. . . is pulley diameter a concern? I've been running a cable through mostly one, sometimes two pulleys (made for such things) attached to trees to correct out-of-line pulls on firewood logs, strictly a 1:1 deal. I'm wanting to increase pulling power to 3:1 via a pulley on an anchor tree and another on a stump to to be removed, then on to the winch. I am concerned about bending moment on the cable as it passes through the pulley attached to the anchor tree where the load should be highest. The cable is 1/2".
- Thread starter ScottNC
- Start date
Only thing I'd add is cable type as well
Some is rated for tighter bends than others
It's 35° and raining here since last night, so I didn't venture out before posting to the equipment shed, but I did during a lull in the rain. The 'snatch blocks', a term I should have used instead of 'pulleys' have metal tags: size 4 1/2", 1/2" cable and 4 ton. That should answer my question since their diameter is what I was worried about. Given my intentions of using a 3:1 on the stumps is using a separate cable on the stump end to reduce the chance of damage to my winch cable something that's typically done? Winch is rated at 10K, so a bit more than the snatch blocks but, by powering it with the tractor external hydraulics the pump bypass kicks in before the winch is maxed.
john in la
Well-known Member
A snatch block for 0.5 inch cable will have a sheave size of about 4.5 inches.
A good snatch block manufacture should have all the calculations done for you with the rating of the snatch block.
What you have to worry about is if the snatch block and cable is rated for the load and where to hook the snatch block to get the maximum pull.
Lets say you are pulling a tree to be cut down and need 4000 lbs of pull to do the job.
If you hook the snatch block at the anchor point all you did was change the direction of the pull.
So the entire cable will see 4000 lbs of pull and the snatch block will see 8000 lbs to move a 4000 lb load.
But if you hook the snatch on the tree you are cutting down (the moving load) the snatch block will see 4000 lbs while the cable will only see 2000 lbs of pull to move the same 4000 lb load.
The direction of pull will also effect what the cable will hold.
Say you hook the end of the cable to the tree you are trying to move and the snatch block to the anchor point and the two cables are 90 degrees from each other.
Like above all you did was change the direction of pull.
But since the cables are not pulling 180 degrees from one another you need to add the angle factor multiplier.
At 90 degrees the multiplier is 1.41 and at 180 degrees the multiplier is 0.00.
So with the same 4000 lb of pull needed the cable now sees (4000 x 1.41) 5640 lbs and the snatch block sees (8000 x 1.41) 11,280 lbs of pull to move the same 4000 lb load.
A good snatch block manufacture should have all the calculations done for you with the rating of the snatch block.
What you have to worry about is if the snatch block and cable is rated for the load and where to hook the snatch block to get the maximum pull.
Lets say you are pulling a tree to be cut down and need 4000 lbs of pull to do the job.
If you hook the snatch block at the anchor point all you did was change the direction of the pull.
So the entire cable will see 4000 lbs of pull and the snatch block will see 8000 lbs to move a 4000 lb load.
But if you hook the snatch on the tree you are cutting down (the moving load) the snatch block will see 4000 lbs while the cable will only see 2000 lbs of pull to move the same 4000 lb load.
The direction of pull will also effect what the cable will hold.
Say you hook the end of the cable to the tree you are trying to move and the snatch block to the anchor point and the two cables are 90 degrees from each other.
Like above all you did was change the direction of pull.
But since the cables are not pulling 180 degrees from one another you need to add the angle factor multiplier.
At 90 degrees the multiplier is 1.41 and at 180 degrees the multiplier is 0.00.
So with the same 4000 lb of pull needed the cable now sees (4000 x 1.41) 5640 lbs and the snatch block sees (8000 x 1.41) 11,280 lbs of pull to move the same 4000 lb load.
Mule Meat
Well-known Member
If your snatch blocks are single line. You will need three of them to achieve a 3:1 ratio.
Most guys here use synthetic winch rope and Redridge Industries Recovery Rings rated at 22,000 lb. Recovery rings are much more compact, easier to use stronger than a lot of hook type snatch blocks. It would be nice if they would make them for steel cable.
Most guys here use synthetic winch rope and Redridge Industries Recovery Rings rated at 22,000 lb. Recovery rings are much more compact, easier to use stronger than a lot of hook type snatch blocks. It would be nice if they would make them for steel cable.
DoubleO7
Well-known Member
- Location
- Crystal River, FL
Go to this website, they have "resource pages" that will be useful in completing your task safely.
www.thecrosbygroup.com
The Crosby Group - Material Handling Solutions
The Crosby Group - a world leader in the material handling industry with premier shackle, hook and block products for rigging and lifting. Browse our catalog and find a sales rep today.
www.thecrosbygroup.com
When doing multi-line with snatch blocks, the places where you will have issues is in how you attach the snatch blocks and to what. I did triple line rigging with two snatch blocks pulling 25,000# shipping containers rolling on logs with a 12k winch. Line from one container corner, to snatch block attached on backhoe with loader bucket dug in the ground, back to snatch block attached to other container corner, and then to the winch on the back of the truck. Backhoe and truck positioned side by side. First container corner and truck see up to 12k pull and the rigging needs to account for that. The other container corner and the backhoe see up to 24k pull due to the double line at each point so those need to be solid for that loading. Even with the 18,000# backhoe loader dug in it still pulled the backhoe forward a bit as the "dig" solidified. The container could see up to 36k total pull. These are serious forces and anything breaking loose can easily kill you. Wireless winch remotes are nice so you can stay well out of the potential line of fire.
