Pooh_Bear
Platinum Member
- Joined
- Jan 2, 2005
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- Tractor
- Early 1949 Ford 8N
PTO 'string cutter' ?
- Thread starter PILOON
- Start date
- Views: 6781
LBrown59
Super Star Member
- Joined
- Oct 27, 2004
- Messages
- 16,831
- Tractor
- 2003 Kubota BX1500/2004 Kubota Bx23/2005 Kubota BX1500
I need to get 4 to 6 feet out from the rear tire.Pooh_Bear said:
This thing and others i've seen similar to it won't do that.
RonMar
Elite Member
To cut grass cleanly, It is not so much RPM, as tip velocity of the cutting string that is important. The one that Pooh bear linked to has a 3130 RPM spindle with 540 PTO RPM. That triangular deck shape houses a large pully under the gearbox, and a small pully out at the spindle to achieve this 5.8:1 ratio. It has a 24" cut diameter, so the string tips are traveling roughly 328 feet per second. A typical 14" handheld string trimmer has to turn nearly 5400 RPM to get this same string tip velocity which is why their 2 stroke engines really sing... As the string wears/breaks, they don't cut as well. This velocity also applies to blades. That is why most push mowers that are direct driven off an engine shaft don't go much bigger than about 21". A 3600 RPM gas engine driving a 21" blade yields around a 329 FPS at the blade tips...
Anything you build will need to have that same string tip velocity to have a reasonable chance of being successfull.
Good luck
Anything you build will need to have that same string tip velocity to have a reasonable chance of being successfull.
Good luck
Brad_Blazer
Veteran Member
They used to sell weedeater heads with chains instead of string. I remember a story about a man who killed his young granddaughter using that attachment when it broke, flew some 50', and struck her head. Any type of cutter that behaves like a whip will be consumed in the process and occasionally shed chunks. It is much safer it the material is lightweight so it does not shed bullets.
Here is the recall of the "weed wizard"
Recall: Weed Trimmer Heads With Metal Chains Recalled by Weed Wizard -- Nolo
Here is the recall of the "weed wizard"
Recall: Weed Trimmer Heads With Metal Chains Recalled by Weed Wizard -- Nolo
gemini5362
Veteran Member
That is an interesting weed trimmer for a three point hitch. Based on my experience using a weed trimmer with a 6.5 horse engine that trimmer will havae you spending more time replacing string than you do trimming anything other than grass. Basically it looks like the same head that I have on my string trimmer only it has places for 4 pieces of plastic cutting string and mine that I push like a lawn mower only has 2 but same mounting design on the string.
I imagine there is some difference between the chain on that weed wizard and a piece of 5/16 inch chain. Also if it breaks better chance of it not going flying into space when it is underneath the deck and aprons of a brush hog attachment.
I imagine there is some difference between the chain on that weed wizard and a piece of 5/16 inch chain. Also if it breaks better chance of it not going flying into space when it is underneath the deck and aprons of a brush hog attachment.
frank_f15
Super Member, Rest in Peace
i think you will just waste time and material for something that wont work, IMHO just bite the bullet and get a real rotary cutter.
Hey Guys, thanks!
My design is now to be adapted from PoohBear's link (maybe more reach) and I can derive the required speed (thanks RonMar) with a pully arangement easily.
I did , a few years ago, attach steel cable to my Huskvarna weed wacker and stopped fast when I realized that I was hurling bits of cable hither and yonder.
I now use the square nylon (biggest available) lengths in the gripper head with excellent durability.
At first I would fill my pocket with precut lengths expecting to use up a good handfull per drive side, but no they last quite long. In fact I believe I merely used 4 or 5 lengths.
My plan will now be to make a 3 point mount for the gear box and a side arm as per PoohBear's link (essentually an offset channel box) with a quill arrangement to mount the holder head.
In fact I might even purchase the conversion adaptor as sold for my Husky and attach it to the quill. (the quill being a shaft and 2 bearings, unless I simply buy one)
It can't work any worse than my big husky weed wacker does, only I can sit and drive rather than walking! (Getting old--er and lazier)
Also I can raise or lower at will with the 3 point.
