Tractor backhoe - homemade

[BFreaky]

I design wheel loaders for a job, and your craftsmanship and design exceeds most factory made construction machinery...

Will you make a SERIOUS subframe under that MTZ, in order not to rip the bolts right out of the rear axle castings, or worse, rip the backend casting ??

Thanks. Do you think the current subframe is not strong enough? I made this one from steel plates 25x320 mm, 15x160 mm (we use metric system) and bolted them with high strenght bolts 12.9 quality. If this backhoe stays within 1000 - 1100 kg of it's own weight it will not present a problem for this tractor to carry and work with. I'm using a 3.1 m disc harrow which weights 850 kg for almost 5 years now. It was used without this subframe and there was no problem so I believe it will also work with this backhoe. Afkors, any good advice and opinnion is always welcome :thumbsup:

 

[Renze]

We use metric too (i'm from Holland)

Using a disk harrow is a totally different load than a backhoe: When doing serious digging, like pulling treestumps or rocks, your backhoe is likely to go pull the MTZ off the ground with all its four wheels, tipping over the outriggers instead of over the rear axle. It puts quite some strain on the mounting points on the back of the tractor, thats why heavier backhoes are attached with a subframe instead of the 3pt lift. The simple weight of the backhoe itself, really is nothing compared to the forces that come to it when you use full force of the backhoe. (At least, if you design such a beefy backhoe mainframe, i assume the backhoe that will be attached to that, is able to pull your MTZ into the air with all four wheels..). When carrying your disk harrow in the 3pt, the rear axle is your fulcrum, when using the backhoe with outriggers, the outriggers are your fulcrum: the distance of the center of gravity of the tractor, to the outriggers, is double the distance than the distance between the center of gravity of the tractor, to the rear axle. (maybe even more, depending on your design)

===edit: i went back to the first page to see your subframe, and deleted some things about the frame because you already take the right route

Just a question: is the horizontal bar, the 230x25mm bar you mentioned ? And what size of bolts are you using ?
http://i45.tinypic.com/25phifc.jpg

I dont mean to say your construction will fail (or: the casting you bolt your construction to, will fail) but just warning you: the tractor rear axle housing is the weakest link in this construction, not the backhoe itself.

If in doubt, it might be a good idea to weld those vertical bars to the backhoe subframe so there will be absolutely no movement there: if you make sure that connection takes up a bending moment, the force on the tractor rear axle housing (where your trailer drawbar normally attaches) is only vertical shear in downward direction, and at the end of the backhoe subframe, where it connects to the front loader subframe, you only get a vertical force in upward direction. Then you lead in the forces into the tractor chassis equally.

 

[RobertBrown]

Great post in a great thread.
It just proves once again that there is no end to the knowledge base here.
I for one am really looking forward to seeing how this works out.
I would like to know how Bfreaky got the measurements for the plate that mates to the tractor casting at the back. Those c-c measurements are so critcal to the design and strucural integrity.

 

[BFreaky]

We use metric too (i'm from Holland)

...

Just a question: is the horizontal bar, the 230x25mm bar you mentioned ? And what size of bolts are you using ?
http://i45.tinypic.com/25phifc.jpg

I dont mean to say your construction will fail (or: the casting you bolt your construction to, will fail) but just warning you: the tractor rear axle housing is the weakest link in this construction, not the backhoe itself.

If in doubt, it might be a good idea to weld those vertical bars to the backhoe subframe so there will be absolutely no movement there: if you make sure that connection takes up a bending moment, the force on the tractor rear axle housing (where your trailer drawbar normally attaches) is only vertical shear in downward direction, and at the end of the backhoe subframe, where it connects to the front loader subframe, you only get a vertical force in upward direction. Then you lead in the forces into the tractor chassis equally.

Ou, sorry, then we both use metric measurements.
The horizontal bar is 15x160 mm with M18 bolts. I understand the forces you are talking about and hope it will work out fine. I tried to move the stabilizers as close to the tractor rear axle as possible. Distance between rear axle and center of stabilizers is 1300 mm. It could not be less because the mainframe would get too close to the rear wheel. I had to consider the fact that eventually there will be some dirt on the tires so it needs some space to drop down from the tires...
If I weld the subframe after some time it could result in cracks on tractor chasis where the bolts come in...or do you think otherwise?

RobertBrown, I measured the back of the tractor and avoided all non-removable parts of tractor chasis.

 

[Renze]

Actually i think you're safest when the connection between your backhoe subframe and the horizontal bars, is absolutely rigid, so there is no bending moment on the rear wall of your rear axle casting, just a vertical force. Then the attachment near the front loader consoles will also take up a vertical force.

