Storrick, Version C,

with Rack Chock

Installed on Rack

Side & Top Views

Technical details

I made my rack chocks in February, 2005 from a piece of 316 stainless steel. My rack chock is 15.5 mm. thick and sized to tightly fit the rack frame. Instead of making a new rack, I used one of my existing racks (Storrick, Version C) and to demonstrate the rack chock. I will not describe the rack frame or other bars here.

I made my pair of rack chocks, as follows:

Turn and face a disk to the desired thickness
Drill and tap a small central hole to allow bolting the disk to a stub mandrel
Turn a U-shaped groove in the disk's circumference, sized to fit the host rack
Chuck the rack chock in a 3- or 4-jaw chuck, bore the central hole to size (about 13 mm. for 11 mm. rope), and round the edges
Saw the disk in half to get two rack chocks
Use a rat-tail file to groove a rope path on one side of the rack chock

Once I installed the rack chock, I used a hammer to crimp the groove closed on the rack frame to keep the rack chock from falling out.

Comments

I have to thank Warren Anderson for bringing the Rack Chock to my attention. He sent me an email saying,

In about 1980 a bunch of us were exploring some alpine caves in Wyoming including Columbine Crawl. I think that a caver from Idaho Falls named Rick Rigg invented this device - at least he had a friend that owned a machine shop and manufactured these. Most of us used this device in those days. It's a doughnut turned out of hard steel and then sawed in half. It's quite abrasion resistant. This one has been in my rack since then and has never worn out. The great things about it are that it effectively makes your rack longer and that it centers the rope. ...[T]he rope goes through the notch in the chock. On my rack this makes it about 7/8" longer.

This is a really wonderful invention. I've always been surprised that it hasn't caught on or that someone else hasn't thought of the same idea.

What surprises me is that Rick Rigg is the caver that got me into the NSS back in 1971. He and I caved together in Wyoming around 1980 as well, but I don't remember seeing his rack chock. Perhaps I saw it and just forgot?

Warren is correct about the rack chock wearing well, and about its effectively making the rack longer. One down side of the rack chock is that stainless steel is not a great heat conductor compared to aluminum. I may make an aluminum version someday to test it for wear. Another, more serious defect is that it is only designed for single-line rappels. Of course, if one needs to rappel a doubled line, they can simply bypass the rack chock.