Omni block 4.5

RBJtree

RBJtree

Branched out member
Location
Pittsburgh
How much would you trust one of these? 6000lb wll, would you negitive rig 2000 lb logs onto it? 3000? 4000? I don't have any omni's yet. I assume the build quality is great. What is the sliding plate locking mechanism like?
www.gaparboristsupply.com

Rock Exotica Omni Block 1.1

The Omni-Block 1.1 swivel pulley from Rock Exotica combines a swivel with a pulley in a patented design that saves vertical height and lets you remove and install the rope while keeping the pulley attached to the anchor. It can replace a conventional pulley, carabiner & swivel and is lighter...
www.gaparboristsupply.com www.gaparboristsupply.com
 
southsoundtree said:
If you negative-block a 500 pound piece, you're getting way, high forces already. A 4000 pound piece negative-blocked, dropped, would explode that block.
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I am well aware of the forces created by dropping objects. A 4000lb object dropped at freefall will, according to most sources, 4000lbs x feet of distance. 6000lbs on that block is working load, not tensile. Tensile is 30,000 lbs. Even if your rope runner sucks and lets the log free fall 6 feet and snaps it to a stop, 6 × 4,000 = 24,000. Not saying I would trust a 30,000 lbs rated block to do that, but it shouldn't explode on the first cycle. Otherwise, the rating is incorrect.
 
I have seen it in several places including yale's web site. It does seem too simple to me, but it seems to work out based on testing. I even saw a live demo using an enforcer that supported that formula.
 
What gives me pause is the demo on yales web site showing how a static rope will break well below tensile strength when exposed to a shock load. I wonder how steel and aluminium respond to shock loads near tensile strength.
 
I didn't find what your referenced on yalecordage.com.

Can you link it, please?


Largely, any piece that is of huge weight is going to have the COG freefall several feet at least, when negative blocking.

50' of rope in the system versus 150', snubbed off, will be different beasts.


(I edited my wording in a previous post to say I meant 'snubbed off' where I mistakenly wrote 'dropped')
 
As was discussed in another thread (I can't remember which one) some of the numbers in the artical on the energy absorption of their ropes doesn't match the numbers they list in the catalog, but the formula for energy of a falling object does correspond to what I have seen other places (once again, I don't remember where) and to the test results I witnessed with the enforcer.
 
A Block generally sees twice the force regardless of the rope in the system.
And The sling that attaches it should be matched accordingly.

If It’s a 30000lbs tensile strength block with a 6000lb work load that’s @5-1 safety factor with both legs of the rope. So on a single leg there should be no more 3000lbs @5-1. So if you half that again it makes a 1500lbs piece maximum if you want a @10-1 safety factor per leg. To me that would be pushing it... especially if shock loading.

I am pretty sure that is correct 1500lbs x 2 legs of rope equals 30000/3000 =10-1

I’m gonna agree with southsoundtree. I’d be keeping it under 500lbs
To be honest there are so many proper arborist blocks to choose from...
 
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Finky198 said:
A Block generally sees twice the force regardless of the rope in the system.

If It’s a 30000lbs ts and 6000lb work load that’s @5-1 safety factor with both legs of the rope so a single leg should be no more 3000lbs @5-1 so half that again makes a 1500lbs piece maximum if you want a @10-1 safety factor per leg and to me that would be pushing it... especially if shock loading.

I am pretty sure that is correct 1500lbs x 2 legs of rope equals 30000/3000 =10-1


I’m gonna agree with southsoundtree. I’d be keeping it under 500lbs
To be honest their are so many proper arborist blocks to choose from...
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I agree there are many nice blocks and I have a couple. I'm just interested in this one because it swivels and I can detach the rope from the block without detaching the sling from the block.
 
That's the main reasons I like them as well, I have an Omni block 1.5 loopie, but I only use it for light duty "non dynamic rigging" and as a midline attachable redirect. It work's great for that.

People have long since debated whether the Omni's are pulleys or blocks........
Regadless of what they are called there are definitely some limitations.
 
I have all of the OmniBlock pulleys except that 4.5 monster. I love them, but I don't negative rig with them. The big 2.6 one I admit to occasionally negative rigging smaller stuff, 100 lbs. or so, onto it. It hasn't balked. But, I wouldn't try to chunk down a spar with one. When I've dropped stuff onto the 2.6, it was limbs that were above the block, but out away from the stem.

