Mechanical Advantage Pulley Quiz

Eric Frei

<Very interesting PDF located in this post regarding rigs like this ... Mechanical Advantage tests using pulleys>

Just a lil quiz.

This is a true scenario I performed yesterday to pull a tree over that was back leaning over a house with no Kanga access.

I had 3 pulleys and rigged as seen in the diagram.

I have numbered all the parts of the ropes (8 in total) so you can write what force is on each part and what the total force is on the tree.

Also to make you really think I did this job on my own, so I pulled on the rope etc and did the cutting, any ideas on how I managed to do that safely?

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Jeff Darby

Here's my answer..LOL?
1:600kgs
2:600kgs
3:400kgs
4:200kgs
5:100kgs
6:100kgs
7:600kgs
8:600kgs..?

you probably took up the tension,but not to much,executed your cuts to when you new it could be pulled over, then you pulled it over...???

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OutofMytree

Trick question.

There is no SAFE way to operate in our industry alone.

OutofMytree

Now we have the issue of safety out of the way. Could I get some clarification on the actual rigging please.

The diagram suggests that the 3/4 pulley is attached directly to the rope between sections 1 and 2. Is this so? If so, how as it attached?

The answer to this will determine the forces involved.

As to how strain is taken up and held, I can't remember what devices you own but I would do it using my portawrap and tie off when the stick was over vertical. When working on suspect trees I will often forgo a scarfing cut and simply apply a back cut whilst the pressure is maintained. This method is simple and safe where the butt of the stick may bounce or roll into danger. Once the stick is down I section it from the top down and release the base last of all. Needless to say this technique works only for green timber that will not tear easily like Eucs.

newguy18

In order to do it safely you had to dead end the line while cutting,unless one of the pulleys has a built in rope grab.

lets see
1. 100 kgs
2.100kgs
3.300 kgs
4.200 kgs
5.100 kgs
6. 100kgs
7.800 kgs
8.700 kgs

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old schooler

Eric Frei

You dont have the issue of safety out of the way, what you have is your opinion of it, which is likely coming from lessor knowledge of the job than mine.

There is no law that says I cannot work alone.

This is a good one, of course the pulley is attached to the main pull line, it's pretty much a standard "Z Rig" for pull overs. How it is attached makes no difference to the forces upon it.

That is dangerous, and doing it especially when loaded spells barber chair. You wont find that in any book as a technique. I will throw my weight around on this one and say anybody doing this, you are nuts and simply don't know better.

Scarfs or notches give you control and direction. If the detachment of the log from the butt and "losing it" down a hill etc is an issue then butt tie it for crying out loud. Buy yourselves some "shit" rope for the sacrificial function, I use 14mm Silver or 20mm silver rope for such applications, cheap but effective. At 2.27minutes into the video on this post/thread you'll see it in action ... along with a 2X rig for the Kanga to pull on.

Lopped and Topped Tallowood Removal Brisbane

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Eric Frei

Excellent NG,

As you pull on "leg 6" all you need is a prussik between the black post and the pull line to hold ... the tension you put on the rope. I physically pulled and leaned back sliding the prussik up to bite hard, similar to climbing isn't it?

What I have done here is turned the pic and put in some forces to assist. This is just like when you are lowering in the tree now. It should help you work the others out.

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Jeff Darby

This method is dangerous, and so far I would say you have been lucky, scarf and back cut using the the uncut section of your scarf and back cut as a directional hinge this is the way professional arborist use day in day out, if there's a danger of it getting away butt tie it! as has been metioned.
Barber chairing claims many lives every year around the world,..it generally rips the unlucky person's head clean off!
JayD

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OutofMytree

Thank you for clarifying the attachment of rope 8. The method of attachment was for my edification as provided there is no slip you are correct in saying that attachment method does not affect force.

The distribution of forces is as follows.

6 = 100kg
5 = 6 therefore 5 = 100kg.
4 = 5 + 6 = 200kg.
3 = 4 = 200kg.
8 = 3 + 4 = 400kg.
2 = 3 + 4 = 400kg.
1 = 2 + 8 = 800kg.

