Editing Spring-loaded camming device (section)

==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.