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Cams in flares-- how much can the lobes be offset?
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caughtinside


Jul 10, 2006, 9:17 AM
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Cams in flares-- how much can the lobes be offset?
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...before the placement is worthless?

Here is my situation. I did a climb on Saturday that was completely flared. No joke, the entire crack flared, from the bottom to the top. I was able to get some good offset nuts in a couple spots, but for the most part, the crack was tight hands to fist, all flaring.

Normally, I will hunt around a flare, for SOME part of it that looks at least semi regular, where I can stick a cam and the lobes will be more or less equal. I think I got one of those on this climb, the rest, no dice.

I had at least 4 cam placements where the lobes were noticeably different in terms of expansion. Lobes in the back, cammed tight, 85%. Lobes up front, maybe 65% cammed (rough guesstimate on % here). But it was the best I could do.

So, my question is, how much is too much? I didn't feel great climbing above these things, because they didn't have the bomber feel of a cam in a parallel crack. But I tested them anyway, took a 15-20 footer onto a #2 camalot, which held (and also zippered a 'bomber' nut lower down.) Went back up, reset it, and climbed up again.

Oh, and I take responsibility for the nut zippering, I slung it short and wasn't at a stance where I could extend it.

So, I thought I'd take this to the good folks at RC and open myself up to a few suggestions, and undoubtably a good deal of ridicule. Bring it on, says I!


billl7


Jul 10, 2006, 9:43 AM
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Re: Cams in flares-- how much can the lobes be offset? [In reply to]
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I'm certain that if each pair of cam lobes is evenly deployed then there is no issue assuming a constant angle camming unit; I'll go further out on a limb and say that it does not matter if a given pair of lobes is unevenly deployed. Out side of the usual over-deployment and direction of loading related failures, the real issue is the angle of the flare and how much it encourages the cam to squirt out in direction of pull or sideways. Perhaps the answer lies in how much margin of error is allowed for in the designed cam angle.

'course, there are the usually issues of integrity of the rock, texture of the lobe surface, etc..

Looking forward to hearing input from others.

Bill L.


caughtinside


Jul 10, 2006, 9:54 AM
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Re: Cams in flares-- how much can the lobes be offset? [In reply to]
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Hmm, good point. Yes, in this case each pair of lobes was evenly deployed.


crotch


Jul 10, 2006, 10:39 AM
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Re: Cams in flares-- how much can the lobes be offset? [In reply to]
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My biggest apprehension with flares is that the rock doesn't make a lot of contact with the cam lobes, often just touching the inside edges of each lobe.

Evaluate each pair of lobes independently. If you had a cam placed with all 4 lobes just like the deepest 2 lobes and you would consider it bomber, then those back lobes are bomber. Same evaluation for the outside pair. If you had those lobes in the same configuration with the same amount of rock contact in a more parallel crack would you trust the cam? If so, then the front lobes are good.

Edit to add: My comments refer only to front-to-back flares, and not top-to-bottom flares which are an entirely different subject.


reg


Jul 10, 2006, 12:12 PM
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Re: Cams in flares-- how much can the lobes be offset? [In reply to]
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IMS (if memory serves) cams should not be placed in flares more then 7deg out of parrelle - you start to lose that coefficient of friction and she'll pop out on her own! (all this her and she stuff is the old salt in me commin out - sorry)
here's a link with some info but search around for yourself
http://www.bigwalls.net/climb/camf/index.html


caughtinside


Jul 11, 2006, 1:55 PM
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Re: Cams in flares-- how much can the lobes be offset? [In reply to]
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In reply to:
My biggest apprehension with flares is that the rock doesn't make a lot of contact with the cam lobes, often just touching the inside edges of each lobe.


Edit to add: My comments refer only to front-to-back flares, and not top-to-bottom flares which are an entirely different subject.

That was my big concern as well, although it did seem like the lobes had good contact. Not just at the edge of the lobes.

But while it was mostly a front to back flare, it also opened up a tad in the down direction, adding to the insecurity.

Doesn't seem like there is too much interest or knowledge on the subject, as opposed to the 'trad climbing is slow' thread...


shockabuku


Jul 11, 2006, 2:12 PM
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Re: Cams in flares-- how much can the lobes be offset? [In reply to]
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Reg-

The coefficient of friction doesn't change with the angle; that is only based on the surfaces in contact. What changes is the direction of the net force applied to the rock from the cam lobe. If the flare is too great, the force is not applied with enough perpendicular component to the rock (the part of the force that determines the frictional force) and there's then not enough friction to hold. I think the critical flare angle (cam failure) depends on the cam material and rock type which determine the coefficient of friction. The article you reference states that if the tangent of the camming angle exceeds the coefficient of friction, the cam will fail. For a coefficient around .3 (referenced value in the article for rock on aluminum, but it varies), the cam angle has a max value of 16-17 degrees. The article also states "Modern camming units optimize range and holding power with cam angles near 14.5 degrees." If that's all correct, then we have about 2 degrees buffer as a maximum for a flare. Doesn't seem right. Where did I go wrong?