The locking of force requires some tie off like a portawrap or as Bill suggested even advancing a prussic and given that it is restraining only 100kg of direct force that would work. I can't say as I have ever used a prussic other than for climbing so this a new idea for me.

OutofMytree

Perhaps I should clarify what I said regarding not using a scarf. I do not pull whole trees or even signifiacnt sections of trees upright. If that was the impression I gave then pardon my poor grammar. The technique I use and described is for vertical sticks one man hauling can control which on the ground are no heavier than 2 men would drag. In the event of a whole tree or significant portion of one leaning in a direction it cannot be felled in I block it down with or without rigging as required.

OutofMytree

Eric I am shocked and dismayed by your response to one man working alone in a hazardous enviroment. It may or may not be legal, that was never under discussion. It is simply not safe. I may be at risk of another ban but I will not be moved on this clearly dangerous practise. It is unsafe to work solo and promoting that does you no credit.

Eric Frei

Absolute BULLSHIT.

In fact provide me where it says felling operations are best carried out with more than one person, you have no idea WTF you are on about.



What are the safety distances for felling operations?

Who should be outside of those distances?

In fact not having others around is way safer.

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Jeff Darby

We are taught to access the hazards before we undertake our work at hand, while Eric working alone might not be ideal work scenario, I'm sure he considered the safest way to undertake the work at hand with available resourses. as you might have noticed Eric holds one of highest qualification in arboriculture you can achieve, they do not give these away lightly nor do you find them in kellog's packets, it was in his best judgement to undertake this particular job the way he did.
Judge not or ye be judged

JayD

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Eric Frei

You know what is dangerous?

Jims selling tree franchises like lawn runs.

Bugger me... experts in 4 weeks!

I suppose you think this was dangerous too then?
Triple felling, mad man or magic?

By the way, NO ONE HAS GOT THE RIGHT ANSWERS YET for what this thread is really about!

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Jeff Darby

Now that this has been mentioned, this really pisses me off!..We study hard to acheive our qualifications just to be undermined by people who litterally have little to no experience4 weeks training in our field of expertise is two parts of bugger all....yet out go these people and hoodwink the public in thinking they are indeed professional in what they do...What a joke!!!
JayD

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fosheezy

yeah i'll have a crack at this one cause this stuff interests, me even though i don't fully understand it...

points 5 and 6 100kg
point 7 600kg
point 1 800kg
point 8 400kg
and points 2, 3 and 4 whatever 600 divided by 3 is.

and just for the vote i think it would indeed be safe to tension the rope to be taut but not bending the top of the tree towards the line, backcut, then if it doesnt go on its own mosy over to the rope and finish up the tension to bring the thing down... easy, and nice work too eric- probably the safest possible way to do the job on your own.

peace out

Eric Frei

Here's the scene of the day.

Back leaning dual leadered Qld Waratah, (400mm DBH and 12m ht) .... at 3m high co-dominant included fork (one other lower co-dom already torn out by storm).

Roped the read co-dominant at around 7m high with the rope going past the front co-dominant. This way we are pulling it together not apart plus pulling the rear co-dominant forward, crack already present in fork, climbing is HIGH risk when felling is an option. Front leader was ahead of centre but I left it there to assist with forward weight, some times amateurs cut off easy bits that can help, weight forward of a hinge is an advantage, dont just cut it off because you can.

Set up all the rigging, light pretension with prussik back up, cut hinge, make back cut but not to hinge thickness, insert wedge.

Have 3 witnesses present, customer and two neighbours watching outside of fell zone. Very controlled environment all know what is going on and who to call if anything goes wrong.

After first back cut with thick hinge more pre-tension on rope, tree sits still nothing happening.

Make back cut to desired hinge thickness, slight lift but tree doesn't go, tap wedge. Go to pull rope and heaved it over, all went perfect, easy, safe, controlled.

Tree was also side leaning, compensated with pie shaped hinge and adjusted gun. Pull rope running past front leader was against a branch that helped keep it straight too.

After it hit the ground everyone was quite surprised how it all came together, no stress, no panic, no running around fretting "pull the rope, pull the rope".

