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Topic Date User

Cams Ripping At Arapiles - common? 12-Oct-2009 At 2:15:18 PM Richard

Message

On 12/10/2009 GerryN wrote:
>Has rock type got anything to do with
>holding power of cams?

Some interesting quotes from on line searches:

"CAMS were developed in the 1970s for the smooth parallel sided cracks of Yosemite" - see on line page 89 "Guide to Climbing By Tony Lourens" http://books.google.com.au/books

According to http://web.mit.edu/custer/www/rocking/cams/cams.body.html a cam will fail in a parallel crack if tangent of the angle between the cam's contact point with the rock, and the axis if rotation of the cam is less than the the coefficient of friction.

(Essentily the same info / explanation exists at wikipedia - http://en.wikipedia.org/wiki/Spring-loaded_camming_device but they omit the info on the maximum force the cam will hold - a vital part of the consideration.)

What this means is, the smoother the rock, the lower the angle of beta needs to be (a more open placement is required), for the cam to carry its maximum load (eqn 2). But the lower the angle of beta, the lower the maximum force that this cam will hold is. (eqn 5).

So as rock gets smoother and smoother, you want to place the cam with a more and more open angle, so it will carry the maximum force it can, but that maximum force is getting gettting lower and lower.

That's what the theory says...