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slapezio


Jan 7, 2008, 2:29 PM
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Re: [rgold] Link Cam Report [In reply to]
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What do you mean by axle loads of 20-28kN are a consequence of the rating limits? Does this mean that a cam rated at 10kN and loaded to 8kN may fail because the axle sees a force of 16kN?


Partner rgold


Jan 7, 2008, 4:35 PM
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Re: [slapezio] Link Cam Report [In reply to]
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In reply to:
What do you mean by axle loads of 20-28kN are a consequence of the rating limits? Does this mean that a cam rated at 10kN and loaded to 8kN may fail because the axle sees a force of 16kN?

I am assuming---very reasonably---that a 10kN rating means 10 kN applied to the stem, where the load would be for a falling climber. In a parallel-sided crack, this means that the axle would have to be (more than) able to handle a 20 kN load from the cams on one side, so an 8 kN load that applies 16 kN to the axle would not be a problem and certainly should not produce a break.


healyje


Jan 7, 2008, 4:46 PM
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Re: [baja_java] Link Cam Report [In reply to]
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baja_java wrote:
ok, Joseph, tell me this first. do you think the failure of the OP's cam on Left Ski Track happened within the design spec's, or beyond the design spec's? you think the rotation into blockage causing torque leading to a part snapping is what happened, i believe (correct me if that's not the case)

Michael said OP's opinion was that there was no discernable manufacturing or materials defect - what would that lead you to conclude? I would conclude the linkage was subject to forces which exceeded the design spec - which in turn would leave no option but to speculate as to how that could have happened. And speculate is all we can do in this case as you couldn't reconstruct the intial placement or produce an accurate dynamic model of what transpired.

baja_java wrote:
don't worry, i'll get to the rest of that mess you replied with. there are some very basic ideas that you just don't get, and i'll go over them with you. but first, answer the above question

Done, and please do get 'messy'.

baja_java wrote:
Healyje wrote:
I understand just fine, and don't need the math to explain the graph or rgolds description of the phenomena. I also don't need the math after thirty three years of climbing to know most convential cams will blow out of flares rather than break. One will on rare occasion - but the vast, overwhelming majority blow, not break.

by the way, if you went ahead and skipped the math, that means you've never proven to yourself that what Vaino described is true. you merely took his words for it and keep regurgitating what he said you're supposed to think. that's vastly different than truly understanding something.

I don't need to 'prove' it to myself - the cogent explanations by curt, rgold, and others such as - "increasing the flare angle of the crack has exactly the same effect as decreasing the cam angle of the unit" - are completely adequate for the purposes of this discussion and understanding the affect on com placements in flares. The math may be rocket science, but the concept of the effect of [apparent (in the aviation sense of the word)] cam angles increasing and decreasing as a result of placements in flares is not. I've 'got' it, thanks.

baja_java wrote:
you've made it apparent that you've never encountered the phenomenon he described out in nature on your own, so that removes the possibility that you could've understood that from direct experience.


Well, I've already said I've blown two cams in flares and pulled dozens more over the years so, quite the contrary, I'd say I have quite a bit of 'direct experience' it.

baja_java wrote:
one can glean an understanding from Vaino's formulation if they aren't allergic to math like you are, who can't understand what the math conveys. that's important because the how's and the why's are in the math. why do you think Vaino went through the trouble of including them, if he could've just summarized his gist in a few paragraphs? math is just a language. like English or Italian. i understand it fine. that's why i'm not afraid of math like you are, and often stumped by math like you are.

