What if I don't run PTO speed?

[Grrrr]

My experience of a big flail mower is that you really want them spinning around at their rated speed. The one I use is about 9 foot wide behind a 130 HP tractor.

We always run it at 540RPM because we find you get a much better cut. If it is going slower, then it tends to mash the grass rather than slicing it off.

I also learnt the hard way that if you are chopping anything long and strandy like straw or brambles you really wanted it spinning or if it gets bogged down for a bit the weeds will wrap around the rotor and you get a right blemming mess to cut out.

Also, at rated RPMs, the tractor will keep going relatively the same speed up hill and you will have good engine braking going down. At near idle, I know most tractors will lug right down going up, to the point you have to raise the throttle, and run away with you goign down hill. Not fun if you are cutting on a slope.

With rotary cutters they seem to cut well at whatever speed, but you get more of a vacuum effect at higher speeds pulling the grass into the blades more.

 

[Lunk]

My Branson 's 540 PTO speed in the 540E setting is achieved at 1700 RPM. I've been running a 5' cutter at 1800 RPM in heavy weeds / 4' marsh grass.

Cuts it clean / does not lug engine / economical / seems to be happy tractor.

Normal PTO - 540 pto speed is reached at 2600 RPM.

That seems a little high for my purposes. I guess a lot depends upon what you're cutting...

 

[WTA]

I can only get away with the 540E setting in grass here. If there are big tumbleweeds or anything I need to go to the regular 540 mark on the tach. I go through shear bolts like crazy at the lower setting.

On any kind of reciprocating equipment it will be best to run at rated speed for it. It's what they were designed for. If any of you have run a mounted tiller before at a low RPM then I'm sure you know why. They will vibrate your fillings loose at low speed but at 540 pto speed they smooth out. My hay baler isn't much different I've discovered. It will work ok at the 540E setting till I hit a big row of grass then it breaks a shear bolt. I haven't broken a bolt yet at rated speed. That's because it has more momentum to carry everything through the stroke at rated speed. At low speed the torque of my engine just tears things up.

Old pumps I used to run in the navy were the same way, Turbine powered steam pumps could handle low speeds without a problem. Reciprocating steam piston pumps needed to go at full speed on the governor or things would break. The one ship I had the serious misfortune or working in with old antique reciprocating steam engines absolutely hated anything but full speed. That was only 12 knots I think but the vibration and banging smoothed out to a point where I didn't feel like my fillings were going to pop out. On a "dead slow" bell the thing felt like it was going to fly apart. We could actually see the connecting rods bending under the stress of going back down on the stroke. I'm not kidding. Thankfully the only time we had to light that one off was to drive it to India where it got stripped out and made ready to be a target ship. It was about 80 years old when it was finally retired. The momentum the heavy moving parts have at full speed has a lot to do with how well any reciprocating machine works.

 

[Flatheadyoungin]

Lot's of good advice, here....

most of what i need to cut to clear some land is heavy, several years old, grass....you know how it twists and is hard to cut.......i'll probably have to run her pretty hard to get it back in shape.......after that i can probably "granny" it

also, my blades are nicked up and very dull......a buddy with a fail said don't worry about it until after i clear the land and mulch up some of the larger stuff.........then put a new set of blades on or sharpen the ones i have....

there again, i'm just chomping at the bit to get this land deal closed! i'm just trying to get all my ducks in order and make sure all my equipment is ready for the task.........hopefully nothing will lay down on me so i can spend time working the land, not working on equipment.....but we know how that goes...

 

[Mickey_Fx]

Lot's of good advice, here....

.....

also, my blades are nicked up and very dull......a buddy with a fail said don't worry about it until after i clear the land and mulch up some of the larger stuff.........then put a new set of blades on or sharpen the ones i have....

You nailed it right there. Dull blade will do a poorer job taking more power in the process. I suspect you could get a better cut running a lower speed with properly sharpened blades and less stress in the process.

 

[Bob_Young]

I keep the bush hog blades sharp and typically mow at PTO speeds between 440 and 480 RPM. Used to do this because I was never sure what I'd hit and didn't want a lot of energy in the driveline when I hit it. Now that the place is cleaned up fairly well, I've continued the practice as I've seen no benefit to running faster.

 

[Glowplug]

I think it makes more sense to have relatively dull blades and possibly mow at a lower PTO rpm when you are clearing land so that you can get more chopping, mulching, pulverizing of the bigger stuff like saplings. Then once it's been cleared and mowed a few times put on new sharp blades and mow to get a clean cut. . .at whatever ground speed and engine speed that takes. Just my 2 cents!

 

[schmism]

i run my 5' hog at about 1800 rpm, for light cutting i can run 1500-1600. for heavy thick grass i run 2200 or better as it really bogs the tractor down at lower RPM.

MY 5' tiller first pass i run at about 1800, second pass at 2500. i just want more cuts per min to really get a nice fine seed bed.

 

[3RRL]

I think flail and rotary cutters should be run at or near rated PTO to get full advantage of the centrifugal force. That is not to say a variance in speed can't be done, because it can for sure.
My PTO has 2 speeds, 540 PTO and 720 PTO at 2300 engine rpm. Does yours have 2 speeds?
Tough, heavy duty cutting I use my 540 PTO (2300 engine rpm) to get the hp I need to cut through the tough stuff and not bog the engine down. However, for light duty rotary mowing of fields, I use the 720 PTO speed and run the engine at 1725rpm, which makes the PTO spin at 540 PTO rpm. My Kama is a 55hp, (50 PTO hp), so at 1725 engine rpm I have plenty of horsepower. Not only that, but peak engine torque occurs right at the mid 1700 rpm range, so the engine is at or near peak torque range to keep from bogging down anyway. I save on fuel and wear and tear a little. I just match up the ground speed to suit and kick back.

 

[Grrrr]

I think flail and rotary cutters should be run at or near rated PTO to get full advantage of the centrifugal force. That is not to say a variance in speed can't be done, because it can for sure.
My PTO has 2 speeds, 540 PTO and 720 PTO at 2300 engine rpm. Does yours have 2 speeds?
Tough, heavy duty cutting I use my 540 PTO (2300 engine rpm) to get the hp I need to cut through the tough stuff and not bog the engine down. However, for light duty rotary mowing of fields, I use the 720 PTO speed and run the engine at 1725rpm, which makes the PTO spin at 540 PTO rpm. My Kama is a 55hp, (50 PTO hp), so at 1725 engine rpm I have plenty of horsepower. Not only that, but peak engine torque occurs right at the mid 1700 rpm range, so the engine is at or near peak torque range to keep from bogging down anyway. I save on fuel and wear and tear a little. I just match up the ground speed to suit and kick back.

What your tractor has sounds similar to an Eco PTO found on many bigger tractors, allowing you to use less RPM but still have the 540 PTO speed.

That is very useful for a lot of jobs, where the full power isn't needed and you can save some fuel and have a quieter engine.