Flail Mower Let's talk flail mowers

[Eagleview]

If a change of flails is wanted , they must be the same weight as what is on there now . A pair of "L" shaped knives can be changed for a single "cup/scoop" type flail as they are the same weight but cast hammers cannot be used . Even if they will fit on , the rotor will be out of balance . There is always a lesser amount of flails/hammer/knives on one side of the rotor . The two end counter weights on the rotor make up for this . If heavier flails are used , the counter weights will not be heavy enough to counter their weight .

Just thought I'd add that so people are aware of the fact .

 

[IslandTractor]

The two end counter weights on the rotor make up for this . If heavier flails are used , the counter weights will not be heavy enough to counter their weight .

Is this a universal rule or just for your flail? I wonder why flail manufacturer's don't just balance the rotors naked so that any flail type, used in all the attachment points, would give you a balanced rotor.

 

[leonz]

Is this a universal rule or just for your flail? I wonder why flail manufacturer's don't just balance the rotors naked so that any flail type, used in all the attachment points, would give you a balanced rotor.

The water pail example is a good way to explain this;



If you tie a rope to a water pail and fill it with two quarts of water
and whip it around it takes a smaller effort to spin it and you have
to exert less effort.

The same pail with more water takes more effort and energy hence
the centrifugal force created is greater and requires a heavier balance wieght-
heavier knives are greater wieghts and require greater balance opposite the knife
to counter the centrifugal force -hence two rows of knives for the heavier P hammer
blades and cup knives among others.

The orbit must be even and balanced in order to do the work with out damaging the rotor and bearings.


I hope I did not hijack the thread with my response.


leonz

 

[Eagleview]

I knew you would ask that , I hope you know how much trouble I just went through .

There is always a lesser number of flails on one row of the rotor , these flails are positioned to cut the gaps left by the other rows . The rotors are Dynamically balanced at the factory with the flails attached . As you can appreciate , if the flails were not attached , they would not know how much counter weight to add and exactly where to add it to make up for the lesser amount of flails . As you can see on this old Berti , it has rows of 6 flails and one row of 5 , you can also see the square steel stock counter weights welded on to make up the difference , my Cabe is the same .

I don't know about the mowers with hundreds of little knives as to what they do , if they need counter weights or not as the rows of knives may be equal .

 

[IslandTractor]

I knew you would ask that , I hope you know how much trouble I just went through ..

Yeah, well now I have to go out and flip my mower over (not currently mounted on the 3pt) to count for myself tomorrow. :confused2: I know I have 28 sets of knives (2 per station). I guess that does not allow simple division by 3 or 4 and therefore I guess there is some assymmetry. Too dark to check right now.

I understand your point I just don't understand why they don't simply balance the flail stations so that any number of flails will work. If you consider a centrifuge, they are balanced so that if you put the same weight in all stations the centrifuge is balanced regardless of how much weight you add. I don't see why flail makers would not use that same principle. If you think about it, flails lose weight as they wear. That means they will become progressively out of balance if they are in balance only with fresh flails as shipped from the factory. However, if they are in balance so long as each flail weighs the same (and flail knives do generally wear equally over time) then it would remain in balance as knives wear and would also be in balance if you changed all the knives to a different style. Seems odd to me that they wouldn't do that.

 

[Eagleview]

By doing that , you are only balancing the shaft , not the reciprocating mass . What happens after you balance the shaft and then add the flails in rows of uneven numbers ?

 

[John_in_TN]

Island Tractor is right, your description must apply to specific flail mowers, not to all of them. My JD flail has three rows of blades with 12 blades per row. I am running the lighter "cup" style blades, but can change to the heavier style blades IF I change all of them as a set. I just can't intermix the blade styles.

 

[leonz]

UM no,


You have the rotor and it carries the throw weight of the hangers, knife blades, bolts nuts etc., the rotor is forever balanced with the welded on wieghts to avoid issues with broken knives and the other possible nasties.


The rotors orbit is forever balanced but if the knives are improperly positioned the stress is magnified at that location



The flail mower rotor is the center of the mowers universe and the orbit is small and centralised where the knives and hangers are not stationary plus
the knives are traveling slower than the rotor as the orbit for the knife is larger in diameter and takes longer to travel the circumference than the rotor does.

leonz:thumbsup:

 

[Eagleview]

A flail rotor with flails attached in a balancer and one waiting it's turn . I had seen a better photo of this but can't find it at the moment .

