Flail Mower Flail Mower Vibration

[JG92979]

Hi, I just completed restoring, or resurrecting I guess you would call it, a late 70's vintage Mott 72" Hammer Knife fine cut flail mower. I aquired it for free not working and disassembled needing new cutter shaft bearings that were "obsolete." A simple call to Flailmaster and I was in business. I installed new shaft bearings, replaced missing flails, and welded new flail hangers where necessary. I hooked it up to the tractor to try it out and its got a wicked vibration. I took it off flipped it over & set up a straight edge & noticed the shaft is bent about 1/16" - 1/8" in the middle. Is that enough to make it jump 2-3" off the ground...? Does anyone know if there is a out of round tolorance? I'm going to set up my Porta-power tomorrow after work and try and straighten it and see if that solves it. I have used 3pt hitch flails and boom flails for 10yrs 1000+hrs and have lost flails and welded on hangers before and never had a vibration like this before. Any thoughts...? Thanks.

[Oldtractorfixer]

I am sure you probably already checked, but are the flail knives evenly distributed around the shaft so that is not out of balance.
Sounds more like a balance problem than a "bent" problem. I wouldn't expect 1/8" to cause that severe a vibration.

[greg_g]

There are slight out of round tolerances, evidenced by the presence (or availability) of balance weights on the rotating shaft. But it sounds to me like yours has strayed well out of that territory. When you finish the straightening attempt however, you'll still probably need to fine tune with a few counter-weights. Those that are made for my Ford 917H are somewhat like the flat self-adhesive wheel weights that go on chrome and alloy wheels.

That said, you may have lost a balance weight or weights. But I'd work on that curvature too.

//greg//

[leonz]

Hi, I just completed restoring, or resurrecting I guess you would call it, a late 70's vintage Mott 72" Hammer Knife fine cut flail mower. I aquired it for free not working and disassembled needing new cutter shaft bearings that were "obsolete." A simple call to Flailmaster and I was in business. I installed new shaft bearings, replaced missing flails, and welded new flail hangers where necessary. I hooked it up to the tractor to try it out and its got a wicked vibration. I took it off flipped it over & set up a straight edge & noticed the shaft is bent about 1/16" - 1/8" in the middle. Is that enough to make it jump 2-3" off the ground...? Does anyone know if there is a out of round tolorance? I'm going to set up my Porta-power tomorrow after work and try and straighten it and see if that solves it. I have used 3pt hitch flails and boom flails for 10yrs 1000+hrs and have lost flails and welded on hangers before and never had a vibration like this before. Any thoughts...? Thanks.

I want to welcome you as the newest member
of the Flail Mower Nation- onward and upward;


AAAAYYYYYYYY Caramba LUCY YOU GOT PROBLEMS.

The flailmower rotor has to be removed and balanced;
Or bite the bullet and purchase a new rotor and you will
get a mower a mower that will outlive all your tractors.


Now to understand why this is happening the
centrifugal force of the flail weldments,
knive hangers and knives in the orbit has
essentially decayed and become slightly
elliptical and the the combined mass of
the elliptical orbit of the entire shooting
match is making it hop like a rabid rabbit.

The flail mower rotor is deflecting an eighth
of an inch to one quarter of an inch each time
it is rotating and the the entire mass is reacting
to the centrifugal force created by the entire weight
of the flailmower rotor, weldments/mounting
stations. knive hangers and knives.


Please do not use your porta-power to straighten
it as you will only make it much worse and you
will destroy your new bearings.

You need to remove the flailmower rotor and take
it to a driveline shop to straighten it add back the
balancing weights if needed.

Just to illustrate to you what happened to me with
a rental and the amount of torque a power take
off can create-

I rented a tricycle JD 3020 gas tractor and
a seven foot john deere flailmower to mow
pasture when I was still at home and helping
around the place.

So anyway I got to mowing and on the forth lap
around one of the lower link pins broke or
popped out and the next thing I new the entire
mower was spinning because the upper link also
popped out iand the other pins dropped out and
the next thing I new the PTO shaft was spinning
the entire body of the mower needless to say I
shut it off in a hurry and prevented any damage.

IT was a spincter clinching moment for sure!!!!!

I wanted to show you how much torque a power
take off can create when the entire thing is unbalanced.

The other thing is the new bearings will be damaged if
you try to use a porta power on the flail mower rotor which
is rotating at plus 2,000 R.P.M.when operating.

I want you to think of it this way; if you take a pail of water
that is half full and attach a two pound weight to one side of
the partially filled bucket and tie a rope to it then try to get
it airborne and try to spin it like a rope lasso you could
disclocate your shoulder if you manage to get it to spin.

The amount of deflection is in the thousandths of an inch
because the rotor must be counter balanced with welded
weights to correct the natural imperfections on the flail
mower rotor shaft.

If the drive line shop has a high speed shaft balanceer or
access to one they can find the bad spots/bend it back
properly and reattach the balance weights as it must be
done very carefully each time weight is added to counter
the weight opposite it that was attached or must be corrected
with the proper pressing back of the shaft to recreate the original center line.


Please, I do not want to see you or anyone else get hurt.

[JG92979]

Well, I spent about 2 hrs the other day attempting to straighten the cutter shaft. I set up a straight edge across the top and used a floor jack and jacked it against its self in the housing. It had a gradual wOw in the middle and I got it as close to perfect as I possibly could. If u checked it now and I didn't tell you it was bent you could never tell which way it was bent. Its not good enough though, it might be a little bit better but its not usable and quite dangerous like this. I have no idea what could be throwing it out of balance this far. I even tried taking flails off to see if it would balance and made no difference. I have no idea whats the matter...

[Hooked_on_HP]

You need to get the rotor balanced. Check with your local tractor dealer. The straw choppers on older combines are like the flail mower and have to be balance. They should be able to tell you whare to get it done.
Bill