On Friday, December 18, 2020 at 9:45:04 AM UTC-5, Stuart Venters wrote:
... a maximum acceptable rope strength

This is a bit of thread drift, but I think this is the elephant in the room and warrants a bit of discussion. The weak link has a mandated maximum strength, which means that non-destructive testing can't tell us much about it.. If we test to destruction, we learned about the rope, but we also broke it in the process. Whoops.

With non-destructive testing, the most we can say about the weak link is that it will fail at most at 110% of the rope's rated breaking strength. This isn't very comforting, especially for life-saving gear which sees years of field service.

So without effective testing, we have no way of knowing if the safety system will perform as advertised, unless we can 1) precisely bound the upper breaking limit and then 2) somehow test the minimum breaking strength.

With this in mind, one possible solution is to use stitches to precisely calibrate the breaking load. Climbing gear companies do this in order to reduce the shock from falling: https://youtu.be/ABMLFed7TcE. The number of threads is linearly related to the breaking strength, so you can fine tune it to a great degree.

So a weak link could be made by simply stitching webbing together and then protecting the stitches from abrasion. However, the precision required means this is not something which can be done outside of controlled conditions. While I could do a great job on my home sewing machine, I could also do a crappy job. It's like repacking a parachute, anyone can do it but who do you trust to do it correctly?

In contrast, splicing onto thimbles has the nice feature of being something we can do at home and get very similar results to the professionals.