Building Anchors with Spring Loaded Cams
Pull Test Using Metolius Camming Units
So we did some back yard testing and while what we found wasn’t particularly astonishing, it was never the less, very interesting.
We purposely used some marginal placements with our Metolius camming units. Some more marginal than others. We found a range from 1.8 kN (400 lbs) to 7.8 kN force or (1700 lbs). That former was super marginal and the latter was solid and bomber. As the video describes, we never really failed the placement due to the stretch in the rope. Who knows what it would have been. NOTE: We used a 32:1 MA!!!!
I pulled this video piece out as it became much more relevant to us at RLA due to some of the projects we have coming up as well as personal project Torrey is heading next week. I can’t say where or what at this point, but I can tell you it has to do with using natural anchors and placement anchors (nuts and camming units) to build slackline/highline systems in the backcountry. We’ll be able to relive and retell the tales… so stay tuned.
In short, what we found was the culture of the rock and not cam itself was the determining factor of failure.
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About rock strength
Rock will fail in 2 basic ways: either a relatively large piece breaks off or the surface layer is crushed under the pressure of the cam lobe allowing the cam to “track out.” You must assess the integrity of the rock and choose the soundest possible location for your placements. Look for fractures in and around the walls of a potential placement that could denote weakness, as well as pebbles, crystals or micro-flakes that could snap off.
Be extremely suspicious of placements behind flakes or blocks. As we said before, cams exert a tremendous amount of outward force in a fall, so they can expand or even lever off even seemingly solid flakes or blocks. Passive protection is often a better choice behind flakes or blocks.
Mitigate the danger of rock failure by spreading the force between the cam lobes and the rock over as large an area as possible — always use the largest cam lobe surface area that will fit in any given placement. In other words, choose the largest unit that will fit the placement and always opt for a 4-cam unit over a 3-cam unit, if it will fit — if the placement is deep enough to accommodate a Fat Cam, even better.
Peace on your Days