540 RPM rotary cutter run 1000 RPM

[rutwad]

I know this is not recommended, nor do I choose to do it. But what would likely fail if a 540 cutter was run at 1000?

 

[PoorPlowboy]

Spindle (gearbox output shaft) bearings would likely be the first to seize from overspinning. When they seize the PTO shaft ujoints or PTO drive gear inside the tractor will be the next item to explode.

 

[GManBart]

Spindle (gearbox output shaft) bearings would likely be the first to seize from overspinning. When they seize the PTO shaft ujoints or PTO drive gear inside the tractor will be the next item to explode.

I was going to guess the input shaft bearings first...higher rotation, and higher side loads, but then I started thinking maybe the output shaft gear since that's where the 90* turn happens. Regardless, I think it would get ugly!

 

[rutwad]

On a 15' cutter, is it different gears at the splitter compared to a 540 or in the individual gearboxes?

 

[banjodunn]

G'day blade speed would be excessive could lead to catastrophic failure of the cutter bar and that would be ugly:shocked::shocked:


Jon

 

[Garycw]

I have a broken joint on drive shaft now that the po ran 1000 rpm in heavy brush. Luckily that was all that happened. When I told him he couldn't do that with a 540 rated bushog and is why it broke, he looked surprised & puzzled.

 

[Gary Fowler]

I am surprised that is all you have broken if he ran it very long at 1000 RPM. I many times run mine in the 750 range (I have 540,750 and 1000 speed pto) but I reduce the throttle position from 1950 rpm (rated PTO speed ) to 1450-1500 RPM which is about 72% of the rated speed same as the ratio of 540/750. I save a bit of fuel that way and it still doesn't lug the engine. Running a 540 rated bushhog at 1000 could have stressed the blade mounting bolts, the gear box and bearing and seals. I am sure the gearbox got hotter than he!! if he ran it very long so the seals might be leaking now also. Keep a check on your gearbox oil, if it still has some in it!!

 

[Baby Grand]

Since the rotational energy is proportional to the square of the rotor speed, your blades will have almost 4 times the kinetic energy of their design point, if run at the 1000 rpm setting and at full PTO speed. I'd be most concerned about losing the pivot pin on one of the blades and having the blade exit the mower, possibly right through the steel deck. Where it would wind up and who/what it would damage would be a crapshoot. Figure an effect range of 1000 feet.

 

[Capricious]

"... I many times run mine in the 750 range...."


Well, to expand upon the O.P.'s question, do many run cutters over the 540 (but less than 1000)?

I am going brush-hogging tomorrow, and I have a 3-speed PTO. At 540 or thereabouts I am sometimes leaving stems & such in my trail, and would like a bit cleaner cut.

 

[LD1]

I guess it would depend on the particular gearbox.

Its not uncommon to see a wide range of blade tip speeds. ~17000+ fpm blade tip speed on the upper end, and down as low as 10000fpm on others.


IF you have a slower FPM cutter, it would take close to 1000rpm to equal what some of the faster cutters are running. And those dont have any different blades, bolts, stump jumpers, etc. Just a different ratio gearbox.

In the world of gearboxes, bearings, u-joints, etc, 1000rpm is nothing. The issue becomes the HP rating. Or rather torque.

Now if you already had a cutter pushing over 15000fpm blade speed, then yea, that would be spinning the blades way too fast.

Not suggesting anyone try it, but if I had a 1000pto, I would probably use it and run it around 850-900 on my cutter which is a 10000fpm one. It would actually be easier on the driveline, cause higher RPM's allow you to transfer the HP with less torque. Thats why higher HP tractors usually run them, and why PTO shafts of the same HP rating can be made lighter if for a 1000RPM application.