calculating load loss using fork extensions 2

[micjk]

I'm trying to find a way to calculate the max load a fork lift can handle if you are using fork extensions, for example I have a lift rated at 5400 lbs at 24 in load center. How would I figure max capacity at 36 in load center. Reason I am asking is I have a gear box that I have to remove and will have to use 6 ft extensions to be able to get to it. Gearbox weighs 680 lbs. Don't need anyone to calculate it just steer me in the direction of a formula or where I could find one. I'll do the math. Personally I think I am well within the safety "bounds" of the equipment.

Roy Gariepy
Maintenance and Reliability Dept.
Dorlastan Fibers LLC.
Goose Creek, South Carolina USA

 

[unclesyd]

At the change in centers that your are contemplating it is just a ratio of distances. 24/36 x rated load

 

[micjk]

Thanks unclesyd,
Thats exactly what I'm looking for
Kind regards,

Roy Gariepy
Maintenance and Reliability Dept.
Dorlastan Fibers LLC.
Goose Creek, South Carolina USA

 

[tygerdawg]

This is a question for the manufacturer's Engineering department.

But their answer **MAY** go something like this:

(allowable bending moment on the stock fork) = (5400 lbf) X (24 inches) = 129,600 lbf-in

(AND it should be higher than that due to an unknown Safety Factor.)

Do the substitution for 36 inches, then
(allowable load @ 36") = 3600 lbf

Anybody else have a more accurate approach?


TygerDawg

 

[ARenko]

You need 6 ft extensions, but the load center only moves out one ft? Are you measuring the load center from the center of the front wheel?

It's basically the ratio of the load centers, but the manufacturer may also consider the effect of the weight of the fork extensions if you asked them for a number. Doesn't look like you need to worry about it though based on your numbers.

 

[JStephen]

The load center should be measured from the back of the forks. You can figure that moment is either limited by strength of the forks or by overturning about the front axle. If limited by strength of the forks, just design so that original moment at that point is not exceeded. If limited by overturning, design so that the original moment about the front axle is not exceeded. If, as quite likely, you don't know what limits the load, use the lessor of the two resulting loads. And don't forget to include the weight of the extensions themselves in the calculations.

 

[ARenko]

Last time I purchased a forklift I asked what was meant by 24" load center and was told it was 24" from the center of the front wheel. Seemed that wouldn't even get you on the forks, but I thought maybe that is just how they standardize to compare different fork trucks.

 

[ARenko]

A quick google search confirmed you're right JStephen - it is measured from the back of the forks. Considering this, the ratio of load centers is only applicable to calculating the allowable load on the forks themselves to resist bending. A different ratio would apply [(24+x)/(36+x)] to calculating the new load based on overturning about the front axle.

 

[unclesyd]

The front wheel is used as pivot point in respect to total weight forward of the axle. If the rear wheels start to lift the truck is over loaded, a safety check.

Here is what we used for extended reach lifting with fork trucks.
Check the fork truck attachments .pdf

http://www.vestilmfg.com/products/mhequip/booms.htm