It seems to me that, regardless of angle, if it holds on a yank test, it should hold on a fall since all of the forces grow proportionally.


boombewm


Jul 11, 2006, 2:26 PM
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Re: Cams in flares-- how much can the lobes be offset? [In reply to]
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In reply to:
Reg-

The coefficient of friction doesn't change with the angle; that is only based on the surfaces in contact. What changes is the direction of the net force applied to the rock from the cam lobe. If the flare is too great, the force is not applied with enough perpendicular component to the rock (the part of the force that determines the frictional force) and there's then not enough friction to hold. I think the critical flare angle (cam failure) depends on the cam material and rock type which determine the coefficient of friction. The article you reference states that if the tangent of the camming angle exceeds the coefficient of friction, the cam will fail. For a coefficient around .3 (referenced value in the article for rock on aluminum, but it varies), the cam angle has a max value of 16-17 degrees. The article also states "Modern camming units optimize range and holding power with cam angles near 14.5 degrees." If that's all correct, then we have about 2 degrees buffer as a maximum for a flare. Doesn't seem right. Where did I go wrong?

It seems to me that, regardless of angle, if it holds on a yank test, it should hold on a fall since all of the forces grow proportionally.


http://www.esplatter.com/images/am/explode.gif


davidji


Jul 11, 2006, 3:08 PM
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Re: Cams in flares-- how much can the lobes be offset? [In reply to]
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In reply to:
It seems to me that, regardless of angle, if it holds on a yank test, it should hold on a fall since all of the forces grow proportionally.

The forces don't continue to grow proportionally indefinitely, and cams have been known pop at thresholds exceeding a bounce test. I think it's intuitively obvious that that can happen. The only thing I can imagine that would make anyone expect otherwise is a little too much focus on introductory physics.


shockabuku


Jul 11, 2006, 7:34 PM
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Re: Cams in flares-- how much can the lobes be offset? [In reply to]
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Davidji-
Intuition and physics don't always agree. I do agree that I think cams will probably pull at loads heavier than a bounce test, but I'm not really sure of the mechanism. Anyway, not to be rude, but do you have an answer to the question?


davidji


Jul 11, 2006, 10:06 PM
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In reply to:
I do agree that I think cams will probably pull at loads heavier than a bounce test, but I'm not really sure of the mechanism.

As best I can tell the physical properties that allow us to model friction in certain ranges for certain materials as friction force = coeff of friction * normal force are not well understood. Certainly not by me. The thing is when that does equation work, it only work in a limited range. Your friction force will not increase indefinitely. Here again the intuitively obvious applies: intuition tells us things fail, metal deforms, rock chips, etc. Is that the mechanism when the device pops out? It certainly can be part of it, as you sometimes see tracks in the rock or deformation of the cam lobes after a cam pops out. The actual behavior may be far more complex, but it behaves just as a person would expect: it holds to a point, then it doesn't.


reg


Jul 12, 2006, 5:44 AM
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Reg-

The coefficient of friction doesn't change with the angle

thanks for the heady explanation - it caused me to look up the word coefficent cause I did not know what it ment - webster say's: "a number that serves as a measure of some property or characteristic" - still seems to fit to me - but i'm learin every day


In reply to:
If the flare is too great, the force is not applied with enough perpendicular component to the rock (the part of the force that determines the frictional force) and there's then not enough friction to hold.

that's what I'M talkin about!
In reply to:
If that's all correct, then we have about 2 degrees buffer as a maximum for a flare. Doesn't seem right. Where did I go wrong?

can't help ya

In reply to:
It seems to me that, regardless of angle, if it holds on a yank test, it should hold on a fall since all of the forces grow proportionally.

I tend to agree with others below on this - my bottom line is to stay away from all but the least of flares - where I climb there is often other choices.
thanks again for the info


rmiller


Jul 12, 2006, 6:35 AM
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Re: Cams in flares-- how much can the lobes be offset? [In reply to]
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I don't know if this would always hold true, but when I was on El Cap I took a 25 footer onto a yellow alien with only 2 lobes in the crack. So to me, as long as a pair of lobes are good, go for it. Now, if you listen to that advice you are crazy! Go buy some hybrid or offset cams for those flares!


tradrenn


Jul 12, 2006, 5:13 PM
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Re: Cams in flares-- how much can the lobes be offset? [In reply to]
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Some of you might be interested in this:

http://www.rockclimbing.com/topic/115866

I think it is sort of similar issue, only one half of cam is placed correctly.