I don't know shit about the fine points of English either, but that doesn't stop me from generally understanding what people are saying or being able to express myself. I don't 'hate' math, nor am I 'afraid' of it - it's just not something I've had any concentrated exposure to over the years. Actually, I'd love to take a break and recoup that lost ground - I have Berlinski's 'A Tour of the Calculus', Davis/Hersh's 'The Mathematical Experience', and Gleick's 'Isaac Newton' sitting on a shelf three feet from me as we speak that I've been meaning to re-read for motivation [to try once again] to get off my ass and do so. It would no doubt be great if we could all be Vanios and Goldstones, but some of us are doomed to think and climb at reduced capacity and struggle to get by with what we've been granted.

baja_java wrote:
nor does that means i'm obsessed by it either. there isn't some compulsion to see the world in numbers and data like you hope as the typical stereotype suggests. you're so afraid of this incomprehensible language that you need to convince yourself that other people who use it must use it to an obsessive degree, that they must be abnormal, because at least that would mean your lack of ability in using it would at least seem somewhat normal. here's another thing. for my pay grade, to borrow someone's phrase from earlier, i'm embarrassingly inept at computers and all this fancy technology you seem to think others like me should be hopelessly dependent on. i know enough to do what i need to do, that's all, and that's ok with me. yes, there are people who "obssesses" more about it, but to me, computers are just a tool. same with cams or nuts. the person still do the thinking that would apply the tools. so please, give it a rest with your incessant attempts to paint other people as techno drones like that's some deficiency that keeps them from relating to your beautiful great world views

Once again you completely misinterpret what I'm saying. When I say a lot of the attitudes on display in this thread and others, both here and on other climbing sites, are often bi-polar at two extremes, I'm not saying engineers are explicitly and necessarily in one or the other. But many of the comments from folks with such advanced knowledge have clearly come down on the side that the design is 'flawed' (to use your term - and a conclusion I completely disagree with) and that they need to either be pulled from the market and / or redesigned. Others in that learned camp - on both sides of the issue - appear to be on a vain search for 'data' which does not, and is never going to exist. I do happen to know a bit about 'data' and animation/modelling/SCADA systems and the demands they can place on computers, and there aren't enough cpu cycles available to be aggregated to accurately model what happened to the Link Cam that broke in the Left Ski Track pod - even if we knew the exact placement it was in.

That's a bit of a bummer, but some generalized theory and experience is all anyone can go on in this case. The math, beyond setting, a stage of basic principles and plausible forces, is of little real utility in figuring out how the cam broke. Ditto for designing a cam to be used out in the real world in perverse, horrorfests like JT and Vedauwoo - it's an Edisonian exercise to a degree by definition. 'Ballpark' is as close as anyone can get which is why decades of hands-on (or offten hands-off) experience actually does count for something in a dicussion such as this one.

And on the 'speculatve' front, how about answering one in return - did you break your Link Cam the day you went out to the Left Ski Track to look at that pod? A simple yes or no would suffice and that answer would probably say about all that is necessary to know until OP gets back to you.


(This post was edited by healyje on Jan 7, 2008, 5:14 PM)


boku


Jan 7, 2008, 4:54 PM
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Re: [philbox] Link Cam Report [In reply to]
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philbox wrote:
...One question though, how would negative flare affect the equations...

Sorry, can't resist:

A negative flare makes the equations irrelevant. You slot a nut there and move on.

;)

Bob K.


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Jan 7, 2008, 5:29 PM
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boku wrote:
philbox wrote:
...One question though, how would negative flare affect the equations...

Sorry, can't resist:

A negative flare makes the equations irrelevant. You slot a nut there and move on.

;)

Bob K.

Let's take a moment to explore where a nut would not work whereas a cam would and still satisfy my question as to negative flares.

So you have a gas pocket in volcanic rock. A nut of any size would simply fall out whereas that cam can be retracted and thus reduce its size to fit inside the gas pocket. So are we still wanting to use a nut or would a cam be the best option for this scenario. I maintain that a cam is the best option and thus we come back to my question as to how negative flares affect the equations. rgold has answered and I accept his answer.

Taken to the logical extreme whereas a Camalot is placed passively so that the cams are fully extended and the cam stops are working against the double axels it would seem self evident to me that there is no force multiplication at work at all. A one times force would be at work in this scenario. So therefore a force of say 200kgs on the biner at the end of the quickdraw would equate to 200kgs of force to the axels combined.


healyje


Jan 7, 2008, 5:48 PM
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Re: [philbox] Link Cam Report [In reply to]
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philbox wrote:
So you have a gas pocket in volcanic rock. A nut of any size would simply fall out whereas that cam can be retracted and thus reduce its size to fit inside the gas pocket.

