Front	Rear

Technical Details

Eric Thunberg made this eight for me in 2014.

This eight is CNC milled from 7050-T7451 aluminum alloy. It is 91 mm. tall, 52 mm. wide, and 10 mm. thick. The rope hole is 23 mm. high and 23 mm. wide. The top center thickness is 10 mm. The shaft length and width are 34 mm. and 32 mm., respectively. The auxiliary hole is 18.5 mm. high and 16.1 mm. wide. The eye measures 19 mm. by 16 mm. The ears are 6.5 and 5.9 mm. long. It weighs 58 g.

There are no markings on this eight.

Comments

Eric wrote me with the following request:

I came across your extremely informative website while researching how to create the smallest / lightest emergency rappel kit. I had also purchased NE Ropes’ product, but was disappointed with the weight, packaging, lack of anchor options, and use of 5mm rope. I purchased a spool of their 3mm rope (string as you call it) and have tested it with a backup harness, and while not ideal, it will suffice in an emergency for my weight.

The problem is that NE Ropes no longer supplies their descender which, from what I can find, is the only one that provides enough friction and was specifically designed for 3mm rope. I've been searching on eBay for a while to no avail, so I was wondering if you would a) sell me yours or b) let me borrow it so I can duplicate it in CAD and have it machined for my own use.

Using dimensions from my site and additional ones that I sent, Eric was able to draw the device in a CAD program. He printed a prototype with a 3D printer, and then had a friend of his make two descenders from with a CNC machine. This is one of them. Eric made his out of aluminum, so it is considerably lighter than the original steel device. Eric tested the device and had these comments:

Gary,

I was finally able to do a test today, a rappel down a 15’ granite masonry retaining wall. Unfortunately the device had too much friction with the 3mm tech cord in both wrapping configurations (I tried the pattern for 3mm as well as 5mm).

I had a backup though, and ended up trying the SMC Personal Escape 8 with a double wrap as pictured under the "most friction" label in the diagram. That worked well for my weight (~165lbs) as it took very light pressure to hold my position and the descent was relatively smooth.

The test did reveal significant fraying where the rope went over the granite edge, and my first attempt at a solution was to order some nomex abrasion sheathing (.25" ID) which should hopefully do the trick.

Even though the micro rappel device didn't pan out, it was a fun exercise and I appreciate your help along the way.

Regards,
Eric

Rigged for 3 mm. String

Rigged for 5 mm. Cord