The ultimate bush hog

sandman2234 · Sep 5, 2006

Ok, getting tired of tearing up bush hogs. I haven't torn up any gearboxes, but am really hard on sheet metal and uprights.
I purchased the main gearbox (1input/3outputs) and a single right angle gearbox off the shelf of a now defunct business. Both are new, but starting to show a little rust on the unpainted surfaces.
I saw a guy on a machinist forumn build his own bush hog, for pretty much the same reasons as me, tired of tearing up lightweight bush hogs. I am probably a little harder on them, but apparently he must have torn one or two up in his time. Anyway, on with the question...

If you were going to build a super strong bush hog, PTO, what would you use for the components, how would you know how big to make the stump jumper (in diameter), how many blades, 2,3,or 4? How long of blades would be best? Shorter or longer, which has the capability of doing a better job of clearing rough woods and thick briar patches? Which design of pto shaft has the least likelyhood of twisting?
Hot dip galvanize would make the whole thing last a lot longer and is available locally, provided the pricing hasn't gone thru the roof like a lot of other metal suppliers.
Here is the link to the discussion we had a while back.
Welcome to the Manufacturing Forum: Summer, and the grass is growing, but I'm ready (finally) [finished my Bush Hog]

David from jax

sandman2234 · Sep 5, 2006

Welcome to the Manufacturing Forum: Bush hog project update

Just located some more on the build of that other bush hog. Thought you guys might like to see the pictures, and maybe spark some ideas.
David from jax

Highbeam · Sep 6, 2006

I bought a cheaper mower and then after the uprights failed from backing into brush I went ahead and improved the uprights to an HD captive pin design. I see this as a major improvement over the OEM. Don't drop it on your fingers when you're fabricating, I crushed one of mine into bone soup.

browns40 · Sep 6, 2006

Hi sandman,

It seems to me that the overall sturdiness of the cutters is usually directly related to the gearbox HP rating...

A 40 HP gearbox isn't intended to shred 2" material... a 90 HP isn't intended to shred 4" material... not to say you can't chew up bigger stuff with a lesser gearbox occasionally, but it won't last.

Likewise, the frame on the lower gearbox hogs really wasn't intended for dealing with a whole lot of tree pushing (probably none are!), it's meant to keep the "shrapnel" in once the blades obliterate it, and smaller bits for smaller gearboxes at that.

I guess what I'm saying is like with anything, you usually end up getting what you pay for.

I would guess a stump jumper 40-50% the overall widthe you build the deck would br pretty good; also 2 blades will be cheaper to replace than 3 or 4 (plus easier to balance); those "star" & "triangle" shaped splined shafts seem really nice

I would look at top of the line cutters & borrow their ideas for the machine rating you are looking for.

Sounds like a fantastic project--look forward to the results!

sandman2234 · Sep 6, 2006

So how do you know the horsepower rating of a gearbox, especially if you buy a hog with one on it used?
David from jax

Highbeam · Sep 7, 2006

"I would look at top of the line cutters & borrow their ideas for the machine rating you are looking for."

That's exactly what I did and I highly recommend it. Even thickness of metal. There are some obvious changes in design philosophy when you step up from economodel to obliterator. 5x the expense too.

I would suspect that the serial number on a gearbox could be tracked back to the manufacturer for HP rating.

browns40 · Sep 7, 2006

Good question on the gearboxes...

Seems to be a correlation with overall physical size of the gearbox with the duty rating of the cutter; also size & # of bolts attaching the gearbox to the deck of the mower...

That said, I wouldn't trust "eyeballing" too far!

Every manufacturer I've researched (JD, Woods, Bush Hog, Rhino, Land Pride, etc.) advertises gearbox rating for each duty line of their machines... most do metal thickness... oftentimes driveline rating & blade tip speed... a search of the manufacturer's lines should give you a close (if not exact) idea of the rating on the box.

As far as hot dipping it, I think it'd be an exercise in futility... to build a cutter that would'nt dent when a 3 lb piece of steel or granite smacks it going 14,000 feet per second would entail building a cutter that weighs more than a tractor, or incorporates some military technology!

