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Author	Cam failure discussion
jezza 22-Apr-2015 12:48:05 PM	I guess the important safety question is 'how do you know that this cam isn't going to slip out?' (because of lower friction rock, not bad placement geometry). After my incident on No Future I tend to give my cams a tug before moving on (rather than set and forget), but to be honest I doubt a quick tug proves much.
Superstu 22-Apr-2015 1:44:25 PM	A quick tug might not prove much but it can make you feel better.
gfdonc 22-Apr-2015 1:56:46 PM	I'm leaving that comment well alone ..
One Day Hero 22-Apr-2015 2:17:16 PM	On 22/04/2015 johnpitcairn wrote: >Don't think "setting" the cam would have >helped, smooth basalt, slight flare. As per the point which the sensible side of this debate is attempting to get across. Had you tested the cam, maybe it would have failed the test, which in turn may have convinced you to look for better gear before continuing upwards.
One Day Hero 22-Apr-2015 2:30:10 PM	On 21/04/2015 Wendy wrote: >Just run a few examples by me again? Start of Erg (as shown in the video), start of Resurrection Corner (I helped carry a bloke out after he smushed himself when cam(s)? pulled out and he decked), Venom, all the ones with slippery glassy rock. Ask Ken. The first time I went up to Frog, he warned me about cams skating out.
Superstu 22-Apr-2015 2:43:24 PM	I once witnessed a quite spectacular deck from Gladiator. Broken ankles and gore etc. Three or four cams had ripped. Back then I had some wacky theory that all of Frog is essentially columns stacked next to each other all squished up, and so there is potential for teeny lateral movement between individual columns, enough to be the difference between cam stick and cam pop. But I'll run with ODH & Ken's on the sharpness of Occam's razor.
Markg 22-Apr-2015 3:21:21 PM	On 21/04/2015 Wendy 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. 9 Years ago at Frog I helped pack some one out from a ground fall on Resurrection Corner. Climber had made the ledge about 6m up. He plugged 2 cams and gave them a tug to test them. He then started to move up, got equal with the second piece and couldn't figure out the move. He down climbed to the ledge and leaned back to get a better view of where to go. Both pieces skated out ending with him 10m down in the scree. Most of the time cams are good at Frog but even now I'd rather slum on passive gear than a cam out there.
Wendy 23-Apr-2015 9:05:04 AM	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.
Jamesmc 23-Apr-2015 7:27:06 PM	It's worth bearing in mind that if the force is small (tug tug tug), the springs help, but if the force is large (falling) then the contribution from the springs will be relatively negligible. Just because a cam holds when you test it doesn't mean it will hold when you fall.
jezza 23-Apr-2015 10:47:25 PM	So looking at the maths in this - http://www.totemcams.com/files/galeria/files/IndarEbazpena.pdf A cam in a flared crack is as likely to hold as a cam in a parallel crack (ie requires same amount of friction for given downwards force) .... - although the forces on the axel/rock can be much, much greater depending on flare angle, potentially leading to drama - if things start to get really flared, the cam might 'roll over' I guess, and then you're hosed That doesn't seem very intuitive. Maybe I am not looking at the maths correctly.
Macciza 23-Apr-2015 11:49:47 PM	James - I think its more a case that the springs help maintain friction at the cam/rock interface to hold it in place. Giving it a tug test that friction and if it is sufficient the cams will start expanding and it will hold, if the friction doesn't balance then the cams slide. This is based on solid rock that doesn't deform. For some Blues sandstone testing it will help work out whether its going to blow too much rock out, or track; sometimes into a better set position. Jezza - I think it shows that flared cracks are LESS likely to holding, in fact that as you increase the flare eventually it simply doesn't work and it falls out . . . Not quite sure what you mean or how you concluded the other stuff, but I think it shows how the Direct Loading method means they hold better in even more flared cracks then normal Spring Loaded cams ...
patto 24-Apr-2015 8:32:44 AM	On 23/04/2015 Macciza wrote: >Jezza - I think it shows that flared cracks are LESS likely to holding, >in fact that as you increase the flare eventually it simply doesn't work >and it falls out . . . >Not quite sure what you mean or how you concluded the other stuff, but >I think it shows how the Direct Loading method means they hold better in >even more flared cracks then normal Spring Loaded cams ... Jezza is correct. For a regular cam a flared crack doesn't mean you need additional friction. So a few degrees flared is no issue at all for regular cams. Though as the flare angle gets anywhere near 2x[camming angle] you get into trouble. In practice failure occurs well before 2x[camming angle] due to lobe compression.
TimP 24-Apr-2015 9:24:54 AM	I'm wondering about the quality of the load on a cam: a short sharp tug in testing is quite different to the dynamic load catching a fall. In the dynamic situation I imagine the cam has time to engage its magic camming angle as the load builds to peak, converting the downwards force to opposing outwards force at the cams, so hopefully aligning to the direction of pull and crushing any loose surface.
