how to build your own custom backhoe subframe

dfkrug · Aug 16, 2023

manytoyman said:
How this of channel is needed if I go that route?

I do not understand the Q, but I recall that the channel was 3.5x1.5x.25". Reinforced at key mounting points where bending moment would be greatest.

LouNY · Aug 16, 2023

Or use your flat stock and make a T shaped rail.

manytoyman · Aug 17, 2023

Haha - yeah that question was foo barred. I was asking how thick the channel steel needed to be, which you answered. I'm going to start looking around to see what I can get my hands on (not retail).

manytoyman · Aug 17, 2023

LouNY, is a T rail two flats welded to make a T? If so I had not thought of that but it would be strong. I've got a 220v Hobart 180 which is good to 5/16... so that's going to be my limitation. Not sure a 5/16 flat stock is going to be strong enough, but assume a 5/16 channel would be. My hoe is going to be a small one so that will help.

LouNY · Aug 17, 2023

manytoyman said:
LouNY, is a T rail two flats welded to make a T? If so I had not thought of that but it would be strong. I've got a 220v Hobart 180 which is good to 5/16... so that's going to be my limitation. Not sure a 5/16 flat stock is going to be strong enough, but assume a 5/16 channel would be. My hoe is going to be a small one so that will help.

Yes, two pieces of flat stock weld together to form a T. V'ed out and welded from both sides you should be able to go up in thickness.

manytoyman · Aug 24, 2023

Question: when people say that backhoes improperly supported can brake a tractor in half (between rear housing and engine housing), what force is causing that? My assumption is it is a situation where the backhoe is pulling down (digging) and hits a rock/root that stops the bucket so the force then transfers up through the hoe and into the tractor ... thus making the tractor raise it's front end if there is enough pressure. Since the hoe can release pressure quickly, once the control is moved the other way the front end of the tractor would come crashing down very quickly AND that would be enough potential force to break the tractor at it's weakest point... in the middle.

So the sub frame would stop this from being a problem because the sub frame itself would hold the tractor together instead of letting the force be only in the middle. A three point BH also adds to the issue because all the force is also going through the rear attachment of the arms and TopLink which then could also be a weak spot in the above scenario.

Just trying to understand the forces to help design the subframe. Does this sound right? Thanks.

dfkrug · Aug 24, 2023

manytoyman said:
Question: when people say that backhoes improperly supported can brake a tractor in half (between rear housing and engine housing), what force is causing that?

A backhoe attachment on a CUT that can deliver 2500psi pressures puts enormous push, pull, lift, and twisting forces on the rear of the tractor. Distributing these forces is the job of the subframe.

The most extreme forces are going to be shock loads that happen when the hoe lifts the tractor's rear off the ground and drops suddenly as the load releases, or when driving around at moderate speeds where the hoe is not supported by the outriggers.

I think the first scenario is most likely to happen when digging stumps/roots. Some folks routinely lift their tractor with the hoe to re-position the machine. That is very stressful, too. Backhoe attachments with subframes are not as forgiving as purpose-built "mainframes" on TLB machines.

manytoyman · Aug 24, 2023

Oops - I had that torque backwards. But the end result is the same whether its the front or back that gets let down quickly. I can also see the issue with driving around - good idea to stick to the BT600-603 units as they are very light compared to most (just 630 pounds without bucket I think).

So the subframe will certainly need to be attached to the ROPs area of the rear end as well as the FEL. Is there a good reason to also try to attach in between those two areas somewhere in the middle?