Good Luck!

sandman2234 · Sep 7, 2006

The hot dip galvanize is to protect the bush hog from one of the worst enemies, RUST! I don't have enough roof space to keep all my junk out of the weather and that would make it one less to worry about. I did one about 15 years ago for a neighbor, and his is still rustfree.
David from jax

Jim_L · Sep 7, 2006

Brown MFG Makes the best bush hogs.
Ive got a 672

Brown Mfg Corp Homepage

browns40 · Sep 7, 2006

Wow! That is some cutter!

Soundguy · Sep 12, 2006

Good paint will keep it from rusting too.

Soundguy

sandman2234 · Sep 14, 2006

Soundguy,
Your right about good paint keeping one from rusting, but how do you keep the underside painted when you use it every week? I know you did a great job on yours, even the underside, but what keeps brush and limbs and bobwire from scratching the paint off? (I know I am not supposed to cut bobwire, but it does happen! Hot dip galvanize is a chemical reaction with the metal and actually bonds below the surface of the metal. It also cost more than paint, but doesn't usually have to be touched up, or reapplied.
David from jax

Soundguy · Sep 14, 2006

For the price of galvanizing.. I can apply alot of paint, either thru a sprayer.. or a roller.

If I was cutting barbwire frequently.. or brush constantly.. i think I'd paint the underside of the hog with ruberized paint.. like pickup bed coating.. or undercoating. Or if I was on the cheap, I'd get a pail of black asphalt paint and just roll it on. Both of those should last a long time.

When I painted mine, I pressure washed the bottom clean.. in most areas it still had JD green paint on it. I knocked all the loose stuff off, gave it 2 coats of primer, and then a couple coats of paint, plus hardner. So far the underside paint is holding up great. If I have to paint the underside again in a coupl e years, no biggie. The wings are easy as pie.. the center section requires a front end loader and some cribbing.. but again.. all in a days work.. etc..

Soundguy

itsgottobegreen · Sep 17, 2006

Jim_L said:
Brown MFG Makes the best bush hogs.
Ive got a 672

Brown Mfg Corp Homepage

I will 2nd that. I watched one of their tree cutters working once. It was taking down 4"-6" maples like they where grass.

I have one of their bed edger / trench masters. Its heavy duty and super slick too. Beats a shovel anyday when trenching.

Tom_Veatch · Sep 19, 2006

browns40 said:
... going 14,000 feet per second would entail building a cutter that weighs more than a tractor ...
quote]

Not only that, but you're going to have to use some really exotic, high temperature material and/or provide some way to cool it. Otherwise it's going to burn up from aerodynamic heating.

Wow, that's almost Mach 13!!!

At least it's a little less than half the Earth's escape velocity, so you won't completely lose the parts if it comes apart. The orbit will be elliptical and intersect the Earth's surface before it goes all the way around.

Maybe somebody dropped a decimal point, or added an extra zero somewhere??

LeadPoison · Sep 19, 2006

I think 14,000 would be "blade feet per minute (bfm)"

MrJimi · Sep 19, 2006

From the talk we had yesterday afternoon, I think he is into making something like this and if you have a fast connection? make sure you watch the videos
Skid Steer Clearing Mowers - Bobcat Skidsteer Brush Mower Attachments & Accessories

or

Flail Mower is Tractor Mounted

or

Skid Steer 6' Rotary Cutter

Jim

browns40 · Sep 19, 2006

OOps, caught!

Blade feet per minute is what I was referring too--guess I went ballistic!

Point was things will hit the inside of any cutter hard & fast.., and how rugged a tool would have to be to avoid deformation with high speed/high mass impacts.

Good eye!

sandman2234 · Sep 19, 2006

I think what you mean is blade tip speed. Speed of the tips are faster than the other end, since they are following a larger circle path.
I noticed they last link Mr. Jimi posted has a HD cutter that is sold as hot dipped galvanized.
David from jax

3RRL · Sep 20, 2006

sandman2234 said:
I think what you mean is blade tip speed. Speed of the tips are faster than the other end, since they are following a larger circle path.
I noticed they last link Mr. Jimi posted has a HD cutter that is sold as hot dipped galvanized.
David from jax

Theoretical question then...
Is there anything..can you go faster than the speed of light?
If you spin the hub at the speed of light, how fast are the blade tips going?