We always used T-stacked Hexs or a Hex/Titon combo for spherical embedded pockets and they always worked great and stayed put. But that is a fair question, though the inversion issue is pretty significant in many cases depending on the size of the entrance hole relative to the pocket.


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Jan 7, 2008, 6:12 PM
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Re: Link Cam Report [In reply to]
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mheyman wrote:
Baja_Java I know you described them – but I can’t tell anything from the photos – we need likely angles to say look, no wonder it broke.

Mark, the key to what i described to you is that the shape guarantees the angles are there, near the back, where the cam was jammed all the way in. it just needs the right cam at the right spot

you can go measure it if you really need to. but instead of that, you can do something even easier, by letting that angle find you, so to speak. say if you just push a cam in there a few times and if something extraordinary happens, don't you think you'd know what's going on inside?

you get what i'm saying?Cool


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Jan 7, 2008, 6:17 PM
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Re: [cracklover] Link Cam Report [In reply to]
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cracklover wrote:
dominic7 wrote:
healyje wrote:
baja_java wrote:
[...seems a cam lobe segment can cam into the rock only when they're fully supported by the barrel of the axle, as in only when it's furled up around the axle, as in the unfurled ones behind that (an outer one) can maybe touch the rock but not cam into it.

We certainly also agree on this point, however, the loose extended segments are also capable of 'snagging' on any placement obstructions in the event of cam rotation and so present some added risk that way.

I've been thinking about LCs rotating into different orientations lately. The inner lobes (assuming the outer lobes are the contacting rotation points) will slide sideways, with the smallest lobes traveling through the largest arc. This is a significant difference between traditional cam designs and the new multi-lobed units which introduces new failure modalities.

Could you explain what you mean? I'm not getting your drift at all.

Thanks,

GO

I drew a picture but it didn't come out very well.

The idea is that when a "traditional" cam rotates into a new orientation there are basically four lobes with four contact points. In an over simplified example, two of the contact points would remain stationary with respect to the rock and act as pivot points while the other two points would scratch along the rock through a small arc. The arc would be pretty colinear with the plane of the lobe and wouldn't provide excessive torque.

In the LC repositioning, there a 12 lobes repositioning, with 4 acting as above. The other 8 lobes describe much larger arcs and, more worrisome, the further they are from the pivot point, the arc traveled is increasingly less colinear with the plane of the lobe - meaning more torque on those lobes.

I should try to draw a better picture and post it.


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Jan 7, 2008, 6:19 PM
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Re: [rgold] Link Cam Report [In reply to]
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Richard,

what are your thoughts on the force amplification exhibited by flares and by the ADT?

would love to hear


healyje


Jan 7, 2008, 6:42 PM
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Re: [rgold] Link Cam Report [In reply to]
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PS - also some clarification is in order relative to the common use of the term 'flare', that in these math/engineering discusssions they are referring to the top diagram, versus other times folks talk about and mean either the bottom one or both...







Partner cracklover


Jan 7, 2008, 7:07 PM
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Re: [dominic7] Link Cam Report [In reply to]
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dominic7 wrote:
The idea is that when a "traditional" cam rotates into a new orientation there are basically four lobes with four contact points. In an over simplified example, two of the contact points would remain stationary with respect to the rock and act as pivot points while the other two points would scratch along the rock through a small arc. The arc would be pretty colinear with the plane of the lobe and wouldn't provide excessive torque.

In the LC repositioning, there a 12 lobes repositioning, with 4 acting as above. The other 8 lobes describe much larger arcs and, more worrisome, the further they are from the pivot point, the arc traveled is increasingly less colinear with the plane of the lobe - meaning more torque on those lobes.

I should try to draw a better picture and post it.

Ah, I follow you now. You're trying to describe a LC that's placed far in a crack, with the smallest cams engaging with the rock, and the larger cams arcing over the rock as the cam rotates. That's what you're trying to describe, yes?

