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Textbook cam placements can pull in smooth stone
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Downward flare present "issues," but not in this case, in which low friction explains what happened. |
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In good squamish granite that would have a fine, but not ideal, placement |
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Robbie Phillips is a 5.14 sport climber who has turned to trad. His gear-placing skills haven't caught up to his climbing ability. In the second video, the climber has three pieces of gear in the crack where Robbie had only a single piece, the first of two to fail in his fall. He was super lucky to walk away sore rather than ending up a paraplegic or dead. A young woman in the Gunks fell that far and was killed last season. |
rgold wrote:The second video shows that the fall is plenty bad enough even when the gear holds.A brain bucket probably would have been useful, but then again it affects the Cool factor! |
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heres the large grey dragon pulling in limetone ...if i had this placement in squamish it would be considered bomber .. |
rgold wrote:Downward flare present "issues," but not in this case, in which low friction explains what happened.Of course. As if you were there. |
rgold wrote:Robbie Phillips is a 5.14 sport climber who has turned to trad. His gear-placing skills haven't caught up to his climbing ability. In the second video, the climber has three pieces of gear in the crack where Robbie had only a single piece, the first of two to fail in his fall. He was super lucky to walk away sore rather than ending up a paraplegic or dead. A young woman in the Gunks fell that far and was killed last season. The second video shows that the fall is plenty bad enough even when the gear holds. As for cams placed by experienced climbers failing in good placements in good granite at Squamish, remember that Doug Phillips, the designer of Metolius cams and founder of the company, in a claim universally and continually poo-pooed by internet savants, said that according to his tests approximately 1 in 20 apparently good cam placements are likely to fail. I have no idea whether that number is in the ballpark or not, but the message ought to be that textbook placements do not mean bombproof protection. Best to think hard about the whole system and not put your eggs in just one basket, otherwise that's what you might be carried off in.he should know how to place gear to jump on that climb ... thats was my meaning ... heres the doug phillips article Better Beta Cam placement rules As the founder and head designer of Metolius, Doug Philips has spent an immense amount of time testing and improving cams over the last twenty years. Here are some tips on cam safety based on his vast experience. Doug Phillips 1. No matter how good a placement looks, you can never be sure it will hold. During my tests, about one in twenty good-looking placements pulled out when loaded. The challenge is to figure out why the cam pulled, and what could have been done to prevent this from happening. To understand why cams fail, we classify pullouts into six basic categories: Lubricants (water, dirt, dust, moss, ice) Poor rock quality Cam movement (walking, misaligned) Poor placement Cam design Poor maintenance Lubricants Anything that gets between the aluminum cam lobe and the solid rock wall can act as a lubricant reducing the friction. Water is an obvious lubricant as is dirt or fine dust. A dirty seeping crack with a thin layer of moss can cause an otherwise good placement to consistently pull out. Poor rock quality There are three categories of rock to avoid: soft, smooth, and weak: Soft rock tends to crush under the load of a fall. The crushed particles act as a lubricant causing the cam to slip. After this type of failure, the cam lobes will often be coated with a thin film of pulverized rock. Smooth or polished rock will not allow the cams to grip. Smooth stone can be found in water polished cracks as well as glacier polished stone. It is very unnerving to watch a cam consistently pull out of a super smooth crack that would otherwise be a perfect placement. Weak or fractured rock will break, causing the cam to loose traction. When a cam pulls out of seemingly solid stone, I often find a small piece of fractured rock near one of the cam lobes. Occasionally a larger chunk of stone gets blown out of the crack due to an existing fracture or weakness in the rock. Cam movement Cams will move from the motion of a passing climber, rope action and impact from a fall. This movement can lead to pullout failures, as the cam is no longer positioned to hold a fall. To prevent this, place the cam so it has room to move and still remain in a good camming position. A long sling will reduce unwanted movement and allow you to fall on the next piece without putting any outward tension on the lower cam. Cam pullout failures commonly occur with a sharp outward or sideways pull rather than the downward pull you had intended. Poor placement Wide flares, bottoming cracks and irregular rock features make it difficult to get solid cam placements. Help