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Any experience using fork extensions on forklifts ?

Milacron

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Never used them before and was wondering if the resistance to bending is as good as the fork itself ? In other words, say you have a 5,000 lb capacity forklift with 6 foot forks and you lift a Brideport mill by the ram that sitting in the middle of a semi trailer. Now with the 6 foot forks, you could do this easily...the forks would bend some but would spring back to original position once you set the mill down.

But say you have the same forklift, but with 4 foot forks and you use a 6 foot fork extension (and I'm talking proper "store bought" ones...like from a material handling supply) to do the same thing. Would the extension handle the weight without getting a permanent bend in it, just as well as the "real" forks ?
 
DT,
De-rate max load, longer forks, larger moment of force, have lifted parts with long forks & had it teeter totter, add four big Lads to the back end to hold it down, definatly not OSHA approved.
Yes they will flex some.
Cheers Les H.
 
I have always heard to reduce the capacity by 50%, at the midpoint of the extensions. IE: 5K lift truck with 4 ft forks, with 6 ft extensions, Max lift would be 2.5 K at 5 ft. Seems like OSHA says that extensions cannot exceed 150% of fork length,IIRC. The fork extensions I have seen, even approved ones, still look feeble to me, I always though of them as just a handy tool to lift items less than a thousand pounds...
 
We had a couple of sets of extensions at work, both shop made and purchased. Both seemed to hold up fine but were probably never loaded anywhere close to their capacity. If your intended use is primarily for overhead lifting, you might consider a boom as an alternative.

FORKLIFT.jpg


It offers a longer reach and a convienient hook. Downside is it takes up a bit more vertical real estate depending on how you rig the load and if you need to fork it, you're out of luck.

Marc -
 
I have store bought ones I use all the time on mine. I find the extension itself is stiff but because they sit on the fork they allow the fork to spring when loaded. Mine don’t taper to a knife edge like a regular fork but are more like channel iron with a bevel cut on the bottom so you're not going to drive the tips under a load to pick it up. I haven't bent one in spite of my occasional abuse but they seem like the type of thing that will get to a point and yield rather than slowly sagging. Bob
 
My experience with them is they are for light-duty work.

With your example above, gaining only 2 feet of extension (I think you meant the 4' forks buried inside 6' extensions) they are going to be fairly stiff. The ones I've been involved with were more like 10' extension over 6 foot forks and were light-duty, but did the job needed with a good bit of flex under load but no yielding, as the closest part of the extension will deflect vertically up before it contacts the inner fork tip, then start to deflect down.

The extensions are rather clumsy because they are covers (inverted channels really).

It's the old conundrum of fork length...long forks give you flexibility in reach but cut down on mobility in tight spaces, usually indoors...
 
In my years of driving a forklift, I have only managed to bend two sets of forks. Both were when fork extensions were in place.
We used them extensively at the mill I worked at, and our in house built ones worked a lot better than the purchased types. Probably because we knew what we wanted to use them for and not for general work. We also had the largest counterweights available from the factory.
David from jax
 
DT if i am understanding correctly, you just want the longer forks to be able to *reach* the mill at the center of the semi-trailer?(4 foot will reach ,but not go under and thru the load safely to pick it up)if that is the case then i would pick it up (with the extensions)then move it over some toward the edge of the trailer,sit it down,move forks in further under load so that the real forks are actually what is picking up the load(of course leaving the extensions installed), then lift again. trying to do a one pick up lift and removal of the mill from the trailer on the end of the fork extensions would be asking for trouble.like has been stated, capacity is lost with the extensions as you move out toward their ends but just to move it a couple of feet like i mentioned should work ok.
 
Good grief spencer, I was just using an example. I've moved a gazzillion machines, most involving way more weight and complexity than my example, and need no education in how to do it.

It surprises me that basically no one seems to have "got" what I'm getting at here yet, so let me try to state it another way. If you have a 6 foot fork and are picking up XXX lbs with weight center point at 5 feet out, will a 4 foot fork with 6 foot extention mounted (i.e. 2 feet of the actual extension juting out unsupported by the fork...and only one foot unsupported with the actual weight on it) handle just as much weight as the 6 foot fork would have, without getting a permenant bend in it ?

