Choosing and Placing Cams (Camming Devices) when Rock Climbing
Camming devices are an invaluable tool for protecting rock climbs, but choosing cams for your rack and using them in the safest most effective manner requires both experience and a bit of back ground information.
We'll start by splitting cams by size i.e. there are micro cams (cam range maxing out around 2.0cm) and mainstream cams (cam range from 2.0cm upwards).
Mainstream cams can themselves be split into 3 main types: single stem, dual stem and double axle.
Aliens ruled the micro cam universe until recently when a continuous series of product failures has seen them being boycotted by climbers.
The success of the Alien was a largely due to a remarkable stem that allowed the lobes to be retracted easily and yet remained exceedingly flexible in all directions. Add to this a very narrow head width, durable construction and soft alloy lobes for extra bite and the result was an awesome micro cam that nobody else came close to challenging.
The picture to the left shows an Alien in a typical placement - a very small pocket - and the ease with which it bends into line with the applied load. A stiffer stem would not bend as easily and could possible apply a levering force to the cams twisting them out of the placement before they had time to engage fully with the rock.
There are many other micro cams - probably the best are the Wild Country Zeros and the Metolius Master Cams.
The Zeros are pretty good; the original models were too short, but that has been rectified now and they have a good flexible stem with a long reach.
The Metolius cams look very good, but the flexibility of the stem is slightly restricted in one plane plus - for UK use at least - there has been some silly penny pinching done on the axle termination as it has been made from carbon rather than stainless steel and the unit seizes up remarkably quickly when used in salty conditions and not cleaned/lubricated.
The other unit that is widely available is the Black Diamond C3, but despite having an impressively narrow head width the stem is far too stiff for this to be recommended.
Micro cams may seem like a luxury when you are starting out, but they are amazingly useful and end up being used just as much as any other cam on my rack. I tend to carry 3 Aliens as my micro cams - the blue, green and yellow - and am just hoping that they don't wear out....
The picture on the left shows a typical micro cam placement in a thin seam - nothing else will go in anywhere along the seam, not even RP's, but a small rock fracture allows this great placement.
There are lots of factors to weigh up when choosing cams apart from their underlying method of construction - weight, camming range, camming angle and variability of camming angle head width, head material + finish, stem flexibility, versatility of the trigger system.
The end objective is simple: protecting a climb as well as possible whilst carrying as little weight as possible; the problem is the lighter units tend to be single axle units with a lower range, whilst the units with larger ranges are relatively heavy. So the question arises - carry a greater number of lighter units with a more restricted range or less, heavier units with each one having a greater range. There is no correct answer and your rack will be built on individual preferences and personal experience. My personal preference is to use light, single stem cams on long routes because having more units means I am able to sew up routes more thoroughly.
A - Weight: Obvious, but lighter is better if it has not compromised safety. Cams are relatively heavy and saving the grams here is critical to keeping your rack light.
B- Camming Range/Angle: Climbers naturally want as much range as possible on each cam so that they cover a wide range of placements. There are several ways of doing this - the simplest method of increasing the range is done by increasing the camming angle, however increasing the camming angle decreases holding power. The generally accepted compromise is that 13.75 degrees offers the best balance between holding power and range.
DMM and Wild Country use this angle, Metolius admirably put holding power first on a lot of their cams and use a lower camming angle.
The other methods involve adding/offsetting axles and cams - the Black Diamond Double Axle C4 Camalots are the most popular big range cam and are very good. The previous generation of Camalots were really far too heavy, but the C4's are a lot lighter. The camalots do seem to still be a bit greedy on camming angle - a study in October 2008 calculated they were using an angle of 14.6 - 14.9 degrees and BD themselves reckon they use 14.5 degrees.
C - Head Width: A narrow head width can be useful at times so that the cam can fit into pockets or pods, but this is generally more relevant to smaller/micro cams. Conversely it is also important not to make larger units too narrow and to to keep the range / width ratio within certain parameters otherwise the unit becomes unstable. One way of reducing head width is to use three rather than 4 cam lobes.
