Textbook cam placements can pull in smooth stone

Yah there's an area in Aus called Frog Buttress that's slick like this. Slick, perfect rhyolite.

I remember I placed a good cam there and watched it slide down the crack..

Miike wrote:I dont think many people posting here have spent much time plugging cams into quartzite.

I (used to) climb NC quartzite pretty often and have taken many falls on cams (Moores wall, Pilot). Never once pulled a cam in these quartzite areas. Cams held just as well in these areas as they do in sandstone or granite areas I climb in. Is quartzite slick in other locations...more like I imagine limestone to be?

Can one of the physics folks (Rgold or someone) address the issue of overcamming?

My impression, perhaps wrong, is that overcammed is fine for protection, but might become fixed gear. Is this entirely wrong, partially correct (dependent on other factors) or right?

Answered previously in this thread by Rgold:

"The entire point of the logarithmic spiral curve is that holding power is independent of the cam position. "Overcamming" should mean cams retracted so tightly that there is no room to retract them further for removal. People use the term incorrectly to refer to a placement in which the lobes are highly contracted but still have more room to be compressed for removal---those placements are actually the best from the point of view of security. I'd call the placement in the video close to ideal."

Thanks.

Eric and Lucie wrote:Cams in perfect placement can pull if the rock is smooth enough PERIOD. That is a simple statement, and it is 100% true. Let's stop arguing the obvious, please. If the friction coefficient of the cam lobe material on the rock is less than the tangent of the camming angle, the cam will pull out. Physics 101. It is why I minimize my use of cams at Eldorado for example. I have pulled cams out of perfect parallel placements by hand there before.

As someone who never climbed there, but might one day. What do you use instead of cams?

Beean wrote:Yah there's an area in Aus called Frog Buttress that's slick like this. Slick, perfect rhyolite. I remember I placed a good cam there and watched it slide down the crack..

I've pulled a few out by hand just for the fun of it in BCC Utah and Seneca WV

J Serpico, nuts, hexes, ball nuts, big bros, knotted cord, tricams... Of course the best option in a perfectly parallel crack is usually a cam, so if it's perfectly parallel and a cam won't work, I'm inclined to think you'd have to find another location for a placement unless it's so small that a ball nut will fit (minimal or no overlap in sizes between cams and ball nuts depending on the sizes you own of each) and even then I assume a ball nut also requires a certain amount of friction. Never placed a big bro so idk if that works in a perfectly parallel crack. I assume it also needs friction anyway.

I've also experienced how hard gear placements are on smooth quartzite. At Devils Lake I had to adjust what I considered a bomber nut or hex placement because they could be fiddled out really easily even after being set firmly.

MorganH wrote: I can pretty much guarantee from the above post that you rarely to never fall on your gear and never climb on gear at your limit.

Perhaps the funniest and most inaccurate statement in this thread so far. I'm over 200 naked. I fall regularly. Sometimes intentionally. Usually onto small gear. Let's get out some day.

Some still want to believe slickness was the only factor. Well, you could have a cam in a downward flare in high friction rock and it may hold. You could have a cam in parallel but slick rock. And it may still blows. But a good leader will take many factors into consideration.

Nobody can argue the placement was good since it failed. Was it due to slick rock or downward flare. Nobody can say for certain. All downward flares are suspect. Add slick rock into the mix and you have a shit placement.

Carry on. Especially those with opinions that don't actually fall on gear.

rgold wrote:I'd call the placement in the video close to ideal.

Avalon'cha wrote: Even after watching it pull out with less than body weight? We all (should) know that close to ideal, can actually be worlds apart in difference, when talking cam placements. Or any gear for that matter! All I know is; smooth polished rock, an ever so slight flare in the direction of pull, and all I'm thinking is "looks like I could get some good brass in the smaller crack"

Forgive my failure of precision. The meaning I thought would be clear is that the configuration of the crack and the placement of the cam within it would be close to ideal for most of the rock types typically encountered by climbers. This was mentioned in order to emphasize the potential role of low friction as opposed to some kind of technical positioning error.

