Standard Double	Lite Single

Overview

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Standard Double
(#3075)

Front	Rear

Left	Right	Open for Rigging

Technical Details

I made this descender in 2021 using photographs and measurements provided by the original designer and owner, Willie Hunt.

This descender is 207 mm. tall, 142 mm. wide, 71 mm. thick, and weighs 1663 g.

The descender has three 1.5 in. (38 mm.) diameter, 3 in(76 mm) long brake bars that slide on three 3/8-16 x 8" UNC bolts. The top bar is solid, with a milled flat on top for the nuts to seat square and two milled rope grooves in the lower rear quadrant. The second bar has three slots to allow removing it for rigging. A 1/4" x 3" (6.4 x 76 mm) pull pin holds this bar in place. The lower bar has a milled flat on the bottom. Each end of this bar has has 1/2" OD, 1/4" ID (13.7 mm. OD, 6.4 mm ID) bronze bearing press-fit ito a hole in the end. Recesses at each end hold bronze bearing discs.

The bolts also pass through a 1 in. (25 mm.) carabiner bar. Springs between the carabiner bar and lower brake bar force the brake bars together. Two oval carabiners connect the carabiner bar to the harness. The carabiner bar is large enough that these carabiners cannot be removed without disassembling the descender.

Connecting links (1/2" x 3/4" x 3-3/8"; 13 x 19 x 86 mm.) connect the carabiner bar to a handle assembly consisting of 1/2" x 1" x 5" (13 x 25 x 127 mm.) side arms and a 1" (25 mm.) handle bar. Stainless steel pins pressed into the handle side pieces engage the bearings in the ends of the lower bar. Pulling the handle down causes the brake bars to separate, reducing friction. Holes are provided to allow reversing this action by moving the connecting link attachment to the handle sides to above the pressed axle pins.

Comments

Rachel Saker found a photo of the original online, and sent it to me in early 2021. She asked if I knew anything about it, adding, “I've never seen any contraption like that… nor do I recall seeing it on your site.” I hadn't seen this one before, and thus began the journey. Rachel contacted the original poster, Willie Hunt, who shared a photo with the following information:

"… it’s a 3-bar rack with a spring loaded auto-stopping mechanism. The control handle allows the user to adjust the friction from full brake to full speed by pulling down on the handle. It was machined to allow for 2 ropes (pull down) and keep the ropes strand separated. I don't have any mechanical drawing of it anymore that I can find (it was machined in 1992), but I can easily take measurement to document what I did:"

Willie then provided numerous additional photos and descriptions of each part, including the dimensions I needed to make a copy. A few questions from me clarified some of the finer points. After winter ended and after finishing some other projects, I made a copy for myself, following the original design but with some minor changes. Willie's response?

“Congratulations! You have the 2nd one of these that ever existed.”

Several of Willie's comments were easy to verify:

1. “It’s WAY over designed!”
2. “There are a ton of other little details.”
3. “Did I mention it’s HEAVY!”

Others required field testing. Obviously, Willie has more experience with his than I do with mine, but my experience matches his. In his words:

1. “The control bar has an over-center action so it locked open for loading the rope(s). Once released the springs push the bottom brakes bar up squeezing the rope enough to stop any descent with sub 300 lbf loads on 11 mm. rope.”
2. “Much of the friction is the device "squeezing" the rope as opposed to surface friction.”

I'm pleased that there are cavers who are continuing to develop new ideas.

As Willie notes, this descender is over-designed and heavy. While considering ways to reduce its weight, the most important observation is that the side arms and handle assemblies do not support the user’s weight, so they only need to be strong enough to separate the bars for controlling one’s descent. With this in mind, there are several options to make a lighter version. Here are a few of them:

1. Reduce the thickness of the connecting links from the carabiner bar to the handle side arms to, say, 1/8" (3 mm).
2. Reduce the thickness of the handle side arms. These need to be thick near the #3 brake bar because of the tapped holes for the other link and the pressed pin going into the brake bar, but the extension going to the handle could be much thinner. Once again, I suggest 1/8" (3 mm).
3. The handle could be much smaller in diameter.
4. The brake bars could be much smaller. The top and bottom bar could probably be reduced to 1" (25 mm.) without difficulty. The middle bar would probably need to be larger (or made from 1" (25 mm.) plate) to provide room for the push pin.
5. There are various places on the brake bars that one could mill away excess material.
6. Taper the ends of the carabiner bar outside the three main bolts.
7. The long steel bolts could be smaller in diameter, say 5/16" (8 mm).

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Lite Single
(#3183)

Front	Rear

Left	Right	Open for Rigging

Technical Details

I made this descender in 2022 using some of the ideas I had after trying the Standard Double version.

This descender is 182 mm. tall, 101 mm. wide, 38 mm. thick, and weighs 769 g.

The descender has two 7/8 in. (22 mm.)and one 1.5 in. (38 mm.) diameter, 2 in (51 mm) long brake bars that slide on two 3/8-16 x 6.25" UNC bolts. The top bar is solid, with a milled flat on top for the nuts to seat square and a milled rope groove in the lower rear quadrant. The second bar has two slots to allow removing it for rigging. A 1/4" x 2-1/4" (6.4 x 57 mm) pull pin holds this bar in place. The lower bar has a milled flat on the bottom.

The bolts also pass through a 5/8 in. (16 mm.) carabiner bar. Springs between the carabiner bar and lower brake bar force the brake bars together.

Connecting links (3/16" x 3/4" x 2-3/4"; 4.8 x 19 x 70 mm.) connect the carabiner bar to a handle assembly consisting of 5" (127 mm.) side arms and a 1" (25 mm.) handle bar. The side arms are 1/2" x 1" (13 x 25 mm.) at the base and 3/4 x 3/8" (19 x 9.5mm) at the handle end. Stainless steel pins pressed into the handle side pieces engage the bearings in the ends of the lower bar. Pulling the handle down causes the brake bars to separate, reducing friction. Holes are provided to allow reversing this action by moving the connecting link attachment to the handle sides to above the pressed axle pins.

Comments

I made this single-rope version and lightened some of the components. The results were better than I expected. The original weighed 1660 g., while the smaller version weighed 780 g., about the same as many standard 6-bar racks. At the same time, the bulk was reduced by two thirds.

Eliminating the bronze bearings was a considerable weight savings, as bronze is dense. There is room for additional weight savings (e.g., switch to thinner bolts). I'll leave it to others to further develop the design, should anyone have the interest.

While these devices work well, I don't see a compelling advantage over, say, a standard rack.

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