of the loops and then send them you along with the remainder of the webbing and thread. You would then use those materials to make 5 more nearly identical loops, sewing a comparable number of stitches in them. Then you would send it all to PMI for testing.

However, I'm not sure that would be a good use of anyone's time, as I cannot see how it makes any difference whether a Speedy Stitcher is used vs another kind of sewing machine. As long as neither machine damages webbing or thread, the same number of stitches are made, and the same thread and webbing materials are used, how can a difference be expected? What logic indicates there would be a difference? Please walk me slowly through your process of logic if you think there would be a significant difference.

Ok, another good issue you brought up is whether the NSS should be sponsoring such testing. My opinion is Yes and No. Yes, the NSS should encourage such testing and should be involved in experiment design, data collection, analysis and reporting.

But No, in my opinion the NSS should not pay money for the experiments to be done. Gear manufacturers need to collect such data anyway in order to assure their own lawyers AND us buyers that the gear is good enough for the purposes intended. That data should be available to buyers. Furthermore, there are self-monitoring groups in many industries, where company reps work together to standardize products and performance specifications. I see no reason that the adventure gear industry couldn't do the same thing (maybe it already is?).
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Postby hunter » Oct 24, 2005 5:42 pm

Buford,
Don't know about Hank but my thinking on this is a bit different from your experiment. These are the reasons I have for being wary of hand sewing:
(not trying to say hand sewing is unsafe, just pointing out my thinking...)

1) I looked and can't find any listed number but I have seen articles where sewn slings are listed with thousands of stitches per square inch. It seems to me that a hand sewn item will probably never have as many stitches as a machine sewn one.
Of course this probably means your thread is stronger so just considering stitches it would be strength*number.

2) Tension matters. If the threads aren't weighted all at once then your strength really isn't the combined strength of your stitches. Using a machine should allow proper tensioning of both the thread and webbing.

I have no basis for the above, just posting why I am personally a bit wary of hand sewing.

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Postby Mark620 » Oct 24, 2005 7:07 pm

I have access to an industrial sewing machine (one used to sew upholstery).

Would 50lb test "spyderwire" Teflon Treated superbraid fishing line - it has the same diameter as 12lb test line, it is also made in strengths up to 90lb, be tough enough to sew my own equipment?

Would the fact that it has Teflon in it make it too slick to hold properly?
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Postby Scott McCrea » Oct 24, 2005 7:11 pm

For some of the best info on sewing, stitching, etc, check out Poynter's Parachute Manual. It is the only thing that I have found that relates to sewing caving gear. There is a wealth of info for making harnesses and such. I'm not saying it's the Bible of harness sewing, just the best thing available. Talk to a seasoned, respected parachute rigger for an education on sewing.

Other than that, and a couple articles published in some old Nylon Highways about sewing, there is not much info out there.

My guess, regarding the Speedy Stitcher, is that you could make a joint with it that will be just as strong as any sewing machine could do. It would just take a LOT longer.

I don't know anything about the braided nylon fishing line, but the average minimum tensile strength for thread that most gear/harness sewers use is between 10-20lbs.
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Postby Mark620 » Oct 24, 2005 7:16 pm

Scott McCrea wrote:I don't know anything about the braided nylon fishing line, but the average minimum tensile strength for thread that most gear/harness sewers use is between 10-20lbs.


I would assume some of the reason for such a low strength would be the fact that strength is proportional to diameter. There are quite a few new materials out there now.
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Postby Scott McCrea » Oct 24, 2005 7:51 pm

Mark620 wrote:I would assume some of the reason for such a low strength would be the fact that strength is proportional to diameter. There are quite a few new materials out there now.


I think it has more to do with economics. 10-20lb thread is plenty good when done properly. Actually, most of the thread used is probably the 10lb variety.
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Postby Buford Pruitt » Oct 24, 2005 11:09 pm

James,

"Thousands of stitches per square inch" is unbelievable. Let me say that a different and unequivocal way: I do not believe that any caving gear manufacturer today is stitching harnesses together using "thousands of stitches per square inch." Let me say it a third time: I don't believe that for a New York minute! :lol:

Think about it. Only 900 stitches per square inch is 30 x 30. When have you ever seen a caving harness sewn with stitches one-thirtieth of an inch apart? That's less than 1 mm apart. "Thousands" would have to be less than a half-millimeter apart! Dude, that has to be seen to be believed. :P Now, webbing itself might have thousands of weaves (or whatever the proper terminology is) per square inch, but that's not what we're talking about.

I have a full body harness made in Italy by a manufacturer with a partially almost unreadable logo, but I think it says "Alp Design." I count it has an average of 6 stitches per linear inch. At critical webbing intersections, the stitching is doubled; that is, two lines of stitches were laid down beside each other in parallel. Even so, in those locations, the densest pattern contains no more than 60 stitches per square inch.

I also have a B&B sit harness. It has four (!) stitches per linear inch of stitching. Four, count 'em! :cry: No double stitching. The densest pattern is appx 34 stitches per square inch.

