Horton H. Hobbs III described the spooled brake bars in Nylon Highway #25 in 1988, but he attributes the design to Buddy Rogers in early 1970. I made my pair in 2004, with some slight changes to the design to suit my own preferences.
Instead of making an entire rack, I used one of my existing racks (Storrick, Version A) and replaced the first and fifth bars. I will not describe the rack frame or other bars here.
I turned the top bar from 1.25" (31.9 mm) 6061-T6 rod. There is a two-groove spools on one end of the rack (13 mm. semicircular grooves) and a 16 mm. carabiner hole on the other end. The rack in Horton's article appears to have a 19 mm. bar diameter, but I followed Horton's recommendation and made mine 25 mm. I also included ideas from Ed Seaman's brake bar design (Nylon Highway #9) and included a turned groove to keep the rope centered.
The lower spool bar has only one groove and no carabiner hole. I made the bar portion 19 mm. in diameter. The resulting bar weighs 69 g.
Horton showed a five-bar rack in his article, but I included a sixth bar for better control. Of course, this eliminates much of the reason for having the spooled bars in the first place, since the upper spool was designed to increase friction on rappel. Not only do they provide a greateer braking angle, but looping the rope over the top spool tends to lift the lowest engaged brake bar, providing the same "power brakes" effect that one has with the J-Bar. The spools can also be used to tie off. If one follows the pattern laid out in Horton's article, the lower spooled bar should be in the fifth position, not the sixth, so that the rope acts to close the bar.
The carabiner hole allos one to clip a chest harness to the bar to keep from falling over backward on rappel. This is not strictly necessary, since one could also clip to the rack frame. A better solution for many people is to go on a diet and lose upper body weight.
I relieved the unstressed side of the bar holes so that they would pivot on the back side of the rack frame. This reduces the likelihood of them bars being knocked loose.
The spool bars add over 100 grams to the rack. The top bar is particularly heavy - about 128 g, similar to many Figure Eights. Worse, the bars make the rack considerably wider, which makes it more difficult to pack. Ironically, one of the benefits of spooled brake bars is that they allow shortening the rack by one bar to save weight and bulk. There is a tradeoff, and each person can form their own opinion, but mine favors a standard rack.
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©2007, Gary D. Storrick