PTO 'string cutter' ?

[PILOON]

While what I really want is a bush hawg, I am toying with the idea of making a glorified 'PTO string cutter' as I think I have the necessary components.

I have a gravely 90 deg gear box that came from a bush hog type tool attachement as well as an assortement of PTO shafts to drive the gear head.

My idea is to weld up a suitable 3 point framework to support this 'box' and fashion a head to attach a cable holder (might be a couple of big washers that would 'clamp' a cable (maybe HD nylon cord or even wire rope).

What I need to 'cut' is ditch growth alongside of my driveways that consist mainly of reeds, berry bushes and generally less than 1 inch new growth.

The gear box is close to a one to one ratio but my tractor has 3 PTO speeds, 550, 750 and I seem to recall the other is a little over 1000 rpm.

What speeds do bush hogs generally spin?

What chances do I have of success?

Anyone ever do a similar project?

What suggests to me that this should be feasable is the fact that there exists self powered walk-behind (8-12hp range) units of this type often demonstrated on TV.

 

[schmism]

What speeds do bush hogs generally spin?

What chances do I have of success?

Anyone ever do a similar project?

What suggests to me that this should be feasable is the fact that there exists self powered walk-behind (8-12hp range) units of this type often demonstrated on TV.

Brush hogs generally get there effective cutting force from the mass of the rotating heavy arse blades.

You have to spin a 'string" so much quicker in order to impart the same energy into your grass/weeds/brush etc.

in short i dont think you could spin your PTO version fast enough with parts on hand.

 

[mjncad]

I like the idea, and I suggest you find out what the walk behind string trimmer spins the trimmer head at, and find a gear box with the proper gear ratio to approximate the same head speed using your PTO.

My only concern is that even with the heaviest nylon string is that you'll spend more time changing broken string than whacking weeds. I quit using string on my gas trimmer, and went with a mini brush cutter head that has three reversible plastic and steel cutting edge blades. It cuts the weeds and I only have to stop for three reasons: 1. The trimmer ran out of gas, 2. I ran out of gas, 3. The job is complete.

Or you could do what one of the hosts on the British car TV show Top Gear did when they went gardening for charity. He used a shotgun for blasting weeds and trimming tree branches. What a hoot!

 

[excelagator]

There is one I saw in an old paper issue in Farm Show mag. It was mounted off to the side of the tractor for wackin' weeds down a long fenceline.

 

[Bird]

What chances do I have of success?

Do keep us informed. And I hope you succeed, but right now, I believe your chances are nil. Many years ago when I first heard of the first string trimmers hitting the market, I wondered why you couldn't just use an electric drill and fishing line. Turned out the answer was real simple; electric drills just don't turn fast enough. I don't know where you could get a gear box that would convert your PTO speed of 540, or even 1000, to the kind of speed necessary for a string trimmer.

 

[gemini5362]

First of all the disclaimer. I have never done this and do not know how well it works. Hopefully someone that has done it will add some experience and practical information to this. Several of the old timers used to tell me that they would use a piece of chain in place of blades on their brush hog. They said it worked better and was a lot cheaper to replace than blades. If that is an accurate description then you obviously dont need the mass of the blades and the rotational speed of the standard brush hog will work. If you are going to build a rotary cutter I would surely try some 5/16 inch chain that will hold up a lot better than the plastic line that is used on string trimmers. I have the push string trimmer with a 6.5 horse engine and when I hit anything big or solid the line does not last long. I think your idea trying to use the string will not be practicable. The chain however might be a workable idea.

 

[Villengineer]

use a belt system to get the rpms up just like they do on rfm's. You could even build a 2 head unit which would cut a wider swath, but keep the trim line shorter.

 

[toivo1037]

Instead of string, or chain, how about some very heavy steel cable...

 

[Treemonkey1000]

Steel cable flexing will break fairly quickly. Plus strands of that breaking off and flying around could puncture people and tires. Chain might work. To get more rpm's couldn't you use a care rearend to change the speed up? If you PTO the axle hub instead of the driveline input you would get more speed I think. A 4:10/1 rearend for example.

 

[LBrown59]

What I need to 'cut' is ditch growth alongside of my driveways that consist mainly of reeds, berry bushes and generally less than 1 inch new growth.

I have what I feel might be a better similar idea
I'm itching to try out if only I had a welder and could weld.
I need it specifically for mowing/trimming out over ditches and banks.