Front View: Closed

Open for Rigging

Top View, Partially Open

Technical Details

Lang Brod designed the Cam Box and described it in Nylon Highway 23 in 1986. His article included mechanical drawings showing its construction. Bob Danielson made this mirror-image copy shortly thereafter, and gave it to me at the 2000 NSS Convention.

My Cam Box is 89 mm. long, 172 mm. wide, 35 mm. high, and weighs 504 g. The front of the cam box is hinged, and swings open to reveal two channels. One of these is plain, and accepts the long foot ascender sling. The back plate has 52 mm. tall vertical slots for attaching the box to a chest strap and 27 mm. wide horizontal slots for attaching shoulder straps.

This is a noncommercial device with no manufacturer markings.

Comments

There are no pulleys in the design, so when the box is closed, the weighted sling drags on the inside of the cover. This provided substantial drag (not to mention requiring a strong and smooth cover). The main rope channel is turned sideways, and a Jumar cam holds the rope in position. I'm not sure that the cam is really needed for a Mitchell system- although it appears to be a safety feature, if for some reason the ascender slings should break, the user will find themselves suffocating while hanging in the chest harness rather than splattered at the base of the drop. This can be addressed by a sling from the box to the seat harness but I've never been able to get such an idea to work well for me. (I tried this idea with the Tomer #14 and #15 boxes in a Pygmy system. It didn't work because sitting down contracts the abdomen. The Mitchell System would do the same). Lang used this box for a pseudo-frog system, not a Mitchell system, so he already had a sling to the seat harness. His foot ascender sling went through the box instead of remaining free as in the standard Frog.

I don't like the fact that opening the front of the box frees the long foot ascender sling. I prefer a box that can be detached from the main line while still holding that sling in place.

The cam box is solid and unlikely to fail, but it is also the heaviest box in my collection, and for that reason alone I would choose another. At the very least, liberal use of a milling machine (such as on the Tomer #12) could remove a substantial quantity of excess aluminum, cutting the weight while still maintaining a strong design.