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Discussion Starter #1
I have been thinking about building my own offset tow behind mower. I have a swisher now but its getting beat to death in the fields I do. I'm thinking of taking a 3pt 60" finish mower and mounting a 15-20hp motor on it to power it and then rig up a tow system.

Some thought are:

How to drive and gear the system. Most small engines are governed at 3600rpm. I'm guessing peak power to be around 3000rpm, would need to gear that down to 540rpm. Chain or belt.

Tow system. The "trailer" type system with a pivot at the back of the tractor is what my Swisher uses. While its a simple system it drives me nuts whenever I turn a corner as it custs the corner in a tighter arc than the tractor leaving an uncut swath of grass. Having an arm mounted solidly off the back of the tractor would make it travel more in line with the tractor(like a 3pt implement) however no pivots need to betaken into account for forward and back and side to side.

Motor, vertical or horizontal shaft? Horizontal shaft would be easier to drive the input on a PTO. Vertical shaft motors are cheap to buy as there are tons of 15-20hp dead or cheap garden tractors with good motors in them that can be bought used for cheap. How could I turn the drive(and maybe gear it down) to drive a PTO input gear box?

Front or back? Since I'm fabbing anyway wouldn't it be better to mount it off the front where I can see it?

Anyone converted a PTO driven unit to self powered? If it goes well maybe I could mount a motor on a 3pt snowblower and use it on the front of my tractor.
 

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OK, I'm puzzled as to why you need to use an external power source. Does your tractor have a three-point-hitch and 540 RPM rear PTO? If so, why not use what you have?

Would a sickle bar mower be better for your needs?

Or how about getting a 1:1 right angle gearbox from Surplus Center and use the tractor to power the offset mower?

If you have no other choice but external power, a vertical shaft engine coupled to a 5:1 - 6:1 reduction right angle gearbox might be what you need. Put the gearbox under the engine with the output shaft powering the mower's existing gearbox. Or a simpler method would be to use a vertical shaft engine powering a straight-line reduction gearbox connected to the mower blades. Of course you need to come up with a shear pin or slip-clutch arrangement to protect the engine.
 

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Discussion Starter #3
Its an offset tow mower(Google swisher) and the tractor is powering my belly mower.

Got a link for a 5:1 reduction box?
 

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Here is a 6:1 reduction gearbox.

But honestly, if you are building this thing I'd look for a used engine on Craigslist. I see small engines with gear reducers on there fairly often for under $200.
 

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If you are beating a Swisher tow behind to death, modifying a 3pt finish mower and towing it will probably yield the same results IMO. Why not just beef up the Swisher to handle the beating your giving it as you already have it and even as far as an engine goes you can always put a bigger twin vertical shaft on it from an old lawn tractor if you grenade the original and still be out less than doing what you are thinking of. Of course I could be totally off my rocker and missed your point too. So as they say results may vary:brow:
 
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Its an offset tow mower(Google swisher) and the tractor is powering my belly mower.
To my knowledge, most belly mowers are powered by a 2,000 RPM mid-PTO. Am I understanding you correctly that you don't have a rear 540 RPM PTO?

What tractor are you using? It almost sounds like you are using a X7xx series or equivalent Lawn & Garden tractor
 

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I lover my Swisher tow behind, it has been flawless for 10 years now. I can't imagine getting better results from another rear mower.

 

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Discussion Starter #8
Thanks for the replies everyone. I'll try answer all the questions.

I'm using a 2720 with a 72 belly mower, towing a 60" swisher to get a 10ft ish cut. The swisher is built very light weight as compared to a RFM and I don't like the tow bar setup. i would also like to switch from side to rear discharge.

JimR thanks for the link but that box is only rated for 8hp, I'll be running 15+hp. Plus the price on it puts it out of the ballpark.

I like the idea of yanking the gear box off the mower entirely and using a vertical shaft engine. Then I can play with the pully sizes to get the blade speed I want.

So far I've found a Farm King 60" RFM for $500 and 15HP motor for $350(new). The motor is a Powerease(Chinese/Honda clone) but has a pretty good rep. No electric start however. I also saw a used 18.5hp vertical shaft motor from a craftsman lawnmower for $300.