Forget the forklift, forget how to "do it", forget the disavantages of the extra thickness..that's all obvious enough.. forget everything else and just concentrate on the forks and extensions from a bending standpoint....that's all I want to know about.

=================================

(on edit) David/Jax's comment got me to thinking and I think I now see the disadvantage of fork extensions over fork as long as the extension is...and that is not what I at first thought. The problem is not that the fork extension will bend, but that the fork it's sitting on will be more likely to bend unfavorably ! The reason for this is a 6 foot fork is designed with it's length in mind and is simply built thicker and heavier at the heel than a 4 foot fork. So the 4 foot fork picking up 5 feet out is more likely to bend the fork itself at the heel !

Same deal with the boom...in fact Marc's forks look bent at the heel in that photo ! Seems like you couldn't lift didly squat with a boom jutting out that far anyway. (not to mention the weight of the boom itself robbing ultimate capacity)

So really, the only way a fork extension would be just as good capacity wise as a fork of the same lenght would be if you sawed off a 6 foot fork to make it 4 feet long ! (and before anyone starts pontificating on how "oh no, you dont want to do that..would be too thick for entry,etc"....I KNOW THAT, JUST MAKING A POINT
;) )

Does everyone agree with this ?
 
Yes and no :D

My answer is cryptic because what David is referring to is the channel extension can essentially be made stronger than the fork...due to strengthening geometry of the channel vs. the standard flat bar "bent the easy way".

But, the load gets concentrated at the tip of the 4 foot (inner) fork, because that's the other point of contact other than the heel.

For your example of only wanting to gain 2 feet of extension (4ft->6ft), I wouldn't feel confined by that at all, unless you are into say 5k loads or more, all bearing on the 2ft extension....(assuming you are using that new 15k propane
)
 
D. It's all proportional.

As was pointed out the usual fork extensions are either home brew from channel (always too weak and prone to fail but adequate for light loads on middling reaches) or factory made with fair engineering.

As I understand you want to know whether the overhang from the forks is up to the load. Here you can't get away from a little discussion and engineering analysis - and the usual safety BS. That part of the beam between the fork and the load center is cantilevered where the section has about 1/8 the total load capacity of a simple distributed load, end supported span as read in the load tables. Usually you can look up the section and follow the table across to the span and divide the safe load there by 8.

By "resistance to bending" I presume you mean stiffness - resistance to deflection. Here I can say hell yes. But the springyness of the system is primarily controlled by the fork section. The extensions them selves are usually quite stiff.

The stiffness of any fork mounted system is dependent on the section of the fork near the mast. You dont have to have much load or extension before the load resonance and deflection combined with terrain and driver's reaction time lead "pilot induced oscillation" a positive feedback situation. These phenomena can have grave consequences. The extension and load combine to amplify the fork deflections and lower the resonances into critical territory. Smart forklift drivers work at creep speed when using a fork extension even with a straight shot down a smooth floor.

As for safe load on the extension (forklift capacity set aside for the nonce,) what you're looking for is a safe cantilevered bending moment per foot. From that you can figure the load extension by the safe cantilevered load moment divided by the load. The result in in feet or inches depending on how the moment is expressed.

Those husky factory made fork extensions and boom lifts that look like the photo above are certainly factory made and should be safety plackarded to the limits of CYA tort protection.

If you want to know the safe load for a mystery fork extension made in the shade of a tree by a farmer or a logger or one made right but whose plackarding is missing you'll have to work out the numbers. Got an ME buddy who does some structural analysis? Feed him lunch and have him look at your problem. I'm sure he can give you some back of the envelope calcs to set your mind at ease.

The safe load on the forks is protected by the stabiliity of the forklift; the counterweight ensures that; think of it as a "gravity fuse." The ability of a forkift to carry suspended loads is frought with peril if the load is extended for some distance and allowed to swing. What is safe as a straight hang may cause the forklift to fall forward if the load swings out from the brakes being applied or a ramp negotiated with the load down hill.

If I insulted your intelligence too bad but your problem is pretty much straight forward out of the book engineering statics.
 