optimize the security of a placement by maximizing cam-to-rock contact. Place good gear before and after difficult-to-protect sections. In my tests, I have occasionally been surprised by a bad looking placements that hold when drop tested. Most of the time however, if a cam looks bad, it will pull out. Cam Design The brand of cam makes a difference. Metolius cams are made with holding power as the primary design criteria. The main variables are cam angle, aluminum alloy, surface contact area, and cam alignment. Cam angle The cam angle we use is 13.25 degrees. This sacrifices range, but increases outward force, making the cams harder to pull out. Aluminum alloy Our aluminum alloy is 7075 for small and midrange cams and 6061 for larger sizes. The 7075 is stronger, maintaining cam shape under load in the small sizes. This is less of an issue in the large cams, so we switch to the lighter weight, less expensive, 6061. Surface contact area Surface contact area is important. More surface area will create more friction increasing the cam’s security. Also, more surface area spreads the load more, improving holding power in soft or weak stone. Our Fat Cams were designed with this in mind. Cam alignment Maximize holding power by lining up the cam lobes with the direction of pull. The original Friends did this by using a rigid stem. The Metolius cam’s relatively stiff “U” shaped body aligns the cam lobes with the direction of pull. Poor maintenance Like all technical equipment, cams require maintenance. This includes cleaning, lubrication, replacing old or worn slings and repairing frayed trigger wires. Be sure to retire worn out cams. 2. Place two good cams at critical spots Because one in 20 cams pull, reduce cam pullout by putting in a second good piece. This gives you a 99.75% chance that one placements will hold. Equalize them if possible. 3. Place the cam in as fully retracted a position as possible without getting it stuck. This is the green zone on our Range Finder system. Tight placements help to guard against the following types of pullout: Pullout due to cam movement Rope movement shifts cams. Long slings help, but you can increase security by placing the largest cam possible. If the cam moves to a wider crack section it will still have good contact with all four cams. Pullout due to poor rock quality If the rock on one side of the crack fails the cam lobes on that side will begin to slip. A cam with a tight placement (green zone) has a better chance of holding. If the rock on both sides of the crack fails, the lobes dig into the rock. The tighter the placement, the more the cam can expand before failure. Pullout due to lubrication When the cam pulls because of wet or dirty conditions it will move through several inches of crack before failure. If only one side of the crack is wet or dirty, the cam lobes on the wet side will tend to slip first. If the cam is in an open position the cams on the dry side will tip out and the placement will fail. In a tight placement the cams on the dry side will not tip out, greatly increasing the chance the placement will hold. I’ve observed a tight cam placement jamming just below the original placement. |
Greg D wrote:Of course. As if you were there.I backed up every claim with reasons. To review: The visual evidence, the fact that the cam was jerked out by hand, the fact that the tiny amount of flare present wouldn't matter in many rock types, combined with an understanding of cam physics and the effect of flares, and finally the experience of another party also having a cam pull from the general location and then going back and testing two cam models and having them pull as well, these results taken all together make an extremely strong case for low friction being the cause and the flare itself having little or nothing to do with it. That said, short of going back and placing pieces in the same crack but not in that barely flared section and repeating the test a bunch of times, no one can say for certain that the flare might not have had some effect. What is, however, unfortunate is to advance the idea that the flare is the real or an important cause of this failure, and thus obscure a critical warning about the behavior of cams in slick rock, a warning that could save lives and prevent serious injuries. |
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Andrew, nice video. |
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Re: "For a cam angle of 13 degrees, that requires a friction coefficient of 0.23 or higher. " |
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Must admit have not read much of the above posts and do not know if the following has been mentioned. I have had quite a lot of cams rip out more so on my sandstone climbs . once one above the other with identical cam and placement .. luckily the lower one held.I have always had a theory about the bounce affect on a cam when a fall is taken .If you think about it for a split second after a fall comes onto a cam the rope stretches then one bounces back and this must loosen the cam for that split second before it is again reloaded...could this be one of the reasons a cam can pull??. Personally I have never fully trusted cams always using if possible a nut placement. |
