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Re: [healyje] link cam broken when fallen on :
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USnavy
Apr 27, 2012, 5:48 AM
Views: 10396
Registered: Nov 6, 2007
Posts: 2667
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healyje wrote: USnavy wrote: No it's not impossible, not even close. The guy that fell on the cam took a factor one fall on it. What likely happened is the cam ran out of range and it umbrellaed. That's is not only very possible, it is very likely. Hey, did you even bother to read what I wrote? healyje wrote: The only way it can happen is to fall on a piece that isn't placed securely, or is placed securely in less than idea rock, and said cam drags to a wider section of the crack where the cam then inverts. That's why you need to pay exceptional attention to detail when placing all forms of small pro. Cams don't " ran out of range", unless they were placed badly Except that's my entire point, in the case of small cams, a "bad placement" is pretty common. Its hard to inspect micro cams and determine how much expansion range is remaining on the back lobes. You can get away with placing a #2 Camalot at 30% cammed, but try that on a 0 TCU and forget about it, it's probably not going to hold any legit lead fall. Watch this video at the 1:00 mark: http://www.youtube.com/watch?v=xparZFsBS40 Note that those cams are being pulled in a 1" thick steel jig, probably made out of T3 steel or something similar. As you might have noticed, the jig does not move or compress at all. So the cam movement you saw in that video is a function of the cam bending and compressing. The same thing happens when you fall on a cam in the real world, just to a lesser extent because you are not loading it to 10 kN like in the video. However, that issue is the less important of the two. The other issue is the compression of the rock. If the rock compresses even just 1/8", that could be sufficient to cause a microcam to rip. When you are talking about softer material like sandstone, forget about it, it is very easy to get material like that to compress when the force on the rock under the lobes is easily in the many thousands of PSI. The entire point I am trying to make is that the difference between a fully retracted cam and a cam that is nearly tipped out is very subtle when talking about microcams. Its very easy, even for experienced trad climbers, to place a microcam with the outside lobes 75% camed, but fail to realize there is a very shallow flair to the crack and the inside lobes are only 25% camed. Microcams have no expansion range below 50%. If you dont get them in a position where all the lobes are fully retracted, you basically have a piece of passive pro at that point. The remaining expansion range could easily be in the 1/32" to 1/16" range which is nothing, just the compression and torsion of the cam on a fall can expend that range.
(This post was edited by USnavy on Apr 27, 2012, 10:55 AM)
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Post edited by USnavy
() on Apr 27, 2012, 5:55 AM
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Post edited by USnavy
() on Apr 27, 2012, 5:57 AM
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Post edited by USnavy
() on Apr 27, 2012, 10:55 AM
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