Balancing flail mower rotor

   / Balancing flail mower rotor #1  

tlj87

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JD 4700, Kubota BX2370-1, Kubota RTV1140CPX, Kubota F3060, Club Car Precedent
In many, many other threads, when someone mentions the need to get a flail mower rotor balanced due to vibration, the response is typically "find a reputable driveline shop and they'll fix you up." I've called all of the reputable driveline shops within 2 hrs. and they all stated they can only balance a shaft with U-joint ends. I also called tractor dealerships that sell flail mowers and they responded that they don't balance shafts and don't know where to direct me.

Where are you all going to get your flail mower shafts balanced?
 
   / Balancing flail mower rotor #2  
Unless you've knocked a few flails/weights off the rotor, it should be in balance from the factory. Make sure all your flails are in place and they are the same. Having a mix of flails will throw it out of balance. The balance weights are welded in place so it pretty hard to knock those off. Also, don't expect a flail mower to be as smooth as a fan. ;)
 
   / Balancing flail mower rotor #3  
I feel your pain.

I called all around me last fall and found a place a almost 3 hours away that would do the job.
 
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   / Balancing flail mower rotor
  • Thread Starter
#4  
Unless you've knocked a few flails/weights off the rotor, it should be in balance from the factory. Make sure all your flails are in place and they are the same. Having a mix of flails will throw it out of balance. The balance weights are welded in place so it pretty hard to knock those off. Also, don't expect a flail mower to be as smooth as a fan. ;)

The subject Alamo mower is 35-ish years old, was owned by the state of NY and was well used. I had the non Pulley side of the rotor built up and turned down then replaced bearings and housings on both ends. All blades are brand new from Flailmaster. I’ve also swapped PTO shafts to rule out that as the source of the vibration.

Next step is to remove all blades and run it without them to see if for some reason the blades are not equal, which if they aren’t would have to be a manufacturer defect as they only have about an hour on them.

This is the vibration:
 
   / Balancing flail mower rotor #5  
When I had work done on the New Holland 918H it was done by an old machine shop but then again they also did driveshafts too but I would check with any machine hop in the area, ya never know... might get lucky.
 
   / Balancing flail mower rotor #6  
Here is a video of a guy making his own.
At about the 9 minute mark he balances the rotor
 
   / Balancing flail mower rotor #7  
I would not be checking for vibrations at idle or with the flail lifted high so the pto shaft u-joints are at such an angle. I would find a hollow for the flail to sit as close to cutting height as you can and sit it on blocks. You don't cut with it 18" in the air at idle, instead, you have it resting on the roller running pto speed (flails flung out) and the u-joints are straight. The video is only showing you testing the u-joints.
 
   / Balancing flail mower rotor
  • Thread Starter
#8  
I would not be checking for vibrations at idle or with the flail lifted high so the pto shaft u-joints are at such an angle. I would find a hollow for the flail to sit as close to cutting height as you can and sit it on blocks. You don't cut with it 18" in the air at idle, instead, you have it resting on the roller running pto speed (flails flung out) and the u-joints are straight. The video is only showing you testing the u-joints.
Thank you. I agree, and I can tell you that the behavior is basically the same when stationary, on the ground, at higher RPMs. There are certain RPM ranges when the the vibration is slightly less or more, but is always there.

I did find that I could register and get a OP manual from the Alamo website, although it's a current version. I did learn the following: "FOR FORWARD ROTATION: Knife pins must be installed with their heads facing away from the cuttershaft
pulley." This is not the case currently, as I put one half on facing one way and the other half facing the other way.
 
   / Balancing flail mower rotor #9  
I never tire of writing about the fact that rotors of mowers or forestry mulchers cannot be properly balanced by the method shown in that video at the 9th minute.

So why can't a mower be balanced without a portable device for dynamic balancing or a balancing machine?

I often hear: "I'll balance the rotor myself, as I've always done before without any devices, using the old proven method. I'll set the rotor on knives, and when it lowers with the heavy point down, I'll weld a weight on top and so on until it stops rotating! as in that video at the ninth minute :)"

Yes, this method works well with static imbalance. Static rotor imbalance is manifested without its rotation, when under the action of gravity, the rotor turns with the heavy point downwards. This type of imbalance can be eliminated by the traditional method - setting the rotor on horizontal guides and adding mass in counterbalance until it stops rotating. Such a method is effective for narrow rotors, whose diameter significantly exceeds their length, for example, for brake disks, single belt pulleys, and grinding disks.
%D0%A0%D0%BE%D1%82%D0%B5%D1%80_statika-600x322.jpg.webp


However, when it comes to balancing long rotors, such as mower shafts or mulchers, this method proves to be ineffective. Consider the situation where on one side of the rotor the heavy point is at the top, and on the other - at the bottom.In a static position, the forces of gravity balance each other, and the rotor remains stationary. But as soon as the rotor begins to rotate, centrifugal force starts acting on these points, pulling them in different directions and causing vibration. This type of imbalance, which only manifests during rotation, is called dynamic imbalance and cannot be eliminated by static balancing methods.
long-rotor-600x322.jpg.webp


To eliminate dynamic imbalance, portable devices for dynamic balancing or balancing machines are necessary, allowing precise identification of the imbalance location and the installation of compensating weights on both ends of the rotor to neutralize it.

Source : Dynamic Balancing of Flail Mower and Forestry Mulcher Rotors

Video of my work:

Thus, the use of specialized equipment for dynamic balancing is a necessary condition for eliminating vibration in long rotors.
 

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