Rmiller: Are you kidding with your post ?


rmiller


Jul 12, 2006, 6:18 PM
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In reply to:
Some of you might be interested in this:

http://www.rockclimbing.com/topic/115866

I think it is sort of similar issue, only one half of cam is placed correctly.

Rmiller: Are you kidding with your post ?

I am not kidding about the 25 footer, but I am kidding about "place the lobes and go." I would never advise someone to do that on a free climb. On an aid climb, however, all is game. Hell on aid climbs, I have used my nut tool as pro and my buddy wedged his helmet in an OW on Lost in America.


norushnomore


Jul 12, 2006, 11:30 PM
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Re: Cams in flares-- how much can the lobes be offset? [In reply to]
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From what I can tell cam angle is not the problem here: flare was in a horizontal direction while you were falling fall in a vertical.

What can be a problem IMHO is as cam coverts vertical force into expansion flaring angle will produce some horizontal component that will be forcing cam out.

It should not matter much except for the initial moment when your cam engages. Based on this I would suggest placing them rather tight, almost jamming inner lobes a bit as cam spring tension along might not be adequate here.


paulraphael


Jul 19, 2006, 9:58 PM
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Re: Cams in flares-- how much can the lobes be offset? [In reply to]
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Davidji-
Intuition and physics don't always agree.

As an example ... the statement above that the coeficient of friction changes with surface area. It's intuitive, but not true. The coeficient of friction is a constant determined by the two materials in contact. The total friction is the coeficient of friction multiplied by the amount of force holding the surfaces together. Surface area has no influence on this. Climbers are the last people on earth to believe it, but it's true.

The reason you want more surface area is to reduce the pressure (and therefore the stress) on both the cam and the rock. If all your fall force is concentrated on a couple of small crystals, the chances are much higher that the cams will deform or the rock will break. More surface area also equals more redundancy. A small crystal of rock breaking is less of a big deal if the load is supported by many other crystals.


curt


Jul 19, 2006, 10:33 PM
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Re: Cams in flares-- how much can the lobes be offset? [In reply to]
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Reg-

The coefficient of friction doesn't change with the angle; that is only based on the surfaces in contact. What changes is the direction of the net force applied to the rock from the cam lobe. If the flare is too great, the force is not applied with enough perpendicular component to the rock (the part of the force that determines the frictional force) and there's then not enough friction to hold. I think the critical flare angle (cam failure) depends on the cam material and rock type which determine the coefficient of friction. The article you reference states that if the tangent of the camming angle exceeds the coefficient of friction, the cam will fail. For a coefficient around .3 (referenced value in the article for rock on aluminum, but it varies), the cam angle has a max value of 16-17 degrees. The article also states "Modern camming units optimize range and holding power with cam angles near 14.5 degrees." If that's all correct, then we have about 2 degrees buffer as a maximum for a flare. Doesn't seem right. Where did I go wrong?

I have highlighted where you went wrong. What actually happens is that the outward force increases rather than decreases as the flare angle becomes greater. Also, the effective working range of the cam decreases--as one would expect, making it easier for the cam to "pop" out. Here's an excellent article on the actual physics involved:

http://www.vainokodas.com/climbing/cams.html

Curt


claramie


Jul 19, 2006, 11:15 PM
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Re: Cams in flares-- how much can the lobes be offset? [In reply to]
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double post


claramie


Jul 19, 2006, 11:22 PM
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Re: Cams in flares-- how much can the lobes be offset? [In reply to]
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Omega Pacific claims that the Link Cams work great for flaring cracks. I've never had the chance to try them out.

For those of you that have used them, do they work well in this scenario? I have always wondered how sturdy these are when each pair of lobes is loaded at drastically different part of its range.

CL


healyje


Jul 19, 2006, 11:27 PM
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In the end it really all just depends on your comfort level with ambiguity and airtime...


Partner philbox
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Jul 19, 2006, 11:49 PM
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Re: Cams in flares-- how much can the lobes be offset? [In reply to]
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Link Cams are awesome for all sorts of outrageous placements, flares included.

For other types of cams just so we don't confuse the Link Cams in this scenario. I have on occasion placed a cam in a horizontal orientation in a flare such as you've described. In other words the stem sticks straight out in relation to the vertical flared crack. This way the cams are more or less camming at a relatively equal rate.

I've fallen on a green Alien thusly orientated and have had to replace this item that I was using from my partners rack. It bent but certainly did not break. The cables didn't look all that brilliant but no safety issue with the cam whatsoever. Meh, I fiddled with the cam and more or less rectified it enough so that I am now able to use it again.

Of course I very much do like my offset Aliens for flared placements but then we are talking about hands sized cracks.

Edit to say that when I place a cam horizontally in a flare I generally look for a back wall to the crack otherwise the cam may become hopelessly overcammed on two lobes in the event of a fall as the cam rotates.


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