Modifying a Forklift

Okay thanks.. I was unsure about it.. but now I'm better. I know we have discussed block and tackle stuff before on cr4 years ago..

To revisit the pulley size idea... if the pulley size increases or decreases, and all other things remain the same... then as the cylinder extends, the pulley rotates more or less based on the diameter of the pulley?? For each unit of distance travel in the cylinder, then the circumferential travel of the pulley is pi x d. (chain travel)

so if I want more power, then don't I get more power with a smaller circumference ??(less chain travel, but the same cylinder travel)

perhaps I'm still confused. it sometimes takes a lot to dislodge incorrect notions.

I'm up now... morning coffee in hand... thinking about what you have said all night.

so I'm going to have to learn this one more in depth, as my "stubbornness" chip still won't let it go. I'll get back to you.

thank you

Chris

that is so awesome I'm speechless!!!

thank you

obvious ga, and simply the best explanation for us slower moving night creatures..... lol

chris

Dear Mr Warner,

Thank you for the pdf. Let me heap more praise on your effort, as in the higher resolution image, it gets even better!! I am humbly thankful for your time and knowledge. It is superb.

Chris

No!

this of course, was the correct answer... but I needed a bigger hammer to get through the dense matter...

They're both correct Chris, but rest assured I'm more than happy to have help beating stuff into you (and it was much clearer on the diameter question)

About 40 years ago as a student I worked for a heavy moving company. They would design machines for specific jobs.

An example was an "acordian" flat bed truck that could be extended to about 100 ft. Another was a stearable bogey for particularily long lond loads (fairly common now).

One job was to remove and replace lathes at an old technical high school. The doorways where narrow and low. They bought a small lift truck that would just fit the width, then cut the mast down to clear the head room. Extended forks and about 500 lb of added counterbalance and they had a successful machine. Their mechanical engineer was brilliant.

As a joke one day the shop crew used a big 50 ton Hyster and picked up one of the truck drivers cars and put it on the roof of the shop. However, someone else not knowing this, delivered the Hyster to a job site later in the day. -----several days later the driver was able to retrieve his car!

The right sized machine makes the job easy!

thank you for that!

chris

so if you had a system that could shift the counterweight dynamically (or preemptively) more to the rear, that the forklift could safely lift more? (or alternativelly, have some forward stabilizing legs put down?)

chris

At one place where I worked the common practice was to stack 8 - 10 50# bags of sackcreate on the tail and four of us 250# guys would hang off the sides and back. We could easily pick up 5000# with a 2000# rated forklift just as long as it was up close to the boom and never went over 6 inches high or was on soft ground!

Still I recommend using the correctly rated machines to do the jobs they where built to do. Gross overloading is just asking for problems that could result in injuries and possible deaths.

I'd run this by my insurance risk manager, first.

There are two reasons there are limits on this stuff in the first place.

1. It helps keep sane people from over-stressing the equipment.

2. Lawyers.

okay... I agree.

perhaps this is too much of a homework question anyway...

cheers,

Chris

you could always replace the counterbalance with one made of lead or DU....

that would put more weight in a smaller space.. which would be good for counterweight. but are they safe? I have no experience with DU. Is lead or DU paintable or would it have to have a plastic shell?

thanks,

Chris

Yes, I worked at TIEM, and we used a tilt table for stablitly testing. This involved giant weights that were calibrated by an outside company that had amazing giant forklifts that separated at the middle so that they could double the length of the forktruck once on site. This made it possible for them to lift amazing loads.

The biggest thing to consider is ramps and such. As stated earlier, almost all forktrucks can lift the counter weight off the ground. The trucks are rated for the load they can lift and still go down a standard ramp without tipping over. And if you experiment, wear a seatbelt. If it goes over, you should stay in the over head guard. Most fatalities happen when people try to jump off and the guard gets them. Its counter intuitive, so the seat belt keeps you from acting on your instincts.

sounds like you have good insights into the forklift design industry... tell us some more stories please.

and yes, my forklift training included videos of guys cut in half by the operator roll cage as they tried to jump off..

thanks,

Chris

Also, many forklifts come in several capicities on the same frame, so a lighter rated forklift may be able to be "upgraded" by changing a few parts, not the least of which would be the counter weight.

If a lift is at it's max, easiest way to increase the capacity would be a bigger lift cylinder or smaller pump. Either will increase the lift and reduce the speed proportionally.

At least in the USA, (Please don't get into the rude American thing, I simply don't know the specific laws and rules in other countries. I am not saying other countries don't have good safety programs) it is only legal to modify a lift truck if you can get approval of the changes from the original manufacturer. -- JHF

Go for it! I wanna see the "Caption This" submission.

yaaaa... no... I have my forklift cert... and training on the 'triangle of forces', etc...

and I take safety pretty seriously on this issue...

