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adatesman
Jun 16, 2009, 5:36 PM
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drector
Jun 16, 2009, 5:36 PM
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angry wrote: It's definitely a matter of perception. [snip] After reading this, I believe they will. [snip]
angry,
If someone told you that your car might have been built with a bomb in it and it could go off at any time, would you still love your car? Now what if Aric told you that you have an Alien with a bad braze that will hold too little to catch a fall? You still want to use them?
The problem with manufacturing defects through bad QC is that it lets in the question of how many bad cams you have. Maybe you happen to be the guy with a rack of Aliens that all have a bad braze. There is no way to know and you are no longer a climber. You're a gambler.
The bad QC is the important issue. The tests confirmed that Aliens have badly placed holes in the lobes and bad brazing. It also suggests that the cam lobes are not properly hardened. There was even the one Alien that got its axle bent at a lower load than expected. It's all signs that using an Alien is like playing craps ... for you life.
I hope that all of your Aliens are manufactured properly and hold all of your falls. Good luck.
Dave
P.S. The Alien offsets I own are the best cams I have discounting the possibility that they might break.
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jt512
Jun 16, 2009, 5:39 PM
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angry wrote: Aric, I know you're trying to alert us to a safety issue but really, you've proven the reliability of aliens.
Well, there is a lot of variability in terms of how their strength, as measured by Aric, compared with their rated strength. The mean of (measured strength) / (rated strength) * 100% was 89.4% with a standard deviation of 16.0%.
The average is dragged down by the smaller cams. The two black Aliens in the sample had the lowest numbers (54.7% and 63.6%), and one of the two blue Aliens in the sample had the third lowest (69.8%).
The 13 Aliens in the sample that were rated for 2700 lbf did the best. They attained 98.0% of their rated strength, on average, with a standard deviation of 11.1%. The mean strength in this subsample was 2647 lbf, with a standard deviation of 300 lbf, giving a coefficient of variation of 11.3%, which is alarmingly high, and indicates the opposite of your conclusion. These data do not "prove the reliability of Aliens." They suggest the contrary.
In reply to: Clearly they are tested on a different surface than you've got and that accounts for all but 2 of the failures.
If Aric's testing has produced results equivalent to UIAA testing—and I'm not saying that it has—then the correct 3-sigma rating for the 2700-lbf-rating Aliens should be in the neighborhood of 1750 lbf. How can you state that such a large discrepancy is "clearly" due to different testing surfaces?
Jay
(This post was edited by jt512 on Jun 16, 2009, 6:33 PM)
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k.l.k
Jun 16, 2009, 5:48 PM
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You know, I don't even care about the numbers. Just look at those brazes in that photo that Healeyje linked.
Just frickin amazing.
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jt512
Jun 16, 2009, 6:13 PM
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adatesman wrote: The full explanation with diagrams and equations is over on Vaino Kodas' site, but what it boils down to is that assuming structural integrity of the unit, a cam will stay in place in a parallel placement regardless of force applied so long as the tangent of the cam angle is larger than the coefficient of friction between the lobe and the surface it is contacting.
Shouldn't that be "less than"?
Jay
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ptlong
Jun 16, 2009, 6:19 PM
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adatesman wrote: The test jig is terrible for representing how the cams would react in this regard, because the frictional coefficient between aluminum and steel is roughly double that of aluminum and most types of rock and therefore the cams will stick with far less available outward force. (Erm... make that should due to the other issues that effect it holding, such as lobe and axle deformation.)
I see. You're saying the jig surface friction is 2x greater than typical rock while angry is claiming the surface is the reason the cams were slipping out.
I don't doubt simple cam theory. I just want to see some proof that what you think you're measuring is real.
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adatesman
Jun 16, 2009, 6:33 PM
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jt512
Jun 16, 2009, 7:06 PM
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ptlong wrote: I'm still curious why Jay couldn't get consistent results measuring the centers while others could.
You're probably confused because you are assuming I am a competent photographer, whereas in reality I probably just suck. I have been unable to get images that meet the three criteria for the software to provide valid measurements of the cam center; namely, sharp focus, centering on the cam axle, and angle aligned with the cam axle. I have a long and tearful history of getting bad lab results, so there is a good chance that other people are getting better photographs than I.
That said, I'm still skeptical of the way people are doing these measurements. No one, as far as I can tell, has performed them in a manner that is controlled well enough to validate the procedure. The following questions remain open:- How much does camera angle and camera centering affect the measurement?
- If (1) is important, then how good has the centering and angle been in the photographs used?
- How much does manual selection of the sampled points bias the measurements or affect their reliability?
- Do repeated photographs and selection of sample points on the same unit produce consistent results?
- In a systematic comparison, how would results for Aliens and other brands compare?
