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Would you climb above this? 8-Jun-2012 At 11:52:53 AM Olbert

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As for an actual physical analysis (assuming you weight the cam, weighting the hex would be suicidal)

First: Friction

Cams rely on friction to work, if the coefficient of friction is not high enough between the aluminium cam and aluminium hex then the cam will slide right out (the concave hex *might* stop this). Despite my initial gut feeling the coefficient of friction between aluminium and aluminium is roughly four times that of aluminium and rock. That means cams would work four times better if placed in an aluminium crack than a rock crack!

So there are no worries about sliding.

Second: Stability

Before weighting anything the hex is held in place by being pushed against the rock by the cam (and vica versa). The force of this push is dependant mainly on the strength of the springs inside the cam. If the springs are strong enough the rig will stay in place in a static situation. If the hex is too heavy it will fall apart before you can set it properly. It's pretty apparent that in this case the cams springs are strong enough.

Third: Weighting

What happens when you weight it? Well as any quick googling of cams will tell you, all the downwards force is opposed by the upwards holding force. The upwards holding force is made up mostly of two equal and opposite forces pushing outwards with only a little bit in the downwards direction.

Side note: Pulling 1kn down on a cam in a parallel crack will result in a the cam pushing outwards at 1000/(sin(alpha)) where alpha is the caming angle, normally approximately 14 degrees. So the outwards force is ~4.1kN.

If the direction of that outwards force which originates from the point of contact between the cam and the hex runs through the point at which the hex is flush with the rock, then everything is stable. If it runs below the section of hex/rock contact then the whole thing is going to want to roll downwards in an exploding manner when weighted. (This would be much simpler with a drawing but that's way to much effort.)

On the face of it, a strong tug would show you whether or not it's stable because nothing is going to slide (coefficients of friction are too high).

All that said, I would imagine the whole set up to get super untrustworthy with any movement. I would be putting at least a standard sling on the cam so that it doesnt move and be super careful not to knock it whilst climbing past. I would also be crying.