I'm asking for other reasons... and not trying to create trouble for anyone.

I'm a firm believer in understanding all the forces and workings of mechanical systems before trying to 'improve' them for specific applications. I don't mind the stern warnings of what not to do...

but is there a safe and right way that one can modify these things for increased lift.. that is what I'm asking. (without rebuilding the hydraulics)

Chris

chris

OH yes, thanks for the LOL today, good but OT

I'm not picturing it... can you make me a quick sketch in paint, or provide a picture please?

thanks,

Chris

Forgive me I do not have your talent or tools for graphic design.

The pulleys have moved the same distance (blue versus white fill) but in the configuration on the right the lift has only moved half as far as the left.

so you are essentially saying to eliminate the pulley action, and go with a straight push by the cylinder.

Yes, that is exactly what I'm saying. In the pulley systems I've seen on fork lifts the pulley increases the travel length so that a 3 foot ram can raise a lift 6 feet. In the initial picture you present I believe the ram end goes inside the box between the two pulleys.

thank you. that is one option on my short list then.

cheers,

Chris

GA! I didn't think of that, but exactly right! Again, GA

Yes, it's true, but if you do that in practice, the 1-side pull of the chain will put radial forces and stress on the shaft of the ram, wearing all seals in no time. You would need to mount a stiff rail and slide the fork platform on bearings thru it.

Oh, wait, I think a mastil is already part of the lifting mechanism, but anyway, you need to re-locate (center) the ram in order to reduce the side pull of the chain.

Yahlasit

when I suggested a dynamic counterweight system.. I would also include an interlock so that it only can lift such loads when not in 'transport mode.. but only in a fixed 'safe' lifting stance.

thanks,

Chris

well yes.. but the danger and instability increases with the height above ground of the load... so I'm thinking it would be pertinent to limit the travel while the load is up.. but perhaps you are right and that won't be the best plan.

thanks

Chris

There are some forklifts designed with an adjustable (fore and aft) counterweight on them. They tend to be larger ones, probably rated at 8K lbs and above, and used by riggers who have to navigate through narrow aisle in plants to remove/install machines. They are sometimes used in conjunction with other rigging tools such as "roller skates", dollies, rollers, etc. to get the biggest capacity from an underrated or smaller foot print forklift.

When lifting near or exceeding the capacity of the fork lift always tilt the mast back as far as possible to put the center of gravity further back from the front drive wheels, which are the fulcrum.

There are many ways that a fork lift can be used in conjunction with other devices to move objects that weight considerably more than capacity of the fork lift. I would explore that path before I would overload a fork lift. A good rule of thumb is that if the load exceeds the hydraulic capacity (no lift when the up lever is pulled) or the whole unit tilts forward and lifts the rear end up then you have exceeded the practical capacity of the fork lift.

Have you ever seen a fork lift with one fork lower than the other? That's because the capacity was exceeded and the lower fork bent. Tough to pick up a pallet or most other loads when the forks are not even.

Also fork lifts tend to fail in less time when they are abused/overworked as compared with when their capacities are respected.

Good Luck, Old Salt

thank you

do you have more info or links to the additional equipment used? (ie rollerskates)

cheers

chris

If I am understanding what you want to do is: Adapt the forklift to lift a much heavier weight than the rating of the FL up while being stationary? I get the picture in my mind of lifting a heavy transformer (or other equipment) from the floor straight up and attaching it to the steel rafters of the building. If so, you can not change the chains as you would lose the lifting height. This would possibly create a serious breach in the chains/pulleys/axles and depending on the age of the lift and wear and tear. Could be a serious accident waiting to happen. It would be best to rent a lift for the day to do this job function. Safety always has to be #1 for all involved in a job like lifting heavy objects more than 3" off the floor. Some things you can get away with, not lifting heavy objects without the right lift capacity. I still have all my fingers and toes. Heavy equipment operator for 35 years. 0 accidents! 0 lawsuits!

yes... safety.

but this is purely hypothetical, so I'm able to put my genie hand on the vehicle to hold it in place while it lifts, and that is sufficient.

I'm just wanting to figure out a mechanism given certain initial conditions.

cheers,

Chris

This pulley arrangement multiplies the fork travel x2 compared to the cylinder, in return for dividing the cylinder force ÷2; no change in power. A bigger pulley just rotates less; same stress on axle.

if the lifting of the fork was entirely by a hydraulic piston then theoretically adding a second piston (two side by side) could enable you to increase the lifting capacity as the weight of the load would be distributed over both pistons- but I am not sure how your forklift lifts the load- the picture shows a chain of sort- I am not sure how that is used... so I have no idea if my idea would work on your forklift...

