Brush Hog mods

[ptsg]

I put those on couple of PTO shafts and they have worked well, especially the one on my old Maschio 48" rototiller when working on soil with hidden old big Rhododendron roots!

Next time though I will run the middle buster first - fewer busted shear bolts...

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Those work indeed very well. For the people that use PTO implements occasionally, I recommend going with these, since the slip clutches tend to get stuck if not used frequently. A lot of people don't know or want to mess with it before using it and can cause some serious damage. The shear bolt always works.

 

[D&D]

The shear bolt always works.

Until someone puts in a grade 8 (or higher) to keep from shearing. Those can be a bear to replace when they bend instead of breaking.

 

[ptsg]

Until someone puts in a grade 8 (or higher) to keep from shearing. Those can be a bear to replace when they bend instead of breaking.

With that style of shear pin yoke, that just doesn't happen. It may break something else though but using an higher grade bolt.

I know mine uses a M8 8.8 bolt. The rototiller uses an M10 8.8 but I suspect this has been drilled to the bigger bolt since the previous owner dealt with a lot of rocks. I've sheared 2 on the tiler so far. I'm using fully threaded bolts so it gets a bit weaker than a partially threaded ones.

 

[LouNY]

Until someone puts in a grade 8 (or higher) to keep from shearing. Those can be a bear to replace when they bend instead of breaking.

A grade 8 will shear cleanly and often fall out when sheared, a grade 5 or less will tend to smear and need to be fought with to remove.
Some equipment specify what grade bolt to use.
Here is an interesting table showing shear strengths for different grades and types of shears, most shear bolt yokes are single shear. Also shows the difference if the shear is in the threaded area or the shank area of the bolt. It doesn't take into account over tightening a shear bolt, best practice is just snugged up with a nylock or jam nut installed.

 

[Gordon Gould]

Here is an hydraulic brush cutter I built for my backhoe a month or so ago. I suppose it fits the thread, since mostly about using chains. I do have a flail mower for the backhoe, which worked fairly well, but it's just an heavy attachment and I wanted something lighter.

Cutting width is about 50 cm or nearly 20". Using 3/8" grade 80 chains. Rotor speed is about 2000 RPM.

It has been painted since, I just haven't taken any pictures of it yet. Still need to test it properly but for that I need to haul the machine over to the remote propriety, however I still have digging work for the backhoe here at home.

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That is a really nice unit. Intriguing !! Could you describe the drive components you have there to get your 2000 RPM and a 20" width. I recognize the hydraulic motor is all. Is there also a gear box? And what flow and pressure do you need to drive it. Thanks.

gg

 

[ptsg]

That is a really nice unit. Intriguing !! Could you describe the drive components you have there to get your 2000 RPM and a 20" width. I recognize the hydraulic motor is all. Is there also a gear box? And what flow and pressure do you need to drive it. Thanks.

gg

So my backhoe has a 17hp Kubota engine and for the hydraulic circuit, I'm running a Parker F11 5cc piston motor/pump, in this case being used as pump. Put out about 3.3 GPM at 2600 PSI for the auxiliary circuit.

The brush cutter, is running another Parker F11 5CC motor, in this case, used as a motor. With all the normal losses in the hydraulic system, this motor, even though is the same as the pump, loses about 500 RPM, so it spins at 2000 RPM.

The motor is mounted to a hub that I machined. This hub uses one top bearing, and two bottom bearings. Then, the rotor, which is all one piece, is connected to the motor using a Love Joy coupler.

I didn't want to put all those forces cutting thick brush directly on the motor.

This is the rotor where the chains attach to. Machined between centers to make sure there was no run-out anywhere to induce vibrations, which worked perfectly as it runs smooth as silk.

This is the hub where the bearings go to. I was test fitting the rotor. You can also see half the coupler. I'm only using grease in this, so I didn't have to add any seals.

This is the motor connected to the rotor and hub but without the motor mount yet. And the motor mount after welding but before any final machining:

I wouldn't want to run much higher than 2000 RPMs. Most of the comercial units, still run a gearbox, just like a tractor cutter, but with an hydraulic motor attached to it. I didn't see the need for one on this small cutter and I want it to be light.

 

[Gordon Gould]

Thank you!! Great info and pictures. You are a talented and knowledgeable man.

gg

 

[BackRoad]

Always in awe of someone who can design to that level of detail...and then actually build it.

 

[RayIN]

Chopping up brush appears to work great. Mowing heavy grass would damage (rip) the grass leaves so much it might not recover.

 

[scootr]

Chopping up brush appears to work great. Mowing heavy grass would damage (rip) the grass leaves so much it might not recover.

In my experience it recovers slower than cutting with a blade... which can be a good thing if you are simply mowing to reduce the fire fuel.