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Textbook cam placements can pull in smooth stone


Greg D · · Here · Joined Apr 2006 · Points: 871

For me and many others, slick rock is a rather obvious factor when on site. But feel free to believe you are playing God and saving lives by pointing out the obvious with long winded explanation that slick rock is slippery.

T Roper · · Masshole · Joined Mar 2006 · Points: 860
Greg D wrote:For me and many others, slick rock is a rather obvious factor when on site. But feel free to believe you are playing God and saving lives by pointing out the obvious with long winded explanation that slick rock is slippery.
It is mid winter lol
Greg D · · Here · Joined Apr 2006 · Points: 871

Actually record highs. 71. Heading out to climb now.

T Roper · · Masshole · Joined Mar 2006 · Points: 860
Greg D wrote:Actually record highs. 71. Heading out to climb now.
yeah its 2 here and snowing again
rgold · · Poughkeepsie, NY · Joined Feb 2008 · Points: 525
Greg D wrote:For me and many others, slick rock is a rather obvious factor when on site. But feel free to believe you are playing God and saving lives by pointing out the obvious with long winded explanation that slick rock is slippery.
The whole point of the OP is that slickness, as it applies to cam holding power, is not always obvious, a fact that is repeatedly born out by some of the other posts. The OP was interested in warning people about a potentially dangerous situation. I guess he was playing god too. I'd call that a matter of common decency and leave religion out of it.
rgold · · Poughkeepsie, NY · Joined Feb 2008 · Points: 525
David Coley wrote: Can someone give me an idea please of what the 0.23 means in terms of common rock types?
According to David Custer in web.mit.edu/custer/www/rock…, the coefficient of friction of aluminum against granite has been measured at 0.38. These students got 0.41 hypertextbook.com/facts/200…, and The Valley Giant folks say 0.5 valleygiant.com/cam_math.html. If Mapeze is around, as a designer he probably has some values, especially for Euro limestone, where cams are known to be less reliable.

Obviously, the particular combination of aluminum against granite is not of great interest to researchers, so it isn’t easy to find values. But beyond that, the simple coefficient of friction concepts found in Amonton’s law are in fact the roughest of empirical estimates and are not any kind of natural law—people write PhD dissertations on friction; it is in fact an extremely complex and far from well-understood concept.

The concept is most applicable to contact between highly polished surfaces, in which the friction forces are primarily influenced by molecular interactions. Once the surfaces are physically irregular, all hell breaks loose because of the variety of ways the bumps and recesses can interact to produce resistance. I think that the almost universal practice of notching cam lobes is intended to leverage potential roughness interactions.

I think the message from research on the subject is that until you get up to loads of geological magnitude, the roughness of the surfaces matters far more than the materials, and so speaking as if there is a coefficient of friction between, say, granite and aluminum is far from illuminating.

When surface roughness and deformability matters, so does contact area, in which case one of the fundamental precepts of AmontonÂ’s law is out the window. (Everyone knows more shoe rubber on the rock produces more adhesion, even though AmontonÂ’s law would say not.)

Another important issue is the well-known disparity between static and sliding friction. Since cams often move when a fall happens, the applicable coefficient of friction may well be the lower sliding value rather than even a locally-measured static value. Then there is the fact, totally unrelated to friction, that a well-placed cam fails not because frictional forces are insufficient to hold it in, but because of shear yield stresses on the aluminum lobe material. In such cases there will be evident gouging of the cam and it may be possible to find aluminum deposited on the crack walls. (I've seen the aluminum left behind in testing jigs but not in real rock.)

Given that AmontonÂ’s law may be a poor description of what happens between a cam lobe and crack wall, I think it is something of a miracle that cams designed in accordance with that law work anywhere near as well as they do.
Marc801 C · · Sandy, Utah · Joined Feb 2014 · Points: 65
Greg D wrote:For me and many others, slick rock is a rather obvious factor when on site. But feel free to believe you are playing God and saving lives by pointing out the obvious with long winded explanation that slick rock is slippery.
Was it difficult inserting that stick up your butt?
Jim Titt · · Germany · Joined Nov 2009 · Points: 490
rgold wrote: Given that AmontonÂ’s law may be a poor description of what happens between a cam lobe and crack wall, I think it is something of a miracle that cams designed in accordance with that law work anywhere near as well as they do.
Given that to calculate the normal force between the aluminium and the rock you have to calculate the friction in that crudest of bearing systems, a metal to metal bush then it´s all going to be a bit hit and miss anyway.
Especially when some parts have a tendency to corrode:-)
rob.calm · · Loveland, Colorado · Joined May 2002 · Points: 630
Healyje wrote: Hmmm, almost don't know what to make of that. Depending on the cliff Eldo is bomb for all kinds of pro. Never had a cam of any kind pull or move on me there. Had one explode into a million pieces there, but never had one pull.
Agreed. Maybe the reference is to the quartzite Supremacy Crag.

R.c
Ray Hellinger · · Gunnison, CO · Joined Feb 2006 · Points: 350

The rock is smooth. The placement is good. I've placed, and fallen, on plenty of placements just like that. The question I would ask, is what is the status of the spring mechanism in the cam. If it old, or the springs are gummed up, it may not be providing an outward force when weighted.

teece303 · · Highlands Ranch, CO · Joined Dec 2012 · Points: 598

Springs can prevent walking (and they provide the [trivial] outward force to hold the cam when unweighted), but they don't provide outward force when *weighted:* the weight of the climber does. I think you're misunderstanding the action of an SLCD, Ray?

