Rotary Cutter PTO RPM actual vs ideal

[TexasHill Country Rancher]

Hello all,
I am running a JD CX20' batwing rotary cutter, or a JD HX 14' lift type rotary cutter, both of which are nominal 1000 RPM.
I now have a JD 6615 with digital dash, which shows the actual PTO RPM.
According to the digital dash, I am almost never actually running at 1000 RPM, no matter how hard I try to adjust the throttle. (Engine speed is about 2250 RPM at that time.)
My question is this:
How critical is the RPM speed of the rotary driveline for these shredders (or any other PTO equipment?)
Since I assume that being off by 10 - 50 RPM is no big deal, the question is: what is the acceptable variance, and when does it matter? It still cuts at 600 rpm, although not as thoroughly.
What are the consequences of running a driveline too slow? Efficiency of cut? Longevity of machine?
I can imagine the dangers of too fast; I might discover the failure point of the driveline, but what is the safety factor?
I appreciate anyone who has an opinion on this; I know many of you tractor pros have many decades of experience with this kind of equipment, and I am a newbie.
I would appreciate even more, someone who has some knowledge based on facts or engineering information.
Thanks for reading this far, and for any insight you can give.

 

[DieselBound]

Think momentum. Running slower means that there's less momentum. If one is encountering tough/tall grass (or brushy material) then there is going to be more resistance to the blades, possibly causing more shock loading on components (belt driven stuff is likely more forgiving; and, of course, clutched PTO shafts also will be able to manage if too much shock, though I'd think for grass one would have to have the clutch set light).

"Speed kills." Yes, having the equipment running too fast can "kill," though mostly the "kill" will be what you're cutting. There's a point, however, in which running at a higher speed (and more momentum) is more than what's needed. It kind of depends on the "feel" of how the engine is holding the load and the results of the cutter. Although I have no experience with 1,000 rpm PTOs, I'm just guessing that it's the same as with 540 rpm PTOs- it's a centerline rpm point; sometimes going a bit under and sometimes going a bit over is what real world would want in order to agree with your desired results.

 

[countrybumpkin]

When I'm running a cutter I have two settings, idle and full throttle.

 

[Dave M7040]

If you look into shear bolts for drive lines running at 1,000 rpm's vs those at 540 rpm's, the slower speed pto shaft requires considerably larger shear bolts to protect itself.

By running the 1,000 rpm pto above 1,000 you are reducing the stresses it experiences. On the other hand, running a 1,000 rpm pto at 600 rpm is increasing the stresses on the pto shaft.

Seems backwards but that is the simple engineering.

Often, if you go to the implement being driven by 1,000 rpm pt shaft, you will find the implement's rotational speed is slowed down in the gear box. The physical blade tip speed needs to stay within certain limits to not be dangerous.

The higher rpm pto is there to allow you to move more engine horsepower to the implement. It reduces the cost of the pto shaft and also the physical size and weight.

Dave M7040

 

[rustyshakelford]

Doesn’t have to be right on the money at 540 or 1000. Worse to be higher than lower. To get the advertised blade speed and “best” cut you’re supposed to be at rated speed. I Set my batwing to around 550 and leave it alone. Sometimes it’s drops to 500, rarely it’ll go to 560 for a short time. In lighter grass I’ll run in epto. I save a ton a fuel. It goes from 5gph to around 2-2.5

Brett

 

[buickanddeere]

Operating a pto generator the rpms had better make 60Hz.