Jay
(This post was edited by jt512 on Jun 16, 2009, 7:07 PM)
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roy_hinkley_jr
Jun 16, 2009, 7:21 PM
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jt512 wrote: That said, I'm still skeptical of the way people are doing these measurements. No one, as far as I can tell, has performed them in a manner that is controlled well enough to validate the procedure. Jay
Thank you Jay. These were such obvious questions they should have been addressed long ago. Similarly, there is a lot that Aric doesn't understand about what he's trying to test or the standards and how they are created. He'd rather insult Roy than deal with legitimate concerns about how he is going about things. Whatever.
The real issue is that there still isn't any safety concern that has been proven. Lots of doubts, mostly ill-informed conjecture, and certainly weak quality control. But all and all a tempest in a teacup.
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jt512
Jun 16, 2009, 7:43 PM
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roy_hinkley_jr wrote: jt512 wrote: That said, I'm still skeptical of the way people are doing these measurements. No one, as far as I can tell, has performed them in a manner that is controlled well enough to validate the procedure. Jay
To clarify, I was referring to the determination of the cam center.
Jay
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cracklover
Jun 16, 2009, 7:47 PM
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adatesman wrote: ptlong wrote: adatesman wrote: The test jig is terrible for representing how the cams would react in this regard, because the frictional coefficient between aluminum and steel is roughly double that of aluminum and most types of rock and therefore the cams will stick with far less available outward force. (Erm... make that should due to the other issues that effect it holding, such as lobe and axle deformation.) I see. You're saying the jig surface friction is 2x greater than typical rock while angry is claiming the surface is the reason the cams were slipping out. I don't doubt simple cam theory. I just want to see some proof that what you think you're measuring is real. Close... What I'm saying is that the frictional coefficient of aluminum on steel is ~2x the frictional coefficient of aluminum on rock. This coefficient is for the base materials and ignores special surface treatments like texturing. While the texture will certainly play a minor role in the cam holding, the mechanics behind how these things work is entirely based on friction and not dependent at all on the texture of the surfaces. Additionally I believe that the fact that some of the Aliens and all of the other cams I've tested did not slip out of the fixture points conclusively to the effect of the texture of the plates being negligible.
Aric, the trouble I'm having is that I don't see any correlation between effective cam angle and the point at which the cam slipped.
For example, here are the cams for which I was able to determine an effective cam angle, ordered by angle. I've broken them down into thirds for the purpose of getting averages:
sample rating failure failure angle RATING Soft avg failure avg rating
Mode kN % Lobes kN %
-----------------------------------------------------------------------------
3 12 braze 9.3 14 77.50% Y (not counted due to braze failure)
23 9.8 pulled 6.8 15 69.39% Y 11.24 90.94%
1 12 pulled 10.6 16 88.33% Y
15 12 pulled 13.5 16 112.50% Y/N
6 15.5 pulled 14 16 90.32% Y/N
9 12 pulled 11.3 17 94.17% N
14 12 broke cable 12.1 17 100.83% Y 11.86 94.38%
8 12 pulled 11.1 18 92.50% Y/N
18 12 broke cable 12 18 100.00%
2 15.5 pulled 11.4 18.5 73.55% N
21 12 pulled 12.6 19 105.00% N
12 12 broke cable 12 19 100.00% Y
17 12 pulled 11.8 20 98.33% Y
20 12 pulled 9.9 21 82.50% N 11.36 89.82%
19 12 pulled 12.6 21 105.00% Y
16 12 broke cable 14 21 116.67% Y/N
7 8.25 pulled 5.25 22 63.64% Y
4 15.5 pulled 12.6 22 81.29% N
5 15.5 pulled 13.8 23 89.03% N
Now you could make the argument that the cam angle in and of itself is not high enough to cause these cams to rip, but in conjunction with the very soft lobes on some of the cams, the effective angle quickly grows until it gets too high and the cam slips out of the fixture.
But the data doesn't directly support that, either. Of the four cams in this sample where the failure mode was not slipping (12, 14, 16, 18), you find them in the middle and upper third of cam angles, and all three that have hardness ratings had particularly soft metal lobes.
So, really, I'm at a loss to say why the cams are pulling from the fixture, though I can say pretty confidently that the softness of the lobes and the cam angle aren't the biggest factor.
I'm certainly curious to see what you find out about the axles. Perhaps that's the missing piece of the puzzle.
What do you think?
GO
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adatesman
Jun 16, 2009, 8:09 PM
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shoo
Jun 16, 2009, 8:10 PM
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angry wrote: To me, this is incredibly confidence inspiring. The worst of the aliens tested held loads greater than a fall would have generated and the rest held more than they were rated for.
I think you're paying attention to the wrong thing here.
Yes, all of these cams held an amount of force that would be expected in a lead fall under near ideal conditions (the point of debate being the plates used in the fixture).