 

[sodamo]

Now I'm curious :laughing:

Mine came with both sets:
28 Hammers - mounted in 4 rows of 7

Second set is the grass knives 56 mounted in pairs, 4 rows of 7.

I just changed them out this past week.

But If asked, I'd been willing to bet the hammers outweighed the knife pairs. Guess tomorrow, I'll have to check.

 

[Eagleview]

Maybe these ones with equal rows don't have counterweights and it doesn't matter if the hammer sets are heavier or lighter ? We only get the European ones down under .

Can you check this sodamo while your there ?

 

[IslandTractor]

UM no,


You have the rotor and it carries the throw weight of the hangers, knife blades, bolts nuts etc., the rotor is forever balanced with the welded on wieghts to avoid issues with broken knives and the other possible nasties.


The rotors orbit is forever balanced but if the knives are improperly positioned the stress is magnified at that location



The flail mower rotor is the center of the mowers universe and the orbit is small and centralised where the knives and hangers are not stationary plus
the knives are traveling slower than the rotor as the orbit for the knife is larger in diameter and takes longer to travel the circumference than the rotor does.

leonz:thumbsup:

Leonz I think there are a number of errors in your statements.

Welding on balance weights does not in any way "avoid issues" with broken knives. A rotor with missing knives will be out of balance regardless. I can usually tell when I have lost a set of knives by a change in the type of vibration from the mower (not severe, just a change).

The knives are actually traveling faster than the rotor not slower. The knives complete one revolution in exactly the same time (RPM) as the rotor shaft however as they are farther from the shaft they travel a longer circumference and therefore must be traveling faster.

 

[J_J]

Yeah, well now I have to go out and flip my mower over (not currently mounted on the 3pt) to count for myself tomorrow. :confused2: I know I have 28 sets of knives (2 per station). I guess that does not allow simple division by 3 or 4 and therefore I guess there is some assymmetry. Too dark to check right now.

I understand your point I just don't understand why they don't simply balance the flail stations so that any number of flails will work. If you consider a centrifuge, they are balanced so that if you put the same weight in all stations the centrifuge is balanced regardless of how much weight you add. I don't see why flail makers would not use that same principle. If you think about it, flails lose weight as they wear. That means they will become progressively out of balance if they are in balance only with fresh flails as shipped from the factory. However, if they are in balance so long as each flail weighs the same (and flail knives do generally wear equally over time) then it would remain in balance as knives wear and would also be in balance if you changed all the knives to a different style. Seems odd to me that they wouldn't do that.

I agree with you on the balance, only when new. Below is a picture of odd and even hammers. On the 5 hammer row, they have to add a counter weight to balance against the 6 row hammers. If any one of them gets damage or wears on one side, the flail will come out of balance. If you resharpen, you risk being out of balance unless you do the same grind on each hammer. You could weight each one and grind off some more for equal weight.

If one were to lose a hammer, you can still adjust by filling in the missing hammer from one off the end. You have to remove another one from opposite sides of the rotor, to keep the balance.

About the only people that could balance a rotor after use would be something like a drive-line shop . I don't know if they would do that kind of thing though.

 

[J_J]

As far as the the rpm, everything on the rotor is at the same rpm. The tip of the flail blades will be moving at the faster velocity.

 

[leonz]

The rotor needs to balanced as it is made from solid bar stack and must be machined or balanced if the round bar stock is not machined that why there are wieghts welded to them.

In our case the rotor was made into a hollow pulley and the steel sheet was welded to the pulley ends and rough balanced/magnets after the hangers/knives were attached then welded with the wieghts.

The whole mess gets into G force calculations and throw wieghts and I am not awake yet



The blade tips are spinning at a slower speed than the center of the rotor from what I remember.

when i wake up I will do the math and place it here.

 

[IslandTractor]

OK, I have risked life and limb to dig around under the Caroni flail while it was precariously suspended from the FEL. :ashamed: Here is what I found:

The Caroni TM1900 rotor has a symmetrical balanced array of flail knife stations. There are two opposite rows of 8 stations each with two knives and two opposite rows of 6 stations each also with two knives. This makes a total of 28 stations (8+6+8+6) and 56 knives.