The grass cutting I do is large rural areas(around radio towers). The grass only gets cut a few times a year so it gets long. The ground is rougher than a lawn but not so rough as to need a rough cut mower. I've been doing these sites for 8yrs so all the rocks have been removed, its just long/tough prairie grass. For 7years I used a 932 Front Deck commercial mower like golf courses use. Last year I got the 2720 after the 932 finally packed it in. The Swisher has 2 seasons on it and I'm constantly replacing belts, straightening the deck and tow arm. Its struggles in the tall grass as the deck isn't very deep.
 

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Does the suggested 5HP per 12" of cut apply to rear finish mowers like it does with rotary cutters? If so, you may want to increase the engine size.

According to Tractor Data, you have 23.5HP at the rear PTO, which is plenty to run the finish mower; but whether you can power the belly mower and a finish mower at the same time could be problematic.

I've never used such a setup, let alone see one in action; so I'm guessing that when you make a turn, the offset mower has a large amount of pivot that would bind up a driveshaft from the rear PTO to a right-angle gearbox on the mower. Also assuming the mower pivots at the drawbar/tractor interface, what keeps the thing tracking straight with an offset pull?
 

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If that tow bar is just a big "L", adding some triangulation to it would make a ton of difference with strength.

Jim


Sent from my iPhone using Tapatalk
 

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Discussion Starter #11
Does the suggested 5HP per 12" of cut apply to rear finish mowers like it does with rotary cutters? If so, you may want to increase the engine size.

No

According to Tractor Data, you have 23.5HP at the rear PTO, which is plenty to run the finish mower; but whether you can power the belly mower and a finish mower at the same time could be problematic.

No I could not power both at the same time, nor could I power an offset rear mower. Driveline angles would be too severe.

I've never used such a setup, let alone see one in action; so I'm guessing that when you make a turn, the offset mower has a large amount of pivot that would bind up a driveshaft from the rear PTO to a right-angle gearbox on the mower. Also assuming the mower pivots at the drawbar/tractor interface, what keeps the thing tracking straight with an offset pull?
Yes

The mower has more issues than just the strength of the tow bar. I don't like how it tracks and leaves strips of grass when turning a corner.

You guys are just going to have to trust me when I say the Swisher isn't working how I'd like it to and I think I can build something better. Lets concentrate on brainstorming a new setup. :thumbup1gif:
 
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OK, so separate engine power it is.

So I'm going to suggest something that attaches to your three-point-hitch that keeps the mower tucked in closer to your tractor. When making a tight turn you lift it like you would a rotary cutter; but on gentle turns it should be able to stay at cutting height. I'd also put a counterweight on the left side like the articulated boom rotary cutters have.
 

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Discussion Starter #13
I've been racking my brain as well on how to best mount it. I originally thought off the three point hitch however it needs to be able to articulate side to side so if I come up on a side hill it can follow the ground contour.

A regular 3 pt implement follows directly behind the tractor so it doesn't need to move on a separate plane.

I've thought about as few options such as trailer spindles, hiem joints, trailer balls, or combination of.
 

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Do you have any hydraulic ports at the rear?

What I'm thinking is using a simple hinge parallel to the tractor centerline that would allow the mower to float within a certain range, then use a double-acting hydraulic cylinder to latch/unlatch the mower when you need to lift it with the 3PH. Latch to lift, unlatch to mow. If you don't have a rear port, you could accomplish the same thing with a 12VDC linear actuator; though it will probably be slower.
 

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If you could use a sickle bar mower that would increase your cutting width, but won't mulch the grass clippings. It will lay it down. No big deal if you cut often, but once the grass gets tall you would basically be mowing hay and not picking it up. That might be something to consider, if the situation will allow it.

I don't have the thread handy, but Dieselshadow set up a 7' sickle bar mower on his 2720 to mow a steep bank. That might be worth considering, if for no other reason that perhaps you could mount your RFM deck to the arm of the sickle.
 
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