Minimum bend radius for termination of rigging set-up?

jakebuck258

New Member
Location
USA
Would a 1 1/2 inch thimble be acceptable to rig through for a termination end of your set-up? That would be the big thimble or the #3. Anybody have any input? I’m trying to use it for part of a DWT set up
 

laddo

Member
Location
New Orleans, LA
The diameter of the bend/thimble should be at least 4x’s the diameter of the rope for proper/recommended bend radius.

So if you have a .5 inch climb line, the diameter of the thimble needs to be at least 4 inches. At least that’s how it works with pulleys and blocks


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Reach

Well-Known Member
Location
Atglen, PA
The diameter of the bend/thimble should be at least 4x’s the diameter of the rope for proper/recommended bend radius.

So if you have a .5 inch climb line, the diameter of the thimble needs to be at least 4 inches. At least that’s how it works with pulleys and blocks


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Right on the concept, but you might want to check your math. 4x0.5=2
 

Jonny

Well-Known Member
Location
Buffalo
Do y’all really follow this guideline for polyester and nylon ropes?

Am I being reckless and unsafe rigging shit on 1/2” 12 strand or double braid rope with a single ring... maybe 1” bend?

Full disclosure, I’m probably gonna keep doing it, but interested to hear anyways.
 

laddo

Member
Location
New Orleans, LA
Do y’all really follow this guideline for polyester and nylon ropes?

Am I being reckless and unsafe rigging shit on 1/2” 12 strand or double braid rope with a single ring... maybe 1” bend?

Full disclosure, I’m probably gonna keep doing it, but interested to hear anyways.

I’m pretty sure even the manufacturer’s recommended using a double ring setup if used as a terminal rigging point because of bend radius


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TheTreeSpyder

Well-Known Member
Location
Florida>>> USA
Material and construction would be a factor
>>newer materials breaking some of old thumb rules especially.
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Olds-cool(old school) thumb-rule on 1/2" etc/ arbo lines was/is 4x diameter judging for 50% loss,
>>~ same as later knots in same system is theory.
>>so more uniform strength in chain
Then Brocky gives the 8x recommendation for full strength
>>but then probably no such thing as 100%/seems as all else must be trickle loss at least, but close enough
>>but then if weaken connected section of line with 50-70% efficiency knot
>>the weakest link will dictate the system strength
>>irrespective of the 8x pulley set to minimize same efficiency loss but at the arc, not knot.
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Newer materials like Dyneema need much larger bend ratio
(and almost as slick as teflon/teflon mating that actually matches teflon/steel CoF =.04, nylon/aluminum is .25 and nylon/steel .4 CoF!!!)
>>and some things even need special groove base to best support that rope or cable 'loaded belly' in that groove
>>right size of sheave across also matters as to how much allows rope to flatten at high loading
>>these are care and supports for the loaded 'hose' that has force raging thru
>>should have right rated sheave size groove for rope diameter across and belly support
>>width of sheave spoken hear another consideration.
>>to conserve most efficiency like is precious jewel, need to do so from all these many facets of consideration.
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BUT, those are individually separate loaded legs of load/control compounded to pull on pulley @ 2xLoad as potential.
Eye Splice (properly done) is different animal, to me is 2 legs combined as 1 against load
>>and so each leg carries half, not full load
>>compounding is simply back to full load at eye
And compared to most knots, the control/Bitters side of eye pulls most properly along the main loaded leg primary, instead of shearing across 90degrees at wrenching to break angle
(rather than inline column support angle of splice)
Smooth eye taper/hand off/translation of force from 2 to 1 gives less dynamic, softer impact of change.
These hallmarks most mimic base rope constructions anyway, not knots.
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Those are the older rules, less seen now, companies try to make fewer commitments can be sued for and newer materials are game changers, so global rules of thumb out the window, need rite ratio for target materials etc.
>>just as real people, sound and established, respectables will tend to quote tensile etc. more conservatively
>>more head room for wear, mistake etc. >> less problems/litigation etc. stating strength deep into powerband
>>braggarts tend to state tattered fringe edge of powerband as mainstay w/less headroom, perhaps even over-inflated.
.
 

Phil

Well-Known Member
Location
Oak Lawn, IL
thumb-rule on 1/2" etc/ arbo lines was/is 4x diameter judging for 50% loss,
Do you have a source for this strength loss number?
The charts I have show the following strength loss per the bend ratio:

1 to 1 = 40%4 to 1 = 15%
1.5 to 1 = 35%5 to 1 = 12%
2 to 1 = 30%6 to 1 = 10%
3 to 1 = 20%8 to 1 = 5%
 

Phil

Well-Known Member
Location
Oak Lawn, IL
When the heck did they make it 8:1?!


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Notice it says "should" not "shall"... it's just a recommendation...If you want to maintain "maximum efficiency". In reality, 4:1 seems the accepted industry standard. I look at things like the pinto Rig and similar sized pulleys. What's the sheave diameter? Maybe 1.5"? If you use a 1/2" line you're only at a 3:1. I certainly wouldn't lose sleep over rigging small to medium branches in that. The important thing is to know that bend radius is a factor in rope strength. Take that info in to consideration when deciding load size for rigging and stay within the WLL for your setup.
 

TheTreeSpyder

Well-Known Member
Location
Florida>>> USA
i think the 4:1 50% standard recommendation less seen because of the newer materials and throwing a global shotgun number over wide range of materials and constructions that simply don't have the same deformity response. Again, a conservative company will find that a covered hiney is a happy hiney!
 

Tom Dunlap

Here from the beginning
Administrator
After hearing Don Blair talk about this a few times I got a complete understanding when I bought...then read and studied...Arborist Equipment.

