CMI - ROPE JACK

SingleJack

Active Member
#1

The CMI Rope Jack is a Mechanical Advantage tool for pre-tensioning static lines, light lifting and cabling. The Rope Jack is small enough and light enough to be carried aloft by a climber for Mechanical Advantage within the crown. The length of the handle on the Rope Jack limits excessive loading to avoid rope damage.

Under no circumstances should a cheater bar be used to increase leverage as it may damage the unit, the rope, or severely injure personnel. lt is designed to be used by only one individual using one hand only; lt shall be removed before any'shock' load is applied; lt shall NOT be used for heavy or dynamic loads as there are other tools available for those applications. It can attach mid-line and can run virtually any length of rope. The MA is approximately 5:1 - no pulleys, no extra rope, minimum weight, minimum friction, quick, easy on-off, works well 'topside', too. The CMI Rope Jack is used to remove slack & stretch for lowering and to lift the tips on light limbs without having to break out the big guns. It is NOT for heavy loads. Cams, even 'untoothed' like a Rescucender and Gibbs, have been shown to shred a rope with high loading. There are much better tools for the heavy work.

The rope jack is approved for life support use as long as another form of progress capture device is used in conjunction with the device. Never use the Rope Jack by itself for hauling human cargo. The CMI Rope Jack is approved for static ropes from 3/8-5/8" diameters. Testing has shown that a single person can generate somewhere between 300-800 pounds of force while using the Rope Jack. Testing revealed CMI ascenders will strip the sheath of brand new 1/2" rope at roughly 1500 pounds. To remove a load from the Rope Jack, pull the handle and allow the trailing cam to loosen, then pull handle again and allow the forward cam to loosen. Releasing the Rope Jack will take a little practice. The Rope Jack should be relieved from tension a little bit at a time off each cam.
 

Keeth

Active Member
#6
I can see sooo many uses..., and sooo many problems...

In disaster relief I've used a rope puller in the canopy many times and it's always been hassle. This thing will be perfect for those scenarios. However, I can see overloading it happen very quickly.

Do the holes in the handle mean the advancing cam is adjustable? It looks like you could safeguard against too much pull by reducing the MA. Is that what's going on there?

Super cool idea and definite future purchase!
 

TimBr

Well-Known Member
#8
Hey, Jack! Sorry if I haven't been following you on YouTube as much as I maybe should be, but I have a vague recollection of a video you shot while working up in a tree, in which you utilized a similar, but possibly more simply made device. If so, I guess I did not realize at the time that I was looking at a prototype of your own invention.

Congratulations on succeeding at bringing a product to market, if so.

The use I would envision for this device would be to tension up the rope for a speedline while up in a tree. One could put a running bowline around a tree on the ground, and pull the other end up into the tree. With your tool, a climber would be free to move and re-tension the speedline as needed.

Thanks for going to all of the hard work to bring another great product to market. It seems like a few of the members of this particular forum are just thoroughly changing the way arb work is done, all around the world. Too cool, and congrats again.

Tim
 

SingleJack

Active Member
#9
Thanks for the encouraging comments. In addition to the POW vid, I've got plans (time permitting) for videos showing the CMI ROPE JACK in use with: Pull-line, Speedline, Cabling, and AR Pick-off … etc.
… stay tuned & BE SAFE (y)
 

SingleJack

Active Member
#10
I can see sooo many uses..., and sooo many problems...

In disaster relief I've used a rope puller in the canopy many times and it's always been hassle. This thing will be perfect for those scenarios. However, I can see overloading it happen very quickly.

Do the holes in the handle mean the advancing cam is adjustable? It looks like you could safeguard against too much pull by reducing the MA. Is that what's going on there?

