The ultimate bush hog

[RobJ]

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?

Well it depends on what size mower of course!!!

Geez...

 

[sandman2234]

Don't think it would matter, by the time the sonic boom hit it, from exceeding the speed of sound (which is considerably slower), you would have a mess anyway.
David from jax

 

[Highbeam]

Well if the speed of sound hits somewhere around 1000 fps and the 14000 fpm is really 233 fps then it would be no trouble for the tractor engine to spin things up to the sound barrier If you could get the gears. Cripes, I could grab the 1000 rpm PTO lever and get 500 fps right there. What would happen?

 

[TOMDUALLY]

I don't know but let me stand obout two counties away when you test it and I might be able to tell you which direction it went. LOL

 

[sandman2234]

Remember, the RPM of the pto is measured in minutes, while sound barrier is measured in fps. The diameter of the blade circle for larger single blade mowers has a faster blade tip speed for the same rpm.
I located my calculations for the long gone mower I built. It was designed to run off a gasoline engine, (3500rpm) and blade tip speed was a concern. As it turned out, I sold it without the motor, and adapted it to a 540 pto, so the blade tip speed really wasn't a factor.
I also used 750fps as the speed of sound. Not quite sure where I got that information, but maybe it was my built in safety margin.( or maybe just an error on my part)
David from jax

 

[Highbeam]

It doesn't matter if the pto rpm is measured in revs per year. If you double the pto speed you double it. If the blade tip speed is 14000 fpm at any pto speed and you double the pto input speed then you get 28000 fpm at the tips.

Good fun but the mower blades are plenty fast as they are.

 

[schmism]

I also used 750fps as the speed of sound.

unless your useing your brush hog at like 10K feet thats a bit low

Acoustics Chapter One: Speed of Sound

speed of sound at sea level @ 68deg F = 1128fps

 

[sandman2234]

The finish mower I built years ago was my first, and I was cautioned about blade tip speed, after I had most of it set up. Knowing the guy that gave me the "speed of sound" numbers, he probably allowed for some error on my part, and I probably allowed for some errors in his calculations, and the end result was something way below the speed of sound.
Then I changed from a gasoline engine, to a pto, using the same pulleys, so it was a mute point.
David from jax

 

[Turkeyman]

Brown makes the Utimate Cutter. Mine ( mid 1980's model) is terrible on grass but great on weeds and trees. I think is is rated at 14,000 FPS. The gear box is an old Borg Warner and is only rated for 90 hp. The stump jumper is square and 3/4 thick and weighs in the mid 300 lb range. The blades (4) look like axe heads and are 10" long and 1' thick. At 1600 lbs it is built like a tank.
The rear wheel has a tree deflector built in to push trees off to one side when you back into them.

I would suggest that you build a folding door on yours if you can. It would make it much safer to use.

 

[sandman2234]

Can you describe what a folding door is?
Would really like to see a pic of yours, especially the rear wheel deflector.


I was out tearing up my bush hog again today, and wondered if it is a good idea to consider offsetting the bush hog a foot or so to one side, to cut stuff that you really don't want to drive over? I could build a 7' one, and have it trac even with the wheel on one side, and overhang about a foot on the other side. Probably a little harder on u-joints, but I can stand that (I think).
Anyone ever seen a bush hog with an offset?
Next question... why not?
David from jax

 

[Soundguy]

I've seen lots of 10' and 12' cutters that are nothing more than 15' and 18' batwings with a single side wing missing, making them the center section, and a wing section. Depending on the design, that gives you a front distribution gearbox, and two blade driving gear boxes, or a power dividing and blade driving gearbox on the center section that drives the wing sections, except there is only one wing.. etc.

You can find ditch bank mowers.. etc that have offsets. However.. on the ones i've seen, the pto driveline is straight behind the tractor, and the gearbox setups on the mower take care of the geometry for powering the rest of the gear boxes that drive blades.. etc.

Soundguy

 

[RobJ]

I was out tearing up my bush hog again today, and wondered if it is a good idea to consider offsetting the bush hog a foot or so to one side, to cut stuff that you really don't want to drive over? I could build a 7' one, and have it trac even with the wheel on one side, and overhang about a foot on the other side. Probably a little harder on u-joints, but I can stand that (I think).
Anyone ever seen a bush hog with an offset?
Next question... why not?
David from jax

Just put a longer blade on one side. That'll do it!!

 

[sandman2234]

Yea, yea, that's it, I'll just put a longer blade on one side...
Wonder what I will do about the problems that idea creates?
David from jax

 

[Turkeyman]

The folding door is where the back top of the mower is lifted by a hydr ram to expose the blade and allowing the blade to contact a tree without the tree bending. A push bar with two HD shock absorbers push the tree away from the tractor. Sorry I can never post pictures but look at the Brown Web site, Alimo Make one as well and so does Rhino - Lumber Jack model with a push bar. I have seen plenty of Brown's in the real world but never a Alimo or Rhino model.

Google "Woodboss" which has a video of one in action.
Google "Hinton Tractor" and you can see their power line tractors in a NH or Kubota.
Both build professional ROW equipment. Mowers that run 50 hrs a week for 45 weeks a year.

Brown also make 8- 10 ft models of Super Duty mowers too.

 

[sandman2234]

Most bush hogs are rated at FPM for the blade tips, whereas the speed of sound is rated at Feet Per Second, which is 60 times as fast for the same number of Feet per minute. An easy thing to overlook, but approaching the speed of sound with blade tips is possible with the horsepower available on a tractor, especially on larger single spindle mowers. The larger the diameter of the cutting circle, the faster the blade tip goes to make a single revolution of the gearbox shaft.
David from jax

 

[Doug W.]

OK, So if I have this right (about tip speed)
In Asia,Europe and other Metric regions of the world
we would be looking at what, 25.4 times the speed of sound over there?
Lets see.............4,267,200 mm/sec.

Now that's haulin

 

[andrewj]

I'm surprised at all the off topic, tip speed, space shuttle door gunner B.S. I had to wade through! Respectfully guys, can we keep this about the ultimate bushhog and respect the guy's thread? wink and a smile!

 

[sandman2234]

Andrewj,
I don't mind sifting thru a little cow manure, in order to find some good information.
Hopefully you looked at the links to the bush hog building from the PM board. That guy built one nice bush hog.
The last one I build was more of a finish mower, using 3 blades and 8' of deck to handle the grass.
If I ever get slowed down, I am going to build another, if I have any spare metal left, as I am fixing to start a project that is going to use up a lot of my scrap metal laying around.
I hate paying new prices for steel...

David from jax

 

[Dave1801]

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

I clicked on this link, but I couldn't find anything about a bush hog?


thanks for any help.
Dave

 

[LBrown59]

I clicked on this link, but I couldn't find anything about a bush hog?


thanks for any help.
Dave

2 year old thread.
Guess i have help bringing old post /threads back to life.