Homemade Hydrolic Brush Cutter/ Land Clearing attachment for Bobcat

   #1  

cnicholls

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Apr 16, 2010
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Hey Guys... im a new poster, but year long lurker.

I am a general DIY guy with many hobbies. The most recent has been fabrication of attachments for my older 743 bobcat. I am lucky to have a awesome scrap yard that i found about an hour away from my new house. They are a scrap yard, but mostly a combine graveyard. So most of my hydraulics come from there.. motors $20 cylinders $10-$30... hoses $5 with pioneer fittings!

Anyways. I am working on my latest attachment which is a Hydraulic Brush Cutter. The main gearbox and the blades are brand new from ebay.

The gearbox is made for a pto shaft that is a 1 to 1.98 up ratio. I welded to hubs together from tractor supply for the coupler. And the steel is from scrap I had laying in the pile. The sheet is 1/8 The main 3/8 U channel is from a grain truck frame I scrapped out.

My goal is to get it done for under $500 and I am under so far.

$ 20 Used hydraulic motor
$ 45 Hoses and adaptors
$ 19 Hub assemblies
$170 40HP Gear Box PTO
$ 68 22 ス Blades
$ 46 Carrier Hub


Its not quite ready for a spin yet, but I wanted to share I am a newbie welder so please don稚 judge my welds too much.
 

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   #2  

davo727

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Nice work! What part of the world are you in?

Im sure you plan on keeping any and all persons way far away from your machine when its operating in case anything departs. :thumbsup:
 
  
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#3  
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cnicholls

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Hey thanks,
I am here in Toledo, OH. I have gotten allot more done in on the cutter in the last few evenings, its getting darker out earlyer so i have more time to tinker in the garage. Have been welding all the seams. I moved the push bar forward, got the saftey screen in. Added the 3x4 U channel for the bottom runners. Ill take some pictures....

Do you think a 743 will spin this ok? It has a 11 gpm standard flow.

The pump is rated at 800 -900 rpm at 17 gpm max 3400 psi.
 
   #4  

jcims

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Hey thanks,
I am here in Toledo, OH. I have gotten allot more done in on the cutter in the last few evenings, its getting darker out earlyer so i have more time to tinker in the garage. Have been welding all the seams. I moved the push bar forward, got the saftey screen in. Added the 3x4 U channel for the bottom runners. Ill take some pictures....

Do you think a 743 will spin this ok? It has a 11 gpm standard flow.

The pump is rated at 800 -900 rpm at 17 gpm max 3400 psi.

I'm not sure if this is valid with hydraulic motors, but:

( 11 gpm / 17 gpm ) * 850 rpm = 550 rpm

Looks like you nailed it.
 
   #5  

VroomVroom

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Mahindra 2816 HST, Super M farmall, J5 bombardier, 230 timber jack skidder
I am interested in seeing how this works out as I need something to clear alder brush on old logging roads. Keep it up, send some pics.
 
   #7  

J_J

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What you haven't told us is the displacement and rpm, and the psi rating of the hyd motor. It may be a high speed low torque motor, or a high torque low speed hyd motor. What rpm do you expect the motor to run.

Using 540 rpm from a tractor PTO, as a reference.

If the gear box were connected directly, the brush hog shaft would turn at 1,069 rpm, with the PTO at 540. If the hyd motor, can turn at 1000 rpm, then the shaft speed will be 1980 rpm. What rpm are you expecting to achieve at the brush hog shaft? All this will determine blade tip velocity. You should also think of relief valves across the hyd motor.

You mentioned a pump. Is it a pump or a hyd motor?
 
   #8  

2458n

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I think he will be using the "pump" on the bocat. The high flow pump if the Bobcat is so equipped would be 16 gpm.
 
   #9  

J_J

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Are these the figures from your Bobcat?

[ Bobcat pump is rated at 800 -900 rpm at 17 gpm max 3400 psi ].


