Backhoe stressess and material?

[andyfletcher]

I am interested in building a backhoe for my 424IH. I'll tap power close to my accessory spool. There is not much mention about forces and cylinder power required for specific moments of force for a homemade backhoe on this forum. I suppose if I simply follow your plans of ready made ones here I can't go wrong.

Something slightly larger than a CADPLAN but less than a full size would be great.

I'm concerned about mechanical and power issues. I would guess it could be possible to under design and have a boom that would function at snails pace,etc.

I was wondering about stressess inherent in the two boom poles, and the bucket swivel force I would assume not so important. It would seem the Bucket Boom would require more force than the main boom. The main boom more for lifting the load and it's own weight, whereas the bucket boom requiring the force to move the bucket through the material.

The cylinder specs for the BB would be calculated considering moments about the swivel location. For example I would assume for a 3000 lb pull at the bucket and a 7ft boom with pivot that is a foot from the cylinder attach point, a cylinder of around 18000 lbs would be required. At 9GPM for tractor pump that would be a slowwwww shovel.

Also considered is swing power. I don't think the steel I will use, 3X3 3/16 tubing can withstand swivel power, ie: pushing material sideways with the bucket. I think it could barely take being pulled through the dirt, but can't say for sure.

Are my concerns warranted? Do you think I should go to 4X4 tubing, or 1/4in thick 3X3 tubing? Any tips on cylinder selection?

thanks.

 

[MMM]

I have the ARP875 which is older version of Amerequip 8600. The bucket is by far the strongest function. They make most of the OEM hoes. The digging forces are listed here.

 

[keeney]

The easiest way to design something this complicated is to copy a design that has already proven itself to work.

Take a look at backhoes produced by a brand-name manufacturer. You don't need to copy every detail exactly, but the gross dimensions, especially the pin to pin distances, the cylinder pin locations relative to the joints, the cylinder sizes, the basic material thicknesses, pin diameters, and the shape cross sections will get you "in the ballpark".

Some of the tricky parts of the design:

The bucket curl geometry such that it can dig as desired and hold the dirt up to some maximum dump height. There are trade-offs in dump height and angle vs. curl digging force vs. vertical-digging un-curl travel. Some designs have multiple pin locations for the bucket to adjust these trade-offs.

Other trade-offs are in the area of digging force vs. cycle time for a given hydraulic flow and pressure. Larger cylinders give more digging force, but are slower for a given GPM.

Weight vs. Reach

Reach vs. Digging force.

Bucket size vs cycle time.

Bucket size vs force per bucket-lip-inch.

Curved boom to clear the edge of the hole vs straight for ease of fabricaiton.

Boom cylinder on top or even inside boom tube to keep it clean vs underneath for best lift capacity.

Replacable bushings vs simple welded-on.

Control valve complexity

Rock/frost digging vs loose/bulk material removal.

Maximum height to clear garage door.

Maximum weight for tractor.

Ground clearance

Max digging depth.

Max loading height - loading trucks, or just dumping in a pile near the hole.

There are significant safety concerns if the mounting to the tractor. If the unit comes loose and rises up (due to trying to force the bucket down into the ground), it can crush the operator between the hoe and the tractor (or rollbar).

- Rick

 

[andyfletcher]

Wow! Thanks MMM & Keeney

Didn't expect so much info!!!

Andy

 

[Catmando]

Keeney, You covered about everything. As you mentioned the pin to pin distances are really quite critical. I would suggest that prior to welding up he make a model out of wood to see if he can get the motion he wants.