Super cool idea and definite future purchase!
The CMI ROPE JACK would be perfect for many applications including "disaster relief". However, when used as directed on the CMI site (http://www.cmi-gear.com/collections/frontpage-new-products/products/rope-jack) it's almost impossible for one person - one handed to overload the rope. The holes in the handle are to reduce weight while aloft and are intended to serve no other purpose. From the testing done by CMI:
"… lt is designed to be used by only one individual using one hand only; lt shall be removed before any 'shock' load is applied; lt shall NOT be used for heavy or dynamic loads …
… Testing has shown that a single person can generate somewhere between 300-800 pounds of force while using the Rope Jack. …"

It can be a useful tool when used in a safe manner for which is was designed … BE SAFE.
(y)
 

Keeth

Active Member
#13
...it's almost impossible for one person - one handed to overload the rope.
I'm a bit hefty in the tree like Oldoak and Simpleiowa. With our body weight alone we could easily exceed 800 lbs with one hand (and I'm probably the lightest and most weak of the three.) We don't intend to exceed limits, it's just a consequence of gravity. I promise I won't overload mine!

After watching people overload everything else in tree work, I know how easy it will be to overload this device as well. The only saving grace is that most of the people that would be prone to do so won't be smart enough to get one in the first place.
 

SingleJack

Active Member
#15


We don't intend to exceed limits, it's just a consequence of gravity. I promise I won't overload mine!

I never doubted your capability … just thought "limits" needed to be restated (y)

Of course, it is possible to overload the rope with the Rope Jack. However, to reach the 'shredding' point listed in the tests by CMI of ~1500 pounds, that would require a ~300 pound pull. That's not something the average person could do with one hand on the handle.
I'm just hoping that most people will appreciate the uses and limitations for the Rope Jack. I want to do my best to make sure if (and when) it does get mis-used, it's not because of any mis-representation on my part.
;)
 

SingleJack

Active Member
#17

Tensioning a Pull-line with the CMI ROPE JACK - a demonstration of the ROPE JACK at 1:1, 2:1, 3:1 & 4:1.

Four Mechanical Advantage techniques are demonstrated using Rope Jack to tension the line. This is just a demonstration of the potential of the Rope Jack for tensioning a line. Detailed Mechanical Advantage instruction is beyond the scope of this video.

Typically, a 100 pound pull of one-person with one-hand on the handle, the 5:1 Mechanical Advantage of the Rope Jack can apply 500 pounds of force directly to a pull-line - well within the load capacity of the cams and rope. When coupled through one pulley at a 2:1 MA, that same Rope Jack force can load the pull-line to 1000 pounds. When coupled through two pulleys at a 3:1 MA, the resulting pull is 1500 pounds. And, When coupled through two pulleys in tandem at a 4:1 MA, the load on the pull-line is 2000 pounds.

The Rope Jack (practical upper limit at 1:1) can apply nearly 800 pounds of force directly to a pull-line. Correspondingly, through a 2:1 the Rope Jack can apply approximately ~1600 pounds; 3:1 = ~2400 pounds; and 4:1 = ~3200 pounds.

Safe use of the Rope Jack is the responsibility of the user. Details can be found at CMI:
https://www.cmi-gear.com/products/rope-jack
 
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D x D

Active Member
#18
I tend to use a come-a-long for many of these applications but that limits me to the length of cable. For pretensioning the cable is usually enough length, however pulling a distance is usually is a pain. Sure I can use a capturing prussic but that is a pain too.

This device could be the best of both. Nice.

I do have a question, when you say no dynamic load, is that a rule or a suggestion? :) For example if I pretension a top that I will let drop, is that ok to still have the device as part of the tension system? I would think yes (but don't know) as the load will be reduced on the system vs. a system that captures the drop.
 

SingleJack

Active Member
#19
I tend to use a come-a-long for many of these applications but that limits me to the length of cable. For pretensioning the cable is usually enough length, however pulling a distance is usually is a pain. Sure I can use a capturing prussic but that is a pain too.

This device could be the best of both. Nice.

I do have a question, when you say no dynamic load, is that a rule or a suggestion? :) For example if I pretension a top that I will let drop, is that ok to still have the device as part of the tension system? I would think yes (but don't know) as the load will be reduced on the system vs. a system that captures the drop.
THANKS
FWIW - IMO:::
Come-a-long … prussic = PITA
"NO dynamic load" with Rope Jack … but I DO NOT (ever) rule - i suggest
I would NOT drop a load (pun intended) with a Rope Jack in the system - But, I'm ultra conservative (aka, 'safe').
For a dynamic load, I would "suggest" removing the Rope Jack from the rigging - as shown in the OP vid.
 
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