Cams sliding out of quartzite cracks

A couple of nights ago I was practising solo aid on a local quartzite crack. I built a 3 piece equalized anchor with 2 cams and a bolt and started up the crack. My first piece was 0.3 BD C4. I top stepped in my aiders and placed a 0.4 C4. I clipped by daisy/aider combo to the cam and moved into that ladder. As I took a step up, the cam unexpectedly ripped as did the 0.3 below it. I bounced off the belay ledge, which thankfully was snow covered, and came to rest upside down about 3 feet below. My silent partner locked up fine and the anchor held my fall. I watched my headlamp plummet 40 more feet to the deck. Somewhat miraculously, I was unscathed and just had to start laughing about how f'in crazy that was.

Both cams were in what I would consider to be "bomber" placements. They were not under/overcammed, all lobes were equally retracted and had great contact with the rock. Both cams were undamaged and the rock did not blow out. The crack wasn't wet, icy, muddy, or dirty. The rock is extremely smooth quartzite and it appears that there wan't enough friction between the cam and the rock and they simply slid out. However, I am confused because both cams initially held my weight. This is a route that I have free climbed multiple times and the 0.4 protects a somewhat tricky move over a bulge. Typically, the belayer doesn't anchor in on this ledge. This same fall when free climbing would have sent both climber and belayer off the ledge with disastrous consequences.

My question is has anyone else experienced cams sliding out of cracks and are any other makes of cams less likely to behave this way? Maybe someone who knows more about physics can give a more detailed explanation of why this happened.

Thanks,
Dan

BCC, greasy begining to a trade route

See Figure 4
vainokodas.com/climbing/cam…

"Physically, this means that in a parallel crack, the coefficient of friction between the rock and the cams must be larger than µ or the cams will slide down the wall and the device will pull out of the crack. This is why µ cannot be increased indiscriminately. On the other hand, if µ is made too small, the range of the cams will not be very great, and the following forces will all increase: the compression force on the cams, the outward force on the walls, and the shear forces on the axle. Also, the ability of the device to work inside of a flared (non-parallel) crack will be limited, as will be shown next."

In slippery cracks use passive pro

Daniel Winder wrote:A couple of nights ago I was practising solo aid on a local quartzite crack. I built a 3 piece equalized anchor with 2 cams and a bolt and started up the crack. My first piece was 0.3 BD C4. I top stepped in my aiders and placed a 0.4 C4. I clipped by daisy/aider combo to the cam and moved into that ladder. As I took a step up, the cam unexpectedly ripped as did the 0.3 below it. I bounced off the belay ledge, which thankfully was snow covered, and came to rest upside down about 3 feet below. My silent partner locked up fine and the anchor held my fall. I watched my headlamp plummet 40 more feet to the deck. Somewhat miraculously, I was unscathed and just had to start laughing about how f'in crazy that was. Both cams were in what I would consider to be "bomber" placements. They were not under/overcammed, all lobes were equally retracted and had great contact with the rock. Both cams were undamaged and the rock did not blow out. The crack wasn't wet, icy, muddy, or dirty. The rock is extremely smooth quartzite and it appears that there wan't enough friction between the cam and the rock and they simply slid out. However, I am confused because both cams initially held my weight. This is a route that I have free climbed multiple times and the 0.4 protects a somewhat tricky move over a bulge. Typically, the belayer doesn't anchor in on this ledge. This same fall when free climbing would have sent both climber and belayer off the ledge with disastrous consequences. My question is has anyone else experienced cams sliding out of cracks and are any other makes of cams less likely to behave this way? Maybe someone who knows more about physics can give a more detailed explanation of why this happened. Thanks, Dan

I've heard of several instances of perfectly placed cams pulling out of very smooth quartzite or limestone cracks. In fact, I've pulled a perfectly placed cam out of a very smooth limestone crack with just a tug. As was mentioned upthread, if the coefficient of friction between the cam lobe and the rock is too low it will pull out.

A cam that has less pronounced knurling certainly wouldn't hurt anything either. Mo' surface area, mo friction...kind of a like a F1 car tire vs knobby A/T tires.

Those Totem cams might be a good way to go for slicker rock, the lobes do have some diagonal knurling but nothing like some of the other manufacturers out there.

Oh and btw, glad you didn't get hurt!

Actually, more surface area != more friction.

( physlink.com/education/aske…)

Smaller surface area might get more of a bite by deforming the rock...?

Larger surface area might catch a nub or something?

But on a polished, hard surface? It's a wash.

"Actually, more surface area != more friction."

while theoretically this is true, I'd much rather have more surface area so that there is more of a chance for the cam lobe to deform into some kind of irregularity within the rock to help it hold.

Kinda surprised no one's mentioned the obvious... In slick rock don't use cams with large cam angles like BD. Metolius would be a better choice in that situation due to the relatively small cam angle.

Aric Datesman wrote:Kinda surprised no one's mentioned the obvious... In slick rock don't use cams with large cam angles like BD. Metolius would be a better choice in that situation due to the relatively small cam angle.

