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Cam Physics Explanation Please!
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Oct 28, 2013
ARowland wrote:
I thing a carabiners efficiency has been meansured to be in neighborhood of .7 IIRC. 1.7x isn't so far off. And hey, maybe the top piece is a DMM revolver?

It depends on the load. I have measured carabiner efficiency values as low as 42% for a top rope fall with a light person. For a lead fall, one can expect around 1.6ish, as you said. I have tested values ranging from 1.55 - 1.7. The UIAA assumes 1.66x for the purpose of writing some of their standards.
20 kN
From Hawaii
Joined Feb 2, 2009
665 points
Oct 29, 2013
Aric Datesman wrote:
Except in cases where it's keyholed, in which case it's square peg/round hole and there's no outward force. Long story short, there's a whole lot of "it depends" going on with passive pro, and it's much harder to quantify than with active gear.


Ok, but how about for an idealized case, match fit between rock and nut, and, if you like, frictionless rock? Just for a ballpark comparison between nut and cam...
Optimistic
From New Paltz
Joined Aug 29, 2007
244 points
Oct 29, 2013
Wild Country's "The Cam Book" was helpful for my understanding of cam mechanics.

wildcountry.com/files/public/2...

Alternatively, here are two excerpts:
wildcountry.com/files/public/H...

wildcountry.com/files/public/H...
michaelp
Joined Apr 28, 2013
110 points
Oct 29, 2013
dorky helmet
Optimistic wrote:
Ok, but how about for an idealized case, match fit between rock and nut, and, if you like, frictionless rock? Just for a ballpark comparison between nut and cam...


If it's frictionless, then it should reduce to the wedge case where the force increases by 1/tan(wedge angle)..
hikingdrew
From Los Angeles, CA
Joined Jul 20, 2013
36 points
Oct 29, 2013
hikingdrew wrote:
If it's frictionless, then it should reduce to the wedge case where the force increases by 1/tan(wedge angle)..


Which doesn't really apply nowadays, given that with most nuts now have curved surfaces. Then you also have to look at the yield point of the material and point loading to see if the nut slides or lets the rock bite in, which then puts us back to the square peg/round hole scenario.

As I said, it's much harder to quantify this for passive gear.
Aric Datesman
Joined Sep 16, 2008
145 points
Oct 31, 2013
peregrine falcon. I think he is a young one, maybe...
nicelegs wrote:
I just stick it in and hope for the best.



I agree, let the engineers do the math. As long as you know what a good placement is your good to go
climber57
Joined Nov 30, 2012
35 points
Oct 31, 2013
climber57 wrote:
I agree, let the engineers do the math. As long as you know what a good placement is your good to go


(engineer chuckling amusedly over the implication that strength of materials is that intuitive.)

Ever climb shale, limestone or tufa? :)
Aric Datesman
Joined Sep 16, 2008
145 points
Oct 31, 2013
"Scott" at the tunnel
Aric Datesman wrote:
Ever climb shale, limestone or tufa? :)

Tufa is limestone....
Taylor J
From new mexico, new england
Joined Nov 30, 2010
363 points
Oct 31, 2013
taylor januskiewiecz wrote:
Tufa is limestone....


So Frankenjura is full of Tufa? News to me, and climbs very different IMO.
Aric Datesman
Joined Sep 16, 2008
145 points
Nov 1, 2013
Aric Datesman wrote:
So Frankenjura is full of Tufa? News to me, and climbs very different IMO.


Are you maybe thinking of "tuff", ie welded tuff? I'm no geologist, but I've always heard the word tufa applied to a rib or column on limestone, not to a distinct rock type. Tuff, I'd thought, was the rock type, some kind of conglomerate.
Optimistic
From New Paltz
Joined Aug 29, 2007
244 points
Nov 1, 2013
Aric Datesman wrote:
So Frankenjura is full of Tufa? News to me, and climbs very different IMO.


The Frankenjura is limestone from the Jurassic period, hence itīs name. Tufa (in the form of calcerous sinter) is rare around here, Iīve never seen anything substantial in the Franken but probably in the caves there is some.
Tuff is consolidated volcanic ash, there is none in the Franken.
Jim Titt
From Germany
Joined Nov 10, 2009
195 points
Nov 1, 2013
The top of the tufa on Magma
Welded Tuff is found in areas like Smith Rock and Big Chief. It can be pretty hard and protected with cams, but isn't generally as solid as Granite. Patrick Mulligan
Joined Oct 12, 2011
1,183 points
Nov 1, 2013
Ah, yes. Tuff, not tufa. Sorry sbout that. Aric Datesman
Joined Sep 16, 2008
145 points


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