View Full Version : Failure test of homemade buckle
Yet another post from me.
Today, I made a pair of aluminum buckle's based on andersj's design (http://www.hammockforums.net/forum/showthread.php?t=2357)
As promised, I just implemented my Mythbuster's-style test.
The goal: Simulate my hammock setup with my Civic.
The buckle is designed to thread onto a tree-hugger. There's a cleat on the other end to attach the hammock line to. I'm using 2.8mm Spyderline, which claims to be rated to 1,200 lbs and 1" Speer polypro webbing.
I made a prototype buckle yesterday that is almost the same as my final version. The difference is that the "bars" are slightly thinner and the overall buckle is slightly wider. I attached a loop of unused webbing to this and lark's headed it onto the tow loop of my car. Then I got a length of unused Spyderline and tied it to a very sturdy metal pole and lashed the line to the buckle. The resultant setup left the whole thing in a level line.
I drove very slowly away until I heard a pop. When I checked on it, the line was still attached, but the sheathing had separated. Also, the line had gotten very weird. It had stretched out and become very stiff.
I tried again, this time just using the core (Dyneema? Very slippery) and heard another pop. This time the line was no longer attached. I couldn't tell if it had broken at the lash or just pulled out. I tied the lash again and threw a couple half hitches in behind it. This time, the line broke clean in the middle.
Examining the pieces afterwards, everything but the line looked perfect. Zero signs of wear on the webbing or buckle. I traced the buckle beforehand and it showed no change at all. Also, using my counter, I verified that it was still completely flat.
Based on this, I feel comfortable saying that:
1. Spyderline is more than strong enough for hammocking.
2. The buckle is even stronger than that.
3. Driving at two in the morning until something breaks kicks ***. I wish I was a Mythbuster.
Obviously, this wasn't a genuinely scientific test and only went through one trial. But it was enough for my peace of mind. I think I'll feel as safe as I ever have hanging over broken glass and crocodiles.
Have at it, armchair engineers. I still have a buckle to break.
that is really good to know. Now I need to choose a setup I like. So many options!
BillyBob58
11-19-2007, 09:29
What is interesting to me is: The 700 lb Speer webbing held up longer than the 1200 lb Spider line. Would this be due to the knots? But even the webbing also had a larks head. Interesting indeed!
I kind of had a feeling it was going to go that way. The Spyderline broke in the middle, too, not at one of the knots.
NCPatrick
11-19-2007, 09:47
I think you'd just need to post video of the testing/breaking process, and you can be an honorary mythbuster...
We have to get you some other myths to bust...
Take-a-knee
11-19-2007, 10:08
That was way cool Patrick, thanks for doing that and sharing it.
No problem - it was a good time. Video is an excellent idea. I'll see if I can do that.
Walking Bear
11-19-2007, 10:57
You found the weak link in the setup. Good to Know. For safety with your test methods toss a blanket over the setup and then do the test. The blanket will absorb any energy and stop any flying parts.
Good thinking. Although, then I'd never get to answer the question, "What's that big hole in your fender from?"
By video taping it you can also see what is happening just before the "pop". You could also hook another car up instead of the pole and try and tow it down the street and see what happens.
I'm not sure the scientific value of towing another car, but I very much like "see what happens" part.
The big lesson that I've taken away from this is that the forces required to mess up the line, much less the buckle, seem to be on a whole other level than we exert hammocking.
I'm leaning toward applying some measured weight to it next, but I don't have access to much. Between my friend and I, we might have 500 lbs of plates, but I'm sure that won't do anything.
The 700lb webbing rating is probably safe working load vs the 1200 lb failure load of the spyderline.
Sailing ropes strengths typically are FAILURE loads not safe working loads which would be usually a half to a third of the failure load depending on application.
BillyBob58
11-20-2007, 10:51
That would be something good to know for certain, one way or the other. So all of this time I have been impressed with the superior rating for various ropes relative to their weight, and the whole time I was comparing apples to oranges? Apparently so. I thought they were both rated breaking weight, while buckles and such were rated "safe working load", which was 1/3 to 1/2 of the actual break point.
So if webbing is rated as "safe working load", that would mean Speer 1" polypro 700lb webbing has a breaking point of 1400-2100 lbs, and the Strapworks 1" polyester 3500 lb would be expected to break at 7000 to 10500lbs? If so, WOW! But some how I don't think so, but I certainly don't really know.
Does anybody here know how these various ropes, webbing and devices are actually rated, breaking strength or safe working load? The last I heard, rope and webbing were rated at the breaking point while devices ( hitchcraft, buckles, etc) were rated for safe working load. Is this incorrect?
You have to check the specs provided for each and if its just a number without clarification its not terribly useful. I'd wager that the 1" Speer is a 700 lb working strength, but the 1" Strapworks is 3500lb breaking strength.
Many webbing tie downs and tow straps give both numbers... and yes they're usually 1/3.... I have seen 2" webbing tow straps with failure strengths in the 25-30 THOUSAND pounds range...
I do know that most of the time sailing ropes strengths are given as failure strengths.
So that would be an easy explanation why the rope failed before the webbing... There could be other less obvious answers...
