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Old 05-01-2014, 10:52   #106
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Re: Load Testing Results

What I find fascinating is how little thread holds a ton.

a. I've seen data. Much of it is so poorly explained to be useless, and the rest is all over the board, like knots. The heart of it seems to be ~ 100%.

b. I don't understand why pattern matters very much. I know some folks say a box is best... and yet nearly all climbing gear is sewn with bar tacks. The reason is that bar tacks are easier, create huge stitch count, and thus wear better. No matter the stitch pattern, the efficiency is high.

c. Bar tacks are better for pealing force, which can be limiting before shear in real-world use. This may be the case in your 50-stitch test (happens SO fast you wouldn't see it). Try a row across at the throat, then 50. As it is, the first stitch is holding too much pealing force, depending on the throat angle.

The pealing force on your first stitch is probably ~ 25#, which added to the shear stress is too much. The zipper would be instantaneous.

(another Excel generated JPG!)



d. As we have discussed, better figure on some loose and cut threads. That is wear and tear. Test with some cut threads.


Sail Delmarva: More Testing--Stitiched Eyes in Webbing
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Old 05-01-2014, 11:38   #107
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Re: Load Testing Results

Here are my two 50 stitch tests. I have asked sailrite to look over all my numbers and assumptions about machine stitches. But the two numbers below are just plain raw factual test results, and so are 'right for sure'.

machine sewing (breaking at % of stitching tensile strength) break load (lbs)
50 streight stitches down webbing V92 thread 1090
50 streight stitches across webbing V92 thread 1020
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Old 05-01-2014, 14:42   #108
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Re: Load Testing Results

FWIW, the instructions for my Pfaff 130 (given to me by my Mom; it had been hers) for the use in home sewing, recommended a minimum of three back-stitches to lock a seam.

When I zigzag, I drop the feed dogs, and do three non-running stitches, to lock the zigzag row.

With hand stitching, one back stitch, three wraps on the needle, and pull through.

So, when you sew splices, do you take any back stitches to "lock" the row of stitches?

Do you think "locking" is unnecessary?

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Old 05-01-2014, 16:17   #109
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Re: Load Testing Results

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Originally Posted by Ann T. Cate View Post
a minimum of three back-stitches to lock a seam..

With hand stitching, one back stitch, three wraps on the needle, and pull through.

So, when you sew splices, do you take any back stitches to "lock" the row of stitches?

Do you think "locking" is unnecessary?
Knots and splices I know something about . . . But high load sewing I am just a hack and am hoping to learn from you all.

So . . . The last stitching test was essentially a 50 stitch bar tack with 10 stitches x 5 passes . . . So it should have been well "locked". By comparison the one above it was a long 25 stitch forward and then 25 back /lock. There is no significant difference (the second is slightly stronger). But I consider all these machine stitch test results "less than expected" so I would be delighted to learn and test some other better way.

With my hand stitching I tie both end to the fabric. At the start I go thru the material, come back and tie a surgeon knot and the continue the stitching. At the end I take 2 or 3 round stitches thru the fabrics and "half hitch" them. These all seem to test extremely well and repeatable, so I am comfortable with that proceedure.
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Old 05-01-2014, 19:49   #110
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Re: Load Testing Results

Testing on a specialty line - dyneema core and dyneema cover (NER WR2) . . . This tends to perform like a dyneema single braid of the same diameter at the core - eg the cover provides chafe and uv protection but not added strength nor added knot holding power. A bowline will slip at about 32% (of line strength) until the bowline jams up against the pin, and then the cover will break and the core slide thru the knot at about 47%. The Estar knot will break (both core and cover together) at 57%.

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Old 05-01-2014, 20:39   #111
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Re: Load Testing Results

More of a soft shackle topic, but this seems to be the hot thread.





These were tied from used 5/16 polyester double braid and, as you can see, broke at very near line strength (broke over carabiner--might have tested higher with thimble). The knot is a double fisherman's. In this 15-year old line (failed at 1700 pounds in prior spliced dogbone test, about 45% of new) tested to 2500 pounds and in new line I would expect about 6000 pounds... and nothing high tech. I've used these for years, securing covers and as sail ties, but also occasionally genoa tacks and anchor chains to bridles.

I knew it would be strong, though I still learned one thing; if these are to be used to high load factors, the knot needs some serious pre-setting. After breaking notice that the knot is quite small in the loop. Not important for low-load applications, and the loop can be tightened with extended seizing.

There are several advantages to consider, compared to an Amsteel soft shackle:
  • Easy to make any length.
  • Dead simple.
  • Though the materials are not as strong, the efficiency is higher, 74% vs ~40%.
I would love to see this tested to higher loads in new materials. I'm not sure if any high mod fiber rope will hold the knot to high efficiency.
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Old 06-01-2014, 05:52   #112
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Re: Load Testing Results

I have also noticed that knots seem to be weaker as percent of line strength in used line line than in new line. For example, for the 15-year old 5/16" line used above:

New 4500 pounds
Used 1700 pounds

New bowline 3600 pounds (80%)
Used bowline 800 pounds (47% of line strength) (18% of new strength)

On the other hand, splices tend to stay at 90% of line strength.
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Old 06-01-2014, 06:08   #113
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Re: Load Testing Results

^^ I will have to do a "stopper" knot strength test.

