3 point lift capacity with boom pole

[widefat]

I am getting ready to buy a 3 point boom pole.

The tractor (K L3200) specs say the 3 point lift capacity is\:
1998 lbs at the lift points
1435 lbs 24in behind the lift points.

What does that mean?

Is it:

Tractor ---> 3 point hitch ----> 24in behind 3 point ----->Mid boom ----> boom end
Capacity -------1998 lbs-------------1435lbs---------------------? lbs--------------? lbs

If the above applies, then the lift capacity mid boom, and at the end of the boom, will be significantly lower?
If 24 inches behind the lift point just happens to coincide with the mid boom point, then the lift capacity would be 1435 lbs at that point?

 

[4570Man]

I suspect you can lift the front wheels off the ground which throws a real monkey wrench in all this math.

 

[Fallon]

I was unable to lift my front wheels with a 3pt forklift & filling an IBC tote until the 3pt wouldn't lift anymore. I think the 3pt has less lift capacity than the loader & engine provide counterbalance on the economy L 3000 series.

The further out, the less leverage & the lesser lift capacity. Goes for all 3pts, loaders & hoes.

 

[CalG]

Calculation of boom lifting is not as simple as resolving loads on points.
One first must determine what is the limiting element of the boom lifting action.

Is it over turning the tractor backwards around the rear axle?

Is it exceeding the rear axle load capacity?

Is it exceeding the hydraulic force limits offered by the 3ph system?

Is it exceeding the shear strength of the lifting arms or pivot pins and eyes.

That would be a difficult determination at first pass. For the boom pole application, we know from experience that the tractor will lift the front end off the ground long before we exceed the load capacity of the rear axle. This may not be the case when lifting /carrying close in to the rear of the tractor.

I believe if we were to examine typical failure modes for trying to lift too much with a boom pole. Damage to the tractor would be confined to two components. Namely, the top link, and the lower lift arm inner carry pins/shaft. The hydraulic system and lift arms are "protected" by the hydraulic system pressure relief valve. But I have seen bent and broken outer lift arm pins. and stripped lift arm splines.

So, id I were trying to "calculate" boom lift capacity, I would run the numbers on what it would take to lift the front wheels (as mentioned in the post above) Add suitcase weights if I thought the 3ph mount would hold the forces.
Then I would run some numbers based on lifting arm capacity. (use the @3ph capacity number, and the upper lift arm lever length) Calculate the load capacity of the boom as a ratio of lifting arm lengths.

If carrying the load while moving, the actual load on the pins could easily treble due to inertia and momentum.

 

[teg]

There were some discussion about this before... but I could not find them

I have the L2800 which has the same lift capacity... I was able to lift 590 pounds from the end hook of my boom pole (if that helps you any). If was a bit scary since I still had the very jerky hitch and my tractor bounced around. Really thought the top link would rip the back of the tractor off...

I think your assumptions are correct.

 

[bcp]

Hard to calculate. The 3 point linkage is not a simple lever or a parallelogram. Every "arm" is a different length, and your lift capacity would change every time you moved the boom or changed the top link length.

Bruce

 

[widefat]

ahah....

http://www.tractorbynet.com/forums/attachments/33242-formula-fou-figuring-lift-capacity.html

and

http://www.solid.iei.liu.se/Publica...8/LIU-IEI-TEK-A--0800433--SE_Svante_Johansson

 

[pwright]

So what are the actual specs of the boom pole you are looking to get? If it is a light weight boom that can only lift 500 lbs at the end then chances are the boom is going to fail long before you reach the limits of the 3pt on your tractor.

 

[stuckmotor]

I once let wife drive my WD while I worked a dirt scoop made to be pulled by a horse. I can still see the front end up in the air when she popped the clutch. I don't do that anymore, she could have cut a back flip and destroyed my tractor.

 

[LD1]

Yep, so simple answer. Lots of threads on the topic.

The 3ph is not a simple lever. And it's dynamic (adjustable).

Toplink lenght and what hole you choose will make a BIG impact on its capacity.

If you want a pretty good idea of what it can lift, thin in terms of a ratio of lift heigh of the hook point, and lift height of the 3ph ends.

Let's say you hook up the boom. And from full down to full up the lift arms move 20". And we know there is 2000# (rounded) lift capacity there as per spec. And with that 20" of movement, the boom tip moves 80"...... Which is 4 times more......means you would have 4 times less lift. Or 500# (less the boom weight).

If you understand that simple enough, now move the toplink around to different holes and see how much difference it makes is that ratio. That's the same difference it would make on your lift capacity.

The top hole on the tractor is going to make the tip of the boom move LESS....so more capacity. Bottom hole is just the opposite.

I could build a boom pole that would raise perfectally parallel if you wanted. Meaning for every 20" the arms move, the boom tip moves the same amount. Then there wojldnt be any loss of lift capacity other than the boom weight. Weather the hitch and TL would handle it is another story