Results 1 to 8 of 8
  1. #1
    Bronze Member
    Join Date
    Jan 2004
    Posts
    91
    Location
    Eastern CT
    Tractor
    new holland tc- 35

    Default Rotary cutter blade balance

    Any ideas on the best way to balance a set blades for a rotary cutter. I am familiar with balancing blades with a center bolt but it is not as straight forward with a free swinging brush cutter blade.


  2. #2
    Veteran Member
    Join Date
    Jan 2002
    Posts
    1,927
    Location
    Home-1+ acres New Hope, TX / 24 acres-Fannin County
    Tractor
    JD 950

    Default Re: Rotary cutter blade balance

    I think the only thing you could do is to weigh each blade on a fairly sensitive scale to ensure each weighed the same. That is not truly "balancing" the blades after they are installed. But until they come up with a "blade spin balancer", I think it is the best you will do.

  3. #3
    Elite Member SPIKER's Avatar
    Join Date
    Jun 2002
    Posts
    3,981
    Location
    Ohio, Jeromesville, Ashland County
    Tractor
    Jinma 284

    Default Re: Rotary cutter blade balance

    probably the only REAL wat to do it would be to use TWO scales, set up like how they mesure piston connection rods. measuring each end, then each blade would be close enough to consider the same weight... basically though if the two weight about the same then it probalby is close enough.

    maybe if you are concerned that one blade has a big chunk out of it then take the other blade and wack it hard too! this leads back to that 50 HR service test question posted back in the owning operation forum! [img]/forums/images/graemlins/tongue.gif[/img]

    anyhow good luck
    Mark M [img]/forums/images/graemlins/ooo.gif[/img]

  4. #4
    Elite Member
    Join Date
    Oct 2000
    Posts
    3,044
    Location
    Windham County, Conn
    Tractor
    Ford 2120 , New Holland TN75D, Hitachi UH083LC Excavator

    Default Re: Rotary cutter blade balance

    Balance a brush hog blade. Something I have never done or see anyone do. I run my blades ususlly until a piece brakes off and then you can tell they are out of balance [img]/forums/images/graemlins/frown.gif[/img] Even then I usually replace only the broken half. Just remember, unlike finish mowers, these blades are getting the c#@p beat out of them each time you use them. And the loads definately aren't equal.

    My thoughts after "hogging" for over 30 years.

    Andy

  5. #5
    Elite Member
    Join Date
    Oct 2000
    Posts
    3,044
    Location
    Windham County, Conn
    Tractor
    Ford 2120 , New Holland TN75D, Hitachi UH083LC Excavator

    Default Re: Rotary cutter blade balance

    By the way, if you really feel a need to balance them, why not take a piece of metal lets say 12" long, 4" wide and 3/8 thick and drill 3 holes in it. 2 near each end to bolt the blade to. and one in the center. You could then do a static balance on any pointed object like you do with a conventional blade. The weighing method talked about above won't work since balancing weight has nothing to do with statically or dynamically balancing around a central pin. To illustrate this imagine your mower running with a 5 lb weight mounted 6" out on a zero weight arm on one side and a 5 lb weight mounted 2 feet on a zero weight arm on the other side. Even though the arms would weight the same I wouldn't want to spin it very fast. Just looking at one dynamic, Angular Momentum which is equal to mass times velocity times distance from the point of rotation, at only 100 rpm shaft speed the short 6" would be going 100*6*3.14 or 1884 inches per minute and have angular momentum of 1884 times it's mass and the long 24" arm would be going 100*24*3.14 or 7776 inches per minute nad have angular momentum of 7776 times its mass which is the same as the other arm and drops out of the equation. All in all not a very balanced affair. [img]/forums/images/graemlins/shocked.gif[/img] Both sides would balance using the "scale method" [img]/forums/images/graemlins/confused.gif[/img] The 2 scale method is somewhat better.

    Andy

  6. #6
    Elite Member
    Join Date
    Oct 2000
    Posts
    3,044
    Location
    Windham County, Conn
    Tractor
    Ford 2120 , New Holland TN75D, Hitachi UH083LC Excavator

    Default Re: Rotary cutter blade balance

    By the way, if you really feel a need to balance them, why not take a piece of metal lets say 12" long, 4" wide and 3/8 thick and drill 3 holes in it. 2 near each end to bolt the blade to. and one in the center. You could then do a static balance on any pointed object like you do with a conventional blade. The weighing method talked about above won't work since balancing weight has nothing to do with statically or dynamically balancing around a central pin. To illustrate this imagine your mower running with a 5 lb weight mounted 6" out on a zero weight arm on one side and a 5 lb weight mounted 2 feet on a zero weight arm on the other side. Even though the arms would weight the same I wouldn't want to spin it very fast. Just looking at one dynamic, Angular Momentum which is equal to mass times velocity times distance from the point of rotation, at only 100 rpm shaft speed the short 6" would be going 100*6*3.14 or 1884 inches per minute and have angular momentum of 1884 times it's mass and the long 24" arm would be going 100*24*3.14 or 7776 inches per minute nad have angular momentum of 7776 times its mass which is the same as the other arm and drops out of the equation. All in all not a very balanced affair. [img]/forums/images/graemlins/shocked.gif[/img] Both sides would balance using the "scale method" [img]/forums/images/graemlins/confused.gif[/img]

    Andy

  7. #7
    Epic Contributor Bird's Avatar
    Join Date
    Mar 2000
    Posts
    37,226
    Location
    Texas

    Default Re: Rotary cutter blade balance

    While I don't think balancing those blades is very critical, I did just what BB TX said. When I removed my blades and sharpened them a bit on the bench grinder, then I weighed each of them on the same 20# scales I had; ground them to a point that the scales showed they weighed the same.

  8. #8
    Veteran Member
    Join Date
    Aug 2001
    Posts
    1,002
    Location
    Vermont
    Tractor
    NH TC33D

    Default Re: Rotary cutter blade balance

    </font><font color="blue" class="small">( While I don't think balancing those blades is very critical, I did just what BB TX said. When I removed my blades and sharpened them a bit on the bench grinder, then I weighed each of them on the same 20# scales I had; ground them to a point that the scales showed they weighed the same. )</font>

    If you want to take Bird's method one step further (and correct for the angular momentum concept mentioned in another post):

    In addition to making the two blades weigh the same, you need to make sure that each blade balances at the same point... that is, the balance point of each blade should be at the same distance from that blade's bolt hole (rather than trying to balance it at the midpoint as you do with a single, double-ended lawnmower blade). Grind a bit off one end or the other of the blad to move the balance point, then recheck that blade's weight &amp; balance against the other blade.

    As Bird said, however, it's probably not that critical. The bearings in a rotary mower are built to take a lot more abuse than in a finish mower (I believe a rotary mower spins more slowly than a belly-mount finish mower as well).

    John Mc

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
© 2013 TractorByNet.com. TractorByNet is a registered trademark of IMC Digital Universe, Inc. Other trademarks on this page are the property of their respective owners.