That said, I wouldn't have put the cam there and wouldn't have used a cam at all unless I had run out of nuts. But the "downward flare" that people are citing is barely perceptible and within the ability of standard cams in, say, unpolished granite to withstand. If I had to put a cam in such a spot, I wouldn't ordinarily be terribly worried. I have for sure fallen on more flared placements than that.

By the way, at least in theory cams in downward flared cracks are not more likely to slip out. What happens in theory is that the forces on cam components go up---without bound---as the crack flare approaches the camming angle, which means the cam will break, or before that the lobes will experience shear yield failure. Jerking on a cam is not going to produce forces that break the cam, so the cam popping out as it did is most likely due to low friction and not the crack flare.

Eric and Lucie wrote:It is why I minimize my use of cams at Eldorado for example. I have pulled cams out of perfect parallel placements by hand there before.

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.

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.

I've encountered some jasper-like rock in Eldo that wouldn't give me warm fuzzies if I placed a cam in it, but I don't think there's any cracks in Eldo that are both so continuous and so smooth that a cam would just skate out, and you had no other options. There's plenty of routes with junk gear in Eldo, but its not because the rock is too slick.

Eric and Lucie wrote:For those who would like to understand the physics behind all this, here is a nice description of the function of traditional cams and Totem cams: totemcams.com/files/galeria… Among other things, it shows that Totem cams increase their holding power compared to classic cams by a factor that varies from 1.59 (when fully closed) to 1.67 (when fully open). In other words, in theory, a Totem cam will hold in rock that is ~60% slicker than a traditional cam made from the same material. Yet another way of thinking about it is that a Totem cam will give you a wide camming range (due to its steep "geometric" camming angle of 20.35 degrees), yet simultaneously provide the holding power of a cam with a much lower camming angle (the "effective" camming angle of a Totem cam is about 13 degrees).

Some inaccuracy here.

The numbers given (1.59 and 1.67) are geometric ratios on Totem cam lobes that are not the unique factors to determine the holding power. The real holding power on Totem Cams is given by those ratios, the camming angle (20.35º) and cam lobes material (Al 7075-T6). Resuming, we say that the effective camming angle (or "real" camming angle) of Totem Cams is not constant and varies from 12.52º to 13.13º depending on cam lobes retraction (more "overcammed" = lower effective camming angle = greater holding power).

The other important variable is cam lobes material (and their surface finish!!). Is hard to compare the holding power of different camming angles (or effective camming angle in the case of Totem Cams) and different materials. My experience says that the combination chosen in Totem Cams offers a holding power that is not surpassed by any other cam on the market. But the difference is not so clear as mentioned in the comment here (~60%). I would speak about 6-10% superior holding power comparing to cams with Al 7075-T6 cam lobes (less if Totem cam lobes are opened more than 66%).
I would be delighted to see a test of a Totem Cam in such placement!

And by the way, it's always a good idea to take off the anodizing layer of cam lobes edges with sandpaper. Some brands apply a layer that is too hard and the holding power decrease is noticeable.

mapeze:
I agree with everything you wrote.
I should have been more clear; my post should have read "Among other things, it shows that Totem cams increase their holding power compared to classic cams BUILT WITH THE SAME GEOMETRIC CAMMING ANGLE by a factor that varies from 1.59 (when fully closed) to 1.67 (when fully open). In other words, in theory, a Totem cam will hold in rock that is ~60% slicker than a traditional cam made from the same material AND WITH THE SAME GEOMETRIC CAMMING ANGLE".

Clearly you would not build a classic cam with a 20 degree camming angle (the geomoetric camming angle of Totem cams), because if wouldn't hold too well, but the point is that by designing their cam the way they did, they are getting it to hold as well as any classic cam on the market (because of the 13 degree effective angle), yet provide much more range.

Thanks for catching this!

To provide some additional context to the debate here, back in October my partner pulled a piece from the same spot on the same route. In her case it was an 0.4 C4 camalot, and she was merely hanging on it; it failed under body weight (and she doesn't weigh very much). She has been trad climbing for many years with many falls, and had never had a piece fail previously.

I don't know the OP, Andrew, personally, but we live in the same town, have friends in common, and he has a rep as a solid, experienced climber. 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.

