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Reason to avoid tip contact in gears

  1. Mar 26, 2014 #1
    Hi,

    When I was studying some gear drawings, I found the tip relief given for all the gears. I find the reason that it avoids the contact between tip of driving flank and root side of driven flank. What is the intention of avoiding this condition? What if I don't give a tip relief?
    Thanks.
     
  2. jcsd
  3. Mar 26, 2014 #2

    maajdl

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    A tip contact can make much more wear and even damage.
    Pressure is of course high is such contacts.
     
  4. Mar 26, 2014 #3
    //A tip contact can make much more wear//

    What is the reason for this, Maajdl?
     
  5. Mar 26, 2014 #4

    maajdl

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    stress concentration
     
  6. Mar 27, 2014 #5

    Baluncore

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    Spur gears must always operate with a slight clearance. This does not significantly effect the rolling contact of ideal involute profiles. However, clearance has a side effect in that, as load is passed from one tooth to the next, it is possible for the incoming tooth tip to impact the mating dedendum surface. That will produce a significant meshing noise and stress the tooth. A progressive tip relief by a couple of thousandths of an inch, replaces the impact with a smooth engagement that is quieter and less damaging.

    Tip relief is preferable to dedendum relief since it does not weaken the cantilever of the tooth.
    Similarly, crowning relief can be used to reduce noise due to axial misalignment.
     
  7. Mar 27, 2014 #6
    Thanks for a very clear explanation, Baluncore. Is it true that tip relief introduces / aggravates transmission error in return?
     
  8. Mar 27, 2014 #7

    Baluncore

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    As the torque is transferred from one tooth to the next there is a period during which both teeth are in contact. Tip relief is only applied to the part of the tooth face where the contact is being made and the load is still being carried on the unrelieved portion of the previous tooth.

    Transmission accuracy is unaffected so long as the tip relief is outside the region with single tooth contact.
     
  9. Mar 29, 2014 #8

    Baluncore

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    Tip relief and crowning are both introduced to reduce the percussion of teeth as they contact.
    Tip relief is most important on spur gears operating under load.
    Crowning is important on helical gears, or spur gears with minor deviations of shaft alignment.
     
  10. Mar 31, 2014 #9
    Thanks a lot, Baluncore! As usual, the information you have given are of top-notch quality!
     
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