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Forklift load calculations - One forklift versus two ?

Milacron

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Say one has a 15,500 lb rated forklift and one wants to lift a VMC that weighs 15,500. But it is 88" wide, such that the best one can do is 44" load center.

15,500 x 24 = 372,000 / 44 = 8,455 lbs.... which would indicate even with additional counterweight added it is unlikely the 15,500 truck could be coaxed into lifting this VMC. In fact one would need 28,000 lb capacity to lift the VMC with one forklift*

Now, assuming one has two forklifts to lift the VMC at both ends... but the second forklift is a little smaller... 10,000 lb capacity. At 44" load center this one would lift only 5,455 lbs. Thus even with two folklifts, one on each side of the VMC, the lift could not be done. (8,455 + 5455 = 13,910 lb )

Or could it ? Intuitively, in spite of the math, it seems like my particular two forklift scenario would work however... am I missing something ? Perhaps in that scenario the load center is really where the fork of each forklift first encounters the edge of the cast base of the VMC ?

https://www.practicalmachinist.com/yang1.jpg

*And yes I know once one gets to that sort of capacity sometimes forklifts are rated at 36" load center but that is besides the point
 
I've done the 2 forklift routine a couple times on rollformers, punch presses and a 50x100" Haas gantry router(the larger gantry on y design with a 9x15' footprint.

Communication is a major concern to be addressed.

On the roll former, side by side was easy-- we could see each other. We did 15,000 with (2) 8,000# lifts(hysters).

One press we had to bring in the building 100' with a downhill slope that leveled out. Neither lift could lift it and we had a lift (neighbor) pick it off the truck and set it on the ground... But he said too risky to take it down the hill to the building..... It was about 10 degrees that day. Anyway, one lift was overhead and the second was underneath and the changing angles had to be compensated constantly-- we almost lost it by getting out of sync. It would have easily flipped either lift.... But the overhead was certainly higher risk. We couldn't have eye contact/communication like with the roll formers.

I'm thinking if 2 pieces of heavy wall tubing (2.5"x6")sufficient for the weight and easy of fork insertion about 7' long.... May be a way to inctease safety. I'd clamp some angle to the tube to prevent slide off if height gets out of sync.

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Also, by having these 2 cross members (cradle) doesn't this push the weight closer to the mast and enable a closer to capacity lift? If your fork is enclosed in heavy wall tube, can you still flip it? Assume class 4 or less. The round bar hanging forks wouldn't help.

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I don't think load center applies in the two forklift scenario. The reason a load center is spec'd is to prevent the forklift from falling forward, but if something else like another forklift is preventing falling then why would load center matter? Imagine you were lifting a loaded elevator car. The elevator being on rails can't tip in any direction so why would there be any load center to worry about?
 
I don't think the number of forklifts will change the tipping point for each forklift.
If over loaded on the tip of the forks you will tip.

A second forklift obviously changes the weight and load center of the lift, but each forklift is still limited by how much and how far out.
 
The load center of the machine is 44 inches, the load center for each forklift would be the percentage of the load. If the forklifts are picking up the machine from opposing sides each forklift will bear some percentage of the load. Because the lifts are not the same capacity the bigger lift will have a higher burden but, it would not be at the full load center of the machine. Imagine force vectors for each lift, they wouldn't be at the center of mass, they would be at the center of their portion of the load.

Steve
 
Now, assuming one has two forklifts to lift the VMC at both ends... but the second forklift is a little smaller... 10,000 lb capacity. At 44" load center this one would lift only 5,455 lbs. Thus even with two folklifts, one on each side of the VMC, the lift could not be done. (8,455 + 5455 = 13,910 lb )

Or could it ? Intuitively, in spite of the math, it seems like my particular two forklift scenario would work however... am I missing something ? Perhaps in that scenario the load center is really where the fork of each forklift first encounters the edge of the cast base of the VMC ?

If you can position the forklifts so the machine is being supported closer to opposite sides, with the center of gravity between. Then yes, you can calculate the load center based on where you contact the forks. If everything solid and flat (or somehow the edge is pronounced or blocked-up, so taking the load) under the machine, and your fork tilt isn't angled up - putting the pressure further out on the fork, then it even can be calculated from the edge.

