working load limit on fiddle blocks?

SWL isn't the best measure. It is better to have the breaking strength. Then, the user can set their own safety factors.

It's quite easy to calculate all of the numbers and find the breaking strength.
 
Jeff, you don't rig off a 5:1. You tension the rope with it, lock it off on a porty or something and then loosen the 5:1. The 5:1 never takes the shock load, the load line does.
 
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Jeff, you don't rig off a 5:1. You tension the rope with it, lock it off on a porty or something and then loosen the 5:1. The 5:1 never takes the shock load, the load line does.

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Man... that is what I was thinking. Im still not sure as to why the question was asked. Is it just to know or are you woundering due to the reason you load and lower with it. Thats alot of rope.
 
No user information is listed by the distributor for the fiddle blocks. How much tension can be put into the rope of the pulley system with many years of service from the fiddle blocks is what the original poster is asking. Jeff is using a 10:1 safety factor in his rigging systems. He wants hardware that can be used to reflect his thoughts about a proper safety factor in the rigging systems he builds.

Whiz: I bought boat type fiddle blocks made by Wichard from Sherrills several years ago. They were the small fiddle blocks of 2 sizes offered at that time. I built the system for 1 person because of the tensile strength of these specific fiddle blocks. I will not allow more than one person to use this setup. It can be broken. The advantages of using my fiddle blocks are they're small, easy to store and attach to a rope. The blocks have a device which capturers the tension in the pull line in the system without extra hardware. The system being questioned in this thread also has a tension capturing device built in it.

If you don't have the money to invest in several(2 or more) systems, I'd buy the cmi's since they can be used with several people pulling on the reaved line. I'm betting the average person weighs roughly 200 pounds. 3 people would weigh 600 pounds. This would mean the actual pulleys and connectors would be rated at 6000 pounds tensile strength with a 10:1 safety factor, or 3000 pounds tensile strength with a safety factor of 5:1.

Joe
 
Thing is, do you need a 10:1 safety factor for gear that isn't designed for dynamic loading. The safety factor is compensation for loads multiplied by shock. A fiddle block is for inhauling or tightening a load bearing rope. The load bearing rope and it's anchor should have the 10:1 safety factor.
 
no rigging gear is designed for dynamic loading hence the 10 2 1 safety factor
fyi i bringing some iron work into tree work. when i have experimented enough i will post a full dissertation with a video.
 
But what I'm saying Jeff, is you DON'T RIG a load off of it. It's purpose is to tension a line (hence the prussic). The line is what you rig with, it holds the load, not the FB. Once it's tightened, you release the fiddle block (before you cut) so it never sees a load that's in motion. A fiddle block works in parallel with the load line, not in series. The same safety factors don't apply.

Do you honestly think that a fiddle block with only a 500# safe working load would have any value to an arborist? The thing is capable of exceeding that by a factor of 2 with just one 200# guy.
 
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If you don't have the money to invest in several(2 or more) systems, I'd buy the cmi's since they can be used with several people pulling on the line reaved through the pulleys. I'm betting the average person weighs roughly 200 pounds. 3 people would weigh 600 pounds. This would mean the actual pulleys and connectors would be rated at 6000 pounds tensile strength with a 10:1 safety factor, or 3000 pounds tensile strength with a safety factor of 5:1.

Joe

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This above isn't correct. 3 people at 200 lbs. = 600 lbs. 600 lbs x5= 3000 lbs. output of tension. Safety factor in rope getting the 5:1 tension would mean the rope needs to have a tensile strength of 15,000 lbs, or 30,000 lbs. for 10:1. The cmi pulley with the 2 inch dual-sheave(from the Sherrill catalog): 3000 lbs. distributed between 3 side plates = 1000 lbs. per plate. The tensile strength of the cmi pulley is listed at 11,000 lbs. The suggested wll listed in the catalog is 1,000 lbs. which is an 11:1 safety factor. With an output of 3000 lbs. there's still more than a 3:1 safety factor for these pulleys.

Any thoughts?

Joe
 
I hope that people pay close attention to this thread. I know personaly I have seen in person or have seen on tree blog sites such as this one, guys useing loaders or trucks to tension a system. This should open there eyes to how bad of an idea that is.
 
Brion Toss showed me a very clever two speed handy billy. It will operate at 4:1 or 8:1 and is super easy to configure.

Joe is right on with his calculations and details.

NEVER use a mechanical device to add the piggyback MA/FB/Handybilly to the rigging. Friction hitches have built in slipping so that the input load doesn't destroy the rigging point.
 
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...NEVER use a mechanical device to add the piggyback MA/FB/Handybilly to the rigging. Friction hitches have built in slipping so that the input load doesn't destroy the rigging point.

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Exactly. Any heavy load bearing line should be secured/terminated with friction hitches; the 3W prusik being very common. Some opine that neither knots nor hardware should be used on heavily loaded lines.
 
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this all depends on application and design factor

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Well how do you mean that? Are you saying that you are going to have a means of measuring the pounds of force at your object being pulled and also your anchor? Thats the only real way I see for someone to know how much force they are putting onto there line. Or are you just going to guess when its a good time to stop pulling?

I dont want to sound as if I am attacking, I just want to know the line of thinking you are on.
 
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