The image to the left shows a typical 3CU placement in a small pocket that would not take a standard 4 lobed unit.
D - Head Material/Finish: Using a softer alloy for the cam lobes can improve grippiness and is a potentially advantage on smaller cams (i.e. Aliens), but on larger cams there is greater risk of cams collapsing if the material is not strong enough - especially if you want to reduce weight and panel the cam lobes. Thus most larger cams use 7000 series aluminium alloy whilst smaller cams can potentially use a softer, weaker 6000 series alloy.
In all cases I always remove any anodising from the biting faces of the cam lobes as this seems to improve its holding power.
E - Stem Flexibility: This roles into the single / double stem argument quite well.
Wild Country Friends are single stem units - see left - whilst DMM 4CU units are double stem units - see right.
These units are good to compare because they both use exactly the same cam lobes as they are both manufactured by DMM. In my experience there is not much difference in versatility, action or holding power in sizes 1.0 upwards. Under size one I prefer a flexible single stem device such as the Alien or the larger WC Zeros. Even the standard single stem devices tend not to work optimally here because the axle terminations are often too long.
I find both units easy to operate with and without gloves and equally good as each other in both shallow horizontal and shallow vertical cracks.
Shallow crack placements are the key test of any cam because this type of crack often does not allow the stem of the cam to be orientated in the direction of a potential fall. In this situation a cam should ideally be able to bend freely into the plane of the fall to avoid any leverage being imparted onto the cam head.
The images of the grey DMM 4CU show a good placement in the LH image with the stem running parallel to the rock face. The key thing here is to extend the cam so that the rope does not move the cam from it's optimum position - the double sing system on the DMM cams proves very useful here and also saves on quickdraws.
The actual cam head placement in the RH image is good, but the stem of the cam is sticking out a long way from the rock - it is in this situation that you need a flexible stem that will bend with the load rather than lever the stem - if the frame/stem can not bend then the stem could be damaged or the cam lobes could be levered out of the placement.
The third picture shows the cam under load - the cam frame is flexible enough to distort and the axle terminations are short enough not to suffer a levering moment. Perfect.
Older cams often had solid stems - these have the advantage that are very durable, but they are generally poor for shallow horizontal placements, because the stem sticks out too far and will be either bent in a fall or will lever the cam out of the placement. In this situation it is good to be able to tie off the cam close to the head - as in the image to the right.
It is also worth bearing in mind when placing cams that they are handed i.e. the cams on one side of the head are closer together than on the other side. This allows the security of some placements to be altered radically depending on which way round the cam is placed.
In the pictures below the same cam has been placed in the same pocket, but in one orientation (right hand image) only 3 of the cam lobes engage with the rock creating an unstable placement.
However you only have to turn the cam through 180 degrees and all 4 cams engage and the placement becomes good.
In this placement a 3CU with a narrower head width would also have fitted well. The right hand image also shows the relatively short axle terminations on the 4CU. Short axle terminations are good because they are less likely to suffer bending damage, allow the cam to flex more easily and allow more load to be directed onto the head in a direct line.
In general when placing cams you should have each side of the cam evenly closed and the cams in the completely closed to 3/4 closed position. The cam will still normally hold well in the completely closed position, but if you push an over-cammed cam in too far then you may well have trouble getting it out later.
The image of the green 2.5 cam in the horizontal break shows a cam that has been placed well - both sides are evenly closed, the cams are in the mid position and there is plenty of contact with the rock. Thus even with the break being slightly flared the placement is solid and would hold in most falls.
The next size up - a DMM 4CU 3.0 fits into the same break but needs to be over-cammed to fit. This does not affect the security of the placement, but could lead to problems removing the unit if the break was deep and the cam walked further in - in this case the crack bottoms out almost immediately and so this is not a problem.