Engineering advice needed

[RFB]

I am planning to build a boom pole to lift roof trusses. (I have a Kubota 5303HSCT/853FEL with a Bradco QA pallet fork (3700 lb capacity) attachment.)

I am thinking of using the fork(s) as the base for the pole: either sliding the pole over the fork, or welding rectangular brackets onto the pole to then slide over the forks. I was also thinking of using a chain and ratchet binder attached from the pallet base to a welded ring (about 2/3 of the way towards the end of the pole) to use as cantilevered support.

I have attached a crude concept drawing to try to illustrate.

My primary question is, what is stronger for the proposed use: round pipe, or square tube, and what wall thickness/guage should I use.

Any other advice is always welcomed.

 

[Renze]

I dont know what you mean, is 3700 lb (1678 kg) the capacity of your forks, or your loader ? It seems a bit much for a compact bota though but i can be wrong..

Anyways, a tube 100x100x4 mm will do just fine if you use the chain, i think, because your loader doesnt have the tilt power on this length of arm. Does the bucket tipping function have a safety relief valve ??

Re what is stronger, round or square tube, it depends on what size is available.. Square is easier to weld your strips and plates to....

 

[RFB]

The 3700 figure was to identify the pallet fork attachment; some have less capacity. The FEL will not go that high, but will reliably lift 3000lbs based upon previous usage. I have a good counterweight; a 1000 lb sub-frame backhoe.

For my needs, the ease of welding the brackets is secondary to the available strength of the boom material. So, I am back to round or square, and what wall thickness?

 

[RonMar]

Need more info...
1. What is the all up weight and HP of your tractor/loader(didn't find a 5303 listed with Kubota)?
2. What is the "breakout force" rateing or "maximimum lift" rateing for your loader?
3. What is the max height to the pivot point of your bucket/loader forks(max height at the end of the loader lift arms)?
4. How heavy are the trusses you intend to lift?
5. How high do you have to lift them?

The forks might be rated for 3700 pounds but that rateing is irrelevant if the loader structure that is carrying it is not rated to that same weight or greater.

I would not weld it to a fork, but I might consider using the fork backplate structure(with forks removed to save weight) if heavy duty enough.

The boom pole like any structural element will be the least resistant to bending or side loads. Next weakest will be compression loads(but vastly stronger than side loads) and the strongest will be tension loads. Triangualtion is your friend. The cable from the top of the fork bucket to the boom is good. I would however connect this cable all the way out to the end of the boom. Running it to the middle makes a stress point there subjecting the boom to a side/bending load and that will make the boom the weakest at that point. Using 3 cables would be better, one from each top corner of the top of the bucket and one in the center as this will provide some stiffness from side to side(3 triangles in 3 different planes) as well as spreading the load across more of the bucket backplate. With the cables all the way out to the tip, they will be in tension and the main boom pole will be in compression(the two strongest modes). About half way along the length of the boom you might want to add smaller riser poles between the cable and the boom pole. This will help stiffen the boom pole from bending under the compression load. The ammount of weight being lifted and the length of the boom will determine what diameter and thickness the boom pole needs to be to resist the compression the load will put it under. For this application, round is stronger than square for a given weight.

 

[hockeyhead]

How long will your boom pole be?
How much weight do you want to lift at the end of your boom pole??

in general, steel square tubing is 30% stronger the round in equal size/diameter and equal wall thickness. steel square tubing also is 22% heavier in equal size/diameter and equal wall thickness (more steel).
you need to supply more info.
have you considered I-beam ?

 

[RFB]

Sorry for the typo, it is a 5030HSTC with the 853FEL

I do not have the breakout/lift numbers you asked for, but I am producing spec pressure 2650-2700 psi and have lifted (with the pallet forks) 3000lb (weighed) sod pallets.

I am undecided on the length, I was thinking somewhere between 10 & 20 feet.

I see the logic of the added support cables you suggested. My intended loads will be more vertical than horizontal (at least as much as possible) and will be in 100's of lbs rather than 1000's of lbs (roof trusses)

 

[SPYDERLK]

RFB, I am not able to fully understand your situation from the info i can perceive, but you raise a very good question regarding choice of material shapes. Responding in the dim let me just state a few truths:
1) Round tubing will be most efficient shape (strength per mass) in compression, torsion, and tension loading. It is ideally shaped to self rienforce and hence retain its optimum shape for these loadings. No stress concentration developes for these loadings;
2) Square or rectangular tubing and I beams are good for bending loads but are poor torsionally;
3) An I beam combined with a light gauge round tube - - 1/2 on each side of the web will give you a convenient construct offering excellent performance in torsion and bending;
4) Realize that torsional loads always occur where there is a bending moment - - according to Murphys Law;

Use round tubing as much as you can. It is serendipitous elegance.
Larry

 

[Pooh_Bear]

You may be able to lift 3000 pounds with the pallet forks,
but add another 10 feet to the moment arm and it drops to 300 pounds lift.
Add 20 feet and it drops to 150 pounds lifting power.
Keep this math in mind for you designs.

Pooh Bear

 

[MrJimi]

I built a homemade boom for my Case and its 10 feet long and my arms will raise 9 and a half feet, total of 19.5 feet, here is a picture lifting about 400 pounds from the ground. 3 inch schedule 40 pipe.

Jim

 

[RonMar]

Pooh Bear summed it up nicely. It dosn't take much for 100 pounds to exert 1000 pounds of force, just a 10' displacement on the end of a boom. You also have to add to that the weight of the boom structure so 100 pounds at the end of a 10' boom will probably exert close to 1200 pounds on the loader at the bucket pivot point. Also very important to consider is that this is static load. Add any movement to the suspended load that must be absorbed by the structure(such as driveing over bumps at the jobsite to place the truss) and you can easilly double and tripple the force exerted on the structure. Force = mass X acceleration.

The breakout rateings are important for figuring how long the boom can be and how much weight you can lift on the end of it. You gave your system hyro pressures, what are the diameter of the loader lift and rollback cylinders and of the rods used in them? How long are the lift arms(measured from lift arm pivot to bucket pivot point)? Where do the lift cylinders attach along the lift arms(how far from lift arm pivot)?