|Front: Cocked||Rear: Cocked|
I made my Safety Rappel Cam in 1976.
My Safety Rappel Cam rig weighs 409 g. Basically, the Safety Rappel Cam is a modified Gibbs Ascender. Shock cord is added to cause the ascender to close (there were no spring-loaded Gibbs at the time) and a metal catch was fabricated to keep the cam open. The catch fit into notches filed into the shell, and a thin cord with a clip attached was tied to the catch. 1.9 m. of 11 mm. Goldline is spliced to the cam with a ribbon eye splice, and then the splice is wrapped with cord and covered with beeswax.
Don Davison developed the Safety Rappel Cam while he was Chairman of the Safety and Techniques Committee of the NSS, and published his design in the August 1976 NSS News. He made kits for sale, and CarolJo Rushin-Elron gave me two of these at the 2016 NSS Convention. One kit was for making one cam, the other for making two:
As far as I know, I am the only person (other than Don) that ever built a Safety Rappel Cam. I did not have one of his kits, so my catch was fabricated differently, the shock cord that I used was larger, and the attachment to the shell was different.
Goldline is a very stiff, tight lay climbing rope, and conventional splices do not work well with it, hence the ribbon eye splice. I can attest that it is a more difficult splice to make than a traditional short splice.
The Safety Rappel Cam was tied to the caver’s harness with the Goldline spliced to the cam. In this manner, the Safety Rappel Cam is independent of the seat maillon. The thin cord was clipped to the caver's chest. The idea was that if the caver fell backward, the cord pull would pull the catch free, and the cam close, stopping the descent.
I don't use a rappel safety myself, for a number of reasons that may or may not apply to other people. Everyone must make their own choice.