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Cam failure discussion 23-Apr-2015 At 9:05:04 AM Wendy

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On 22/04/2015 tris wrote:
>>Just run a few examples by me again? I can't remember ever actually taking
>>a big winger at Frog, but this theory about friction apparantly applies
>>regardless of the force. If it's going to go, it'll go with a tug as
>much
>>as a fall. Which I assume is the reason for thinking a tug is a somehow
>>sufficient test as well. In the light of that, I have slumped onto plenty
>>of gear at Frog. None of them moved.
>
>One example is Erg (direct start). There have been a number of cams pulled
>on this climb resulting in ground falls (have a look at youtube for proof).
>
>This climb has rock that is quite polished down low. You probably won't
>find out until you take a fall as I am not sure if you can get into a good
>enough position to give the cam a solid tug during the start moves. You
>could lower down and give it a good test.
>
>In the video from the original thread, it looks like the guy gave the
>cam a really solid tug. When I am setting/testing cams, I don't think I
>pull on them that hard (and I am not sure if this is hard enough to completely
>"test" the camming action). Surely there is a level of force involved
>that would overcome the little amount of friction present in slick rock
>which is less than that of bodyweight or a fall?

I've copied one of the posts about tug vs fall

"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."

So if the piece held a tug, it should hold a fall, if friction is the problem. I am going to continue with the theory that when you rip 5 pieces of gear, the rock is not the problem ... The video doesn't show anything about the quality of the placements, they could all be bollocks for all we know. I have actually sat my way up that DS many years ago and strangely enough, didn't rip a piece. As for the start of Resurection Corner, well, it is hard and pumpy for it's grade. It takes large sizes. Maybe people are not placing much gear or placing tipped out cams because they don't have enough large gear and don't place well or check thoroughly because it's pumpy and they just want to move on.

I've also taken falls on to small cams at the start of Child in Time and Wild One which surely have to count as polished cracks?

And Damo, Ken never warned me about that. Maybe he trusts my judgement more than yours :)? Despite that, as I can't remember any particularly concerns with all the assorted gear of yours I've removed, if you said you had ripped 5 pieces out of the start of Erg because the rock has no friction, I'd give that a lot more credence than some random ripped 5 pieces of gear and blames slick rock. People rip gear all the tip. Mostly it has to do with bad placement not rock.

I tried placing cams in a variety of polished cracks at the Mt yesterday, and I am sad to report that I didn't get a single one to come out under a Wendy weld. Including a 3 camalot in a polished flare that I wouldn't have chosen to use if actually relying on it but I still wouldn't go placing a piece like that when it really mattered. One purple link cam did resettle slightly in the crack under the first tug. Repeated tugs failed to get it to move at all.

I don't think it's unreasonable to warn people that slick rock can be a concern. It's something to think about when placing gear, just like the myriad other factors to think about. But before saying that slick rock is the cause of all of these failures, I think people need to look at whether their placements are actually the issue. I haven't found that Australian crags in general have continual slippery cracks where you have to be reliant on pieces in slick rock. There is enough variation in the rock texture to be able to place gear where it won't come out for lack of friction. Making a call on the rock texture is part of exercising normal judgement in placements.