Gear failure (small cam)
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While climbing the route "groovy" in the gunks on sunday my partner ripped a yellow totem basic, resulting in one of the inner lobes umbrella-ing. The fall was tiny (cam approx waist level) and he had a solid nut less than a foot below the cam so no injuries. The cam was placed by an inexperienced leader who insisted it was perfectly placed |
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Take home lesson #1: Never trust a single piece of gear. |
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Malcolm Daly wrote:You should change the title of the thread.+1 ... at least until you get more info. I'm w/Mal in suspecting placement failure. |
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JSH wrote:If it umbrella'd out ... it had room to umbrella.+1 placement issue... |
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1. small nuts over small cams anyday if you can find a good placement |
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Sounds like user error. I wipped on that yellow totem basic on Sunday. The fall was decent and clean and presumably generated a sizeable force on that thing. It held, no worries. With that cam, you know if they aren't placed right they will umbrella and fail. That being said those cams are just bomber small pieces with the flexible stem, and the go to in the finger ranges. |
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umbrella = placement or rock failure not gear failure |
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The small mastercams in shallow placements where the lobes are only slightly retracted can be pulled by flexing the cable the right way. Flexing the cam at the "coil" around the cable can push the trigger bar back, slightly retracting one set of lobes. It's a reproducible problem. |
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What's everyone's definition of small cams? |
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divnamite wrote:What's everyone's definition of small cams? Yellow Basic is the similar size as the C4 .4, no? That's pretty decent size cam.anything up to and including a purple C4 ... which is the same as the biggest red TCU incidentally ;) |
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Lots of people have already said it: this isn't a case of gear failure. |
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i would define small cams as being in the silver or purple tcu range (ie black and blue aliens; silver, purple, and maybe green c3's; etc). once you get into the blue tcu/green alien size, there is a quite a bit more margin in terms of range that is used when the cam is loaded. |
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rgold wrote:It may not be intuitive, but having a rigid stem actually increases the likelihood that the cam will function appropriately, and this is a reason why C3's are preferable to Aliens in such placements.Can you elaborate here? In my thinking, more rigidity increases the effective lever arm on the stem, causing rotational forces on the lobes (i.e. a higher ratio of outward force on the upper lobes:lower lobes). I would think that minimizing this lever arm (i.e. a more flexible stem) would be advantageous in a placement which is perpendicular to the fall direction. Edit: also worth noting that I don't have a good intuitive grip on exactly how this works with the c3's weird u-stem system, as it also rotates when pulled on. |
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i completely disagree with rgold on that point. |
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Small cams are bomber when placed well but because there is less surface area on the cams they are less forgiving than larger cams. I don't regard any of the c4s as small cams. |
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shoo wrote: Can you elaborate here? In my thinking, more rigidity increases the effective lever arm on the stem, causing rotational forces on the lobes (i.e. a higher ratio of outward force on the upper lobes:lower lobes). I would think that minimizing this lever arm (i.e. a more flexible stem) would be advantageous in a placement which is perpendicular to the fall direction. Edit: also worth noting that I don't have a good intuitive grip on exactly how this works with the c3's weird u-stem system, as it also rotates when pulled on.I think it's similar to the sentiments expressed here: alpineexposures.com/pages/b… Further more one of the designers at Black Diamond had something quite interesting to say that hadnt actually occured to me that might help dispel some of the flexible vs stiff rumors out there: Not only do we have tests to show that it (the stiffness of the stem) is not a problem, but we have tests that show too much flexibility is a problem in certain placements. Think about how cams work in a perfect placement: you pull straight down on the cams, that force is converted to a rotational force on the cams, and the surface of the cams push against the rock surface. Now place a highly flexible cabled cam in a vertical bottoming crack (the stem is sticking out horizontally). Should be good right? Think again about how the cams need to work. Pull straight down on this placement and youll notice a large component of the downward force is acting parallel to the cam surfaces. This is not how the cam is designed to work. The cams will not push against the rock surface without a force perpendicular to the cams plane of movement. In short, it stops camming and acts like a nut placement. You need some torque on the placement to convert the parallel load to more of an outward one that can act on the cams. This torque is provided by the stiffness of the cable, or the length of the shank of head terminal, or some combination of both. In testing, the high flexible cables did not generate the torque necessary to hold the falls and the units slid sideways out of the placement at very low loads. We even made C3s proto types out of softer cable, only to watch them fail our bottoming crack test because of this issue. |
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When I think of pockets I think tri-cams not ridgid stems. maybe I am misunderstanding something. |
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rgold wrote: It may not be intuitive, but having a rigid stem actually increases the likelihood that the cam will function appropriately, and this is a reason why C3's are preferable to Aliens in such placements. Of course, such pockets are sometimes, but not always, an excellent place to drop in a good nut.In many conditions, this is not at all true. In pin scars, the long/wide rigid stem of the C3 often forces the cam to be placed with the stem close to parallel to the ground. The added moment arm on the stem from even a small fall can be enough to break it. I've personally seen a C3 fail (snap) in this type of placement, where an alien/totem the same size holds perfectly. |
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John Peters wrote: I think it's similar to the sentiments expressed here: alpineexposures.com/pages/b…That may be true of C3s with the U-stem, but I am not so convinced for single stems or as a general statement. Think about a perpendicular placement with a solid stem vs. a perfectly flexible cable. The solid stem would simply want to rotate out of the placement and puts enormous stress loads on the axle. It is less clear what would happen with the super flexible stem, but the short lever arm would prevent this from happening. Perhaps there is a happy medium depending on a number of factors, but I think that a blanket "stiffer is better for perpendicular placements" is probably inaccurate, unless I am missing something. |
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JSH wrote:If it umbrella'd out ... it had room to umbrella.this |
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Folks who doubt my comment ought to read the BD engineering account just above posted by John Peters. Although theoretical in nature when I made them, there seems to be confirmation from testing. |