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BoKu
Trad climber
Douglas Flat, CA
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Topic Author's Original Post - Nov 6, 2006 - 03:33pm PT
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I'd like to get set up doing some basic pull-testing on cams and perhaps some other climbing gear.
My plan is to use a hydraulic pullback ram of known cylinder bore to pull on cams inserted in artificial cracks. Measuring the hydraulic pressure in the ram and multiplying it by the piston area should yield the pull force.
I figure I'd create a steel frame to hold everything, and arrange this test rig so that the cam could be inserted into the space between two stone slabs. The width of this artificial crack could be adjusted using threaded rods.
I know that this is not a particularly professional way of going about it, but I think that it would yield results that are at least in the ballpark of what you might expect using professional equipment.
My first test article will probably be one of those KROK cams that are being offered on eBay.
Two questions:
* Does anybody see any blatant errors or misconceptions in this scheme?
* Does anybody know whether or not I need to use real stone for the surfaces of the artificial crack? I'm considering just trying two paving stones. The paving stones are attractive because they're economical and fairly uniform in texture.
Thanks, Bob K.
http://www.hpaircraft.com
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noshoesnoshirt
climber
hither and yon
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Will the paving stones withstand the pressure exerted by the cam faces without cracking or trenching?
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Inner City
Trad climber
East Bay
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It can't be long before Ed H. is going to offer some helpful hints here.
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Ksolem
Trad climber
LA, Ca
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One thing to consider. The performance of the cam will depend to some degree on how suddenly it is loaded.
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Moof
Trad climber
A cube at my soul sucking job in Oregon
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See:
http://home.pacbell.net/takasper/slcd/no9test.html
Why not use a steel surface? Coefficient of friction should be enough to stick.
Most concrete I've tangled with is in the 3-5 kpsi rating. So a medium sized cam with say 4 1/4"x1/4" contact points will have 1/4 square inch of contact area. A 14 degree cam angle will give you an outward force ~4x the pulling force. So 1000 lbs of pull force will put a pressure on your concrete paver of 16,000 psi at the contact points. Probably will turn the surface to dust.
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Jello
Social climber
No Ut
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What are you testing for - holding power or material strength? If you're testing for holding power, the surfaces of your rig need to be the same rock type as you're testing for. A cam will pop right out of a mild flare in hard, smooth quartzite, whereas it might hold well in the same flare in granite or good sandstone. In the late 70's I did a lot of pull and drop-testing on cams in actual placements in varied rock types. We used an in-line dynomometer to record the forces.
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Ksolem
Trad climber
LA, Ca
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Yes. My earlier comment was based on the assumption that you were testing for holding power, otherwise why ask about the medium. I would think that drop testing and shock loading will tell you more of what you need to know unless you are simply looking for manufacturing defects...?
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rgold
Trad climber
Poughkeepsie, NY
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Jello: "In the late 70's I did a lot of pull and drop-testing on cams in actual placements in varied rock types. We used an in-line dynomometer to record the forces."
You don't happen to have some records of those results, do you? Especially the drop testing?
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BoKu
Trad climber
Douglas Flat, CA
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Topic Author's Reply - Nov 7, 2006 - 11:09am PT
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Thanks to all for your thoughts on this topic!
Jello: What are you testing for - holding power or material strength?
Mostly I'm interested in the material strength; or rather the overall strength of the protection device. The reason I'm concerned about the friction surface is that I want results consistent across different tests, and I don't want the device slipping out during tests. The paving stones are also attractive because they're cheap enough that I can replace them after every few tests, or maybe just flip them over. It hadn't occurred to me to use a steel surface as someone suggested; I'd have thought that the steel-to-aluminum interface wouldn't develop enough friction to test an SLCD to its rated strength. I guess I'll have to give that a try!
My plan for using a commercially available hydraulic pressure gauge to measure the force should theoretically be about as accurate as the gauge itself - which is around +/- 2% for a typical gauge. I could get closer by buying a more expensive gauge, but then that starts putting the costs of the machine more in line with just buying an inline dynamometer as has been suggested. And I don't want this to get too expensive; I'd prefer to spend more money buying gear than destroying it...
One fairly economical possibility would be to use the hydraulic measurement, but to borrow an inline dynamometer to calibrate the machine. That should narrow down the fuzzband to around +/- 1% or so; about as finely as you can read a 4" 270-degree guage. My experience with commercial pressure gauges is that after a few cycles they tend to settle down to a relatively consistent deviation.
Thanks again, Bob K.
http://www.hpaircraft.com
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G_Gnome
Boulder climber
Sick Midget Land
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Why would you do this just to test the strength of the unit. I am sure you could call the manufacturers and ask them on average when their cams blow to bits. Seems a lot of trouble and expense for no gain. Besides, the placement usually fails long before the cam fails.
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Mungeclimber
Trad climber
one pass away from the big ditch
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BoKu,
Use real stone. Artificial or concrete equivalents will not have the same matrix that is strong enough to deform the metal cam lobe surface to get that friction bite.
My experience is from aiding on concrete cracks with a metolius 3cam unit from the 80s. Failed under body weight.
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Russ Walling
Social climber
Out on the sand, Man.....
