A cam is a structure with the shape of a curve with the important feature that it always forms the same angle with it's tangent, at every point of the curve. This curve is called an equiangular curve.
The word "cam" or is used in calimbing lingo as a generic name for all SLCD (Spring Loaded Camming Devices). Similar curves are used in other devices as the RescueScender, the Ropeman, in Tricams etc. The cam was first iintruduced into protection and the climbing world in the 1930's by the Russian alpinist Vitaly Mikhaylovich Abalakov. Abalakov made a few other developments, includiung the Abalakov, obviously called after him.
All cams are built along the line that is a part of a spiral, one that circles the center, moving outwoards while at the same time keeps a constant ange with its tangents (a more detailed description can be found on the equiangular curve page). This is the basic form of all cams. In Wild Country Friends, for example, the force is applied along a line leading from the spiral focal point to the contact point of the friend with the rock. This point is on the crack wall. Since the crack wall is a tangent to the cam's curve, the angle, and thus the force, remains constant for every crack size. The three lower figures show a cam in differnt size cracks. It is obvious that the angle remains constant (arrows point at the contact point).
The angle remains constant because this is how we built the cams in the first place as an equiangular curve. This angle determins the direction of the force, which in turn determins the friction. If the ange is constant, so is the friction. That means that given the same load, the cam will have the same friction independent of the crack width. So, a Friend will have the same holding power in thin and wider cracks, a Rescuecender will hold similarly on small diameter and larger diameter ropes. Furthermore, the biger the load, the more the friction. In other words, It will hold "better" with bigger loads, as ong as the friction is larger than the load.
The base angel of the curve (that's the angle between the curve and the tangent), determins two things:
- The ammount of friction and the holding power of the cam. The smaller the angle, the more friction you get.
- The range of crcks the device will be good for. The larger the angle, the greater the range.
A cam with marginaly larger angle than 90° will have excelent grip but almost no Range at all.
Contributions to this page were made by Mica Yaniv and others...