This was my exact thought as well.

Interesting replies, but nobody has addressed the main mystery: Why did they slide out in a fall when they had initially held his weight?

It is a little disconcerting to me, as I have often judged the security of a placement by first weighting the piece.

Maybe the piece jiggled to a new position after he weighted it, and the new position had a lower coefficient of friction?

Or did the coefficient of friction decrease with increasing force? Would this be a property of quartzite-aluminum, or does it hold for most metals against mineral?

The jiggling is the easiest explanation, though it does seem a little coincidental that it happened to both pieces. But if this is the case, then the better cams to get are the ones that jiggle less, not necessarily the ones with the smaller opening angle.

A friend and I experienced a similar occurrence this past summer. He ended up with some fractured vertebrae. He blew 2 cams, a BD and a Metolius. I went back and did some testing and was able to also make an OP link cam and a tri cam pop out of the same crack.

The smaller cam angle on a metolius should help but only to a certain degree, when there is not a high enough coeff of friction between the 2 materials you will eventually pull it out with enough force.

The reason it held body weight is because there was a lot lower force on it which was not enough to overcome in impulse force needed to break friction, the fall had enough force to do that.

The main lesson is don't trust super smooth rock. When you can place in constrictions and use nuts do it.

Good read. Glad I can learn from this

Totem cams are supposed to be better in smooth rock than anything else. The prevalence of slick limestone placements in Europe was one of the motivations for their development.

The cams you had were probably marginal relative to the available friction. They either moved or were moving when you stepped up, and that was enough to put them over the edge.

In theory, a cam that holds body weight will hold any bigger load (until it fails because of sheer yield failure in the lobes or axle breakage). But this theory is based on the use of the classical formulation of coefficient of friction, which may not be an accurate way to describe how metal and rock interact.

There were some tests done a few years ago that suggested that vigorous setting of a cam increased its holding power in a fall. This cannot be explained by the coefficient of friction theory, and suggests that getting the metal to "bite" may be helpful.

I've experienced similar on the slick quartzite at devil's lake where I placed an ideally cammed #1 camalot and gave it a yank to set it and it ripped out of the rather shallow placement almost sending me flying. Like Kirk mentioned - passive pro is the way to go in super slick rock.

I wonder if anyone has ever tried putting a very thin (e.g., spray-on) layer of rubber on cam lobes. And how did it work out?

I'm thinking paint-film thinness, not enough to alter the camming angle or to produce sheared-off chunks under a heavy load. The idea would be to just have the cams stay in place, not to increase their range of placement.

Not that I'd advocate anyone to try such a thing in a real use, but am wondering if such a thing has been tested under controlled conditions.

One solution was pitched to Trango ages ago, and IIRC Mal told me it looked promising, but the folks working on it for a school project graduated and didn't take it past the proof of concept stage.

appft1.uspto.gov/netacgi/np…

The contact with rock was explained by Jardine in the 70's.. "the teeth are cosmetic only"

Also a .3 has very little expansion range, a slight movement can easy be a millimeter or so.This amy explain the initial hold of these cams

i am almost positive that original Friends, made in UK were tested on limestone and maybe slate , but remember this is when a #1 was the smallest

I have had cams in seemingly perfect placements pull on me with nothing more than a tug. Twice in Yosemite on the Leaning Tower and four times in Hawaii on a smooth basalt crack. It does happen.

rgold wrote:In theory, a cam that holds body weight will hold any bigger load (until it fails because of sheer yield failure in the lobes or axle breakage).

If you disregard rock strength, sure. However, by disregarding rock strength you invalidate that statement for most placements. I have encountered countless placements that would hold bodyweight but would likely fail to stop a fall. Most placements will not hold up to the breaking strength of the cam. Typically, that type of strength is only found in solid, high-density, parallel cracks.

"If you disregard rock strength, sure. However, by disregarding rock strength you invalidate that statement for most placements."

20 kN, I'm not sure you're getting what is being said (maybe you are, apologies if I'm confused).

The physical theory behind camming devices relies totally on friction. It states that if a cam can hold ANY force (a tug, body weight, etc.), it can hold ANY fall, up to the point when either the cam breaks or the rock breaks. Period.

Since neither the cam nor the rock broke here, it points out quite clearly that there are some idealizations in the theory of cams that don't hold up in practice. This isn't really about breaking cams or rock, but rather an important limitation of our understanding of cams.

It's right there in the Wild Country cam book: if it holds body weight, it'll hold your fall, assuming the rock is good and you don't break the cam (unlikely). That doesn't quite hold, apparently, in super slippery rock of excellent quality, which is worth knowing,

Could this failure be due to the differences in static and kinetic friction?

I'm thinking that while stepping up some torsional movement was introduced to the lobe/rock interface and static friction was lost.

Also cool provisional patent Aric, thanks for the link!

Sounds like Devil's Lake and yes, I've seen cams slide out of that polished quartzite.