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qtm
Aug 24, 2006, 10:31 PM
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Disclaimer: Don't try this at home. If you decide to pull test your own gear, that's your responsibility. Don't pull test with your car, there are some nasty chemicals like battery acid all around a car and garage and it's not safe to have your gear anywhere near it. If you want your gear tested properly, send them out to be tested.
Ok, that said, I wanted to pull test my aliens. I'm not headed out to the crag this week, but wanted to have some reasonable assurances that none of my cams were going to break under body weight. So how to test them without destroying them?
Well, a 3mm cord has a break strength around 2KN. With a knot on each end, it should decrease the break strength by 30% or so, which should result in a "fuse" somewhere over 1KN. Here's what it looks like.
http://img242.imageshack.us/...893/pulltest1oa0.jpg
The red cord is the 3mm "fuse". It's connected to the alien (with a locking biner) with a 7mm cord.
The 7mm cord is looped around the stem.
http://img167.imageshack.us/...931/pulltest3bv5.jpg
This will pull slightly off axis, but I didn't want to loop the rope over the lobes on the far side and twist the lobes outward.
I attached the following to my trailer hitch. I wanted to see how strong the fuse was, so I pulled. A really hard pull, with all my body weight, managed to break the fuse. I also hooked a second test fuse to my roof rack and stepped on it, and it held my body weight (180lbs) and a slight bounce, so I think that's probably under the 2KN (although I don't know for sure).
Here's the pull rig.
http://img167.imageshack.us/...047/pulltest2do3.jpg
Ok, I *should* have attached it to the trailer hitch the other way; so the alien is attached to the trailer hitch and I would have the fuse end in my hand. The way I have it rigged, when the fuse breaks, the biner and the alien come flying at me... but the alien hitting me was preferrable to the alien touching a dirty garage floor.
So this worked pretty much as I expected. I'm not sure if it actually proved anything, but I think it means that the cams will at least hold body weight. I might try using a loop of 3mm fuse instead of a single strand, that will increase the force but still be well below what it takes to damage the cam.
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fourfa
Aug 24, 2006, 11:41 PM
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the failure mode is that the stem cable pulls out of the head sheath? It's not obvious to me from the threads I've read, sorry.
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tim
Aug 25, 2006, 12:37 AM
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Why not just use lengths 3-4mm cord for a funkness, and set the cam in a vise? It's a lot more reproducible and a stiff pull won't fuck up the lobes (unless, of course, the cam is defective... but then the expected failure mode is a braze failure, and the head should come off intact).
I tested mine in this fashion, albeit with a full-strength funkness cable and a from-the-elbow motion. Using 3mm or 4mm cord is more reproducible.
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qtm
Aug 25, 2006, 2:02 AM
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fourfa: Yes, that's the reported failure mode.
Tim: I don't have a benchtop vise, and I doubt too many people out there do. And when I was young, I ripped the benchtop vise off the mountings trying to bend a heavy piece of steel, so I'd rather not suggest people try pull tests with a vise.
A car works well, and a lot of people have cars. You can't really rip out the tow hooks in a car, so it's pretty good as an anchor to pull against.
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billcoe_
Aug 25, 2006, 4:41 AM
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Great thinking! Much better than what I just posted on the injury thread about this which said:
"I did some research on putting together a force measuring and testing device to test these and it would be priced out of my league. Russ's thing of having a strong dog on a leash, with a screamer connected to your bumper and the Alien with a cat walking in front to activate the dog may have some merit after all. :lol:
I don't think any old Schnauzer will do either, you'd need a big Rottweiler or an Irish Wolfhound kind of dog. :roll:
But at least it would be some kind of QC check!
Anybody have a stout dog they want to volunteer to be an Alien tester? Pay is all the Friskies they can eat, and of course the odd occasional cat as well for when breakage does occur."
I like your idea better for sure! You get a trophy.
Regards
Bill
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keinangst
Aug 25, 2006, 1:12 PM
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In reply to: fourfa: Yes, that's the reported failure mode.
Interesting...I always though the failures were due to axle deformation/disintegration rather than "de-sheathing"
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qtm
Aug 25, 2006, 2:15 PM
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OT... but I think those kids just attached the rope to the bumper, which isn't all that strong.
Tow hooks are usually welded to the frame. Ok, maybe you can break off hooks if you try to lift the vehicle vertically, but you they should be enough to drag the vehicle around.
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j_ung
Aug 25, 2006, 2:24 PM
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Nice thinking, but can't you get even more force from a standard bounce test? (I'm not really an aid climber, so I'm asking, not telling.)
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qtm
Aug 25, 2006, 3:25 PM
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Probably. You could just take the alien and the 7mm cord and hook that to the 2nd step on a metal staircase and jump on it.