Both harnesses have rather stout twist laid, nylon (?) thread that appears to be equivalent in size or actually thicker than my 40-lb braided fishing line. It may not be as strong as 40 lb test or it may be stronger, but it appears to be thicker than 10 lb or 20 lb line.

You make a good point that not all stitches are tensioned at once and therefore a connection might be weaker. Now, that might indeed make a difference, but how much? Gotta test it and see, because nylon line stretches and the harness wouldn't have to be tensioned much before all my stitches were tensioned.

Furthermore, when tensioning a set of stitches, I suspect they will "even out" under the load because they are crossed over each other rather than being tied to each other. If so, there might not be any uneven tensioning after the stitched intersection is "cured" in action, although it would almost certainly not be as tight as a commercially stiched connection.

On the other hand, my speedy stitching is laid down at an average of 8 stitches per linear inch, and in the case of my FW leg loop, 48 stitches per square inch. Relative to 34 and 60 stitches per square inch, without testing I'd have to conclude that my stitching lies somewhere between Alp Design and B&B in strength.

I'm comfortable with that.
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Postby hunter » Oct 25, 2005 1:24 pm

Buford,
Guess I have to eat crow on this one. I went out and looked at some of my climbing gear which is in my truck, my caving stuff isn't. Per square inch was a lousy term for me to use since some joints have rows of stitching spread out and some don't. Per joint though I'm seeing at most 400 or so stitches. I have some spetra/dynema slings which have stitches stacked on top of each other but nothing in nylon.

I'm still thinking about the tension thing. The nylon will give some but if the nlyon around each thread gives the same amount then I would expect tension to matter. Maybe slipping of the threads would even out your stitching.

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Postby Buford Pruitt » Oct 25, 2005 1:27 pm

"slipping of the threads" was what I meant. You just said it better. :wink:
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Postby hank moon » Oct 26, 2005 1:09 pm

I use 40-lb test braided nylon fishing line. Can your machine stitch that thread? To make it a comparable test, I would buy a new spool of that twine and a sufficient length of webbing to make 10 loops. I would make 5 of the loops and then send them you along with the remainder of the webbing and thread. You would then use those materials to make 5 more nearly identical loops, sewing a comparable number of stitches in them. Then you would send it all to PMI for testing.


*** I propose a simpler plan: you send me 5 samples of handmade slings, sewn as strong as you can make them. I have them tested and make a report for publication. I don't have access to a sewing machine and don't see the need to make a comparison between hand-sewn and machine-sewn with that specific thread. We know that most commercially-available slings used by cavers and climbers have an MBS of 22 kN, so we can use that number for a comparison (if one is necessary). The main goals of the testing would be to see how strong the handsewn runners are, and how consistent the strength (quality control).

However, I'm not sure that would be a good use of anyone's time, as I cannot see how it makes any difference whether a Speedy Stitcher is used vs another kind of sewing machine. As long as neither machine damages webbing or thread, the same number of stitches are made, and the same thread and webbing materials are used, how can a difference be expected? What logic indicates there would be a difference? Please walk me slowly through your process of logic if you think there would be a significant difference.


*** I think testing the handsewn runners is inherently valuable since there is apparently scant data on their strength. Since we don't have this data, the logic is simply to produce some and make it available.

Ok, another good issue you brought up is whether the NSS should be sponsoring such testing. My opinion is Yes and No. Yes, the NSS should encourage such testing and should be involved in experiment design, data collection, analysis and reporting.

But No, in my opinion the NSS should not pay money for the experiments to be done. Gear manufacturers need to collect such data anyway in order to assure their own lawyers AND us buyers that the gear is good enough for the purposes intended. That data should be available to buyers. Furthermore, there are self-monitoring groups in many industries, where company reps work together to standardize products and performance specifications. I see no reason that the adventure gear industry couldn't do the same thing (maybe it already is?).


*** The adventure industry in this country has no "watchdog" group that I'm aware of. I think it would be a great idea for the NSS to perform this function (to some extent) b/c ex-industry testing can yield interesting surprises. For example, there are several foreign magazines that take it upon themselves to perform testing on available equipment. The tests often show that some manufacturers are misrepresenting their products. This kind of accountability system is good for everyone. The NSS news is especially suited for this role as it is mostly non-commercial in nature. Hard to imagine a U.S. climbing magazine sponsoring such testing for fear of tweaking their advertisers.

Hunter, Scott, Ian: thanks guys! :) Yeah, my opinion is just an opinion - just as right/wrong/other as anyone else's...

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Postby Tim White » Oct 26, 2005 1:29 pm

hank_moon wrote:commercially-available slings used by cavers and climbers have an MBS of 22 kN,


Hank- Correct me if I'm wrong...but doesn't testing on commercially available sewn slings and runners show that the webbing breaks somewhere other than in/at the stitching?

Commercially available sewn slings sure seem like the way to go for me. I’ve done the speedy stitching for years and now prefer to just pay the $$$ or have Berta sew up what we need on her commercial sewing machine. :wink:

I wonder just how many cavers still use a speedy stitcher?

I’d like to see the results of your proposed testing!
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