To me these are no brainers, backed up, safe and sound. Overkill on leverage, over kill on SWL design safety. The only dangerous part is traversing from the tree to the pull rope ... take a wide berth and keep an eye on the tensioned pull rope, see that go slack then run.

This wasn't a big tree, 400mm DBH and 12m tall, however it was a dangerous tree.

When I cut up the log the crack was through the stem and joined the other crack of the previous fallen co-dom at around a 60 degree angle, so this could have easily busted apart. Cracked apart on ground impact.

There was no-one other than me inside the danger zone.

There was protocol in place in case something went wrong (very rare when backed up so well using decent gear and knowledge).

If some-one wants to add $200 to the cost of this simple job to add another staff member into the overheads and danger zone then good on you, I dont, I put jobs together that I can do on my own and do them. What next, 2 men to trim a hedge? 2men to grind a stump?

How about no man touches this job till they get qualified just like other trades, then they'll be playing with a full box of dice not some half assed ideas likely learnt from another industry bad habit hack.

STILL NO-ONE HAS THE RIGHT ANSWER ON THE PULLEYS.

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Tree Machine

for the sake of simplicity lets just say it is attached using a rope-grab of some sort. If the line is wire-rope, a cable grab. Either way, assume (for the problem) zero slippage, just as we assume for the pulley zero friction.


This setup, at the other end is a single ascender linked to a Pro Traxion; a true pulley, but it is cammed, so any gain is frozen in the moment.

It made pulling my wife's tree out of the ground reasonably easy. A transplanting job I would otherwise hate to do, made fun by the simple fact I could work with a handful of gear. This setup was nearly identical to Ekka's scenario rig, minus one leg.

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Eric Frei

Hey Jim, you haven't answered the questions though. Come on mate have a crack.

On my diagram (the blue rope) they say count the "legs" to know the MA, 3 parts means 3X MA. So there's another tip.

Jim, on yours a little hard to tell but how many "legs" of rope? Looks like 5 if you pull on the end with the overhand knot and pull parallel straight back.

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Garry Brockley

My answer is
6=100
5=100
4=200
3=200
8=400
2=200
7=400
1=600

well thats how i see it

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Victor Lindsay

Okey,
5-100
6-100
3-200
4-200
8-400 force is applied directly to one with prussic, correct?
1-400
unsure about 7 and 2

Thats my shot, am i right?

Eric Frei

Here we go, I wrote it into the diagram.

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newguy18

lol,felling solo is dangerous,my first 18 months in the industry was all by myself,both on and off the ground,lowered pieces down and then went down,untied them and reascended,slow difficult and not to mention stupid.What Eric did was one of the better ways to go about it.

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old schooler

Garry Brockley

i thank you, i thank you, no, no honestly thankyou

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newguy18

whos being thanked?Eric for providing the answers?

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old schooler

Eric Frei

In this example there's 3 pulleys again, and as you can see by design of this system you only have 4x MA not 6 like the last example.

By thinking out your pulley systems you can gain a lot more MA.

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Done it

Bugger, I knew the answer. I learnt all that stuff when I built my tipper trailer, back in the 80's, it goes through 4 pulleys.

Anyway, this one looks a bit easier than carting a Forrest Devil around.

Phased1

FWIW, I get the same numbers as Ekka,...... now that the answers are posted.............

I personally use this setup a lot,and often working alone.
The only "possible?" difference is, I always use a ratcheting pulley (prussiks work too) in the system so I any force applied to the system/ tree is held in the system and I use a redirect pulley (extra pulley, third pulley, etc) so the rope I haul on is at the tree I'm cutting, therefore no need to move.
Even when I have someone else pulling on the haul rope I use a ratcheting pulley and a redirect so they're out of the way.

I prefer to use this type of system as opposed to pulling with a vehilce or powered winch as I can estimate the forces involved.
For argument sake I figure a guy can pull his own body weight, for easy math say 200lbs, 100kgs.
Just my 2 cents.
Phased1

Eric Frei

Any of you guys with ratcheting pulleys, please post a pic of it.

We have some rescue styles that are mainly designed for kermantle ropes (up to 13mm dia) ... but I'd be looking for something different perhaps.

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jim1nz

We use this in conjunction with the standard double rigging pulley.

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