Cam testing: Friction surface

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Messages 1 - 35 of total 35 in this topic
BoKu

Trad climber
Douglas Flat, CA
Topic Author's Original Post - Nov 6, 2006 - 03:33pm PT
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
noshoesnoshirt

climber
hither and yon
Nov 6, 2006 - 03:52pm PT
Will the paving stones withstand the pressure exerted by the cam faces without cracking or trenching?
Inner City

Trad climber
East Bay
Nov 6, 2006 - 03:56pm PT
It can't be long before Ed H. is going to offer some helpful hints here.
Ksolem

Trad climber
LA, Ca
Nov 6, 2006 - 04:41pm PT
One thing to consider. The performance of the cam will depend to some degree on how suddenly it is loaded.
Moof

Trad climber
A cube at my soul sucking job in Oregon
Nov 6, 2006 - 05:01pm PT
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.
Jello

Social climber
No Ut
Nov 6, 2006 - 05:26pm PT
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.
Ksolem

Trad climber
LA, Ca
Nov 6, 2006 - 08:03pm PT
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...?
rgold

Trad climber
Poughkeepsie, NY
Nov 6, 2006 - 08:57pm PT
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?
BoKu

Trad climber
Douglas Flat, CA
Topic Author's Reply - Nov 7, 2006 - 11:09am PT
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
G_Gnome

Boulder climber
Sick Midget Land
Nov 7, 2006 - 11:33am PT
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.
Mungeclimber

Trad climber
one pass away from the big ditch
Nov 7, 2006 - 11:54am PT
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.
Russ Walling

Social climber
Out on the sand, Man.....
Nov 7, 2006 - 12:18pm PT
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.
Jello

Social climber
No Ut
Nov 7, 2006 - 12:39pm PT
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.
maldaly

Trad climber
Boulder, CO
Nov 7, 2006 - 01:36pm PT
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
BoKu

Trad climber
Douglas Flat, CA
Topic Author's Reply - Nov 7, 2006 - 02:04pm PT
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.
steelmnkey

climber
Vision man...ya gotta have vision...
Nov 7, 2006 - 02:15pm PT
Guess everyone needs a hobby.
TradIsGood

Fun-loving climber
the Gunks end of the country
Nov 7, 2006 - 06:23pm PT
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.
Ed Hartouni

Trad climber
Livermore, CA
Nov 12, 2006 - 08:53pm PT
take a look at this:
http://web.mit.edu/custer/www/rocking/cams/cams.body.html
and
http://home.pacbell.net/takasper/slcd/no9test.html
and
http://tc.engr.wisc.edu/UER/uer96/author2/content.html (figures are missing?)

the coefficient of friction is probably not well defined (granite-aluminum is taken to be 0.38) and dependent on the rock you are using. That alone would be an interesting study... using sandstone, gneiss, granites (many types), 'Gunks conglomerate, etc...
rgold

Trad climber
Poughkeepsie, NY
Nov 13, 2006 - 02:27am PT
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.
kubko

climber
Slovak Republic, Europe
Nov 13, 2006 - 08:41am PT
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!
rgold

Trad climber
Poughkeepsie, NY
Nov 13, 2006 - 11:04am PT
"I guess with cams the success rate would be much better, but it would sure be interesting to see the results of such test!"

Yeah, I suspect the test would be an eye-opener. I'd sure like to have my judgement evaluated in this way. But I think you are wrong about the ``success rate'' being better for cams. The factors affecting cam security are more numerous, more complex, and harder to judge than those affecting piton security. However, as far as the actual numbers go, I wonder whether the tests you mention involved climbers judging pitons they themselves had placed, or rather judging pitons already in place. Obviously, the latter is much harder to do, and if the numbers you mention applied to in-situ evaluation, then they aren't quite as shocking.
kubko

climber
Slovak Republic, Europe
Nov 13, 2006 - 12:38pm PT
I wonder whether the tests you mention involved climbers judging pitons they themselves had placed, or rather judging pitons already in place.

The pitons were already place (some of them for a long time) - that was the point of the test to see how reliable is climbers' judgment with regard to in-situ (old) pitons, as old pitons are abundant in many areas in europe and are often relied on by those who choose not to carry a hammer (a majority I would guess) where no clean protection works.

Sorry, I should have made that clear right away.


BoKu

Trad climber
Douglas Flat, CA
Topic Author's Reply - Dec 4, 2006 - 06:04pm PT
Quick update - My wife says a package just arrived from the Ukraine. It can only be my new KROK #3 cam!

Also, last weekend I finally got around to actually breaking some climbing gear with my hydraulic puller:

This new, unused, Rock Empire 20cm long, 12mm wide Spectra dogbone broke at 25.6kn (116% of its 22kn rating). It held at that force for about 30 seconds, during which it made occasional crick and pop noises before suddenly letting loose with bang.


This Omega Pacific bent-gate biner came with a set of Dirtbag quickdraws. It was used for two seasons before testing, and showed only normal wear and tear.


Testing the biner in gate-closed condition to the limits of my equipment (26kn, 108% of its 24kn rating) distorted the spine of the biner slightly, but it showed no other distress. The gate operated smoothly once the force was released.

My policy is to permanently retire any gear tested to over 50% of its rated strength. Therefore, I decided to destroy the biner by testing it in gate-open condition.

The biner broke with a sharp report at 9.2kn, 131% of its rated 7kn gate-open strength.

If I have any spare time next weekend I'll set up the artificial crack I'll use to test the KROK cam. For that test, I'll have a camera handy during the actual test.