All of mine, the literature that comes with it says they're intended for static rigging. I don't know about the 4.5, but I suspect it might be the same. It's also a heavy beast. The problem is that with the swivel, impact loads will eventually beat the shit out of the swivel bushings. I do know a guy who beats the shit out of his 2.6 this way, and it's getting real sloppy with the swivel rattling and knocking. The rest of it just looks scuffed up, but mechanically fine. No axle slop, just the swivel. He is perfectly aware that he's using it outside of its intended use, and that RE isn't going to honor the warranty with that kind of blatant abuse. He just doesn't care. He can afford another one.

I typically use the 2.6 as the main block, and the 2.0 versions for redirecting the rigging line, ala "fishing pole" style... with either a Stein RC-1000 at the base (if I have a groundie) or a Rig N' Wrench in there along the way (if I'm working solo or only with my wife helping me).

These pulleys are a work of art. The midline attachable side-plate arrangement is flawless, and can be operated with one hand. Just a beautiful design.

The 1.5 size is perfect for TIP pulley in DdRT.
 
The 4.5” Omniblock looks badass and has caught my eye before, I just haven’t seen any reviews from tree guys. I’d lift and lower 2000lbs on it all day, but not negative rig big stuff on it.
Dynamic rigging on the aluminum swivel would worry me. If I’m spending that kind of cash on a rigging block, I’d probably get a DMM Impact.
I got the 2.6” Material Handler Omni and I love it, takes pretty much any static load I’d throw at it with a 1/2” rope. Also got a 1.5” Omni that I keep for climbing, just girthed on a loop runner. Really beautiful and well made pulleys.
 
Finky198 said:
A Block generally sees twice the force regardless of the rope in the system.
And The sling that attaches it should be matched accordingly.

If It’s a 30000lbs tensile strength block with a 6000lb work load that’s @5-1 safety factor with both legs of the rope. So on a single leg there should be no more 3000lbs @5-1. So if you half that again it makes a 1500lbs piece maximum if you want a @10-1 safety factor per leg. To me that would be pushing it... especially if shock loading.

I am pretty sure that is correct 1500lbs x 2 legs of rope equals 30000/3000 =10-1

I’m gonna agree with southsoundtree. I’d be keeping it under 500lbs
To be honest there are so many proper arborist blocks to choose from...
Click to expand...
Ding Ding... If you tie a piece off to the spar and drop it, it's x1 per foot + weight. Add a block and lock up the porty it's (x1 per foot + weight) x2 . Aka 500 lbs falls 5' on a block, and not allowed to run at all (ignoring rope length and stretch) looks more like 2500 + 500 x 2 = 6000
 
Dispite knowing a base tie roughly doubles load on a tip, I never think of rigging that way. I guess I am always thinking in terms of is my rope strong enough. Usually my block is the strongest part of the system, followed by the brake, then the slings, then rope. Good reminder that load on the block and the sling holding the block are doubled.
 
southsoundtree said:
The rope must be the weak link, or you'll be rocketing the block toward the brake/ lowering device, or brake toward the block. Hopefully, you never break anything, especially a block or brake.
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Damn right! We can't have big chunks of metal flying around! Of course, I prefer not to have uncontrolled logs and ropes flying around either, but I agree, the block, break, and slings need to be stronger than the rope and account for force multiplication. So if the breaking strength of your rope is 10, the block and sling should be double plus saftey margin, and the break and sling >10 plus saftey margin.
Basicaly, the omni 4.5 with 3/4 inch capacity is useless as an impact block because its just not strong enough for the rope it can hold, and to big and heavy for the rope that would match its rating. As an overhead rigging point its probably great, but I never need 3/4 inch rope on an overhead rig.
 
That is correct, At times doing big picks having big block and 3/4 rope can come in handy, for some static loads you can also use 5-1 WLL but those decisions should be made on a case by case basis...
 
RBJtree said:
Damn right! We can't have big chunks of metal flying around! Of course, I prefer not to have uncontrolled logs and ropes flying around either, but I agree, the block, break, and slings need to be stronger than the rope and account for force multiplication. So if the breaking strength of your rope is 10, the block and sling should be double plus saftey margin, and the break and sling >10 plus saftey margin.
Basicaly, the omni 4.5 with 3/4 inch capacity is useless as an impact block because its just not strong enough for the rope it can hold, and to big and heavy for the rope that would match its rating. As an overhead rigging point its probably great, but I never need 3/4 inch rope on an overhead rig.
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Just to argue for the sake of arguing. Isn’t the SWL already built into the 6k or whatever the block is rated at? That’s certainly in the 3/4” land of rope running smoothly.
 
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