Frankly I didn't know how little force it would take to break the 3mm fuse. I wasn't sure I could break it with a bounce test. I expected I would need more force, which was to be provided by the car. By increasing the number of loops or size of the fuse, you can put increasingly larger loads on the piece. Without a force meter I can only guess at how much force is actually applied though.
I'll be satisfied if it pulls to somewhere near half the rated strength.
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renohandjams
Aug 25, 2006, 4:43 PM
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Many of you might already know this, but just in case you don't many of the new CCH cams post recall have "tensile tested" stamped on the copper at the base. My point being, this may be obvious, if you have a new alien cam that says "tensile tested" on it the testing has already been done in a controlled environment and there really isn't any point for you to redo it.
Older cams on the other hand are a different story.
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bobruef
Aug 25, 2006, 5:20 PM
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In reply to: ... My point being, this may be obvious, if you have a new alien cam that says "tensile tested" on it the testing has already been done in a controlled environment and there really isn't any point for you to redo it...
true, if you're willing to take CCH at their word.
I also recall reading on their website, durring the first brazing failure fiasco, that all cams are produced in house (ie- no outsourcing). Then, they reported, after the fact, that failures were due to improper cooling methods used by outside contractors (which made for a conveniently reasonalbe, discrete batch of cams to be recalled).
Now another, "in-house", "pre-recall fiasco" cam has failed at the braze. This, in addition to their handling of the brazing issue, the misdrilling issue, and the guy who very recently recieved a cam that was simply the wrong size (after the stringent QC measures supposedly went into place), make it hard for me to take them at their word. I'm more likely to believe the alleged former employee who remarked on the inconsistent and dubious craftsmanship practices of CCH employees.
I always took CCH at their word, regarding the safety of their cams. I even took them at their word regarding the safety of non-dimpled aliens after the fiasco. At this point, I find it hard to trust that a cam was tested because CCH says so. Credibility is a valueable comodity, that in this case, has been squandered.
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kimgraves
Aug 26, 2006, 3:30 AM
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Hi Gang,
A kN is about 250 lbs. The 3mm I have is rated at about 300 lbs. Considering you want to test to about half the rated strength it would seem to me that 3mm isn't thick enough. It seems like a funk test would be a better test - or bounce testing them.
But more importantly, if the cam does break, then what? Do you just retire it or get into a fight with CCH? Seems like to me that if you have doubts - and I think you should - it would be a better idea to return all your Aliens to CCH for testing. Wagner tested mine even though they were not the recalled ones. It's just the price of postage - cheap insurance. And if you can't trust Dave to test them, then maybe you shouldn't be climbing on them anyway. You can't go wrong by not using them.
Best, Kim
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slacklinejoe
Aug 26, 2006, 4:43 AM
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Very true, send it in if you have your doubts.
I did however think up another test though, rig it in-line with an insane tight slackline. If it'll handle a nice jump tight line on hard jumps that approaches 1,000 lbs of pull. Back it up so if the head pops off you aren't sending shrapnel your way.
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qtm
Aug 26, 2006, 3:19 PM
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In reply to: Hi Gang, A kN is about 250 lbs. The 3mm I have is rated at about 300 lbs. Considering you want to test to about half the rated strength it would seem to me that 3mm isn't thick enough. It seems like a funk test would be a better test - or bounce testing them. But more importantly, if the cam does break, then what? Do you just retire it or get into a fight with CCH? Seems like to me that if you have doubts - and I think you should - it would be a better idea to return all your Aliens to CCH for testing. Wagner tested mine even though they were not the recalled ones. It's just the price of postage - cheap insurance. And if you can't trust Dave to test them, then maybe you shouldn't be climbing on them anyway. You can't go wrong by not using them. Best, Kim
As I said in the original post, if you're concerned with your cams, send them out to be tested.
A 3mm cord is 1KN, looped it is around 2KN, double and loop and you have a fuse around 4KN. You can't generate 4KN in a bounce test.
A 4mm cord is rated 3KN, so a single strand with knot will be over 2KN. Maybe it's better to use a single strand of 4mm, but I only had 3mm cord lying around.
Yes, you can send all your cams out to be tested. But what happens when you pick up a new cam? Sending cams out individually to be tested will add 25% to the price of each cam. A foot of 3mm cord costs 25 cents. While I trust BD, Metolius, WC... why not pull test them yourself if it only costs 25 cents a cam and takes only a few minutes?
What happens if it breaks? It shouldn't. But if it does, then it's probably a good thing it didn't break while you were falling on it. If you broke it because you looped the 7mm cord wrong and pulled strictly on one side of the stem instead of the stem itself, well, that's why the first line said "don't try this at home."
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qtm
Aug 26, 2006, 3:24 PM
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In reply to: Very true, send it in if you have your doubts. I did however think up another test though, rig it in-line with an insane tight slackline. If it'll handle a nice jump tight line on hard jumps that approaches 1,000 lbs of pull. Back it up so if the head pops off you aren't sending shrapnel your way.