The short answer is you have to check each on a case by case basis. A number alone means little, but is often used for marketing.
BillyBob58
11-20-2007, 11:43
Thanks. And I wouldn't be surprised if Speer uses a more conservative rating.
There's a thread around somewhere about a guy breaking his Speer webbing. I want to say it was right in the middle, but I don't remember for sure. That's the only time I remember hearing of that, which seemed to be the common sentiment.
I've always felt that my biggest enemy is wear, which is one of the reasons I switched to the buckle and ring. My tree huggers (homemade Speer webbing) were mutated all to hell from the line being lashed to them and that was that fat blue Byer rope. Probably had less than fifteen nights on them and they were all smushed and melty looking. Seemed to me like if something was going to fail, that's where it was going to happen.
BillyBob58
11-20-2007, 11:58
And there have indeed been a number of recent HH hugger failures at that exact point. At Neo's hangout, Skinnybadger's huggers looked bad after the first use. Mine still look reasonable after a year of occasional use.
Cannibal
11-20-2007, 12:02
There's a thread around somewhere about a guy breaking his Speer webbing. I want to say it was right in the middle, but I don't remember for sure. That's the only time I remember hearing of that, which seemed to be the common sentiment.
I think that was slowhike. But he also said he was hanging with a pretty long span from tree to tree; not a normal hang.
TiredFeet
11-20-2007, 16:50
Just looked on the strapworks web site under FAQs. Quoting their site:
*Q: What is the strength rating I need?
*A: A strap's overall strength is limited by its weakest point. This can be the webbing or it can be the buckle. You need to understand that there are "breaking" strengths and there are "working loads". The breaking strength is where the webbing or the buckle will actually fail under a static load (a dead lift, for instance). On the other hand, working loads are a recommended maximum load to use considering other factors like impacts, shocks to the strap from dropping or jarring, etc. Most manufacturers recommend 33-50% of the breaking strength as the actual working load (we figure at 50%). If your buckle is rated at 1000 lbs, and your webbing is rated at 500 lbs, you have to figure your working load as 50% of the webbing's rating, or 250 lbs. Our cam strap webbings are rated as follows...Lightweight Polypropylene-600 lbs; Heavyweight Polypropylene-900 lbs; Flat Nylon Webbing-3500 lbs; and Polyester-3500 lbs.
That seems to indicate that they think webbing is rated at breaking strength.
warbonnetguy
11-22-2007, 11:13
I'd wager that the 1" Speer is a 700 lb working strength, but the 1" Strapworks is 3500lb breaking strength.
nope, both are breaking strength. heavy wt polypro has a breaking strength of 700-800# per inch of width depending on where you get it. that means 2" would be 1600# and 1/2" would be 400#
the strapworks is 3500# is the break strength as well.
i haven't seen any webbing rated on a safe working load, except everything sold at home depot or walmart etc...
line is only stronger than webbing for it's weight b/c you can get line made from spectra and vectran. webbing usually comes in polyester/nylon/polypro, which is all weaker # for # than high tech fiber. this is the main reason, i'm sure there is some strength difference between a 12 strand braid and a webbing weave, but the main difference is from the fiber it's made of.
BillyBob58
11-22-2007, 12:02
nope, both are breaking strength. heavy wt polypro has a breaking strength of 700-800# per inch of width depending on where you get it. that means 2" would be 1600# and 1/2" would be 400#
the strapworks is 3500# is the break strength as well.
i haven't seen any webbing rated on a safe working load, except everything sold at home depot or walmart etc...
line is only stronger than webbing for it's weight b/c you can get line made from spectra and vectran. webbing usually comes in polyester/nylon/polypro, which is all weaker # for # than high tech fiber. this is the main reason, i'm sure there is some strength difference between a 12 strand braid and a webbing weave, but the main difference is from the fiber it's made of.
All of which still leaves me surprised that the 1200 lb line broke before the 700lb webbing. Particularly since it broke in the middle instead of at the knot.
Of course, there are always many other variables, sometimes unknown ones, such as wear or exposure to elements. Or, I suppose, even a bad batch from the manufacturer or normal manufacturer tolerances.
warbonnetguy
11-22-2007, 12:19
that is odd. i've heard of other spectra breaking in the middloe of the line rather than the knot. the numbers themselves make sense otherwise. 1200# line with knot=600#, which should be weaker than 700# webbing with stitches rather than a knot, as stitched webbing should keep almost all it's strength.
the location of the break is a bit confusing though.
The line wasn't worn, it was right off the roll as was the webbing. I still need to break that buckle, so I'm happy to execute any more tests you guys come up with.
jeffjenn
11-25-2007, 13:21
Patrick, how much does each buckle weigh, & where did you get the alum.?
I don't have a very precise scale, just a dial kitchen one. Two rings and two buckles weigh just under 2 oz., so about half an ounce.
I ordered the AL from http://www.onlinemetals.com. It was $15 or $20 for two big pieces shipped. If I were to do it again, I'd get the 1.5" wide stock and just use that width.
Ah, check that. I would NOT go to 1.5". I knew there was a reason I used a weird size. It has to fit through my SMC ring and 1.5" looks to be just a little big for that. As is, it fits through great.