Editing Spring-loaded camming device

{{short description|Piece of rock climbing or mountaineering protection equipment}}
{{redirect|SLCD}}
[[File:Klim friends.jpg|thumb|A selection of spring-loaded camming devices of differing sizes]]
[[File:Creeks Giving - Climbing in Indian Creek, Utah - 29.jpg|thumb|Climbers often carry a large number of cams on traditional climbs.]]

A '''spring-loaded camming device''' (also '''SLCD''', '''cam''' or '''friend''') is a piece of [[rock climbing]] or [[mountaineering]] [[Protection (climbing)|protection]] [[Climbing equipment|equipment]]. It consists of two, three, or four [[Cam (mechanism)|cam]]s mounted on a common [[axle]] or two adjacent axles, so that pulling on the axle forces the cams to spread further apart. It is then attached to a [[sling (climbing equipment)|sling]] and [[carabiner]] at the end of the stem. The SLCD is used by pulling on the "trigger" (a small handle) so that the cams retract together, then inserting it into a crack or pocket in the rock and releasing the trigger to allow the cams to expand. A pull on the rope, such as that generated by a climber falling, will cause a properly placed SLCD to convert the pulling force along the stem of the unit into outwards pressure on the rock, producing massive amounts of friction and preventing the removal of the unit from the rock. Due to the large forces exerted on the rock when an SLCD is fallen on, it is very important that SLCDs are only placed in solid, strong rock.<ref name="freedom">{{cite book | edition = 7 | editor = Cox, Steven M. |editor2=Kris Fulsaas | title = [[Mountaineering: The Freedom of the Hills]] | publisher = The Mountaineers | isbn = 0-89886-828-9| location = Seattle | year = 2003}}</ref>

==History==
[[Vitaly Mikhaylovich Abalakov|Vitaly Abalakov]]'s invention of the Abalakov Cam was the first application to climbing of the principle of a cam to climbing equipment. His cams were sections cut out of a pulley wheel and bear a remarkable resemblance to today's [[tricam]]s. Since these shapes were eccentric, the intercept angle of the cam changed as the cam rotates and expands.

In 1973, [[Greg Lowe]] filed for a patent for a cam that had a "constant intercept" angle. Using a [[logarithmic spiral]]<ref>{{cite book|url=https://books.google.com/books?id=jpcXCRMyDGwC&q=Abalakov+Cam&pg=PA44|title=The Climbing Dictionary: Mountaineering Slang, Terms, Neologisms & Lingo: An Illustrated Reference|author=Matt Samet|publisher=The Mountaineers Books|year=2011|isbn=978-1-594-85503-0|page=44}}</ref> shape resulted in a uniform angle between the rock and each lobe of the cam; this constant angle is designed to always provide the necessary friction to hold a cam in equilibrium.<ref>[http://www.duke.edu/~mak25/research.html Duke SLCD research] {{webarchive|url=https://web.archive.org/web/20081025052215/http://www.duke.edu/~mak25/research.html |date=2008-10-25 }} retrieved (2009-08-05)</ref> Designed so that a load produces a rotational force, the logarithmic cam shape allowed for a single device to fit securely in a range of crack sizes.

Modern SLCDs were invented by [[Ray Jardine]] in 1978 (US patent 4,184,657)<ref>{{Citation
| last = Jardine
| first = Raymond D.
| title = United States Patent: 4184657 - Climbing aids
| access-date = 2009-12-21
| date = 1980-01-22
| url = http://patft.uspto.gov/netacgi/nph-Parser?Sect2=PTO1&Sect2=HITOFF&p=1&u=%2Fnetahtml%2Fsearch-bool.html&r=1&f=G&l=50&d=PALL&RefSrch=yes&Query=PN%2F4184657
}}</ref> and sold under the brand name of "Friends". Ray designed a spring-loaded opposing multiple cam unit with a more stable 13.75 [[degree of arc|degree]] camming angle and an innovative triggering mechanism. (The term ''friend'' is widely used by climbers to refer to SLCDs in general, but properly speaking it refers to the brand popularized by [[Mark Vallance]] and manufactured by [[Wild Country (company)|Wild Country]]). Other popular brands include [[Black Diamond Equipment|Black Diamond]] [[Camalot]]s, Metolius Power Cams, DMM 4CUs, Trango FlexCams, and CCH Aliens.

==Modern use==
[[File:Camalot_number_6.JPG|thumb|right|Use of a cam in a large crack]]
The invention of SLCDs revolutionized rock climbing because it meant that parallel and flaring cracks could be easily protected. Furthermore, unlike [[piton]]s, SLCDs can be removed easily without causing damage to the rock, which made [[clean climbing]] (climbing without damaging the rock) practical on many more climbs. Since the invention of the Technical Friend (that replaces the original one-piece [[machining|machined]] alloy shaft with a [[brazing|brazed]] assembly incorporating a length of thick [[stainless-steel]] cable, which is better able to cope with loading over an edge), there has been a great deal of development of the SLCD by a variety of manufacturers. For example, the adoption of the dual axle design by Black Diamond, the invention of three-lobed camming units to fit smaller cracks, and the more recent invention of the Link Cam by Omega Pacific, a design that allows one SLCD to span an even larger range of crack sizes. SLCDs are sold in various sizes to fit a diverse range of cracks from about {{convert|6|-|300|mm|in|sigfig=1}} wide, though devices of below about {{convert|10|mm|in|sigfig=1}} or above about {{convert|100|mm|in|sigfig=1}} are not often seen. To fit non-parallel cracks, there are SLCDs with asymmetrical "offset" cams and devices that expand the lobes independently (Totem Cam).

[[Traditional climbing|Traditional climbers]] frequently climb with numerous and variously sized SLCDs to cover a wide range of crack sizes, often having multiples of the same size, depending on the protection requirements of the climb. Some popular climbing areas like [[Indian Creek (climbing area)|Indian Creek, UT]] have extremely consistent feature sizes that require climbers to carry double-digit numbers of the same size SLCDs to properly protect a route.

==References==
{{reflist}}

==External links==
{{Commons category|Spring-loaded camming devices}}
*[http://web.mit.edu/custer/www/rocking/cams/cams.body.html Elastic Model of SLCD Holding Power]
*[http://www.vainokodas.com/climbing/cams.html Engineering Principles Used in the Design of Camming Devices]

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[[Category:Climbing equipment]]
[[Category:Mountaineering equipment]]
[[Category:Soviet inventions]]
[[Category:Russian inventions]]
[[Category:Springs (mechanical)]]