If that is the pump on the Bobcat, then the displacement of the pump would be about 4.4 cu in. Pumping 17 GPM's at 3400 psi, would take about 40 HP. and if you select the right hyd motor, you could be putting about 34 HP out to the brush hog.

If the hyd motor is around 6 cu in, running 17 GPM through it at 3000 psi, would give a torque of 238 ft lbs,and 655 rpm from the hyd motor, turning the gear box, at a 1 : 1.89 ratio, would turn the brush hog shaft 1238 rpm.
 
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#10  
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cnicholls

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The pump is from my bobcat, that is rated at 11 gpm the motor is rated at max-17gpm @ 900 rpm.

My max is 11 so it will run slower, thus approx 550 rpm I am using a stock gearbox for a pto driven brush hog. So Im thinking it should work.

I am using a swing blade design. Not sure what to expect, but im nevious to try it out. Should be ready for showtime this week, got side tracked with paying jobs... i just hate that....
 

J_J

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Bush Hog/Brush Hog gear box ratios are close to 1 : 1 up to 1 : 2.

Some tractors may have more that one PTO speed.
 
  
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#12  
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cnicholls

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The gearbox I am using is a 1 to 1.92.

At 1100 rpm +/- any idea as to what to expect? power wise? will it take a while to spin up? Im a little nervious on this one.
 

J_J

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If you think the rpm from your hyd motor will be around 550, then rpm times 1.92 = 1,056 rpm brush hog shaft speed.

The blades will cone up to speed based on the tractor rpm/pump GPM's fairly quickly. and the speed of the brush hog shaft will be based on how much hyd fluid you put to the motor. Are you going to use a variable speed valve like the one below, or a solenoid valve to actuate the hyd motor? You should have a relief valve across the hyd motor.

https://www.surpluscenter.com/item.asp?item=9-4169-10&catname=hydraulic
 
  
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#14  
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cnicholls

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The valve and the pump are all built into the bobcat, normally i just hook up the line feed direct to any motor or cylinders.

By the way thanks for the surplus center link, i just wasted an hour dreaming!

Does anyone have any input on the value of a lovejoy connection vs a direct coupling.
 
   #15  

maxfior

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Interesting build... Where is this scrap metal place you speak of, I'm in Bowling Green and always looking for a decent place, thanks!
 
  
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#16  
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cnicholls

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The name is Kunkle Farms in Fayett OH. Not sure of the phone number. I just was there this weekend, bought some more goodies. Working on a zero turn mini backhoe.
 

maxfior

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The name is Kunkle Farms in Fayett OH. Not sure of the phone number. I just was there this weekend, bought some more goodies. Working on a zero turn mini backhoe.

Thanks man, I'll have to check it out!
 

digger doug

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Oct 6, 2008
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You'll do O.K....not great, but you can do a good bit of work with it.
It's more of a "Get it spinning up, and then rush in till it stalls"

Even on my JD 240 with 15 gpm it's better, but still not like a gear drive on a tractor (as mentioned above).

Hi grass is the worst for loading, with brush, there's a allot more
of air in between stalks, to keep the disc spun up, and it works better.

Sometimes when cutting brush, I find it better to lift it up, and then drop it
down on the brush cutting the thinnest branches first as it comes down.
Also, my JD seems to take the oil coming from the lift cylinders, and re-use
it to the motor, I get a bit more speed doing this maneuver.

Also, many times the edge of a field (where the brush is) brush is there because
someone piled rocks there. Going straight in, you will hit them every time.
Dropping down, you will remove the tops, and see the hazard before
you hit it.

Here's mine, note I went with an open design (no regrinding/mulching) and only 4' wide,
because of my limited flow.
Bobcat 642 Trimming brush along treeline - YouTube
And some pictures:
Thrash-A-Matic 1. - YouTube

I've since made version 2.0, no video yet, but some pictures:
Thrash-A-Matic 2. - YouTube
 
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Fallon

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Interesting machine. But I'm guessing the OP sorted it out sometime in the past 7 years. ;-p
 
 
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