So, I worked through the physics for a parallel-sided crack. And I came to the conclusion that the coefficient of friction must be greater than the tangent of the cam angle for the cam to hold, a result which I think I've seen elsewhere. For a cam angle of 13 degrees, that requires a friction coefficient of 0.23 or higher.

Then I tried to do the physics for a flared crack, and I concluded that ... the coefficient of friction must be greater than the tangent of the cam angle INDEPENDENT OF THE AMOUNT OF FLARE. Theoretically, if the walls are smooth, you can pull a cam through a modest constriction just as easily (up to the same coefficient of friction) as you could pull it from a parallel crack or even a flared crack. Seems highly counter-intuitive, and not what I was expecting. Have I made an error, or is this (mathematically) correct?

I can think of reasons why this theoretical case wouldn't translate to the real world. In particular, if the lobes initially slip but the crack is parallel or constricting they'll have a chance to re-engage, perhaps at a spot where the friction is a bit better. Also, in a flaring crack the outward forces are increased, encouraging failure modes that involve pulverizing/breaking the rock or deforming the cam.

Anyway, thanks to the OP. I know I'll be more careful in slick rock (thankfully not much of it here in New England) even if the geometry looks favorable.

kevin neville wrote:Then I tried to do the physics for a flared crack, and I concluded that ... the coefficient of friction must be greater than the tangent of the cam angle INDEPENDENT OF THE AMOUNT OF FLARE. Theoretically, if the walls are smooth, you can pull a cam through a modest constriction just as easily (up to the same coefficient of friction) as you could pull it from a parallel crack or even a flared crack. Seems highly counter-intuitive, and not what I was expecting. Have I made an error, or is this (mathematically) correct?

Yes, that is correct. As you point out, in theory at least, flare angle makes no difference to the likelyhood that a cam will slip! But as you pointed out, deformations of the cam and the rock are not accounted for in that simple theory.

Excellent summary of the math, borrowed from totemcams.com/files/galeria…

Your math is right; it's what I alluded to above. Cams do not, in principle, slip out at lower loads in flares less than the camming angle. But if you look at your calculations for the magnitude of, say, the compressive forces on the axle as the flare angle increases, you'll see that the loads increase without bound as the flare angle approaches the cam angle, so that the cam will break or fail or destroy the rock surface (as I also mentioned above).

Of course, flares present other problems, primarily that the placement will probably not tolerate any cam motion, which means you may have a placement that is good from the load-bearing point of view but unstable and so practically marginal.

At this point it is case closed: low friction is a problem in this area and almost certainly accounts for the OP's observation.

If you go to the link provided above, mountainproject.com/v/hairy…, you'll read not only about the failure very similar to the one described by the OP, but also that subsequent testing confirmed the fact that cams just aren't holding:

Originally he had a yellow alien in there and that pulled when he fell. We were both shocked as the placement looked pretty good. Later we set up a top rope to hang there and recreate the scenario. We put in the alien again, clipped a sling and stepped in it and it pulled repeatedly with less than full bodyweight. Then we put in an orange TCU with similar results.

The jerk test saved the OP from something potentially much worse. Known slippery rock or not, I'm a firm believer in testing most cam placements with one or more vigorous jerks---not just a mild peremptory tug. For one thing, the theory says that if the cam can withstand such a jerk, it will also withstand a fall load. (Of course the theory does not account for cam motion, rock crumbling, and lobe deformation, so sadly the jerk test is not conclusive, it is only evidence in the right direction.) Secondly, I've read a study (does anyone have a link, I can't find it now) that found that vigorous jerking induced some kind of "setting" that resulted in higher pull-out thresholds for the placements.

I believe at some point on one of the sites the Metolius folk said there was no point in 'setting' a cam. I never have, but it's definitely a case of to each his own.

rgold wrote:Secondly, I've read a study (does anyone have a link, I can't find it now) that found that vigorous jerking induced some kind of "setting" that resulted in higher pull-out thresholds for the placements.

Don't have the link, but I recall reading that, too. I think it was someone from BD. May have been on recdot.

BTW - thank you to the OP for taking the time to film and post.

GO

Seems like downward flares present some issues after all. I thought someone mentioned that at the beginning of the thread. Can't remember who. Ya'll are so cute.