Next Return

Charlton Lever Cam

Mounted on Gibbs Ascender Side View of Cam
Mounted on Gibbs Ascender Open for Rigging
Side View of Cam
Top View of Cam Bottom View of Cam
Open for Rigging
Top View of Cam
Open for Rigging
Bottom View of Cam

Technical Details

Jim Charlton described his lever cam in the January 1978 NSS News. I made my Charlton Lever Cam in 2008.

I made my cam by milling a piece of 6061-T6 aluminum plate. This Charlton lever cam is 43 mm. tall, 156 mm. wide, 15 mm. thick, and weighs 102 g. I used Figure 41 from Bob Thrun's book Prusiking as a pattern for the cam face, following the R=0.75+0.0075Ø [inches] formula given in the caption as the later Gibbs cam formula. I scaled the handle dimensions from photographs in Charlton's article.

The cam face on the Charlton Lever Cam is smooth with a groove running down the center.


Charlton describes his cam as having an involuted surface. Whether this is technically accurate or not, the spiral I used is a close approximation. Charlton discusses how this allows "short creeping rappels into the primary rappel device," but warns about scenarios that can cause "total catastrophic release." I agree completely: do not even think about using this as a rappel device.

What do I think of it as a rappel safety? Anyone reading my site long enough knows that I dislike rappel safeties for a variety of reasons. I'll pass on the Charlton Lever Cam as anything more than a historical curiosity, but in that regard, it (or something very similar) inspired the IMO extension Extension Arm.