Sheave block mechanical advantage?

[Billy Bee]

I am no physics major, I know a block and tackle increases pulling power, but with just one pulley, like on a sheave block does it increase mechanical advantage, or is it just 1 to 1. I want to persuade some trees to fall were I want them to.
Thanks,
Bill

 

[dougtrr2]

Moving/movable pulleys increase mechanical advantage. Fixed pulleys only change direction.

Doug in SW IA

 

[Billy Bee]

Kinda what i figured. I don't need a lot of persuasion, so it will work. Changing direction is what I want to do, so I can pull one direction away from where I want the tree to fall.

 

[RNeumann]

Yep the pulley has to move to create advantage. With just one pulley the winch line will need to go from the winch to the object you want to move and back to an anchor point at the winch. The pulley would be at the object that you want to move. This is a simple 2:1 system.
This is roughly twice the force and half the winch speed.

 

[Industrial Toys]

Maybe, I don't understand.

But . . .

With one pulley, now the rope is doubled and you are gaining a 1-2 advantage (If I said that right) and the one loose end is attached to some fixed point, other then the pulling point.

So regardless of what the pulley is doing, you measure advantage as to how much line you are pulling in relation to how much your load moves.

My Dad taught me that when I was around five. My toys were a couple of clothes line pulleys and some rope.

 

[oosik]

I don't quite understand your last sentence there IT, but with one pulley attached to the tree, the winch line out - thru the pulley and back and attached to the winch or an attachment point on the winch vehicle - you have doubled your winch pull( example - 5000# to 10,000#) and cut the winch cable retrieval speed in half(basically).

 

[Industrial Toys]

Pulley attached to Tree.

One free end to, let's say a (large) tree in the direction you are pulling.

And the other end to the tractor or winch.

You are now pulling twice as much line for the movement of the target, effectively giving you a 2-1 advantage.

So thinking, about it, if you had a Winch, you could attach (the other free end) to the vehicle with the winch, but not without a winch.

 

[Snobdds]

A pulley has to be attached to the load, to be considered a mechanical advantage. If the pulley is attached to the anchor, it's just a change of direction.

Mechanical advantage are always in odd numbers, due to having to have an anchor point. Example, 3:1, 5:1 etc.

 

[hslogger]

If you are not at the least bit certain what you are reading on this post, go search block and tackle uses and set ups. Just a short note. As indicated in other posts, you hang the block from the tree. You run the the pull or winch line from the pulling source through the bock and then back to the winch or a deadman in close proximity. You double your power.

Now, if you have that line quartered on the block or at any angle,you are decreasing your power.
Say you want to have your pulling device on the side someplace you need to use a directional block that has no true pulling power but merely gives you the opportunity to pull from another place to take you presumably away from danger. So in that instance, you will have a power block AND a directional block.

You "might" want to hang your tree block in some way to hopefully minimize the possibility of damaging it when the tree falls. Best not to hang the block tight but hang a long chain or rope from the the tree, attach your block there. That way when the ship hits the fan, you block will most likely escape abuse.

Pulling a tree over is a tricky deal for backyard experimentation. Often pulling is not necessary. TENSION is the tool to persuade a stubborn one, and pulling one over 180 degrees is a challenge to do with out extreme danger to the inexperienced.
play safe.

 

[Industrial Toys]

I am having a cheap 2500 # portable electric winch delivered today. I would like to pick up some free concrete steps (Five High) and drag them onto a trailer.

Are most cheap winches rated for what the capstan can pull or what the winch frame can withstand? Applying mechanical advantage in multiples could easily exceed the strength of the winch castings, I would think.

And yes, I agree. getting some trees down can be EXTREMELY tricky and dangerous. Browse Youtube for Many examples of this gone wrong.

 

[RNeumann]

A pulley has to be attached to the load, to be considered a mechanical advantage. If the pulley is attached to the anchor, it's just a change of direction.

Mechanical advantage are always in odd numbers, due to having to have an anchor point. Example, 3:1, 5:1 etc.

You can have even number mechanical advantage.

 

[Spanner]

You can indeed.
And there are several other errors in earlier posts in this thread.
The following article may help explain:

Pulley | encyclopedia article by TheFreeDictionary

 

[Brad_Blazer]

If you pull with some tension T and have some number of strands N at the same tension leading to the object you want to move, the total pulling force is T multiplied by N. (neglecting friction)

 

[RNeumann]

If you pull with some tension T and have some number of strands N at the same tension leading to the object you want to move, the total pulling force is T multiplied by N. (neglecting friction)

And angle/distance between winch and anchor

 

[turnkey4099]

You can have even number mechanical advantage.

yep. I commonly use 2x1 and 4x1. from anchor to pulley on load. 2nd line is from anchor through pulley attached to the free end of line coming from the pulley on load and back to the winch.

I've moved some huge logs using just my 1/2 ton F150 2x...actually a 1x as the positrac doesn't work. Drawback with 4x1 is you have to pull 40 ft of cable to more the load 10 feet.

 

[Egon]

Ahh - look up pulleys & mechanical advatage. Basically the distance the load moves compared to the distance the puller moves will tell the tale.

 

[bcp]

To simplify, count the number of lines going to the moving object. That is your mechanical advantage to one.

Bruce

 

[dougtrr2]

Take some time to look over the entire operation. How much persuading on the direction of fall are you going for? Keep in mind that there can be a massive amount of energy stored in a tree. If it starts going the wrong way you may not be able to stop it. Check you tube for idiots with chainsaws to get some great pointers on what NOT to do. Be careful out there.

Doug in SW IA

 

[Billy Bee]

Take some time to look over the entire operation. How much persuading on the direction of fall are you going for? Keep in mind that there can be a massive amount of energy stored in a tree. If it starts going the wrong way you may not be able to stop it. Check you tube for idiots with chainsaws to get some great pointers on what NOT to do. Be careful out there.

Doug in SW IA

The trees are dead ash about 10 in. at the base, and maybe 30 ft. tall. They are close to the road and I don't want to fell them in the road. I am going to fell them parallel to the road. I could probably do it with no "persuasion" , but I want to be sure. I have used my sheave block many times on trees much larger than these. I understand the dynamics of the energy stored in a tree, I would never try to force a tree to go where it flat won't go. I wear chaps,forestry helmet,ear and eye protection,steel toed boots, and always make sure I have a clear escape route. Yes I have seen the videos, the idiots and also the informative how to videos from Stihl and Husqvarna. I try to be as safe as I can, for myself and bystanders. I have great respect for trees, even after they are down they can hurt you. I will be careful.
Thanks for your concern,
Bill

 

[LD1]

Its already been covered, but keeping it simple.....

With a single pulley.....with the pulley anchored solid and not intended to move......nothing more than a change of direction
With the pulley attached to what you are wanting to move, and thus the pulley moves....2:1 advantage in force....half speed