There are no welded balance weights and as evident from the finding above, none would be necessary as it is a balanced arrangement of knives.

So, I guess this means that there are two types of flail rotors; those that are inherently balanced like the Caroni, and those that require welded counterweights to offset the assymetrical blade arrangement. I'm sure some flail engineer can expouse on the virtues of each type. For my purposes it just seems that the inherently balanced type has the advantage of being able to change blade type/weight without needing to dynamically rebalance the rotor (so long as all blades are changed at once). It also allows the rotor to remain in balance as knives wear so long as they wear relatively evenly. There are no gaps in the cutting with this 8x6x8x6 station arrangement so I don't see any disadvantages of the balanced type.

 

[leonz]

Ok I am more awake now, lunch, town, etc.

I have attached a few goodies in files for everyones

examination.


In one case, a john deere flail knife model
using 540 rpm and having V belt drive travels
at 100 miles per hour while at work cutting with
the 2 row knife rotor.

The rotor being smaller in diameter than the circumference
of the knife path rotates faster than the knives as it is smaller
in curcumference-

the anology is the smaller tire rotates at a faster rpm to obtain the same miles per hour, boat trailer tires and high speed go carts with chainsaw engines and tuned pipes are a good example of this.

oversimplifying it the race track scenario come to mind where the inside lanes are less in distance traveled than the outside lanes

If I knew how to create subscript and superscript and the square root sign I would do that here but I am not that profficient :ashamed:




about steel round stock steel in general:


The way steel is made and its processing after it is cast determines iuts behavior and quality as far as its size and condition for a specified use. high carbon steels are heavier and have a higher tensile strenth if my mind has not drawn a total blank. The way a steel is prepared is one major issue as steel is rolled and rolled and rolled either by cold rolling or hot rolling it directly out of the continuos casting machine where it will cool naturally if it is not drenched and achieve its designed diameter after cooling.

Some flat steel is further cold rolled after it is cast and cooled and delivered to the end user to be further milled
and cut with die wheels and rolled further for roofing sheets for example to create the ribs to add strength to the narrow roofing sheet.

Bar stock for a flail mower may have both a high carbon steel for heavy brush grinding or low strength steel if used for grass and intermittant brush mowing.

The tolerance for machining is paramount as the shft stock must cut at each end to permit the fitting of a fixed sperical roller bearing for the pulley side and one floating sperical roller bearing for the floating bearing on the open side.



Some flail heads are not really a flail head where it is a drum with weldments that accept conical carbide mining bits to grind brush, stumps, and trees on a boom arm arrangment mower head.






At least we all like our flail mowers anyway:thumbsup:



leon

 

[IslandTractor]

The rotor being smaller in diameter than the circumference
of the knife path rotates faster than the knives as it is smaller
in curcumference-

the anology is the smaller tire rotates at a faster rpm to obtain the same miles per hour, boat trailer tires and high speed go carts with chainsaw engines and tuned pipes are a good example of this.

oversimplifying it the race track scenario come to mind where the inside lanes are less in distance traveled than the outside lanes


leon


at least we all like our flail mowers anyway:thumbsup:

Leon, your examples actually prove that the flail knives move faster than the rotor. Consider the smaller tire analogy. In order for the smaller tire to go the same distance in a given time (miles per hour) as the larger tire the smaller tire must run at higher RPM. That is to say if the smaller tire (rotor) was running at the same RPM as the larger tire (flails) it would be traveling slower.

Likewise, the race track shows that at any given ground speed you will complete the circuit (RPM) by being in the inside lane because there is less ground to cover. To finish the race in a tie, the outside runner (flail knife) must travel faster over the ground than the runner in the inside position (rotor).

Thus the flail knife travels faster than the rotor through space even though they have identical RPM.

And, yes, we are in agreement that we all love our flails, balanced or unbalanced.:thumbsup::laughing:

 

[leonz]

but the orbit is larger in diameter because of the radius length and so the knife is always lagging behind the rotor.

If I have the ambition Monday I will borrow/buy a contact tachometer and a speed gun/light tach and repeat the math.


leonz

 

[KennyV]

Thus the flail knife travels faster than the rotor through space even though they have identical RPM.

And, yes, we are in agreement that we all love our flails, balanced or unbalanced.:thumbsup::laughing:

Thats correct but the unbalanced ones do tend to give me "bad vibrations" ...