conflicts of interest, stitches, and eggs

[Buford Pruitt]

Hank,

I might be agreeable to spend an hour or two one evening sewing a couple of slings, but 5 could take all evening around my house and I'm not THAT interested. How about others here? Tim? :lol:

If you do this experiment, you do owe it to us to write it up. You would also need to compare the results with comparable gear, even if you only used manufacturer's data.

OTOH, if Tim is right about the webbing failing and not the stitching, then why are we talking about this in the first place? :lol:

[Tim White]

OTOH, if Tim is right about the webbing failing and not the stitching, then why are we talking about this in the first place? :lol:

I was referring to commercially available sewn slings and runners. It would be interesting to see if hand sewn slings break at the stitching or if the webbing fails.

[hank moon]

I was referring to commercially available sewn slings and runners. It would be interesting to see if hand sewn slings break at the stitching or if the webbing fails.

I can just about guarantee you that a hand-sewn sling will break at the join. True that machine-sewn slings do not always break at the join as it is typically stronger than the webbing.

[hunter]

Hard to imagine a U.S. climbing magazine sponsoring such testing for fear of tweaking their advertisers.

Hank,
Not sure this is totally true. This years review of cams in climbing magazine discussed an ultra light cam with lobe cutout that worried the testers. They broke it and reported in the article that the breaking point was to low and that weight was not worth gear that might fail.... Although I don't think they generally test everything for failure a lot of the gear reviews in climbing are harsh enough that I, as a reader, would never buy the gear. I'll look up the issue tonight and make sure I'm correct on this...

I've never heard of an oversight organization but doesn't REI test all the gear they sell? I remember a display about REI's destructive testing of all climbing equipment they sell at the store in Seattle. I looked on their website and didn't see anything so maybe someone knows more on this than I do....

James Hunter

[hank moon]

Not sure this is totally true. This years review of cams in climbing magazine discussed an ultra light cam with lobe cutout that worried the testers. They broke it and reported in the article that the breaking point was to low and that weight was not worth gear that might fail.... Although I don't think they generally test everything for failure a lot of the gear reviews in climbing are harsh enough that I, as a reader, would never buy the gear. I'll look up the issue tonight and make sure I'm correct on this...

Musta missed that one...let me know which issue, eh? Could be the beginning of civil responsibility for the mags!

I've never heard of an oversight organization but doesn't REI test all the gear they sell? I remember a display about REI's destructive testing of all climbing equipment they sell at the store in Seattle. I looked on their website and didn't see anything so maybe someone knows more on this than I do....

REI does test everything...they even have their own internal test standards, based largely on the EN standards with some of their own requirements added. But, they don't publish their results so far as I know.

[hunter]

...let me know which issue, eh?

Climbing No. 238, Article "New Cams Tested", Page 76. The CAMP Air-Cam and Jet Cam were tested and failed at 8Kn vs a similar size BD at 14kn

Yeah, never seen REI publish anything, probably to much liability. They just don't sell something that failed.

Maybe the whole problem here(the states) is liability. If you publish results below the manufacturers and aren't careful you could get sued...

James Hunter

[hank moon]

Climbing No. 238, Article "New Cams Tested", Page 76. The CAMP Air-Cam and Jet Cam were tested and failed at 8Kn vs a similar size BD at 14kn

Yabbut...the article also mentions that the strength of the CAMP cams is well within the limits set by UIAA, so not much controversy there. By contrast, articles in some European climbing magazines have revealed products (most notably helmets) that do not meet the standards to which they are labeled (!).

[hunter]

Hmm, I guess I see your point.
At the same time though I can only find one US store selling these cams so I think comments like climbing's probably have some affect. Of course it could just be supply. I do think it is positive that a magazine saw a potential weakness and tested it, using the results in a review.

Gettings slightly off topic for caving I guess... Anyway, I hope the sling tests happen, I would like to see the results.

James

[hank moon]

I do think it is positive that a magazine saw a potential weakness and tested it, using the results in a review

Sin duda...

[Geary]

I thought I would add my two cents regarding the stitching discussion. Sorry, I've been off the discussion board for a little while.