D.,
I don't think the weight of the forklift boom would make too much difference.I was interested in one similar in size to the one in Mark's photo at an auction earlier this year.I picked up the fork side of the boom and I'm guessing it was about 200-300lbs.Two bidder's bid it up to $400-500 irrc.

I've been looking for a good set of extensions too.I can't remember seeing any at auctions that weren't bent or abused in some fashion.

I would like to be able to unload a truck box or 20' shipping container for storage. I have been looking for some long forks at a reasonable price for a while with no luck.
 
As I understand you want to know whether the overhang from the forks is up to the load.
That is what I wanted to know, but after David/Jax's post I now realize the manufactured fork extensions are up the task, but the forks themselves may not be.

As to the 'gavity fuse' that is a good way to state it, but of course having lifted all manner of machines with most manner of forklift am well aware of the geometry involved.

But while we're pontificating on forklift hoisting geometry irrelevant to the actual point of my topic, I might as well point out one of the ironies of forklift capacity ratings for others to chew on.

And that is, forklifts load capacity is usually downrated the higher the mast can go. The irony of this is that you actually have *more* capacity the higher you go if the mast it tilted back all the way. The higher you go in a back tilt situation, the further back is the CG of the load, thus less counterweight is needed for a given load.

Also, forklift capacity should in theory be exactly the same with the load 12 feet up as it is 12 inches up...if the mast is kept perfectly level and you are on level surface.

But of course the reason they downrate them in that situation is a valid reason, as they worry that the operator unaware of this little tidbit will pick up more than he should in a high tilt back situation, and then as he lowers the load the geometry becomes unfavorable as he gets lower and the gravity fuse comes into play in a potentially diasterous manner !

I presume they also worry about folks not keeping it tilted back and actually tilting forward some, with equally unwelcome results.

As such, for safety purposes, the higher masts on the newer forklifts, have their tilt back angles limited on purpose. Which is one thing I like about the shorter masts, as they have full tilt back capabilty, which can be useful not so much to gain capacity but to gain safety on loads prone to fall forward if you have to travel slightly downhill in forward traction or were to hit a bump in the asphalt.
 
I will disagree with Forest, when fork extensions are used, the CG moves out to the tips of the machine's forks, and it is the tips of the forks that bend. In HS I worked at my friends dads boat shop, we had 14 foot extensions on a 10k forklift, moved 3k boats all day, one of the guys lifted a boat bow in instead of bow out, bent the machine forks tips as soon as he moved the boat. The cg was to far forward.
 
Forks are not any thicker when made longer unless you request it and then there is no real reason to as all capacities are calculated with 48" forks and when using longer ones the added weight of the material and the added lost load center will lower the capacity and has to be so stated on the capacity plate to be OSHA conforming.As to fork extensions, they are also made to pick up a longer than standard load and should be up against the fork carriage. When you are picking up out past the fork many extensions, depending how the hooks are designed, they want to *kickup* at the fork heel and tilt forward if they don't have a securing method to keep them from sliding or pulling off as well as something to lock them down. You can bend anything when past the fork but if they are of a good quality I doubt that that little amount will affect it? But that advice is free and worth that much-NOTHING!
 
Forks are not any thicker when made longer unless you request it
I'm shocked by that comment big, as it simply makes no sense. In fact, as regards to Class 4 forks at least, I went over this very subject with the fork manufacturer when I ordered new ones back in 2002, where they told me the longer the forks, the heavier they are...not just because they are longer but because the longer they are the beefier the heel and "foot" area have to be to anticipate the added stress.
 
any fork extentions I have been around I would not trust for full load. If this is a common problem do it right and get the real fork you want.
 
D. Why would you be shocked? You missed my point completely. You are getting less capacity to eliminate added stress.You Can only pick up half as much4' x 8' plywood picking from the 8' end as you can the 4' way if you want to calculate in. lbs. so whats the deal?5000# plywood on 24"L.C. =120,000 IN. LBS. TURN IT AROUND And pick it up the 8' way and you have 2500 lbs. on a 48" l.c. = 120,000 in. lb.wheres the added stress IF you go by the rules?You should not be trying to lift the full 5000 # bundle the long way,thats 240,000 in. lbs.
 








 
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