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For me and many others, slick rock is a rather obvious factor when on site. But feel free to believe you are playing God and saving lives by pointing out the obvious with long winded explanation that slick rock is slippery. |
Greg D wrote:For me and many others, slick rock is a rather obvious factor when on site. But feel free to believe you are playing God and saving lives by pointing out the obvious with long winded explanation that slick rock is slippery.It is mid winter lol |
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Actually record highs. 71. Heading out to climb now. |
Greg D wrote:Actually record highs. 71. Heading out to climb now.yeah its 2 here and snowing again |
Greg D wrote:For me and many others, slick rock is a rather obvious factor when on site. But feel free to believe you are playing God and saving lives by pointing out the obvious with long winded explanation that slick rock is slippery.The whole point of the OP is that slickness, as it applies to cam holding power, is not always obvious, a fact that is repeatedly born out by some of the other posts. The OP was interested in warning people about a potentially dangerous situation. I guess he was playing god too. I'd call that a matter of common decency and leave religion out of it. |
David Coley wrote: Can someone give me an idea please of what the 0.23 means in terms of common rock types?According to David Custer in web.mit.edu/custer/www/rock…, the coefficient of friction of aluminum against granite has been measured at 0.38. These students got 0.41 hypertextbook.com/facts/200…, and The Valley Giant folks say 0.5 valleygiant.com/cam_math.html. If Mapeze is around, as a designer he probably has some values, especially for Euro limestone, where cams are known to be less reliable. Obviously, the particular combination of aluminum against granite is not of great interest to researchers, so it isn’t easy to find values. But beyond that, the simple coefficient of friction concepts found in Amonton’s law are in fact the roughest of empirical estimates and are not any kind of natural law—people write PhD dissertations on friction; it is in fact an extremely complex and far from well-understood concept. The concept is most applicable to contact between highly polished surfaces, in which the friction forces are primarily influenced by molecular interactions. Once the surfaces are physically irregular, all hell breaks loose because of the variety of ways the bumps and recesses can interact to produce resistance. I think that the almost universal practice of notching cam lobes is intended to leverage potential roughness interactions. I think the message from research on the subject is that until you get up to loads of geological magnitude, the roughness of the surfaces matters far more than the materials, and so speaking as if there is a coefficient of friction between, say, granite and aluminum is far from illuminating. When surface roughness and deformability matters, so does contact area, in which case one of the fundamental precepts of Amonton’s law is out the window. (Everyone knows more shoe rubber on the rock produces more adhesion, even though Amonton’s law would say not.) Another important issue is the well-known disparity between static and sliding friction. Since cams often move when a fall happens, the applicable coefficient of friction may well be the lower sliding value rather than even a locally-measured static value. Then there is the fact, totally unrelated to friction, that a well-placed cam fails not because frictional forces are insufficient to hold it in, but because of shear yield stresses on the aluminum lobe material. In such cases there will be evident gouging of the cam and it may be possible to find aluminum deposited on the crack walls. (I've seen the aluminum left behind in testing jigs but not in real rock.) Given that Amonton’s law may be a poor description of what happens between a cam lobe and crack wall, I think it is something of a miracle that cams designed in accordance with that law work anywhere near as well as they do. |
Greg D wrote:For me and many others, slick rock is a rather obvious factor when on site. But feel free to believe you are playing God and saving lives by pointing out the obvious with long winded explanation that slick rock is slippery.Was it difficult inserting that stick up your butt? |
rgold wrote: Given that Amonton’s law may be a poor description of what happens between a cam lobe and crack wall, I think it is something of a miracle that cams designed in accordance with that law work anywhere near as well as they do.Given that to calculate the normal force between the aluminium and the rock you have to calculate the friction in that crudest of bearing systems, a metal to metal bush then it´s all going to be a bit hit and miss anyway. Especially when some parts have a tendency to corrode:-) |
Healyje wrote: Hmmm, almost don't know what to make of that. Depending on the cliff Eldo is bomb for all kinds of pro. Never had a cam of any kind pull or move on me there. Had one explode into a million pieces there, but never had one pull.Agreed. Maybe the reference is to the quartzite Supremacy Crag. R.c |