Imagine:
Two people side by side lifting a couch from one end - unless your wrists, and your buddy's wrists are much stronger than mine - not going to happen; unless you count it tilting while the one end easily comes up and the other drags. One person goes around to the other side: no problem. Both stand behind it; you might get it up each supporting the back with one hand, but it's really trying to tip you ahead - same center of gravity as if you had a fork under it supporting the front at the tip and back near the mast; even with two: same thing just each has half (or 40/60 or 30,70% etc) of the weight. Now, one person goes to the center, one centers in front, now again no problem - both lifting as easily as one on each end, though the couch itself a little less stable as you move around.

If your destination is too tight for both forklifts in the right spot, can you borrow or cheaply rent a couple machine dollies for one end and let the forklift do the work from the other? All the positioning math comes out the same, but a with little less onus on perfect communication.
 
You guys have failed statics and dynamics. The forklift can lift up to its maximum rated weight at any point along the fork. It makes no difference to the lifting cylinder or the mast. Oil pressure in the cylinder is the same regardless of the loads location along the fork. The reason the maximum lift is derated as you move out on the fork is because of the tip hazard, not because the machine can’t lift the weight. If you mitigate the tip hazard somehow you can lift more weight further out on the fork.


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Don't really need Dynamics here; statics covers the question.

At a glance, every post, but the one with a link and noting that it wasn't directly relevant here, was trying to keep the rear end on the ground rather than doubt cylinder force.

It still comes down to how close to the mast a given arrangement will apply the load.

edit:
Perhaps in that scenario the load center is really where the fork of each forklift first encounters the edge of the cast base of the VMC ?

https://www.practicalmachinist.com/yang1.jpg

Directly to the point: If arranged as in the photo, and If both edges used in the calculation are solid - then yes. It still takes some level ground, or creative rigging, to avoid really taxing the proficiency of the lift operators. Even at that patience and perfect communication are a must.

I've pulled a trailer away from, or back under, a load supported from each side several times. That's not too awkward, but the couple times I've tried moving with something supported like pictured, the pucker factor is exponentially worse! Unfortunately, I'm usually crazy enough to coax Mrs. to handle the other side; she gets a little flustered if the pucker factor get's too high. :eek:
 
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Have done this a few times and will never ever ever do it again, unless we're on a sub in the Pacific and there's a Jap aircraft carrier on the horizon and we need to get that hatch closed.

Say you have a 30,000 lb load and a 20,000 lb lift and a 15,000 lift. You carefully raise the machine, everything looks fine, sloooowly I turned, step by step then NIAGARA FALLS ! One lift hits a little bump or something, the machine bounces up then starts to tip over onto the smaller lift, the small lift starts to topple, the big lift is actually making it worse.

Want to talk shit in pants ?

IF you have two superbly experienced guys who know their stuff, they immediately simultaneously without a word both drop the forks as fast as they can, which evens out the load and gets the machine onto the ground safely (in about .3 seconds). In fact, during a successful maneuver you won't even have time to shit your pants, it happens that fast.

Or if it isn't successful, you'll be doing more than shit the old pantaloons ... you're going to be picking up 30,000 lbs of scrap and fixing a big hole in the driveway. Or repairing the building where the machine just punched a hole on its way down.

Saw this once. That was enough. I never ever ever want to be near that situation again.

I hate two-lift lifts. If you can put one on each side of a truck and drive the trailer out from underneath, maybe. But driving it around ? Not on your life, mama !
 
Witnessed it with a good rigger picking up a 84" dia. x 14' high Bullard.

IIRC a 30k and a 60k on sides of a large lowboy.

Just lift, and pull the trailer out.

They kept it level, but any deviation should cause more weight on the lower one, start blowing off the relief valve on that one,and it's game over.

Where's Machtool ?
 
They kept it level, but any deviation should cause more weight on the lower one, start blowing off the relief valve on that one,and it's game over.

There must be different arrangements out there. I've never heard a relief go off when idle or lowering, only when applying pressure, but usually anything I operate is on it's second, or third, or...., life.

Even if the lift isn't an issue though, a small mis-step could quickly make a rear-end light. Fortunately a SMALL error there will reposition the load back toward the mast as the angle shifts slightly - then back as things level again. But best not to find out the hard way, on a VMC, whether feeling a shift in the weight or a light steering wheel is an easily corrected error or the beginning of an ugly domino effect.
 
Say one has a 15,500 lb rated forklift and one wants to lift a VMC that weighs 15,500. But it is 88" wide, such that the best one can do is 44" load center.

