Author Topic: JRB Hitch, a secure, quick release hitch  (Read 9586 times)

agent_smith

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Re: JRB Hitch, a secure, quick release hitch
« Reply #45 on: August 31, 2021, 03:16:23 AM »
Hello John,

I've attached an image of another longitudinal test rig.
This test rig does not require a tractor.
But, you will need a lever hoist (probably at least 3 ton capacity).
Just in case you don't already own one... Link: https://www.safetyliftingear.com/news/post/what-is-a-lever-hoist

If you're going to do this type of testing on a regular or ongoing basis, I recommend that you purchase a load cell.

The Rock Exotica 'Enforcer' load cell is good BUT, it only is rated to 20kN.
This fine for smaller scale cordage, but not for 11mm class ropes.

I've ordered (and am still waiting) the new Linescale 3 load cell.
Link: https://www.linegrip.com/linescale-3/

They aren't cheap - but, you will have the independence to run your own tests and make measurements.

You've asked about sourcing test labs - I think they will be a waist of your money (and time).
If you do find a commercial test lab, they will simply follow the usual mindset of 'pull-it-till-it-breaks'.
This doesn't tell you much.

In your case, testing should investigate things like:
[ ] stability in various loading profiles (eg longitudinal verses perpendicular loading profiles)
[ ] jamming threshold (indeed, you will likely declare your JRB hitch to be jam proof)
[ ] EN892 versus EN1891 (type A) ropes - and differences in how the JRB hitch performs
[ ] mapping observed damage points to location within your JRB hitch
[ ] security and stability when subjected to slack shaking, cyclic loading. and vigorous pulse loading
etc etc

Generally speaking, at least 5 tests need to be repeated to collect a reasonable sample size.
Remember, when conducting MBS yield tests, always test in pairs (ie 2 identically tied knots).
You will always have one 'survivor' knot specimen to closely inspect.
You will know that the 'survivor' knot specimen was loaded right up to its MBS yield point.

Make sure that you eliminate as many variables from your tests as possible.
Things like diameter of the timber host and its roughness are all variables that you need to control.

...

For perpendicular tests, you should also be able to use a lever hoist between 2 pine logs.
Anchor each pine log securely (eg bearing against steel post concreted into the ground).
The 2 pine logs are oriented parallel to each other - the lever hoist in-between.
JRB hitch tied on each pine log.
No tractor required (refer image below).

The reason I suggest pine logs is because it eliminates a variable (roughness).
It will be easy for other testers around the world to try to repeat your results - because pine logs are common/universal.
What you want is a repeatable test.

EDIT NOTE:
If you do use a load cell, you will need to protect it when performing MBS yield tests.
There might be some recoil - and you don't want your expensive load cell getting damaged.
I normally encase my load cell inside clear bubble wrap so I can still read the LCD screen.
I also attach a leash - to limit any momentum/recoil effect.
« Last Edit: August 31, 2021, 03:20:07 AM by agent_smith »

JRB

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Re: JRB Hitch, a secure, quick release hitch
« Reply #46 on: September 30, 2021, 03:14:43 AM »
Agent Smith,
I have not forgotten about our conversation here, just entertained with other things lately... I may create a new thread soon with a friction hitch I have been working on....

But back on topic, after some debate with myself about how much I will use it, I have ordered a Linescale 3.

I also have procured two sections of wooden utility poles, a strong, cylindrical host, that should be quite uniform and readily available at any location.

As for the prescribed test, I feel that there is a problem with what you pictorially depicted: You show a JRB hitch tied to two fixed anchors and a pulling force created between the two. The problem is that I would need something STRONGER than the JRB HITCH in order to tie the other ends of the rope to the pulling device and the scale.  I did a test like this before and the JRB Hitch broke a scaffold knot tied to the rigging hardware, twice.  I am not aware of anything that will reliably survive more tension than the JRB Hitch.  I realize that a tensionless hitch is considered nearly 100% efficient, but it would require a large diameter cylinder and some rigging I don't have in order to attach it to a scale and a strong enough winch, which I also don't have.

I am attaching a crude diagram, depicting a test that I believe I can safely rig and execute, basically making one host fixed and one host pulled, with the scale outside rather than inside.  Of course, the tension should be the same up until the break point. I heed your warning about protecting the scale... and have not pictured any necessary restraints for doing so.  Comments?

Lastly, I saw the standard certifications you cited for static and dynamic ropes, but do you have a recommended rope that should be used?  Brand and product?  I can foresee this hitch being used with static or dynamic ropes and for a variety of purposes, and so although I would tend to prefer a static rope in my own applications, I am comfortable testing either.

« Last Edit: September 30, 2021, 06:30:49 PM by JRB »