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Another oil thread

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  • Far Canal
    Far Canal
    3 years ago
    Ok, fair enough.
    Only other thing I can think of is the gears are not cut accurately enough.
  • drod
    drod
    3 years ago
    how good are the bearings you are using? New bearing each time you build the gearbox? Nitrile ? (nitride) hardening, good for cams and crankshafts, not so good for gear hardening. case hardening is better for gears. 
  • steelo
    steelo
    3 years ago
    What did engineers say beagle?
  • beaglebasher
    beaglebasher
    3 years ago
    As I  said steelo  I didnt manage to  get to the meeting but apparrently they came to a conclusion.   ( two young engineers )
    Their  conclusion was there is a resonant frequency being produced which is interfering with the harmonic balance of  Albert Einsteins  theory  of Principia  Mathematica

     which is causing a sympathetic vibration and some other fukin bullshit.
    FC nailed it. The major problem with this gearbox is the boss got the gears made on the cheap.  Not cut  accurately enough.


  • steelo
    steelo
    3 years ago
    Hey bb. What was the outcome of this. Did you try the oil. Get the gearbox going?  
  • beaglebasher
    beaglebasher
    3 years ago
    Just got a new batch of gears made last week. We built one gearbox and filled it with a heavy duty diff oil ( not the Redline,  long story )  and gave it a run on the  test bench.  It definitely ran quieter than the other gears but at roughly  3/4 speed it started rattling its head off just like before.  It smooths out if you  increase the speed just like before. 
    We pulled it apart and all the  teeth were intact but it only ran for 20 minutes so its still a work in progress. 
  • Wideglider
    Wideglider
    3 years ago
    BB, what is this gearbox used for?
  • speedzter
    speedzter
    3 years ago
    from what little I can see, I suggest you need bearing support  outboard of the pinion shaft.
  • beaglebasher
    beaglebasher
    3 years ago
    That would definitely help speedzter but there is no way to  do it. 
    Its a PTO from a ride on lawnmower Wideglider.  Still at the  design stage. 
  • Hoodeng
    Hoodeng
    3 years ago
    Which gears in that set are the driver and driven? and what are their dimensions? Is the larger tooth gear on the other side of the bearing being driven or the driver? What torque is being put through this shaft?
    There does not look to be any spalling on the undamaged section, oil quite probably is not the problem.
    It looks like the small diameter pinion is winding up out of shape and loosing its designed contact, and consequently tearing up one end of the larger gear, this would also manifest itself as vibration.
    If you are stuck with the design can the smaller shaft be extended and have another support bearing fitted? if the design is fundamentally wrong small fixes are not going to address the problem. Is there a precedent box in production elsewhere similar that is working to its design?
  • beaglebasher
    beaglebasher
    3 years ago
    The small gear is the  drive. Roughly 20mm diameter from memory.  The one that is getting damaged is the driven.
    Not exactly sure how much torque is being transferred but probably too much! 
    An extra bearing would help but without a major re design  there is not enough room. 
    It is  a prototype so there is nothing else to compare it to.  
  • Hoodeng
    Hoodeng
    3 years ago
    With the drive like that there could be a lot of twisting/flexing in the small drive gear, especially along such a long unsupported contact area. Set it up and run a dial indicator along the flank of one of the teeth,not sure if it is optical illusion but the shaft looks twisted.
    If that shaft is twisting/ flexing in operation it would explain the damage at the drive end of the larger gear. This would also explain the vibration when spooling up. Would be good to know the torque loading on that drive.
    How long is the small gear section, it looks to be 40-50mm long, does it need axial grooving?
    Small very high speed gears run relatively thin synthetic oils.
  • fatbat
    fatbat
    3 years ago
    Hoodeng has said pretty much everything I was gonna contribute 
  • beaglebasher
    beaglebasher
    3 years ago
    This has been a bit of a head fuck allright.    What do you mean by axial grooving Hoodeng? The length of engagement is around 40 mm , again from memory. I havent had much to do with that project for a few weeks cos we are busy with other stuff but I keep an eye on whats going on.
    Again from memory I think it has to handle roughly 130 - 150 lbs / ft . Again from memory I think its supposed to handle roughly 12 KW at the output .
    My personal opinion is it needs a major re design.   If everything was made bigger it would solve a few problems but it would defeat the purpose of what we are trying to do.  




  • Hoodeng
    Hoodeng
    3 years ago
    130 to 150 ft lb through that profile! Wow! What is the diametral pitch?

    Axial grooving is when a ring is machined into the teeth's o/d on long gear engagements at intervals , much like a parting tool cut that goes to just under the root of the tooth. This gives an escape for lubricant that is trapped in the base of the teeth in long engagements. An example of this is in the S&S pre 99 pump body's, that little groove cut in the body at the contact point of the teeth.
    Not saying this is a fix, but an option. Just looking at the driver and driven teeth, that looks to be about 4/1 reduction, can it be done with two reductions instead of one? this would help, but the torque loading for the size of the teeth as you said looks to need a whole new design with margin to correct. The guy that designed that threw the Lewis formula out the window it looks.


  • beaglebasher
    beaglebasher
    3 years ago
    The 150 lbs/ft is at the output shaft. The ratio is over 5 to 1 so in theory the actual torque on the drive shaft would be less.
    I think  the boss is resigned to the fact it needs to be re-designed but that won't be cheap.
    I had to google  Lewis Formula. 
    Don't know what it has to do with a gearbox but.
  • dicko
    dicko
    3 years ago
    looks like the driven gear, or the drive gear ,is actually twisting out of alignment under load and the teeth will then not mesh in a straight line for the full length of the driven gear. hence chattering etc.  more support needed on both drive and driven gear. which means another bearing.

  • steelo
    steelo
    3 years ago
    This should see you on your way BB. No oil required either. Don't thank me
    legogear.jpg
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