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Go to one of them there rock yards and pick up some flagstone stuff.... real nice units from Utah and the like.... Quartz Monzonite is what they were calling it last time I was in one..... probably lies, but it would be nice to climb on. All thicknesses available for a couple of bucks a pound.
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Jello
Social climber
No Ut
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rgold- Unfortunately, I have no idea where the test results from the '70's might be. They were part of the Lowe Alpine files, so they still might be found somewhere in one of the Lowe Alpine offices, but the company has changed hands several times since 1988, and they could be at any of several locations in the US, UK, or even Europe. Actually, Malcolm Daly might have a better idea, as he was the last hardware manager at LAS, prior to the sale in 1988.
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maldaly
Trad climber
Boulder, CO
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BoKu, rgold,
Those results are long gone. LAS gave up the hardware business after jello and I left and I think they just threw all the stuff out. I managed to score the test rig though and am still using it. We called it the Ball-buster because we made it while we were developing the LoweBalls.
I made a fixture which could hold rock panels of varying types and found that what many of the comments above speculate, true. Rock pavers, cement, brick and the like (the cheap stuff) would just blow up. Cultured stone--countertop stuff) would last for a while but the sawed face was too smooth to hold any kind of flare angle. I'd get about ten pulls before these would crack. Real rock is the way to go with granite gravestone being the mot durable.
If all you want to do is test for ultimate cam strength, use steel plates. Have a machine shop texture the surface to the cam lobes won't slip. Think of a file face.
For your tests to be meaningful you'll need to test all cams in an identical manner. The cams sould be opened to the same percentage (max-min/2 will give you the 50% range) and they should all be tested through the cable loop or stem hole. This will be hard with cams like the G2 Camalots, Forged Friends or Tech friends.
Get an in-line pressure digital pressure gauge that will give you a peak reading. It's important because you'll want to be looking at the cams while you crank the hydraulics. You'll be amazed. Also, be careful. Get a big sheet of plexiglas and put it between your eyeballs and the test ficture. Stuff will go flying.
Good luck.
Mal
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BoKu
Trad climber
Douglas Flat, CA
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Topic Author's Reply - Nov 7, 2006 - 02:04pm PT
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G_Gnome: Why would you do this just to test the strength of the unit. I am sure you could call the manufacturers and ask them on average when their cams blow to bits. Seems a lot of trouble and expense for no gain. Besides, the placement usually fails long before the cam fails.
Well, for one I'm not sure I believe everything the manufacturers say about their stuff. For example, those new KROK cams, where they say "All climbing equipment we sell is tested and have appropriate documents from the Ukrainian government and testing organizations." That might mean they have UIAA/CE test approvals, it might not.
As for how much trouble and expense it is, one of my goals is to see if I can build a test machine that has usable accuacy at minimum cost and trouble. I've got all of the steel I need, and the hydraulics are on order from Harbor Freight. Judging by sailplane production tooling I've been welding together for the last four weekends, it should only take about half a day to weld up the test frame. I don't think that's too much time or trouble. And besides, I'll be able to reuse a lot of this stuff for static testing the sailplane parts.
As for recording the results, what I'd probably do is arrange the setup so that the gauge is next to the unit under test, and just video the test with a camcorder so that both the test subject and the gauge are in frame.
And, yeah, a piece of acrylic or polycarb between people and the test subject sounds like a good precaution. I'm sure bits will fly.
Thanks again to all, Bob K.
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steelmnkey
climber
Vision man...ya gotta have vision...
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Guess everyone needs a hobby.
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TradIsGood
Fun-loving climber
the Gunks end of the country
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If you are going to go to all that trouble, why not set up a "Consumer's Reports" - call it Gear Reports, for example. Sell the results to the community.
Sounds like a great idea. Don't take any advertising money, etc. Charge $25 / year. Once you have it set up, gear to destroy will probably be free.
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rgold
Trad climber
Poughkeepsie, NY
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Nov 13, 2006 - 02:27am PT
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Aliens notwithstanding, I'm not all that concerned about the strength of the units themselves. Holding power in real rock, not kitchen counters, is what matters.
I'm not saying this is terribly practical, but here's the test I'd like to see: cams are placed in various situations in real rock. For each placement, an experienced climber or group of experienced climbers each rate the placement on some reasonable scale from "marginal" to "bombproof." Then the cams are tested.
What would interest me is not the failure loads per se, I already know these can range from less than body weight to several thousand pounds. I'd be interested in whether the experts' evaluations correlated well with the actual holding power of the units tested.
'Cause what I'd like to know is whether or not the conventional wisdom is true that experienced climbers can reliably judge cam holding power, especially in the case of small to medium-sized cams.
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kubko
climber
Slovak Republic, Europe
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Nov 13, 2006 - 08:41am PT
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rgold, something like this has been done withe regard to pitons. Pit Schubert (safety guru at german mountaineering union)described such a test in his book. The results were surprising - the estimates of experienced climbers were way off - the best by some 50%, the worst by 300% IIRC. Mostly the people tended to overestimate the holding power of the piton.
I guess with cams the success rate would be much better, but it would sure be interesting to see the results of such test!
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