Bob K.
Tahoe climber

climber
Texas to Tahoe
Dec 4, 2006 - 07:56pm PT
Cool thread!
Please keep letting us know how the testing goes - particularly if you do catch a manufacturing company lying/making mistakes with their strength specs.

Thanks!

-Aaron
BoKu

Trad climber
Douglas Flat, CA
Topic Author's Reply - Dec 11, 2006 - 07:56pm PT
Well, I've had some time to get a good look at that Petrenko cam. I disassembled it for a good look at the parts, put it back together, and did a pull test up to 7.5 kn. Here are some pictures so far.

The cam in the pull tester, with about 7.5 kn applied. The gauge indicates about 1460 psi; the effective piston area is 1.153 in^2, so the tension is 1460*1.153=1683 lbf = 7.48 kn.


An overall view of my test setup showing the hydraulic pump, the pullback ram, the test chassis, and the test crack. The test crack is a pair of 3/4" steel plates, with the inside surfaces textured with a rough grinder.


A closeup of the cam lobes engaged with the test crack. The unit held fine at 7.5 kn. The crack width is 1.75", which is halfway between the min and max sizes.


I'll post more about the test, but first I need some help. Can anybody who's done cam testing like this drop me a line? I have some questions about how to interpret some of the results I observed.

Thanks, and best regards to all

Bob "BoKu" K.

Mungeclimber

Trad climber
one pass away from the big ditch
Dec 11, 2006 - 09:03pm PT
Rad Boku!

Why not just email the guys at Black Diamond. I'm sure they would help with the configuration, but obviously wouldn't release any 'trade secrets'. Ya never know.
BoKu

Trad climber
Douglas Flat, CA
Topic Author's Reply - Dec 14, 2006 - 10:55am PT
Okay, I've got a new surface to test with. I used an air hammer (like a handheld jackhammer) with a chisel insert to apply a rough knurling to the steel plates of the test crack. That should create enough starting friction to continue testing.

What's going on is that I'm doing test comparisons between the Petrenko Links #3 and the Rock Empire Comet #3. Both cams are geometrically very similar. The size range and cam profiles are almost identical, as is the cam spacing along the axle.

The problem I had was that the Petrenko cam would engage the steel surface for pull testing, but the RE cam would not. So I couldn't do a pull test on the RE to compare the effects of the pull test. I think it might mean that the lobes of the Petrenko cam are softer than those of the RE, but I won't know that for sure without getting Rockwell hardness tests of both cams to compare.

With the steel surface knurled, I can now crank both cams up to 7.5 kn and see how much local yielding there is of the cam lobe surfaces at the contact point. That will provide a good basis for comparison between the two.

Bob K.
spyork

Social climber
Land of Green Stretchy People
Dec 14, 2006 - 04:35pm PT
Hey Bob, cool stuff. I want to see pictures of exploding cams! Action shots!

Save some gear for actual climbing though...

Steve
Tom

Big Wall climber
San Luis Obispo CA
Dec 14, 2006 - 06:03pm PT
I've used plain steel, about 1/2" thick, in a frame with parallel sides. When I first tried uncleaned steel, the residual grease and oil allowed the cams to slide. I cleaned the steel, left it outside a couple of days and allowed it rust. After that, there was no tendency for the cams to slide out. They would lock right up.

You might want to look into getting a load-cell, which mounts in series with the cam and the pulling rig, and you can hook up to a PC to get more accurate data.
BoKu

Trad climber
Douglas Flat, CA
Topic Author's Reply - Dec 15, 2006 - 06:37pm PT
> Hey Bob, cool stuff. I want to see pictures
> of exploding cams! Action shots!

I'll try. But I suspect that most cams will die with a whimper, not a bang.

> I've used plain steel, about 1/2"
> thick, in a frame with parallel sides.

That's basically what I tried, using 3/4" steel that I had on hand. I "conditioned" it with a rough grinding wheel and degreased it. It still wouldn't grip some cams. Hence the knurling.

> You might want to look into getting
> a load-cell, which mounts in series
> with the cam and the pulling rig, and
> you can hook up to a PC to get more
> accurate data.

I'd like to do that, and I may some time in the future. But that's thousands of dollars worth of stuff versus the two-hundred odd dollars my current 25.6 kn +/- 2% setup cost me. Breaking climbing gear isn't lucrative enough to justify the extra expense.
paganmonkeyboy

climber
mars...it's near nevada...
Dec 22, 2007 - 05:35pm PT
so how did the testing ever turn out ?
stumbling around ebay I found a ton of KROK cams for sale...
http://stores.ebay.com/gear4rocks
ExtraBlue

Ice climber
the ford VT
Sep 15, 2010 - 11:51am PT
any update on the Krok test?
klk

Trad climber
cali
Sep 15, 2010 - 12:54pm PT
Schubert's stuff is always interesting:


http://www.amazon.de/Sicherheit-Risiko-Fels-Eis-Sicherheitsforschung/dp/3763360166/ref=sr_1_3?s=books&ie=UTF8&qid=1284568904&sr=1-3
adatesman

Trad climber
philadelphia, pa
Sep 15, 2010 - 03:11pm PT
Dunno if he posted about it here, but he did put it up on RC ages and ages ago.

http://www.rockclimbing.com/cgi-bin/forum/gforum.cgi?post=1515428#1515428
Steve Grossman

Trad climber
Seattle, WA
Sep 15, 2010 - 09:05pm PT
Find a stoneyard that has guaged granite blocks or have some reasonably uniform blocks cut. You can easily epoxy threaded rod for attachment and use a layer of two part masonary epoxy to wet set your blocks into your steel test armature. The goal is even face compression.

Borrow a video cam!
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