Textbook cam placements can pull in smooth stone

Cams can pop at less than body weight on the smooth stone present on the lower highway crags of Mt. Lemmon. I was able to pull two different size/brand cams from the same crack at less than body weight.
Watch yourself out there.
This video is from the crack of Hairy Interlude at pinhead wall
youtube.com/watch?v=-WPM1Hd…

Maybe I am wrong, but I would hardly describe that cam placement as, "textbook," seems pretty over cammed to me. I understand how smooth rock can reduce the coefficient of friction on the lobes, but still, seems like a different cam might be the better option there. Also, placing the cam higher up in the crack and not above an area in the crack that opens up.

Yes, hardly 'textbook'. Either higher where the crack flares slightly downward or an inch lower and sunk back would be much better placements.

Taylor Badeau wrote:Maybe I am wrong, but I would hardly describe that cam placement as, "textbook," seems pretty over cammed to me. I understand how smooth rock can reduce the coefficient of friction on the lobes, but still, seems like a different cam might be the better option there. Also, placing the cam higher up in the crack and not above an area in the crack that opens up.

Yup you're wrong that cam is at the optimal range. The placement is an outward flare though. A different spot would be better. Still is shocking!

rocknice2 wrote:Still is shocking!

Shouldn't be anymore shocking an event than someone getting dropped by a belayer with a grigri. Marginal cams can and do pull.

Taylor Badeau wrote:Maybe I am wrong, but I would hardly describe that cam placement as, "textbook," seems pretty over cammed to me.

It seems to be a common misconception that over-camming equates to a less bomber placement. The only thing that over-camming means is that you might get your cam stuck. Otherwise it is just as bomber as a "textbook" placement.

If you look at the range-finder on Metolius mastercams, you'll find that you can't actually pull the trigger far enough to contract the lobes to the end of the green "ideal placement" range.

Of course the fact that Metolius does this is not hard proof that over-camming is safe, but I could probably dig up the mathematical models and studies of the physics of camming devices that I've done if that's necessary.

First mistake they made was not using a c4 in that crack.

definitely needs a bolt next to that crack

Healyje wrote: Shouldn't be anymore shocking an event than someone getting dropped by a belayer with a grigri. Marginal cams can and do pull.

Hahaha, yeah. WTF "text book" is the OP reading?..... Seriously though, he needs a good mentor before he falls off a cliff & crushes some innocent bystanders......or even worse, offers more advice.

Really, there is nothing terribly the matter with that cam placement. It isn't ideal; the crack is slightly flared downward at the placement, but to a degree within what cams can usually handle. The crack variations wouldn't matter in most climbing areas.

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.

Cams depend on coefficient of friction. If it isn't high enough, they will pull, and the effect will be the same if you jerk them by hand or fall on them, because they press on the crack walls with a force proportional to the load. (Actually, well-placed cams in appropriate rock fail for a completely different reason having to do with the deformation of of the lobes and shearing of the lobe material.)

I'd take the post at face value and be extremely cautious about cam use in that area. I've read and heard a number of reports that certain limestone and basalt areas also have low enough rock friction to produce cam failures for what seem to be ordinary placements. Moreover, rock friction can vary locally from crack to crack and also within a particular crack. Water-polishing might make certain crack sections slick.

You can count the Niagara Escarpment crags among the "certain limestone areas" you allude to. Too many experienced climbers have decked here when "bomber" cam placements have inexplicably pulled. The "the leader must not fall" (at least when above cams) ethos is alive and well here.

That's a neat thing about cam physics: they use just friction to hold. So assuming the rock doesn't change, it's actually exactly what you'd expect for a low friction situation: it should result in a cam that pulls out by hand or body weight. If friction is insufficient, a cam will fail right away, as soon as even tugged upon.

The high friction situation is the same (again, assuming no rock change or cam walk, up to the deformation failure of the cam). That is, if a cam is holding a tug or body weight, it should stay in the crack until something breaks.

What the theory doesn't really predict is that there are sound cam placements that will hold body weight but then fail at 2kN or something. They are supposed to be binary, yes/no placements: they slide out with a tug, or they hold up to their limit (again: assuming a sound placement and and no rock change or cam walk, which are big deals and things that do need to be considered).

At least, that's what I've read. I'm not a mechanical engineer, but I play one on the Internet.

A good example of why you should try and "set" your cams with a good yank is important. It test the placement for just such a risk. I know I've had cams, ball nuts etc all "pop" from seemingly solid placements.

Also a good example of why Totem Cams can be superior. They were made to address just such an issue.

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

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"

Healyje wrote:Yes, hardly 'textbook'. Either higher where the crack flares slightly downward or an inch lower and sunk back would be a much better placements.

I'm 100% with you on the alternate placements, mine would have been buried up high for sure, I say buried cause I'd want room for my hand/fingers in that spot

I´d have sunk a Rock 7 in that nicely tapering crack lower down but then I´m old-skool.

IMO, there's nothing inherently wrong with that placement. I'd have trusted that placement in any of the rock I regularly climb on to hold hold a fall, or at the very least to aid off of. I've taken numerous falls off of cams that looked just like that or worse. Admittedly, I've never plugged gear in slick limestone, but everywhere I've climbed on gear, that placement should have been just fine. Overcamming should not affect the holding power of this or any other cam. This is a good example of why the friction of particular rock types can influence the quality of cam placements.

Looks to me like the best constriction is up higher.

I took my first fall on trad gear on a similar placement with slick rock(mine was slightly more flaring, but not much more). Weighted the piece and it popped. Fortunately my tri cam 7 feet below held, still ended up being a 15 foot fall.

mattm wrote:Also a good example of why Totem Cams can be superior. They were made to address just such an issue.

This was my first thought as well. Not an inherently bad placement, but simply a poor choice of cam for that rock. Not all cams are for all rock types, and the metolius tcu in the video was probably the last type of cam I would choose for that placement; much less surface area on a tcu when compared to a C4, Mastercam, or Totem.

Scott Scharfenberg wrote: It seems to be a common misconception that over-camming equates to a less bomber placement. The only thing that over-camming means is that you might get your cam stuck.

Amen.