If so, what's your point? Those outer cams are floppy, they're not pushed against the rock by the axle/force of fall, but only by their springs.

GO


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Jan 7, 2008, 8:02 PM
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In reply to:
mheyman wrote:
Baja_Java I know you described them – but I can’t tell anything from the photos – we need likely angles to say look, no wonder it broke.

Mark, the key to what i described to you is that the shape guarantees the angles are there, near the back, where the cam was jammed all the way in. it just needs the right cam at the right spot

you can go measure it if you really need to. but instead of that, you can do something even easier, by letting that angle find you, so to speak. say if you just push a cam in there a few times and if something extraordinary happens, don't you think you'd know what's going on inside?

you get what i'm saying?Cool

here, see if this helps. and no, this isn't a blueprint of my ride to the next Heaven's Gate II meeting



i'm not that computer savvy. drawing is fun anyway. the blue are the outside surfaces, the red the insides. the flare angle changes the most near the side walls and the back wall

as you can see in the Side View, any point you start from on that oval outside lip, as you move inward from the mouth toward the backside, you're guaranteed to encounter a spot along the way where the flare angle equals the cam angle. it's just a matter of where that spot is located from the back wall, and whether you have the cam of just the right size to place there


curt


Jan 7, 2008, 8:50 PM
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Re: [healyje] Link Cam Report [In reply to]
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healyje wrote:
PS - also some clarification is in order relative to the common use of the term 'flare', that in these math/engineering discusssions they are referring to the top diagram, versus other times folks talk about and mean either the bottom one or both...





Your top diagram shows the scenario where the type of force multiplication described by Kodas will occur. The bottom diagram does not--as long as both the inner and outer sets of cams are placed so as to be within their working range. Additionally, there will be no rotation of the cam in the bottom situation if the cam angles of the cams are indeed constant and the applied force is normal to the cam lobes (i.e. along the cam stem) as shown in the diagram.

Curt


healyje


Jan 7, 2008, 9:13 PM
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Re: [curt] Link Cam Report [In reply to]
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curt wrote:
Your top diagram shows the scenario where the type of force multiplication described by Kodas will occur. The bottom diagram does not--as long as both the inner and outer sets of cams are placed so as to be within their working range. Additionally, there will be no rotation of the cam in the bottom situation if the cam angles of the cams are indeed constant and the applied force is normal to the cam lobes (i.e. along the cam stem) as shown in the diagram.

Curt, yeah, that's Kodas' diagram on top. We're throwing around the term 'flare' and some folks may be thinking about the bottom diagram when they read that word and just wanted to be sure folks understand which one the math discussion applies to.

Rotation most often comes into play when a cam is placed, or has rotated up into, the top diagram orientation and then, in a fall, attempts to reach the orientation of the bottom diagram (assuming, in this case you were looking down the same crack in both pictures versus what we've otherwise been talking about).


healyje


Jan 8, 2008, 1:27 AM
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Re: [blondgecko] Link Cam Report [In reply to]
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Bill Coe came over tonight with his new video camera and I gave a shot at a breaking my new Link Cam - with bare hands and a pair of pliers in the absolute absence of any scientific or engineering rigor. We'll post up the video once Bill sorts out getting it off his camera and up onto youtube. But the upshot is, like blondgecko, I too now have some deep Link Cam imprints in the base of my palms and the Link Cam has some deep plier scratches, but other than that, it is still intact. This was one of the larger gold Link Cams which gave me more leverage on the linkages it than the smaller red one. I first attempted to break on of the outside lobe's last segment while it was still seated in on the inner segment / barrel. This first attempt to break it was by pressing inwards towards the stem with the base of both palms. It did move and then deflect to the point it felt as though it might be on the verge of snapping, but I was unable to push it over that edge.

Next try was by completely extending one of the segmented lobes all the way out so it was completely unseated, grasping it by the end, placing my thumb on the middle segment and trying to snap it off. Once again it moved to the side, deflected considerably, but I could not break it. The third and fourth attempts were basically a repeat of those two attempts only with a regular pair of pliers. In all four cases It was not possible to break the linkages, mainly due the the inability to hold the the cam solidly enough with the other hand.