Macciza 24-Apr-2015 12:00:26 PM	Cant agree Patto - look at the equations at the end of the standard cam models for parallel vs flared cracks. As the flare approaches the cam angle more friction is require to hold it . Where do you get the 2x figure from? Are you suggesting that deformation is the main reason cams fail in flared cracks? Back on topic, some of the variables for a cam to hold include the angle of the cam, and the material that the cams are made from (and finish etc), This will account for varying results for different brands in identical conditions. Different materials and finishes have different frictional, compressive and shear strengths, as do the rock they are placed in. Basically BrandX may work perfectly well where BrandY would simply fail. These factors may account for much of the variance between peoples experience.
jezza 24-Apr-2015 12:17:42 PM	On 24/04/2015 Macciza wrote: >Cant agree Patto - look at the equations at the end of the standard cam >models for parallel vs flared cracks. As the flare approaches the cam angle >more friction is require to hold it . Where do you get the 2x figure from? >Are you suggesting that deformation is the main reason cams fail in flared >cracks? What? Look at the maths again. Under normal cams, flared cracks there's an equation that shows cam angle required for a given friction coefficient. Doesn't depend on flare angle. Flare angle has a powerful effect on compressive forces on the cam though. That actually makes sense to me intuitively at last. If it's buried on the back of a downward facing flared crack and you fall on it, that cam is going to get stressed all right. It's going to have to work harder so as not to unwind. I'm pretty sure Patto meant 1/2 x, not 2x. As the flare angle approaches the camming angle, the outward force produced by the cam approaches infinity (according to the maths in the attachment).
Macciza 24-Apr-2015 1:23:30 PM	Hmm, lets see Standard Cam Parallel - T= 4.R.sin(alpha) Alpha is cam angle Standard Cam Flared - T= 4.R.sin(alpha-beta) Beta is flare angle. Clearly it relies on beta - as beta approaches alpha then it becomes sin(0) which is 0 I had since guessed he was looking at the whole flare, doubling beta, which is measured from vertical here, is that how you are getting half? . . . Ill have to find an engineer . . .
patto 24-Apr-2015 1:28:58 PM	On 24/04/2015 Macciza wrote: >Cant agree Patto - look at the equations at the end of the standard cam >models for parallel vs flared cracks. As the flare approaches the cam angle >more friction is require to hold it . That is not what the equations suggest. In all cases tan(α) < μ is the friction requirement. >Where do you get the 2x figure from? The total flare of a crack is 2x β. >Are you suggesting that deformation is the main reason cams fail in flared >cracks? The maths shows that in ultra flared cracks when β > α no grip initiates the cam doesn't hold at all in fact spring pressure will probably push the cam out! When α < β and friction is good {tan(α) < μ} then the cam will hold on placement. However lobe compression reduces the contact and can result in placement failure. >Back on topic, some of the variables for a cam to hold include the angle >of the cam, and the material that the cams are made from (and finish etc), >This will account for varying results for different brands in identical >conditions. Different materials and finishes have different frictional, >compressive and shear strengths, as do the rock they are placed in. Basically >BrandX may work perfectly well where BrandY would simply fail. >These factors may account for much of the variance between peoples experience. That doesn't say much. Why back away from objective statements towards subjective? Going back to the mathematics, bigger cam angels are better for flares but are worse for glassy cracks. This is why aliens are so good in high frictiion granite, along with softer lobes they hold flares well. Totems combines the advantages of outward force (grip) along with good flare behaviour.
patto 24-Apr-2015 2:06:23 PM	On 24/04/2015 Macciza wrote: >Hmm, lets see >Standard Cam Parallel - T= 4.R.sin(alpha) Alpha is cam angle >Standard Cam Flared - T= 4.R.sin(alpha-beta) Beta is flare angle. >Clearly it relies on beta - as beta approaches alpha then it becomes sin(0) >which is 0 You are using the wrong equation. Plus you are reversing the dependent variables of the equations in a fashion that makes no sense. (T, tension applied to cam is an independent variable) The equation for reaction force is R=f(T,β,α) as given. ie the equation is telling you the reaction force as dependent of tension, flare and cam angle. The hold or no hold friction circumstance is given by {tan(α) < μ} in both cases!
Hendo 24-Apr-2015 3:00:48 PM	I wonder if low friction rock can cause cams that are not in the direction of load to slip because the cam would need to provide friction perpendicular to the lobes, even if just momentarily.
One Day Hero 26-Apr-2015 10:20:18 PM	On 23/04/2015 Wendy wrote: >People rip gear all the time. Mostly it has >to do with bad placement not rock. What are the attributes of a bad cam placement then?

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