As a side note to put things in perspective, the loaders we build at work will last 20.000hrs on average, some 32.000hr machines are still being used as backup on 24/7 glass factories, so from where i come from, i might have the tendency to over engineer hobby projects...


I have a Bobcat skidsteer attach backhoe, converted to tractor use. By no means it has the power to pick my 3011 up, so i just attach it to the 3pt hitch: It used to be a 4 point attachment, so i welded a triangle as top link connection: That gives plenty of stability given the ratio between backhoe power and tractor weight. but my backhoe is made of 8mm steel at most, where you are welding 20mm with doubled reinforcement plates

Our company sold wheel loaders with pallet forks, dozer blade, hoisting jib and a front mounted backhoe attachment to the Dutch army in the 90's, and everytime one is in the shop for service, i'm dreaming of hooking one of these Schaeff backhoes to the back of my 5718. I will need the frontloader to counterbalance it then, and attach it to the back of my frontloader subframe which i extended all the way to the back of the tractor: i kept a backhoe in mind when building my loader subframe 7 years ago..

Meanwhile i keep extending that little bobcat attachment backhoe, extending the outriggers, perhaps extend the dipper stick, and if i run into its limits again, perhaps extend and reinforce the main boom as well... Well its just hobby, so time is free

 

[BFreaky]

What's the name of the company you work for?
Feel free to attach some images of your loaders, I'm curious how they look.
Hahaha, well I have the same tendency to over engineer projects. It's safer that way. I just might weld the rear attachment points of the subframe or at least weld a support plate to minimize movements between plates.

 

[ThomasH]

Because of the forces which are multiplied when leveraging the tractor frame / rear housing / etc. when the hoe is extended and pulling against something, most all backhoes are capable of digging 6 feet or more have a substantial sub-frame which attaches to the front loader mounts and rear stabilizer mounts. When using the backhoe, the bucket is lowered and takes the stresses which would otherwise be applied to the engine and front axle; and the rear stabilizers are lowered to raise the rear wheels off the ground. Therefore the stresses are applied to the loader frame in the front and rear stabilizers, and not the tractor itself.

Also, depending on the amount of fluid in your backhoe itself, the rule of thumb is that the backhoe fluid reserves are at least 10x the digging depth in order to give the fluid time to defoam and cool. Fluid cooling is an important design consideration in locations where the equipment is operated in excess of 32 degrees celsuis. My Case backhoe has about a 25 US gallon tank and it is considered full when cool at 20 gallons.

That said, I am very impressed with your fabrication skills.

 

[ThomasH]

Because of the forces which are multiplied when leveraging the tractor frame / rear housing / etc. when the hoe is extended and pulling against something, most all backhoes which are capable of digging 6 feet or more have a substantial sub-frame which attaches to the front loader mounts and rear stabilizer mounts. When using the backhoe, the bucket is lowered and takes the stresses which would otherwise be applied to the engine and front axle; and the rear stabilizers are lowered to raise the rear wheels off the ground. Therefore the stresses are applied to the loader frame in the front and rear stabilizers, and not the tractor itself.

Also, depending on the amount of fluid in your backhoe itself, the rule of thumb is that the backhoe fluid reserves are at least 10x the digging depth in order to give the fluid time to defoam and cool. Fluid cooling is an important design consideration in locations where the equipment is operated in excess of 32 degrees celsuis. My Case backhoe has about a 25 US gallon tank and it is considered full when cool at 20 gallons. It also has hollow subframe members that hold an additional 5 gallons of hydraulic fluid and also aid in cooling.

That said, I am very impressed with your fabrication skills.

 

[BFreaky]

My backhoe will have 13.2 gallons (50 liters) of hydraulic fluid for each pump so I believe it will cool down without problems, especially because tanks are incorporated into main frame so there are large metal surfaces which will take over the heat and disperse it into air...

 

[Biohazarus]

Hi all, I am following this thread with lots of enthusiasm. Excellent travail BFreaky!!!

I am in the planning of building a towable backhoe. Mine won't be as heavy duty as yours. My overall weight limit would be set at 2500lb, because my SUV towing limit is 3500lbs.
Any clue on the weight of yours?

Still your craftsmanship is really inspiring. Tough of using square tubing for the boom and arm, but you inspired me to go more stylistic. I have a really good laser cutting guy that is sometime cheaper then me buying the raw material!!!

Simple question, would you post your CAD drawing? If not, I would totally understand, lots of implication that out might not want to go through.
If you plan to post them, I like Gradcad.com. There are some excavator/backhoe draft, but yours would be a built design and it have a really nice appeal!