Also for ditch management the offset arrangement is COOL!
But the info I needed was RPM's, so thanks guys!
Oh, yes I'll post pic's, probably as a finished project with stages.
Heck I could also adapt a 16" saw blade for bigger stuff! Why not? I do that now on my Husky wacker. (12" blade)
Using an offset belt drive I like as I feel that this is somewhat a safety feature as with 'just right' tension (OK, now I need to have a tensioner=easy enough) I can introduce controlled slippage to prevent sudden stoppage in the event I hit a stray piece of rebar for example.
Sure, I'll have safety shields etc as I know what it is like to have pebbles etc hitting the legs (even dry twigs hurt).
I found that something like HD inner tube rubber or carpet does an excellent job in absorbing/deflecting flying bits and pieces.
My design is now to be adapted from PoohBear's link (maybe more reach) and I can derive the required speed (thanks RonMar) with a pully arangement easily.
I did , a few years ago, attach steel cable to my Huskvarna weed wacker and stopped fast when I realized that I was hurling bits of cable hither and yonder.
I now use the square nylon (biggest available) lengths in the gripper head with excellent durability.
At first I would fill my pocket with precut lengths expecting to use up a good handfull per drive side, but no they last quite long. In fact I believe I merely used 4 or 5 lengths.
My plan will now be to make a 3 point mount for the gear box and a side arm as per PoohBear's link (essentually an offset channel box) with a quill arrangement to mount the holder head.
In fact I might even purchase the conversion adaptor as sold for my Husky and attach it to the quill. (the quill being a shaft and 2 bearings, unless I simply buy one)
It can't work any worse than my big husky weed wacker does, only I can sit and drive rather than walking! (Getting old--er and lazier)
Also I can raise or lower at will with the 3 point.
Also for ditch management the offset arrangement is COOL!
But the info I needed was RPM's, so thanks guys!
Oh, yes I'll post pic's, probably as a finished project with stages.
Heck I could also adapt a 16" saw blade for bigger stuff! Why not? I do that now on my Husky wacker. (12" blade)
Using an offset belt drive I like as I feel that this is somewhat a safety feature as with 'just right' tension (OK, now I need to have a tensioner=easy enough) I can introduce controlled slippage to prevent sudden stoppage in the event I hit a stray piece of rebar for example.
Sure, I'll have safety shields etc as I know what it is like to have pebbles etc hitting the legs (even dry twigs hurt).
I found that something like HD inner tube rubber or carpet does an excellent job in absorbing/deflecting flying bits and pieces.
gemini5362
Veteran Member
I will be eagerly awaiting to see your results.
I also use the largest multiside plastic pieces that you can get for a weedeater on mine. If I am cutting in anything that has any kind of large brush in it or big weeds even. I have gone through a dozen strings in a couple of hours. I usually buy a row of the string then cut it to lengths to thread in my unit. Like I said I am eagerly awaiting to see your unit and find out how well it works
I also use the largest multiside plastic pieces that you can get for a weedeater on mine. If I am cutting in anything that has any kind of large brush in it or big weeds even. I have gone through a dozen strings in a couple of hours. I usually buy a row of the string then cut it to lengths to thread in my unit. Like I said I am eagerly awaiting to see your unit and find out how well it works
dqdave1
Veteran Member
Maybe chainsaw chain instead of nylon.
dqdave1 said:
That would scare me as one link at the required rpm would result in about the same velocity as a .22 cal bullet, remember, I tried using wire rope on my string cutter and was finding bits of wire imbedded in my trousers and exposed skin.
If anything I'd prefer a saw blade as blades are designed for reasonably high RPM usage plus there are thousands of weed wackers running them.
Also a blade will cut weeds no problem with advantage of also handling the weeds reeds etc.(might make for more slimy gooey juice than a string however)
In the last hour I was gathering the components that I would use to fab up my 'tractor wacker' and it should not be a very long project to assemble.
The most difficuly will be fitting a suitable pully to my gearbox, but worst come to worst I might simply weld one to the gearbox output shaft as afterall it will become dedicated to the project anyway.
