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The Climbing Club • View topic - A Bible On Placing Cams

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 Post subject: A Bible On Placing Cams
PostPosted: Wed Jul 13, 2011 1:07 pm 
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Most all climbing pro, but especially cams, are not designed for the purpose they are used for, if in "designed" you want the same "factor of safety" that applies to anything OSHA (or related or similar) would require [if climbing pro were designed with a factor of safety of 8 or a factor of safety of 10, then the smallest nut that would be certified by OSHA might be the size of a brick with steel cables the size of your thumb and the size of the smallest cam might be a Valley Giant 18-inch [which is far far larger than a Camalot #6] but with metal parts at least 4 times thicker than they are now]

an ideal cam placement includes but is not limited to -

stem pointing to the ground,

head perpendicular to the stem,

sufficiently long sling to prevent cam being lifted while the climber climbs up past the cam placement,

space vertically above the head so that the head is not "bottomed out" against rock,

relatively smooth inside walls of the crack without nubbins, rugosities, etc which might impair the cam's ability to freely rotate

cam placements are less than ideal if they include -

flared crack which flares from thinner at the head of the cam and is wider near the bottom of the stem, as a flared crack changes the contact angle of the cam lobes surface to the rock surface which changes the physics in such a way as to generate increased camming forces when the cam is loaded (whether loaded dynamically from a lead fall or loaded somewhat less dynamically when bounce testing while aiding) and these increased camming forces can - deform cam lobes or break cam lobes, deform the cam's axle or break cam's axle, pulverize rock - any of which can result in the placement failing

stem of cam not pointing to the ground [which can easily happen as the climber begins to climb after making the placement when they climb up past their placement and their rope gently lifts the cam by rotating the cam's head orientation in the crack, which is why using a full length 24-inch runner is a great idea because it almost fully limits the possibility of this happening] then as the cam placement is loaded, the stem will be loaded first and since it's not in the direct of fall [it's not pointed to the ground] the stem will transmit the force as a torque force to the cam head, the stem will cause a rotational force on the cam head that will both try to rotate out and down on the pair of lobes closer to the face of the rock and also try to rotate in and up on the pair of lobes further back in the crack, there are at least 2 main concerns when the stem of cam is not pointing to the ground -

#1 the cam head is able to rotate and then maybe the cam lobes are in a narrower section of rock and the cam is fixed [yes, it holds the fall and that is very good, but now the piece is fixed and you cannot get it out] or maybe the head rotates and now the cam lobes are in a much wider section and the cam fails because the lobes are bent backward [except the Black Diamond cams with double axles may hold when the lobes are fully open, but depending on the exact situation the BD double axle cams may also fail in this position due to many other specific variables]

#2 the cam head is not able to rotate, this can happen when the crack becomes smaller where the cam is trying to rotate into, this can happen when there are nubbins or rugosities inside the crack that the lobes get hung up on their lateral edges / faces during cam head rotation [much more likely to happen to Omega Pacific Link Cams when they are deployed in the tighter 1/3 of their working range because of the unfolded outer link or the unfolded 2 outlinks getting caught up on the nubbins, etc while the center of the cam head is trying to rotate], when the cam head is not able to rotate, then in the case where nubbins, rugosities, small edges, etc are in the way, there will be forces applied to the side faces of the lobes that the lobes were never designed to deal with and the lobes may bend, the lobes may break, the axle may bend, the axle may bread and in any of these cases the placement may fail