However, the actual amount of force held had a very large variance (jt512, please chime in here if I say something wrong, it's been a while since my last stats course). Think about the force held on a distribution here. Large variance = wide distribution. The wider the distribution, the more cams there are that would be expected to fail below a given amount of force.
All we can really take from these tests (and for lack of more data and further analysis, this is even a stretch) is that the median and mean cam will hold a typical lead fall worth of force. However, given the wideness of the distribution, I would hazard a guess that there are probably plenty of cams out there that would not do so. Without knowing more about the distribution of force held by the cams, this is only a guess.
What really important here is the question of how many aliens are out there that WILL NOT hold a fall.
Given the unpredictability in the force held, the variety of failure modes, my guess would be quite a few
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boku
Jun 16, 2009, 8:13 PM
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adatesman wrote: As I mentioned in the OP, unfortunately my tester can't get reliable readings on the axles due to the V-anvil (the thing that holds it) being slightly off center which results in the penetrator sliding off when the main load is applied...
Aric, did you consider just cutting the axles in half and testing the cut face? Just curious.
Thanks, Bob K.
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hafilax
Jun 16, 2009, 8:17 PM
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boku wrote: adatesman wrote: As I mentioned in the OP, unfortunately my tester can't get reliable readings on the axles due to the V-anvil (the thing that holds it) being slightly off center which results in the penetrator sliding off when the main load is applied... Aric, did you consider just cutting the axles in half and testing the cut face? Just curious. Thanks, Bob K.
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qtm
Jun 16, 2009, 8:22 PM
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1. Very little. Aric demonstrated in the original thread, post #24.
2. Using the same technique, the non-aliens consistently produce good results while aliens produce offcenter results. Consistent results for dozens of cams from several people seems to indicate that the individual procedure doesn't make much a difference and isn't affected greatly by camera angle or zoom or whatever.
3. Manual selection produces much better results. As long as you select actual points on the lobe, which can be difficult if the lobe is worn or damaged.
4. Yes. To the point the aliens are consistent with what other people have posted.
5. Exactly as we have been saying.
So what exactly do you consider a controlled manner? The first round, I clamped the cam stem in a big clamp, took pictures from a controlled height at the same zoom.
Second round, I held the alien by hand, resting on the table, and the camera in macro mode 4" away, under different lighting.
A few pictures in a third test, backlit to give me a dark profile.
Consistent results (as long as I picked the points manually) all the way through. Results consistent with other people, whatever methods they used.
Seems obvious to me.
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cracklover
Jun 16, 2009, 8:30 PM
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How much does camera angle and camera centering affect the measurement?
I believe Aric addressed this in an earlier post on the misdrilled axle holes thread.
The gyst of it is that with enough angle you can get the central point to move around relative to the middle of the axle of course, because the axle is closer to the camera. With that said, I've not had the level of difficulty you have in getting the axle centered.
If (1) is important, then how good has the centering and angle been in the photographs used?
Certainly a valid question. I'll say this for my photos - whatever technique I've used has been good enough so that all the photos I've taken of my non-CCH cams has shown the center point to line up consistently, and all the repeat photos I've taken of the same cam has given me the same results.
How much does manual selection of the sampled points bias the measurements or affect their reliability?
Don't know.
Do repeated photographs and selection of sample points on the same unit produce consistent results?
For me, yes.
In a systematic comparison, how would results for Aliens and other brands compare?
Unfortunately (for many reasons) I don't have many other small cams at my disposal at the moment. Using the software on larger cams isn't really a fair comparison, since if they're off by a mm or two, you'd hardly notice, and the affect on the effective cam angle would be negligible.
GO
(This post was edited by cracklover on Jun 16, 2009, 8:31 PM)
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angry
Jun 16, 2009, 8:38 PM
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I feel like I'm really taking a beating here for my opinion on Aliens.
As I stated yesterday, I am not defending them to Aric nor do I think he's got an axe to grind.
I don't think of them as a car or a bolt or an airliner. I don't now, and never have used them with the implicit idea that they were infallible. That said, I've taken many many falls on everything I own. I probably owe everyone who's ever belayed me a handjob.
I'm an extremely cautious climber. I'm constantly weighing the cost/benefit of placing more pro or trusting my ability to climb on. I've got both eyes and my (overactive) imagination running the scenario of what would happen if I fell at any time and what would happen if my gear ripped. I'm happy to say that most of these scenarios are far more benign than I imagine them to be, I know this because in my time, they have ALL played out.
Leeper hangers, ice curtains collapsing while I'm on them, tipped out cams in choss, nuts between two crystals, ice screws in foam, a fixed RURP, blown tendons, and a core shot in my rope. Sorry, I don't hang it out so far that a cam holding 2kn (or 4) less than it should will affect me in any meaningful way.
Someone on this forum once said, "Three pieces between me and the ER/morgue" I completely agree.