Great idea! Get a friend to jump on and you can generate even more force.
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sonyhome
Aug 28, 2006, 11:47 PM
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* I suspect using a 4mm string would not work:
- the cordelette will break at a greater force than rated. There must be an error margin built in. You would have to measure that breaking force first. Maybe with a screamer that blows at 6kN?
- The impact force curve must be very different from a leader fall: The slope is likely much steeper, and also it breaks causing a weird load behavior on the cam.
* Using a slack line I would not know if it's good, but at least it would be a more gentle pull test it seems.
* A bouce test might already be good: How much force does that generate on the gear? There's no dynamic part in the system to absorb the shocks to the cam so it could be quite a bit already... Anybody knows?
[edit]ah... someone says 2kN or more.
* The best would be a tensile test, with a dynamic rope held by the cam, and a weight, using the height to simulate the impact force. Say you make the weight take a factor 1 fall, the rope is tied on the cam and the weight, and you remember your rope's rated max impact force. It is higher (~9kN) than your cam's rating (~6kN). Then you ask some guy (aka not me) how much the weight to drop should be to get 3 or 4kN on the cam.
* Of course you could just set the piece on a wall, double it up or mock lead with an extra TR, and drop test to see the cam working in normal conditions on no more of a fall than what you'd be willing to take on lead?
BTW, from onlineconvertion
In reply to: 1 kilogram = 2.2046 lb 1 kiloNewton = 101.97162 kilogram 1 kiloNewton = 224.80894 pound
Also, CCH tested to these specs when they analyzed their cams for failure during recall (see CCH notice):
In reply to: 0.33 - 0.50 : 1800 lbs / 8kN 0.75 - 1.00 : 2000 lbs / 8.9kN 1.25 - 2.50 : 2500 lbs / 11.1kN |
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qtm
Aug 29, 2006, 3:42 AM
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A 4mm cord is rated around 2KN. A loop is 4KN. Maybe it breaks at 5KN. Even at 6KN, it's still only 75% of the rated strength of the black Alien, 66% of Blue and Green. I think that's a large enough margin. There's also the knot, which decreases the strength, which adds to the margin. But there's really no way to tell exactly how much force, it's just a ballpark figure.
In reply to: The impact force curve must be very different from a leader fall: The slope is likely much steeper, and also it breaks causing a weird load behavior on the cam.
Too steep? My subaru isn't going to accelerate anywhere near as fast as a falling climber, I doubt it could accelerate at 0.5G. Besides, the way I'm pull testing is on an incline, to allow the car to slowly roll (in neutral) and apply the force slowly. An actual pull-test machine pulls slowly as well, so neither applies force as quickly as a real fall. I don't know if that makes a difference, but if the industry relies on slow pull test machines, then a pull by the car is good enough for me. Of course I'm no one special, not even an engineer, so don't take my word for it. Send your cams out to be tested if you're concerned.
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gunkiemike
Jul 2, 2009, 5:15 PM
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Resurrecting this thread because I spent some time this morning pulling a couple Aliens to ROUGHLY 1000 lb in my garage. It was fun and, since the units didn't fly apart, slide out, or bend at the axle, it makes me feel good.
The key to being able to do this is a parallel-sided gap between two concrete slabs that comprise my garage floor. It's well-aged concrete, and the gap, which varies in width from about 0.5 to 1.25 inch, fits yellow and red Aliens perfectly. You could probably find useful cracks like this between urban sidewalk sections.
So I stuck the Aliens in about an inch, compressed to mid-range.
I made a fuse by sewing 185 stitches of household polyester thread in a 1x2" pattern to fashion a loop of 1" tubular Mil-Spec webbing. I knew from previous work that the number of stitches is proportional to breaking strength (see the "load bearing sewing" thread for confirmation of this key aspect) and quickly calibrated my sewing with half a dozen loops that I broke under partial body weight. Bathroom scale measurements allowed +/- 10 lb indication of loads. The results were quite linear between 9 and 30 stitches, with repeatability in the 5-10% range. Loop strength worked out to roughly 5 lb per stitch.
Rigged a crowbar between a jackstand and a hydraulic floor pump, and jacked it til the stitching broke.
The yellow and red I tested were both 0702 dated. Both survived in fine shape: no lobe damage and only slight embossing of the plastic covering on the cable loop.
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fresh
Jul 2, 2009, 8:42 PM
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real men test aliens by slacklining with them.
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hafilax
Jul 2, 2009, 8:52 PM
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There's got to be a way to calibrate the force of a mass dropped from a certain height attached to a piece with a sling in order to do this kind of test. People could test aid gear as well like rivet hangers etc. I would guess that it would be more consistent than a fuse type measurement.
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adatesman
Jul 3, 2009, 12:54 PM
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