The double fisherman slipped as a bend in new amsteel. However, The "noose" loading on the soft shackle stopper is a different sort of loading than on the bend, so I am not sure if it will slip or hold. Worth a test.

Yes, the stoppers knots do compress. My impression is that you should definitely leave some tail showing, rather than cutting them near flush to the stopper as some people do, because when you get above the loads used to set the knot you probably will suck more tail into/thru the knot.
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Old 06-01-2014, 06:30   #114
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Re: Load Testing Results

Quote:
Originally Posted by estarzinger View Post
^^ I will have to do a "stopper" knot strength test.

The double fisherman slipped as a bend in new amsteel. However, The "noose" loading on the soft shackle stopper is a different sort of loading than on the bend, so I am not sure if it will slip or hold. Worth a test.

Yes, the stoppers knots do compress. My impression is that you should definitely leave some tail showing, rather than cutting them near flush to the stopper as some people do, because when you get above the loads used to set the knot you probably will suck more tail into/thru the knot.
Right or wrong...

When making soft shakles I trim the tail because I find it gets in the way. However, I do set the knots by clamping the tails in a vice and dropping a weight on the loop repeatadle, after setting my weight first. Also, I cut the tails about 1 inch, melt the ends, and mash the blob flush to the knot; the "head" should not pull through easily.

Your concern is real.
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Old 06-01-2014, 07:34   #115
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Re: Load Testing Results

Stopper knots is bare dyneema . . . I just tested three different designs:

The diamond is, exactly as we suspected, breaking at 46% of line strength
The Ashely stopper, which looks the business, slipped at 27%
And the double fisherman stopper slipped at 15%.

So, of the common stopper's, the diamond is the only one that does not slip in bare dyneema.

I am suspecting that if we modify either the Palomar or EStar knots into stoppers that we can get to 50%, but they will not have the nice ball shape of the diamond, so I am not sure if the extra 4% is worthwhile. But this stopper testing does confirm the inherent 180% strength potential of the soft shackle. With the locks and bury's and construction imperfections perhaps knocking off another 10%
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Old 06-01-2014, 08:14   #116
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Re: Load Testing Results

Estarzinger,
Did you test any Kohlhoff style Soft Shackles yet?
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Old 06-01-2014, 08:38   #117
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Re: Load Testing Results

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Estarzinger,
Did you test any Kohlhoff style Soft Shackles yet?
The ones you show in that picture are exactly what I have been using on board Hawk and primarily been testing.

But I don't believe those are technically 'Kohlhoff style'. I think Kohlhoff have no bury . . . like these:

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I have tested several variants, and the diamond knot is the common weak point, and they all break at the diamond knot at about the same load. There is some indication that a shorter bury is better than a longer one (because it is hard/impossible to get equal tension on the bury and the cover), and the 'no bury' 'Kohlhoff' may be best, but it is hard to sort that out in the data from the constructional variation noise.
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Old 06-01-2014, 11:23   #118
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Re: Load Testing Results

Has anyone added a third component to the soft shackle? Splice, diamond knot, and maybe a washer ? Something that would give equal stress all around the diamond knot?

Issues: chafe, strength of washer
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Old 06-01-2014, 11:41   #119
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Re: Load Testing Results

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Has anyone added a third component to the soft shackle? Splice, diamond knot, and maybe a washer ? Something that would give equal stress all around the diamond knot?

Issues: chafe, strength of washer
Seems a dog bone would be a good solution to alleviate the stress, but someone needs to produce a cheaper one.
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Old 06-01-2014, 11:58   #120
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Re: Load Testing Results

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Seems a dog bone would be a good solution to alleviate the stress, but someone needs to produce a cheaper one.
You can replace the diamond with a spliced on short piece (say 2") of aluminum rod (a couple dollars at ace hardware for a 3' length), which would eliminate the diamond weakness. I have done some testing on that and you then end up with about 240% strength (vs 170% with the diamond). The weak point now becomes the small bend where the 'noose' closes.

But one of the beauties of the soft shackle is that it is 'just a piece of rope' that anyone can make up in about a minute. And for most people, the diamond is plenty strong enough. I mostly use soft shackles made with 1/4" line on Hawk, but I realize after this testing that 1/8" line would be strong enough for almost all my applications.

-----------------------------------------

I just took the test bench apart for inspection and upgrade. I used a mostly 'glued' construction (with machine screws just to clamp it in place), the first time I have done that with aluminum, and am pleased that it appears to have held up perfectly, despite my putting about 2" of bend in it at peak load. I am going to add an additional beam which should triple it's stiffness.

I did bend the two bolts that anchors the hydraulic rams. I had expected they would be the weak point, as I just used some 1/2" stainless bolts I had laying around, while the rams are sized for 5/8" pins. I will rebuild with grade 9 5/8".

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While the bench is out of action, I plan to do some 'drop tests'. I have a 50lb weight and I just need to find a clear 6' drop with a strong anchor above it.
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