15,500 x 24 = 372,000 / 44 = 8,455 lbs.... which would indicate even with additional counterweight added it is unlikely the 15,500 truck could be coaxed into lifting this VMC. In fact one would need 28,000 lb capacity to lift the VMC with one forklift*

Now, assuming one has two forklifts to lift the VMC at both ends... but the second forklift is a little smaller... 10,000 lb capacity. At 44" load center this one would lift only 5,455 lbs. Thus even with two folklifts, one on each side of the VMC, the lift could not be done. (8,455 + 5455 = 13,910 lb )

Or could it ? Intuitively, in spite of the math, it seems like my particular two forklift scenario would work however... am I missing something ? Perhaps in that scenario the load center is really where the fork of each forklift first encounters the edge of the cast base of the VMC ?

https://www.practicalmachinist.com/yang1.jpg

*And yes I know once one gets to that sort of capacity sometimes forklifts are rated at 36" load center but that is besides the point


When you run 2 trucks, your load center (of a rigid machine) actually gets to near zero. (right up to the mast)
At least as long as you don't try to tip your forks back too far.

Two 15's will doo WAY more work than a 30 would ever dream of, and have significantly less impact on the floor!


----------------------

Think Snow Eh!
Ox
 
In my mind the load center will be where the forks contact the lift point on the machine. It seems to me the load center would only be at the mast if you were lifting off of the enclosure.
I'm not any sort of rigger or crane operator though.
 
Say one has a 15,500 lb rated forklift and one wants to lift a VMC that weighs 15,500. But it is 88" wide, such that the best one can do is 44" load center.

15,500 x 24 = 372,000 / 44 = 8,455 lbs.... which would indicate even with additional counterweight added it is unlikely the 15,500 truck could be coaxed into lifting this VMC. In fact one would need 28,000 lb capacity to lift the VMC with one forklift*

Now, assuming one has two forklifts to lift the VMC at both ends... but the second forklift is a little smaller... 10,000 lb capacity. At 44" load center this one would lift only 5,455 lbs. Thus even with two folklifts, one on each side of the VMC, the lift could not be done. (8,455 + 5455 = 13,910 lb )

Or could it ? Intuitively, in spite of the math, it seems like my particular two forklift scenario would work however... am I missing something ? Perhaps in that scenario the load center is really where the fork of each forklift first encounters the edge of the cast base of the VMC ?

https://www.practicalmachinist.com/yang1.jpg

*And yes I know once one gets to that sort of capacity sometimes forklifts are rated at 36" load center but that is besides the point

Could it be done- yeah maybe. Personal call whether that’s wise though. How experienced are BOTH operators, and the 3rd guy supervising, figuring the 2 bull drivers won’t be in good visual contact. Pushing it like that with both machines getting light in the loafers at that point, a tiny overcorrection by one could lead both machines to lose steering. Fairly simple repositioning give her a go, but sharp turns or grades think it out.
 
With 2 forklifts, you can effectively move the weight all the way to the back of the forks, if you have your tilt on both set right, and you have one on each side. Let’s say you have a 15k lift and a 5k lift, if you have 2 operators that know what they are doing, you now have 20k of lifting capacity, regardless of how wide the piece is.

If you don’t go up and down perfectly together, on of the lift’s rear wheels can get light, and this is usually when people freak out, but it is no real cause for concern, because the other lift will take up its slack.

It should also be noted though, that according OSHA, when doing a tandem lift, you have to de-rate both machines by half. So according to OSHA, 2 lifts won’t pick more than 1.
 
Let’s say you have a 15k lift and a 5k lift, if you have 2 operators that know what they are doing, you now have 20k of lifting capacity, regardless of how wide the piece is.

Not quite.

Let's say that your 15K has 5' forks.
Your lift is 20' long and weighs 20K.

Your 15K can only assume 10K of the load at best - at the tips of the 5' forks (not that it could take a 10K load that far out anyhow)

That leaves 10K for your 5K to lift, and while THAT truck CAN use the back of the forks for a higher rating, it's not likely gunna be able to cover 10K.


So - in the case of the 20' long lift, with a 5 and 15K trucks, with 5' forks on the 15K, My guess is that you would likely max out somewhere around 14K load, ass_u_ming that the load was even along it's lengths.

If the lift was only 10' long, then it should work - yes, but as you get longer distance between trucks, the less that you can split the load.


--------------------------------

Think Snow Eh!
Ox
 








 
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