In the end, I'm still more worried about the rock I place my gear into and the thunderstorms building behind me than I am about the ultimate strength of my cams.
Sorry for the drift Aric, but I felt that I needed to defend myself.
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cracklover
Jun 16, 2009, 8:53 PM
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Hey Angry, I didn't mean to put any kind of beatdown on you. In fact, I think we agree entirely, aside from two points:
1 - Spin. The spin you're putting on it is that Aliens are bomber. I don't think the evidence bears that out at all, especially for leaders just getting into the game.
2 - the difficulty of putting a > 5kN force on your gear. You know this, of course, but a fall early on a pitch, even a short fall, can put large forces on your gear. Unless I misunderstood, some of your posts belie that fact.
But overall, I'm in the same boat as you, and aside from two of my Aliens (with the worst drilled axles) I'll still be using them. Of course, I already have stated in other threads that I only trust them to around the 5kN that I've personally tested them.
GO
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jt512
Jun 16, 2009, 8:54 PM
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angry wrote: Sorry for the drift Aric, but I felt that I needed to defend myself.
I don't think anyone here is attacking you personally. We're just questioning your conclusions.
Jay
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adatesman
Jun 16, 2009, 8:57 PM
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jt512
Jun 16, 2009, 9:32 PM
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qtm and cracklover, I realize that several people have done enough work to answer some of my concerns informally, but no one has yet done a systematic, well-controlled study of the validity of the procedure, in which the methodology of the study and the results have been rigorously documented.
The procedure of estimating the cam center relies on the the subjective judgment of the operator to position the camera properly and to pick accurate sample points. For me to be convinced that this procedure produces valid, reproducible results, I would have to have been able to produce them myself (which I couldn't), or I'd have to see convincing data, presented in a manner that I could analyze. The effect of human error in this procedure needs to be studied more thoroughly and better understood. You may have informally examined this issue sufficiently to convince yourselves of the validity of your data, but to convince a skeptical third party, a more rigorous study is needed.
Jay
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cracklover
Jun 16, 2009, 9:39 PM
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adatesman wrote: When you were going through your analysis did you notice anything in regards to which axles bent most? I've been busy publishing all the photos to the web today so haven't been able to look at any of this yet. -a.
Here's the data:
axle sample rating failure angle rating average average avg %
bent number kn kn % angle fail kN rating
no 3 12 9.3 14 77.50% 18.4 9.4 77%
no 9 12 11.3 17 94.17%
no 8 12 11.1 18 92.50%
no 20 12 9.9 21 82.50%
no 7 8.25 5.25 22 63.64%
no 24 8.3 4.5 54.22%
slight 1 12 10.6 16 88.33% 18.2 11.8 99%
slight 14 12 12.1 17 100.83%
slight 21 12 12.6 19 105.00%
slight 12 12 12 19 100.00%
slight 17 12 11.8 20 98.33%
yes 23 9.8 6.8 15 69.39% 19.7 11.1 89%
yes 2 15.5 11.4 18.5 73.55%
yes 19 12 12.6 21 105.00%
yes 16 12 14 21 116.67%
yes 5 15.5 13.8 23 89.03%
yes 22 9.8 8.1 82.65%
very 15 12 13.5 16 112.50% 18.0 13.4 95%
very 6 15.5 14 16 90.32%
very 4 15.5 12.6 22 81.29%
This time I broke it into quartiles, based on the amount of bending I saw in your pics. I think it's pretty obvious that there's an excellent correlation both to the amount of force the cam saw, and to the relative strength of the cam (which is really just saying the same thing, but factoring in the size).
However I see no correlation to the effective cam angle, or to the general softness of the lobes. I haven't checked to see if cams with some soft and some hard lobes have a correlation. This one might be tricky, as it might depend on which lobes are soft (outer, inner, etc). But in general, simple softness of lobes doesn't have a correlation.
Of course the axle hardness numbers might be very interesting here, too.
The only conclusion to draw here is pretty simple - the more force the cam felt, both in absolute kN, and relative to the size of the cam, the more the axle bent. I know this is a no-brainer, but I'm afraid I don't see any more interesting correlations.
GO
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cracklover
Jun 16, 2009, 9:45 PM
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adatesman wrote: cracklover wrote: What do you think? I think we're entering the land of ill-informed conjecture Roy is complaining about.   Seriously though, I think there's a definite problem with Aliens there somewhere given that some of them didn't slip and other brands never seem to have a problem.
What I mean is that neither the degree of softness of the lobes, nor the degree of high effective angle due to mis-drilled axle holes, seem to explain the Aliens slipping from the fixture.
So since you're making the argument for those being the primary reason why Aliens are slipping out of the fixture, I thought perhaps you'd like to defend that idea in light of your data.
GO
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adatesman
Jun 16, 2009, 10:00 PM
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