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Rigid-stem friends



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By Ryan Williams
Administrator
From London (sort of)
Dec 9, 2012
El Chorro

The way I understand it, the rigid stem provides more leverage in a horizontal placement than a flexi stem. So simply adding a tie off point closer to the cam head of a flexi cam would not accomplish the same thing.

Of course I'm relatively uneducated compared to the people who are still following this thread - so maybe I misunderstood.


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By Aric Datesman
Dec 9, 2012

Yup, you've got it right.

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By JLP
From The Internet
Dec 9, 2012

Alex Stenzel wrote:
I compared the weight of an rf 3 1/2 and a camalot no.3. and the rf is 176g and the camalot 198g. About 20% less weight for the rigid stem! Regress or progress?

The #3 C4 is larger than a 3.5 Friend. There is actually little to no weight savings with Friends over C4's.

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By Gunkiemike
Dec 9, 2012

Aric Datesman wrote:
True, but they're flexible all the way to the attachment on the lobe, which prevents any of the leverage effect.


That's the whole idea: minimize, or in the case of the Totems, eliminate the leverage. Cuz leverage is bad, at least that's how Camhead and I understand what rgold has said on the subject. I don't personally have anything to add one way or another; just pointing out the design feature of the Totems.

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By rogerbenton
Dec 9, 2012
Whoever this guy is, he's just plain irresponsible.

gunkiemike, i love a .45 too but if you ever get the chance to try a sig .40.

my new fav by far.

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By wivanoff
Dec 9, 2012
High Exposure

Gunkiemike wrote:
That's the whole idea: minimize, or in the case of the Totems, eliminate the leverage. Cuz leverage is bad, at least that's how Camhead and I understand what rgold has said on the subject. I don't personally have anything to add one way or another; just pointing out the design feature of the Totems.


I hope RGold clarifies, because what you wrote is not how I'm understanding what he wrote. I'm reading that leverage is bad when there is a long moment arm away from the placement and you can bend the stem. But leverage can be good when it's close to the rock and helps the cam to "cam". The first case he mentions is a horizontal crack and the second case is a vertical crack.

RGold wrote:
In the first case, the downward load on the stem produces an outward force on the cam which is a fraction of the total load, so it would take a lot to extract the cam. I know of some rigid-stem placements that were made in flaring horizontals in the Gunks BITD that might not hold at all with today's flexible stems.


^^^^ Here I'm picturing a horizontal placement in a shallow crack with the gunks tieoff almost right at the edge of the rock. The rigid stem is resting on the rock at the bottom lip of the horizontal crack. The crack is not deep enough so that the gunks tie off turns the corner over the edge. Any force is downward and trying to pull the rigid stem into the rock lip. Outward force on the cam is somewhat less in this circumstance. A flexible stem would "turn the corner" and provide more direct outward pull.

RGold wrote:
In the second case, a flexible stem loads the cams almost perpendicular to their expansion plane, nearly nullifying the mechanical principles that make a cam work. The rigid stem provides torque that gives the cams a chance to expand against the crack walls.


^^^^^ Here I'm picturing a cam placed in a shallow vertical crack with the stem trying to stick out parallel to the ground. With a flexible stem cam, the load on flexible stem cam is almost parallel to the cam axle or as RGold words it "almost perpendicular to their expansion plane" and has little torque. Like it makes the cam want to slide vertically rather than rotate.
In that circumstance, a tied off rigid stem would minimize the moment arm but still provide some rotational torque that tries to move the upper lobes outward and the lower lobes inward. However, the lower lobes can't go very much inward because it is a shallow crack.

At least, that's how I read it. Corrections are welcome.

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By rogerbenton
Dec 9, 2012
Whoever this guy is, he's just plain irresponsible.

i read things exactly as wivanoff describes.


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By Aric Datesman
Dec 10, 2012

Yup, wivanoff's got it. I recall a discussion somewhere a long while back (RC?) that dug into the issue and had some great diagrams that made the how&why more easy to understand. Don't have a link handy though...

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