Ray Hellinger · · Gunnison, CO · Joined Feb 2006 · Points: 350

No, I understand it completely.....if the springs are not functioning, the lobes do not push out to make contact with the rock, and when you weight it, it pulls. That is most likely the explanation for the cam in the video.

teece303 · · Highlands Ranch, CO · Joined Dec 2012 · Points: 598

Hmm... that scenario seems extremely unlikely to me, Ray.

The springs are strong enough to hold the cam in place, and indeed they look completely fine in the video, yet week enough to somehow negate the ability of the cam cables to pull down on the lobes, and thus rotate the cam lobes into the rock, and securing it when weighted or fallen upon?

I would need some major convincing to believe that. Do you have experience with this?

To me, it seems that the springs would have to be so bad that the cam would be obviously wobbly and wonky in the placement. Otherwise, they are strong enough to do their job (which is pretty minimal). Am I off base?

This really looks like a slam dunk case of very slippery rock to me.

slim · · Unknown Hometown · Joined Dec 2004 · Points: 1,085
Healyje wrote: Hmmm, almost don't know what to make of that. Depending on the cliff Eldo is bomb for all kinds of pro. Never had a cam of any kind pull or move on me there. Had one explode into a million pieces there, but never had one pull.
say what? i met you a few years ago and you said you had only done one route in eldo in the mid 70's. not sure what cams you were using...
Glenn Schuler · · Monument, Co. · Joined Jun 2006 · Points: 1,320
slim wrote: say what? i met you a few years ago and you said you had only done one route in eldo in the mid 70's. not sure what cams you were using...
One of these most likely......

cam
Healyje · · PDX · Joined Jan 2006 · Points: 290
slim wrote: say what? i met you a few years ago and you said you had only done one route in eldo in the mid 70's. not sure what cams you were using...
Yeah, the 'Makanda Traverse' which basically went from below the start of Rosy Crucifixtion over to Yellow Spur and finished up on it. Pre-cams, just nuts. Made it to Yellow Spur with one nut for the belay. But then I didn't really trust any anchors back then and basically stanced all the belays whenever possible by and large avoiding weighting anchors even when holding solid lead falls. So it wasn't that big a deal and wasn't all that uncommon to end up with just one or two nuts for the belay. Also hip belayed all the routes on our to Eldo trips in the 70's - didn't care much for belay devices back then either.
T Roper · · Masshole · Joined Mar 2006 · Points: 860
Healyje wrote: Yeah, the 'Makanda Traverse' which basically went from below the start of Rosy Crucifixtion over to Yellow Spur and finished up on it. Pre-cams, just nuts. Made it to Yellow Spur with one nut for the belay. But then I didn't really trust any anchors back then and basically stanced all the belays whenever possible by and large avoiding weighting anchors even when holding solid lead falls. So it wasn't that big a deal and wasn't all that uncommon to end up with just one or two nuts for the belay. Also hip belayed all the routes on our to Eldo trips in the 70's - didn't care much for belay devices back then either.
damn Joe, your memory sure is good for an old timer!

I didnt care much for sex, drugs and rock-n-roll but I eventually got used to it
Healyje · · PDX · Joined Jan 2006 · Points: 290
slim wrote: say what? i met you a few years ago and you said you had only done one route in eldo in the mid 70's. not sure what cams you were using...
Slim, misread what you wrote. When I said I'd only 'done' one route in Eldo, I meant I'd only done one FA, not that I'd only climbed one route. We climbed all over the place. The Bastille Crack was my first roped solo in '75 in fact. Went back not long ago and did it again after about 30 years and it was like being in a frigging time machine...

Miike wrote: damn Joe, your memory sure is good for an old timer! I didnt care much for sex, drugs and rock-n-roll but I eventually got used to it
Similar to my experience. It took a couple of decades to learn to climb reasonably hard without them, and I can do it; it's just suboptimal at best.
Paul Davidson · · Unknown Hometown · Joined Jan 2007 · Points: 605
Charles Vernon wrote:What I'm taking away from this is that two experienced climbers both thought this was a solid piece that would hold a fall, and they were both wrong, which suggests that there's a lesson for other experienced climbers here.
+1 - some of that lower Lemmon rock is ultra-smooth but this is eye opening.
rob.calm · · Loveland, Colorado · Joined May 2002 · Points: 630
rgold wrote: I think that the almost universal practice of notching cam lobes is intended to leverage potential roughness interactions. I think the message from research on the subject is that until you get up to loads of geological magnitude, the roughness of the surfaces matters far more than the materials, and so speaking as if there is a coefficient of friction between, say, granite and aluminum is far from illuminating.
A historical note.

When Friends first came out decades ago, one could write to their inventor, Ray Jardine, if you had questions. The grooves on one of my Friends had worn smooth. I wrote to Ray. He replied and said not to worry as they have more friction that way like a climbing shoe or the tires on a drag racer. The grooves were mainly cosmetic.

Rob.calm
Guideline #1: Don't be a jerk.

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