Tractor Sizing Tractor pto for 7 foot cutter

[Texasmark]

I easily run a 6' with my Ford 3000, about 36 PTO hp. My terrain is varied and I found out that you can have too big a cutter unless you are on pretty level terrain. Neighbor had a 7' years ago and as stated they are very large and heavy and the weight is way back from the lift point so the "ft-lbs" gets into the equation meaning that the front of the tractor can get light without adequate counter weight (4wd and loader helps that). I had an 8' with dual dolly wheels and yes it was shorter.....2ea 4' cutters side by side, but it was wide and even with 2 dolly wheels I had scalping and all. Probably went through 6 or so cutters looking for the right size and as stated, 6' medium duty (get the 65 hp gearbox with med duty) was the best all around and that was my last purchase which I am currently using.

Other thing on the 6' is that it is the same size as my tire width so I know exactly where the mower is when doing a fence row. Some like that others like to have the mower sticking out. On the 8' I had I wound up in the fence more than once trying to guess where the fence was trying to get as close as I could to it. Course I could have come back with a riding mower and done the fence.....but my riding mowers don't have AC...grin.

HTH,
Mark

 

[bigbull338]

personally i would not buy a 6060 but thats just me.because if you want a cab tractor id go with the 7060 because a cab uses 5 to 10hp of the tractor.

 

[Gary Fowler]

I have a LS P7010 with a 7 foot cutter with 1/4" thick deck. It really squats the rear tires when I lift it too. In heavy grass, it will tax that 70 HP also. If you want to use a 7 foot mower, get at least 60 PTO HP or you will be going very, very slow in heavy grass. I have no experience with 8 foot cutters but I would think that powerwise, it would take as much or more power to turn them in heavy brush. IT may be easier to start spinning and weigh less, but that should be about it.

 

[xring100]

I have no experience with 8 foot cutters but I would think that powerwise, it would take as much or more power to turn them in heavy brush. IT may be easier to start spinning and weigh less, but that should be about it.

Gary I definetly agree with that logic the 7 footer has a lot of rotational inertia to get going but once its spinning it should be of some benefit as it wants to stay in motion more so when it hits the thick stuff

 

[Bigfoot62]

I run a 7 foot BH27 on my M8540 next frame size up. Im sure the M6060 would run it fine in tall light brush. Youll need front weights if you plan on running with no loader. With the M7060 you also get limited slip front differential.

If I start hitting lots of thick stuff with sapplings it can tax the 75 pto hp I have available. Normaly it runs it just fine without even flinching.

The M7060 and M6060 share the same frame only differences in size should he tires. I don't think id want to drop down to an L60 series or its cheaper sister in disguise the MX series and run a 1300- 1400 lb cutter on it thats almost 11 feet long

Bush hog recomends a minimum of 55 pto hp to run the 7 footer

I agree.

I have a Rhino 7' and it's a load behind my 70hp if I'm in really heavy grass or brush. It literally pulls harder on the engine than my 10' twin spindle cutter. I personally wouldn't want any less tractor than what I have for the 7'.

 

[GManBart]

Gary I definetly agree with that logic the 7 footer has a lot of rotational inertia to get going but once its spinning it should be of some benefit as it wants to stay in motion more so when it hits the thick stuff

Bigfoot62 seems to contradict t his theory if he's comparing a 7' single spindle to a 10' twin spindle cutter, and the 7' model taxes the engine more.

 

[PoorPlowboy]

I know from personal experience that an 8ft twin spindle bush hog is a good load on a Kubota 7040 in thick grass but are otherwise matched pretty well together. Nothing annoys me more than mowing or bushhogging with too much cutter and not enough weight and horsepower. Too light of a tractor and the cutter does the bouncing and steering for you. Too few horsepower and you can easily double or more time spent in the field.

 

[Texasmark]

On driving force required for different sizes it's area and "moment of inertia" as stated.

The moment arm on a 7' is 3 1/2' so a pound of resistance out at the tip is 3 1/2# of resistance to the driving power; on an 8' it's 2 +2 =4 or 14% more resistance to turning on the 8'. So there is some advantage to the single 7'. However the area that the blades see on the 7' is 38 sq. ft. [pi x (d/2)exp 2] whereas for the 8' it's 12.5 for each side for 25. The 7' is exposed to 52% more grass while cutting and that's why it takes more hp.

Edit: On the inertia in the arm, agree for the 7' running at the same 540 pto and gear box ratio it has more as the blade weighs more than one of the 8' and due to the larger radius it's running 75% faster at the tip. So (mass x acceleration)exp2 says you have a whole lot more whack for something like a sapling. However, you have to get the sapling under the deck first of all and second, the power source has to continue to feed that increased load if in a constant medium....tall grass.

That's the way it looks from here.
Mark

 

[Fallon]

In your area equations you need to divide by 2. If you properly set the front lower than the rear, the back half of the blades isn't cutting or dragging in the stubble & robbing HP.

Also I believe most rotary cutters aim for the same ballpark blade tip speed. If you spin longer blades at the same RPM as you mentioned the force on the blade goes way up. I believe they keep the maximum speed if the tips down so they don't self destruct.

 

[TSO]

For what it's worth, I have an 8 ft dual blade Ford (old school) brushog ... and my Massey 1648 hydro (36.5 PTO HP) has no problem with it.