Spring-loaded camming device
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A spring-loaded camming device (also SLCD, cam or friend) is a piece of rock climbing or mountaineering protection equipment. It consists of three or four cams mounted on a common axle or two adjacent axles, so that pulling on the axle forces the cams to spread further apart. The SLCD is used by pulling on the "trigger" (a small handle) so the cams move together, then inserting it into a crack or pocket in the rock and releasing the trigger to allow the cams to expand. At this point the climbing rope can be attached to a sling and carabiner at the end of the stem.
[edit] History
Vitaly Abalakov's invention of the Abalakov Cam was the first application to climbing of the principle of a constant-angle curved surface, with a cam shape based on the mathematical logarithmic spiral. Designed so that a load produces a rotational force, the logarithmic cam shape allowed for a single device to fit in a range of crack sizes without a change in the loading pattern, making it predictable and stable.
In 1973 Greg Lowe filed for a patent for a spring-loaded version of the Abalakov Cam.
Modern SLCDs were invented by Ray Jardine in 1978 (US patent 4,184,657) and sold under the brand name of "Friends". Ray designed a spring-loaded opposing multiple cam unit with a more stable 13.75 degree camming angle and an innovative triggering mechanism. ("Friend" is now widely used by climbers to refer to SLCDs in general, but properly speaking it refers to the brand now manufactured by Wild Country.) Other popular brands include Camalots, and Aliens.
[edit] Modern use
SLCDs are sold in various sizes to fit a diverse range of cracks from about 1 cm to 15 cm wide. Advertised ranges of dimensions for some commercial lines of cams as of September 2006 (minimum compression of the smallest cam in a product line to maximum expansion of the largest cam): Black Diamond Camalots .78cm to 19.5cm, CCH Aliens .84cm to 5.97cm (approximated), Metolius Cams .85cm to 11.85cm, Omega Pacific Link Cams 2.11cm to 6.4cm, Wild Country Friends .55cm to 19.4cm, Trango FlexCams 1.0cm to 10.8 cm, Valley Giants 14.5cm to 30.5cm.
The invention of SLCDs revolutionised rock climbing because it meant that climbs with parallel cracks could be protected. Furthermore, unlike pitons, SLCDs can be removed easily without causing damage to the rock, and made clean climbing (climbing without damaging the rock) practical on almost all climbs.