Couple of points on hand stitching. Yes, if you do a good enough job (what every that is), you can hand stitch webbing to be as strong (or stronger) then commercially available sewn webbing (when new). Again, it depends upon how good of a stitching job was performed on the commercial work. Hand sewn webbing jobs can actually exceed the breaking strength of the webbing if done well.

I believe it was John Stannard, a very well know climber who first did testing on hand sewn webbing and published an article in Off Belay in the mid to late 70's. I think I still have the article somewhere.

Anyway, there are a lot of factors that go into making a strong stitch job including; webbing type; thread type, size, twist, bonding; stitch pattern, stitches per inch; tension, needle type; compatibility of webbing and thread; etc. It can get relatively complicated pretty fast.

Couple of points, I've broken a lot of webbing trying to isolate each of the factors in stitching and I've come to a couple of conclusions, (I really should write this up in an article but I've been saying it for a couple years)

1. The amount of thread in an average sewn harness wouldn't make a good shoe string. Considering most of us wouldn't rappel on a shoe string, think carefully about your sewing

2. Don't climb or rappel from a distance any higher than you're willing to jump unless you are sure of your equipment and techniques.

3. More stitches, to a point are better then less but there is more then meets the eye related to thread size and pattern.

For example, many climbing harnesses and webbing use bar tacks. These are sewn by a surger. They are very strong when new but do not hold up under caving conditions and I don't believe they have any place in caving. Why are they used, because they are strong when new, quick to sew, require very little skill, and look neat. However, it is the only stitching pattern (type) that I have seen actually fail under caving conditions.

4. Why do bar tacks fail. This goes back to the need to make sure that your thread and webbing are compatible. Thread should pull tight into the webbing so that it does not have a high profile. If the thread sticks out of the webbing, it is the first thing that comes into contact with the rock and is susceptible to abrasion. If the thread is pulled too tightly into the webbing, it can cause an indention and is likely to collect dirt, thereby abrading the thread. It is very hard, because of the density of the stitch, to get the tension correct on a bar tack. Very few commercially made harnesses have correctly sewn bar tacks. While it may not be a big deal for climbing, it does make a difference in caving.

5. Certain patterns provide optimum stitching efficiency but you can overcome that by using more stitches.

6. You can roughly approximate the breaking strength of a sewn junction by counting the number of intact stitches and multiplying by the breaking strength of the thread. The junction is actually stronger since there are a few other factors that come into play - like the friction between the two pieces of joined webbing.

Enough for now, I've got to go check out the PBS special Rx for Survival. I'll try and get back and post some more later.

Geary Schindel

In the interest of full disclosure, I'm also President of Karst Works, Inc. and I do speak for the company.

[Scott McCrea]

Thanks for the education, Geary.

[hank moon]

Hand sewn webbing jobs can actually exceed the breaking strength of the webbing if done well.

Geary, thanks for posting - got data? :)

If you do this experiment, you do owe it to us to write it up. You would also need to compare the results with comparable gear, even if you only used manufacturer's data.

'Course I"ll write it up! I also plan to include some commercial slings from several mfgs in the mix.

Buford and anyone else interested: the offer still stands to break some hand-sewn slings and gather some data on the strength of joins to which you might be currently trusting your life. I propose that each participant produce at least 3 samples, each sewn from 1" mil-spec webbing with thread and needle of choice. I will be using a Speedy Stitcher with the standard "heavy duty" waxed thread that is frequently sold with the stitcher. Use whatever stitch pattern/density you have been using. The joins should be of reasonable length, say, no longer than 4". Please contact me sideband (hmoonoomh@gmail.com) if interested.

[Tim White]

Issue #3 of Nylon Highway has a reprint of the 70’s Off Belay article: [i]“How Strong is a Stitched Splice of Nylon Webbing?â€

[Tim White]

Nylon Highway Issue #7, page 10 has Bob Thrun's article from 1968 "Sewn Seat Slings".
http://caves.org/section/vertical/nhback/NH07.pdf
Yes...it's old :P but interesting test results on various stitching patterns that many hand sewers use.

[Scott McCrea]

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

In the newly posted out-of-print Nylon Highways, I found an article on sewing with stitching awl. It's in #17, Dec '83. LINK