Bill and I were both more than a bit impressed by just how strong the linkages formed by this new molding technique are. My guess is if the cam had been mounted in a vice I still would not have been able to break a seated cam lobe assembly with my hands, but would have definitely been able to with the pair of pliers. However, to really know whether a Link Cam segmented cam lobe assembly is as strong as a convential cam lobe you'd have to take one of each cam matched in size, mount them by the axle to a bench or device, and then laterally deflect the end of each one until it breaking while meauring how much each deflected and how much force was required for each. That, or just doing it with two bare cam lobes mounted off their axles. Regardless of the design of any such test, the numbers of interest to me beyond the 'flare factor' math would be lateral deflection required to break both the Link Cam segmented cam lobe and a Metolius, BD, Trango, and / or WC cam lobe. Knowing those numbers would give you a much better idea of which cams would be most likely to break in rotation versus pull.

My take after this informal 'test'? It's the same as before - given I couldn't break one with my hands or a pair of pliers, until someone with the appropriate gear can show the Link Cam's segmented cam lobe assemblies break at the same or greater lateral forces than unsegmented cam lobes I am still of the opinion they are significantly weaker. It should be a simple matter for someone, OP or a third party, who have the gear to do such a test if they want to dispell such perceptions. I believe I know someone capable of such testing, but that will take me a little time to arrange. The other thing which hasn't changed is my opinion that I still wouldn't hesitate to use a Link Cam. In fact, once I rewound the spring and put the trigger wire stud back in its plastic trigger mount (it came out during our 'test') I'd use the one I just tried to break after giving it a test fall. And, I still maintain you should only use these babies with care and in clean placements.

My hat's still off to OP and Lowe for having the vision and gumption to put out such an innovative product, but just because I couldn't break it with my hands or a pair of pliers in no way means you can wield these complex devices with impunity and without careful thought at every placement.

I'll post another round if I can arrange for someone with the gear to do a more formal lateral lobe testing. Bill, thanks again for swinging by with your camera and Link Cams to compare with mine.


notapplicable


Jan 8, 2008, 5:31 AM
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After you stated your intentions of using a pair of pliers to break the lobe assembly I assumed you would be mounting the cam in a vice so that it would remain static. Even when using the pliers you are still pretty much limited to your own physical strength to break the lobe.

The real question is how to measure the forced needed to cause failure. Without the use of hydraulics, I'm thinking that something very crude could be rigged using a torque wrench.

Perhaps this needs a new thread, as it is not really related to the accident or the discussion concerning modes of failure. Just a thought.


dingus


Jan 8, 2008, 5:59 AM
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That's cool healyje. Perhaps next time you decide to chide me for 'not getting it' you'll remember this thread.

DMT


(This post was edited by dingus on Jan 8, 2008, 5:59 AM)


healyje


Jan 8, 2008, 6:05 AM
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The pliers were merely to get a better grip and a bit of extension on the cam lobe, my intention was only to use hand power alone. Beyond that if you are going to go to that much trouble you might as well go to a real testing arrangement and get 'data'. Though again, the 'data' I'm really interested is an answer to the question: how strong are the Link Cam's segmented cam lobe assemblies compared to a comparable unsegmented cam lobe when subjected to lateral forces - weaker, comparable, or stronger. Given they are admittedly stronger than they appear at first glance and can not be broken by hand - at least in the shape I'm currently in - one has to shift up to a test bench for the answers, so you might as well get exact answers in that case.

But the question does in fact have a direct bearing on the original Left Ski Track (LST) accident, any discussion of modes of failure, and the general use of these cams out in the 'wild'. The LST cam broke as did another of baja's [somehow] - the question that needs to be answered, and where the real speculation lies, is whether the statement 'any make cam would have broken (versus blown) in these cases is true or not. I still do not believe that is the case and believe Link Cams are more vunerable to breakage because of the mechanical linkages. Hey, I'd love to be proven wrong, but until I am, I'm standing by my opinion mechanical linkages are inherently weaker than solid material - and hence the need to be more careful and circumspect when using them.


healyje


Jan 8, 2008, 6:15 AM
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dingus wrote:
That's cool healyje. Perhaps next time you decide to chide me for 'not getting it' you'll remember this thread.