Janicholson
Well-known Member
- Location
- Central MN St. Cloud
Two items that I think are important:
Real "wire rope" cable is what is being discussed. Cable is also what is used for guy wires on utility poles and it is not wire rope.
If the Thing being pulled/moved is connected to the force with one strand of the wire rope, that strand is taking the entire force as multiplied. Jim
Real "wire rope" cable is what is being discussed. Cable is also what is used for guy wires on utility poles and it is not wire rope.
If the Thing being pulled/moved is connected to the force with one strand of the wire rope, that strand is taking the entire force as multiplied. Jim
Mule Meat - Maybe I'm missing something? Maybe I'm only 2:1? The winch will be against the bottom of a tree (keeps the load off the 3-point) and square to the stump to be pulled. The cable goes from the winch to a snatch block on the stump, from there it goes to the second snatch block on the anchor tree then back to the stump where it terminates. Jon in LA - the anchor tree lies half way between the winch and the stump off to one side. The distance between the cable from the winch and the cable at the anchor where they pass will be about two feet. Double07 - I will check out your link.
The stumps are three plus inch trash trees in a slight pushed-up berm of shale rock in a field edge, roots around here are normally shallow due to the soil. But, after reading the replies, stored energy makes me nervous. I may hedge my bets and revert to a shovel and axe once the rain stops. After ruining a good mood and wondering at about two hour in point, what could possibly still be holding this thing, if the stump is all wobbly I may then go at it with the winch. I haven't been on a first name basis with the ER doctor for a couple of decades, I'd kinda like to keep it that way.
The stumps are three plus inch trash trees in a slight pushed-up berm of shale rock in a field edge, roots around here are normally shallow due to the soil. But, after reading the replies, stored energy makes me nervous. I may hedge my bets and revert to a shovel and axe once the rain stops. After ruining a good mood and wondering at about two hour in point, what could possibly still be holding this thing, if the stump is all wobbly I may then go at it with the winch. I haven't been on a first name basis with the ER doctor for a couple of decades, I'd kinda like to keep it that way.
Janicholson
Well-known Member
- Location
- Central MN St. Cloud
john in la
Well-known Member
Maybe this will explain it a little better.
With 2 snatch blocks you should be using the far right 3 part line configuration.
The red arrow is your winch.
Your 10,000 winch will need one 20,000 lb snatch block one 30,000 lb snatch block and cable rated for 10,000 lbs.
This assumes all pulls have the cable running 180 degrees (parallel) to each other.
Like I said in the other post you start pulling off to one side and things change and you have to know the angle to get the right multiplier.
This diagram will also prove you can get 3 to 1 ratio with two snatch blocks if you do it right.
Edit: let me add one thing before the correct police brings it up.
If you hook the dead end of the line to the load and not to the bottom snatch block you can get away with two snatch blocks rated at 20,000 lbs each.
With 2 snatch blocks you should be using the far right 3 part line configuration.
The red arrow is your winch.
Your 10,000 winch will need one 20,000 lb snatch block one 30,000 lb snatch block and cable rated for 10,000 lbs.
This assumes all pulls have the cable running 180 degrees (parallel) to each other.
Like I said in the other post you start pulling off to one side and things change and you have to know the angle to get the right multiplier.
This diagram will also prove you can get 3 to 1 ratio with two snatch blocks if you do it right.
Edit: let me add one thing before the correct police brings it up.
If you hook the dead end of the line to the load and not to the bottom snatch block you can get away with two snatch blocks rated at 20,000 lbs each.
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caterpillar guy
Well-known Member
Boy I would for get about the second tree deal and just run my line from the winch to the snatch block on the tree being moved then back to the winch/snatch block then back to the load and back to the winch so I had 4 lines running through a snatch block on the moving item and then pulleys at the winch so no other anchor is needed thus a in line pull with less work to hook up and inline pulling so no whipping of a line if it broke. Ad yest you need a snatch block ratted for the pull of the 4 lines mostly so you don't break the pulley pin and then think about the method of attaching the snatch block to the load. It will need to be as heavy as the pulling force of the hook at the snatch block or a 10,000 winch with 4 lines would develop roughly 40,000 pull so the snatch block needs to be able to handle that plus the attaching method needs to be able to also. if not then issues will be had and with a not so nice way possibly. Cables can do a lot of damage to things and not just people if they break under tension.
Looks like my rigging plan for 3:1 was sound - but the equipment isn't stout enough unless the recent rain makes for an easy pull. Might rig it just to see but if there isn't evidence early on the stumps moving I'm going the shovel and axe route. Use the winch for the finale.
john in la
Well-known Member
Hook the dead end (the anchor) as low to the ground as you can to reduce the leverage.
Hook the live end (the tree you want to move) as high as you can without causing the tree to snap in two to increase the leverage.
Hook the live end (the tree you want to move) as high as you can without causing the tree to snap in two to increase the leverage.
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