It stuns me how many things are said with no understanding of what they are based on. These days it is SOOOOO easy to find information. Along the way there is always some little treasure to be found.

Don didn't do the engineering or lab based research. He went to the rope makers and asked them for their recommendations.
 

TheTreeSpyder

Well-Known Member
Location
Florida>>> USA
i believe that is True Blue, and manufacturer Samson is very proud of their product;
>>just not so much as to make such a claim themselves i believe.
>>as Tom eludes to, about no one is going to test these ropes as much, as often, for as many years especially while maintaining a solid chain technical documentation(as if could be taken to court, or maybe just co$t millions if miss something could have done etc.), as a solid manufacturer that is in for the long game. They even have data on variances of build etc. years before product to market and sister products that development was stopped on that give more definition as close contrasts etc.
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Film rating does show smallest loss for this in my memory tho.
>>conservative stewardship of these forces would not be to jump immediately to such an extreme ..
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Phil, what is source for the bend radius table please?
>>is it by chance an eye radius and not bit/bollard/pulley radius table?
Termination of force handles differently than pass-thru.
example Half Hitch as termination around Standing Part after a Turn vs. Half Hitch as pre-fix to Timber in Killick.
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Here is my view of efficiency of strength loss on arc of seems has to be some deformity at contact, how flat rope/webbing cross compares as more defining contrast back to round rope, and then the too tight a bight kinda thermal view (as discussed in film):
Types-of-rope-arcs-that-take-some-fibers-from-tension-service-leveraging-same-load-to-fewer-fibers-of-now-greater-tension_resize1000px.png

The same load to fewer fibers, leverages more force thru them each.
The importance of round rope, host and combined architecture is very key to how all this works in individual parts and then in concert.
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Some numbers and visuals to elastic comments and different materials and how much of the tensile strength is encroached upon to extrude elastic dampening effect :

samson-elognation.jpg
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THEORY
i think that rope mechanix are arc(mostly mean 180 arc slices towards or opposing input direction) controlled.
Mostly, and as we deal with, as termination (Hitch) and coupling (Bend) of external focused/directional linear force converted to internal diffused/directionless radial arc control.
Round Binding not the same, is INTERNAL RADIAL input from within controlling arcs, so no conversion(loss) to radial.
Bag Knot as Hitch gets linear input, degrading thru controlling arcs to nip, with compounding at arc apex . Same Bag Knot used for Round Binding, now has internal, radial glow of bursting force feeding into controlling arcs. The rope tension all around is equal, not degrading to the nipping nor any compounding like pulley as these are both from directional forces.... Also, their is no conversion loss, so radial mirrors radial as response, for equal force around w/o frictional compounding loss nor directional compounding force.
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Linear rope run can only friction control with sine, and compound effect by distance. (cosine dedicated to support against load only)
Covert to arc control, avails to bigger matrix of being able to use all of force, cosine and sine against load, AND friction control, that is now compounded by DEGREES. Rope arc does this just as stone bridge arc uses all compression not to crumble under tension that has very low non-malleables have low tolerance for. Rope arc force direction is just reversed to tension, not compression of stone.
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Rope arcs in capstan/bollard compound mostly friction.
Rope arcs on pulley seek to compound reciprocal factor of same arc :force!
These 2 arc mechanics are a model of opposing extremes of what arc may compound. These 2 are our benchmarks that all linear fed knot arcs are between.
The amount of friction variable itself, dictates how much of each 'parent' benchmark extreme is revealed/inherited by the particular knot arc.
my shared spreadcheat for CoF's, cos/sin/tan, base capstan article att_frict(link)
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The compounding 2/1(pulley) point at top of arc apex, is also best nip position. BUT not seen in Round Binding. Capstan/bollard and pulley effects not seen in Round Binding, only from linear inputs.
THEORY: The compounding pulley effect, is the counter intuitive residual directional axis of the focused linear input persisting thru the arcs. Compounding faces the direction of input or reverse, but maintaining that directional axis(vertical or horizontal etc.)
per direction of initial input load imposed (until 90 degree rope part if any switches this directional axis to cross axis)
How’s about that 1:1 bend in every loaded running bowline?

i believe that is fair view, but that Half Hitch(HH) in most loaded Standing Part(SPart) of Bowline, encompasses 2 rope diameters, exports only half of what was input linearly to 1 leg of eye, as other half comes from choke of HH.
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Persistence of linear force thru arcs may also be witnessed in Bowline HH. As long as final bight thru HH around eye is short enough to be rigid enough to keep HH perpendicular to SPart, the HH is not in the line of force from SPart to eye, and is looser, as like a HH pre-fixxing a Timber etc. in Killick. BUT lengthen bight so now HH can fall into forceline and it is now taut full turn around. It is tighter now that in the line of persisting force, this can fail, sloppy build like Sheepshank, (that does add another catch/HH, but as rolls out of what we make i see as full turn a round in usage). The Killick force line will likewise report that the linear in forceline stretch between HH and Timber is tighter than HH. BUT if pull at right angle to spar/not lengthwise, now the arc is tighter and the part between HH/cross and Timber is less so, by the direction of input to same arcs, to reveal the directional linear persisting thru radial control ! Just as the Bag Knot, only now more directionaly imposed, we can see the same framework of rope, gives connected rope parts that can be used differently. Rope can take advantage if architecture exists to do so. Just as if linked rigid parts, to assmeble themselves to respond differently to different loadings, if the architecture/positions exist to do so. Killick can do this going from right angle pull to ABoK's lengthwise pull, but Timber alone not trustworthy enough, does not have the architecture in positions to avail to/against this direction change in same manner.
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i love this stuff, but guess i should stop here!
Been a long road, but this is what i have come back with!
 
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