That I could not break them with my 'by hand' conjecture does not in any way mean that the linkages are not substantially weaker than an unsegmented cam lobe. It simply means they are not quite as flimsy as they appear - I have not changed my opinion they still appear far weaker than their conventional unsegmented counterparts. That they passed the equivalent of a 'sniff' test should in no way lend any type of confidence you can slam these about with wild abandon - not when they are breaking out in the 'wild', which I also have no doubt we'll be seeing more of as time goes by.


(This post was edited by healyje on Jan 8, 2008, 6:32 AM)


jt512


Jan 8, 2008, 7:40 AM
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healyje wrote:
...the question that needs to be answered, and where the real speculation lies, is whether the statement 'any make cam would have broken (versus blown) in these cases is true or not.

While that question might be interesting, I don't think it is really all that important. The question that is important is whether link cams are more prone to failure by any mechanism than conventional cams when (improperly) placed with the cam axle parallel to the direction of the anticipated force.

Jay


dingus


Jan 8, 2008, 7:42 AM
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OK. If you learn something interesting please post it.

Cheers
DMT


jt512


Jan 8, 2008, 7:50 AM
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dingus wrote:
OK. If you learn something interesting please post it.

Cheers
DMT

I found it interesting that somebody would waste his time trying to break a cam by hand when the manufacturer has already posted the results of tests carried out under controlled conditions.

Jay


dingus


Jan 8, 2008, 8:02 AM
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Re: [jt512] Link Cam Report [In reply to]
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I think its cool to put one's money where one's mouth is. Healyje spent a hundred bucks give or take, to put his hand-wringing theory to test.

Bravo!

And what's more he posted the results even though they were quite contrary to his stated expectations. So he healyje has integrity as well.

In the end he will no more change my mind than I his.... he's like you in this respect too. JT512 changes his own mind when he feels evidence warrants it.

So in the end? I'd rather shake healyje's hand and smile, than not.

You too for that matter.

Cheers
DMT


healyje


Jan 8, 2008, 8:14 AM
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Re: [jt512] Link Cam Report [In reply to]
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jt512 wrote:
While that question might be interesting, I don't think it is really all that important. The question that is important is whether link cams are more prone to failure by any mechanism than conventional cams when (improperly) placed with the cam axle parallel to the direction of the anticipated force.

Jay, I believe that we are saying the same thing - will they pull or break easier than conventional cams in response to lateral forces imposed by rotating and / or leveraging as they load in a fall? Basically are they any more likely to break compared to a convential cam in suboptimal placements - inlcuding cams placed or rotated up to the orientation you mention.


Partner dominic7


Jan 8, 2008, 8:27 AM
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Re: [cracklover] Link Cam Report [In reply to]
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cracklover wrote:
dominic7 wrote:
The idea is that when a "traditional" cam rotates into a new orientation there are basically four lobes with four contact points. In an over simplified example, two of the contact points would remain stationary with respect to the rock and act as pivot points while the other two points would scratch along the rock through a small arc. The arc would be pretty colinear with the plane of the lobe and wouldn't provide excessive torque.

In the LC repositioning, there a 12 lobes repositioning, with 4 acting as above. The other 8 lobes describe much larger arcs and, more worrisome, the further they are from the pivot point, the arc traveled is increasingly less colinear with the plane of the lobe - meaning more torque on those lobes.

I should try to draw a better picture and post it.

Ah, I follow you now. You're trying to describe a LC that's placed far in a crack, with the smallest cams engaging with the rock, and the larger cams arcing over the rock as the cam rotates. That's what you're trying to describe, yes?

If so, what's your point? Those outer cams are floppy, they're not pushed against the rock by the axle/force of fall, but only by their springs.

GO

If they are moving into a decreasing volume position or across a non-uniform surface I would think there could be significant shearing forces on the lobes.

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