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Scenario:
I have on site a telescopic forklift that is capable of lifting 1 tonne at its maximum extension/radius (13m). This safe lifting value increases the higher the forks go!
If I want to lower something into a hole ie via the use of chains attached to the forks does the safe lifting value decrease?
Fwiw I say yes it does! Sales man rep type says no!
yes, it's to do with the moment around the pivot (your front wheels)
as the jib comes down in an arc, the vertical force (thanks to gravity and the description of an arc by the jib end) moves away horizontally from the pivot. In order to prevent the forklift tilting forward the total mass on the jib when horizontal with the ground needs to be less than when it's up in the air to stay safe.
If the load is hanging straight down underneath the jib head on a chain though it is acting in the same way as if it was sitting on the forks themselves.
is safe lifting defined by tipping risk or arm snappage risk ?
regardless, presumably 1 tonne fully extended and only just held off the floor is maximal force on the arms
IANAForkliftdriver
Yes it does.
(But I have no idea why)
[source: I once got a MASSIVE bollocking for trying almost exactly the same thing as this at Hull Docks 🙂 )
This safe lifting value increases the higher the forks go!
So it can lift something safely at height that it cant lift off the ground AWESOME.
Have you considered using pulleys so it i technically lifting as it lowers?
forklift pivots on contact patch of the front wheel, it is the distance from the pivot point weight that matters, and also any counter weight acting against. if the weight is below the pivot it can still apply leverage.
Think L shaped cranks.
It'll be fine.
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Perhaps.
No, it increases... It's to do with the distance from the pivot point as stoner states... So as you go above a horizontal arm this decreases (ie the load is now less than 13m from front wheels). If you took it to extremes and had the load vertically above the front wheels then there is no turning moment and max weight is no longer determined by risk of overturning... As you go below horizontal, the same thing happens - doesn't matter how long the chain is - gravity only works in a downward direction so if the chain is 1m or 10m gravity is still acting on the load in exactly the same downward direction.
No quals to back this up but photos of outcome please 😉
as an Ex Hyster salesman I would say as long as the load is rated within it's capable lifting height then you'd be fine. The ballast on the back of the truck should prevent it from bucking up and the main concern would be the load not bending the forks or stressing the mast.
I would however say:
ensure nobody is underneath the load
Ensure the hole is smaller than the forklift 😆
Oh and I only lasted six months before getting the bullet
So it can lift something safely at height that it cant lift off the ground AWESOME.Are you sure about this?
Have you considered using pulleys so it i technically lifting as it lowers?
Try lifting a car battery over your head with straight arms. Then try it with the battery as close to your body as possible.
Lifting something out of a pit with a chain is the same as lifting something off the floor.
It won't snap , it's the tipping forward into 3.5m hole risk. Telehandler so stabilisers will be out. So stoner are you saying there is no extra load. The weight will be packs of blocks on a block grab directly beneath the forks.
Do you mean a forklift or telehandler? I'm an AP btw.
Bit confused now, but basically 13m out from the front wheels with the load is the greatest risk of tipping. As you go up or DOWN from this the load comes nearer to the front wheels, so the risk of tipping reduces. There may be issues with the machine not being designed to support loads below ground level, but the physics are straightforward...
Keep the boom horizontal and doesn't matter how long the chain is, you've still only got the same weight acting on forks. So use a chain block to lower below ground level and no issues...
Lifting something out of a pit with a chain is the same as lifting something off the floor.
If the weight is being lifted through the front wheels then i would agree, but it is not the mast/heel etc on a forklift enforces a lever of about a foot minimum. a standard pallet puts the weight a bit further forward. this is part of the reason for tipping the mast back, another being flipping the truck by embedding the fork ends in the ground...
take the weight high or low and the lever increases because a force is being applied to turn the forklift around the front wheels.
It's down to centre of gravity, if dropping the load into the hole is moving the centre of gravity forward it will reduce the safe load, thinking about it as the load goes down the centre of gravity will move forwards.
However if anything goes wrong you're in a world of smelly stuff unless whatever attachements you're using are rated appropriately. I'd only consider doing this (and I've done some less than approved things with FLTs) if you're really sure the load is well within the normal plated capabilities of your truck. If you're asking questions on here my guess is they're not.
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Same thing happens as the load is lowered.
just do it and take it easy! non of this working out stuff!
if the back wheels come off the ground its too much. Oh and ware a helmet 😀
If you look at the photo, you'll see that the fork telescope isn't vertical. So as the forks rise, the CoG of the load moves back. So if you're lifting something in/out of a hole, that location isn't relevant, it's to do with where the chains are attached to the forks and the height of the forks.
this is one of the few FLT's i drive in the military.
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Providing what you are lifting is 1 tonne or less and you rig your load with the chains at the back of the forks, it'll be fine. The maximum working load of the machine will be calculated at the worst point in the arc of the jib, i.e straight out in front of the machine. If you are going to exceed the safe working load of the machine you are asking a bit of a different question.
To clarify I will attach the lifting rig to the forks via two sleeves. Centred below this will be 3m of chain and then a mechanical block grab that works like a scissor. Drop this over pack of blocks. Lift the boom. At this point as I drive towards the edge of the pit the forks will be say 3.5 m in the air with the u/s of the blocks just above the ground. Reach pit edge, stabilisers down, boom out. I will then lower the pack into the pit at which point the pack is now below the machine. Eventually the boom will be approximately at ground level! All this done with a 13m telehandler.
sounds ok you have stabs so shouldn't be a prob
Stability is governed by radius and load. From the lifting position, the radius will increase as you lower until the boom is horizontal. Lowering further will decrease radius. At your maximum radius, is the total weight of the load (including lifting attachments) less than that shown on the load chart?
From the way you have described it my gut feeling is that it will work; obviously with the usual precautions of exclusion zone below the lift etc. However, I have a nagging feeling that SWL changes drastically once the load is below the level of the tele-handler, even though your boom will be level, but I'm at home and haven't got references to hand. They aren't designed to be used as you describe.
My professional attitude is "What do your RAMS and Lift Plan say?" Required by LOLER Regs. You are using it as a crane and it should be treated as such.
Oh and ware a helmet[b]-cam[/b] 😀
Baron_VD has a point, RAMS, Lift Plan, LOLER competant person/AP. Worry is that you are having to ask if this is safe, so the question is, are you a competant person to assess the task, if you think not, then stop and find someone who is.
Please get this recorded and posted up though as it does sound quite interesting....
Is it on a conveyer belt?
Try lifting a car battery over your head with straight arms. Then try it with the battery as close to your body as possible.
now lift it back over your head again, straight arms, but this time the battery is smeared with butter, now get someone to tickle you.
Don't forget attachments,block grab chains etc weight is considered as part of the load so you may not be able to lift/lower a full tonne of blocks.
It's not a worry as I've undertaken this same project in the past. I just wanted to know the actual science behind the scenario. The actual swl of the tele is 3.5 tonne up close and at no point will it be required to boom fully out. I treat safety on site very seriously and have been around long enough I reckon to be considered "competent".
Just wing it then.
Watch this vid first,
http://m.youtube.com/#/watch?v=Tqd4aPs5WTA&desktop_uri=%2Fwatch%3Fv%3DTqd4aPs5WTA