_{Now I'm really biting my tongue - FFS!}

Hi DJ,

I think you are right about twinning the cylinder. It would double the cylinder area, and the hydraulic pressure would be the same, so the volume of fluid would drop. All I can think of is ensuring that the fluid reservoir might have to be enlarged.

But again, this is all hypothetical, and I don't have a forklift. I've driven many kinds of them and have an operator cert.

cheers,

Chris

What a dud! It didn't even go off!

"With no weight on the rear wheels, the forklift continued in a straight line, right over the edge."

"bombing around on the forklift" takes on new meaning.

talk about "following the ordinance."

Chris

Big Forklift Accident : His Last Day.....

I see your forklift accident and raise it with a "Klaus forklift driver" video..

http://www.youtube.com/watch?v=p_h6oAj5p1g

Puts a new perspective on training videos...

Here is the full version

http://www.youtube.com/watch?v=0jmnFARPexw&feature=related

Don't watch it if your squeamish...

Germans, who'd of thought they'd have a sense of humour...

omg... while watching the first one, i came across this.

makes me think a 'dirty underwear' thread might have a few posts...

chris

If you increase the lifting capacity, you would have to up rate all the other parts.

the strength of the mast, pivots, axles,wheels,brakes,counter balance,forks,

Just get a bigger truck thats designed for the max load required.

if after you modify a truck an accident should happed you would be in deep sh*t

with the authorities

Byt the way the main limiting factor is the hydrulics and the main lift ram,

followed by all the other components that support the ram,and fork carrige

http://www.google.co.uk/search?hl=en&rls=com.microsoft:en-US&rlz=1I7GPCK_enGB411&&sa=X&ei=eXgYTfKxJIjMhAfdoKS4Dg&ved=0CBkQvwUoAQ&q=design+and+theory+of+fork+lift+truck+lift+hydraulics&spell=1

Thanks Peter,

you are right about the consequences of an accident. so a design that doesn't change the basic parameters is required.

you are also right about all the other factors that are part of the design, and would have to be considered. It is a complex operation that may well be equivalent to purchasing a new larger class vehicle.

but this is just a thought experiment, so we get to ignore certain factors, or take them for granted.

cheers,

Chris

We would call Tubby to hang off the counterweight if we had a heavy bunk of lumber to move when the big lift was busy. He would stay on if we kept the forks tilted back and lowered on flat ground or frontward up a ramp. He had an infuriating habit of jumping off at the wrong time. This would let the load slip off the forks and the rear end come crashing down on the steering wheels.

Tubby didn't have a high school education, but he understood leverage just fine.

omg...

sounds like he got an F in school, and is a C in forklift leverage...lol

Chris

Being a motorcycle nut, I'd have to add the olde saying about the weakest link in the chain...

is the nut behind the wheel?

cheers,

Chris

It certainly would!

I like both the moving the counterweight back idea and the front supports idea. The "extra" counter weight could possibly be mounted on the side(s) of the FL with a mechanism that would move/push it to the rear as needed or even as part of the lift mechanism. The front "temporary" supports could be made with heavy duty castors mounted so they could do some movement and provide front support as well. This would need some thought so it would clear the front forks.

My thoughts so far without losing any sleep yet! (don't get your fur caught in the mechanisms! )

No!

This would limit the width of the load but take care of the tipping.

Use the top of the verticals as fulcrums for beams with ropes or links to the forks and moveable counterweights out on the back. Think Dutch bridges.

How can one increase the lift capacity of an hydraulic forklift without modifying the original design? All of your options are a change to the design! Think about your question!

I rather think that Chris is "Bench Racing" and so is looking for relevant information to improve his knowledge on forklifts per se rather than actually doing something "silly".

yes, actually a friend asked me... so I was curious what could be done.. but i think we are down to just a few options. I just wanted to be somewhat comprehensive in my thinking, and what better place to find out than cr4?

Well if you want to design one, move the front axles as near as possible to the load center of gravity.

This is always a compromise on wheel diameter against the floor/road characteristics, but the axles are the fulcrum, so every bit forward is a 'double effect' on 'tail weight' leverage.

I like the one you showed earlier... with the 'outriggers' in front... I'm just wondering if those could be assistive scissor lifts somehow that can be brought to bear once the forks are in place.

thanks

Chris

Touché.

Or, you could always simply call in John Hutchison to "lighten" the load in the first place.

(just a bit of "off-center" humor )

As goofy as that might look, I would guess that nothing was actually overloaded in that set-up. It could make a good class exercise to explain why or why not. (Can't do any calcs w/o knowing the weight of that ring gear assembly.)

excellent thank you!