stem of cam not pointing to ground when the crack is bottoming, this is when the cam cannot be placed with stem pointing to ground because the crack is not deep enough to place the head of the cam slotted straight in, it's when you try to slot the cam axle parallel with the ground but the last lobe doesn't get inside the crack because the crack is not deep enough, and so you place the cam with the stem lifted up slightly so that all 4 lobes can get inside the crack, and the problem with this is that the head of the cam is not able to rotate into the line of fall because the head of the cam that is buried at the back of the crack is up against the back of the crack, this will place most all of the total force of the fall onto the outer pair of lobes and since the inner part of the head is not able to rotate because it's touching the bottoming crack then the stem of the cam will continue to load the head in a rotational way which is not in-line with the lobes and so the outer lobes will be supporting a majority or most all of the load force and the load will include an extra force of rotation which the lobes were never designed for, this may cause deformation of the lobes since only 1 pair are handling the majority of the total lode, it may cause the lobes to break due to severe loading and / or due to the rotational force, it may cause deformation of the axle or destruction of the axle, any of these may result in the placement failing

Wild Country Zeros are cams whose stems are fully flexible, they are the only cams with such stems. They are also 1 of only 2 types of cams whose flexible stems are flexible bending "front" and "back" which is useful for horizontal cracks and also flexible bending "side" to "side" which is useful when placing the head vertical to the ground such as in a very shallow crack.

CCH Aliens are cams with a very short rigid stem and most of the stem is somewhat flexible and the flexible part of the stem is flexible in "front" to "back" bending for horizontal placements and flexible in "side" to "side" for shallow cracks with the head in a vertical position, the axle pointing to the ground.

Metolius Master Cams are very similar to the CCH Aliens with a very short rigid stem on the cam head and then a flexible cable.

Black Diamond C3s I have no experience with but I believe the stems are somewhat flexible, but only flexible in the "front" to "back" and not very flexible in the "side" to "side".

All other cams have less flexibility in their stems than these 3 cams, and the degree of flexibility does vary quite a bit.

Wild Country Friends [not Tech Friends] are perhaps the only well known cam that have inflexible stems, they do not bend as they are solid metal bar.

With a very flexible stem, some degree of extra safety [completely untested and unknown in specific values of forces to anybody] may be had in that the cam head when placed in a position where the axle is not parallel to the ground, the cam head will see far less rotational forces from the stem. If you were to compare a Wild Country Zero cam with a Wild Country Friend cam, each placed with the axle pointed to the ground and the head for any reason fixed and unable to rotate, you will quickly see that the rigid stem of the Friend will place significant rotational force, torque, on the head, whereas, the Zero cam stem is fully flexible right up to the head unit and so the torque applied to the vertically aligned head would be smaller, much smaller.

other non ideal cam placements include but are not limited to:

one pair of lobes is cammed tightly and the other pair of lobes is cammed loosely

when speaking of a cam placed in a flare, understand that flare does not need to be the overall description of the crack, the crack may be nearly parallel sided, but perhaps there is some gentle undulations on each wall, there could be a situation where the exact place you leave your cam, the cam's experience is that it's in a flare, even though a quick eyeball of the entire overall area of the crack is that is more or less parallel sided, this is a subtle example of a "local flare" and occurs in my experience more often than rarely [i don't place my cams in "local flares" at least, i try to ascertain if it's a local flare, but i'm saying that i see this phenomenon of a "local flare" more often than rarely]

And, from Omega Pacific:

What was revealed was interesting, but not necessarily revolutionary: well-placed gear holds better than compromised placements and the difference between “good” and “bad” placements can, sometimes, be extremely subtle. The idea that you can simply stuff a cam into a crack and assume it’s good is a dangerous one. We used to call it “Nutcraft” when we studied the nuances of how passive pro interacts with rock and climber and I think “Camcraft” is just as important, even if it's not always obviously so.

One interesting thing we noted was how important "setting" the piece was. A simple tug on the [cam] before it's loaded made a difference in whether the [cam] held or popped. Even some compromised placements that were spit

So, tugging on your gear, including your cams, helps to "set" the piece and this is a good thing. Uhm, but passive pro doesn't need gnarly tugging, be kind to your second.


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PostPosted: Wed Jul 13, 2011 4:42 pm 
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PostPosted: Thu Jul 14, 2011 8:10 am 
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Longshanks
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